Biogen (BIIB) and Stoke Therapeutics (STOK) announced the publication of final data from the BUTTERFLY study, a prospective, two-year natural history study in people with Dravet syndrome. 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. Highlights from the research, published November 14, 2025, in Neurology, the medical journal of the American Academy of Neurology, include: 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. Major motor seizure frequency increased by 10.6 percent over two years.
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