Furthermore, genetic influences are known to interact with the environment (gene-environment interaction; GxE; Dick and Kendler, 2012). Twin studies have provided evidence of these effects with respect to peer substance use and genetic risk for adolescent alcohol use behaviors. Adolescents with high genetic liability for alcohol and other substance use were more vulnerable to the adverse influences of their best friends’ substance use than adolescents with low genetic liability (Harden et al., 2008). The interplay between genetic and peer influences for adolescent alcohol use behaviors are also evidenced by genetic association studies, where for example, adults carrying at least one copy of the long allele of the dopamine D4 receptor gene (DRD4) were more influenced by their close friends’ alcohol use in the development of their own heavy episodic drinking than those without the long allele (Mrug and Windle, 2014), although this study was limited by a relatively small sample size and focused on only a single polymorphism in DRD4. Investigations with respect to PRS in the context of GxE have recently emerged as well, as high PRS for alcohol
