Segment Information (Details) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2025 USD ($)	Jun. 30, 2025 USD ($)	Mar. 31, 2025 USD ($)	Sep. 30, 2024 USD ($)	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Sep. 30, 2025 USD ($) segment	Sep. 30, 2024 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment							1
Number of reportable segments | segment							1
Program specific expenses:
Revenue under licensing agreements	$ 0			$ 0			$ 0	$ 925
Total research and development expenses	17,241			16,285			54,372	45,570
General and administrative specific expenses:
Total general and administrative expenses	6,557			5,895			21,427	16,448
Net loss	(20,953)	$ (22,016)	$ (22,647)	(20,217)	$ (18,492)	$ (16,921)	(65,616)	(55,630)
Reportable Segment
Program specific expenses:
Total research and development expenses	17,241			16,285			54,372	45,570
General and administrative specific expenses:
Total general and administrative expenses	6,557			5,895			21,427	16,448
Other income	2,845			1,963			10,183	5,463
Net loss	(20,953)			(20,217)			(65,616)	(55,630)
Rett syndrome | Reportable Segment
Program specific expenses:
Total research and development expenses	5,559			3,444			17,135	8,261
Batten disease | Reportable Segment
Program specific expenses:
Total research and development expenses	136			1,832			1,382	4,756
Early Discovery | Reportable Segment
Program specific expenses:
Total research and development expenses	614			1,329			2,621	4,500
Personnel-related | Reportable Segment
Program specific expenses:
Total research and development expenses	5,449			4,512			15,978	13,787
General and administrative specific expenses:
Total general and administrative expenses	2,248			2,016			6,944	6,081
Stock-based compensation | Reportable Segment
Program specific expenses:
Total research and development expenses	1,669			1,272			4,815	3,211
General and administrative specific expenses:
Total general and administrative expenses	1,697			1,201			6,007	2,620
Manufacturing | Reportable Segment
Program specific expenses:
Total research and development expenses	3,111			3,220			9,856	9,014
Other | Reportable Segment
Program specific expenses:
Total research and development expenses	703			676			2,585	2,041
General and administrative specific expenses:
Total general and administrative expenses	905			1,074			3,270	2,408
Professional and consultant fees | Reportable Segment
General and administrative specific expenses:
Total general and administrative expenses	1,088			969			3,335	3,469
Office-related | Reportable Segment
General and administrative specific expenses:
Total general and administrative expenses	$ 619			$ 635			$ 1,871	$ 1,870