Neurogene Inc. (NASDAQ: NGNE) announced it has completed dosing in its Embolden registrational trial of NGN-401, a gene therapy for Rett syndrome. The company dosed 25 participants, exceeding its initial target of 20 due to demand from the Rett syndrome community.

The trial's statistical analysis plan had pre-specified an intent-to-treat population of up to 24 participants. Neurogene elected to overenroll and dose all eligible participants already in screening to ensure timely completion of dosing.

Embolden is a multi-center, single-arm, open-label, baseline-controlled registrational trial evaluating the efficacy, safety and tolerability of a one-time dose of NGN-401 at 1E15 vg in females with Rett syndrome ages three and older. The primary endpoint combines a Clinical Global Impression-Improvement score of ≤ 3 and a gain from baseline of any one developmental milestone from a pre-specified list.

The primary analysis for the planned Biologics License Application submission is expected after the first 24 participants complete 12 months of follow-up, with topline data anticipated in the second half of 2027. The threshold for success requires a 33% minimum response rate, or 8 of 24 participants.

As of June 7, 2026, NGN-401 at the 1E15 vg dose has been generally well-tolerated across 35 participants. No cases of hemophagocytic lymphohistiocytosis were reported at this dose level in either the Phase 1/2 trial or the Embolden trial.

The company plans to present updated interim safety and efficacy data from the Phase 1/2 trial, including at least 12 months of follow-up for all 10 participants, in mid-2026.

NGN-401 is an investigational AAV9 gene therapy that delivers the full-length human MECP2 gene and includes Neurogene's EXACT transgene regulation technology. The therapy has received multiple regulatory designations including Breakthrough Therapy and Fast Track designations from the FDA.