A Study of Soticlestat as an Add-on Therapy in Children, Teenagers, and Adults With Lennox-Gastaut Syndrome

Open to people ages 2-35

1. Has documented clinical diagnosis of Lennox-Gastaut Syndrome (LGS).
2. Has ≥8 major motor drop (MMD) seizures each month in the 3 months prior to Screening based on the historical information and has ≥8 MMD seizures per 28 days during the 4 to 6 week prospective Baseline Period.
3. Weighs ≥10 kg at the Screening Visit (Visit 1).
4. Failure to control seizures despite appropriate trials of at least 2 anti-seizure medications (ASMs) based on historical information, and is currently on an anti-seizure therapy or other treatment options considered as standard of care (SOC).
5. Currently taking 0 to 3 ASMs at stable doses for at least 4 weeks before the Screening Visit (Visit 1); ASM dosing regimen must remain constant throughout the study.

1. Admitted to a medical facility and intubated for treatment of status epilepticus 2 or more times in the 3 months immediately before Screening (Visit 1). Status epilepticus is defined as continuous seizure activity lasting longer than 5 minutes or repeated seizures without return to Baseline in between seizures.
2. Unstable, clinically significant neurologic (other than the disease being studied), psychiatric, cardiovascular, ophthalmologic, pulmonary, hepatic, renal, metabolic, gastrointestinal, urologic, immunologic, hematopoietic, endocrine disease, malignancy including progressive tumors, or other abnormality that may impact the ability to participate in the study or that may potentially confound the study results. It is the responsibility of the investigator to assess the clinical significance; however, consultation with the medical monitor may be warranted.
3. Considered by the investigator to be at imminent risk of suicide or injury to self, others, or property, or the participant has attempted suicide within 12 months before the Screening Visit (Visit 1). Participants who have positive answers on item numbers 4 or 5 on the Columbia suicide severity rating scale (C-SSRS) before randomization/dosing (Visit 2) are excluded. This scale will only be administered to participants aged ≥6 years.