Segment Information (Details) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2025 USD ($)	Mar. 31, 2025 USD ($)	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Jun. 30, 2025 USD ($) segment	Jun. 30, 2024 USD ($)
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		$ 925		$ 0	$ 925
Total research and development expenses	19,366		15,744		37,131	29,285
General and administrative specific expenses:
Total general and administrative expenses	6,715		5,315		14,869	10,553
Net loss	(22,016)	$ (22,647)	(18,492)	$ (16,921)	(44,663)	(35,413)
Reportable Segment
Program specific expenses:
Total research and development expenses	19,366		15,744		37,131	29,285
General and administrative specific expenses:
Total general and administrative expenses	6,715		5,315		14,869	10,553
Other income (expense)	4,065		1,642		7,337	3,500
Net loss	(22,016)		(18,492)		(44,663)	(35,413)
Rett syndrome | Reportable Segment
Program specific expenses:
Total research and development expenses	7,052		2,798		11,576	4,817
Batten disease | Reportable Segment
Program specific expenses:
Total research and development expenses	401		1,734		1,246	2,924
Early Discovery | Reportable Segment
Program specific expenses:
Total research and development expenses	720		1,705		2,007	3,171
Personnel-related | Reportable Segment
Program specific expenses:
Total research and development expenses	5,125		4,557		10,529	9,275
General and administrative specific expenses:
Total general and administrative expenses	2,212		1,964		4,696	4,065
Stock-based compensation | Reportable Segment
Program specific expenses:
Total research and development expenses	1,575		1,375		3,146	1,939
General and administrative specific expenses:
Total general and administrative expenses	1,833		939		4,310	1,419
Manufacturing | Reportable Segment
Program specific expenses:
Total research and development expenses	3,635		2,815		6,742	5,794
Other | Reportable Segment
Program specific expenses:
Total research and development expenses	858		760		1,885	1,365
General and administrative specific expenses:
Total general and administrative expenses	1,080		783		2,364	1,334
Professional and consultant fees | Reportable Segment
General and administrative specific expenses:
Total general and administrative expenses	970		998		2,247	2,500
Office-related | Reportable Segment
General and administrative specific expenses:
Total general and administrative expenses	$ 620		$ 631		$ 1,252	$ 1,235