Stoke Therapeutics (Nasdaq: STOK) and Biogen (Nasdaq: BIIB) presented clinical data on zorevunersen, an investigational treatment for Dravet syndrome, at the 16th European Epilepsy Congress in Athens, Greece, running September 5-9.

The data, drawn from Phase 1/2a open-label extension studies, cover more than five years of clinical experience in patients with Dravet syndrome. Four-year results showed reductions in seizures and improvements in cognition and behavior in patients receiving zorevunersen alongside standard anti-seizure medicines. Statistically significant improvements in cognition and behavior were recorded at one, two, three, and four years compared to baseline.

A new exploratory sub-analysis showed reductions in generalized tonic-clonic and focal-to-bilateral tonic-clonic seizures, which are classified as the most severe seizure types and are associated with the highest risk of sudden unexpected death in epilepsy, or SUDEP. A separate sub-analysis showed improvements in quality of life through 28 months of treatment, as measured by the EuroQol Visual Analog Scale.

Of the 81 patients enrolled in the Phase 1/2a studies, 93% continued into the open-label extension studies. As of the four-year data cutoff, 77% of those patients remained enrolled. More than 930 doses have been administered as of July 31, 2026. Elevated cerebrospinal fluid protein values were observed in approximately 94% of patients, with 59% classified as a treatment-emergent adverse event. No serious clinical manifestations or cases of hydrocephalus were reported.

The companies said zorevunersen has been generally well tolerated, with some patients treated for more than five years.

The global Phase 3 EMPEROR study, enrolling 162 patients across the U.S., U.K., and Japan, has completed enrollment in its primary analysis population. Enrollment in Europe concluded with 34 participants. A data readout is anticipated in the third quarter of 2027, with a rolling New Drug Application submission to the FDA planned for the second half of 2027.

There are currently no approved disease-modifying therapies for Dravet syndrome. The safety and efficacy of zorevunersen have not been evaluated by any regulatory authority.