Early Clinical Characteristics Of Dravet Syndrome And Analysis For Gene Mutation Screening

Background and Objective:Dravet Syndrome（DS）is a rare infantile onset of epilepsy encephalopathy.It was offically renamed from Severe Myoclonic Epilepsy in Infancy（SMEI）by International League against Epilepsy（ILAE）in 2001,which includes SMEI and infantile severe myoclonic epilepsy borderline（SMEB）.The main clinical features of the disease are the onset of infancy,the normal growth and development of the disease before the onset of the disease.The onset of the disease as comprehensive,unilateral or unilateral alternating,febrile or non febrile seizures,and the postive rate of the onset of EEG examination and head magnetic resonance examination results are low.With the growth of children,variety types of onset such as myoclonic seizures and atypical absence began to appear subsequently.It also obtain symptom such as developmental delay,cognitive dysfunction,ataxia and so on,and poor response to antiepileptic drugs treatment.The main causes of the disease as the voltage dependence of sodium channel alpha-1 subunit gene（SCN1A）mutations,accounting for more than 80%of children with DS,and other causes include PCDH19,STXBP1,GABRA1,GABRG2,GABRB3,SCN1B,SCN2A gene mutations.SCN9A and Cacnalg gene can be used as the modifying gene of children with Dravet Syndrome.If the children with highly doubt or clarity diagnosis DS,Valproate（VPA）,Stiripentol（STP）,Topiramate（TPM）and Benzodiazepines（BZ）are recommended for use.But early clinical performance of DS children lack of characteristic,and the EEG and head MR examination provide limited leads.Seizure frequency is moderate at onset,once a month or even less until the end of the first year of life.Seizures may repeatedly affect the same body area for several months,misleadingly pointing to possible focal epilepsy.An early diagnosis is necessary in order to avoid the antiepilepticdrugs（AEDs）that can aggravate the seizures,suchas carbamazepine,Oxcarbazepine and lamotrigine.This study examined the clinical and genetic aspects of 13 DS families diagnosed in the last five years,with a view to summarizing the early clinical features and genetic characteristics of DS children.Objects and Methods:Peripheral blood samples from DS pediatric patients who hospitalized in the Department of Neurology.Clinical data was compiled into a table for retrospective analysis.Exon target capture combined with second-generation sequencing technology was used to screen mutation of 308 epilepsy-related genes.After analysis by the RTA software（real-time analysis,Illumina）,the CASAVA software v1.8.2（Illumina）,BWA and GATK,sequencing quality was assessed,and single nucleotide variation（SNV）reports were obtained.Furthermore,ANNOVAR,PolyPhen-2,SIFT,HGMD database,dbSNP database and 1000 Genome database were used to conduct variation annotation and analysis to confirm candidate pathogenic mutations.Finally,the PCR-Sanger method was used to assess probands and their family members,as well as normal controls to confirm the pathogenic mutations.Results:The DS patients included 7 boys and 6 girls.Age at disease onset was 5-11 months,averaging 8 months.Nine first-onset cases showed complex febrile seizures（CFS）.Onset within 1 year:2 cases of abnormal EEG,3 cases of abnormal head MR,3 cases with status epilepticus,7 cases showed all three CFS characteristics（1.persistent time of convulsions over 15 min;2.focal onset type;3.onset times more than once within 24h）.There were 8 EEG abnormalities,3 cases of the head MR anomaly,8 cases showed SE,and 11 showed all 3 CFS characteristics in 3 years.11 SCN1A mutation sites were detected,Eight children showed single SCN1A mutations（c.4363G>A,c.2835C>G,c.2985T>q c.1029-3C>A,c.2714C>A,c.1118T>G,c.3078delG,c.4577C>T）;1 showed combined SCN1A（c.4233₄234insAT）,SCN9A（c.2132T>C）and KCNQ2（c.1491G>C）mutations;1 showed combined SCN1A（c.2332-1G>C）and SLC6A8（c.1151-8C>T）mutations;1 showed combined SCN1A（c.4328A>T）and TSC2（c.4250G>A）mutations;2 showed no related gene mutation.In these 11 SCN1A mutations,10 were De Novo,9 were reported for the first time and 1 SCN1A mutant family was found.Conclusions:1.DS children with the first seizures in infancy,usually manifested as complex febrile seizures onset,and the abnormal detection rate of EEG and head MRI was low,but many CFS features are exhibited in the early stage of the course of disease.2.In this study,11 SCN1A mutations were found in 13 families,84.6%（11/13）of SCN1A mutations,SCN1A mutations are the major pathogenic genes in children with DS.Missense mutations identified in DS,occurred more frequently in the pore region of Nav1.1.3.A total of 11 SCN1A mutations were identified including 9 reported for the first time（c.4363G>A,c.2332-1G>C,c.2835C>Q c.4328A>T,c.1029-3C>A,c.2714C>A,c.1118T>Q c.3078delG,c.4577C>T）,and the SCN1A mutation spectrum was enriched.