ETX101

A one-time gene therapy that targets the genetic root cause of Dravet syndrome by increasing production of the Nav1.1 protein specifically in the inhibitory brain cells where it matters most. Early data suggests cognitive benefits when given before age 2. Received FDA Breakthrough Therapy Designation in January 2026.

ETX101 delivers genetic instructions that boost production of the Nav1.1 sodium channel protein, but only in the specific brain cells (GABAergic interneurons) that need it most. These are the cells that normally prevent seizures by calming overactive brain circuits. A single injection into the brain's fluid aims to provide long-lasting correction of the protein deficiency that causes Dravet syndrome.

Clinical trials have reported a favorable safety profile with no treatment-related serious adverse events across 4 dose levels tested. As with all gene therapies, potential risks include immune reactions to the viral vector. Long-term monitoring is ongoing.

Delivered as a single intracerebroventricular (ICV) injection into the fluid-filled spaces of the brain during a surgical procedure. This is a one-time treatment designed to provide lasting benefit.

ETX101 is currently in phase 2 clinical trials for Dravet Syndrome. It has not yet received FDA approval.

Both target the underlying SCN1A deficiency in Dravet syndrome but through different approaches. Zorevunersen is an antisense oligonucleotide that requires ongoing intrathecal injections every 4 months to boost Nav1.1 production from the existing working gene. ETX101 is a one-time gene therapy delivered by AAV9 that provides lasting genetic instructions to increase Nav1.1 expression specifically in GABAergic inhibitory neurons. ETX101 aims for a durable one-time treatment, while zorevunersen requires chronic dosing.

In Dravet syndrome, the Nav1.1 protein is most important in GABAergic inhibitory interneurons, which are the brain cells responsible for calming overactive neural circuits. Increasing Nav1.1 in excitatory neurons could potentially worsen seizures. ETX101 uses a cell-type-specific regulatory element that restricts gene expression to inhibitory neurons, ensuring the protein boost occurs only where it is needed and avoiding the risk of making seizures worse.

Interim data from the POLARIS program showed positive efficacy signals across 4 dose levels, with no treatment-related serious adverse events. Notably, children treated before age 2 showed substantial acceleration in cognitive skill acquisition by 16 weeks after injection, suggesting that early intervention may provide additional developmental benefits beyond seizure control.

ETX101 is not yet approved and is available only through clinical trials. The pivotal ENDEAVOR Part 2 study dosed its first patient in May 2026, and Encoded expects enrollment to finish by the end of 2026. The POLARIS program includes trials in the US, UK, and Australia. Families interested in enrollment should discuss eligibility with their neurologist and check ClinicalTrials.gov for active sites.

ETX101 is given as a single intracerebroventricular (ICV) injection, meaning it is injected directly into the fluid-filled ventricles of the brain during a neurosurgical procedure. This route ensures the AAV9 vector reaches brain cells throughout the central nervous system. While more invasive than a spinal injection, it may provide more complete brain coverage. The procedure is a one-time event.