In addition, initial descriptive statistics and bivariate analyses suggested large and significant differences in allele frequency between White and African American respondents in the COGA sample. Specifically, 53 % of African Americans carried the high-risk genotype on SNP rs279871 compared to only 32 % of Whites (X2 = 54.29; p < 0.001). Prior research demonstrated no significant association between GABRA2 variation and alcohol dependence in African American samples (Covault et al. 2007; Drgon et al. 2006; Enoch et al. 2010; Gelernter et al. 2009), and the same pattern is evident among African Americans in the current COGA analysis sample. Moreover, African Americans have two additional common haplotypes within the distal haplotype block, suggesting that rs279871 may not be an appropriate tag SNP for this population (Enoch 2008; Enoch et al. 2010). Consequently, the current analysis examining gender-specific GxE in alcohol dependence using SNP rs279871 was restricted to a sub-sample of Whites (294 African Americans were dropped from the analysis sample).
