Intangible Assets

6 Months Ended

Mar. 31, 2024

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 assets:

	Gross Carrying Amount		Accumulated Amortization		Impairment		Net Carrying Amount		Useful Lives
	(in thousands)								(in years)
As of March 31, 2024
Patents	$	21,728	$	14,097	$	—	$	7,631	14
License	3,129		1,348		—		1,781		21
Total intangible assets, net	$	24,857	$	15,445	$	—	$	9,412
As of September 30, 2023
Patents	$	21,728	$	13,321	$	—	$	8,407	14
License	3,129		1,274		—		1,855		21
Total intangible assets, net	$	24,857	$	14,595	$	—	$	10,262

Intangible assets are reviewed annually for impairment and more frequently if potential impairment indicators exist. No impairment indicators were identified during the six months ended March 31, 2024 and 2023.

Intangible assets with definite useful lives are amortized on a straight-line basis over their useful lives. Intangible assets amortization expense was $0.4 million for each of the three months ended March 31, 2024 and 2023, and $0.9 million for each of six months ended March 31, 2024 and 2023. 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 March 31, 2024:

	Amortization Expense
Year Ending September 30,	(in thousands)
2024 (remainder)	$	850
2025	1,700
2026	1,700
2027	1,700
2028	1,700
Thereafter	1,762
Total	$	9,412