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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RevenueFromContractWithCustomerAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Revenue from Contract with Customer [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityShellCompany_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Shell Company</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityShellCompany_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Shell Company</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ScheduleOfActivityWithinLiabilityForSaleOfFutureRoyaltiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of activity within liability for sale of future royalties.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ScheduleOfActivityWithinLiabilityForSaleOfFutureRoyaltiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Activity Within Liability For Sale Of Future Royalties [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ScheduleOfActivityWithinLiabilityForSaleOfFutureRoyaltiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Activity Within Liability for Sale of Future Royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Accrued Liabilities, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Segment Reporting</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Cash and Cash Equivalents, at Carrying Value, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Cash and Cash Equivalents, at Carrying Value, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Cash and Cash Equivalents, at Carrying Value, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and cash equivalents</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash and Cash Equivalent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PreFundedWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Pre Funded Warrant</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PreFundedWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Pre Funded Warrant [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PreFundedWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Pre Funded Warrant [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CustomerOneMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Customer One.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CustomerOneMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Customer One [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CustomerOneMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Customer One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonRule10B51ArrModifiedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non-Rule 10b51 Arr Modified [Flag]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonRule10B51ArrModifiedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non-rule 10b5-1 arrangement modified.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonRule10B51ArrModifiedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-Rule 10b5-1 Arrangement Modified</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_USAndCanadaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">US And Canada</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_USAndCanadaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">U.S. and Canada [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_USAndCanadaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">U.S. and Canada.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and Development Arrangement, Contract to Perform for Others, Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Research and Development Arrangement, Contract to Perform for Others, Type [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Common Stock, Shares, Issued, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Shares, Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Asset Class</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Class [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedCashNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Cash, Noncurrent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedCashNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted cash included in other non-current assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_LatinAmericaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Latin America</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_LatinAmericaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Latin America [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRepurchaseOptionAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Repurchase Option Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRepurchaseOptionAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty Repurchase Option Amount.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRepurchaseOptionAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty repurchase amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Foreign currency translation adjustments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Business Combination [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFilerCategory_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Filer Category</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFilerCategory_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Filer Category</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities and Equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total liabilities, noncontrolling interest and stockholders' deficit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PayablesAndAccrualsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payables and Accruals [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringCostAndReserveAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Type [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TimeDepositsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Time Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TimeDepositsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Time Deposits [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TimeDepositsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Time deposits.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialInstrumentsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialInstrumentsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Instruments Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfRestructuringAndRelatedCostsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring and Related Costs [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfRestructuringAndRelatedCostsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Total restructuring charges recognized on the Condensed Consolidated Statements of Operations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Goodwill, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Goodwill, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Goodwill, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherNoncashIncomeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherNoncashIncomeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other Noncash Income (Expense), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherNoncashIncomeExpense_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherNoncashIncomeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Noncash Income (Expense)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentIncomeInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Investment Income Interest, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentIncomeInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentIncomeInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Income, Interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Noncurrent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Marketable securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_SegmentGeographicalDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Geographical</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_SegmentGeographicalDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Geographical [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Payment for intangible asset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Payments for intangible asset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments to Acquire Intangible Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InventoryFinishedGoods_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Inventory, Finished Goods, Gross, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InventoryFinishedGoods_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Finished goods</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InventoryFinishedGoods_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Inventory, Finished Goods, Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsRestrictedCashAndCashEquivalentsPolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsRestrictedCashAndCashEquivalentsPolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash, Cash Equivalents and Restricted Cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetBackedSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Asset-backed Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetBackedSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset-Backed Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInventoryCurrentTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Inventory</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInventoryCurrentTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Inventory, Current [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Receivable, Allowance for Credit Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Accounts Receivable, Allowance for Credit Loss, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Accounts Receivable, Allowance for Credit Loss, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue related reserves</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashInterestExpenseOnLiabilityForSaleOfFutureRoyaltiesAndCapitalizedToPropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non Cash interest expense on liability for sale of future royalties and capitalized to property plant and equipment.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashInterestExpenseOnLiabilityForSaleOfFutureRoyaltiesAndCapitalizedToPropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non Cash Interest Expense On Liability For Sale Of Future Royalties And Capitalized To Property Plant And Equipment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashInterestExpenseOnLiabilityForSaleOfFutureRoyaltiesAndCapitalizedToPropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-cash interest expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DeferredCompensationAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Deferred compensation assets.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DeferredCompensationAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Compensation Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DeferredCompensationAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred Compensation Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock options, granted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisaggregationOfRevenueTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Disaggregation Of Revenue [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisaggregationOfRevenueTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Disaggregation of Revenue [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PercentageOfGrossAccountsReceivableBalance_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of gross accounts receivable balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PercentageOfGrossAccountsReceivableBalance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Gross Accounts Receivable Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PercentageOfGrossAccountsReceivableBalance_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of gross accounts receivable balance.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Earnings Per Share, Basic, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share, Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net loss per share, basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisaggregationOfRevenueTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Disaggregation of Total Revenues</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisaggregationOfRevenueTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Disaggregation of Revenue [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total current liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Accounts receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase (Decrease) in Accounts Receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjustments to reconcile net loss to net cash used in operating activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborationAndLicenseMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaboration And License [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborationAndLicenseMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collaboration and license.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborationAndLicenseMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaboration and license</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring and Related Cost, Number of Positions Eliminated, Period Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restructuring plan, workforce reduction percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRevenueForSalesInNorthAmericanTerritioryMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Revenue for Sales in North American Territiory [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRevenueForSalesInNorthAmericanTerritioryMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty revenue for sales in north american territory.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRevenueForSalesInNorthAmericanTerritioryMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty Revenue in North American Territory</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity, Attributable to Parent [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stockholders' deficit:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntitySmallBusiness_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Small Business</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntitySmallBusiness_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Small Business</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Retained Earnings (Accumulated Deficit), Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Retained Earnings (Accumulated Deficit), Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Retained Earnings (Accumulated Deficit), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated deficit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings (Accumulated Deficit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TheodoreHuizengaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Theodore Huizenga [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TheodoreHuizengaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Theodore huizenga.