The absence of interactive effects between PRS and close friend substance use on heavy episodic drinking outcomes may also be due to the stringent test of GxE that were conducted in the current study, where parental knowledge and school substance use effects were statistically controlled within a rigorous development framework. Few studies have accounted for concomitant social processes (i.e., familial, school and peer influences) in the study of GxE, and it is speculated that the effects of specific environmental influences on adolescent behavior may be overestimated without considering multiple social influences simultaneously (Jaccard et al., 2005), particularly in the context of GxE. Furthermore, the presence of gene-environment correlations may confound the study of GxE effects (Knafo and Jaffee, 2013). For instance, adolescents with a genetic propensity for alcohol use problems and behaviors may select (or attract) peers who also engage in substance use behaviors, suggesting that the same genes responsible for conferring risk for alcohol use problems may be simultaneously influencing environmental exposure as well. One safeguard against confounds driven by multiple social influences involved in GxE and gene-environment correlations
