Biogen and Stoke Therapeutics Announce Presentations of Clinical Data from Studies of Zorevunersen for the Potential Treatment of Dravet Syndrome at the 36th International Epilepsy Congress

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– 3-year data from open-label extension (OLE) studies demonstrate the potential for disease modification with durable seizure reductions and improvements in cognition and behavior on top of standard anti-seizure medicines – – Substantial improvement in overall seizure burden and seizure free days observed with ongoing treatment – CAMBRIDGE, Mass. and BEDFORD, Mass. , Aug. 25, 2025 (GLOBE NEWSWIRE) -- Biogen Inc. (Nasdaq: BIIB) and Stoke Therapeutics , Inc. (Nasdaq: STOK), a biotechnology company dedicated to restoring protein expression by harnessing the body’s potential with RNA medicine, today announced presentations of new clinical data from studies of zorevunersen at the 36th International Epilepsy Congress (IEC), taking place August 30 – September 3, 2025 in Lisbon, Portugal . Zorevunersen, an investigational antisense oligonucleotide, is being evaluated as a potential disease-modifying medicine for the treatment of Dravet syndrome in the global pivotal EMPEROR Phase 3 study. “With these additional clinical data, we are developing a long-term understanding of the potential for zorevunersen to improve outcomes for patients by addressing the underlying genetic cause of Dravet syndrome,” said Barry Ticho , M.D., Ph.D., Chief Medical Officer of Stoke Therapeutics. “The substantial and durable reductions in seizures and improvements in cognition and behavior in patients already receiving standard anti-seizure medicines support the potential for disease modification. We look forward to sharing and discussing our latest zorevunersen data, including new analyses related to improvements in seizure free days and quality of life, with the world’s leading epilepsy experts at this premier congress.” “The zorevunersen data generated to date are encouraging and support the design of the Phase 3 EMPEROR study now enrolling and dosing patients,” said Katherine Dawson , M.D., Head of the Therapeutics Development Unit at Biogen. “The effects observed so far are bringing greater awareness to Dravet syndrome as a neurodevelopmental disorder while generating increasing interest in EMPEROR.” Details of the presentations at IEC are as follows: Title: Zorevunersen demonstrates potential as a disease‑modifying therapy in patients with Dravet syndrome through durable seizure reduction and improvements in cognition, behavior, and functioning with up to 36 months of maintenance dosing in open-label extension studies Oral Presentation Date & Time: Sunday, August 31 , 3:15 – 4:15 PM WEST/ GMT +1 (10:15 – 11:15 AM ET ) Oral Presenter: Andreas Brunklaus , M.D., Consultant Paediatric Neurologist at the Royal Hospital for Children, Glasgow, Honorary Professor at the University of Glasgow , member of Dravet Syndrome UK's Medical Advisory Board Title: Substantial improvements in overall seizure burden and seizure free days in patients with Dravet syndrome treated with zorevunersen: Results from Phase 1/2a and open-label extension studies Poster Presentation Date & Time: Monday, September 1 , 1:45 – 3:15 PM WEST/ GMT +1 (8:45 – 10:15 AM ET ) Poster Presenter: J Helen Cross, MB ChB, Ph.D., Professor, The Prince of Wales’s Chair of Childhood Epilepsy and Head of the Developmental Neuroscience Programme at University College London Great Ormond Street Institute of Child Health, Honorary Consultant in Paediatric Neurology, President of the International League Against Epilepsy Poster Number: P351 Title: EMPEROR Phase 3 study design: Evaluation of zorevunersen as a potential disease-modifying therapy for Dravet syndrome Poster Presentation Date & Time: Monday, September 1 , 1:45 – 3:15 PM WEST/ GMT +1 (8:45 – 10:15 AM ET ) Poster Presenter: Joseph Sullivan , M.D., FAES, Professor of Neurology and Pediatrics and Director of the Pediatric Epilepsy Center of Excellence at the University of California San Francisco Poster Number: P358 Additional Company Presentation: Title: Emerging Concepts and Therapeutics in Dravet Syndrome: From Burden to Breakthroughs Date & Time: Tuesday, September 2 , 1:55 – 3:05 PM WEST/ GMT +1 (8:55 – 10:05 ET ) Presenters: Stéphane Auvin , M.D., Ph.D., FAES, Epileptologist and Child Neurologist, Chair of the Pediatric Neurology Department at Robert Debré University Hospital & Université Paris ; Kelly G. Knupp , M.D., Professor, Pediatrics-Neurology, University of Colorado Anschutz Medical Campus , Children’s Hospital Colorado; and Scott Perry , M.D., Medical Director, Neurology; Co-Director, Jane and John Justin Neurosciences Center; Medical Director, Genetic Epilepsy Clinic , Cook Children's Hospital About Dravet Syndrome Dravet syndrome is a severe developmental and epileptic encephalopathy (DEE) characterized by severe, 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. 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.1 About Zorevunersen Zorevunersen is an investigational antisense oligonucleotide that is designed to treat the underlying cause of Dravet syndrome by increasing NaV1.1 protein production in brain cells from the non-mutated (wild-type) copy of the SCN1A gene. This highly differentiated mechanism of action aims to reduce seizure frequency beyond what has been achieved with anti-seizure medicines and to improve neurodevelopment, cognition, and behavior. Zorevunersen has demonstrated the potential for disease modification and has been granted orphan drug designation by the FDA and the EMA. The FDA has also granted zorevunersen rare pediatric disease designation and Breakthrough Therapy Designation for the treatment of Dravet syndrome with a confirmed mutation not associated with gain-of-function, in the SCN1A gene. Stoke has a strategic collaboration with Biogen to develop and commercialize zorevunersen for Dravet syndrome. Under the collaboration, Stoke retains exclusive rights for zorevunersen in the United States, Canada, and Mexico; Biogen receives exclusive rest of world commercialization rights. About the EMPEROR Study The EMPEROR Phase 3 Study (NCT06872125) is a global, double-blind, sham-controlled study evaluating the efficacy, safety and tolerability of zorevunersen in children ages 2 to

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