Before treatment, the children in the trial were averaging 17 seizures every month. That number became the baseline against which zorevunersen would be measured — and the drug moved it sharply.
According to results published in The New England Journal of Medicine, the experimental therapy cut seizures by as much as 91 percent in children with Dravet syndrome, a rare genetic epilepsy that resists most existing treatments. The trial, led by University College London and Great Ormond Street Hospital, involved 81 children between the ages of two and 18 in the United Kingdom and the United States.
Dravet syndrome does more than cause seizures. The condition is tied to long-term neurodevelopmental difficulties, feeding problems, movement challenges, and an elevated risk of premature death. Current medications fail to fully control seizures in many patients, and no approved therapy directly targets the disorder’s cognitive and behavioral effects.
How the Drug Works
The mechanism behind zorevunersen — developed by Stoke Therapeutics in collaboration with Biogen — goes after the genetic root of the condition. Most people carry two working copies of the SCN1A gene, which produces a protein essential to normal nerve cell signaling. In children with Dravet syndrome, one copy fails to produce enough of that protein. The drug works by increasing production from the functioning copy, aiming to restore more normal neurological activity.
Participants received doses of up to 70mg, administered through lumbar puncture. Some received a single dose; others received additional doses two or three months later across a six-month treatment period. Seventy-five of the 81 children continued into follow-up extension studies, which together with the initial trial spanned three years. Over that period, researchers tracked seizure frequency, cognitive function, behavior, and quality of life.
Safety Profile and Next Steps
The early studies were primarily designed to assess safety and tolerability. Most reported side effects were mild, and the drug was well tolerated by the majority of participants. Researchers also noted early signals that the therapy may ease some of the disorder’s effects on thinking and behavior, though the trial was not sized to draw firm conclusions on those outcomes.
Professor Helen Cross, Director and Professor of Childhood Epilepsy at the UCL Institute of Child Health and an Honorary Consultant in Paediatric Neurology at Great Ormond Street Hospital, described the results as meaningful for families with few options. “I regularly see patients with hard-to-treat genetic epilepsies with impacts that go beyond seizures and it’s heart-breaking when treatment options are limited,” she said. “This new treatment could help children with Dravet syndrome lead much healthier and happier lives.”
The announcement says a larger Phase 3 trial is now underway to further evaluate the drug’s effectiveness across a broader patient population.
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