The Relationship Between Depressive Personality Disorder and Major Depressive Disorder: A Population-Based Twin Study

Objective: One of the most important controversies regarding depressive personality disorder is the overlap with mood disorders. The aim of this study was to estimate the genetic and environmental sources of covariance between depressive personality disorder and major depressive disorder and to what extent genetic, shared, and unique environmental factors are specific to each disorder. Method: A total of 2,801 young adult twins from the Norwegian Institute of Public Health Twin Panel were assessed at personal interview for depressive personality disorder and major depressive disorder with the Structured Interview for DSM-IV Personality and the Composite International Diagnostic Interview. Bivariate Cholesky models were fitted to the data by using the Mx statistical program. Results: In the best-fitting model, the covariation between depressive personality disorder and major depressive disorder were accounted for by genetic and unique environmental factors only. A model that did not include genetic factors specific to major depressive disorder was rejected. The authors found no clear evidence for gender differences in sources of comorbidity of depressive personality disorder and major depressive disorder. Conclusions: Although depressive personality disorder and major depressive disorder share a substantial proportion of genetic and environmental risk factors, the results from this study support the hypothesis that the two disorders are distinct entities with overlapping, but not identical, etiologies.