お知らせ • Nov 17
Stoke Therapeutics, Inc. and Biogen Inc. Announce Publication of Two-Year Natural History Data Demonstrating the Severity of Dravet Syndrome
Biogen Inc. and Stoke Therapeutics, Inc. announced the publication of final data from the BUTTERFLY study, a prospective, two-year natural history study in people with Dravet syndrome. Dravet syndrome is a severe developmental and epileptic encephalopathy (DEE) characterized by recurrent seizures and significant cognitive and behavioral impairments. There are currently no approved disease-modifying medicines to treat Dravet syndrome. The BUTTERFLY study evaluated the impact of Dravet syndrome on adaptive functioning and neurodevelopment over two years in children and adolescents ages 2 to 18 years old. Major motor seizure frequency was evaluated as a secondary outcome measure. In the study, patients were treated with standard-of-care, including anti-seizure medicines (ASMs). Highlights from the research, published November 14, 2025, in Neurology, the medical journal of the American Academy of Neurology, include: Regardless of the age at which patients with Dravet syndrome entered the study, neurodevelopment plateaued at the developmental age of approximately two years old. This created a gap that widened over time versus what would be expected for children with typical development. Results showed that over the course of the two-year study, patients experienced minimal changes in cognition and behavior, including communication, motor skills and personal skills, compared to typical neurodevelopment expected for children of the same age. Assessments of cognition and behavior used in BUTTERFLY were pre-determined endpoints that were incorporated into this natural history study to support use in future clinical studies of Dravet syndrome. They included the Vineland Adaptive Behavior Scale, Third Edition (Vineland-3); Bayley Scales of Infant Development, Third Edition (BSID-III); and Wechsler Preschool and Primary Scale of Intelligence, Fourth Edition (WPPSI-IV). These assessments, as well as other outcome measures used in BUTTERFLY, are consistent with the primary and secondary endpoints of the pivotal, global Phase 3 EMPEROR study evaluating zorevunersen as a potential disease-modifying medicine for the treatment of Dravet syndrome. Major motor seizure frequency increased by 10.6 percent over two years (average of 14.3 seizures/28 days at baseline; p=0.63; n=23). Dravet syndrome is a severe developmental and epileptic encephalopathy (DEE) characterized by recurrent seizures as well as significant cognitive and behavioral impairments. Most cases of Dravet are caused by mutations in one copy of the SCN1A gene, leading to insufficient levels of NaV1.1 protein in neuronal cells in the brain. More than 90 percent of patients continue to experience seizures despite treatment with the best available anti-seizure medicines. Complications of the disease often contribute to a poor quality of life for patients and their caregivers. Developmental and cognitive impairments often include intellectual disability, developmental delays, movement and balance issues, language and speech disturbances, growth defects, sleep abnormalities, disruptions of the autonomic nervous system and mood disorders. Compared with the general epilepsy population, people living with Dravet syndrome have a higher risk of sudden unexpected death in epilepsy, or SUDEP; up to 20 percent of children and adolescents with Dravet syndrome die before adulthood due to SUDEP, prolonged seizures, seizure-related accidents or infections. Dravet syndrome occurs globally and is not concentrated in a particular geographic area or ethnic group. Currently, it is estimated that up to 38,000 people are living with Dravet syndrome in the U.S. (~16,000), UK, EU-4 and Japan. There are no approved disease-modifying therapies for people living with Dravet syndrome.