Internalizing syndromes often co-occur with social and interpersonal difficulties, particularly poor marital quality. In the current study, we examined possible mechanisms behind the frequent co-occurrence of poor relationship quality and internalizing syndromes. Specifically, we evaluated whether the genetic and environmental influences on an internalizing factor score vary as functions of the level of marital quality. Findings from the current study support the existence of an etiologically coherent, moderately heritable internalizing spectrum that accounts for the phenotypic co-occurrence among the internalizing syndromes. After accounting for the general internalizing factor, there were no disorder-specific genetic influences, suggesting that phenotypic internalizing disorders (e.g., depression) are all possible expressions of the same genetically-influenced latent liability, with specific manifestation dependent on environmental stressors.
