title: The heritability of avoidant and dependent personality disorder assessed by personal interview and questionnaire.
abstract: OBJECTIVE
  Personality disorders (PDs) have been shown to be modestly heritable. Accurate heritability estimates are, however, dependent on reliable measurement methods, as measurement error deflates heritability. The aim of this study was to estimate the heritability of DSM-IV avoidant and dependent personality disorder, by including two measures of the PDs at two time points.
  
  
  METHODS
  Data were obtained from a population-based cohort of young adult Norwegian twins, of whom 8045 had completed a self-report questionnaire assessing PD traits. 2794 of these twins subsequently underwent a structured diagnostic interview for DSM-IV PDs. Questionnaire items predicting interview results were selected by multiple regression, and measurement models of the PDs were fitted in Mx.
  
  
  RESULTS
  The heritabilities of the PD factors were 0.64 for avoidant PD and 0.66 for dependent PD. No evidence of common environment, that is, environmental factors that are shared between twins and make them similar, was found. Genetic and environmental contributions to avoidant and dependent PD seemed to be the same across sexes.
  
  
  CONCLUSIONS
  The combination of both a questionnaire- and an interview assessment of avoidant and dependent PD results in substantially higher heritabilities than previously found using single-occasion interviews only.
authors.affiliation: Department of Mental Health, Norwegian Institute of Public Health, Oslo, Norway. line.gjerde@fhi.no
authors.forename: L C
authors.initials: LC
authors.lastname: Gjerde
authors.forename: N
authors.initials: N
authors.lastname: Czajkowski
authors.forename: E
authors.initials: E
authors.lastname: Røysamb
authors.forename: R E
authors.initials: RE
authors.lastname: Orstavik
authors.forename: G P
authors.initials: GP
authors.lastname: Knudsen
authors.forename: K
authors.initials: K
authors.lastname: Ostby
authors.forename: S
authors.initials: S
authors.lastname: Torgersen
authors.forename: J
authors.initials: J
authors.lastname: Myers
authors.forename: K S
authors.initials: KS
authors.lastname: Kendler
authors.forename: T
authors.initials: T
authors.lastname: Reichborn-Kjennerud
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D003859:Dependent Personality Disorder / Q000453:epidemiology / Q000235:genetics; D004200:Diseases in Twins / Q000453:epidemiology / Q000235:genetics; D005260:Female; D020022:Genetic Predisposition to Disease / Q000453:epidemiology / Q000235:genetics; D006801:Humans; D007406:Interview, Psychological; D008297:Male; D009664:Norway; D011795:Surveys and Questionnaires; D055815:Young Adult