In European ancestry families, we found evidence consistent with our hypothesis that parents’ genotypes, both transmitted and non-transmitted to offspring, are associated with adolescent externalizing behavior. By incorporating parental genotypes and child genotypes into models predicting adolescent externalizing behavior, our results show that parental externalizing polygenic scores were uniquely associated with adolescent externalizing behavior, above and beyond the effect of adolescent externalizing polygenic scores. This indicates that genetic associations with externalizing behavior reflect both direct and indirect genetic influences. The association between parental externalizing polygenic score and adolescent externalizing behavior, independent of the genetic risk that is directly transmitted, provides evidence for genetic nurture. Our results add to the growing evidence highlighting the importance of both direct and indirect genetic effects (Bates et al., 2018; Kong et al., 2018; Saunders et al., 2021; Wang et al., 2021). The fact that parental externalizing polygenic scores predicted adolescent externalizing behavior over and above the effect of the adolescent’s externalizing polygenic scores suggests that some environmental factors associated with parental externalizing polygenic loading influence adolescent externalizing behavior.
