Mechanisms of Gene– Environment Interaction Effects in the Development of Conduct Disorder

ABSTRACT—The gene–environment interaction effect in the development of conduct disorder is one of the most im-portant discoveries of the past decade, but the mechanisms through which this effect operates remain elusive. I pro-pose a model of these processes that focuses on the indi-vidual’s response to a threatening stimulus in ongoing social interaction. The individual’s response coordinates three interrelated systems: neural, autonomic, and infor-mation-processing. In each system, adaptive, evolution-arily selected response patterns characterize normal responding, but in psychopathology these patterns have gone awry. Antecedents of individual differences in these response patterns arise from genetic polymorphisms, ad-verse environmental experiences early in life, and their interaction. Programs of research are proposed to test hypotheses in the model through longitudinal, experi-mental, and clinical intervention methods. This model can serve as a template for inquiry in other forms of develop-mental psychopathology. We have learned more in the past 2 decades about the devel-opment of conduct disorder than we had in the previous 2 mil-lennia. We now know that the fundamental building blocks of this debilitating condition involve an interaction effect between one’s genetic context and threatening life experiences. That is, early experiences of physical maltreatment and harsh parenting have been found to predict later conduct disorder, but only among those individuals who are born with a polymorphism in the monoamine oxidase A (MAOA) gene. Although important, this discovery does not provide an un-derstanding of how conduct disorder develops. What remains to be discovered are the mechanisms through which this gene– environment interaction effect occurs. Answering this question will enhance treatment efficacy for adolescents with this disor-der, foster novel preventive interventions for high-risk children, and provide a template for understanding the development of psychopathology more generally. Thus, the question of mecha-nisms in gene–environment interaction effects is one of the most important questions to be answered in psychology in the next 2 decades