Genotype-phenotype Relationships In 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" in2008. Scheffer reported a seemingly unrelated familial epilepsy syndrome that called generalized epilepsy with febrile seizures plus (GEFS+) in1997. 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 of6years 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" in2008. 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 γ-aminobutyric acid receptor GABRG2and GABRD. However, SCN1A is the major gene in GEFS+and related epilepsies since other genes were only reported in a few families. In1998, the first gene for GEFS+was identified when they reported a mutation of SCN1B, encoding the beta1subunit of the sodium channel, in a large Australian family with GEFS+. In2000, Escayg and colleagues identified mutations in SCN1A, encoding the alpha1sodium channel subunit, in two GEFS+families. The second ion channel implicated in GEFS+is the GABAA receptor. The gamma2subunit 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 NaV1.1channel 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 SCN1A mutation. Early diagnosis of the functional consequences of those mutations guides selection of effective AEDS and avoidance of AEDS that aggravate seizures.[Subjects and Methods]1. Subjects:We collected17families of the Han-nationality population in southern China with genetic epilepsy with febrile seizures plus. And200healthy 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 the Guangdong General Hospital between2010and2013. The study was approved by the Guangdong General 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 were obtained from78members of GEFS+families and200healthy comparisons. Genomic DNA was extracted from the blood samples with QIAamp DNA Mini Kit. The primers for the exons and exon-intron boundaries of SCN1A, SCN1B, GABRG2, GABRD were designed and rechecked with the UCSC Genome Browser website and NCBI/Primer-Blat. The PCR products were purified and DNA sequencing was performed with the ABI3730, and then analyzed the sequences.[Results]1. In this study,11.76%(2/17) of GEFS+families have mutations of SCNIA,5.88%(1/17) of GEFS+families have mutations of SCN1B, and have no mutation in the GABRG2or GABRD genes with polymerase chain reaction methodology followed by Sanger sequencing.2. In this study, we identified two novel SCNIA mutations associated with GEFS+in two Chinese families. In family one, proband and his younger sister had a history of febrile seizures plus, his father had a history of febrile seizures, the seizure type classified as tonic-clonic seizure, valproate was effective for seizures. DNA sequence analysis in the proband, younger sister and father revealed a same heterozygous nucleotide transition (C.425G>A) in exon3of SCNIA, which results in a substitution of Cysteine by Tyrosine at position142of SCNIA protein (p. C142T). The mutation was detected in all patients of this GEFS+family, but neither in the unaffected family members nor200normal controls. The novel missense mutation (p. C142T) is located in the S6/DI domain. The142Cysteine residue is highly conserved among the al-subunits of sodium-channels from drosophila melanogaster and danio rerio to humans. In family two, proband had a history of febrile seizures plus, the seizure type classified as tonic-clonic and focal seizures. Seizure aggravation induced by oxcarbazepine while effective by Levetiracetam. DNA sequence analysis in the proband and mother revealed a same heterozygous nucleotide transition (c.1719C>A) in exon11of SCNIA, which results in a substitution of Serine by Arginine at position573of SCNIA protein (p. S573R). The novel missense mutation (p. S573R) is located in the S5-6/DIV domain. The573Arginine residue is also highly conserved.3. We identified a novel SCN1B Synonymous mutation associated with GEFS+in a Chinese familiy. In this family, proband and his mother had a history of febrile seizures plus, the seizure type classified as tonic-clonic seizure, Valproate was effective for seizures. DNA sequence analysis in the proband and mother revealed a same heterozygous nucleotide transition (c.270G>T) in exon3of SCNIA, but have no effect on the substitution of amino acids of SCNIA protein.4. Four SCNIA Single nucleotide polymorphisms (rs7580482, rs2298771, rs150638891, rs150570058), one SCN1B SNP (rs3746255), two GABRG2SNPs (rs11135176, rs211037), and one GABRD SNP(rs2229110) were identified in GEFS+families in this study.[Conclusions]1. Genomic DNA from17GEFS+families were screened for mutations in the exons of SCNIA, SCN1B, GABRG2and GABRD using PCR methodology followed by Sanger sequencing. Two novel SCN1A missense mutations (C142T, S573R), one SCN1B Synonymous mutation were detected (V90V). Our results expand the spectrum of SCN1A mutations and provide novel insights between the SCNIA mutations and the clinical variations of GEFS+.2. The localization of missense mutations in SCNIA identified in patients with GEFS+is distinct in terms of clinical symptoms and responses to antiepileptic drugs. Mutation in the S6region of SCN1A with the presence of tonic-clonic seizure, Valproate was effective for seizures.Mutation in the pore region of SCNIA is strongly associated with tonic-clonic and focal seizures, Seizure aggravation induced by oxcarbazepine while effective by Levetiracetam. The discovery of specific location of SCNIA mutations may influence the phenotype-genotype relationships and clinical management, treatment choices in patients with GEFS+.