A history of parental addiction is a strong predictor of AUDs and DD in their offspring and is associated with more severe symptoms [60]. Although the genetic risk of externalizing disorders transmitted from parents to child influences the likelihood that the child will be exposed to early-life stress and will develop the disorder, several studies have shown that childhood stressors have an independent effect on the risk of adult externalizing disorders, including AUDs and DD [20, 61]. A longitudinal study of twins and their parents illustrates this point by demonstrating that there is a direct causal effect of childhood adversity on child conduct disorder over and above any indirect genetic correlation [62].
