We found that polygenic scores derived from results of a large multivariate genomic analysis of externalizing spectrum behavior/disorders (Karlsson Linnér et al. in press) were associated with adolescent externalizing behavior in an independent sample of European ancestry. Our polygenic scores were derived using results from a multivariate genomic approach of externalizing behaviors/problems that included a range of clinical and non-clinical traits related to the externalizing spectrum. Notably, the phenotypic adolescent externalizing behavior in our sample was derived using age-appropriate, similar externalizing phenotypes, but not directly overlapping with the externalizing phenotypes in the discovery GWAS (Karlsson Linnér et al. in press). The observed polygenic association is consistent with evidence from twin and family studies that much of the genetic influences on any externalizing psychopathology/behavior is broadly shared with other externalizing spectrum behavior/problems (Kendler et al. 2003; Krueger et al. 2002; Young et al. 2000). In addition, as hypothesized, externalizing polygenic score predicted greater peer substance use, which in turn was associated with adolescents’ subsequent externalizing behavior, while controlling for prior level of externalizing behavior. Our results indicated that peer substance use
