The present findings provide important support for a significant contribution of common SNPs in the prediction of vulnerability to substance dependence. Although our findings provided some support for highest heritability observed in DD relative to other ways of defining vulnerability to substance dependence, the associations among the definitions point to shared underlying genetic variation across all three different ways of defining vulnerability to substance dependence. Taken together, these important findings reinforce the utility of examining common variation in SNPs as well as some ability to generalize across studies using different definitions of vulnerability to substance dependence.
