Paternal genetic risk is a robust predictor of offspring psychiatric disorders, with additional “indirect genetic effects” observed for internalizing and substance use conditions in adoptive and stepfather relationships. Rearing effects were most pronounced for substance use disorders.

Question In an adoption study of major psychiatric illness, what results would be obtained if offspring risk were predicted not from the phenotype of the parents but from their genetic risk?

Findings In this cohort study, paternal genetic risk was associated with offspring risk of illness for all disorders in genetically related father-offspring pairs. In an indirect pathway, genetic risk in adoptive and stepfathers predicted risk in their offspring for internalizing and substance use disorders but not for schizophrenia or bipolar disorder.

Meaning Indirect genetic effects from the father may have an impact on offspring risk of internalizing and substance use disorders.