Alternative titles; symbols
HGNC Approved Gene Symbol: GABRA4
Cytogenetic location: 4p12 Genomic coordinates (GRCh38): 4:46,918,900-46,993,581 (from NCBI)
Gamma-aminobutyric acid (GABA) receptors are a family of proteins involved in the GABAergic neurotransmission of the mammalian central nervous system. GABRA4 is a member of the GABA-A receptor gene family of heteromeric pentameric ligand-gated ion channels through which GABA, the major inhibitory neurotransmitter in the mammalian brain, acts. GABA-A receptors are the site of action of a number of important pharmacologic agents including barbiturates, benzodiazepines, and ethanol (summary by Whiting et al., 1999).
For additional general information about the GABA-A receptor gene family, see GABRA1 (137160).
Yang et al. (1995) isolated a cDNA clone corresponding to the human GABRA4 subunit from a human cerebral cortex cDNA library. The deduced 554-amino acid protein showed 92% and 88% identity to the bovine and rat sequences, respectively. The alpha-4 subunit most closely resembled the alpha-6 (GABRA6; 137143) subunit, with 64% amino acid similarity. In vitro functional expression studies showed that recombinant GABA receptors containing the alpha-4 subunit were insensitive to benzodiazepine agonists but showed some sensitivity to partial and inverse agonists.
By immunohistochemical microscopy of mouse brain sagittal sections, Chandra et al. (2006) found strong Gabra4 expression in the thalamus, and moderate expression in the striatum and molecular layer of the dentate gyrus.
By PCR using primers designed from full-length GABRA4, Mu et al. (2002) identified a truncated GABRA4 variant in human and mouse cDNA libraries, resulting from the last coding exon spliced out-of-frame to the first 2 coding exons. The translated product has the N-terminal signal sequence followed by 39-amino acids and has 2 of the 3 N-glycosylation sites in full-length GABRA4 but lacks all 4 transmembrane segments. Human embryonic kidney cells transfected with the truncated mouse cDNA expressed the peptide in cytoplasm and secreted it into culture medium.
By cotransfection in human embryonic kidney cells, Mu et al. (2002) found that the truncated GABRA4 isoform reduced GABA currents produced by full-length GABRA4 expressed with GABRB1 (137190) and GABRG2 (137164)-short subunits, but it had no effect on current kinetics. No such effect was found following coexpression of truncated GABRA4 with GABRA1 (137160) subunit. Mu et al. (2002) concluded that the truncated GABRA4 variant may play a posttranslational regulatory role in intracellular folding, glycosylation, or assembly of the full-length GABRA4 subunit.
In pubertal mice, Shen et al. (2010) found that expression of inhibitory alpha-4-beta-delta-GABA-A receptors, composed of GABRA4, the beta-2 GABA-A receptor (GABRB2; 600232), and the GABA-A delta receptor (GABRD; 137163), increases perisynaptic to excitatory synapses in the CA1 hippocampus. Shunting inhibition via these receptors reduced N-methyl-D-aspartate receptor (see 138249) activation, impairing induction of long-term potentiation (LTP). Pubertal mice also failed to learn a hippocampal, LTP-dependent spatial task that was easily acquired by delta-null mice. However, the stress steroid THP (3-alpha-OH-5-alpha(beta)-pregnan-20-one), which reduces tonic inhibition at puberty, facilitated learning. Shen et al. (2010) concluded that the emergence of alpha-4-beta-delta GABA-A receptors at puberty impairs learning, an effect that can be reversed by stress steroid.
Mu et al. (2002) determined that the GABRA4 gene contains 9 coding exons.
Using rat brain cDNAs for the specific receptor subunit, Danciger et al. (1993) assigned the murine Gabra4 gene to chromosome 7 using somatic cell hybrids and positioned the gene by analysis of the progeny of 3 genetic crosses. The Gabra4 gene mapped to proximal mouse chromosome 7 in apparent proximity to the previously mapped Gabrb3 gene (137192).
By PCR analysis of somatic cell hybrid DNAs and by similar analysis using DNAs from a chromosome 4 regional mapping panel, McLean et al. (1995) mapped the human GABRA4 gene to 4p14-q12, defining a cluster comprising the GABRA2 (137140), GABRA4, GABRB1 (137190), and GABRG1 (137166) genes.
