Gene Therapy Redefines Hope for Dravet Syndrome Beyond Seizure Control

SOUTH SAN FRANCISCO, CA – September 08, 2026 – In the world of biotechnology, a true breakthrough is one that doesn't just manage a disease, but fundamentally alters its trajectory. New data from Encoded Therapeutics suggests its investigational gene therapy, ETX101, may be on the cusp of doing just that for children with Dravet syndrome, a severe and often devastating form of epilepsy. The results, presented at the 16th European Epilepsy Congress, paint a picture of a treatment that extends far beyond seizure control, offering the tantalizing possibility of reversing developmental delays and rewriting the future for these young patients.

For decades, the standard of care for Dravet syndrome has been a frustrating cycle of managing symptoms. Caused by a mutation in the SCN1A gene, the disorder leads to relentless, drug-resistant seizures, profound cognitive and motor impairments, and a significant risk of premature death. Existing therapies, while sometimes offering partial relief from seizures, do little to address the underlying genetic cause or the associated neurodevelopmental decline. Encoded’s latest update from its POLARIS Phase 1/2 trials suggests a new paradigm may be within reach.

A Dual-Action Breakthrough

The data presented by Encoded demonstrates that a single administration of ETX101 delivers not just substantial, but also durable, seizure reduction. In participants who have been observed for a full year, those at the two highest dose levels experienced a median reduction in monthly countable seizure frequency of approximately 79% and 89%, respectively. These are not merely statistical wins; for families living under the constant threat of the next seizure, such reductions can be life-altering.

“With longer follow-up and additional data available, we are encouraged by the magnitude and durability of seizure reduction following a single administration of ETX101,” said Sal Rico, M.D., Ph.D., Chief Medical Officer of Encoded Therapeutics. “Importantly, the emerging clinical profile extends beyond seizure control.”

It is this extension “beyond seizure control” that represents the most significant departure from the status quo. The data indicates that ETX101 is fostering progressive gains in cognition and adaptive behavior. In children treated before the age of two, developmental trajectories, as measured by the Bayley-4 cognitive scale, began approaching the range expected for neurotypical children. This is a profound divergence from the developmental stagnation typically observed in Dravet syndrome, where the gap with healthy peers widens over time.

Furthermore, across the full age range of trial participants, clinically meaningful improvements were noted in communication, motor skills, and socialization. The oldest participant in the cohort, treated at nearly four years old, not only saw a substantial drop in seizures but also experienced meaningful developmental gains. This suggests the therapy's benefits are not limited to the very youngest patients.

“In clinic, we see how persistent seizures and developmental challenges shape daily life for these children and their families,” noted Professor Ingrid Scheffer, a pediatric neurologist who presented the data. “When a single treatment of ETX101 has shown gains in seizure control and neurodevelopment, as observed in POLARIS, it suggests we may be able to fundamentally change the trajectory of this disease—giving us genuine reason for hope.”

Engineering Hope: The Science of Gene Regulation

The innovative power of ETX101 lies in its elegant approach to a complex genetic problem. The SCN1A gene, whose malfunction causes Dravet syndrome, is too large to fit inside the standard AAV9 viral vector used for many gene therapies, making traditional gene replacement impossible. Instead of replacing the faulty gene, Encoded’s platform uses a strategy of gene regulation.

The therapy delivers an engineered transcription factor designed to bind to the patient's own DNA and selectively increase the expression of the existing SCN1A gene. Crucially, it does so only within the specific inhibitory neurons where the gene's dysfunction causes the most damage. This precision targeting, achieved through the company's proprietary vector engineering, aims to restore the delicate balance of brain activity without causing off-target effects. By boosting the gene's natural output, ETX101 effectively corrects the haploinsufficiency—the state of having only one functional copy of the gene—that is the root cause of the disease.

This one-time treatment, administered directly into the cerebrospinal fluid, is designed to provide a durable, long-term benefit, moving medicine from chronic management to a potentially curative intervention.

The Path Forward: Navigating Trials and Safety

No gene therapy advances without rigorous scrutiny of its safety. To date, ETX101 has been well-tolerated, with no treatment-related serious adverse events reported across more than 20 participants and follow-up extending to nearly two years. The most common side effects have been transient and asymptomatic elevations in liver enzymes and drops in platelet counts, known class effects of AAV therapies that resolved in all participants. This favorable safety profile is a critical component of its potential.

Encoded is now pushing forward with its pivotal ENDEAVOR Part 2 study, a randomized, double-blind, sham-controlled trial—the gold standard in clinical research. This study will provide the definitive data regulators at the FDA and EMA will need for approval. The company has already secured a slate of designations from the FDA, including Breakthrough Therapy and Regenerative Medicine Advanced Therapy (RMAT), signaling the agency's recognition of ETX101's potential to address a significant unmet need and potentially expediting its path to patients.

The Broader Landscape

Encoded's progress is emblematic of a broader shift in biotechnology, where platform technologies are being leveraged to tackle a range of previously untreatable neurological disorders. The company is already applying its gene regulation platform to other conditions like Angelman syndrome and Lennox-Gastaut syndrome. This model, focusing on a core technological competency and applying it across multiple diseases, mirrors the platform-based strategies that have driven innovation in the tech sector for years.

If successful, ETX101 will not only provide a transformative option for the Dravet community but will also serve as a powerful proof-of-concept for the gene regulation approach in neurology. It highlights a future where the focus of treatment is not just on mitigating symptoms, but on precisely correcting the underlying biology of disease, offering a chance for patients to reclaim their developmental potential.