This group of epilepsies are typically is characterized by onset of seizures from day 1 of life to 5 years (peak 12 months). Both sexes are affected, however the male to female ratio is 1:2. Antecedent (including birth) history, head size, neurological and developmental findings reflect the underlying cause (if known). Myoclonic status epilepticus is often the initial presenting seizure type, however other initial seizure types may also occur. Prognosis is unfavorable with severe neurological and developmental impairments typically seen.