Testing trait depression as a potential clinical domain in schizophrenia.

The DSM-5 includes depression as a dimension of psychosis. We tested whether persistent experience of depression, called 'trait depression', is a clinical feature separate from psychosis and several well-known, trait-like deficits of schizophrenia. 126 individuals with schizophrenia and 151 control participants completed the Maryland Trait and State Depression questionnaire, with a subset completing measures of cognition and functional capacity, and diffusion tensor imaging (n=73 patients and 102 controls for imaging analysis). Subjectively experienced, longitudinal trait depression is significantly higher in patients with schizophrenia compared with controls. Higher trait depression scores were associated with more severe psychosis. Surprisingly, individuals with higher trait depression manifested less cognitive and global functioning deficits. In addition, trait depression scores were positively associated with fractional anisotropy of white matter. Trait depression appears to be a highly relevant clinical domain in the care of patients with schizophrenia that also has distinct relationships with some other known traits of the disease. Trait depression may be an important contributor to the clinical heterogeneity of schizophrenia.