Relationship Between SCN1A Gene Mutation And Drug Efficacy In Chinese Families With Genetic Epilepsy With Febrile Seizures Plus

The name of "genetic epilepsy with febrile seizures plus" (GEFS+) was changed from "generalized epilepsy with febrile seizures plus" in 2008. Scheffer reported a seemingly unrelated familial epilepsy syndrome that called generalized epilepsy with febrile seizures plus (GEFS+) in 1997. This syndrome was based on recognizing a pattern of epilepsy phenotypes or syndromes in a family where family members had seizure disorders of markedly different severity. The mildest end of the spectrum and the most common phenotype is classical FS. Next most frequent is febrile seizures plus (FS+) where FS continue past the typical age of 6 years and/or afebrile convulsions occur. Seizures in FS+usually peter out by the early teens but occasional convulsions in adult life occur. The phenotypes in GEFS+increase in severity and complexity such that FS or FS+may be associated with a range of generalized seizure types including absence, myoclonic or atonic seizures. The most "severe" phenotype in GEFS+families was Myoclonic-Astatic Epilepsy (MAE). As with all clinical research, the concepts continued to evolve through observation of familial GEFS+patterns. Until now, the GEFS+was reported as an autosomal dominant-inherited epilepsy featured by FS in childhood and subsequent heterogeneous afebrile seizures, the spectrum consist of severe myoclonic epilepsy of infancy (SMEI), also called Dravet syndrome, intractable childhood epilepsy with generalized tonic-clonic seizures, partial epilepsy with antecedent FS. Because although generalized epilepsies predominate in GEFS+ families, focal or partial epilepsies are well recognized with and without preceding FS. A range of partial seizure types are now recognized in GEFS+ including hemiclonic seizures and complex partial seizures with temporal lobe semiology. So Scheffer proposed changing the name of GEFS+ to "genetic epilepsy with febrile seizures plus" from "generalized epilepsy with febrile seizures plus" in 2008. GEFS+ is a familial epilepsy syndrome where at least two family members have phenotypes consistent with the GEFS+ spectrum. GEFS+ is distinguished by many phenotypes showing a predisposition to seizures with fever. GEFS+ families may just show one phenotype within them such as FS, but more typically, they show a pattern of phenotypic heterogeneity.Mechanisms of febrile seizures generation include the following aspects, elevating brain temperature (hyperthermia) in itself alters many temperature-sensitive neuronal functions. The fever-promoting pyrogen interleukin-1β contributes to fever generation and fever leads to the synthesis of this cytokine in Hippocampus. Genetic background may influence the susceptibility to developing a seizure with fever. Genes coding sodium channels, GABAA receptors, and interleukins have been implicated in the susceptibility to febrile seizures.Several genes have been reported to be associated with GEFS+, including voltage-gated sodium-channel subunit SCN1A and SCN1B, and y-aminobutyric acid receptor GABRG2 and GABRD. However, SCN1A is the major gene in GEFS+and related epilepsies since other genes were only reported in a few families. In 1998, the first gene for GEFS+was identified when they reported a mutation of SCN1B, encoding the beta 1 subunit of the sodium channel, in a large Australian family with GEFS+. In 2000, Escayg and colleagues identified mutations in SCN1A, encoding the alpha 1 sodium channel subunit, in two GEFS+ families. The second ion channel implicated in GEFS+is the GABAA receptor. The gamma 2 subunit gene, GABRG2, has mutations reported in families with GEFS+ alone and in other kindreds with childhood absence epilepsy as well. There has been an unconfirmed report of a variant in the delta subunit gene, GABRD, in a small family with GEFS+showing functional changes. GABRD may be a susceptibility gene, however, this finding requires replication. The NaV1.1 channel encoded by the SCN1A gene is the most frequent target of mutations.Optimization of treatment in epilepsy has the potential to improve developmental outcome. Voltage-gated sodium channels initiate action potentials in brain neurons, and sodium channel blockers, such as Carbamazepine, Oxcarbazepine, Lamotrigine, Phenytoin, Topiramate, Lacosamide, zonisamide, Felbamate and Rufmamide are used in therapy of epilepsy. Benzodiazepines, Phenobarbital, Valproate, Topiramate, Gabapentin,Vigabatrin, Felbamate, Tiagabine acting on GABAa receptors (GABAARs) mediates inhibitory synaptic transmission in the brain. The fact that the most GEFS+ mutations are missense while the major Dravet syndrome mutations are truncations emphasize the importance of intrinsic nature of each SCNIA mutation. To explore the relationship between gene mutation and clinical efficacy has a great clinical value for Accurate treatment[Subjects and Methods]1. Subjects:We collected 103 families of the Han-nationality population in southern China with genetic epilepsy with febrile seizures plus. And 200 healthy comparisons. Children in the comparison group had no history of febrile seizures, seizure or seizure-like episodes, or any diagnosed neurological disease. We enrolled those patients from the pediatric department of our Hospital between 2010 and 2015. The study was approved by our Hospital Ethics Review Committee. Parents of all