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Dravet syndrome has long represented one of the most challenging pediatric epilepsies encountered in neurology and genetic medicine. Caused primarily by loss‑of‑function variants in SCN1A, the disorder emerges in infancy with prolonged febrile seizures and evolves into a lifelong condition marked by treatment‑resistant epilepsy, developmental delay, and significant morbidity. As the gene and cell therapy community gathers for the American Society of Gene and Cell Therapy (ASGCT) Annual Meeting, the field’s attention is turning toward approaches capable not only of reducing seizures but also of altering the developmental trajectory that defines the disorder. This year’s Presidential Symposium features new data on ETX101, an investigational gene regulation therapy from Encoded Therapeutics, that appears to move the needle on both fronts.

Encoded Therapeutics, a clinical‑stage biotechnology company developing precision genetic medicines for severe neurological disorders, has engineered ETX101 as a one‑time AAV9‑based therapy designed to increase expression of SCN1A. Rather than replacing or editing the gene, ETX101 aims to restore physiologic sodium channel function in inhibitory interneurons. The company’s Phase I/II POLARIS program is evaluating the therapy across multiple international sites in children ranging from six months to seven years of age.

The dataset presented at the ASGCT Presidential Symposium expands the emerging clinical profile of ETX101, incorporating additional patients, early readouts from the highest dose level, and longer‑term follow‑up. Across the cohort, treatment with a single intracerebroventricular dose produced a robust and dose‑dependent antiseizure effect that persisted through 52 weeks of observation. At dose level three, children experienced a median seizure reduction of approximately 76%, a notable finding given that this developmental window is typically associated with escalating seizure burden despite standard therapies. Early data from the top dose level suggest even stronger responses in participants who did not receive sirolimus, consistent with preclinical evidence that the drug can dampen protein expression.

Beyond seizure control, the therapy appears to influence developmental domains that are rarely improved in Dravet syndrome. Children who reached one year of follow‑up demonstrated measurable gains across communication, motor function, and other adaptive behaviors, as assessed by caregiver‑reported Vineland Adaptive Behavior Scales. Particularly striking were the trajectories of children treated before age two. In this group, cognitive assessments showed early and sustained divergence from the stagnation observed in the ENVISION natural history study, with trajectories more consistent with neurotypical development over the first year after treatment.

Families and clinicians have taken note of the dual signal emerging from the POLARIS dataset. “Parents of children with Dravet syndrome live with the fear of every seizure and the heartbreak of watching development stall,” said Mary Anne Meskis, CEO of the Dravet Syndrome Foundation. “To see the early and robust seizure reductions paired with meaningful developmental gains is profoundly encouraging. Families have been waiting for therapies that don’t just manage symptoms but give their children a chance to keep learning and growing.”

Encoded’s chief medical officer, Sal Rico, MD, PhD, underscored the significance of the findings. “Watching these young children not only achieve durable seizure reduction but also show early evidence of neurodevelopmental rescue is truly remarkable,” he said. “These data reinforce our belief that ETX101 has the potential to change the course of the disease and future outlook for the Dravet community.”

ETX101 has been well tolerated across all four dose levels, with no treatment‑related serious adverse events. Transaminase elevations, a known AAV class effect, were the most common treatment‑related finding; they were asymptomatic and resolved with standard management.

As the ASGCT community continues to explore the boundaries of genetic medicine, ETX101’s early results highlight the promise of targeted gene regulation as a therapeutic modality. For a disorder like Dravet syndrome, the possibility of addressing both seizures and developmental delay marks an important moment for the field.

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