652 JOURNAL OF STUDIES ON ALCOHOL AND DRUGS / SEPTEMBER 2010 Effect of Paternal Alcohol and Drug Dependence on Offspring Conduct Disorder: Gene–Environment Interplay*

ABSTRACT. Objective: Not only are substance-use disorders and ex-ternalizing disorders frequently comorbid, they often co-occur in families across generations. The current study examined the role of genetic and environmental infl uences in the relationship between paternal histories of drug dependence or alcohol dependence and offspring conduct disorder using an offspring-of-twins design. Method: Participants were male twins (n = 1,774) from the Vietnam Era Twin Registry, their offspring (n = 1,917), and mothers of the offspring (n = 1,202). Twins had a his-tory of drug dependence, alcohol dependence, or neither. Based on the father’s and his co-twin’s drug-dependence or alcohol-dependence history and zygosity, risk groups were constructed to refl ect different levels of genetic and environmental risk that were then used to predict offspring conduct disorder. Results: After controlling for potentially confounding variables, the offspring of men with a history of drug dependence or alcohol dependence had signifi cantly higher rates of conduct disorder