As we successfully identify genes involved in psychiatric disorders, the next important step will be to characterize the pathways of risk associated with identified genes. This must involve studying how these genes affect risk across development and how the risk associated with susceptibility genes may change as a function of the environment. Here we describe analyses from one such effort. An association between GABRA2 and increased risk for adult alcohol dependence had been established across multiple studies. We extended these findings by genotyping GABRA2 in an independent community sample of children, followed longitudinally from childhood through young adulthood. Using data on externalizing behavior as reported at 9 time points between ages 12 and 22 years, we used person-oriented latent class analysis to identify 2 classes of trajectories of externalizing behavior; most of the sample (83%) showed a decrease in externalizing behavior from early adolescence to adulthood, while 17% 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
