The genetic influence on any behavioral outcome likely depends on exposure to certain environments; for example, an individual cannot become addicted to a drug, regardless of their genetic liability, if they were never given the opportunity to experiment with it in the first place. It is becoming clear that research on addiction should not be restricted to study of environmental or genetic effects in isolation, but rather that their interactions (G x E) should be considered, including the tendency of people to non-randomly assort to particular environments (G - E correlation). However, the majority of studies in drug addiction do not account for G x E interactions, though a few examples in alcoholism have been reported. Several studies have reported interactions of 5-HTTLPR, MAO-A-LPR and DRD2 TaqA1 genotypes with family relations, maltreatment, or negative life events on alcohol use, intoxication, and dependence (reviewed in (36), Supplementary Table 1). Additional instances where the influence of genetic variation on function may depend on gene-environment interactions have been studied. The association between increased 5-HTT expression and low levels of response to alcohol as
