Genetic medicine company Neurogene Inc (NASDAQ: NGNE) on Monday reported updated positive long-term clinical data from its Phase 1/2 trial of NGN-401 gene therapy in females with Rett syndrome, showing sustained and progressive developmental gains across all participants.

Across 10 participants, a total of 47 developmental milestones were gained, averaging 4.7 per patient, with all participants improving on Clinical Global Impression-Improvement scores and achieving at least one developmental milestone. The company reported continued improvement over up to 30 months of follow-up, with no plateau or loss of milestones observed.

The treatment demonstrated a generally well-tolerated safety profile at the 1E15 vg dose, with no treatment-related serious adverse events or dose-limiting toxicities reported as of 16 June 2026. Most adverse events were mild or moderate and consistent with known risks of AAV gene therapy.

Neurogene also confirmed dosing has been completed in its Embolden registrational trial, with topline data expected in the second half of 2027.