A rare epileptic encephalopathy of childhood characterized by seizures, an electroencephalographic (EEG) pattern of electrical status epilepticus in sleep (ESES) and neurocognitive regression in at least 2 domains of development. This syndrome encompasses the previous syndromes epileptic encephalopathy with continuous spike-wave in sleep and atypical childhood epilepsy with centrotemporal spikes (also previously known as pseudo-Lennox syndrome and atypical benign partial epilepsy). The disease is developmental and/or epileptic encephalopathy with spike-wave activation in sleep (Monarch Disease Ontology entry MONDO_0800501). Also known as: CSWS, CSWSS syndrome, DEE-SWAS, EE-SWAS, EESWAS, ESES with language regression, LK syndrome, LKS.