Stratified analyses of African Americans (N=420) provided trending evidence of main effects. In the interaction model set with GxE product terms, peer drinking had a hazardous effect on first intoxication (HR=1.62, 95% 1.27–2.08) and first DSM-5 symptom (HR=1.98, 95% CI 1.50–2.61); rs1229984 had a trending protective effect on first intoxication (HR=0.32, 95% CI 0.08–1.27) and first DSM-5 symptom (HR=0.35, 95% CI 0.05–2.28); and interaction terms were insignificant (p>.7). The limited sample size of African Americans combined with the low frequency of the rs1229984 minor allele limits power to detect interactions in this analysis. Nonetheless, the robust effect of peer drinking in both ancestry groups and the well-established role of rs1229984 across ancestry groups lends support for our conclusions drawn from the combined sample.
