The Factor Structure of Common Psychiatric Disorders and Their Genetic and Environmental Risk Factors in Adolescence

The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline Factor analyses among adults have indicated that the structure of common mental disorders may be described parsimoniously with a two factor model, with mood and anxiety disorders loading on a latent internalizing factor and antisocial behavior disorders and substance use disorders loading on a latent externalizing factor. However, little is known about the structure of mental disorders among adolescents and how posttraumatic stress and its constituent subfactors, attention deficit hyperactivity disorder, and oppositional defiant disorder would fit into such a model. Similarly, little is known about the structure of genetic and environmental influences on common mental disorders. These questions were addressed via factor analyses and multivariate twin models of a sample of adolescents aged 10 – 19 years representative of the population of Colorado (n=3867) who were assessed for eight common disorders. Factor analysis results indicated that while a two factor model fit adequately, a three factor model with attention deficit hyperactivity disorder, oppositional defiant disorder and conduct disorder forming one factor of externalizing, and substance abuse/dependence symptoms and conduct disorder forming a second factor of externalizing fit better. Posttraumatic stress disorder loaded as strongly on internalizing as the more prototypical internalizing disorders, and each of its constituent subfactors loaded more strongly on internalizing than externalizing. Twin models indicated that, in contrast to a prior study among adults, iv neither genetic influences nor nonshared environmental influences could be constrained to two factors and that the best fitting model included three common genetic factors that do not conform to an internalizing–externalizing structure. These results suggest that the structure of adolescent psychopathology can be parsimoniously summarized by an internalizing–externalizing model with two factors of externalizing, and that the structure of both genetic and environmental influences do not conform to the phenotypic structure.