GABRG2 Research Articles

GABRG2 Deletion Linked to Genetic Epilepsy with Febrile Seizures Plus Affects the Expression of GABAA Receptor Subunits and Other Genes at Different Temperatures

Mutations in γ-aminobutyric acid A receptor (GABAA) subunits and sodium channel genes, especially GABRG2 and SCN1A, have been reported to be associated with febrile seizures (FS) and genetic epilepsy with febrile seizures plus (GEFS+). GEFS+ is a well-known family of epileptic syndrome with autosomal dominant inheritance in children. Its most common phenotypes are febrile seizures often with accessory afebrile generalized tonic-clonic seizures, febrile seizures plus (FS+), severe epileptic encephalopathy, as well as other types of generalized or localization-related seizures. However, the pathogenesis of febrile seizures remains largely unknown. Here, we generated a GABRG2 gene knockout cell line (HT22GABRG2KO) by applying the CRISPR/Cas9-mediated genomic deletion in HT-22 mouse hippocampal neuronal cell line to explore the function of GABRG2 in vitro. With mRNA-seq, we found significant changes in the expression profiles of several epilepsy-related genes when GABRG2 was knockout, some of them showing temperature-induced changes as well. Kyoto Encyclopedia Gene and Genomic (KEGG) analysis revealed a significant alteration in the MAPK and PI3K-Akt signaling pathways. We also observed an up-regulation of the matrix metalloproteinases (MMPs) family after GABRG2 knockout. Furthermore, the significant decrease in expression of GABRA1 and CACNA1A (but not others) with an increase in temperature is a novel finding. In summary, mutations in the GABAA receptor can lead to a decrease in numbers of receptors, which may cause the impairment of GABAergic pathway signaling. This data has been the first time to reveal that GABRG2 mutations would affect the function of other genes, and based on this finding we hope this work would also provide a new direction for the research of GABRG2 in GEFS+. It also may provide a molecular basis for the severity of epilepsy, and guide the clinical medication for the treatment of the epilepsy focused on the function on GABAA receptors, which, might be a new strategy for genetic diagnosis and targeted treatment of epilepsy.

Genetic variants in RET, ARHGEF3 and CTNNAL1, and relevant interaction networks, contribute to the risk of Hirschsprung disease.

Hirschsprung disease (HSCR), the most common enteric neuropathy, stands as a model for complex genetic disorders. It has recently been demonstrated that both ARHGEF3 and CTNNAL1 map to the RET-dependent HSCR susceptibility loci. We therefore sought to explore whether genetic variants within RET, ARHGEF3 and CTNNAL1, and their genetic interaction networks are associated with HSCR. Taking advantage of a strategy that combined the MassArray system and gene-gene interaction analysis with case-control study, we interrogated 38 polymorphisms within RET, ARHGEF3 and CTNNAL1 in 1015 subjects (502 HSCR cases and 513 controls) of Han Chinese origin. There were statistically significant associations between 20 genetic variants in these three genes and HSCR. Haplotype analysis also revealed some significant global P values, i.e. RET_ rs2435357-rs752978-rs74400468-rs2435353-rs2075913-rs17028-rs2435355 (P = 3.79×10-58). Using the MDR and GeneMANIA platforms, we found strong genetic interactions among RET, ARHGEF3, and CTNNAL1 and our previously studied GAL, GAP43, NRSN1, PTCH1, GABRG2 and RELN genes. These results offer the first indication that genetic markers of RET, ARHGEF3 and CTNNAL1 and relevant genetic interaction networks confer the altered risk to HSCR in the Han Chinese population.

