GABRA2 Research Articles

Cerebellum volume in high-risk offspring from multiplex alcohol dependence families: Association with allelic variation in GABRA2 and BDNF

Offspring from families with multiple cases of alcohol dependence have a greater likelihood of developing alcohol dependence (AD) and related substance use disorders. Greater susceptibility for developing these disorders may be related to structural differences in brain circuits that influence the salience of rewards or modify the efficiency of information processing and AD susceptibility. We examined the cerebellum of 71 adolescent/young adult high-risk (HR) offspring from families with multiple cases of alcohol dependence (multiplex families), and 60 low-risk (LR) controls with no family history of alcohol or drug dependence who were matched for age, gender, socioeconomic status and IQ, with attention given to possible effects of personal use of substances and maternal use during pregnancy. Magnetic resonance images were acquired on a General Electric 1.5-Tesla scanner and manually traced (BRAINS2) blind to clinical information. GABRA2 and BDNF variation were tested for their association with cerebellar volumes. High-risk offspring from multiplex AD families showed greater total volume of the cerebellum and total gray matter (GM), in comparison with LR controls. An interaction between allelic variation in GABRA2 and BDNF genes was associated with GM volumes, suggesting that inherited variation in these genes may promote early developmental differences in neuronal proliferation of the cerebellum.

Fotosensitif Epilepsilerde Klinik ve EEG Bulgularının GABA Reseptör Alfa 1 Alt Ünitesi (GABRA1) Geni Mutasyonları ile İlişkisinin Araştırılması

Objective: Although photosensitive epilepsy (PE) is commonly observed, its pathophysiology has not been clarified yet. However, relevant literature indicates that genetic factors play an important role. Our aim was to investigate whether there is a relationship between the clinical and electroencephalographic (EEG) features and the possible mutations/polymorphisms in the GABA receptor alpha 1 subunit (GABRA1) gene in patients with PE by scanning this gene. Methods: 54 patients diagnosed as having PE according to International League Against Epilepsy (ILAE) criteria were included in the study. The patients were analyzed in terms of gender, clinical and syndromic features, response to treatment, EEG features, and photoparoxysmal response (PPR) types. Mutation screening was done by denaturing high-performance liquid chromatography (DHPLC) on all exons belonging to GABRA1 gene. Results: We could not detect any mutation in GABRA1 gene in patients with PE. Four single-nucleotide polymorphisms (SNPs) in GABRA1 gene were observed, but none of them were associated with amino acid changes. Besides, when comparing the patients having these SNPs with the remaining patients without any SNPs in regard to clinical and EEG features, we were not able to find a statistically significant difference for GABRA1 gene. Conclusion: The lack of mutations in the GABRA1 gene indicates that this gene is not predominantly involved in the etiopathogenesis of PE in the Turkish population. In order to get more precise evidence, the research should be extended by increasing the number of patients and by investigating other genes related to GABA. (Archives of Neuropsychiatry 2011; 48: 39-43)

The role of genetic variability in the SLC6A4, BDNF and GABRA6 genes in anxiety‐related traits

The aims of this study were to test the individual association of the serotonin transporter gene (SLC6A4), the brain-derived neurotrophic factor gene (BDNF) and the GABA(A) α(6) receptor subunit gene (GABRA6) with anxiety-related traits and to explore putative gene-gene interactions in a Spanish healthy sample. A sample of 937 individuals from the general population completed the Temperament and Character Inventory questionnaire to explore Harm Avoidance (HA) dimension; a subsample of 553 individuals also filled in the Big Five Questionnaire to explore the Neuroticism dimension. The whole sample was genotyped for the 5-HTTLPR polymorphism (SLC6A4 gene), the Val66Met polymorphism (BDNF gene) and the T1521C polymorphism (GABRA6 gene). Homozygous individuals for the T allele of the T1512C polymorphism presented slightly higher scores for HA than C allele carriers (F = 2.96, P = 0.019). In addition, there was a significant gene-gene interaction on HA between the 5-HTTLPR and Val66Met polymorphisms (F = 3.4, P = 0.009). GABRA6 emerges as a candidate gene involved in the variability of HA. The effect of a significant gene-gene interaction between the SLC6A4 and BDNF genes on HA could explain part of the genetic basis underlying anxiety-related traits.

