Bedford, Massachusetts, USA September 3, 2026
Stoke Therapeutics and Biogen have presented new long-term clinical data supporting the potential disease-modifying profile of zorevunersen, an investigational antisense oligonucleotide being developed for Dravet syndrome, at the 16th European Epilepsy Congress (EEC) in Athens, Greece. The newly presented evidence includes four-year open-label extension data from Phase 1/2a studies, showing sustained reductions in seizures alongside continued improvements in cognition and behavior in patients receiving zorevunersen on top of standard anti-seizure medicines. The companies also reported exploratory analyses showing reductions in severe seizure types associated with a higher risk of sudden unexpected death in epilepsy (SUDEP). Additional findings demonstrated improvements in quality of life through 28 months of treatment. The long-term observations add to the clinical evidence supporting further development of zorevunersen as a potential disease-modifying treatment for Dravet syndrome, a severe developmental and epileptic encephalopathy associated in most cases with pathogenic variants in the SCN1A gene.
Durable Seizure and Neurodevelopmental Findings
The four-year open-label extension results provide the most important clinical update from the EEC presentation. Following participation in the Phase 1/2a studies, 93% of eligible patients, or 75 of 81 participants, continued into the open-label extensions, while 58 of 75 patients remained in the studies at the four-year data cutoff. Patients treated with zorevunersen continued to experience durable seizure reductions, while statistically significant improvements in cognition and behavior were reported at one, two, three and four years compared with the open-label extension baseline. A separate exploratory analysis focused on the most severe seizure categories, including generalized tonic-clonic and focal-to-bilateral tonic-clonic seizures. These seizure types are particularly important in Dravet syndrome because of their association with significant morbidity and mortality. The companies reported substantial reductions in these severe seizures through three years compared with the Phase 1/2a baseline, strengthening the rationale for continued evaluation of zorevunersen in a population where seizure control remains a major treatment challenge.
Quality of Life and Long-Term Safety
Beyond seizure frequency, the EEC data provide evidence on outcomes that may have direct relevance to the daily lives of patients and caregivers. An additional analysis showed substantial improvements in quality of life through 28 months in the open-label extension studies compared with the Phase 1/2a baseline, measured using the EuroQol Visual Analog Scale. The companies also reported that zorevunersen remained generally well tolerated, with some patients receiving treatment for more than five years. As of July 31, 2026, more than 930 doses had been administered across the Phase 1/2a and ongoing open-label extension studies. Elevated cerebrospinal fluid protein levels were observed in approximately 94% of patients, with 59% classified as treatment-emergent adverse events; however, the companies reported no serious or severe clinical manifestations associated with these elevations and no reports of hydrocephalus. These long-term safety observations will remain important as zorevunersen advances through pivotal development and the companies continue building the evidence required for potential regulatory review.
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Phase 3 EMPEROR Advances Toward 2027 Readout
The long-term findings come as zorevunersen moves through the pivotal Phase 3 EMPEROR study, which is designed to evaluate the efficacy, safety and tolerability of the investigational medicine in children aged 2 to under 18 years with Dravet syndrome and a confirmed SCN1A variant not associated with gain-of-function. Enrollment in the planned primary analysis population across the United States, United Kingdom and Japan has been completed, with 162 patients enrolled, while European enrollment has also been completed with 34 participants. The global study compares zorevunersen administered through lumbar puncture with a sham procedure over a 52-week treatment period. The primary endpoint is the percentage change from baseline in major motor seizure frequency at Week 28, with additional assessments covering seizure durability, cognition, behavior and safety. Phase 3 data are anticipated in the third quarter of 2027, with the results expected to support Stoke’s planned rolling U.S. New Drug Application submission during the second half of 2027. If successful, the program could represent a significant step toward introducing a treatment designed to address the underlying biology of Dravet syndrome rather than focusing solely on seizure control.
Source:Stoke Therapeutics,press relese
