v3.22.2.2
Intangible Assets
 12 Months Ended
Sep. 30, 2022
Goodwill and Intangible Assets Disclosure [Abstract]  
Intangible Assets INTANGIBLE ASSETS
Intangible assets subject to amortization include patents and a license agreement capitalized as part of the Novartis RNAi asset acquisition in March 2015. The following table presents the components of intangible asset:
Gross Carrying AmountAccumulated AmortizationImpairmentNet Carrying AmountUseful Lives
(amounts in thousands)(in years)
As of September 30, 2022
Patents$21,728 $11,770 $— $9,958 14
License3,129 1,125 — 2,004 21
Total intangible assets, net$24,857 $12,895 $— $11,962 
As of September 30, 2021
Patents$21,728 $10,217 $— $11,511 14
License3,129 977 — 2,152 21
Total intangible assets, net$24,857 $11,194 $— $13,663 
Intangible assets are reviewed annually for impairment and more frequently if potential impairment indicators exist. No impairment indicators were identified during 2022 and 2021.
Intangible assets with definite useful lives are amortized on a straight-line basis over their useful lives. Intangible assets amortization expense in each of 2022, 2021, and 2020 was $1.7 million. None of the intangible assets with definite useful lives are anticipated to have a residual value.
The following table presents the estimated future amortization expense related to intangible assets as of September 30, 2022:
Amortization Expense
Year Ending September 30, (in thousands)
2023$1,700 
20241,700 
20251,700 
20261,700 
20271,700 
Thereafter3,462 
Total$11,962