Zorevunersen in Children and Adolescents with Dravet Syndrome.

BACKGROUND

Dravet syndrome is a severe developmental and epileptic encephalopathy caused primarily by SCN1A haploinsufficiency. Risks of sudden unexpected death in epilepsy and cognitive deficits are higher among patients with this syndrome than in the general population with epilepsy. The effects of zorevunersen, an antisense oligonucleotide designed to up-regulate Na_V1.1 sodium channels, in patients with Dravet syndrome are not known.

METHODS

We enrolled patients 2 to 18 years of age with Dravet syndrome who were receiving standard antiseizure medications in two phase 1-2a, open-label, multicenter studies (MONARCH and ADMIRAL). Patients were included in either a single-ascending-dose cohort, in which zorevunersen (10 to 70 mg) was administered on day 1 only, or a multiple-ascending-dose cohort, in which zorevunersen (20 to 70 mg) was administered two or three times in a 3-month period. Patients eligible for rollover to the two open-label extension studies (SWALLOWTAIL and LONGWING) continued to receive zorevunersen (≤45 mg) every 4 months. The safety and pharmacokinetics of zorevunersen were assessed in the primary analysis; clinical effects were also evaluated.

RESULTS

A total of 81 patients were enrolled in the phase 1-2a studies. As of May 30, 2025, a total of 75 patients had entered the extension studies. Most adverse events were mild or moderate. The most common adverse event was post-lumbar puncture syndrome (in 25% of patients) in the phase 1-2a studies and was an elevated protein level in cerebrospinal fluid (in 45%) in the extension studies. One patient had suspected unexpected serious adverse reactions, 1 had an adverse event that led to study withdrawal, 2 died from sudden unexpected death in epilepsy, and 1 died from malnutrition. Patients who received 70 mg of zorevunersen (one, two, or three doses) in the phase 1-2a studies, followed by up to 45 mg in the extension studies, had a median change from baseline in convulsive-seizure frequency ranging from -58.82% to -90.91% across 1-month intervals during the first 20 months of the extension studies. The data supported improvements in overall clinical status, quality of life, and adaptive behavior with continued treatment for up to 36 months in the extension studies.

CONCLUSIONS

The safety profile and initial clinical improvement support the continued development of zorevunersen as a potential disease-modifying treatment for Dravet syndrome. (Supported by Stoke Therapeutics; MONARCH and SWALLOWTAIL ClinicalTrials.gov numbers, NCT04442295 and NCT04740476, respectively; ADMIRAL and LONGWING ISRCTN Registry numbers, ISRCTN99651026 and ISRCTN12811235, respectively.).

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