Dravet syndrome drug zorevunersen targets the genetic cause, and the results go beyond seizure control

Ann & Robert H. Lurie Children's Hospital of Chicago

Owen is 12 years old. He has Dravet syndrome. His seizures were not controlled by medications. He had intellectual disability and gait abnormalities. Then he enrolled in a clinical trial at Ann and Robert H. Lurie Children's Hospital of Chicago.

Today, Owen's seizures are significantly reduced. His language has improved. His behavior has changed enough that he is making friends, something his mother Austin describes as new. He can participate in activities with neurotypical peers.

The drug responsible is zorevunersen, and the clinical data supporting it have just been published in The New England Journal of Medicine.

A half-dose problem with a full-dose target

Dravet syndrome sits on a single gene. Patients have a mutation in one copy of SCN1A, a gene that encodes a sodium channel subunit critical for nerve cell function. The other copy is normal. But one working copy produces only half the protein the brain needs, a situation geneticists call haploinsufficiency. That deficit causes seizures, and it also drives the cognitive, motor, and behavioral impairments that define the condition.

Every approved treatment for Dravet syndrome works downstream. Anti-seizure medications try to calm overactive neural circuits, but they do nothing about the underlying protein shortage. Zorevunersen, developed by Stoke Therapeutics, works upstream. It acts on the normal SCN1A gene, effectively telling it to work harder and produce more protein to compensate for the broken copy.

The drug is delivered by lumbar puncture directly into the cerebrospinal fluid.

85% fewer seizures at three months

The Phase 1/2a trials, conducted across multiple US and UK centers and co-led by Dr. Linda Laux at Lurie Children's, enrolled 81 patients aged 2 to 18 who were already on standard anti-seizure medications. Patients who received two to three doses of 70 mg zorevunersen experienced a reduction in motor seizures of nearly 85% at three months and 73% at six months.

Seventy-five patients continued into open-label extension studies, receiving 45 mg every four months. In the extension, seizure reduction ranged from 58% to 90% over the first 20 months.

But the result Laux calls unprecedented is what happened beyond seizures. For patients in the extension studies for more than 36 months, expressive and receptive communication improved significantly. Quality of life scores went up. Adaptive behavior improved. No approved Dravet treatment has previously demonstrated effects on these non-seizure dimensions of the disease.

The safety profile

Nearly all patients experienced at least one adverse event, but most were mild to moderate. Post-lumbar puncture syndrome occurred in about 25% of patients during the initial trials. In the extension studies, the most common finding was elevated cerebrospinal fluid protein, observed in 45% of participants. None of those patients developed increased intracranial pressure or hydrocephalus. Only one serious adverse event was judged to be related to the treatment.

The lumbar puncture delivery method is inherently more invasive than oral medication, requiring a clinical procedure every four months. For families managing a condition as severe as Dravet syndrome, that trade-off may be acceptable, but it is a consideration for broader adoption.

Open-label caveats

These were open-label studies. Every participant and every clinician knew the drug was being administered. There was no placebo group. That design is standard for early-phase safety studies, but it means the efficacy numbers come with caveats. Expectation effects can inflate perceived improvements, particularly for subjective outcomes like behavior and quality of life. The patients who continued into extension studies were likely the ones responding best, which could bias the long-term data upward.

A Phase 3, double-blind, placebo-controlled trial is now underway and will provide the rigorous comparison needed to confirm whether the early signals hold.

If they do, zorevunersen would be the first treatment for Dravet syndrome that addresses the disease at its genetic source rather than managing symptoms after they appear. For families like Owen's, the distinction between treating a symptom and treating a cause is not academic. It is the difference between controlling seizures and getting a life back.