Structure and etiology of co-occurring internalizing and externalizing disorders in adolescents

Abstract

Several studies suggest that a two-factor model positing internalizing and externalizing factors explains the interrelationships among psychiatric disorders. However, it is unclear whether the covariation between internalizing and externalizing disorders is due to common genetic or environmental influences. We examined whether a model positing two latent factors, internalizing and externalizing, explained the interrelationships among six psychiatric disorders (major depressive disorder, generalized anxiety disorder, separation anxiety disorder, attention-deficit/hyperactivity disorder, oppositional defiant disorder, and conduct disorder) in adolescents, and whether there are common genetic and environmental influences on internalizing and externalizing latent factors. Multivariate behavior genetic analyses of data from 1162 twin pairs and 426 siblings ascertained from the general population via the Colorado Center for Antisocial Drug Dependence (CADD) were conducted. We found support for a model positing two latent factors (internalizing and externalizing). These factors were moderately heritable and influenced by significant common genetic and nonshared environmental influences. These findings suggest that co-occurrence of internalizing and externalizing psychopathology in adolescents results from both genetic and environmental influences.

Figure I

Three alternative multivariate models. A = additive genetic influences; E = nonshared environmental influences; MDD = major depressive disorder; SAD = separate anxiety disorder; GAD = generalized anxiety disorder; ADHD = attention-deficit/hyperactivity disorder; CD = conduct disorder; ODD = oppositional defiant disorder.

Figure II

Results of the full bivariate common factor model (Figure 2A) and results of the final bivariate common factor model (Figure 2B). A = additive genetic influences; C = shared environmental influences; E = nonshared environmental influences; r_A = correlation between genetic influences on internalizing and externalizing disorders; r_C = correlation between shared environmental influences on internalizing and externalizing disorders; r_E = correlation between nonshared environmental influences on internalizing and externalizing disorders; MDD = major depressive disorder; SAD = separate anxiety disorder; GAD = generalized anxiety disorder; ADHD = attention-deficit/hyperactivity disorder; CD = conduct disorder; ODD = oppositional defiant disorder.