Environmental adversity and increasing genetic risk for externalizing disorders.

CONTEXT Studies of gene-environment interplay in the development of psychiatric and substance use disorders are rapidly accumulating. However, few attempts have been made to integrate findings and to articulate general mechanisms of gene-environment influence in the emergence of psychopathology. OBJECTIVE To identify patterns of gene-environment interplay between externalizing disorders (antisocial behavior and substance use) and several environmental risk factors. DESIGN We used quantitative genetic models to examine how genetic and environmental risk for externalizing disorders changes as a function of environmental context. SETTING Participants were recruited from the community and took part in a daylong assessment at a university laboratory. PARTICIPANTS The sample consisted of 1315 male and female twin pairs participating in the assessment of the Minnesota Twin Family Study at age 17 years. MAIN OUTCOME MEASURES Multiple measures and informants were used to construct a composite of externalizing disorders and composite measures of 6 environmental risk factors, including academic achievement and engagement, antisocial and prosocial peer affiliations, mother-child and father-child relationship problems, and stressful life events. RESULTS A significant gene x environment interaction was detected between each environmental risk factor and externalizing such that greater environmental adversity was associated with increased genetic risk for externalizing. CONCLUSIONS In the context of environmental adversity, genetic factors become more important in the etiology of externalizing disorders. The consistency of the results further suggests a general mechanism of environmental influence on externalizing disorders regardless of the specific form of the environmental risk.