47 total developmental milestones gained across 10 participants, with durable treatment effect and no plateau or milestone loss through 30 months of follow-up

100% of participants improved in CGI-I score and gained ≥1 developmental milestone, with an average of 4.7 milestones per participant, and all gaining ≥1 developmental milestone in the past 12 months

Developmental milestones were gained in a progressive, stepwise sequence, suggesting a restart of development post-treatment

NGN-401 at the 1E15 vg dose remains generally well-tolerated (N=35) as of data cutoff date of June 16, 2026

Dosing complete in the EmboldenTM registrational trial with no treatment-related SAEs or DLTs as of data cutoff date of June 16, 2026, with topline data anticipated in 2H 2027

Company to host investor/analyst webcast today at 8:00 a.m. ET

Neurogene Inc. (NASDAQ:NGNE), a clinical-stage company founded to bring life-changing genetic medicines to patients and families affected by rare neurological diseases, today announced updated, positive data from its Phase 1/2 clinical trial evaluating NGN-401 gene therapy for the treatment of females with Rett syndrome.

Across 10 participants, 47 total developmental milestones were gained (average of 4.7 per participant), with both pediatric and adolescent/adult participants demonstrating clinical response and continued, progressive improvements through 30 months of follow-up, with no plateau or loss of milestones observed.