A Study of Soticlestat as an Add-on Therapy in Children and Young Adults With Dravet Syndrome

The drug being tested in this study is called soticlestat (TAK-935). Soticlestat as an adjunctive therapy will be assessed for efficacy, safety, and tolerability in pediatric and adult participants with DS. The study will enroll approximately 142 pediatric and young adult patients. Participants will be randomized at a 1:1 ratio to receive standard of care (SOC) plus one of the following adjunctive therapies: * Soticlestat or * Placebo The total daily dose of study drug will be calculated based on body weight in the 4 weeks Titration Period. Following the Titration Period, participants will continue to receive the same dose in the 12-weeks Maintenance Period. This multi-center trial will be conducted worldwide. The overall time to participate in the study will be from 22-25 weeks. At the end of the Full Treatment Period, participants have the option to either complete the study and taper off the investigational product or to enter the OLE if they meet eligibility requirements. If participants discontinue, they will be followed-up on phone call approximately 14 days after the last dose of study drug for safety.