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Patrick Cossette - One of the best experts on this subject based on the ideXlab platform.
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γ-Aminobutyric acid receptor alpha 1 subunit loss of function causes genetic generalized epilepsy by impairing inhibitory network neurodevelopment
Epilepsia, 2018Co-Authors: Eric Samarut, Patrick Cossette, Amrutha Swaminathan, Raphaëlle Riché, Meijiang Liao, Rahma Hassan-abdi, Solène Renault, Marc Allard, Liselotte Dufour, Nadia Soussi-yanicostasAbstract:Objective: In humans, mutations of the γ-aminobutyric acid receptor subunit 1 (GABRA1) cause either mild or severe generalized epilepsy. Although these epilepsy causing mutations have been shown to disrupt the receptor activity in vitro, their in vivo consequences on brain development and activity are not known. Here, we aim at unraveling the epileptogenesis mechanisms of GABRA1 loss of function. Methods: We generated a gabra1 −/− zebrafish mutant line displaying highly pen-etrant epileptic seizures. We sought to identify the underlying molecular mechanisms through unbiased whole transcriptomic assay of gabra1 −/− larval brains. Results: Interestingly, mutant fish show fully penetrant seizures at juvenile stages that accurately mimic tonic-clonic generalized seizures observed in patients. Moreover , highly penetrant seizures can be induced by light stimulation, thus providing us with the first zebrafish model in which evident epileptic seizures can be induced by nonchemical agents. Our transcriptomic assay identified misregulated genes in several pathways essential for correct brain development. More specifically, we show that the early development of the brain inhibitory network is specifically affected. Although the number of GABAergic neurons is not altered, we observed a drastic reduction in the number of inhibitory synapses and a decreased complexity of the GABAergic network. This is consistent with the disruption in expression of many genes involved in axon guidance and synapse formation. Significance: Together with the role of GABA in neurodevelopment, our data identify a novel aspect of epileptogenesis, suggesting that the substratum of GABRA1-deficiency epilepsy is a consequence of early brain neurodevelopmental defects, in particular at the level of inhibitory network wiring.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
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a mutation in the gabaa receptor α1 subunit is associated with absence epilepsy
Annals of Neurology, 2006Co-Authors: Snezana Maljevic, Klaus Krampfl, Joana Cobilanschi, Nikola Tilgen, Susanne Beyer, Yvonne G Weber, Friedrich Schlesinger, Daniel Ursu, Werner Melzer, Patrick CossetteAbstract:Objective To detect mutations in GABRA1 in idiopathic generalized epilepsy. Methods GABRA1 was sequenced in 98 unrelated idiopathic generalized epilepsy patients. Patch clamping and confocal imaging was performed in transfected mammalian cells. Results We identified the first GABRA1 mutation in a patient with childhood absence epilepsy. Functional studies showed no detectable GABA-evoked currents for the mutant, truncated receptor, which was not integrated into the surface membrane. Interpretation We conclude that this de novo mutation can contribute to the cause of “sporadic” childhood absence epilepsy by a loss of function and haploinsufficiency of the GABAA receptor α1-subunit, and that GABRA1 mutations rarely are associated with idiopathic generalized epilepsy. Ann Neurol 2006;59:983–987
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mutation of gabra1 in an autosomal dominant form of juvenile myoclonic epilepsy
Nature Genetics, 2002Co-Authors: Patrick Cossette, Anne Lortie, Lionel Carmant, Lidong Liu, Kateri Brisebois, Haiheng Dong, Michel Vanasse, Jeanmarc Sainthilaire, Andrei VernerAbstract:Although many genes that predispose for epilepsy in humans have been determined, those that underlie the classical syndromes of idiopathic generalized epilepsy (IGE) have yet to be identified. We report that an Ala322Asp mutation in GABRA1, encoding the alpha1 subunit of the gamma-aminobutyric acid receptor subtype A (GABA(A)), is found in affected individuals of a large French Canadian family with juvenile myoclonic epilepsy. Compared with wildtype receptors, GABA(A) receptors that contain the mutant subunit show a lesser amplitude of GABA-activated currents in vitro, indicating that seizures may result from loss of function of this inhibitory ligand-gated channel. Our results confirm that mutation of GABRA1 predisposes towards a common idiopathic generalized epilepsy syndrome in humans.
Robert L. Macdonald - One of the best experts on this subject based on the ideXlab platform.
