Genetic Factors As Modifiers of Susceptibility to Negative Peer Influences On Alcohol Use From Adolescence to Adulthood

Both social environment and genetic factors have been implicated in alcohol use. Recent studies also point to the presence of gene by environment (G x E) interactions, such as specific genetic polymorphisms being associated with increased susceptibility to environmental influences (Belsky & Pluess, 2009). For instance, peer influences on heavy drinking were stronger among young adults with the long allele of the DRD4 gene (Larsen et al., 2010). The same polymorphism was related to greater alcohol dependence among young adults involved in Greek college organizations (Park et al., 2011). However, it is not clear whether DRD4 polymorphism modifies susceptibility to peer influences before or after young adulthood (van der Zwaluw et al., 2012). The present study examines interactive effects of DRD4 and friends’ alcohol use on subsequent alcohol use from middle adolescence to adulthood.

The sample includes 349 participants (59% female, 96% White) who were assessed at five points between mean ages 16 and 33. At each assessment, participants reported on their own alcohol use and the proportion of close friends who used alcohol (in adolescence) or drank heavily (in adulthood). Genotyping of DRD4 polymorphism was conducted from saliva samples. Multiple regressions predicted alcohol use at subsequent time points from friends’ alcohol use, DRD4 (dichotomized as low vs. high risk), and their interaction, adjusting for alcohol use at baseline, sex, ethnicity, and family income.

Having the long allele of DRD4 interacted with friends’ drinking in adulthood (ages 24 and 29), but not in adolescence (ages 16 and 17). Specifically, friends’ alcohol use in adolescence predicted subsequent drinking regardless of DRD4 genotype. However, friends’ drinking in adulthood was associated with later increased heavy drinking only among participants with the long allele of the DRD4, and not among those without this genetic risk. This pattern of results replicated across multiple measures of alcohol use and alcohol problems.

The results provide strong evidence that the long allele of DRD4 increases individuals’ susceptibility to friends’ heavy alcohol use in adulthood, but not in adolescence. The findings are consistent with behavior genetic studies reporting strong environmental influences on adolescent drinking, with the role of genetic factors increasing in adulthood (Kendler et al., 2008). Adults with the long allele of DRD4 may benefit from interventions designed to help them reduce affiliations with heavy drinking friends or decrease these peer influences. Additional genetic markers are currently being genotyped and will be included in the presentation.