Potential role of GABA A receptor subunit; GABRA6, GABRB2 and GABRR2 gene polymorphisms in epilepsy susceptibility and pharmacotherapy in North Indian population

Background GABA A receptors influence the susceptibility to seizures, and variations in the receptor genes can contribute to antiepileptic drug resistance also. Methods We investigated the possible associations of single nucleotide polymorphisms (SNPs) present in GABRA6 c. 1512 T>C, GABRB2 c. 1412 C>T, and GABRR2 c. IVS2C>G genes of GABA A receptors in epilepsy susceptibility and drug resistance in northern Indian patients with epilepsy. After screening a total of 202 healthy controls and 401 epilepsy patients were enrolled in study. The genotyping was done by PCR-RFLP methods. Results The GABRA6 c. 1512 T>C, polymorphism was conferring risk for epilepsy susceptibility for TC (P = 0.018), CC (P = 0.0001) genotype and for C allele (P = 0.0002). Another polymorphism GABRB2 c. 1412 C>T was also conferring high risk for epilepsy susceptibility CT (P = 0.012), TT (P = 0.778) genotype and for variant T allele (P = 0.034) but was not associated with drug resistance. No association was found with epilepsy susceptibility or with drug resistance in case of GABRR2 c. IVS2C>G gene polymorphism. Conclusion Overall, our findings suggest significant involvement of alpha ( GABRA6) and beta ( GABRB2) subunits of GABA A receptor in epilepsy susceptibility in north Indian population.

Temporal control of a dendritogenesis-linked gene via REST-dependent regulation of nuclear factor I occupancy

Developing neurons undergo a series of maturational stages, and the timing of these events is critical for formation of synaptic circuitry. Here we addressed temporal regulation of the Gabra6 gene, which is expressed in a delayed manner during dendritogenesis in maturing cerebellar granule neurons (CGNs). Developmental up-regulation of Gabra6 transcription required a binding site for nuclear factor I (NFI) proteins. The amounts and DNA binding activities of NFI proteins were similar in immature and mature CGNs; however, NFI occupancy of the Gabra6 promoter in native chromatin was temporally delayed in parallel with Gabra6 gene expression, both in vivo and in culture. The trans-repressor RE1 silencing transcription factor (REST) occupied the Gabra6 proximal promoter in CGN progenitors and early postmitotic CGNs, and its departure mirrored the initial onset of NFI binding as CGNs differentiated. Furthermore constitutive REST expression blocked both Gabra6 expression and NFI occupancy in mature CGNs, whereas REST knockdown in immature CGNs accelerated the initiation of both events. These studies identify a novel mechanism for controlling the timing of dendritogenesis-associated gene expression in maturing neurons through delayed binding of NFI proteins to chromatin. They also establish a temporal function for REST in preventing premature promoter occupancy by NFI proteins in early-stage postmitotic neurons.

Role of GABRA2 in moderating subjective responses to alcohol.

