title: Dimensional representations of DSM-IV cluster A personality disorders in a population-based sample of Norwegian twins: a multivariate study.
abstract: BACKGROUND
  The 'odd' or 'Cluster A' personality disorders (PDs) - paranoid, schizoid and schizotypal PDs - were created in DSM-III with little empirical foundation. We have examined the relationship between the genetic and environmental risk factors for dimensional representations of these three personality disorders.
  
  
  METHODS
  These personality disorders were assessed using the Structured Interview for DSM-IV Personality (SIDP-IV) in 1386 young adult twin pairs from the Norwegian Institute of Public Health Twin Panel. Using Mx, a single-factor independent pathway twin model was fitted to the number of endorsed criteria for the three disorders.
  
  
  RESULTS
  The best-fit model included genetic and unique environmental common factors and genetic and unique environmental effects specific to each personality disorder. Total heritability was modest for these personality disorders and ranged from 21% to 28%. Loadings on the common genetic and unique environmental factors were substantially higher for schizotypal than for paranoid or schizoid PD. The proportion of genetic liability shared with all Cluster A disorders was estimated at 100, 43 and 26% respectively for schizotypal, paranoid and schizoid PDs.
  
  
  CONCLUSIONS
  In support of the validity of the Cluster A construct, dimensional representations of schizotypal, paranoid and schizoid PD are all modestly heritable and share a portion of their genetic and environmental risk factors. No evidence was found for shared environmental or sex effects for these PDs. Schizotypal PD most closely reflects the genetic and environmental liability common to all three Cluster A disorders. These results should be interpreted in the context of the limited power of this sample.
authors.affiliation: Department of Psychiatry, Medical College of Virginia of Virginia Commonwealth University, Richmond, VA 23298-0126, USA. Kendler@vcu.edu
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: Svenn
authors.initials: S
authors.lastname: Torgersen
authors.forename: Steven H
authors.initials: SH
authors.lastname: Aggen
authors.forename: Michael C
authors.initials: MC
authors.lastname: Neale
authors.forename: Ted
authors.initials: T
authors.lastname: Reichborn-Kjennerud
mesh_terms: D000328:Adult; D016000:Cluster Analysis; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D039721:Diagnostic and Statistical Manual of Mental Disorders; D004200:Diseases in Twins / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D008297:Male; D009664:Norway; D010260:Paranoid Personality Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics; D010554:Personality Disorders / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*; D015203:Reproducibility of Results; D012307:Risk Factors; D012557:Schizoid Personality Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics; D012569:Schizotypal Personality Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics; D012737:Sex Factors; D012931:Social Environment; D014429:Twins, Dizygotic / Q000235:genetics / Q000523:psychology; D014430:Twins, Monozygotic / Q000235:genetics / Q000523:psychology