303 Identification of candidate genes related to temperament in Brahman cattle

Abstract The objective of this study was to identify genomic regions and genes associated with beef cattle temperament. Temperament, measured as exit velocity (EV; m/s), was recorded in 1,370 Brahman cattle from Texas A&M AgriLife Research at Overton, TX. We identified two groups of temperament-contrasting animals. Cows were calm if their EV of 0.16–3.41 m/s and bulls if their EV was 0.4–3.12 m/s (n-119). Cows were temperamental if their EV was 3.55–7.66 m/s and bulls if their EV was 3.13–10.83 m/s (n = 79). The 198 animals were genotyped using the GGP-HD-150K chip. 139,376 SNPs were evaluated for association with temperament. 13 SNP′s were associated with EV (P < 4.0E-05). The SNPs GABRG2-26484, NRXN3-26436 and TBX20-191081 are located in introns of the GABRG2, NRXN3 and TBX20 genes, respectively. The GABRG2 gene encodes a GABA receptor, the major inhibitory neurotransmitter in the mammalian brain. The NRXN3 gene encodes receptor proteins related to chemical transmission at synapses. TBX20 is a member of the T-box transcription factor family expressed in the developing stages of heart, limbs, eye and ventral neural tube. To test the effect of these 3 SNP′s on EV, Pen-Score and Temperament-Score, a general linear model was fitted including the fixed effects of sex of calf and year of birth, and the individual effect of the 3 SNPs. The marker TBX20-191081 was associated with the three traits evaluated (P < 0.01), where the GG genotype was associated with the calmest temperament. The GG genotype had a significant effect on EV (P < 0.0001) that was 1.35 and 1.95 m/s slower than AG and AA, respectively. For TS, the GG genotype had a TS that was 1.41 and 1.24 DS less than those of the AA and GA genotypes. Our study indicates that genetic control of cattle temperament has a wide network of genes with divergent functions and genetic background specificity.

INVESTIGATION OF THE LEVEL OF GENE EXPRESSION OF SUBUNITS OF GABA RECEPTOR AFTER ADMINISTRATION OF KLOFLUBICIN

The article presents the results of determining the level of expression of genes encoding GABA receptor subunits GABRA1, GABRB2, and GABRG2 in the hippocampus of rats 24 hours after a single intramuscular administration of the antagonist of the chloro-ion channel of GABA receptor of kloflubicin in a dose of LD25, LD40, LD50, and LD75. It is revealed that kloflubicin has no influence on the relative level of GABRG2 gene expression. At the same time, the relative level of GABRA1 gene expression increases 7,5, 7,0, and 5,0 times after administration of kloflubicin in a dose of LD40, LD50, and LD75, respectively. The relative level of GABRB2 gene expression also increases 3,6 and 2,6 times after administration of kloflubicin in a dose of LD50 and LD75, respectively. It is assumed that increase in the level of gene expression of GABRA1 and GABRB2 in rats after administration of kloflubicin in doses above LD25 is a compensatory reaction of the body to the effect of physiologically active substance, and subunits encoded by these genes α1 and β2, respectively, are included in the mechanism of convulsive effect.

Mutational screening of GABRG2 gene in Pakistani population of Punjab with generalized tonic clonic seizures and children with childhood absence epilepsy

BackgroundEpilepsy is a multifaceted and multistep disorder that disrupts the proper functioning of neurons. It is becoming increasingly clear that the responsiveness of neurons depends on the appropriate trafficking of ions across the channels in the membrane of neurons. In line with this notion, impairment among these ion channels due to mutations has gain increasing attention in molecular neuroscience. MethodsMutation analysis of the coding exons (exon 3, 5 and 9) was performed by sequencing GABRG2 to identify any complex biological entities among two different types of epilepsies. ResultsSequencing of the candidate gene “GABRG2” revealed a single polymorphic site in exon 3 in the children with absence epilepsy and generalized tonic clonic seizures. However, this single nucleotide alteration was more common in the patients with childhood absence epilepsy patients compared to the generalized cases. ConclusionA silent mutation was identified at locus 27,909 C > T in 30.66% of the total screened or analyzed cases. However, no single nucleotide polymorphism was identified in exon 5 of GABRG2 in a Pakistani population, in contrast to a study of Chinese patients with childhood absence epilepsy.

Association of GABAA Receptor Gene with Epilepsy Syndromes.

