Table 1.

Developmental and epileptic encephalopathies by age

	Age of Onset	Sex	Etiology	Electroclinical Characteristics
Neonatal-infantile onset
Early infantile DEEs (previously Ohtahara syndrome or early myoclonic epilepsy)	≤3 mo of life	M = F	Genetic or structural/metabolic	Clinical: Abnormal neurological findings, neurodevelopmental deficits. Seizures: tonic (independent of sleep), myoclonic, epileptic spasms, sequential.
				EEG: Burst suppression pattern; multifocal epileptiform discharges; hypsarrhythmia may appear. Seizure patterns are bilateral or focal onset, depending on seizure types.
Epilepsy of Infancy with Migrating Focal Seizures (EIMFS)	First year of life	M = F	Mainly genetic	Clinical: Neurodevelopmental delay, focal motor tonic or clonic seizures.
				EEG: Migrating EEG patterns during ictal events, multifocal discharges
Infantile spasms syndrome (ISS)	3–12 mo (1–24 mo)	M > F	Structural/metabolic, genetic, unknown	Clinical: Epileptic spasms, other seizures may occur; neurodevelopmental disorders, intellectual disabilities.
				EEG: Hypsarrhythmia, electrodecremental responses (ictal or interictal), multifocal epileptiform discharges.
Dravet syndrome	3–9 mo (1–20 mo)	M = F	Genetic	Clinical: Neurodevelopmental deficits. Prolonged hemiclonic seizure with fever in the absence of infectious/structural brain lesion; myoclonic, focal impaired awareness, atypical absences, atonic seizures, nonconvulsive status epilepticus, tonic and tonic-clonic seizures in sleep.
				EEG: Focal or multifocal epileptiform abnormalities and seizures, photoparoxysmal responses.
Etiology-specific syndromes: KCNQ2, CDKL5, PCDH19, SCL2A1, pyridoxine and pyridox(am)ine 5′-phosphate dependent epilepsy, glucose transporter 1 deficiency syndrome (Glu1DS), Sturge–Weber syndrome	First year of life	M = F; M < F (PCDH19, CDKL5)	Genetic	KCNQ2-DEE: Sequential or focal tonic seizures, burst suppression; autonomic symptoms, epileptic spasms. Burst suppression or multifocal EEG.
				CDKL5-DEE: Tonic seizures, epileptic spasms. hypermotor tonic spasms; movement disorders.
				PDE, P5PDE: Intrauterine or early-life seizures; focal seizures, spasms or generalized tonic-clonic; response to pyridoxine or P5P. EEG: burst suppression or multifocal discharges.
				Glut1DS: Intellectual disability, low CSF-to-plasma glucose ratio, generalized seizures (myoclonic, myoclonic-atonic, generalized tonic-clonic, absences). EEG: 2.5–5 Hz spike wave.
				PCDH19-DEE: Intellectual disability, autism spectrum disorder; focal impaired aware to tonic or atypical absence seizures. EEG: focal onset seizures.
				Sturge–Weber: Facial port wine stain, progressive neurological course, epilepsy, hemiparesis, psychomotor delay, strokelike events, psychiatric disorders, glaucoma. Focal motor seizures, febrile seizures, infantile spasms, myoclonic-atonic, gelastic seizures. EEG: Asymmetric, focal epileptiform activities.
Gelastic seizures with hypothalamic hamartoma	First year of life	M = F	Structural, genetic-structural	Clinical: Normal neurological exam initially, deficits appear later; precocious puberty; gelastic seizures with mirthless laughter (mandatory), gelastic and dacrystic seizures, focal impaired awareness or generalized seizures; other types of seizures may occur.
				EEG: Focal or generalized
Childhood onset
Myoclonic-atonic epilepsy	2–6 yr	M > F	Genetic	Clinical: Seizures: myoclonic-atonic (mandatory), atonic, myoclonic, absence, generalized tonic-clonic.
				EEG: 3–6 Hz (poly)spike-slow wave discharges, generalized, activated in sleep; generalized paroxysmal fast.
Lennox–Gastaut syndrome	18 mo to 8 yr	M > F	Structural/metabolic, genetic	Clinical: Tonic seizures in sleep (mandatory), atypical absence, atonic, myoclonic, focal impaired awareness, generalized tonic-clonic, epileptic spasms.
				EEG: Slow spike-wave (≤2.5 Hz), generalized; generalized paroxysmal fast; focal or multifocal slow spike-wave may be seen.
DEE with SW activation in sleep (D/EE-SWAS)	2–12 yr	M = F	Structural, genetic	Clinical: Neurocognitive/behavioral deficits that ameliorate/resolve with resolution of SWAS; seizure types depend on etiology: focal or focal to bilateral, typical, or atypical absences, atonic, negative myoclonus.
				EEG: Slow background; focal or multifocal discharges; marked activation of diffuse epileptiform discharges in sleep (>50% of sleep, 1.5–2 Hz spike-wave runs).
Febrile infection related epilepsy syndrome (FIRES)	2–17 yr	M > F	Infectious/postinfectious	Clinical: Developmental regression, intellectual disabilities, attention or behavioral problems, motor dysfunction. Focal or multifocal seizures, superrefractory status epilepticus.
				EEG: Slow background, multifocal epileptiform discharges; extreme delta brushes. Increasing frequency of focal onset seizures (focal >10 Hz evolving to rhythmic spike-waves).
Hemiconvulsion-Hemiplegia-Epilepsy Syndrome (HHE)	<4 yr	M = F	Unknown, structural/metabolic, genetic	Clinical: Focal (clonic) febrile status epilepticus and persistent hemiparesis, aphasia when dominant hemisphere involved; focal or focal to bilateral motor seizures.
				EEG: Focal or lateralized rhythmic ictal delta, focal recruiting (10 Hz) rhythms.
Variable age onset
Progressive myoclonus epilepsy (PME)
Unverricht–Lundborg (EPM1)	7–13 yr	M = F	Genetic	Clinical: progressive course; myoclonus induced by touch / photic stimulation, more pronounced upon awakening; other generalized seizures may occur.
				EEG: Photosensitivity; generalized polyspike and wave (ictal).
Lafora disease (EPM2)	6–19 yr	M = F	Genetic	Clinical: Vision loss, cognitive decline, cerebellar symptoms. Myoclonic and generalized tonic-clonic seizures.
				EEG: Photosensitivity; spike wave and polyspikes, no activation in sleep.
Neuronal Ceroid Lipofuscinosis (NCL)
CLN2 (late infantile)	2–4 yr	M = F	Genetic	Clinical: Language delay, progressive course, multiple seizures febrile and afebrile, including myoclonic.
				EEG: Photoparoxysmal response at low frequencies.
Juvenile CLN3	4–10 yr	M = F	Genetic	Clinical: Visual loss progressive, macular degeneration, optic atrophy, retinitis pigmentosa.
				EEG: Diffuse spike and wave discharges, slow background.
Adult NCL (Kufs)	11–50 yr	M = F	Genetic	Type A: PME with dementia and ataxia.
				Type B: Dementia with cerebellar or extrapyramidal motor symptoms but not PME.

The list of developmental and epileptic encephalopathies (DEEs) follows the 2021 proposal of the International League Against Epilepsy (ILAE) Task Force on Nosology and Definitions for epilepsy syndromes (5–7). F, female; Glut1DS, Glucose Transporter 1 (SLC2A1) deficiency syndrome; M, male; NCL or CLN, neuronal ceroid lipofuscinosis; PDE, pyridoxine-dependent epilepsy; P5PDE, pyridox(am)ine 5′-phosphate (P5PD)-dependent epilepsy.