A Clinical Trial of PRAX-562 in Subjects With Developmental and Epileptic Encephalopathies (DEE)

Inclusion Criteria:

• Has a documented variant in SCN2A with onset of seizures occurring in the first 3months of life or has a diagnosis of SCN8A-DEE supported by both clinical andgenetic findings.

• Has a seizure frequency as follows:

• At least 8 countable motor seizures in the 4 weeks immediately prior toScreening as reported by the parent/legal guardian or in the opinion of theinvestigator as documented in medical notes.

AND o At least 8 countable motor seizures during the 28 day Baseline Observation Period (during which seizure frequency is recorded in a daily seizure diary).

• Additional inclusion criteria apply and will be assessed by the study team.

Exclusion Criteria:

• Has any clinically significant or known pathogenic or likely pathogenic geneticvariant other than in SCN2A and SCN8A or a genetic variant that may explain orcontribute to the participant's epilepsy and/or developmental disorder.

• Has a documented, functionally characterized loss-of-function (LoF) missense variantor a presumed LoF variant (nonsense or frameshift variant) based on genetic testingand/or clinical evidence that prior exposure to a sodium channel blocker (SCB)medication worsened seizures.

• Has 2 or more episodes of convulsive status epilepticus requiring hospitalizationand intubation in the 6 months prior to Screening.

• Additional exclusion criteria apply and will be assessed by the study team.