Depending on the control group to which we compared heroin-dependent cases, the magnitude of observed associations varied markedly. The comparison of cases with ATR controls found scant evidence of association. Although p values exceeded 0.01 for all SNPs, rs877138 (p=.037) was among those nominally associated. Greater evidence of association was observed in the comparison of cases to neighborhood controls; however, no p value for any SNP was within an order of magnitude of the significance level required to correct for multiple testing. Our analyses that divided neighborhood controls into subgroups based on lifetime history of licit and illicit drug dependence found that the association signal became stronger as the exclusion was defined more narrowly to exclude only individuals with lifetime history of illicit drug dependence.
