title: Dimensional representations of DSM-IV cluster B personality disorders in a population-based sample of Norwegian twins: a multivariate study.
abstract: BACKGROUND
  The personality disorders (PDs) in the 'dramatic' cluster B [antisocial (ASPD), histrionic (HPD), narcissistic (NPD) and borderline (BPD)] demonstrate co-morbidity. However, the degree to which genetic and/or environmental factors influence their co-occurrence is not known and, with the exception of ASPD, the relative impact of genetic and environmental risk factors on liability to the cluster B PDs has not been conclusively established.
  
  
  METHODS
  PD traits were assessed in 1386 Norwegian twin pairs between the age of 19 and 35 years using the Structured Interview for DSM-IV Personality Disorders (SIDP-IV). Using the statistical package Mx, multivariate twin models were fitted to dimensional representations of the PDs.
  
  
  RESULTS
  The best-fitting model, which did not include sex or shared family environment effects, included common genetic and environmental factors influencing all four dramatic PD traits, and factors influencing only ASPD and BPD. Heritability was estimated at 38% for ASPD traits, 31% for HPD traits, 24% for NPD traits and 35% for BPD traits. BPD traits had the lowest and ASPD traits the highest disorder-specific genetic variance.
  
  
  CONCLUSIONS
  The frequently observed co-morbidity between cluster B PDs results from both common genetic and environmental influences. Etiologically, cluster B has a 'substructure' in which ASPD and BPD are more closely related to each other than to the other cluster B disorders.
authors.affiliation: Department of Psychology, University of Oslo, Blindern, Oslo, Norway. svenn.torgersen@psykologi.uio.no
authors.forename: S
authors.initials: S
authors.lastname: Torgersen
authors.forename: N
authors.initials: N
authors.lastname: Czajkowski
authors.forename: K
authors.initials: K
authors.lastname: Jacobson
authors.forename: T
authors.initials: T
authors.lastname: Reichborn-Kjennerud
authors.forename: E
authors.initials: E
authors.lastname: Røysamb
authors.forename: M C
authors.initials: MC
authors.lastname: Neale
authors.forename: K S
authors.initials: KS
authors.lastname: Kendler
mesh_terms: D000328:Adult; D000987:Antisocial Personality Disorder / Q000175:diagnosis / Q000235:genetics / Q000523:psychology; D001883:Borderline Personality Disorder / Q000175:diagnosis / Q000235:genetics / Q000523:psychology; D015331:Cohort Studies; D015897:Comorbidity; D039721:Diagnostic and Statistical Manual of Mental Disorders; D004200:Diseases in Twins / Q000175:diagnosis* / Q000235:genetics* / Q000523:psychology; D005260:Female; D006677:Histrionic Personality Disorder / Q000175:diagnosis / Q000235:genetics / Q000523:psychology; D006801:Humans; D008297:Male; D015999:Multivariate Analysis; D009664:Norway; D010554:Personality Disorders / Q000175:diagnosis* / Q000235:genetics* / Q000523:psychology; D012307:Risk Factors; D012931:Social Environment; D014429:Twins, Dizygotic / Q000235:genetics / Q000523:psychology; D014430:Twins, Monozygotic / Q000235:genetics / Q000523:psychology; D055815:Young Adult