Genetic risk was indexed by a single item, high risk on the GABRA2 gene, identified via SNP genotyping and association analyses as being linked to alcohol dependence. Genotyping and association analyses are described in detail elsewhere (Edenberg et al. 2004). A total of 31 SNPs initially demonstrated significant association with alcohol dependence using the average Pedigree Disequilibrium Test (Martin et al. 2000). The SNP used here (rs279871) was chosen because it showed the strongest association with DSM-IV alcohol dependence in prior research, and has been used as a proxy for the LD block (Dick et al. 2006b, 2013; Edenberg et al. 2004). This SNP was also associated with increased risk for drug dependence in adulthood, as well as conduct disorder and externalizing behaviors in childhood (Agrawal et al. 2006; Dick et al. 2006a; Dick et al. 2009). In COGA data, the LD between rs279871 and the synonymous exonic coding variant rs279858 was complete (D’ = 1, r2 = 1; 1,000 genomes pilot 1 data for CEU). Increased risk for a clinical diagnosis of alcohol dependence was associated with carrying two
