Neurogene, a biotechnology company developing genetic medicines for rare neurological conditions, has completed dosing in its EMBOLDEN registrational trial of NGN-401 — an investigational one-time gene therapy for Rett syndrome.
The trial, which aims to evaluate the safety and potential benefits of NGN-401 in females with Rett syndrome aged three and older, originally planned to enroll 20 participants but expanded to 25 due to strong interest from families and the Rett syndrome community.
What the trial is studying
NGN-401 is designed to deliver a functional copy of the MECP2 gene, which is typically affected in people with Rett syndrome. The therapy is administered as a single dose directly to the brain and nervous system.
The EMBOLDEN trial is evaluating whether participants show meaningful clinical improvement and achieve new developmental milestones over a 12-month period. Results from the trial are expected in the second half of 2027.
Safety so far
As of 7 June 2026, the therapy has been generally well-tolerated across 35 participants treated at the current dose level. No cases of a serious immune complication called hemophagocytic lymphohistiocytosis (HLH) have been reported at this dose.
Interim results from an earlier Phase 1/2 trial showed sustained improvements across multiple developmental areas, with participants continuing to gain new skills over time. Updated data from that earlier trial, including at least 12 months of follow-up for all 10 participants, is expected in mid-2026.
What this means
Completion of enrollment is an important step forward, bringing this potential treatment closer to regulatory review. If the trial demonstrates meaningful benefit, Neurogene plans to seek approval from regulatory authorities to make the therapy available to eligible patients.
Rachel McMinn, CEO of Neurogene, thanked the participants, families and clinical investigators for their partnership and trust in the development of NGN-401.
Looking ahead
RSE will continue to monitor developments in gene therapy research for Rett syndrome. While much work remains, advances like these represent hope for families affected by Rett syndrome across Europe and beyond.
For more information about the EMBOLDEN trial, visit neurogene.com or speak with your clinical team.
