Neurogene’s AAV9 Gene Therapy NGN-401 Earns FDA Breakthrough Therapy Designation for Rett Syndrome

NEW YORK — February 26, 2026 —

Neurogene Inc. announced that the U.S. Food and Drug Administration has granted Breakthrough Therapy designation to NGN-401, an investigational AAV9 gene therapy for Rett syndrome.

The designation is based on interim Phase 1/2 data (cutoff: October 30, 2025) demonstrating clinically meaningful, durable, and multidomain functional improvements, including continued skill acquisition over time. The FDA’s review included patient-level data and supporting video documentation.

NGN-401 is a one-time, intracerebroventricularly administered AAV9 gene therapy designed to deliver the full-length human MECP2 gene using Neurogene’s proprietary EXACT™ transgene regulation platform to tightly control MeCP2 expression on a cell-by-cell basis. The therapy aims to broadly target the brain and nervous system based on nonclinical biodistribution data.

NGN-401 is currently being evaluated in the Embolden™ registrational trial, with dosing completion expected in Q2 2026. The company also plans to present additional interim Phase 1/2 clinical data in mid-2026.

In addition to Breakthrough Therapy designation, NGN-401 has received multiple regulatory recognitions, including RMAT, Fast Track, Orphan Drug, Rare Pediatric Disease designations, and selection for the FDA’s START Pilot Program.

If successful, NGN-401 could represent a best-in-class, one-time AAV9 gene therapy for patients living with Rett syndrome, a rare and severe neurodevelopmental disorder with significant unmet medical need.