The following table summarizes the components of the Company’s intangible assets for each of the periods indicated:


	As of December 31,
	2022			2021
	(in thousands)
In-licensed rights	$	8,573		$	8,573
Patents		5,106			12,382
Software licenses		302			299
Intangible assets, gross		13,981			21,254
Less: accumulated amortization		(6,403	)		(7,015	)
Intangible assets, net	$	7,578		$	14,239

The in-licensed rights relate to agreements with BioMarin and UWA. As a result of the FDA approval of EXONDYS 51, VYONDYS 53 and AMONDYS 45, the Company recorded in-licensed rights of $1.0 million, $0.5 million and $0.5 million, respectively, related to its agreement with UWA. Following the execution of the settlement and license agreements with BioMarin in July 2017, the Company recorded a $6.6 million intangible asset related to EXONDYS 51 in the U.S. The in-licensed rights are being amortized on a straight-line basis over the remaining life of the related patent because the life of the related patent reflects the expected time period that the Company will benefit from the in-licensed right. For more information about the in-licensed rights, please read Note 3, License and Collaboration Agreements. For all the years ended December 31, 2022, 2021 and 2020, the Company recorded $0.7 million, respectively, of amortization related to the in-licensed rights.

Patent amortization expense was $1.1 million, $0.6 million and $0.6 million for the years ended December 31, 2022, 2021 and 2020, respectively. The Company also expensed the remaining net book value of previously capitalized patents that were later abandoned of $6.0 million, $0.5 million and $0.1 million for the years ended December 31, 2022, 2021 and 2020, respectively, which were included in research and development expenses on the consolidated statements of operations and comprehensive loss.

Amortization related to internal use software was less than $0.1 million for the years ended December 31, 2022 and 2021, respectively, and $0.5 million for the year ended December 31, 2020.

The following table summarizes the estimated future amortization for intangible assets:


	As of December 31, 2022
	(in thousands)
2023	$	1,032
2024		1,026
2025		969
2026		837
2027		767
Thereafter		2,947
Total	$	7,578