Associations Pending Confirmation
Autism (209850) is a common neurodevelopmental disorder with a significant genetic component. Research suggests that multiple genes contribute to autism and that epigenetic effects or gene-gene interactions are likely contributors to autism risk. Gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the adult brain, has been implicated in autism etiology. Ma et al. (2005) screened 14 known autosomal GABA receptor subunit genes for single-nucleotide polymorphisms (SNPs) in 470 white families with autism. SNPs were used in a family-based study for allelic association and for genotypic and haplotypic association analysis, and subjected to extended multifactor-dimensionality reduction (EMDR) analysis to identify the models with locus joint effects. These studies led to the conclusion that GABRA4 is involved in the etiology of autism and eventually increases autism risk through interaction with GABRB1. In a follow-up study to Ma et al. (2005) with an expanded dataset of 557 non-Hispanic Caucasian families with autism, Collins et al. (2006) confirmed the association of autism to several SNPs in the GABRA4 gene (rs1912960, rs17599165, and rs17599416). In an independent dataset of 54 African American families with autism, Collins et al. (2006) found a significant association with 2 different SNPs in the GABRA4 gene (rs2280073 and rs16859788). Further analysis suggested an interaction between the GABRA4 and GABRB1 genes in susceptibility to autism.
For discussion of a possible association between early-onset epilepsy and mild neurodevelopmental delay and variation in the GABRA4 gene, see 137141.0001.
The existence of a GABRA gene cluster on chromosome 4, and the cluster of 4 other receptor genes on chromosome 5, namely GABRA1 (137160), GABRA6 (137143), GABRB2 (600232), and GABRG2 (137164), provided further evidence that the number of ancestral receptor subunit genes has been expanded by duplication within an ancestral gene cluster. McLean et al. (1995) observed that, if duplication of the alpha gene occurred before duplication of the ancestral gene cluster, then a heretofore undiscovered subtype of alpha subunit should be located on human chromosome 15q11-q13 within the gene cluster that presently has 3 known members at the locus for Angelman (105830) and Prader-Willi (176270) syndromes.
In rats, Roberts et al. (2005) found that an increase in transcription of Gabra4 was mediated by Egr3 (602419) in response to pharmacologically induced seizures.
Chandra et al. (2006) found that Gabra4-knockout mice were superficially indistinguishable from their wildtype littermates. However, in electrophysiologic recordings, knockout mice lacked tonic inhibition in dentate granule cells and thalamic relay neurons. Behaviorally, knockout mice were insensitive to the ataxic, sedative, and analgesic effects of the hypnotic drug, gaboxadol. Chandra et al. (2006) concluded that tonic inhibition in dentate granule cells and thalamic relay neurons is mediated by extrasynaptic GABA receptors containing GABRA4.
This variant is classified as a variant of unknown significance because its contribution to early-onset epilepsy and mild neurodevelopmental delay has not been confirmed.
In a 5.5-year-old girl with early-onset epilepsy and mild neurodevelopmental delay, Vogel et al. (2022) identified a de novo heterozygous c.899C-T transition (c.899C-T, NM_000809.3) in the GABRA4 gene, resulting in a thr300-to-ile (T300I) substitution at a conserved residue in the transmembrane domain. The variant, which was found by exome sequencing and confirmed by Sanger sequencing, was somatic mosaic in the patient (in 17% of sequencing reads). Somatic mosaicism was found in the blood and oral mucosa, consistent with postzygotic origin. The variant was not present in the gnomAD database. Electrophysiologic studies in Xenopus oocytes transfected with the variant showed normal GABA-elicited amplitudes and dose-response curves, but increased desensitization, indicating faster channel inactivation compared to controls. Cells with the variant were nearly insensitive to an endogenous neurosteroid at saturating GABA concentrations, whereas control cells showed potentiation of GABA-evoked responses in the presence of the neurosteroid. The authors suggested that the combination of accelerated desensitization and lack of seizure-protective neurosteroid function of the variant GABRA4 subunit may destabilize the tonic GABA-related inhibition of neuronal excitability. The patient had a suspected febrile seizure at 10 weeks of age. At 3.5 years, she developed sleep-related seizures occurring in clusters; EEG showed right frontal origin with rapid generalization. Seizures were initially refractory to most antiepileptic medication, but she became seizure-free for 2 years on zonisamide and brivaracetam. She had mild neurodevelopmental delay, mainly affecting speech, first noted at age 2 years. At age 5, she had dyspraxia, deficits of attention and executive function, and impaired speech and language comprehension, but was able to receive special education.
Ahring et al. (2022) demonstrated that expression of the variant T300I GABRA4 with the GABRB2 (600232) and GABRD (137163) subunits resulted in increased GABA receptor sensitivity to GABA, increased current amplitude, and faster desensitization kinetics compared to controls. The findings were consistent with a gain-of-function effect of the variant on these extrasynaptic GABA receptors.
