We also found evidence of joint effects between parental divorce/discord and offspring genetic risk for alcohol problems in predicting alcohol outcomes. There was evidence of gene-environment interaction on an additive, but not on a multiplicative scale. The lack of evidence for interaction on a multiplicative scale indicates that the magnitude of associations between parental divorce/relationship discord on offspring alcohol outcomes did not differ based on offspring polygenic loading. Said another way, the pathogenic influence of these forms of family stress on offspring alcohol outcomes was not limited to, for example, offspring with high PRS. Instead, the evidence for interaction on an additive scale suggests that the joint effects of parental divorce/discord and children’s genetic risk for alcohol problems exceed the sum of their individual effects. In other words, the risk associated with familial adversity is compounded by offspring’s polygenic loading for alcohol problems. This suggests that individuals with a higher genetic loading may need only minimal familial stress to experience an increased risk for alcohol problems. In contrast, individuals with a lower genetic loading may need higher levels of familial