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TheodoreHuizengaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Theodore Huizenga [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NatureOfOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Organization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NatureOfOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Nature of Operations [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherCurrentAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Current Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherCurrentAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Current Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-Based Awards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Organization, Consolidation and Presentation of Financial Statements [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CommercialAndDevelopmentActivityReimbursementsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commercial and Development Activity Reimbursements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CommercialAndDevelopmentActivityReimbursementsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commercial And Development Activity Reimbursements [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CommercialAndDevelopmentActivityReimbursementsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Commercial and development activity reimbursements.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AmendmentFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amendment Flag</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AmendmentFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amendment Flag</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltiesTransactionCostsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalties transaction costs net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltiesTransactionCostsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalties Transaction Costs Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltiesTransactionCostsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalties transaction costs net.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ProductsAndServicesDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Product and Service</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ProductsAndServicesDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Product and Service [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities and Equity [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liabilities, Noncontrolling interest and Stockholders' Equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressPostalZipCode_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Postal Zip Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressPostalZipCode_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, Postal Zip Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash used in operating activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Operating Activity, Including Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingCodmProfitLossMeasureHowUsedDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting, CODM, Profit (Loss) Measure, How Used, Description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TwoThousandTwentyFiveOMERSAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Twenty Five OMERS Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TwoThousandTwentyFiveOMERSAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Two Thousand Twenty Five OMERS agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TwoThousandTwentyFiveOMERSAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2025 OMERS Agreement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Available For Sale Securities [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and Development Arrangement, Contract to Perform for Others, Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Research and Development Arrangement, Contract to Perform for Others, Type [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_SeriesSeedPreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series seed preferred stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_SeriesSeedPreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Series seed preferred stock.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_SeriesSeedPreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series Seed Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentInterestRateEffectivePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Effective annual interest rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentInterestRateEffectivePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument, Interest Rate, Effective Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressAddressLine1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Address Line One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressAddressLine1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, Address Line One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Hierarchy and NAV [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_IssuanceOfCommonStockUnderEquityPlanAwardsNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock under equity plan awards, net of tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_IssuanceOfCommonStockUnderEquityPlanAwardsNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Issuance Of Common Stock Under Equity Plan Awards Net Of Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_IssuanceOfCommonStockUnderEquityPlanAwardsNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Issuance of common stock under equity plan awards, net of tax.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net income (loss) per share:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PercentageOfRoyaltiesSold_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Percentage of Royalties Sold</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PercentageOfRoyaltiesSold_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of royalties sold</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PercentageOfRoyaltiesSold_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of royalties sold.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BalanceSheetLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balance Sheet Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BalanceSheetLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Financial Position Location, Balance [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Type [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilitiesForSalesOfFutureRoyaltiesPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liabilities for Sales of Future Royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilitiesForSalesOfFutureRoyaltiesPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities for Sales of Future Royalties [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilitiesForSalesOfFutureRoyaltiesPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Liabilities for Sales of Future Royalties [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonProfitFoundationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non Profit Foundation [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonProfitFoundationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non Profit Foundation [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonProfitFoundationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non Profit Foundation [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments to Acquire Debt Securities, Available-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchase of marketable securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_StockholdersEquityTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stockholders Equity [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_StockholdersEquityTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders Equity [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_StockholdersEquityTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Stockholders equity table.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Warrant or Right [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentType_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentType_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TypeOfArrangementAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaborative Arrangement and Arrangement Other than Collaborative</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TypeOfArrangementAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangement and Arrangement Other than Collaborative [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaborative Arrangement and Arrangement Other than Collaborative</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangement and Arrangement Other than Collaborative [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Central Index Key</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Central Index Key</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Cash Equivalents and Marketable Securities Classified as Available For Sale Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments, Debt and Equity Securities [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CrysvitaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Crysvita</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CrysvitaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Crysvita [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CrysvitaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Crysvita.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net (decrease) increase in cash, cash equivalents and restricted cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event Type [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock equivalents excluded from computation of diluted net loss per share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Par or Stated Value Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, par value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of equity from noncontrolling interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noncontrolling Interest, Increase from Subsidiary Equity Issuance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_StockIssuedDuringPeriodValueAtMarketOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock issued during period value at market offering.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_StockIssuedDuringPeriodValueAtMarketOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Value At Market Offering</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_StockIssuedDuringPeriodValueAtMarketOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock in connection with at-the-market offering, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringAndRelatedActivitiesCompletionDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring and Related Activities, Completion Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringAndRelatedActivitiesCompletionDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restructuring and related activities, Completion date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Debt Securities, Available-for-sale, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyStartDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Start Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyStartDate_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty start date.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyStartDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty start date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment in Amlogenyx Inc.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OpenMarketSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Open Market Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OpenMarketSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Open Market Sale [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OpenMarketSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Open market sale.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_SolidAndArcturusMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Solid and Arcturus.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_SolidAndArcturusMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Solid and Arcturus [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_SolidAndArcturusMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Solid and Arcturus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LicenseAndCollaborationAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License and Collaboration Agreement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LicenseAndCollaborationAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">License And Collaboration Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LicenseAndCollaborationAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">License and collaboration agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccruedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total accrued liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccruedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccruedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Liabilities, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CostOfSalesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cost of Sales [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CostOfSalesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cost of sales</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current Fiscal Year End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Current Fiscal Year End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DojolviMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Dojolvi</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DojolviMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Dojolvi [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DojolviMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Dojolvi.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentQuarterlyReport_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Quarterly Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentQuarterlyReport_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Quarterly Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_IncreaseDecreaseInAccountsPayableAccruedLiabilitiesAndOtherOperatingLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts payable, accrued, and other liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_IncreaseDecreaseInAccountsPayableAccruedLiabilitiesAndOtherOperatingLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Accounts Payable Accrued Liabilities And Other Operating Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_IncreaseDecreaseInAccountsPayableAccruedLiabilitiesAndOtherOperatingLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Increase decrease in accounts payable accrued liabilities and other operating liabilities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressStateOrProvince_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, State or Province</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressStateOrProvince_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, State or Province</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashRoyaltyRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non cash royalty revenue.