A childhood-onset epilepsy syndrome where the onset of the condition includes manifestations of cognitive, neurological, or psychiatric impairment, stagnation, or regression, due directly to the underlying etiology. In contrast, an epileptic encephalopathy (EE) is present when the encephalopathy is caused by the epileptic activity. The term developmental and epileptic encephalopathy (DEE) is used when both factors contribute to the patient’s condition.