Whereas genetic epidemiological studies aim to characterize the relative importance of genetic and environmental influences on outcomes, measured genotypic studies have the goal of understanding the risk associated with specific genetic variants. Candidate gene studies examine the association between a particular measured genotype that is selected a priori based on some theoretical rationale for why a particular gene would be associated with the trait of interest. Commonly investigated genes for alcohol use outcomes (and often other psychiatric outcomes) include genes involved in the dopamine system (eg, DRD2), serotonin system (eg, SLC6A4), and alcohol metabolism (eg, ALDH2), among others.8,31–33 Reviews of existing research show that like twin studies, candidate gene research is often lacking in sufficient numbers of AA participants. Much of the work has focused on European and Asian populations.5,9 Samples included in a meta-analysis of the Taq1A polymorphism, studied extensively with respect to DRD2 but now known to be located in neighboring gene ANKK1, and alcohol dependence included no AA participants.33 Similarly, of the samples included in a meta-analysis of the 5-HTTLPR serotonin transporter gene polymorphism and alcohol dependence, 32 only two of the 17 studies included AAs.
