Mapping And Mutation Detection Of Causative Genes For Idiopathic Epilepsy Syndromes FCTE And BFIS, And Mutation Detection For GEFS+

Familial cortical tremor with epilepsy (FCTE) is a rare autosomal dominant idiopathic epilepsy syndrome, characterized by adult-onset fine finger cortical tremor resembling essential tremor, infrequent seizures, features of cortical reflex myoclonus in neuroelectrophysiological study, good response to anticonvulsants, non-progressive course and benign prognosis. Similar symptoms were described within other controversial idiopathic epilepsy syndromes including FEME, BAFME, FAME, ADCME. Causative genes of BAFME, FAME and ADCME were mapped to 8q23.3-q24.1 and 2p11.1-q12.2. However, Causative gene of FCTE was not mapped yet. A large pedigree of Chinese origin affected with FCTE was found in Hunan Province of China. All of affected individuals manifested typical symptoms of FCTE. By linkage analysis, we excluded this family from linkage to 2p11.1-q12.2, while indicated evidence of linkage to chromosome 8. Using fine microsatellite markers, a maximum two-point LOD score of 7.21 for microsatellite D8S199 at recombination fractionθ0.0 was obtained. Recombination results suggest the locus on chromosome 8q23.3-24.23 over 30.5 cM interval between D8S555 and D8S1753. Considering ion channel genes play an important role in the epileptogenesis of idiopathic epilepsies, three potassium channel genes including KCNQ3, KCNV1 and KCNS2 located in and near 8q23.3-24.23 were subjected to mutation detection through polymerase chain reaction (PCR) and direction sequencing. No sequence variants were found in three candidate genes, therefore excluded from the FCTE pedigree. This is the first family case report of FCTE found in China, and for the first time in the world the causative gene locus of FCTE has been identified.Benign familial infantile seizures (BFIS) is an autosomal dominant idiopathic epilepsy syndrome characterized by afebrile seizures, which typically onset from three to twelve months and remit spontaneously within one to three years old, normal psychomotor development outcome and normal finding in physical examination, interictal EEG and neuroimaging. Genetic studies have revealed three causative loci on 19q12-13.1,16p12-q12 and 2q24, and further studies indicate more susceptibility loci may exist. We identified two large BFIS pedigrees from Hunan Province of China. In the previous studies, after exclusion of known loci 19q12-13.1,16p12-q12 and 2q24 as well as mutation in genes KCNQ2, KCNQ3 and SCN2A, causative gene of one BFIS family (Pedigree 1) was indicated to be on novel locus, while that of another BFIS family (Pedigree 2) was mapped to novel locus on 1p36.12-p35.1 through genome-wide scan and fine mapping using microsatellite markers. Then thirty-three candidate genes located on 1p36.12-p35.1 were subjected to mutation detection for Pedigree 2, but no causative variants were found. In this study, we applied SNP linkage beadchip to map causative gene for Pedigree 1. Three candidate loci on 5q22.1-5q32, 9p21.3-9p21.2 and 22q11.21-22q12.1 were obtained. Through linkage analysis using fine microsatellite markers, the most likely locus was linked to 5q31.1-31.2, with a maximum two-point LOD score of 2.84 for microsatellite marker D5S2117 at recombination fractionθ0.0 between D5S2057 and D5S500 over 5.47 cM interval. Subsequently, one candidate gene (GABRG2) closed to 5q31.1-31.2 of Pedigree 1 was selected and subjected to mutation detection by PCR and direct sequencing, but no sequence variant was found. Meanwhile, fourteen candidate genes (SYTL1, FUCA1, EPHA8, SH3BGRL3, AK2, SDC3, MAN1C1, ID3, LAPTM5, PAQR7, RCC1, RUNX3, KCNQ4, GABRD) located/closed to 1p36.12-p35.1 of Pedigree 2, were selected and subjected to mutation detection. Thirteen SNPs were detected, two of which are not reported yet. It is unlikely that the above-mentioned genes are involved in the pathogenesis of the two Chinese BFIS families respectively. The results have laid indispensable basis for further analysis of other candidate genes for to elucidate the molecular pathogenesis of BFIS.Generalized/Genetic epilepsy with febrile seizures plus (GEFS+) is a familial idiopathic syndrome with high phenotypic heterogeneity and genetic heterogeneity. To date, six causative genes have been identified including SCN1A, SCN1B, SCN2A, SCN9A, GABRD and GABRG2. We studied three GEFS+ pedigrees of Chinese origin and found their clinical spectrum include FS, FS+, AS and AFS. Three genes, SCN1A, SCN1B and GABRG2 which are more frequently involved in the etiology of GEFS+, were subjected to mutation detection. By PCR and direct sequencing, a novel mutation c.5383G>A in SCN1A was identified in one of pedigrees. But no sequence variants were found in SCN1A, SCN1B or GABRG2 for two other GEFS+ families, indicating causative variants lie in other candidate genes or are probably not routine point mutations. Further investigations are needed for two other GEFS+ families as to finally disclose the corresponding causative gene(s). Functional study will be carried out to investigate the pathogenesis of the novel mutation c.5383G>A.