title: Genetic and environmental influences on dimensional representations of DSM-IV cluster C personality disorders: a population-based multivariate twin study.
abstract: BACKGROUND
  The DSM-IV cluster C Axis II disorders include avoidant (AVPD), dependent (DEPD) and obsessive-compulsive (OCPD) personality disorders. We aimed to estimate the genetic and environmental influences on dimensional representations of these disorders and examine the validity of the cluster C construct by determining to what extent common familial factors influence the individual PDs.
  
  
  METHODS
  PDs were assessed using the Structured Interview for DSM-IV Personality (SIDP-IV) in a sample of 1386 young adult twin pairs from the Norwegian Institute of Public Health Twin Panel (NIPHTP). A single-factor independent pathway multivariate model was applied to the number of endorsed criteria for the three cluster C disorders, using the statistical modeling program Mx.
  
  
  RESULTS
  The best-fitting model included genetic and unique environmental factors only, and equated parameters for males and females. Heritability ranged from 27% to 35%. The proportion of genetic variance explained by a common factor was 83, 48 and 15% respectively for AVPD, DEPD and OCPD. Common genetic and environmental factors accounted for 54% and 64% respectively of the variance in AVPD and DEPD but only 11% of the variance in OCPD.
  
  
  CONCLUSIONS
  Cluster C PDs are moderately heritable. No evidence was found for shared environmental or sex effects. Common genetic and individual environmental factors account for a substantial proportion of the variance in AVPD and DEPD. However, OCPD appears to be largely etiologically distinct from the other two PDs. The results do not support the validity of the DSM-IV cluster C construct in its present form.
authors.affiliation: Division of Mental Health, Norwegian Institute of Public Health, Oslo, Norway. ted.reichborn-kjennerud@fhi.no
authors.forename: Ted
authors.initials: T
authors.lastname: Reichborn-Kjennerud
authors.forename: Nikolai
authors.initials: N
authors.lastname: Czajkowski
authors.forename: Michael C
authors.initials: MC
authors.lastname: Neale
authors.forename: Ragnhild E
authors.initials: RE
authors.lastname: Ørstavik
authors.forename: Svenn
authors.initials: S
authors.lastname: Torgersen
authors.forename: Kristian
authors.initials: K
authors.lastname: Tambs
authors.forename: Espen
authors.initials: E
authors.lastname: Røysamb
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Harris
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Kendler
mesh_terms: D000328:Adult; D016000:Cluster Analysis; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D008297:Male; D010554:Personality Disorders / Q000175:diagnosis* / Q000453:epidemiology / Q000235:genetics*; D010555:Personality Inventory; D011159:Population Surveillance / Q000379:methods; D015995:Prevalence; D012720:Severity of Illness Index; D012931:Social Environment; D011795:Surveys and Questionnaires; D014427:Twins / Q000235:genetics* / Q000523:psychology*