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


	As of December 31,
	2021			2020
	(in thousands)
Patents	$	12,382		$	11,210
In-licensed rights		8,573			8,073
Software licenses		299			1,554
Intangible assets, gross		21,254			20,837
Less: accumulated amortization		(7,015	)		(7,209	)
Intangible assets, net	$	14,239		$	13,628

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. 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 the years ended December 31, 2021, 2020 and 2019, the Company recorded $0.7 million, $0.7 million and $0.8 million, respectively, of amortization related to the in-licensed rights.

Patent amortization expense was $0.6 million, $0.6 million and $0.4 million for the years ended December 31, 2021, 2020 and 2019, respectively. The Company also expensed the remaining net book value of previously capitalized patents that were later abandoned of $0.5 million, $0.1 million and $0.2 million for the years ended December 31, 2021, 2020 and 2019, 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, $0.5 million and $0.4 million for the years ended December 31, 2021, 2020 and 2019, respectively.

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


	As of December 31, 2021
	(in thousands)
2022	$	1,395
2023		1,394
2024		1,391
2025		1,330
2026		1,200
Thereafter		7,529
Total	$	14,239