GABA has always been an inviting target in the etiology and treatment of epilepsy. The GABRA1, GABRG2, and GABRD genes provide instructions for making α1, ϒ2, and δ subunits of GABAA receptor protein respectively. GABAA is considered as one of the most important proteins and has found to play an important role in many neurological disorders. We explored the association of GABAA receptor gene mutation/SNPs in JME and LGS patients in Indian population. A total of 100 epilepsy syndrome patients (50 JME and 50 LGS) and 100 healthy control subjects were recruited and analyzed by AS-PCR and RFLP-PCR techniques. In our study, GABRA1 965 C > A mutation and 15 A > G polymorphism gene may play an important role in modulating the drug efficacy in LGS patients. The GABRA1 15 A > G polymorphism may also play an important role in the susceptibility of LGS and the inheritance of GG genotype of this polymorphism may provide an increased risk of development of LGS. The GABRG2 588 C > T polymorphism may decrease the duration of seizures in JME patients. The GABRD 659G > A polymorphism may play an important role in the susceptibility of JME and LGS and this polymorphism may also increase the duration of postictal period in JME patients but may decrease the duration of seizure in LGS patients.

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

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

Deletion of Dlk2 increases the vulnerability to anxiety-like behaviors and impairs the anxiolytic action of alprazolam

The purpose of this study was to evaluate the role of the non-canonical DLK2 NOTCH ligand in the regulation of emotional behavior. To this aim, anxiety and depressive-like behaviors were examined in Dlk2 knock-out (Dlk2–/–) and its corresponding wild-type (WT) mice. Furthermore, relative gene expression analyses of corticotropin releasing hormone (Crh) in the paraventricular nucleus (PVN), glucocorticoid receptor (NR3C1) and FK506 binding protein 5 (FKBP5) in the hippocampus (HIPP), and the transcription factors Hes1, Hes5 and Hey1 in the PVN, HIPP and amygdala (AMY) were carried out in Dlk2–/– and WT mice under basal conditions and after exposure to restraint stress. The anxiolytic action of alprazolam and the relative gene expression levels of the GABA-A alpha 2 and gamma 2 receptor subunits (Gabra2 and Gabrg2) were also evaluated in the HIPP and AMY of WT and Dlk2–/– mice.The results reveal that deletion of Dlk2 increased anxiety and depressive-like behaviors and altered the vulnerability to restraint stress on Crh gene expression in the PVN, Nr3c1 and Fkbp5 gene expression in the HIPP, and Hes1, Hes5 and Hey1 gene expression in the PVN, HIPP and AMY. Interestingly, the administration of alprazolam failed to produce an anxiolytic action in Dlk2–/– mice. Indeed, Gabra2 and Gabrg2 gene expression levels were significantly affected under basal conditions and after stress exposure in Dlk2–/– mice compared with WT mice.In conclusion, the results suggest that DLK2 plays an important role in the regulation of emotional behaviors and relevant targets of the stress axis, NOTCH pathway and GABAergic neurotransmission. In addition, the deletion of Dlk2 blocked the anxiolytic response to alprazolam. Future studies are needed to determine the relevance of DLK2 as a potential therapeutic target for the treatment of neuropsychiatric disorders with anxiety or depressive-like behaviors.

Vitamin B6 and homocysteine levels in carbamazepine treated epilepsy of Khyber Pakhtunkhwa.

The study focused on the plasma levels of vitamin B6 and homocysteine in different genotypes of MTHFR (C677T, A1298C) and GABRG2 (C588T, C315T) genes in carbamazepine resistant epilepsy in the population of Khyber Pakhtunkhwa. Patients who were possible candidates for carbamazepine therapy were followed for six months for their seizure control. Plasma levels of vitamin B6 and homocysteine were determined using immunoassay based techniques at baseline and after six months. MTHFR (C677T, A1298C) and GABRG2 (C588T, C315T) genes were genotyped using restriction fragment length polymorphisms. Seizure control during therapy was recorded on a standardized proforma. Low vitamin B6 levels and hyperhomocysteinemia were found in 61.7% of resistant patients (n=34). Resistant patients had the following frequencies of variant genotypes (677CT=38.1% and 677TT=24.4%; 1298AC=42.2% and 1298CC=26.1%; 588CT= 47.6% and 315TT= 33.3%) of MTHFR (C677T and A1298C) and GABRG2 (C588T and C315T) genes. A significant decline in vitamin B6 (P<0.0001) and hyperhomocysteinemia were found in variant genotypes of MTHFR (C677T, A1298C) and GABRG2 (C588T, C315T) genes. Following six months of carbamazepine of therapy in heterozygous variant genotypes of MTHFR (677CT and 1298AC) and GABRG2 (588CT and 315CT) genes, we observed a significant fall in vitamin B6 levels and hyperhomocysteinemia.

