to greater reward sensitivity may be more sensation seeking, more likely to use drugs, and more likely to have break rules to obtain desired ends. Alternatively, the gene set could be heterogeneous, with some variants affecting only alcohol use, some affecting only personality, and some affecting rule-breaking. In this case, one might detect significant enrichment of associations for all externalizing phenotypes, but in this case the genetic influences are operating through processes unique to each phenotype rather than on their overlap. The former interpretation is consistent with results from twin research, which have found evidence for strong genetic influences on a general factor of externalizing. However, for the genetic variants examined by Aliev et al. (2014), these alternative models of genetic influence have not yet been directly tested.