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a structural look at gabaa receptor mutations linked to epilepsy syndromes
Brain Research, 2019Co-Authors: Ciria C. Hernandez, Robert L. MacdonaldAbstract:Understanding the genetic variation in GABAA receptor subunit genes (GABRs), GABRA1-6, GABRB1-3, GABRG1-3 and GABRD, in individuals affected by epilepsy may improve the diagnosis and treatment of epilepsy syndromes through identification of disease-associated variants. However, the lack of functional analysis and validation of many novel and previously reported familial and de novo mutations have made it challenging to address meaningful gene associations with epilepsy syndromes. GABAA receptors belong to the Cys-loop receptor family. Even though GABAA receptor mutant residues are widespread among different GABRs, their frequent occurrence in important structural domains that share common functional features suggests associations between structure and function.
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molecular pathogenic basis for gabrg2 mutations associated with a spectrum of epilepsy syndromes from generalized absence epilepsy to dravet syndrome
JAMA Neurology, 2016Co-Authors: Jing-qiong Kang, Robert L. MacdonaldAbstract:Objective In this review article, we focus on the molecular pathogenic basis for genetic generalized epilepsies associated with mutations in the inhibitory γ-aminobutyric acid (GABA A ) receptor γ2 subunit gene, GABRG2 (OMIM137164), an established epilepsy gene. Observations The γ-aminobutyric acid (GABA A ) receptor γ2 subunit gene, GABRG2 , is abundantly expressed in the mammalian brain, and its encoded γ2 subunit is assembled into αβγ2 receptors, which are the major GABA A receptor isoforms in the brain. The γ2 subunits have a critical role in GABA A receptor trafficking and clustering at synapses. They reside inside the endoplasmic reticulum after synthesis, where they oligomerize with other binding partners, such as α and β subunits, and further assemble into pentameric receptors. Only correctly assembled receptors can traffic beyond the endoplasmic reticulum and reach the cell surface and synapses, where they conduct chloride ion current when activated by GABA. Mutations in GABRG2 have been associated with simple febrile seizures and with genetic epilepsy syndromes, including childhood absence epilepsy, generalized epilepsy with febrile seizures plus, and Dravet syndrome or severe myoclonic epilepsy in infancy. The mutations include missense, nonsense, and frameshift mutations, as well as splice-site and deletion mutations. The mutations have been identified in both coding and noncoding sequences like splice sites. In the coding sequence, these mutations are found in multiple locations, including the extracellular N-terminus, transmembrane domains, and transmembrane 3–transmembrane 4 intracellular loop. All of these mutations reduced channel function but to different extents and by diverse mechanisms, including nonsense-mediated messenger RNA decay, endoplasmic reticulum–associated protein degradation, dominant negative suppression of partnering subunits, mutant subunit aggregation causing cell stress and cell death, and gating defects. Conclusions and Relevance We conclude that the epilepsy phenotypic heterogeneity associated with GABRG2 mutations may be related to the extent of the reduction of GABA A receptor channel function and the differential dominant negative suppression, as well to toxicity related to the metabolism of mutant subunit proteins resulting from each mutant γ2 subunit, in addition to different genetic backgrounds.
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the intronic gabrg2 mutation ivs6 2t g associated with childhood absence epilepsy altered subunit mrna intron splicing activated nonsense mediated decay and produced a stable truncated γ2 subunit
The Journal of Neuroscience, 2012Co-Authors: Mengnan Tian, Robert L. MacdonaldAbstract:The intronic GABRG2 mutation, IVS6+2T→G, was identified in an Australian family with childhood absence epilepsy and febrile seizures (Kananura et al., 2002). The GABRG2 intron 6 splice donor site was found to be mutated from GT to GG. We generated wild-type and mutant γ2 subunit bacterial artificial chromosomes (BACs) driven by a CMV promoter and expressed them in HEK293T cells and expressed wild-type and mutant γ2 subunit BACs containing the endogenous hGABRG2 promoter in transgenic mice. Wild-type and mutant GABRG2 mRNA splicing patterns were determined in both BAC-transfected HEK293T cells and transgenic mouse brain, and in both, the mutation abolished intron 6 splicing at the donor site, activated a cryptic splice site, generated partial intron 6 retention, and produced a frameshift in exon 7 that created a premature translation termination codon (PTC). The resultant mutant mRNA was either degraded partially by nonsense-mediated mRNA decay or translated to a stable, truncated subunit (the γ2-PTC subunit) containing the first six GABRG2 exons and a novel frameshifted 29 aa C-terminal tail. The γ2-PTC subunit was homologous to the mollusk AChBP (acetylcholine binding protein) but was not secreted from cells. It was retained in the ER and not expressed on the surface membrane, but it did oligomerize with α1 and β2 subunits. These results suggested that the GABRG2 mutation, IVS6+2T→G, reduced surface αβγ2 receptor levels, thus reducing GABAergic inhibition, by reducing GABRG2 transcript level and producing a stable, nonfunctional truncated subunit that had a dominant-negative effect on αβγ2 receptor assembly.