Heat induced temperature dysregulation and seizures in Dravet Syndrome/GEFS+ Gabrg2+/Q390X mice

It has been established that febrile seizures and its extended syndromes like generalized epilepsy with febrile seizures (FS) plus (GEFS+) and Dravet syndrome have been associated with mutations especially in SCN1A and GABRG2 genes. In patients, the onset of FS is likely due to the combined effect of temperature and inflammation in genetically vulnerable individuals because fever is often associated with infection. Much effort has been spent to understand the mechanisms underlying fever induction of seizures. In addition to the role of cytokines in FS, previous studies in Scn1a+/− knockout mice, a model of Dravet syndrome, indicated that temperature elevation alone could result in seizure generation, and the effect of elevated temperature inducing seizures was age-dependent. Here, we report the thermal effect in a different mouse model of Dravet syndrome, the Gabrg2+/Q390X knockin mouse. We demonstrated age-dependent dysregulated temperature control and that temperature elevation produced myoclonic jerks, generalized tonic clonic seizures (GTCSs) and heightened anxiety-like symptoms in Gabrg2+/Q390X mice. The study indicated that regardless of other inflammatory factors, brief heat alone increased brain excitability and induced multiple types of seizures in Gabrg2+/Q390X mice, suggesting that mutations like GABRG2(Q390X) may alter brain thermal regulation and precipitate seizures during temperature elevations.

Expanding the phenotypic spectrum of GABRG2 variants: a recurrent GABRG2 missense variant associated with a severe phenotype

Pathogenic missense and truncating variants in the GABRG2 gene cause a spectrum of epilepsies, from Dravet syndrome to milder simple febrile seizures. In most cases, pathogenic missense variants in the GABRG2 gene segregate with a febrile seizure phenotype. In this case series, we report a recurrent, de novo missense variant (c0.316 G > A; p.A106T) in the GABRG2 gene that was identified in five unrelated individuals. These patients were described to have a more severe phenotype than previously reported for GABRG2 missense variants. Common features include variable early-onset seizures, significant motor and speech delays, intellectual disability, hypotonia, movement disorder, dysmorphic features and vision/ocular issues. Our report further explores a recurrent pathogenic missense variant within the GABRG2 variant family and broadens the spectrum of associated phenotypes for GABRG2-associated disorders.

GABRG2 C588T gene polymorphisms might be a predictive genetic marker of febrile seizures and generalized recurrent seizures: a case-control study in a Romanian pediatric population.

IntroductionThis case-control study aimed to assess two single nucleotide polymorphisms of the gene encoding the GABRG2 protein – GABRG2 (3145 G>A) and GABRG2 rs 211037 Asn196Asn (C588T) – in a cohort of pediatric patients from Romania, and evaluate their possible impact on drug-resistant forms of generalized epilepsy and recurrent febrile seizures.Material and methodsOne hundred and fourteen children with idiopathic generalized epilepsy (group 1) or febrile seizures (group 2) were compared to 153 controls. Peripheral blood samples were assessed using polymerase chain reaction-restriction fragment length polymorphism analysis, with results interpreted based on the disappearance of a restriction site in the C allele (122 bp) compared to the T allele (100 bp + 22 bp).ResultsA significant association was found with the TT homozygous genotype and T allele for both febrile seizures and epilepsy for the C588T locus, while GABRG2 G>A 3145 showed no significant association with any type of seizure. The TT homozygous genotype of GABRG2 Asn196Asn polymorphism was more frequent in patients with a history of febrile seizures (p = 0.0001), without a significant association identified for GABRG2-G>A 3145. Composite analysis showed associations with epilepsy for CC-AG (p = 0.02) and CT-AG (p = 0.007) with the CC-AA combination as reference.ConclusionsC588T polymorphism of the GABRG2 gene might be a predictive genetic marker in triggering febrile convulsions. GABRG2 rs211037 TT homozygotes and T allele variants have an increased risk for developing febrile seizures. Recurrent crises and repeated episodes of seizures are more frequent in the GABRG2 Asn196Asn TT genotype polymorphism, with a 45 and 8 times higher risk of developing idiopathic generalized epilepsy and recurrent febrile seizures, respectively.

