Table 3.

Etiologies of severe epilepsy in 114 infants

Etiology	N	Gene mutations identified
Acquired	14 (12%)	N/A
Perinatal/neonatal hypoxic ischemic encephalopathy	5	N/A
Periventricular leukomalacia	3	N/A
Complicated meningitis	2	N/A
Perinatal hypoxic ischemic encephalopathy and hypoglycaemia	2	N/A
Perinatal stroke	2	N/A
Genetic/presumed genetic	62 (54%)	39 (50 tested)
Structural	31	9 (19 tested)
Focal cortical dysplasia	14	BRAF (1), DEPDC5 (1), NPRL3 (1), NF (5), NT (6)
Tuberous sclerosis	5	TSC2 (3), TSC1 (1), NT (1)
Malformation of cortical development (other)	3	NF (2), NT (1)
Polymicrogyria	3	NF (1), NT (2)
Lissencephaly	2	LIS1 (1), NT (1)
Other: achondroplasia, Aicardi syndrome, pontocerebellar hypoplasia, Sturge-Weber syndrome	1 each	FGFR3 (1), NF (2), NT (1)
Metabolic	6	5
Mitochondrial disorder	3	NDUFAF6 (1), FARS2* (1), NF (1)
Other: molybdenum cofactor deficiency, PNPO deficiency, Tay-Sachs disease	1 each	MOCS2 (1), PNPO (1), HEXA (1)
Chromosomal	9	9
Trisomy 21	5	See left
Other: chromosome 2q24.3 deletion (incl. SCN1A and SCN2A genes), chromosome 15q21.3q22.2 deletion, isodicentric chromosome 15, Wolf-Hirschhorn syndrome	4	See left
Single gene	16	16
Channelopathies	11	SCN1A (3), KCNQ2 (3), SCN2A (2), SCN8A (2), KCNT1 (1)
Other: Aicardi-Goutieres syndrome, SMC1A mutation, Sotos syndrome, SYNGAP1 mutation, TBC1D24 mutation	1 each	RNASEH2B (1), SMC1A (1), NSD1 (1), SYNGAP1 (1), TBC1D24 (1)
Unknown	38 (33%)	N/A

N/A= not applicable, NF = not found, NT= not tested,

^*Potentially pathogenic