Functional characterization of the new human GABAA receptor mutation β3(R192H)

Abstract

We screened 124 individuals for single nucleotide polymorphisms of the alpha1, beta3 and gamma2 genes of the GABA(A) receptor in the regions corresponding to the ligand-binding domains on the protein level. In a patient with chronic insomnia, a missense mutation was found in the gene of the beta3 subunit. This mutation results in the substitution of the amino acid residue arginine for histidine in position 192 (beta3(R192H)). The patient was found to be heterozygous for this mutation. Functional analysis of human alpha1beta3(R192H)gamma2S GABA(A) receptors using ultra fast perfusion techniques revealed a slower rate of the fast phase of desensitization compared with alpha1beta3gamma2S GABA(A) receptors. Additionally, current deactivation [a major determinant of inhibitory postsynaptic current (IPSC) duration] was faster in the mutated receptors. This raises the possibility of decreased GABAergic inhibition contributing to insomnia, as some members of the patient's family also suffer from insomnia. The mutation beta3(R192H) might, therefore, be linked to this condition. The intron/exon boundaries of the alpha1 subunit gene were also established and three additional variants were found in the alpha1 and beta3 genes.

Regionally selective effects of GABA on hypothalamic GABAA receptor mRNA in vitro

“…In our separate in vivo study [37], 6 hrs of sleep deprivation increased the β 1 , β 3 and ε subunit mRNA levels in the PF region only similarly to the effects of gabazine in the present study. Also of interest with the regard to our hypothesis is the finding that, in humans, a mutation in the gene for the β 3 subunit is associated with insomnia [38]. Since appropriate mRNA changes occur mainly in the PF region, it will be of interest to identify the mechanisms that regulate the magnitude of GABA A R-mediated inhibition in neurochemically distinct PF neurons.…”

The Genetic Basis of Sleep Disorders

“…The first one including 8 small Japanese families with 21 HLA DR2-positive patients (14 narcolepsy cases with cataplexy and 7 with an incomplete form of narcolepsy) found only a suggestive linkage with a lod score of 3.09 at 4p13-q21 [24]. We have also reported a single large autosomal dominant French family with 4 patients with narcolepsy and clear-cut cataplexy and 10 others affected with the minor Advanced sleep-phase syndrome Period 2 gene 2q37.3 [3] Primary chronic insomnia GABRB3 gene 15q11.2-q12 [4] Narcolepsy -Cataplexy Prepro-hypocretin gene 17q21 [5] form (isolated recurrent naps or lapses into sleep), and identified a 5.15-Mb (12.6-cM) candidate region on chromosome 21q, yielding a maximum 2-point lod score of 3.36 and a maximum multipoint parametric lod score of 4.00 [25]. However, molecular analysis of several candidate genes in the region (including PEP19 gene as an exemple) revealed no mutations.…”

“…However, a missense mutation (a G-to-A transition in exon 6) in the GABRB3 gene on chromosome 15q11.2-q12 encoding the GABAA beta3 subunit was reported in a single patient with chronic insomnia who also had relatives who suffered from the condition ( Table 1) [4]. This mutation, which resulted in an arg192-to-his (R192H) substitution, change the mature beta-3 subunit with a receptor function modification as assessed in vitro.…”

Familial Aggregation of Insomnia

“…3,34,35 Specifically, the neurobiology of insomnia has been linked with genes involved in the neural function (ROR1), 36 circadian rhythm (3111T/C CLOCK), 37 regulation of calcium signaling (CACNA1C, PLCB1), 36,38 serotonin (5-HTTLPR), 39 and GABAergic inhibition (GABRB3). 40 Recently, a sleep-regulating gene (neuromedin U [Nmu]) was associated with a severe form of insomnia, characterized by substantial reductions in sleep time, increased sleep latency, and increased wake time in zebrafish. 41 Given the high rate of familial aggregation of insomnia, the present findings corroborate the relevance of conducting future studies related to the genetic component of insomnia.…”