In the CDP, we used latent class analyses to characterize trajectories of externalizing behavior from age 12 to 22 (Dick, Latendresse, et al., 2009). We identified two classes of trajectories of externalizing behavior: the majority of the sample (83%) showed a decrease in externalizing behavior from early adolescence to adulthood, whereas17% of the sample showed consistent, elevated levels of externalizing behavior that persisted into adulthood. The individuals showing this pattern of persistently high externalizing behavior were significantly more likely to carry the variant of GABRA2 that was originally associated with increased risk for adult alcohol dependence in the COGA sample. Further, we found evidence that the association between GABRA2 and trajectories of externalizing behavior was moderated by parental monitoring: the effect of the genotype on externalizing behavior was stronger under conditions of lower parental monitoring, weaker under conditions of higher parental monitoring (Dick, Latendresse, et al., 2009).
