Beyond demonstrating an early protective role of the ADH1B GA/AA genotypes in the development of these drinking behaviors, the results illustrate that reporting most or all best friends drinking was associated with attenuation of this genetic protection (Figure 2). The observation that social context modifies the effect of an ADH1B variant extends previous studies on alcohol metabolizing variants. Higuchi et al. (1994) found that the proportion of alcohol dependent adults in Japan with one copy of a protective aldehyde dehydrogenase 2 (ALDH2) variant increased between 1979 and 1992, following the increased cultural pressure to drink alcohol. Similarly, Irons et al. (2007) reported that the high-risk environment of sibling substance use was associated with a diminished effect of this ALDH2 variant in East Asian adolescent adoptees, and more recently, this group demonstrated that high parental alcohol use and misuse reduced the effect of the ALDH2 protective allele (Irons et al., 2012). For the ADH1B rs1229984 variant, Hasin et al. (2002) observed a weaker protective role in certain groups, which was hypothesized to reflect differences in environmental exposure to heavy drinking. Our