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mutations in gabaa receptor subunits associated with genetic epilepsies
The Journal of Physiology, 2010Co-Authors: Robert L. Macdonald, Jing-qiong Kang, Martin J GallagherAbstract:Mutations in inhibitory GABAA receptor subunit genes (GABRA1, GABRB3, GABRG2 and GABRD) have been associated with genetic epilepsy syndromes including childhood absence epilepsy (CAE), juvenile myoclonic epilepsy (JME), pure febrile seizures (FS), generalized epilepsy with febrile seizures plus (GEFS+), and Dravet syndrome (DS)/severe myoclonic epilepsy in infancy (SMEI). These mutations are found in both translated and untranslated gene regions and have been shown to affect the GABAA receptors by altering receptor function and/or by impairing receptor biogenesis by multiple mechanisms including reducing subunit mRNA transcription or stability, impairing subunit folding, stability, or oligomerization and by inhibiting receptor trafficking.
Maja Bucan - One of the best experts on this subject based on the ideXlab platform.
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a sequence ready bac contig of the gabaa receptor gene cluster GABRG1 gabra2 gabrb1 on mouse chromosome 5
Genome Research, 1999Co-Authors: Andreas Lengeling, Tim Wiltshire, Chris Otmani, Maja BucanAbstract:The type-A receptors for the neurotransmitter GABA (gamma-aminobutyric acid) are ligand-gated chloride channels that mediate postsynaptic inhibition. The functional diversity of these receptors comes from the use of a large repertoire of subunits encoded by separate genes, as well as from differences in subunit composition of individual receptors. In mammals, a majority of GABA(A) receptor subunit genes are located in gene clusters that may be important for their regulated expression and function. We have established a high-resolution physical map of the cluster of genes encoding GABA(A) receptor subunits alpha2 (Gabra2), beta1 (Gabrb1), and gamma(1) (GABRG1) on mouse chromosome 5. Rat cDNA probes and specific sequence probes for all three GABA(A) receptor subunit genes have been used to initiate the construction of a sequence-ready contig of bacterial artificial chromosomes (BACs) encompassing this cluster. In the process of contig construction clones from 129/Sv and C57BL/6J BAC libraries were isolated. The assembled 1.3-Mb contig, consisting of 45 BACs, gives five- to sixfold coverage over the gene cluster and provides an average resolution of one marker every 32 kb. A number of BAC insert ends were sequenced, generating 30 new sequence tag sites (STS) in addition to 6 Gabr gene-based and 3 expressed sequence tag (EST)-based markers. STSs from, and surrounding, the GABRG1-Gabra2-Gabrb1 gene cluster were mapped in the T31 mouse radiation hybrid panel. The integration of the BAC contig with a map of loci ordered by radiation hybrid mapping suggested the most likely genomic orientation of this cluster on mouse chromosome 5: cen-D5Mit151-GABRG1-Gabra2-Gabrb1-D5Mit58- tel. This established contig will serve as a template for genomic sequencing and for functional analysis of the GABA(A) gene cluster on mouse chromosome 5 and the corresponding region on human chromosome 4.
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physical mapping of the tec and gabrb1 loci reveals that the wsh mutation on mouse chromosome 5 is associated with an inversion
Human Molecular Genetics, 1995Co-Authors: Deborah L Nagle, Christine A Kozak, Hiroyuki Mano, Verne M Chapman, Maja BucanAbstract:In the mouse, mutations in the c-Kit proto-oncogene, a member of the receptor tyrosine kinase (RTK) gene family, have pleiotropic effects on hematopoiesis, pigmentation and fertility (dominant spotting, W). However, in the W sh allele the defect is confined to abnormal pigmentation caused by the disruption of 5' regulatory sequences of Kit leaving an intact structural gene. In this report, the previously published physical map around the Pdgfra-Kit-Flk1 RTK loci is extended by mapping the loci encoding the GABA A (γ-aminobutyric acid) receptor subunit beta 1, Gabrb1 and a cytoplasmic kinase (Tec) 3 Mb proximal to Kit. PFGE analysis of the wild-type (C57BL/6J) chromosome demonstrates the following gene order : cen-Gabrb1-Tec-Pdgfra-Kit, whereas the analysis of W sh /W sh DNA is consistent with the order : cen-Gabrb1-Pdgfra-Tec-Kit. This altered physical map can be explained by an inversion on the W sh chromosome located proximally to the Kit locus and spanning the 2.8 Mb Pdgfra-Tec chromosomal segment. This high resolution physical mapping study identifies large DNA fragments that span the two inversion breakpoints and potentially carry Kit upstream regulatory elements involved in the control of Kit expression during embryonic development.
