Extraction of DNA, standardization and plating were completed in the Department of Psychiatry at the Washington University School of Medicine and genotyping through the Washington University Genome Sequencing Center. 1536 SNPs were designed for genotyping using the Illumina Golden Gate technology that draws on a previous collaboration illustrated in Hodgkinson et al. [48] with substitutions reflecting advances in the literature. Quality control analyses included examining cluster plots to rule out ambiguous genotype calls, checking for Mendelian inconsistencies, incorrect gender assignments and sample swaps, cryptic relatedness, flagging SNPs with low call rates (<95 %), and deviations from Hardy–Weinberg equilibrium (p < 10−6). We selected rs279858, one of the most widely studied GABRA2 SNPs, based on associations with adolescent externalizing problems [8, 9], adolescent sensation seeking [9], adolescent conduct problems [12], adult alcohol phenotypes [16, 17, 20, 23, 24, 28, 29], and adult drug phenotypes [15]. A recent meta-analysis also found that this SNP was associated with adult alcohol use disorders [25]. Numerous SNPs in high LD (r2 ≥ 0.80) with rs279858 in non-Hispanic Caucasian and Hispanic populations (calculated using AMR and
