In summary, we provide evidence that ANKK1 and TTC12 SNPs are strongly associated with substance dependence, substantially overlapping findings from other reports.38–47 Our focus on illicit drug dependence is an important extension of scope beyond that of prior studies. Additional investigations (e.g., deep sequencing) can characterize more definitively the polymorphisms most highly associated with heroin and other illicit drug dependence and determine the gene responsible for the observed association. Finally, our findings highlight the importance of considering substance exposure history when selecting the most appropriate control group for genetic investigations of substance dependence and raise an intriguing possibility that non-dependent, highly substance-exposed controls might prove particularly informative.