James M. Sikela - One of the best experts on this subject based on the ideXlab platform.
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The γ-aminobutyric acid receptor γ3 subunit gene (GABRG3) is tightly linked to the α5 subunit gene (GABRA5) on human chromosome 15q11–q13 and is transcribed in the same orientation
Genomics, 1995Co-Authors: Valerie Greger, Timothy M. Delorey, Richard W. Olsen, J. H. M. Knoll, E. Woolf, K. Glatt, Rachel F. Tyndale, Allan J. Tobin, James M. Sikela, Yoshimichi NakatsuAbstract:Abstract GABAA receptors are heterooligomeric ligand-gated ion channels that mediate the effect of the inhibitory neurotransmitter γ-aminobutyric acid. The GABAA receptors consist of at least 15 different receptor subunits that can be classified into 5 subfamilies (α, β, γ, δ, ϱ) on the basis of sequence similarity. Chromosomal mapping studies have revealed that several of the GABAA receptor subunit genes appear to be organized as clusters. One such cluster, which consists of the GABAA receptor β3 (GABRB3) and α5 (GABRA5) subunit genes, is located in chromosome 15q11–q13. It is shown here that the GABAA receptor γ3 subunit gene (GABRG3) also maps to this region. Lambda and P1 phage clones surrounding both ends of GABRG3 were isolated; the clones derived from the 5′ end of GABRG3 were linked to an existing phage contig spanning the 3′ end of GABRA5. The two genes are located within 35 kb of each other and are transcribed in the same orientation.
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human chromosomal localization of genes encoding the gamma 1 and gamma 2 subunits of the gamma aminobutyric acid receptor indicates that members of this gene family are often clustered in the genome
Proceedings of the National Academy of Sciences of the United States of America, 1992Co-Authors: A S Wilcox, Janet A Warrington, Katheleen Gardiner, Ralph Berger, Paul Whiting, Michael R Altherr, John J Wasmuth, David A Patterson, James M. SikelaAbstract:Abstract The gamma-aminobutyric acid (GABA) receptors are the major inhibitory neurotransmitter receptors in the brain and the site of action of a number of important pharmacological agents including barbiturates, benzodiazepines, and ethanol. The gamma 1 and gamma 2 subunits have been shown to be important in mediating responses to benzodiazepines, and a splicing variant of the gamma 2 subunit, gamma 2L, has been shown to be necessary for ethanol actions on the receptor, raising the possibility that the gamma 2 gene may be involved in human genetic predisposition to the development of alcoholism. We have assigned the human genes encoding the gamma 1 and gamma 2 subunits of the GABAA receptor to chromosomes 4 and 5, respectively, by PCR amplification of human-specific products from human-hamster somatic cell hybrid DNAs. Using panels of chromosome-specific natural deletion hybrids, we have further localized the gamma 1 gene (GABRG1) to 4p14-q21.1 and the gamma 2 gene (GABRG2) to 5q31.1-q33.2. These data indicate that the gamma 1 gene may be clustered together with the previously mapped alpha 2 and beta 1 genes on chromosome 4 and that the gamma 2 gene may be close to the previously localized alpha 1 gene on chromosome 5. To further examine the latter possibility the alpha 1 gene was mapped using the chromosome 5 deletion hybrids and shown to be within the same region as the gamma 2 gene, 5q31.1-q33.2. A PCR-based screening strategy was used to isolate a 450-kilobase human genomic yeast artificial chromosome clone containing both the alpha 1 and gamma 2 genes. Pulsed-field gel restriction mapping of the yeast artificial chromosome indicates that the two genes are within 200 kilobases of each other. The data presented here provide further evidence for the nonrandom organization of the human genome by demonstrating that members of the GABAA receptor gene family often occur in small gene clusters widely distributed in the genome.
Jing-qiong Kang - One of the best experts on this subject based on the ideXlab platform.