Ahring, P. K., Liao, V. W. Y., Lin, S., Absalom, N. L., Chebib, M., Moller, R. S. The de novo GABRA4 p.Thr300Ile variant found in a patient with early-onset intractable epilepsy and neurodevelopmental abnormalities displays gain-of-function traits. Epilepsia 63: 2439-2441, 2022. [PubMed: 35781801] [Full Text: https://doi.org/10.1111/epi.17358]
Chandra, D., Jia, F., Liang, J., Peng, Z., Suryanarayanan, A., Werner, D. F., Spigelman, I., Houser, C. R., Olsen, R. W., Harrison, N. L., Homanics, G. E. GABA-A receptor alpha-4 subunits mediate extrasynaptic inhibition in thalamus and dentate gyrus and the action of gaboxadol. Proc. Nat. Acad. Sci. 103: 15230-15235, 2006. [PubMed: 17005728] [Full Text: https://doi.org/10.1073/pnas.0604304103]
Collins, A. L., Ma, D., Whitehead, P. L., Martin, E. R., Wright, H. H., Abramson, R. K., Hussman, J. P., Haines, J. L., Cuccaro, M. L., Gilbert, J. R., Pericak-Vance, M. A. Investigation of autism and GABA receptor subunit genes in multiple ethnic groups. Neurogenetics 7: 167-174, 2006. [PubMed: 16770606] [Full Text: https://doi.org/10.1007/s10048-006-0045-1]
Danciger, M., Farber, D. B., Kozak, C. A. Genetic mapping of three GABA-A receptor-subunit genes in the mouse. Genomics 16: 361-365, 1993. [PubMed: 8390964] [Full Text: https://doi.org/10.1006/geno.1993.1198]
Ma, D. Q., Whitehead, P. L., Menold, M. M., Martin, E. R., Ashley-Koch, A. E., Mei, H., Ritchie, M. D., DeLong, G. R., Abramson, R. K., Wright, H. H., Cuccaro, M. L., Hussman, J. P., Gilbert, J. R., Pericak-Vance, M. A. Identification of significant association and gene-gene interaction of GABA receptor subunit genes in autism. Am. J. Hum. Genet. 77: 377-388, 2005. [PubMed: 16080114] [Full Text: https://doi.org/10.1086/433195]
McLean, P. J., Farb, D. H., Russek, S. J. Mapping of the alpha(4) subunit gene (GABRA4) to human chromosome 4 defines an alpha(2)-alpha(4)-beta(1)-gamma(1) gene cluster: further evidence that modern GABA(A) receptor gene clusters are derived from an ancestral cluster. Genomics 26: 580-586, 1995. [PubMed: 7607683] [Full Text: https://doi.org/10.1016/0888-7543(95)80178-o]
Mu, W., Cheng, Q., Yang, J., Burt, D. R. Alternative splicing of the GABA(A) receptor alpha-4 subunit creates a severely truncated mRNA. Brain Res. Bull. 58: 447-454, 2002. [PubMed: 12242096] [Full Text: https://doi.org/10.1016/s0361-9230(02)00816-x]
Roberts, D. S., Raol, Y. H., Bandyopadhyay, S., Lund, I. V., Budreck, E. C., Passini, M. A., Wolfe, J. H., Brooks-Kayal, A. R., Russek, S. J. Egr3 stimulation of GABRA4 promoter activity as a mechanism for seizure-induced up-regulation of GABA-A receptor alpha-4 subunit expression. Proc. Nat. Acad. Sci. 102: 11894-11899, 2005. Note: Erratum: Proc. Nat. Acad. Sci. 102: 13351, 2005. [PubMed: 16091474] [Full Text: https://doi.org/10.1073/pnas.0501434102]
Shen, H., Sabaliauskas, N., Sherpa, A., Fenton, A. A., Stelzer, A., Aoki, C., Smith, S. S. A critical role for alpha-4-beta-delta GABA-A receptors in shaping learning deficits at puberty in mice. Science 327: 1515-1518, 2010. [PubMed: 20299596] [Full Text: https://doi.org/10.1126/science.1184245]
Vogel, F. D., Krenn, M., Westphal, D. S., Graf, E., Wagner, M., Leiz, S., Koniuszewski, F., Auge-Stock, M., Kramer, G., Scholze, P., Ernst, M. A de novo missense variant in GABRA4 alters receptor function in an epileptic and neurodevelopmental phenotype. Epilepsia 63: e35-e41, 2022. [PubMed: 35152403] [Full Text: https://doi.org/10.1111/epi.17188]
Whiting, P. J., Bonnert, T. P., McKernan, R. M., Farrar, S., le Bourdelles, B., Heavens, R. P., Smith, D. W., Hewson, L., Rigby, M. R., Sirinathsinghji, D. J. S., Thompson, S. A., Wafford, K. A. Molecular and functional diversity of the expanding GABA-A receptor gene family. Ann. N.Y. Acad. Sci. 868: 645-653, 1999. [PubMed: 10414349] [Full Text: https://doi.org/10.1111/j.1749-6632.1999.tb11341.x]
Yang, W., Drewe, J. A., Lan, N. C. Cloning and characterization of the human GABA-A receptor alpha-4 subunit: identification of a unique diazepam-insensitive binding site. Europ. J. Pharm. 291: 319-325, 1995. [PubMed: 8719416] [Full Text: https://doi.org/10.1016/0922-4106(95)90072-1]