Human twin studies have shown that certain responses to alcohol, including subjective perceptions, are genetically influenced. Previous studies have provided evidence that a low level of response to alcohol predicts future alcohol use disorders in humans. Recent genetic studies suggest an association between alcohol dependence and genetic variation in the γ-aminobutyric acid A (GABA(A)) receptor α2 subunit gene (GABRA2). Based on a haplotypic association of alcohol dependence with GABRA2, we investigated whether GABRA2 alleles are associated with the subjective responses to clamped alcohol concentration. One hundred and ten healthy social drinkers (53 men) underwent the alcohol clamp. Fifteen minutes after the start of an intravenous infusion of alcohol, the breath alcohol concentration was clamped at a target of 50 ± 5 mg/dl for 165 minutes. Subjective physiologic responses to alcohol and stimulant and sedative effects of alcohol were measured repeatedly during the alcohol clamp. Because aldehyde dehydrogenase 2 (ALDH2) has been shown to have a great impact on the subjective responses to alcohol, we divided subjects by ALDH2 genotype for further analyses. To examine the role of genetic variation in GABRA2, 7 single nucleotide polymorphisms (SNPs) that were informative in association studies were included as factors in the analysis. Among these 7 SNPs, 3 SNPs (rs279869, rs279858, and rs279837) located in the middle of the GABRA2 gene showed significant associations with subjective effects of alcohol. Subjects with 1 or 2 copies of the more common allele showed greater subjective responses to alcohol than did individuals homozygous for the alcohol dependence-associated allele regardless of ALDH2 genotype. These findings confirm and extend the observation that the GABRA2 alleles affect the subjective responses to alcohol, and suggest that the genetic variations in GABRA2 might play a role in the risk of alcohol use disorders by moderating the subjective effects of alcohol.

A Polymorphism in GABRA2 Is Associated With the Medial Frontal Response to Alcohol Cues in an fMRI Study

Significant evidence has accumulated to suggest an association between single-nucleotide polymorphisms (SNPs) in the GABRA2 gene and alcoholism. However, research has yet to show an association between these polymorphisms and the human brain's reward system function. In this study, we stratified subjects who had participated in an fMRI study of alcohol cue responses according to their genotype at a SNP in GABRA2 (rs279871) shown to be associated with alcohol dependence (Edenberg et al., 2004). Genotyping showed 13 subjects to be homozygous for the high-risk allele (AA), and 23 subjects to be heterozygous (AG). In fMRI, subjects were exposed to the aromas of their preferred alcoholic drink odors (AO), as well as to appetitive control odors (ApCO) under both alcohol intoxication and placebo control conditions. Homozygous AA subjects had a larger [AO > ApCO] response than did AG subjects in medial frontal cortical areas thought to code reward value. However, AG subjects had a larger [AO > ApCO] effect in the ventral tegmental area. Alcohol intoxication did not alter these group differences. These are the first data to suggest that GABRA2 genotype could affect the brain's responses to cues associated with alcohol.

Lower anxiety and a decrease in agonistic behaviour in Lsamp-deficient mice

In rodents, the Lsamp gene has been implicated in trait anxiety, fear reaction and fear conditioning. Human data link the LSAMP gene to several psychiatric disorders. In this study, we presented a general phenotypic characterization of Lsamp gene-deficient mouse line, created by deleting exon 1b. These mice displayed no gross sensory-motor deficiencies, no overt abnormalities and performed normally in memory and learning tests. However, they responded with increased activity to new environments. Moreover, they displayed reduced anxiety and notable deviations in social behaviour, such as lack of whisker trimming, reduced aggressiveness and reduced dominance. One possible explanation for the anxiolytic-like effect of the deletion of the Lsamp gene is a shift in balance in the Gabra1 and Gabra2 genes in the temporal lobe in favor of the Gabra2 transcript, encoding α2 subunit of GABA A receptors that mediate the stimulating effect of GABA agonists. The overall phenotype of Lsamp-deficient mice, characterized by decreased anxiety and several alterations in social behaviour, makes them a good model for studying the molecular mechanisms behind inadequate social behaviours observed in several psychiatric disorders.

Analysis of Associations between 5-HTT, 5-HTR2A, and GABRA6 Gene Polymorphisms and Health-Associated Personality Traits

The development of personality traits united by the notion of conscientiousness, should promote, along with reduction of anxiety, the physical and mental health. In order to detect the sources of conscientiousness and neuroticism formation, we evaluated associations between polymorphic markers of 5-HTT, 5-HTR2A, and GABRA6 genes and relevant scores of TCI questionnaire in a group of 369 volunteers. Associations of markers VNTR and LPR of 5-HTT gene and marker T1521C of GABRA6 gene with "self-directedness" and the effects of 5-HTR2A gene marker T102C and its interactions with the GABRA6 gene on the "harm avoidance" were detected.

