NGN-401, an AAV9 gene therapy delivering the full-length human MECP2 gene, showed positive interim data in Rett syndrome patients, with all low-dose cohort participants achieving 'much improved' status on CGI-I and significant improvements in RSBQ. The therapy demonstrated skill gains in core clinical areas, including hand function, language, and ambulation, with no signs of MECP2 overexpression toxicity. Neurogene plans to complete low-dose cohort enrollment by Q4 2024 and anticipates additional interim data in H2 2025.