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashRoyaltyRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non Cash Royalty Revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashRoyaltyRevenue_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Non-cash royalty revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentOwnedBalanceShares_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Owned, Balance, Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentOwnedBalanceShares_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares received</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Preferred Stock, Shares Outstanding, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Preferred Stock, Shares Outstanding, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, shares outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Shares Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total comprehensive loss</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross Unrealized Gains</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostSharingPaymentsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cost Sharing Payments [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostSharingPaymentsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cost Sharing Payments [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostSharingPaymentsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cost sharing payments line items.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Warrant or Right [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StatementGeographicalAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Geographical</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StatementGeographicalAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Geographical [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Stock-Based Compensation Expense</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ResearchAndClinicalStudyExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Research and Clinical Study Expenses</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PerformanceSharesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Performance Shares [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilitiesForSalesOfFutureRoyaltiesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Liabilities for sales of future royalties.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilitiesForSalesOfFutureRoyaltiesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities for Sales of Future Royalties [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Property, Plant and Equipment [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets, Noncurrent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborationPayables_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaboration Payables</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborationPayables_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collaboration Payables</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborationPayables_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaboration payables</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Debt Securities, Available-for-sale, Current, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Marketable securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EMEAMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">EMEA [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EMEAMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Europe, Middle East, and Africa</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractExecutionDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contract execution date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractExecutionDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Contract Execution Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractExecutionDate_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Contract execution date.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Sale of Debt Securities, Available-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from sale of marketable securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty Purchase Agreement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Purchase Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty purchase agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ArcturusResearchCollaborationAndLicenseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Arcturus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ArcturusResearchCollaborationAndLicenseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Arcturus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ArcturusResearchCollaborationAndLicenseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Arcturus Research Collaboration And License Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ArcturusResearchCollaborationAndLicenseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Arcturus research collaboration and license agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Other Comprehensive Income (Loss)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">AOCI Attributable to Parent [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_NameOfMajorCustomerDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Customer [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Common, Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Treasury stock , shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockDeferredEmployeeStockOwnershipPlan_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Employee Stock Ownership Plan, Issuance of Shares or Sale of Treasury Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockDeferredEmployeeStockOwnershipPlan_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred compensation obligation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Preferred Stock, Value, Issued, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Preferred Stock, Value, Issued, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Preferred Stock, Value, Issued, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Value, Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, par value of $0.001 per share - 25.0 shares authorized; nil outstanding in 2026 and in 2025</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Selling, General and Administrative Expense, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Selling, general and administrative</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Selling, General and Administrative Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MinimumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Minimum</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MinimumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Minimum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialInstrumentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Instrument [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EmploymentInducementPlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Employment Inducement Plan</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EmploymentInducementPlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Employment Inducement Plan [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EmploymentInducementPlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Employment inducement plan.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current assets:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets, Current [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AnnualLicenseFeePayment_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Annual license fee payment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AnnualLicenseFeePayment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Annual License Fee Payment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AnnualLicenseFeePayment_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Annual license fee payment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel3Member_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Inputs, Level 3 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel3Member_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 3</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PaymentFromSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payment From Sale Of Future Royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PaymentFromSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Payment from sale of future royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PaymentFromSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Payment From Sale Of Future Royalties.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Financial Assets Measured on Recurring Basis</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Assets Measured on Recurring Basis [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current liabilities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities, Current [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProductMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Product sales</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProductMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Product [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProductMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Product Revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringAndRelatedActivitiesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring and Related Activities Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringAndRelatedActivitiesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Strategic Restructuring Plan</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RelatedPartyTransactionsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Related Party Transactions [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsReceivableNetCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Accounts Receivable, after Allowance for Credit Loss, Current, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsReceivableNetCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts receivable, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsReceivableNetCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Receivable, after Allowance for Credit Loss, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredCompensationShareBasedPaymentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Compensation, Share-Based Payments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredCompensationShareBasedPaymentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred Compensation Obligation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InventoryWorkInProcess_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Work-in-process</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InventoryWorkInProcess_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Inventory, Work in Process, Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GeneralAndAdministrativeExpenseMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">General and Administrative Expense [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GeneralAndAdministrativeExpenseMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Selling, general and administrative</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CostsAssociatedWithExitOrDisposalActivitiesOrRestructuringsPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Costs Associated with Exit or Disposal Activities or Restructurings, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CostsAssociatedWithExitOrDisposalActivitiesOrRestructuringsPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restructuring</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInPrepaidExpensesOther_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prepaid expenses and other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInPrepaidExpensesOther_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase (Decrease) in Prepaid Expenses, Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInPrepaidExpensesOther_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Prepaid expenses and other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedCashCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Cash, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedCashCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted cash included in other current assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AvailableForSaleSecuritiesContractualMaturity_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Available-for-sale securities remaining contractual maturities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AvailableForSaleSecuritiesContractualMaturity_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Available For Sale Securities Contractual Maturity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AvailableForSaleSecuritiesContractualMaturity_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Available for sale securities contractual maturity.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Effect of exchange rate changes on cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfRestructuringReserveByTypeOfCostTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Restructuring Reserve by Type of Cost [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfRestructuringReserveByTypeOfCostTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of restructuring charges and amounts paid or settled</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Weighted Average Number of Shares Outstanding, Basic, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares Outstanding, Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares used in computing net loss per share, Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PercentageOfRightToReceiveRoyaltyPaymentsOnNetSales_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Percentage of right to receive royalty payments on net sales</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PercentageOfRightToReceiveRoyaltyPaymentsOnNetSales_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of right to receive royalty payments on net sales.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EuropeanUnionAndSwitzerlandAndTurkeyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty Revenue in European Territory</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EuropeanUnionAndSwitzerlandAndTurkeyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">European Union And Switzerland And Turkey [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EuropeanUnionAndSwitzerlandAndTurkeyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">European Union and Switzerland and Turkey.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EuropeanUnionAndSwitzerlandAndTurkeyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Royalty Revenue in European Territories</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Net of Forfeitures</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Net of Forfeitures, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares granted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Events</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Events [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">APIC, Share-based Payment Arrangement, Increase for Cost Recognition, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">APIC, Share-Based Payment Arrangement, Increase for Cost Recognition</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Beginning balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Ending balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity, Attributable to Parent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total stockholders' deficit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Par or Stated Value Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, par value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashRoyaltyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non cash royalty.