Mutations in GABRG2 receptor gene are not a major factor in the pathogenesis of mesial temporal lobe epilepsy in Indian population.

Aim:This study is focused on GABRG2 gene sequence variations in patients with mesial temporal lobe epilepsy (mTLE). The GABAAreceptor is a heteropentameric receptor and alpha-1 beta-2 gamma-2 subunits combination is most abundant and present in almost all regions of the brain. The gamma-2 subunit (GABRG2) gene mutations have been reported in different epilepsy pathologies. In the present study we have looked for GABRG2 gene sequence variations in patients with mTLE.Materials and Methods:Twenty patients (12 females and eight males, age 4.6-38 years) with MTLE were recruited for this investigation. Patients were recommended for epilepsy surgery after all clinical investigations as per the epilepsy protocol. Ethnically matched glioma or meningioma patients were considered as nonepileptic controls. During temporal lobectomy of amygdalohippocampectomy, hippocampal brain tissue samples were resected guided by intraoperative electrocorticography (ECoG) activity. All 11 exons of GABRG2 gene with their flanking intronic regions were amplified by polymerase chain reaction (PCR) and screened by DNA sequencing analysis for sequence variations.Statistical Analysis Used:Comparison of allele frequencies between patient and control groups was determined using a c2 test.Results and Conclusions:Total five DNA sequence variations were identified, three in exonic regions (c.643A > G, rs211035), (c.T > A, rs424740), and (c.C > T, rs418210) and two in intronic regions (c.751 + 41A > G, rs211034) and (c.751 + 52G > A, rs 34281163). Allele frequencies of variants identified in this study did not differ between patients and normal controls. Thus, we conclude that GABRG2 gene may not be playing significant role in the development of epilepsy or as a susceptibility gene in patients with MTLE in Indian population.

Contribution of GABRG2 Polymorphisms to Risk of Epilepsy and Febrile Seizure: a Multicenter Cohort Study and Meta-analysis.

Gamma-aminobutyric acid receptor (GABA-A) is the most common receptor of fast synaptic inhibition in the human brain. Gamma protein encoded by the GABRG2 gene is one of the subunits of the GABA-A receptor, which plays an essential role in the function of this receptor. Several studies have identified various febrile seizure (FS) and epilepsy risk variants of GABRG2 gene in different populations, but some others did not support these results. The aim of this case-control study is to investigate whether GABRG2 polymorphisms contribute to susceptibility for FS and epilepsy in pooled data of three cohorts, from Malaysia (composed of Malay, Chinese, and Indian), Hong Kong, and Korea. Furthermore, the pooled dataset of these cohorts with previous reports were meta-analyzed for determining the risk effect size of the rs211037 polymorphism on FS and symptomatic epilepsy (SE). The rs211037, rs210987, rs440218, rs2422106, rs211014, and rs401750 polymorphisms were genotyped in the 6442 subjects (1729 epilepsy and 4713 controls). Results of the case-control study showed associations between rs211037 and the risk of SE in the pooled data from all cohorts (T vs. C, p = 3 × 10(-5), and TT vs. CC, p = 2 × 10(-5)) and the risk of partial seizure in the combined data of Malaysia and Hong Kong (both T vs. C and TT vs. CC, p = 2 × 10(-6)). The rs211037-rs210987 and rs2422106-rs211014-rs401750 haplotypes were also associated with susceptibility to SE in Chinese. Meta-analysis of all Asians identified association between rs211037 and FS and SE (T vs. C, p = 4 × 10(-4), and p = 4 × 10(-3), respectively). In conclusion, rs211037 alone may be a risk factor for FS, partial seizure, and SE, and in linkage disequilibrium with rs210987 can contribute to FS and SE in Asians, particularly in Chinese.

