Context: Pharmacobehavioral and pharmacogenetic evidence links γ-aminobutyric acid type A (GABAA) receptors and chromosomal regions containing GABAA receptor genes to ethanol-related responses. The GABAA gene cluster on chromosome 5q34 is of particular interest in the genetics of alcohol dependence because of the γ2 subunit requirement for ethanol's modulatory action on GABAA receptors, previous linkage findings in mice and humans implicating both GABRA6 and GABRG2, and reported associations of GABRA6, GABRB2, and GABRG2 alleles with alcohol dependence. Objective: To determine whether variation at the 5q34 GABA A gene cluster is implicated in differential susceptibility to alcohol dependence. Methods: Two large psychiatrically interviewed samples, a Southwestern Native American population sample (N = 433) and a Finnish sample (N = 511) with alcohol-dependent subjects and unaffected individuals, were genotyped for 6 single nucleotide polymorphisms at the 5q34 GABAA gene cluster. In addition to sib-pair linkage and case-control association analyses, linkage disequilibrium mapping with haplotypes was used. Results: Sib-pair linkage of GABRG2 to alcohol dependence was observed in Finns (P = .008). Association of the GABRB2 1412T allele with alcohol dependence was detected in both populations (Finns, P = .01; Southwestern Native Americans, P = .008), and the GABRA6 1519T allele was associated in both Finns (P = .01) and Southwestern Native Americans (P = .03). Linkage disequilibrium mapping with 3-locus haplotypes yielded evidence for an alcohol-dependence locus at the GABAA gene cluster region in both populations. The most highly significant signals were at 3-locus haplotypes that included 1 or more GABRA6 polymorphisms, with the peak signal at a GABRA6 3-locus haplotype (Finns, empirical P = .004; Southwestern Native Americans, empirical P = .02). Conclusions: We detected sib-pair linkage of 5q34 GABAA receptor genes to alcohol dependence in Finns and found association both in Finns and in Southwestern Native Americans. In both populations, the haplotype localization implicates the region containing the Pro385Ser GABRA6 polymorphism and 2 other polymorphisms at GABRA6.
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