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashRoyaltyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non Cash Royalty [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashRoyaltyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-cash royalty revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis of Presentation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Basis of Accounting, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfStockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Stockholders' Equity [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyAgreementTerminationThresholdAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty agreement termination threshold amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyAgreementTerminationThresholdAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Agreement Termination Threshold Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyAgreementTerminationThresholdAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty agreement termination threshold amount.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collaboration.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaboration [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaboration Revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TypeOfRestructuringDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Type of Restructuring [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UseOfEstimates_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Use of Estimates</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UseOfEstimates_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Use of Estimates, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CreditLossFinancialInstrumentPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Credit Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CreditLossFinancialInstrumentPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Credit Loss, Financial Instrument [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Common [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Treasury Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DeferredCompensationLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Deferred compensation liabilities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DeferredCompensationLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Compensation Liabilities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DeferredCompensationLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred Compensation Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentOwnedAtFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentOwnedAtFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Investment Owned, Fair Value, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentOwnedAtFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Investment Owned, Fair Value, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentOwnedAtFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Owned, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="country_US_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">United States of America</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="country_US_lbl" xlink:role="http://www.xbrl.org/2003/role/label">UNITED STATES</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Accrued Liabilities [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Accrued Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ClinicalMilestoneAggregate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Clinical Milestone Aggregate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ClinicalMilestoneAggregate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Clinical Milestone Aggregate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ClinicalMilestoneAggregate_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Clinical Milestone Aggregate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ManufacturingAndRelatedExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Manufacturing and related expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ManufacturingAndRelatedExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Manufacturing and Related Expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ManufacturingAndRelatedExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Manufacturing and related expenses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingCodmIndividualTitleAndPositionOrGroupOrCommitteeNameExtensibleEnumeration_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting, CODM, Individual Title and Position or Group Name [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AmlogenyxIncMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amlogenyx inc.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AmlogenyxIncMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amlogenyx Inc [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AmlogenyxIncMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amlogenyx Inc [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PlanNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Plan Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PlanNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Plan Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Noncontrolling interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Temporary Equity, Carrying Amount, Including Portion Attributable to Noncontrolling Interests, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Temporary Equity, Including Noncontrolling Interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_MepseviiMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Mepsevii.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_MepseviiMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Mepsevii</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_MepseviiMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Mepsevii [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyPurchaseAgreementCAPAggregatePayment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Purchase Agreement CAP Aggregate Payment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyPurchaseAgreementCAPAggregatePayment_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty purchase agreement cap aggregate payment.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyPurchaseAgreementCAPAggregatePayment_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty purchase agreement cap aggregate payment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInvestmentsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Investments [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PercentageOfGrossAccountsReceivablesFromDifferentCustomer_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of gross accounts receivable balance from different customer</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PercentageOfGrossAccountsReceivablesFromDifferentCustomer_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Gross Accounts Receivables From Different Customer</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PercentageOfGrossAccountsReceivablesFromDifferentCustomer_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of gross accounts receivables from different customer.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_Rule10B51ArrModifiedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Rule 10b51 Arr Modified [Flag]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_Rule10B51ArrModifiedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Rule 10b51 arrangement modified.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_Rule10B51ArrModifiedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Rule 10b5-1 Arrangement Modified</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Treasury Stock, Value, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Treasury stock, at cost, 0.3 shares in 2026 and 0.2 shares in 2025</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborativeArrangementsEffectiveReductionOfExpenseInResearchAndDevelopmentExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and development</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborativeArrangementsEffectiveReductionOfExpenseInResearchAndDevelopmentExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangements Effective Reduction Of Expense In Research And Development Expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborativeArrangementsEffectiveReductionOfExpenseInResearchAndDevelopmentExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collaborative arrangements effective reduction of expense in research and development expenses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborativeArrangementsEffectiveReductionOfExpenseInResearchAndDevelopmentExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Offset to research and development expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_UnitedStatesAndCanadaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Profit Share Territory</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_UnitedStatesAndCanadaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">United States And Canada [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_UnitedStatesAndCanadaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">United States and Canada.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OptionToSellCommonStockAggregateOfferingPrice_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Option to sell common stock aggregate offering price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OptionToSellCommonStockAggregateOfferingPrice_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Option To Sell Common Stock Aggregate Offering Price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OptionToSellCommonStockAggregateOfferingPrice_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Option to sell common stock aggregate offering price.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Related Party</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Related and Nonrelated Parties [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressCityOrTown_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, City or Town</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressCityOrTown_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, City or Town</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NumberOfReportableSegments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of reportable segments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NumberOfReportableSegments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number of Reportable Segments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_SecurityExchangeName_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Security Exchange Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_SecurityExchangeName_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Security Exchange Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonControllingInterestInChangesAndAdjustments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non controlling Interest in Changes and Adjustments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonControllingInterestInChangesAndAdjustments_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Changes and adjustments related to noncontrolling Interest.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonControllingInterestInChangesAndAdjustments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Changes and adjustments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilitiesForSalesOfFutureRoyaltiesTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Liabilities for sales of future royalties.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilitiesForSalesOfFutureRoyaltiesTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities for Sales of Future Royalties [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilitiesForSalesOfFutureRoyaltiesTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liabilities for Sales of Future Royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsAllOtherInvestmentsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments, All Other Investments [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TwoThousandTwentyThreeIncentivePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2023 Incentive Plan</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TwoThousandTwentyThreeIncentivePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Twenty Three Incentive Plan Member</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TwoThousandTwentyThreeIncentivePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand twenty three incentive plan.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CounterpartyNameAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Counterparty Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CounterpartyNameAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Counterparty Name [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Loss before income taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive Securities, Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities, Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentOwnedAtCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Owned, Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentOwnedAtCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contributed by affiliated entities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RegeneronPharmaceuticalsIncMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Regeneron pharmaceuticals Inc.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RegeneronPharmaceuticalsIncMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Regeneron Pharmaceuticals Inc [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RegeneronPharmaceuticalsIncMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Regeneron Pharmaceuticals Inc</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InventoryNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total inventory</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InventoryNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Inventory</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InventoryNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Inventory, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_GenetxMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">GeneTx [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_GenetxMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">GeneTx [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_GenetxMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">GeneTx [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statistical Measurement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statistical Measurement [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DeferredCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Deferred compensation.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DeferredCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DeferredCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total current assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Stock-based compensation expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentPeriodEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Period End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentPeriodEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Period End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Hierarchy and NAV [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Foreign currency translation adjustments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Financial Position [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockUnitsRSUMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Stock Units (RSUs) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockUnitsRSUMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted Stock Units (RSUs) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborativeArrangementAndNoncollaborativeArrangementTransactionsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License and Research Agreements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborativeArrangementAndNoncollaborativeArrangementTransactionsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangement And Noncollaborative Arrangement Transactions Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborativeArrangementAndNoncollaborativeArrangementTransactionsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collaborative arrangement and noncollaborative arrangement transactions disclosure.