OBJECTIVETo investigate the mutations of the sodium channel alpha 1 subunit gene SCN1A in severe myoclonic epilepsy of infancy (SMEI) patients and analyze its inheritance.

METHODSTwenty-three patients consistent with the diagnosis of SMEI were selected for SCN1A mutation analysis. Genomic DNA was extracted from peripheral blood lymphocytes of these patients and their parents. All the twenty-six exons of the SCN1A gene were amplified by PCR and sequenced.

RESULTSIn the 23 SMEI patients, 17 mutations were identified in 17 unrelated SMEI patients. The SCN1A mutation rate was 73.9% (17/23). The mutations included 8 missense mutations (F90S, I91T, A239T, W952G, T1210K, V1335M, V1390M and G1433E), 3 nonsense mutations (R612X, W768X and W1408X), 3 deletion mutations (A395fsX400, L556fsX557 and V1778fsX1800), 1 insertion mutation (Y1241fsX1270), 1 splice-site mutation (IVS10+3 A to G) and 1 synonymous mutation (K1492K), of which 47.1% (8/17) were truncation mutations. Thirteen mutations (F90S, I91T, T1210K, V1335M, G1433E, R612X, W768X, A395fsX400, L556fsX557, V1778fsX1800, Y1241fsX1270, IVS10+3A to G and K1492K) have not been reported previously. Except for F90S, L556fsX557 and V1778fsX1800, the other 14 mutations were de novo.

CONCLUSIONSCN1A is a major pathogenic gene for SMEI. About a half of the SCN1A mutations in SMEI cause truncation. There were no hotspots of SCN1A mutations in SMEI patients, and most mutations were de novo.