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the therapeutic effect of stiripentol in gabrg2 q390x mice associated with epileptic encephalopathy
Epilepsy Research, 2019Co-Authors: Timothy A Warner, Jing-qiong Kang, Nicholas K SmithAbstract:Anti-seizure drugs (ASDs) are widely used and known to increase inhibitory tone on neuro-circuits and reduce aberrant synchronous firing in epilepsy. Some ASDs act as agonist at the GABAA receptor. Stiripentol, known to increase GABAA receptor activity as well as the metabolites of GABAA receptor agonists, is often used in the treatment of an epileptic encephalopathy, Dravet syndrome (DS), which is caused by mutations mainly in SCN1A and in other genes such as GABRG2. We have recently generated a Gabrg2+/Q390X knockin mouse model associated with DS in humans. The objective of the study was to explore the effects of stiripentol in DS with GABAA receptor functional deficiency because of the etiology heterogeneity in DS. Monotherapy (stiripentol or Diazepam) and polytherapy (stiripentol and diazepam) treatments were tested in Gabrg2+/Q390X mice challenged with pentylenetetrazol (PTZ) seizure induction in conjunction with video-monitoring synchronized electroencephalogram (EEG) recordings. A combination of stiripentol and diazepam greatly reduced seizure-related events in Gabrg2+/Q390X mice following PTZ administration and increased survival. However, the treatment of stiripentol alone was mostly ineffective in alleviating seizure-related events except that it reduced mortality in PTZ challenged Gabrg2+/Q390X mice. The study suggests that stiripentol could be only used as add-on therapy for DS with GABAA receptor functional deficiency, which is consistent with the most established clinical application of stiripentol. The study highlights the importance of mechanism-based precision treatment for DS considering the highly heterogeneous nature of etiology in DS and the fact that mutations in different genes give rise to the same clinical phenotype.
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molecular pathogenic basis for gabrg2 mutations associated with a spectrum of epilepsy syndromes from generalized absence epilepsy to dravet syndrome
JAMA Neurology, 2016Co-Authors: Jing-qiong Kang, Robert L. MacdonaldAbstract:Objective In this review article, we focus on the molecular pathogenic basis for genetic generalized epilepsies associated with mutations in the inhibitory γ-aminobutyric acid (GABA A ) receptor γ2 subunit gene, GABRG2 (OMIM137164), an established epilepsy gene. Observations The γ-aminobutyric acid (GABA A ) receptor γ2 subunit gene, GABRG2 , is abundantly expressed in the mammalian brain, and its encoded γ2 subunit is assembled into αβγ2 receptors, which are the major GABA A receptor isoforms in the brain. The γ2 subunits have a critical role in GABA A receptor trafficking and clustering at synapses. They reside inside the endoplasmic reticulum after synthesis, where they oligomerize with other binding partners, such as α and β subunits, and further assemble into pentameric receptors. Only correctly assembled receptors can traffic beyond the endoplasmic reticulum and reach the cell surface and synapses, where they conduct chloride ion current when activated by GABA. Mutations in GABRG2 have been associated with simple febrile seizures and with genetic epilepsy syndromes, including childhood absence epilepsy, generalized epilepsy with febrile seizures plus, and Dravet syndrome or severe myoclonic epilepsy in infancy. The mutations include missense, nonsense, and frameshift mutations, as well as splice-site and deletion mutations. The mutations have been identified in both coding and noncoding sequences like splice sites. In the coding sequence, these mutations are found in multiple locations, including the extracellular N-terminus, transmembrane domains, and transmembrane 3–transmembrane 4 intracellular loop. All of these mutations reduced channel function but to different extents and by diverse mechanisms, including nonsense-mediated messenger RNA decay, endoplasmic reticulum–associated protein degradation, dominant negative suppression of partnering subunits, mutant subunit aggregation causing cell stress and cell death, and gating defects. Conclusions and Relevance We conclude that the epilepsy phenotypic heterogeneity associated with GABRG2 mutations may be related to the extent of the reduction of GABA A receptor channel function and the differential dominant negative suppression, as well to toxicity related to the metabolism of mutant subunit proteins resulting from each mutant γ2 subunit, in addition to different genetic backgrounds.
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mutations in gabaa receptor subunits associated with genetic epilepsies
The Journal of Physiology, 2010Co-Authors: Robert L. Macdonald, Jing-qiong Kang, Martin J GallagherAbstract:Mutations in inhibitory GABAA receptor subunit genes (GABRA1, GABRB3, GABRG2 and GABRD) have been associated with genetic epilepsy syndromes including childhood absence epilepsy (CAE), juvenile myoclonic epilepsy (JME), pure febrile seizures (FS), generalized epilepsy with febrile seizures plus (GEFS+), and Dravet syndrome (DS)/severe myoclonic epilepsy in infancy (SMEI). These mutations are found in both translated and untranslated gene regions and have been shown to affect the GABAA receptors by altering receptor function and/or by impairing receptor biogenesis by multiple mechanisms including reducing subunit mRNA transcription or stability, impairing subunit folding, stability, or oligomerization and by inhibiting receptor trafficking.