children provided informed consent before the children participated the study.2. Clinical context:All participants received evaluations consisting of syndrome, age at onset, seizure types and frequency, clinical course, neuroimaging, and family history, video-electroencephalography (VEEG) monitoring, neurological examination(MRI), the classification of seizure types according to the epilepsy syndrome diagnostic criteria of the International League Against Epilepsy (2010).3. MethodsBlood samples (4 mL) were collected from 65 probands of an epilepsy pedigree, 138 pedigree members and 200 healthy controls and placed into EDTA anticoagulant tubes. Genomic DNA was extracted using a DNA extraction kit We designed a complete kit that synthetized target genes using the Agilent SureSelect Target Enrichment technique. We used this technique to capture the coding regions from 485 candidate genes, including their exons and exon-intron boundaries (1.961 Mbp in total). Equipment and reagents was performed on an Illumina GAIIx platform that was manufactured by Illumina (San Diego, California, USA) using paired-end sequencing of 110 bp. The clean paired-end reads were aligned to the human reference genome build hg19, which was previously annotated using ANNOVAR, in addition to insertion-deletion (indel) and single-nucleotide polymorphism (SNP) calling. In silico pathogenicity predictions of novel missense variants were calculated using Polyphen2. We then formulated a series of filtering criteria to determine every possible pathogenic variant from a large amount of raw data. The reported pathogenic mutations were marked, and select polymorphisms were excluded according to the HGMD Professional database (Version 2013.2), the 1000 Genomes Browser, PubMed and the UCSC database. Validation, parental origin and segregation analyses for the suspected pathogenic variants were performed using conventional Sanger sequencing.[Results]1.In 103 GEFS+families, a total of 19 people in 11 families have SCN1A gene heterozygous mutations, including nine missense mutations (R500Q, V1414A, M350L, L964R, V1362M, N275D, C142Y, S573R, C1274Y), and one Truncation mutation (K1083NfsTer13), five people in 2 families have the same locus R500Q missense mutation.2.The clinical characteristics of SCNIAgene mutations in GEFS family:1) 6 families diagnosed GEFS+, mild clinical symptoms, mainly in FS/FS, the symptom in mutation of M350L, V1414A, V1362M, C142Y, C1274Y is a generalized seizure, N275D for partial seizures; 2) 5 families diagnosed as Dravet syndrome. Clinical seizures in various forms, the symptom in mutation of R500Q, S573R, K1083NfsTerl3 is partial seizures onset then a generalized seizure later, L964R in general seizure onset, then partial seizures later.3.The relationship between mutation of SCN1A gene and drug efficacy in GEFS+ family:1) V1414A missense mutation locate in the sodium channel alpha subunit protein domain DⅢ S5-S6 link, N275D missense mutation locate in the sodium channel alpha subunit protein domain DⅠ S5 and C142T missense mutation located in the sodium channel alpha subunit unit of protein domain D Ⅰ transmembrane segment S6, the patient with the three mutations using valproate therapy is effective to control the clinical attack; 2) M350L missense mutation in the sodium channel alpha subunit protein domain D Ⅰ S5-S6 link, V1362M missense mutation in the sodium channel alpha subunit protein domain D Ⅰ S5, C1274Y missense mutation in sodium channel alpha subunit protein domain DⅢS2,the patient with the three mutations using valproate+levetiracetam treatment, can control clinical symptoms; 3) R500Q mutation locate in the sodium channel alpha subunit protein domain D Ⅰ-Ⅱ link, truncation mutation of K1083NfsTerl3 locate in sodium channel alpha subunit protein intracellular domain DⅡ-DⅢ, S573R missense mutation in the sodium channel alpha subunit protein domain D Ⅰ-D Ⅱ link, patient with three mutations can cause Dravet syndrome, taking oxcarbazepine made the symptoms more seriou and valproate with levetiracetam therapy can reduce the clinical seizures; 4) L964R missense mutation in the sodium channel alpha subunit protein domain D Ⅱ S5-S6 can cause Dravet syndrome, taking oxcarbazepine symptoms made the symptoms more serious and valproate added on levetiracetam and topiramate therapy can reduce the clinical seizures.[Conclusions]1. In 103 GEFS+families, a total of 19 people in 11 families have SCN1A gene heterozygous mutations, including nine missense mutations (R500Q, V1414A, M350L, L964R, V1362M, N275D, C142Y, S573R, C1274Y), and one Truncation mutation (K1083NfsTerl3), five people in 2 families have the same locus R500Q missense mutation.2.SCN1A gene mutation position and GEFs clinical seizure type and drug effect. Missense mutations in V1414A、N275D、C142T, is effective in the treatment of sodium valproate. Missense mutations in M350L、V1362M、C1274Y, is effective in the treatment of sodium valproate added on levetiracetam. patient with R500Q missense mutation,truncation mutation of p.K1083NfsTerl3 or S573R missense mutation can cause Dravet syndrome, taking oxcarbazepine made the symptoms more seriou and valproate with levetiracetam therapy can reduce the clinical seizures; L964R missense mutation can cause Dravet syndrome, taking oxcarbazepine symptoms made the symptoms more seriou and valproate added on levetiracetam and topiramate therapy can reduce the clinical seizures.