In summary, we found that polygenic risk for externalizing disorders in adulthood is associated with externalizing disorders, subclinical externalizing behavior, and several impulsivity-related traits in adolescents and young adults, and is moderated by adolescent parenting and peer factors. Examining how polygenic predispositions for externalizing disorders manifest across development and interact with salient environmental moderators is a potentially useful way to characterize pathways toward disorder. These results raise several high-priority directions for future research. We highlight here two directions that we believe have the greatest promise for advancing our understanding of how genetic predispositions toward adult externalizing disorders manifest earlier in development and interact with environmental factors. First, developing theory-driven, holistic measures of the environment is central for moving this area of research forward. In the present study, as in many gene-by-environment interaction studies, we considered parental monitoring and peer substance use in isolation. However, environmental risk factors are often related to one another, and there is no unified framework for measuring or modeling cumulative risk in gene-by-environment interaction studies. A corollary to this point is that to understand gene-by-environment interactions