Analysis of extreme drinking in patients with alcohol dependence using Pareto regression

We developed a novel Pareto regression model with an unknown shape parameter to analyze extreme drinking in patients with Alcohol Dependence (AD). We used the generalized linear model (GLM) framework and the log-link to include the covariate information through the scale parameter of the generalized Pareto distribution. We proposed a Bayesian method based on Ridge prior and Zellner's g-prior for the regression coefficients. Simulation study indicated that the proposed Bayesian method performs better than the existing likelihood-based inference for the Pareto regression.We examined two issues of importance in the study of AD. First, we tested whether a single nucleotide polymorphism within GABRA2 gene, which encodes a subunit of the GABA(A) receptor, and that has been associated with AD, influences 'extreme' alcohol intake and second, the efficacy of three psychotherapies for alcoholism in treating extreme drinking behavior. We found an association between extreme drinking behavior and GABRA2. We also found that, at baseline, men with a high-risk GABRA2 allele had a significantly higher probability of extreme drinking than men with no high-risk allele. However, men with a high-risk allele responded to the therapy better than those with two copies of the low-risk allele. Women with high-risk alleles also responded to the therapy better than those with two copies of the low-risk allele, while women who received the cognitive behavioral therapy had better outcomes than those receiving either of the other two therapies. Among men, motivational enhancement therapy was the best for the treatment of the extreme drinking behavior.

A computational screen for site selective A-to-I editing detects novel sites in neuron specific Hu proteins

BackgroundSeveral bioinformatic approaches have previously been used to find novel sites of ADAR mediated A-to-I RNA editing in human. These studies have discovered thousands of genes that are hyper-edited in their non-coding intronic regions, especially in alu retrotransposable elements, but very few substrates that are site-selectively edited in coding regions. Known RNA edited substrates suggest, however, that site selective A-to-I editing is particularly important for normal brain development in mammals.ResultsWe have compiled a screen that enables the identification of new sites of site-selective editing, primarily in coding sequences. To avoid hyper-edited repeat regions, we applied our screen to the alu-free mouse genome. Focusing on the mouse also facilitated better experimental verification. To identify candidate sites of RNA editing, we first performed an explorative screen based on RNA structure and genomic sequence conservation. We further evaluated the results of the explorative screen by determining which transcripts were enriched for A-G mismatches between the genomic template and the expressed sequence since the editing product, inosine (I), is read as guanosine (G) by the translational machinery. For expressed sequences, we only considered coding regions to focus entirely on re-coding events. Lastly, we refined the results from the explorative screen using a novel scoring scheme based on characteristics for known A-to-I edited sites. The extent of editing in the final candidate genes was verified using total RNA from mouse brain and 454 sequencing.ConclusionsUsing this method, we identified and confirmed efficient editing at one site in the Gabra3 gene. Editing was also verified at several other novel sites within candidates predicted to be edited. Five of these sites are situated in genes coding for the neuron-specific RNA binding proteins HuB and HuD.

Association study between GABA receptor genes and anxiety spectrum disorders

Human anxiety disorders are complex diseases with relatively unknown etiology. Dysfunction of the Gamma-aminobutyric acid (GABA) system has been implicated in many neuropsychiatric conditions, including anxiety and depressive disorders. In this investigation, we explored four GABA receptor genes for their possible associations with genetic risk for anxiety disorders and depression. Our study sample consisted of 589 cases and 539 controls selected from a large population-based twin registry based upon a latent genetic risk factor shared by several anxiety disorders, major depression, and neuroticism. We subjected these to a two-stage protocol, in which all candidate genetic markers were screened for association in stage 1 (N=376), the positive results of which were tested for replication in stage 2 (N=752). We analyzed data from 26 single nucleotide polymorphisms (SNPs) from four GABA receptor genes: GABRA2, GABRA3, GABRA6, and GABRG2. Of the 26 SNPs genotyped in stage 1, we identified two markers in GABRA3 that met the threshold (P < or = .1) to be tested in stage 2. Phenotypic associations of these two markers failed to replicate in stage 2. These findings suggest that common variation in the GABRA2, GABRA3, GABRA6, and GABRG2 genes does not play a major role in liability to anxiety spectrum disorders.

