Mutation screen of the GAD2 gene and association study of alcoholism in three populations

Synaptic actions of gamma-amino butyric acid (GABA) have been implicated in many facets of ethanol's effects and risk for alcoholism. We examined whether variation in glutamate decarboxylase-2 (GAD2), a gene encoding for a major enzyme in the synthesis of GABA, contributes to risk of alcohol dependence (AD). We screened GAD2 for sequence variants using dHPLC in a population of 96 individuals. Several single nucleotide polymorphisms (SNPs), including four rare non-synonymous polymorphisms, were identified. Thirteen SNPs located in the GAD2 gene were genotyped in a sample of 113 Russian males with AD and 100 Russian male controls. These analyses revealed a modest association between the functional GAD2 -243 A > G SNP (rs2236418) and AD (allele P = 0.038, genotype P = 0.008). An additional sample of 138 Russian males with AD were genotyped for the GAD2 -243 A > G. These analyses supported an association of this polymorphism with AD (combined sample allele P = 0.038, genotype P = 0.0009). We extended these findings to additional populations: a sample of 538 college students assessed using the AUDIT and a sample of European-American (EA) AD subjects (n = 235) and controls (n = 310). Analyses in these populations did not support a role for GAD2 in alcoholism. In summary, the results of an extensive search for an association of GAD2 with AD suggest that variation in GAD2 is not a major risk factor for AD in EAs. The functional promoter GAD2 -243 A > G variant may influence risk for AD in some populations, or its role may be limited to susceptibility to severe AD.