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RevenueRecognitionPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue Recognition</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RevenueRecognitionPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Revenue [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RPIFinanceTrustTwoThousandNineteenMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">R P I Finance Trust Two Thousand Nineteen [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RPIFinanceTrustTwoThousandNineteenMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">RPI finance trust two thousand nineteen.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RPIFinanceTrustTwoThousandNineteenMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">RPI Finance Trust 2019</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TwoThousandTwentyFourEquityIncentivePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Twenty Four Equity Incentive Plan [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TwoThousandTwentyFourEquityIncentivePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Two Thousand Twenty Four Equity Incentive Plan [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TwoThousandTwentyFourEquityIncentivePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2024 Equity Incentive Plan [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Security, Excluded EPS Calculation [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Stock [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherReceivables_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License agreement other receivables</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherReceivables_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Receivables</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommercialPaperNotIncludedWithCashAndCashEquivalentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commercial Paper</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommercialPaperNotIncludedWithCashAndCashEquivalentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commercial Paper, Not Included with Cash and Cash Equivalents [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Liabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Liabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PreFundedWarrantsAndStockIssuedDuringPeriodSharesAtUnderwrittenPublicOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Pre-funded Warrants And Stock Issued During Period Shares At Underwritten Public Offering</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PreFundedWarrantsAndStockIssuedDuringPeriodSharesAtUnderwrittenPublicOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Pre-funded warrants and stock issued during period shares at underwritten public offering.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PreFundedWarrantsAndStockIssuedDuringPeriodSharesAtUnderwrittenPublicOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock and pre-funded warrants in connection with the underwritten public offering, net, shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Instruments [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostOfSalesAndOperatingExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cost of sales and operating expenses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostOfSalesAndOperatingExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cost Of Sales And Operating Expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostOfSalesAndOperatingExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total operating expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_InvestmentInSolidCommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment in Solid Common Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_InvestmentInSolidCommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Investment in solid common stock member.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_InvestmentInSolidCommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment in Solid common stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Weighted Average Number of Shares Outstanding, Diluted, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares Outstanding, Diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares used in computing net loss per share, Diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFileNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity File Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFileNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Securities Act File Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Change in unrealized loss on available-for-sale securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CoverAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cover [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_JohnPinionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">John Pinion [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_JohnPinionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">John Pinion [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_JohnPinionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">John pinion .</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ScheduleOfKeyTermsAndActivityOfSalesOfFutureRoyaltiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Key Terms And Activity Of Sales Of Future Royalties [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ScheduleOfKeyTermsAndActivityOfSalesOfFutureRoyaltiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of key terms and activity of sales of future royalties.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ScheduleOfKeyTermsAndActivityOfSalesOfFutureRoyaltiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Key Terms and Activity of Sales of Future Royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Prepaid Expense and Other Assets, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prepaid expenses and other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeCategorizationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeCategorizationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsNoncurrentAssetStatementOfFinancialPositionExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted Cash and Cash Equivalents, Noncurrent, Asset, Statement of Financial Position [Extensible List]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsNoncurrentAssetStatementOfFinancialPositionExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Cash and Cash Equivalent, Noncurrent, Statement of Financial Position [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SupplementalBalanceSheetDisclosuresTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balance Sheet Components</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SupplementalBalanceSheetDisclosuresTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Supplemental Balance Sheet Disclosures [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_FutureMilestonesPayable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Future milestones payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_FutureMilestonesPayable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Future Milestones Payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_FutureMilestonesPayable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Future milestones payable.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares authorised for issuance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ScheduleOfCollaborationAndRoyaltyRevenueTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share of Collaboration and Royalty Revenue Related to Crysvita</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ScheduleOfCollaborationAndRoyaltyRevenueTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Collaboration And Royalty Revenue Table [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ScheduleOfCollaborationAndRoyaltyRevenueTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of collaboration and royalty revenue.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Sale of Stock [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OptionsToPurchaseCommonStockRestrictedStockUnitsAndPerformanceStockUnitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Options to purchase common stock, restricted stock units and performance stock units.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OptionsToPurchaseCommonStockRestrictedStockUnitsAndPerformanceStockUnitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Options To Purchase Common Stock Restricted Stock Units And Performance Stock Units [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OptionsToPurchaseCommonStockRestrictedStockUnitsAndPerformanceStockUnitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options to Purchase Common Stock, RSUs, and PSUs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OptionsToPurchaseCommonStockRestrictedStockUnitsAndPerformanceStockUnitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Options to Purchase Common Stock, RSUs, and PSUs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StockRepurchaseProgramExpirationDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share repurchase expiration date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StockRepurchaseProgramExpirationDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share Repurchase Program, Expiration Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractWithCustomerAssetsLiabilityCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balance of contract liabilities at beginning of period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractWithCustomerAssetsLiabilityCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Contract with customer assets (liability) current.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractWithCustomerAssetsLiabilityCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Assets Liability Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractWithCustomerAssetsLiabilityCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance of contract liabilities at beginning of period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractWithCustomerAssetsLiabilityCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance of contract liabilities at end of period, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_StockIssuedDuringPeriodSharesAtMarketOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock issued during period shares at market offering.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_StockIssuedDuringPeriodSharesAtMarketOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock in connection with at-the-market offering, net, shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_StockIssuedDuringPeriodSharesAtMarketOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Shares At Market Offering</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringCharges_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Charges</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringCharges_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Restructuring Charges, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringCharges_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restructuring charges</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">New Accounting Pronouncements, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recent Accounting Pronouncements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeSeveranceMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Emplooyee-Related</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeSeveranceMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Employee Severance [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNoteTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Other Comprehensive Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNoteTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Comprehensive Income (Loss) Note [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Beginning balance, shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Ending balance, shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Shares, Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepreciationDepletionAndAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Depreciation, Depletion and Amortization, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepreciationDepletionAndAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Depreciation and amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepreciationDepletionAndAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Depreciation, Depletion and Amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentTransitionReport_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Transition Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentTransitionReport_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Transition Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Research and Development Expense, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and development</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Research and Development Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OrganizationAndNatureOfBusinessTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Organization And Nature Of Business [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OrganizationAndNatureOfBusinessTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Organization And Nature Of Business [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OrganizationAndNatureOfBusinessTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Organization and nature of business.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_SolidBiosciencesIncMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Solid Biosciences Inc [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfCashFlowsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Cash Flows [Abstract]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_FutureContingentMilestonePayments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Future Contingent Milestone Payments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_FutureContingentMilestonePayments_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Future contingent milestone payments.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net Loss Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltiesAgreementTerritories_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalties Agreement Territories</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltiesAgreementTerritories_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalties agreement territories.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltiesAgreementTerritories_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalties agreement territories</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net loss</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CustomerTwoMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Customer Two.