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

Inclusion Criteria:

Part A, Participant:

• Diagnosed with GRIN-NDD with GRIN1, GRIN2A, GRIN2B, or GRIN2D gene variants known toresult in GoF of the NMDA receptor

• Phase 3 Cohort 1 (Qualifying Seizures Cohort) ONLY: Experiencing at least 1 CMS perweek and ≥4 CMS (generalized or focal) during screening

• With history of inadequate response to at least 2 standard antiseizure medications (ASMs)

• Phase 3 Cohort 2 (Without Qualifying Seizures Auxiliary Cohort) ONLY: Withsignificant neurodevelopmental symptoms and a GRIN-CGI-S score ≥4

• On a stable dose of standard ASMs for at least 4 weeks prior to screening and shouldremain on stable doses throughout study participation

• On stable nonpharmacological treatments such as ketogenic diet and should remainstable throughout study participation

Part B:

• Participant has completed Part A and is eligible to continue study participation according to the judgement of the investigator and sponsor.

Exclusion Criteria:

PART A, Participant:

• Has clinically relevant medical, neurologic, or psychiatric condition and/orbehavioral disorder (including those related to GRIN-NDD) that would preclude orjeopardize participant's safe participation or study drug administration or theconduct of the study according to the judgement of the investigator or sponsor.

• Is receiving >4 standard ASMs at screening

• Has a body weight of less than 5 kg at screening

Part B:

• Participant has clinically relevant medical, neurologic, or psychiatric condition and/or behavioral disorder (including those related to GRIN-NDD) that would preclude or jeopardize participant's safe participation of study drug administration or the conduct of the study according to the judgement of the investigator or sponsor.