In conclusion, we leveraged the high degree of comorbid substance dependence in COGA to identify novel loci that may confer risk for both alcohol and drug dependence and parse them from those variants that relate more specifically to alcohol dependence liability (Lai et al., accompanying paper). Our results provide preliminary evidence for ancestrally-specific effects of loci that undergird addiction to alcohol and illicit drugs. Further, we find preliminary ancestry-specific evidence that GWS loci associated with dependence liability are also associated with reward-related VS response providing a compelling putative neural mechanism through which genetic risk might influence dependence liability. Notably, large scale GWAS of psychiatric disorders, with the exception of substance use disorders, have traditionally focused on populations of European ancestry. While the genetics of substance use disorders has been examined in AAs (e.g., 81,82), sample sizes remain fairly modest, especially given the potential expectation of a higher burden of multiple testing. To delineate the role of genetic influences on substance use disorders in such minority populations, who also may further suffer due to restricted access to treatments, targeted data collection is needed.