Diagnostic value of array-based single nucleotide polymorphisms comparative genomic hybridization in Angelman syndrome

Objective To analyze the genotype-phenotype correlations of Angelman syndrome(AS), and to discuss the advantage of applying array-based single nucleotide polymorphisms comparative genomic hybridization(SNP aCGH)in diagnosis of AS. Methods Examination of electroencephalogram(EEG)and intelligence quotient(IQ) evaluation were done for 11 cases diagnosed as AS clinically.Gesell scares were chosen as the evaluation criterion of IQ.The screening techniques was methylation polymerase chain reaction(MS-PCR), then SNP aCGH was used to make genetic diagnosis. Results (1)Eleven cases of AS were confirmed: 1 case had UPD(uniparental disomy), 10 cases were type of deletion, from which 6 cases were deletion(Ⅱ), 4 cases were deletion(Ⅰ). (2)The copy number variations were detected in the region of 15q11-q13, which contained genes like MKRN3, MAGEL2, NDN, SNRPN, SNURF, GABRB3, GABRA5, GABRG3, UBE3A, OCA2, ATP10A.To search online Mendelian inheritance in man, genes above were correlated with AS manifestation.(3)All cases of deletion were 3-5 standard deviation(SD) in weight and height to normal children at the same age and with the same sex, while UPD was below 1.5 SD.Gesell scares showed that the deletion(Ⅰ) was the most serious in mental retardation, deletion(Ⅱ) was moderate, and the UPD was mild.Eight cases were hypopigmentation, and one was the UPD.EEG revealed that 1 case of deletion(Ⅰ) and the UPD were spike occasionally, another one deletion(Ⅰ) was limit EEG.The rest cases displayed slow and spike waves paroxysmally, with amplitude of medium or high, 2.5-3.0 Hz. Conclusions Not only can SNP aCGH make a diagnosis of AS but discriminate the types of genetic pathology.Since different type contributes to a diverse of clinical features and the rate of recurrence is also different, it is significant for family genetic consultation.Moreover, the technology is advantageous for the study on the pathogenesis and gene function. Key words: Array-based single nucleotide polymorphisms comparative genomic hybridization; Angelman syndrome; Genotype; Phenotype

Array-comparative genomic hybridization analysis of a cohort of Saudi patients with epilepsy.

Specific genetic anomalies or non-genetic factors could lead to epilepsy, but in various cases the underlying cause is unknown. Novel technologies, such as array comparative genomic hybridization, may reveal the copy number variants (CNVs), established as significant risk factor for epilepsy. This study carried out a high-density whole genome array- comparative genomic hybridization analysis with blood DNA samples from a cohort of twenty epilepsy patients to search for CNVs associated with epilepsy. Microdeletion of 14q31.1 was observed in four patients including two from the same family with loss of the NRXN3 gene; microdeletion of 15q12 in one patient with loss of the GABRG3 gene, and microduplication of 20q13.33 in three patients with loss of the gene group CHRNA4, KCNQ2, EEF1A2 and PPDPF were also found. These CNV findings were confirmed by real-time quantitative polymerase chain reaction. We have described, for the first time, numerous potential CNVs/genes implicated in epilepsy in the Saudi population. The study presents a better description of the genetic variations in epilepsy, and would eventually enable us to provide a foundation for understanding the critical genome regions which might be involved in the development of epilepsy.

Rare variants in γ-aminobutyric acid type A receptor genes in rolandic epilepsy and related syndromes.

To test whether mutations in γ-aminobutyric acid type A receptor (GABAA -R) subunit genes contribute to the etiology of rolandic epilepsy (RE) or its atypical variants (ARE). We performed exome sequencing to compare the frequency of variants in 18 GABAA -R genes in 204 European patients with RE/ARE versus 728 platform-matched controls. Identified GABRG2 variants were functionally assessed for protein stability, trafficking, postsynaptic clustering, and receptor function. Of 18 screened GABAA -R genes, we detected an enrichment of rare variants in the GABRG2 gene in RE/ARE patients (5 of 204, 2.45%) in comparison to controls (1 of 723, 0.14%; odds ratio = 18.07, 95% confidence interval = 2.01-855.07, p = 0.0024, pcorr = 0.043). We identified a GABRG2 splice variant (c.549-3T>G) in 2 unrelated patients as well as 3 nonsynonymous variations in this gene (p.G257R, p.R323Q, p.I389V). Functional assessment showed reduced surface expression of p.G257R and decreased GABA-evoked currents for p.R323Q. The p.G257R mutation displayed diminished levels of palmitoylation, a post-translational modification crucial for trafficking of proteins to the cell membrane. Enzymatically raised palmitoylation levels restored the surface expression of the p.G257R variant γ2 subunit. The statistical association and the functional evidence suggest that mutations of the GABRG2 gene may increase the risk of RE/ARE. Restoring the impaired membrane trafficking of some GABRG2 mutations by enhancing palmitoylation might be an interesting therapeutic approach to reverse the pathogenic effect of such mutants.

