A Multicenter, Open-label, Pilot Study of Soticlestat (TAK-935/OV935) in Participants With 15Q Duplication Syndrome (Dup 15q) or Cyclin-Dependent Kinase-Like 5 (CDKL5) Deficiency Disorder (ARCADE STUDY)

The drug being tested in this study is called soticlestat. Soticlestat is being tested to treat people with Dup 15q or CDD. This study will assess the effects of TAK-935 on seizure frequency, safety. The study will enroll approximately 30 participants. Participants will be enrolled into 2 groups based on their diagnosis as: Dup 15q or CDD. All participants will be asked to take soticlestat tablets twice daily with or without food. The study comprises of 2 periods: Screening/Baseline Period and Treatment Period (Dose Optimization and Maintenance). The overall time to participate in this study is approximately 30 weeks, including 4 to 6 weeks Screening/Baseline Period, 20 weeks Treatment Period, 2 weeks Taper, and 2 weeks safety follow up period. Participants completing this study will have an option to enroll in the open-label extension (OLE) study, under a separate protocol.