Clinical features and gene mutations analysis in 62 children with early-onset epileptic encephalopathy of unknown causes

Abstract

Objective To study the clinical features and gene mutations of early-onset epileptic encephalo-pathy (EOEE) of unknown causes and to identify pathogenic mutations of EOEE by next generation sequencing. Methods The clinical data of 62 cases diagnosed with unexplained EOEE between June 2013 and June 2015 were obtained and analyzed.Specimens were collected from the selected children and their parents.Next generation sequencing was used to detect epilepsy-related genes, and Sanger sequencing was performed to verify the results and confirm the source of the parents, further to identify suspected pathogenic mutations of EOEE. Results Among 62 cases with unexplained EOEE, 37 cases (61%) were diagnosed as non-specific EOEE, 17 cases (27%) with West syndrome, 6 cases (10%) with Dravet syndrome, 1 case(1%) with Ohtahara syndrome, 1 case(1%) with early myoclonic epileptic encephalopathy.The pathogenic mutations were not detected among 17 cases with West syndrome and the early myoclonic epileptic encephalopathy.Among 37 cases with non-specific EOEE, suspected pathogenic mutations were detected in 7 cases.Three cases of missense mutations for PCDH19 gene, 1 case of frame-shift mutation and 1 case of splice site mutation for CDKL5 gene, 1 case of denovo nonsense mutation for KCNQ2 gene, and 1 case of missense mutation for GRIN2A gene were detected.Among 6 children with Dravet syndrome, 2 cases of frame-shift mutations and 1 case of missense mutation for SCN1A gene were detected, of which 2 cases were of frame-shift mutations, 1 case was denovo mutation, 1 case of missense mutation for SCN1A gene and 1 case of missense mutation for SCN1A combined with SCN9A gene were detected.One case of denovo nonsense mutation for STXBP1 gene was detected.After treatment, 22 cases with clinical seizures were under control, and 40 cases were out of control. Conclusions The clinical phenotypes for children with unexplained EOEE were varied.SCN1A, SCN9A, STXBP1, PCDH19, CDKL5, KCNQ2 and GRIN2A genes detected in China are in accordance with those reported internationally and some gene sites are denovo mutations which have not been reported.The SCN9A gene may be the new pathogenic mutation for Dravet syndrome.And the KCNQ2 gene nonsense mutation may be the lethal mutation. Key words: Early-onset epileptic encephalopathy; Dravet syndrome; West syndrome; Ohtahara syndrome; Gene; Mutation