This group of epilepsies are characterized by repeated episodes of myoclonic status epilepticus that occur over prolonged periods (days). The majority of patients have an underlying chromosomal disorder, others have developmental or acquired structural brain abnormalities. The cause is unknown in one fifth of cases.
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.