A complex neurodevelopmental disorder characterized by a neonatal onset of recurrent seizures, an abnormal neonatal electroencephalographic background with multifocal epileptiform discharges, excessive discontinuity, and/or burst-suppression patterns, and encephalopathy. Seizures may be pharmacoresistant or responsive. Developmental delays persist but vary in severity. In some individuals, subsequent evolution to other epileptic encephalopathy syndromes (e.g. West syndrome) may occur.