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CustomerTwoMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Customer Two [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CustomerTwoMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Customer Two</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyContractExecutionDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Contract Execution Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyContractExecutionDate_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty contract execution date.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyContractExecutionDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contract execution date</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilitiesForSalesOfFutureRoyaltiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Liabilities for sales of future royalties current</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Assets</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_AsiaPacificMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asia Pacific [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_KyowaKirinCollaborationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Kyowa Kirin Collaboration [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_KyowaKirinCollaborationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Kyowa Kirin Collaboration</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringCostAndReserveLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Cost and Reserve [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueDisclosuresAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Disclosures [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyPurchaseAgreementCAPAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Purchase Agreement CAP Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyPurchaseAgreementCAPAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">royalty purchase agreement cap amount.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyPurchaseAgreementCAPAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty purchase agreement cap amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Other Comprehensive Loss, Net of Tax [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_NorthAmericaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">North America</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_NorthAmericaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">North America [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_Regulatorymilestonepaymentsachieved_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Regulatory milestone payments achieved.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_Regulatorymilestonepaymentsachieved_lbl" xlink:role="http://www.xbrl.org/2003/role/label">RegulatoryMilestonePaymentsAchieved</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_Regulatorymilestonepaymentsachieved_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Regulatory milestone payments achieved</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilityForSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Liability for sale of future royalties at end of year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilityForSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liability For Sale Of Future Royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilityForSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Liability for sale of future royalties.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilityForSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Liability for sale of future royalties at beginning of year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostOfSales_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cost of sales</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostOfSales_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cost Of Sales</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostOfSales_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cost of sales.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilityForSaleOfFutureRoyaltiesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Liability for sale of future royalties.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilityForSaleOfFutureRoyaltiesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liability For Sale Of Future Royalties [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Sale of Stock [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Investing Activity, Including Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash (used in) provided by investing activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TwoThousandTwentyTwoOMERSAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Twenty Two OMERS Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TwoThousandTwentyTwoOMERSAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand twenty two OMERS agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_TwoThousandTwentyTwoOMERSAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2022 OMERS Agreement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_Security12bTitle_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Title of 12(b) Security</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_Security12bTitle_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Title of 12(b) Security</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyAgreementCounterpartyName_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Agreement counterparty</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyAgreementCounterpartyName_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Agreement Counterparty Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyAgreementCounterpartyName_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty agreement counterparty name.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MoneyMarketFundsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Money Market Funds</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MoneyMarketFundsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Money Market Funds [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RelatedPartyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Related Party</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RelatedPartyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Related and Nonrelated Parties [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangement and Arrangement Other than Collaborative [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AmendedAndRestatedTwoThousandFourteenEmployeeStockPurchasePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amended and restated two thousand fourteen employee stock purchase plan.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AmendedAndRestatedTwoThousandFourteenEmployeeStockPurchasePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amended and Restated Two Thousand Fourteen Employee Stock Purchase Plan [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AmendedAndRestatedTwoThousandFourteenEmployeeStockPurchasePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amended &amp; Restated 2014 Employee Stock Purchase Plan</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EligibleFutureMilestonePayments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Eligible future milestone payments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EligibleFutureMilestonePayments_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Eligible future milestone payments.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EligibleFutureMilestonePayments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Eligible Future Milestone Payments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilityRelatedToSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liability Related To Sale Of Future Royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilityRelatedToSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Liability related to sale of future royalties.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilityRelatedToSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Liabilities related to the sale of future royalties at beginning of year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilityRelatedToSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Liabilities related to the sale of future royalties at end of year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LiabilityRelatedToSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liabilities for sales of future royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilitiesNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilitiesNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other Liabilities, Noncurrent, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilitiesNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Liabilities, Noncurrent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_LegalEntityAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Legal Entity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_LegalEntityAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Legal Entity [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Changes in operating assets and liabilities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractWithCustomerLiabilityDeductionsDuringPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Contract with customer liability deductions during period.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractWithCustomerLiabilityDeductionsDuringPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability Deductions During Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractWithCustomerLiabilityDeductionsDuringPeriod_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Deductions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds, Issuance of Shares, Share-Based Payment Arrangement, Including Option Exercised</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Proceeds, Issuance of Shares, Share-Based Payment Arrangement, Including Option Exercised, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from the issuance of common stock under equity plans, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Recurring and Nonrecurring [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional Paid-in Capital</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid-in Capital [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Statement Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Income Location, Balance [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_TradingSymbol_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Trading Symbol</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_TradingSymbol_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Trading Symbol</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Related Party Transaction [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltiesEarnedFromInception_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalties Earned From Inception</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltiesEarnedFromInception_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalties Earned From Inception.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event Type [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AllocatedShareBasedCompensationExpenseNetOfCapitalizedInventoryCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AllocatedShareBasedCompensationExpenseNetOfCapitalizedInventoryCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Allocated Share Based Compensation Expense Net Of Capitalized Inventory Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AllocatedShareBasedCompensationExpenseNetOfCapitalizedInventoryCost_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Allocated share based compensation expense net of capitalized inventory cost.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeRelatedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Employee-related Liabilities, Current, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeRelatedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Payroll and related expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeRelatedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Employee-related Liabilities, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ProceedsFromIssuanceOfCommonStockAtMarketOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Issuance Of Common Stock At Market Offering</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ProceedsFromIssuanceOfCommonStockAtMarketOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Proceeds from issuance of common stock at market offering.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ProceedsFromIssuanceOfCommonStockAtMarketOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net proceeds from at-the-market offering</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ProceedsFromIssuanceOfCommonStockAtMarketOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Proceeds from the issuance of common stock in connection with at-the-market offering, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Components</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity Components [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Component</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity Component [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByAssetClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Asset Class</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByAssetClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Class [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BusinessAcquisitionAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Business Combination [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_IssuanceOfCommonStockUnderEquityPlanAwardsNetOfTaxShares_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock under equity plan awards, net of tax, shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_IssuanceOfCommonStockUnderEquityPlanAwardsNetOfTaxShares_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Issuance Of Common Stock Under Equity Plan Awards Net Of Tax Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_IssuanceOfCommonStockUnderEquityPlanAwardsNetOfTaxShares_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Issuance of common stock under equity plan awards, net of tax, shares.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ProfitLossSharingPercentageOnNetSales_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Profit loss sharing percentage on net sales</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ProfitLossSharingPercentageOnNetSales_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Profit Loss Sharing Percentage On Net Sales</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ProfitLossSharingPercentageOnNetSales_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Profit loss sharing percentage on net sales.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MajorCustomersAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Customer [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OrganizationAndNatureOfBusinessLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Organization And Nature Of Business [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OrganizationAndNatureOfBusinessLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Organization And Nature Of Business [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_OrganizationAndNatureOfBusinessLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Organization and nature of business.