Gene-environment interactions in the etiology of adolescent externalizing psychopathology

Objective. The present dissertation tested the hypothesis that the genetic and environmental expression of externalizing psychopathology is moderated by environmental circumstance. Specifically, that genetic influences are relatively more important, and shared-environmental influences relatively less important, in urban settings and under the condition of a non-religious upbringing. Part I of this dissertation examines the relative magnitude of genetic and environmental influences on externalizing psychopathology when measured in adolescents living in urban versus rural Minnesota. Part II asks the same question of adolescents raised in relatively non-religious versus relatively religious homes. Method. The sample consists of 1252 (578 male, 674 female) twin individuals who first visited the Minnesota Twin Family Study (MTFS) when they were approximately 17 years old. Externalizing Psychopathology was assessed with five measures: symptomatology for Conduct Disorder, Oppositional Defiant Disorder, and Adult Antisocial Behavior, plus information about the adolescents, alcohol use and substance-use experimentation. Biometric factor modeling was employed to estimate the proportion of variance in externalizing behavior that is influenced by genetic and environmental factors under the different environmental circumstances. Results. In urban environments, externalizing behavior was influenced primarily by genetic factors, while in rural environments, shared-environmental factors explained most of the variance. Genetic factors were also of primary importance in determining externalizing behavior for males raised in relatively non-religious homes. For males raised in relatively religious homes, shared-environmental factors were most important. This effect of the religious rearing environment did not extend to the female sample. Conclusions. The shift in primary etiological influences, from genetic to shared-environmental, when the environmental circumstance changes from urban to rural or non-religious to religious represents a gene-environment interaction in the development of adolescent externalizing psychopathology.