With an abundance of evidence suggesting the significant role of genes in behavior, it has become increasingly important to clarify how identified genes exert their influence. As such, it is critical that we address questions regarding mechanisms of genetic risk through a developmental lens, using longitudinal designs, and that we further examine how genetic susceptibility may vary as a function of environmental factors. This is the approach we have taken in the present study. Initially associated with alcohol dependence (Wang et al., 2004), CHRM2 has subsequently been identified as a gene that most strongly predisposes to a broad spectrum of externalizing problems in adults (Dick, 2007; Dick et al., 2008). We extended these findings by examining candidate SNPs in CHRM2 within an independent, community-based sample of children, who were followed longitudinally from childhood through young adulthood. With self-reported data from nine time points between the ages of 12 and 22, growth mixture modeling was used to identify three discrete trajectories of general externalizing behavior: 57.8% of the sample showed modest initial levels of externalizing problems that declined over time, roughly