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Comprehensive Income [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MaximumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MaximumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Maximum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statistical Measurement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statistical Measurement [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Common Stock, Value, Issued, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Common Stock, Value, Issued, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Common Stock, Value, Issued, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Common stock investment value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Value, Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, par value of $0.001 per share - 250.0 shares authorized; outstanding - 98.6 in 2026 and 96.6 in 2025</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty revenue.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRevenue_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Royalty revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RoyaltyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RoyaltyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RoyaltyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Royalty</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyPercentageOnNetSales_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of royalty on net sales receives</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyPercentageOnNetSales_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Percentage On Net Sales</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyPercentageOnNetSales_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty percentage on net sales.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccruedLiabilitiesCurrentAndNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Accrued Liabilities, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccruedLiabilitiesCurrentAndNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License agreement accrued liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccruedLiabilitiesCurrentAndNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ScheduleOfCostSharingPaymentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Cost Sharing Payments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ScheduleOfCostSharingPaymentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Cost Sharing Payments Table [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ScheduleOfCostSharingPaymentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of cost sharing payments.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_Rule10B51PlanOneMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Rule 10b51 Plan One [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_Rule10B51PlanOneMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Rule 10b51 plan one.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_Rule10B51PlanOneMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Plan 1</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, shares authorized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Shares Authorized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRepurchaseOptionDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Repurchase Option Description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRepurchaseOptionDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty Repurchase Option Description.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RoyaltyRepurchaseOptionDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Royalty repurchase option description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AtTheMarketOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">At the Market Offering [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AtTheMarketOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">At-the-market offering.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_AtTheMarketOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">At-the-Market Offerings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ManufacturingFacilityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Manufacturing Facility [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ManufacturingFacilityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Manufacturing Related</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RelatedPartyTransactionLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Related Party Transaction [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RevenueFromContractWithCustomerTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RevenueFromContractWithCustomerTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Revenue from Contract with Customer [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityRegistrantName_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Registrant Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityRegistrantName_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Registrant Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_UnderwrittenPublicOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Underwritten Public Offering</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_UnderwrittenPublicOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Underwritten Public Offering [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_UnderwrittenPublicOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Underwritten public offering.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_HowardHornMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Howard Horn [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_HowardHornMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Howard horn.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_HowardHornMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Howard Horn [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Gross Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EvkeezaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Evkeeza.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EvkeezaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Evkeeza [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_EvkeezaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Evkeeza</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashInterestExpenseOnLiabilityRelatedToSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Non-cash interest expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashInterestExpenseOnLiabilityRelatedToSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non Cash Interest Expense On Liability Related To Sale Of Future Royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashInterestExpenseOnLiabilityRelatedToSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non cash interest expense on liability related to sale of future royalties.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashInterestExpenseOnLiabilityRelatedToSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Non-cash interest expense on liabilities for sales of future royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_NonCashInterestExpenseOnLiabilityRelatedToSaleOfFutureRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-cash interest expense on liabilities for sales of future royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherNonoperatingIncomeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Nonoperating Income (Expense)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherNonoperatingIncomeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other Nonoperating Income (Expense), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherNonoperatingIncomeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Additional Paid in Capital, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Additional Paid in Capital, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Additional Paid in Capital, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional paid-in capital</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid in Capital</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Events [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Income Tax Expense (Benefit), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Provision for income taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Expense (Benefit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_Accruedcollaborationpayables_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Accrued collaboration payables.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_Accruedcollaborationpayables_lbl" xlink:role="http://www.xbrl.org/2003/role/label">AccruedCollaborationPayables</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_Accruedcollaborationpayables_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued collaboration payables</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostSharingPaymentsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cost Sharing Payments [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostSharingPaymentsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cost sharing payments abstract.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share Based Compensation Arrangement By Share Based Payment Award [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_UpfrontPaymentsOfCollaboration_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Upfront payments of collaboration.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_UpfrontPaymentsOfCollaboration_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Upfront Payments of Collaboration</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_UpfrontPaymentsOfCollaboration_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Upfront payments of collaboration</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Common Stock, Shares Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Common Stock, Shares Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Other Comprehensive Income (Loss), Net of Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total accumulated other comprehensive loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated other comprehensive loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Receivable, Allowance for Credit Loss, Writeoff</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Credit losses recorded for receivables</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForRestructuring_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments for Restructuring</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForRestructuring_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash settled</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForRestructuring_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Cash settled/ adjustment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments to Acquire Property, Plant, and Equipment, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchase of property, plant, and equipment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments to Acquire Property, Plant, and Equipment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForProceedsFromOtherInvestingActivities_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForProceedsFromOtherInvestingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForProceedsFromOtherInvestingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payment for (Proceeds from) Other Investing Activity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfRestrictedCashAndCashEquivalentsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfRestrictedCashAndCashEquivalentsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restrictions on Cash and Cash Equivalents [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Assets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Assets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Assets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Statement [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restructuring Cost [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Selling, general and administrative</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Selling, General and Administrative Expenses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock shares sold</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Shares, New Issues</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ConsolidationVariableInterestEntityPolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Consolidation, Variable Interest Entity, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ConsolidationVariableInterestEntityPolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Variable Interest Entity, Policy</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Earnings Per Share, Diluted, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share, Diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net loss per share, diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisaggregationOfRevenueAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Disaggregation of Revenue [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CityAreaCode_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">City Area Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CityAreaCode_lbl" xlink:role="http://www.xbrl.org/2003/role/label">City Area Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ResearchGrantAgreementAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Research Grant Agreement [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ResearchGrantAgreementAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Research grant agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), Net of Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other comprehensive income (loss):</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other comprehensive income (loss)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PreFundedWarrantsAndStockIssuedDuringPeriodValueAtUnderwrittenPublicOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock and pre-funded warrants in connection with the underwritten public offering, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PreFundedWarrantsAndStockIssuedDuringPeriodValueAtUnderwrittenPublicOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Pre-funded Warrants And Stock Issued During Period Value At Underwritten Public Offering</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PreFundedWarrantsAndStockIssuedDuringPeriodValueAtUnderwrittenPublicOffering_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Pre-funded warrants and stock issued during period value at underwritten public offering.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_StockholdersEquityLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stockholders Equity [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_StockholdersEquityLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders Equity [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_StockholdersEquityLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Stockholders equity line items.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborationAndRoyaltyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaboration And Royalty [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborationAndRoyaltyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaboration and Royalty</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CollaborationAndRoyaltyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collaboration and royalty.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractWithCustomerLiabilityAdditionsDuringPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Contract with customer liability additions during period.