A combination of suggestive linkage findings (Long et al., 1998; Porjesz et al., 2002; Reich et al., 1998; Williams et al., 1999) and biological plausibility (Buck, 1996; Davies, 2003; Grobin et al., 1998; Koob, 2004; Krystal et al., 2006) led the Collaborative Study on the Genetics of Alcoholism (COGA) to conduct the first fine mapping association study of the GABAA receptor gene cluster, investigating alcohol dependence (AD) and β-EEG activity in a cohort of United States (U.S.) families enriched for alcoholism (Edenberg et al., 2004). The GABAA receptor gene cluster on chromosome 4 comprises four genes (GABRG1, GABRA2, GABRA4 and GABRB1) where the strongest linkage finding in relation to the AD phenotype was detected with markers (D4S3242, D4S2393) close to GABRB1 (Long et al., 1998; Williams et al., 1999). The family-based COGA study genotyped 69 single nucleotide polymorphisms (SNPs) across the gene cluster and only detected significant allelic and haplotypic association with SNPs in GABRA2, where the region of strongest association with alcohol dependence extended from intron 3 past the 3’ end of GABRA2. A recent study by Covault and