Association Study of GABRG2 Polymorphisms with Suicidal Behaviour in Schizophrenia Patients with Alcohol Use Disorder

Background: Schizophrenia is a severe neuropsychiatric disorder where the role of γ-aminobutyric acid (GABA), an inhibitory neurotransmitter, has been implicated in its aetiopathophysiology. Several genes coding for GABA_A subunits, including the GABRG2 gene that encodes the γ₂ subunit, are clustered at 5q31-q35, a chromosomal region that is associated with schizophrenia in genome scan studies. We recently reported GABRG2 to be associated with schizophrenia in our case-control and family samples. Methods: We tested eight single-nucleotide polymorphisms spanning the GABRG2 gene for an association with suicidal behaviour in our schizophrenia sample of European ancestry (n = 197), taking into account history of alcohol abuse or dependence. Results: We found the haplotypes of the rs183294 and rs209356 markers to be significantly associated with history of suicide attempt (p < 0.01) as well as suicide specifier scores (p < 0.05). The association appeared to be originating in patients with a history of alcohol dependence or abuse. Conclusions: Taken together, the results of the present study suggest that GABRG2 may be involved in suicidal behaviour in schizophrenia patients with alcohol dependence or abuse, but replications are required. These results may help in the discovery of novel treatments for alcoholism and/or prevention of suicide.

The GABAA Receptor γ2 Subunit (R43Q) Mutation in Febrile Seizures

BackgroundFebrile seizure is the most common form of childhood seizure. Although its exact cause is unclear, many researchers emphasize the importance of its genetic predisposition. Recent genetic studies revealed the importance of the mutations of the gamma-aminobutyric acid A receptor as the etiology of the febrile seizures. R43Q mutation affecting the γ2-subunit N-terminal domain has been related to childhood absence epilepsy and febrile seizure. MethodsWe investigated R43Q mutations of the GABRG2 gene, located on the long arm of chromosome 5 encoding the γ2-subunit of the gamma-aminobutyric acid A receptor. We studied 44 patients with febrile seizure and 49 children without any febrile seizure who were admitted to our clinic. ResultsWe found that 36% of our patient group, the children who experienced febrile convulsions, had heterozygous R43Q mutation. Statistical studies revealed that heterozygous R43Q mutation of gamma-aminobutyric acid A receptor γ2 subunit was higher in the study group than in the control group (P < 0.01). ConclusionsHeterozygous gamma-aminobutyric acid A receptor γ2 subunit (R43Q) mutation may have an effect in the development of febrile seizures.

Effects of SCN1A and GABA Receptor Genetic Polymorphisms on Carbamazepine Tolerability and Efficacy in Chinese Patients with Partial Seizures: 2‐Year Longitudinal Clinical Follow‐Up

To investigate the tolerability and efficacy of carbamazepine treatment in patients with partial-onset seizures and the association with polymorphisms in the sodium channel α-subunit type 1 (SCN1A), and gamma-aminobutyric acid (GABA) receptor genes among the Chinese Han population. 448 patients were genotyped for single nucleotide polymorphisms selected of the SCN1A and GABA-receptor genes. Monotherapy with carbamazepine (CBZ) was administered to the patients. The effectiveness of CBZ treatment was evaluated with regard to efficacy by the decrease in seizures and tolerability by retention rates. SCN1A rs3812718 A/G with CBZ tolerability (P= 0.038) throughout 24 months of clinical follow-up and the GABRA1 rs2290732 A/G were significantly associated with CBZ tolerability (P= 0.001). The maintenance dose and serum level of CBZ in AA genotype carriers of rs3812718 A/G were significantly higher than those of GG genotype carriers between 3 and 12 months of follow-up. The proportion of AA genotype carriers of rs2298771 A/G with seizure free was significantly higher than that of AG+GG genotype carriers from 3 months to 15 months of follow-up (P < 0.05). rs3812718 A/G and rs2290732 A/G polymorphisms affected the tolerability of CBZ. rs2298771 A/G was associated with efficacy of CBZ treatment.