In summary, our data suggest a gene-environment interaction effect in which the effect of CHRM2 on adolescent externalizing behavior is moderated by parental monitoring. Specifically, the association between the genotype and externalizing behavior is accentuated under conditions of lower parental monitoring. Additionally, there is suggestion of a crossover effect: The genotype associated with the highest levels of externalizing behavior at the low end of parental monitoring was associated with the lowest levels of externalizing behavior at the extreme high end of parental monitoring. These findings may suggest that CHRM2 is a plasticity gene, a gene involved in biological sensitivity to context (Ellis & Boyce, 2008). This would account for the patterns of results observed across studies of CHRM2. We hope our study will act as a springboard for future studies aimed at testing this hypothesis and further characterizing how CHRM2 is associated with a variety of psychological outcomes of interest.
