NGN-401

A one-time gene therapy that delivers a working copy of the MECP2 gene directly into the brain. Uses proprietary self-regulating technology to prevent overexpression, which has been a major safety challenge for Rett gene therapies. Received FDA Breakthrough Therapy Designation.

NGN-401 delivers a functional copy of the MECP2 gene to brain cells using a harmless virus (AAV9) as a delivery vehicle. What makes it unique is Neurogene's EXACT technology, which acts like a built-in thermostat: it automatically adjusts how much MECP2 protein each cell produces, keeping levels in a safe range. This is critical because too much MECP2 is just as harmful as too little.

As a gene therapy delivered directly into the brain, potential risks include immune reactions and neurological effects. Early clinical data has shown a positive safety and tolerability profile. Long-term monitoring is ongoing.

Delivered as a single intracerebroventricular (ICV) injection, meaning it is injected directly into the fluid-filled spaces of the brain during a surgical procedure. This is a one-time treatment.

NGN-401 is currently in phase 2 clinical trials for Rett Syndrome. It has not yet received FDA approval.

EXACT (Expression Attenuation via Construct Tuning) is Neurogene's self-regulating gene expression system. In Rett syndrome, having too much MECP2 protein is just as dangerous as having too little, causing a condition called MECP2 duplication syndrome. EXACT acts like a built-in thermostat: when MECP2 levels get too high in a cell, the system automatically reduces production. This prevents the toxicity from overexpression that has been a major safety challenge for all Rett gene therapy programs.

NGN-401 is given as a single intracerebroventricular (ICV) injection, meaning it is injected directly into the fluid-filled spaces of the brain during a neurosurgical procedure. This delivery route allows the AAV9 vector to reach brain cells throughout the central nervous system. The procedure is a one-time event, and the gene therapy is designed to provide lasting benefit.

Interim data from the Phase 1/2 study showed clinically meaningful functional improvements across multiple domains in treated patients. Patients demonstrated continued skill acquisition over time, meaning they kept gaining new abilities after treatment. The safety profile was positive, with no MECP2 overexpression-related toxicity reported, supporting the EXACT technology's ability to regulate protein levels. FDA granted Breakthrough Therapy Designation in February 2026.

Both are AAV9-based gene therapies delivering the MECP2 gene, but they use different self-regulation technologies and delivery routes. NGN-401 uses EXACT technology and is delivered by ICV injection (into the brain ventricles), while TSHA-102 uses miRARE technology and is delivered by intrathecal injection (into the spinal fluid). Both aim to solve the same MECP2 dosage challenge. Direct comparison of efficacy is not possible since both are still in clinical trials.

Dosing in the Embolden registrational trial finished in June 2026, so it is no longer enrolling. Topline results are expected in the second half of 2027. Families interested in future studies should talk with their neurologist and check ClinicalTrials.gov.