Childhood conduct disorder (CD) involves a persistent pattern of rule-breaking and aggressive behaviors, including bullying other children, stealing, vandalizing and skipping school. CD is one of the most prevalent childhood disorders. Although rates vary according to the population under study, approximately 6–16% of males, and 2–9% of females, are diagnosable with CD.1 CD is associated with serious problems in home and school functioning, and is a strong risk factor for concurrent and future alcohol and other substance problems; several studies of adolescents who have been diagnosed with alcohol use disorders have concluded that among childhood behavioral disorders, CD has the strongest association with alcohol problems.2–5 CD also shows considerable evidence for genetic influence. Retrospective reports of CD have estimated heritability ranging from 40 to 70%.6,7 Prospective reports of CD symptoms in children also show considerable evidence of genetic influence, with heritability estimates on the order of 40–50% in both boys and girls.8 A review of > 100 quantitative genetic studies of antisocial behavior (measured using various methods) converged on a heritability estimate of 50%,9 and a recent multi-informant study of
