Study on the causative genes and analysis of genotypes and phenotypes of Dravet syndrome

Abstract

Objective To identify the rare causative genes of Dravet syndrome(DS) in patients who do not have SCN1A mutation and to analyze genotypes and phenotypes of DS patients with different rare causative genes. Methods DS patients were collected from the Pediatric Department of Peking University First Hospital from February 2005 to August 2016.SCN1A and PCDH19 gene mutations were screened by Sanger sequencing and multiple ligation-dependant probe amplification (MLPA). Next generation sequencing (NGS) for epilepsy-related gene-panel was applied to SCN1A and PCDH19 mutation-negative patients.The phenotypes of DS patients with different rare causative genes were analyzed. Results Six hundred and seventy patients with DS were collected and 556 patients (83.0%) carried SCN1A mutations and 6 patients with PCDH19 mutations.Epilepsy-related gene-panel was applied to remain 108 patients without SCN1A or PCDH19 mutation, and among them 12 patients were detected with 6 rare causative genes, with heterozygous mutations in GABRA1 mutations in 3, GABRG2 in 2 cases, GABRB2 mutations in 2 cases and SCN2A mutation in 1 case, complex heterozygous mutations in TBC1D24 in 2 cases and ALDH7A1 in 2 cases.The clinical phenotypes of 6 patients with PCDH19 mutations were featured by clustering of repeated seizures with short periods of times, only 1 case had an episode of status epilepticus.Patients with GABRB2 mutations had a relatively better outcome of seizure control.Many episodes of myoclonic status were emerging as hallmark features in patients with TBC1D24 mutations.Vitamin B had a dramatic therapeutic effect in patients with ALDH7A1 mutations.The clinical phenotypes of DS patients with GABRG2, SCN2A and GABRA1 had no obvious specificity. Conclusions The rare causative genes in DS patients include PCDH19, GABRG2, SCN2A, GABRA1, GABRB2, TBC1D24 and ALDH7A1.The finding of causative genes GABRB2 and TBC1D24 may enrich the gene spectrum of DS.Patients with PCDH19 mutations are featured by clustering of repeated seizures with short periods of time and rare status epilepticus.Patients with GABRB2 mutations have a relatively better outcome of seizure control.Many episodes of myoclonic status are emerging as hallmark features in patients with TBC1D24 mutations. Key words: Dravet syndrome; Gene mutation; Genotypes; Phenotypes