The effect of radiprodil is assessed in two (2) cohorts of pediatric participants: one (1) cohort of participants with treatment-resistant seizures (with or without behavioral symptoms) (Cohort 1) and one (1) cohort of participants with behavioral symptoms but no qualifying seizures (Cohort 2) caused by Gain-of-Function (GoF) variants in the GRIN gene. As the daily doses of radiprodil will be individually titrated for every participant and all the participants will receive the study drug, this is in effect a single group study.~This study is divided into the following periods:~Screening/Observation Period (five (5) weeks): Investigators assess eligibility followed by a four(4)- week Observation Period to evaluate seizure frequency and/or behavioral symptoms.~Titration Period (up to 43 days): Overnight stay to administer radiprodil twice daily to assigned dose level, assessing plasma concentrations, safety, and tolerability during the titration period. Once a safe and potentially effective dose has been established, the participant will immediately enter the Maintenance Period.~A Maintenance Period (approx. 50 days): During the Maintenance Period, the participant will continue to take the highest safe and potentially effective dose, as identified during the Titration Period. At the end of the Maintenance Period, there will be an additional overnight stay when the participant will either be invited to take part in the extension study, during which the participant will continue taking radiprodil at the usual dose level and making regular visits to the study site or taper off the study medicine for 15 days and enter a safety Follow-up Period (14 days). In this case, the participant will make one (1) last visit to the study site 14 days after his/her last dose of radiprodil.
Study RAD-GRIN-101 is a phase 1B trial to assess safety, tolerability, PK, and potential efficacy of radiprodil for the treatment of GRIN-related disorder in children with a Gain-of-Function (GoF) genetic variant. Subjects' participation in the study is expected to last up to six months.~The study is open-label, so all participants will be treated with radiprodil. After the end of this study, all participants who are still eligible can choose to continue to receive radiprodil as part of an open-label extension period.