Childhood play photograph by Vanessa Bucceri / Unsplash. Representative image, not a trial participant.
For a childhood epilepsy treatment, fewer seizures would already be a major achievement. The more ambitious goal is helping a child keep learning, communicating and gaining everyday skills.
That is the possibility behind ETX101, an experimental gene therapy for a genetic form of Dravet syndrome. On 8 September 2026, developer Encoded Therapeutics reported updated Phase I/II findings presented by Melbourne neurologist Professor Ingrid Scheffer. The results are encouraging, but remain early evidence. Encoded’s September update
The target is one of the brain’s electrical controls
Dravet syndrome can involve prolonged, difficult-to-control seizures and developmental problems. Many cases involve the SCN1A gene, which provides instructions for part of a sodium channel called NaV1.1. These channels help nerve cells generate and transmit electrical signals. A gene change that reduces their function can disturb that communication. MedlinePlus Genetics
The biology helps explain why seizure counts cannot tell the whole story. Brain signalling also supports learning and movement. A treatment aimed at an underlying genetic mechanism therefore needs to be tested against outcomes beyond the number of seizures recorded in a diary.
ETX101 delivers instructions for a regulatory protein designed to increase SCN1A activity in particular inhibitory neurons—the cells that help restrain electrical activity. It uses an engineered, non-replicating virus as a delivery vehicle. This is gene regulation, designed to increase output from an existing gene, rather than cutting out and replacing the faulty DNA sequence. ETX101’s mechanism
Its intended one-time administration is a specialist procedure: an injection into a fluid-filled space within the brain. “One-time” describes the dosing strategy; it does not establish a lifetime benefit. Treatment approach
The promising numbers need their denominators
Encoded reported median seizure-frequency reductions of approximately 76% in five children at one dose level and 60% in nine at another, measured from week five through week 52 or the latest available visit. It also reported developmental gains, including encouraging trajectories among children treated before age two. September clinical update
A median describes the middle of a group’s results. It does not mean every child improved by that amount. The small groups and different observation periods also make comparisons between doses unreliable.
These early studies were open-label: families and researchers knew children received the therapy. Developmental comparisons with a separate natural-history study are useful for generating hypotheses, but cannot provide the same protection against bias as random assignment within one trial. Differences in age, baseline ability, supportive care and assessment can influence the apparent result. Study design
The safety findings also deserve attention. Encoded reported no treatment- or procedure-related serious adverse events through its data cutoff, but seven of 21 participants had raised liver enzymes and three had low platelet counts; the company said these abnormalities resolved. Small studies cannot exclude uncommon or delayed risks. Safety report
The decisive test is already underway
The next stage is ENDEAVOR Part 2. Encoded announced its first participant had been dosed in May 2026, with the pivotal study designed to evaluate 30 infants and young children. “Pivotal” means intended to provide evidence supporting a regulatory application; it does not mean approval has been granted. Pivotal-study announcement
The registered design randomly assigns participants to treatment or a sham procedure with delayed treatment. Blinded assessments include seizure frequency and cognitive development. That structure should make it easier to distinguish a treatment effect from the changes that can occur during childhood and clinical follow-up. ClinicalTrials.gov
On 9 September, Encoded also announced US$275 million in financing, including support for pivotal development and manufacturing. That helps fund the programme; it is not clinical evidence. Financing announcement
For now, ETX101 remains investigational. The result worth watching is whether fewer seizures are accompanied by sustained, measurable gains in daily life—and whether that benefit holds up when the comparison becomes much tougher.
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