In our robustness check, the association between ABCB1 variation and AAB was attenuated after controlling for alcohol dependence, but did not disappear (P=1.3 × 10−2). Gene-based tests do not have corresponding effect sizes, but the beta coefficient for our most significantly associated SNP (rs4728702) was reduced from −0.36 to −0.17. The sample averages for the four drug classes analyzed as part of our pleiotropy analyses are shown in Supplementary Table S1. The results from a series of gene-based tests indicated that ABCB1 variation was associated with alcohol dependence criteria (P=7.1 × 10-5) and cocaine dependence criteria (P=0.01), but not cannabis dependence criteria (P=0.19) or opioid dependence criteria (P=0.50).
