How does one interpret the interaction observed between GABRA2 and parental monitoring? Several different models have been proposed for how social context may alter genetic expression; for example, the environment may trigger, enhance, or compensate for a genetic predisposition.55 We hypothesize that the effect of parental monitoring likely operates through another proposed mechanism by controlling the expression of a genetic predisposition by changing the opportunity to engage in behavior to which an individual may be predisposed. Conditions of high parental monitoring may constrain the behavior of youth, precluding adolescents with high-risk GABRA2 variants from having the opportunity to engage in antisocial behaviors. Conversely, conditions of low parental monitoring may provide greater opportunity for engagement in antisocial acts among those predisposed to such behavior. Many of the gene-environment interactions that have been described in substance use and antisocial behavior in the twin literature appear to act through social control mechanisms. For example, the heritability of alcohol use and externalizing behavior in adolescents is also lower in rural environments compared with urban settings, presumably due to enhanced community monitoring and more restricted access to alcohol, leading to reduced opportunity to express genetic predispositions.8,56,57