The Influence of GABRA2, Childhood Trauma, and Their Interaction on Alcohol, Heroin, and Cocaine Dependence

The GABRA2 gene has been implicated in addiction. Early life stress has been shown to alter GABRA2 expression in adult rodents. We hypothesized that childhood trauma, GABRA2 variation, and their interaction would influence addiction vulnerability. African-American men were recruited for this study: 577 patients with lifetime DSM-IV single and comorbid diagnoses of alcohol, cocaine, and heroin dependence, and 255 control subjects. The Childhood Trauma Questionnaire (CTQ) was administered. Ten GABRA2 haplotype-tagging single-nucleotide polymorphisms (SNPs) were genotyped. We found that exposure to childhood trauma predicted substance dependence (p < .0001). Polysubstance dependence was associated with the highest CTQ scores (p < .0001). The African Americans had four common haplotypes (frequency: .11-.30) within the distal haplotype block: two that correspond to the Caucasian and Asian yin-yang haplotypes, and two not found in other ethnic groups. One of the unique haplotypes predicted heroin addiction, whereas the other haplotype was more common in control subjects and seemed to confer resilience to addiction after exposure to severe childhood trauma. The yin-yang haplotypes had no effects. Moreover, the intron 2 SNP rs11503014, not located in any haplotype block and potentially implicated in exon splicing, was independently associated with addiction, specifically heroin addiction (p < .005). Childhood trauma interacted with rs11503014 variation to influence addiction vulnerability, particularly to cocaine (p < .005). Our results suggest that at least in African-American men, childhood trauma, GABRA2 variation, and their interaction play a role in risk-resilience for substance dependence.

FP38-WE-02 Genetic study of juvenile myoclonic epilepsy (JME) patients and their family members in a university hospital in North India

Background and Objectives: Among the 40-100 million persons with epilepsy worldwide, approximately 50% have generalized epilepsies. Juvenile myoclonic epilepsy (JME) is a common epileptic syndrome and has been classified as idiopathic generalized epilepsy by the International League Against Epilepsy. JME constitutes 10-30% among all cases of epilepsy. The syndrome is characterized by myoclonic jerks, generalized tonic clonic seizures in 80-97% and absence seizures in 12-54% of patients. Age of onset is between 8-20 years with peak age at 15 years. Inheritance in JME is thought to be autosomal dominant with incomplete penetrance. Previous linkage studies on larger JME families have identified 6 different chromosomal loci being involved: 6p12-11, 6p21.3, 15q14, 6q24, 2q22-2q23, and 5q34. Of all the loci identified, only 5q34 lead to identification of a mutation in the GABRA1 gene in a single larger JME family from Quebec, Canada. Candidate gene analyses in multiplex families identified CLCN2 gene as one of the major genes involved in JME. CLCN2 is the first known gene in which both mutations and a common sequence variant confer a range of varying susceptibility effects to genetically complex epilepsies. Such genes are thought to function as genetic “risk factors” but on their own they may not cause epilepsy. These include KCNQ3, BRD2, LGI4, GABRG2 and CACNB4. The objective of this study was to study the genetic association analysis for sequence polymorphisms in the BRD2, LGI4 and GABRG2 genes and the clinical, EEG characteristics in JME probands and their family members.

