In conclusion, the present study adds to the literature by unpacking the cascading developmental processes by which genetic factors confer risk for adolescent behavior. Our results show that polygenic scores from a large-scale multivariate genomic analyses of externalizing spectrum behavior/disorders predicted externalizing behavior among a sample of independent adolescents. Among individuals of European ancestry, in addition to direct genetic effects on adolescent externalizing behavior, our findings show that peer substance use serves as an important mediating pathway by which genetic influences further convey risk for future adolescent externalizing behavior. Externalizing polygenic score predicted higher levels of adolescent externalizing behavior indirectly via peer substance use. More generally, our results indicate that genetically at-risk youth carry risk that is exacerbated through a combination of gene-environment processes. This research underscores the importance of considering the complex interplay between genes and environments when considering etiology and prevention/intervention for externalizing behavior because gene-environment correlation processes serve as mechanisms by which genetic influences, in part, impact adolescent behavioral problems. Understanding the mechanisms of genetic risk for problematic behaviors in youth will be critical for identifying targets for effective prevention and intervention efforts. Additionally, our findings underscore the need for expanded genetic study in diverse populations.
