that similar genetic factors underlie neuroticism and the latent liability to the internalizing spectrum, but environmental factors were largely uncorrelated. Neuroticism largely accounted for the comorbidity among the internalizing disorders, but there were genetic risk factors common to major depression, generalized anxiety disorder, and panic disorder not shared with neuroticism. Internalizing psychopathology is most likely a continuously distributed spectrum of liability to a certain type of pathology, and the specific constellation of symptoms that define a disorder result from this general overarching liability as well as disorder-specific influences (Krueger & Piasecki, 2002). Despite the strong evidence for a genetically coherent factor of internalizing, little research has examined the etiological connections between an internalizing phenotype and key environmental risk factors.