Test of association between GABRA2 (SNP rs279871) and adolescent conduct/alcohol use disorders utilizing a sample of clinic referred youth with serious substance and conduct problems, controls and available first degree relatives

Recent findings have linked the GABRA2 gene with antisocial personality disorder and alcohol dependence (AD) in adults and conduct disorder (CD), but not AD symptoms, in children and adolescents. We sought to replicate previous findings and test for an association between a single nucleotide polymorphism (SNP) in the GABRA2 gene (rs279871) and CD among adolescents. Methods Adolescent patients ( n = 371), 13–18 years old, were recruited from a university substance abuse treatment program. Patient siblings ( n = 245), parents of patients ( n = 355), adolescent controls ( n = 185), siblings of controls ( n = 163) and parents of controls ( n = 263) were included in these analyses (total sample n = 1582). Case-control (using only Caucasian and Hispanic probands) and family-based association tests were completed to test for association between rs279871 and several a priori CD and AD phenotypes. Results For case-control association tests, rs279871 was significantly associated with CD ( p = 0.02) but not AD phenotypes; the result did not survive strict correction for multiple testing. All family-based association tests were non-significant (CD p = 0.48; CD symptom count age corrected within sex p = 0.91; AD p = 0.84; alcohol use disorder p = 0.52). Conclusions Consistent with previous findings, the results do not support the association between GABRA2 SNP rs279871 and AD in adolescents. Our results also do not support an association between rs279871 and CD; the study limitations are reviewed.

CLINICAL STUDY: Predicting the effect of naltrexone and acamprosate in alcohol‐dependent patients using genetic indicators

Acamprosate and naltrexone are effective medications in the treatment of alcoholism. However, effect sizes are modest. Pharmacogenomics may improve patient-treatment-matching and effect sizes. It is hypothesized that naltrexone exerts its effect through genetic characteristics associated with the dopaminergic/opioidergic positive reinforcement system, whereas acamprosate works through the glutamatergic/GABAergic negative reinforcement system. Alcohol-dependent subjects were randomly assigned to either acamprosate or naltrexone. Subjects participated in a cue-exposure experiment at the day before and at the last day of medication. Reductions in cue-induced craving and physiological cue reactivity were measured. Differential effects of naltrexone and acamprosate on these outcomes were tested for different polymorphisms of the opioid, dopamine, glutamate and GABA-receptors. Significant matching effects were found for polymorphisms at the DRD2, GABRA6 and GABRB2 gene. In addition, a trend was found for the OPRM1 polymorphism. This provides evidence for the matching potential of genotypes. It is expected that more effective treatments can be offered when genetic information is used in patient-treatment-matching.

Role of GABRA2 in Trajectories of Externalizing Behavior Across Development and Evidence of Moderation by Parental Monitoring

As we identify genes involved in psychiatric disorders, the next step will be to study how the risk associated with susceptibility genes manifests across development and in conjunction with the environment. We describe analyses aimed at characterizing the pathway of risk associated with GABRA2, a gene previously associated with adult alcohol dependence, in a community sample of children followed longitudinally from childhood through young adulthood. To test for an association between GABRA2 and trajectories of externalizing behavior from adolescence to young adulthood and for moderation of genetic effects by parental monitoring. Data were analyzed from the Child Development Project, with yearly assessments conducted since that time. A saliva sample was collected for DNA at the 2006 follow-up, with a 93% response rate in the target sample. Growth mixture modeling was conducted using Mplus to identify trajectories of externalizing behavior and to test for effects of GABRA2 sequence variants and parental monitoring. Nashville and Knoxville, Tennessee, and Bloomington, Indiana. A community-based sample of families enrolled at 3 sites as children entered kindergarten in 1987 and 1988. Analyses for the white subset of the sample (n = 378) are reported here. Parental monitoring measured at 11 years of age; Child Behavior Checklist youth reports of externalizing behavior at ages 12, 14, 15, 16, 17, 19, 20, 21, and 22 years. Two classes of externalizing behavior emerged: a stable high externalizing class and a moderate decreasing externalizing behavior class. The GABRA2 gene was associated with class membership, with subjects who showed persistent elevated trajectories of externalizing behavior more likely to carry the genotype previously associated with increased risk of adult alcohol dependence. A significant interaction with parental monitoring emerged; the association of GABRA2 with externalizing trajectories diminished with high levels of parental monitoring. These analyses underscore the importance of studying genetic effects across development and of identifying environmental factors that moderate risk.

