Importantly, we find evidence that the association between GABRA2 and trajectories of externalizing behavior is moderated by parental monitoring; the effect of the genotype on externalizing behavior is stronger under conditions of lower parental monitoring and weaker under conditions of higher parental monitoring. This finding is consistent with the evidence of moderation from twin studies in which heritable influences were found to be higher under conditions of lower parental monitoring and lower under conditions of higher parental monitoring.30 However, that demonstration of moderation was only at the level of latent genetic influences—that is, the heritability of the trait was shown to differ, as inferred by comparing monozygotic and dizygotic twin correlations; no specific genes were measured. Herein, we find that the effect of a specific measured gene varies as a function of parental monitoring in the predicted way. These findings underscore the utility of using results from twin studies about how genetic influences act (as inferred by monozygotic/dizygotic twin correlation comparisons) to develop testable hypotheses in relation to the effect associated with specific measured genes.
