on comparisons of twins, not using measured genotypes) on substance use outcomes in adolescence (Dick, Pagan, Viken, et al., 2007; Dick, Viken, et al., 2007); genetic effects assumed greater importance under conditions of lower parental monitoring, presumably because adolescents with lower monitoring have more access to the substance and opportunity to express their genetic predisposition. An interaction between GABRA2 and parental monitoring was tested in an independent sample; a stronger association between the gene and trajectories of externalizing behavior was found under conditions of lower parental monitoring, as was hypothesized based on the twin findings (Dick, Latendresse, et al., 2009). This series of studies illustrates how different literatures and study designs (linkage and association studies, twin studies, and longitudinal, developmental studies) were integrated to characterize a cGxE effect. In this case, the candidate gene under study was selected based on a series of converging pieces of evidence that indicated involvement in alcohol and externalizing outcomes before it was studied in the context of cGxE.