Relation between increased anxiety and reduced expression of alpha1 and alpha2 subunits of GABA A receptors in Wfs1-deficient mice

Mutations in the coding region of the WFS1 gene cause Wolfram syndrome, a rare multisystem neurodegenerative disorder of autosomal recessive inheritance. In clinical studies a relation between mutations in the Wfs1 gene and increased susceptibility for mood disorders has been established. According to our previous studies, mice lacking Wfs1 gene displayed increased anxiety in stressful environment. As the GABA-ergic system plays a significant role in the regulation of anxiety, we analyzed the expression of GABA-related genes in the forebrain structures of wild-type and Wfs1-deficient mice. Experimentally naïve Wfs1-deficient animals displayed a significant down-regulation of α1 (Gabra1) and α2 (Gabra2) subunits of GABA A receptors in the temporal lobe and frontal cortex. Exposure of wild-type mice to the elevated plus-maze decreased levels of Gabra1 and Gabra2 genes in the temporal lobe. A similar tendency was also established in the frontal cortex of wild-type animals exposed to behavioral test. In Wfs1-deficient mice the elevated plus-maze exposure did not induce further changes in the expression of Gabra1 and Gabra2 genes. By contrast, the expression of Gad1 and Gad2 genes, enzymes responsible for the synthesis of GABA, was not significantly affected by the exposure of mice to the elevated plus-maze or by the invalidation of Wfs1 gene. Altogether, the present study demonstrates that increased anxiety of Wfs1-deficient mice is probably linked to reduced expression of Gabra1 and Gabra2 genes in the frontal cortex and temporal lobe.

Two Molecular Pathways (NMD and ERAD) Contribute to a Genetic Epilepsy Associated with the GABAAReceptor GABRA1 PTC Mutation, 975delC, S326fs328X

Approximately one-third of human genetic diseases are caused by premature translation-termination codon (PTC)-generating mutations. These mutations in sodium channel and GABA(A) receptor genes have been associated with idiopathic generalized epilepsies, but the cellular consequences of the PTCs on the mutant channel subunit biogenesis and function are unknown. The PTCs could result in translation of a truncated subunit, or more likely, trigger mRNA degradation through nonsense-mediated mRNA decay (NMD), thus preventing or reducing production of mutant subunit at the transcriptional level. The GABA(A) receptor alpha1 subunit mutation, 975delC, S326fs328X, is an autosomal dominant mutation associated with childhood absence epilepsy that generates a PTC in exon 8 of the 9 exon GABRA1 gene that is 74 bp upstream of intron 8. Using an intron 8-inclusion minigene that supports NMD, we demonstrated that mutant mRNA was substantially reduced, but not absent. Loss of mutant transcripts was blocked by ribosome inhibition or by silencing the NMD-essential gene hUPF-1. In both neurons and non-neuronal cells, the PTC caused substantial loss of mutant alpha1(S326fs328X) subunit mRNA through NMD with a minor portion of the mRNA escaping NMD and producing a mutant protein. The translated mutant protein had reduced stability due to endoplasmic reticulum associated degradation (ERAD) and had enhanced association with molecular chaperones. This study suggests that loss of mRNA due to activation of NMD and activation of ERAD by the mutant protein may contribute to epileptogenesis. The molecular mechanisms outlined here delineate a model for the pathogenesis of many PTC-generating mutations.

Gammaaminobutyric Acid A Receptor Alpha 3 Subunit is Overexpressed in Lung Cancer

The identification of tumor-associated antigens, which are specifically expressed in cancer tissues, is very important for immunotherapy of lung cancer. We have combined the in silico screening and experimental verifying to identify genes that are differently expressed in cancers compared with their corresponding normal tissues. Using these methods, we have identified that GABRA3 gene was overexpressed in lung cancer and rarely expressed in other cancers. Furthermore, GABRA3 protein expression was significantly higher in the lower grade of lung cancer. It may compose functional GABA-gated channel with other subunits. This study demonstrated GABRA3 could be a potential biomarker for diagnosis of lung cancer, and GABAA receptors may play an important role in cancer differentiation.