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractWithCustomerLiabilityAdditionsDuringPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability Additions During Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_ContractWithCustomerLiabilityAdditionsDuringPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Counterparty Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Counterparty Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestorMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investor [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestorMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Third-Party Investor [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LicenseAgreementTermsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License Agreement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LicenseAgreementTermsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">License Agreement Terms [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredRevenueDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Revenue Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Property, Plant and Equipment, Net, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Property, Plant and Equipment, Net, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Property, Plant and Equipment, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property, plant, and equipment, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Property, Plant and Equipment, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total cash, cash equivalents, and restricted cash shown in the statements of cash flows</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Cash, cash equivalents and restricted cash at beginning of period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Cash, cash equivalents and restricted cash at end of period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CorporateBondSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Corporate Bonds</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CorporateBondSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Corporate Bond Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CorporateBondSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Corporate Bond Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Loss from operations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Income (Loss)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Deficit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RelatedPartyPaymentOfContribution_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Related Party Payment of Contribution</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RelatedPartyPaymentOfContribution_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Related Party Payment of Contribution</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_RelatedPartyPaymentOfContribution_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contribution amount paid</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_MereoBioPharma3LimitedMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Mereo</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_MereoBioPharma3LimitedMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Mereo Bio Pharma3 Limited [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_MereoBioPharma3LimitedMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Mereo BioPharma 3 Limited.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel1Member_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Inputs, Level 1 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel1Member_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 1</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Financing Activity, Including Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash provided by financing activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DaiichiSankyoCoLtdMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Daiichi Sankyo</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DaiichiSankyoCoLtdMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Daiichi Sankyo Co Ltd [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_DaiichiSankyoCoLtdMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Daiichi Sankyo Co., Ltd.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeTaxLiabilitiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Deferred Income Tax Liabilities, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeTaxLiabilitiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred tax liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeTaxLiabilitiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Income Tax Liabilities, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Common stock, Beginning balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Investments, Fair Value Disclosure, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Common stock, Ending balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LicensesAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Licenses Agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LicensesAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License Agreement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_LicensesAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Licenses Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostSharingPaymentsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cost Sharing Payments [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostSharingPaymentsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cost Sharing Payments [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_CostSharingPaymentsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cost sharing payments table.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">AOCI, Debt Securities, Available-for-sale, Adjustment, after Tax, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">AOCI, Debt Securities, Available-for-Sale, Adjustment, after Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unrealized loss on available-for-sale securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Securities Available For Sale [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityInteractiveDataCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Interactive Data Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityInteractiveDataCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Interactive Data Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Statement Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Income Location, Balance [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PaymentsMadeUnderAgreement_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Payments made under agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="rare_PaymentsMadeUnderAgreement_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Payments made under agreement</link:label>
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  <xsd:element id="rare_TheodoreHuizengaMember" name="TheodoreHuizengaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_HowardHornMember" name="HowardHornMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_AmendedAndRestatedTwoThousandFourteenEmployeeStockPurchasePlanMember" name="AmendedAndRestatedTwoThousandFourteenEmployeeStockPurchasePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_AtTheMarketOfferingMember" name="AtTheMarketOfferingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_ContractExecutionDate" name="ContractExecutionDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_PercentageOfGrossAccountsReceivableBalance" name="PercentageOfGrossAccountsReceivableBalance" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="rare_DaiichiSankyoCoLtdMember" name="DaiichiSankyoCoLtdMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_SeriesSeedPreferredStockMember" name="SeriesSeedPreferredStockMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_RoyaltyContractExecutionDate" name="RoyaltyContractExecutionDate" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_OptionToSellCommonStockAggregateOfferingPrice" name="OptionToSellCommonStockAggregateOfferingPrice" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_EvkeezaMember" name="EvkeezaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_TimeDepositsMember" name="TimeDepositsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_Rule10B51ArrModifiedFlag" name="Rule10B51ArrModifiedFlag" type="xbrli:booleanItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_LicenseAndCollaborationAgreementMember" name="LicenseAndCollaborationAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_RoyaltyStartDate" name="RoyaltyStartDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_StockIssuedDuringPeriodSharesAtMarketOffering" name="StockIssuedDuringPeriodSharesAtMarketOffering" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_ScheduleOfChangesInFairValueOfInvestmentInSecuritiesTableTextBlock" name="ScheduleOfChangesInFairValueOfInvestmentInSecuritiesTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_PreFundedWarrantsAndStockIssuedDuringPeriodValueAtUnderwrittenPublicOffering" name="PreFundedWarrantsAndStockIssuedDuringPeriodValueAtUnderwrittenPublicOffering" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_Rule10B51PlanOneMember" name="Rule10B51PlanOneMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_CostSharingPaymentsLineItems" name="CostSharingPaymentsLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_CostSharingPaymentsAbstract" name="CostSharingPaymentsAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_RoyaltyAgreementCounterpartyName" name="RoyaltyAgreementCounterpartyName" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_PaymentsMadeUnderAgreement" name="PaymentsMadeUnderAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_TexasAMUniversityMember" name="TexasAMUniversityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_IssuanceOfCommonStockUnderEquityPlanAwardsNetOfTaxShares" name="IssuanceOfCommonStockUnderEquityPlanAwardsNetOfTaxShares" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_PercentageOfRoyaltiesSold" name="PercentageOfRoyaltiesSold" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_RPIFinanceTrustTwoThousandNineteenMember" name="RPIFinanceTrustTwoThousandNineteenMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_RoyaltyPurchaseAgreementCAPAggregatePayment" name="RoyaltyPurchaseAgreementCAPAggregatePayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_NonRule10B51ArrModifiedFlag" name="NonRule10B51ArrModifiedFlag" type="xbrli:booleanItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_AnnualLicenseFeePayment" name="AnnualLicenseFeePayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_RoyaltiesAgreementTerritories" name="RoyaltiesAgreementTerritories" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_MepseviiMember" name="MepseviiMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_UnitedStatesAndCanadaMember" name="UnitedStatesAndCanadaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_LiabilitiesForSalesOfFutureRoyaltiesPolicyTextBlock" name="LiabilitiesForSalesOfFutureRoyaltiesPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_ManufacturingAndRelatedExpenses" name="ManufacturingAndRelatedExpenses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_ContractWithCustomerLiabilityAdditionsDuringPeriod" name="ContractWithCustomerLiabilityAdditionsDuringPeriod" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_FutureContingentMilestonePayments" name="FutureContingentMilestonePayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_AvailableForSaleSecuritiesContractualMaturity" name="AvailableForSaleSecuritiesContractualMaturity" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_RoyaltyRevenueForSalesInNorthAmericanTerritioryMember" name="RoyaltyRevenueForSalesInNorthAmericanTerritioryMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_DeferredCompensation" name="DeferredCompensation" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_NonControllingInterestInChangesAndAdjustments" name="NonControllingInterestInChangesAndAdjustments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_NonCashInterestExpenseOnLiabilityRelatedToSaleOfFutureRoyalties" name="NonCashInterestExpenseOnLiabilityRelatedToSaleOfFutureRoyalties" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="rare_UpfrontPaymentsOfCollaboration" name="UpfrontPaymentsOfCollaboration" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="rare_LiabilityRelatedToSaleOfFutureRoyalties" name="LiabilityRelatedToSaleOfFutureRoyalties" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_PercentageOfRightToReceiveRoyaltyPaymentsOnNetSales" name="PercentageOfRightToReceiveRoyaltyPaymentsOnNetSales" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_OrganizationAndNatureOfBusinessLineItems" name="OrganizationAndNatureOfBusinessLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_ProceedsFromIssuanceOfCommonStockAtMarketOffering" name="ProceedsFromIssuanceOfCommonStockAtMarketOffering" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="rare_Regulatorymilestonepaymentsachieved" name="Regulatorymilestonepaymentsachieved" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="rare_CrysvitaMember" name="CrysvitaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_ProfitLossSharingPercentageOnNetSales" name="ProfitLossSharingPercentageOnNetSales" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_OpenMarketSaleMember" name="OpenMarketSaleMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_ProceedsFromRoyaltiesReceivedFinancingActivities" name="ProceedsFromRoyaltiesReceivedFinancingActivities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="rare_OrganizationAndNatureOfBusinessTable" name="OrganizationAndNatureOfBusinessTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_DeferredCompensationLiabilitiesMember" name="DeferredCompensationLiabilitiesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_ResearchGrantAgreementAbstract" name="ResearchGrantAgreementAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_DeferredCompensationAssetsMember" name="DeferredCompensationAssetsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_LiabilitiesForSalesOfFutureRoyaltiesCurrent" name="LiabilitiesForSalesOfFutureRoyaltiesCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_ResearchAndClinicalStudyExpenses" name="ResearchAndClinicalStudyExpenses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_CollaborativeArrangementAndNoncollaborativeArrangementTransactionsDisclosureTextBlock" name="CollaborativeArrangementAndNoncollaborativeArrangementTransactionsDisclosureTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="rare_TwoThousandTwentyTwoOMERSAgreementMember" name="TwoThousandTwentyTwoOMERSAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_CostOfSales" name="CostOfSales" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="rare_ClinicalMilestoneAggregate" name="ClinicalMilestoneAggregate" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_CollaborativeArrangementsEffectiveReductionOfExpenseInResearchAndDevelopmentExpenses" name="CollaborativeArrangementsEffectiveReductionOfExpenseInResearchAndDevelopmentExpenses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_Accruedcollaborationpayables" name="Accruedcollaborationpayables" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="rare_CustomerTwoMember" name="CustomerTwoMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_EuropeanUnionAndSwitzerlandAndTurkeyMember" name="EuropeanUnionAndSwitzerlandAndTurkeyMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_UnderwrittenPublicOfferingMember" name="UnderwrittenPublicOfferingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_RPIFinanceTrustMember" name="RPIFinanceTrustMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="rare_LicensesAgreementMember" name="LicensesAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
</xsd:schema>
