Beeline: A Phase 3 Study in GRIN-related Neurodevelopmental Disorder

Participants are assigned in a 1:1 ratio to receive either radiprodil or placebo during Part A with the opportunity to receive radiprodil in the Open-Label Extension, Part B. The dosing regimen includes a fixed titration schedule over 4 weeks. This study is divided into the following parts: Part A: Randomized, double-blind, placebo-controlled * Screening/Observation Period: To assess eligibility * Titration Period (approximately 4 weeks): Titration of radiprodil or placebo to target dose * Maintenance Period (Part A): Target dose of radiprodil or placebo maintained for 12 weeks (Phase 3 Cohort 1) or 24 weeks (Phase 3 Cohort 2) * Tapering and Follow-up Period: Gradual decrease and Follow-up Period for participants not entering Part B Part B: Open-label safety follow-up period * Open-Label Treatment Period: Participants will continue to receive radiprodil until such time as either the participant withdraws/is withdrawn from the study, sponsor terminates the study, or market access is available * Tapering and Follow-up Period: Gradual decrease and follow-up observation period for participants upon leaving the study