title: Genetic and environmental contributions to depressive personality disorder in a population-based sample of Norwegian twins.
abstract: BACKGROUND
  Depressive personality disorder (DPD) was introduced in DSM-IV as a new category requiring further study. The aim of this study was to estimate genetic and environmental contributions to DPD in a population-based twin sample, and include data on criteria performance, prevalence and diagnostic overlap.
  
  
  METHODS
  Axis I and Axis II diagnoses were obtained by structured interviews in a population-based sample of 2794 young adult twins. Statistical analyses included correlation and factor analysis based on polychoric correlation coefficients, and diagnostic overlap applying adjusted odds ratios. Contributions from additive genetic and common and unique environmental influences to the liability to DPD were computed using structural equation modelling, applying a multiple threshold variable.
  
  
  RESULTS
  Liability to DPD could best be explained by additive genetic and unique environmental factors, with heritability estimates of 49% (95% CI 0.41-0.57) in females and 25% (95% CI 0.12-0.40) in males. The best-fitting model indicated that some of the genes contributing to DPD differ between men and women. Chronbach's alpha was 0.87. 2.0% of participants fulfilled the criteria for DPD, and overlap was most pronounced for dysthymic disorder and avoidant personality disorder.
  
  
  CONCLUSIONS
  Low prevalence rates and subsequent inclusion of subthreshold criteria could have influenced parameter estimates, especially in males.
  
  
  CONCLUSIONS
  DPD was almost twice as heritable in females as in males, comparable to previous studies on major depression. The proposed criteria showed good measurement properties, and DPD was not completely subsumed within any other disorder.
authors.affiliation: Department of Mental Health, Norwegian Institute of Public Health, Oslo, Norway. ragnhild.orstavik@fhi.no
authors.forename: Ragnhild Elise
authors.initials: RE
authors.lastname: Ørstavik
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Kendler
authors.forename: Nikolai
authors.initials: N
authors.lastname: Czajkowski
authors.forename: Kristian
authors.initials: K
authors.lastname: Tambs
authors.forename: Ted
authors.initials: T
authors.lastname: Reichborn-Kjennerud
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D003866:Depressive Disorder / Q000453:epidemiology / Q000235:genetics* / Q000523:psychology; D004200:Diseases in Twins / Q000453:epidemiology / Q000235:genetics* / Q000523:psychology; D019263:Dysthymic Disorder / Q000453:epidemiology / Q000235:genetics / Q000523:psychology; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D008297:Male; D009664:Norway; D010554:Personality Disorders / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics* / Q000523:psychology; D012307:Risk Factors; D012737:Sex Factors; D012931:Social Environment