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 December 31, 2024
Patents	$	21,728	$	15,261	$	—	$	6,467	14
License	3,129		1,459		—		1,670		21
Total intangible assets, net	$	24,857	$	16,720	$	—	$	8,137

As of September 30, 2024
Patents	$	21,728	$	14,873	$	—	$	6,855	14
License	3,129		1,422		—		1,707		21
Total intangible assets, net	$	24,857	$	16,295	$	—	$	8,562

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


	Amortization Expense
Year Ending September 30,	(in thousands)
2025 (remainder)	$	1,275
2026	1,700
2027	1,700
2028	1,700
2029	795
2030 and thereafter	967
Total	$	8,137