Genetic-environmental interaction in the genesis of aggressivity and conduct disorders.

BACKGROUND The purpose of this study was to determine the effect of an adverse adoptive home environment on adoptee conduct disorder, adult antisocial behavior, and two measures of aggressivity, all of which are behaviors that contribute to adult antisocial personality disorder and that also are associated with increased vulnerability to drug abuse and/or dependence. METHODS The study used an adoption paradigm in which adopted offspring who were separated at birth from biologic parents with documented (by prison and hospital records) antisocial personality disorder and/or alcohol abuse or dependence were followed up as adults. They and their adoptive parents were interviewed in person. These adoptees were compared with controls whose biologic background was negative for documented psychopathologic behavior. Subjects were 95 male and 102 female adoptees and their adoptive parents. RESULTS Multiple regression analysis was used to measure separately genetic and environmental effects. It showed that (1) a biologic background of antisocial personality disorder predicted increased adolescent aggressivity, conduct disorder, and adult antisocial behaviors, and (2) adverse adoptive home environment (defined as adoptive parents who had marital problems, were divorced, were separated, or had anxiety conditions, depression, substance abuse and/or dependence, or legal problems) independently predicted increased adult antisocial behaviors. Adverse adoptive home environment interacted with biologic background of antisocial personality disorder to result in significantly increased aggressivity and conduct disorder in adoptees in the presence of but not in the absence of a biologic background of antisocial personality disorder. CONCLUSIONS Environmental effects and genetic-environmental interaction account for significant variability in adoptee aggressivity, conduct disorder, and adult antisocial behavior and have important implications for the prevention and intervention of conduct disorder and associated conditions such as substance abuse and aggressivity.