title: A longitudinal study of personality and major depression in a population-based sample of male twins.
abstract: BACKGROUND
  The relationship between personality and psychiatric illness is complex. It is not clear whether one directly causes the other.
  
  
  METHODS
  In a population-based sample of male twins (n=3030), we attempted to predict major depression (MD) from neuroticism (N) and extraversion (E) and vice versa, to evaluate the causal, scar, state, and prodromal hypotheses. In a longitudinal, structural equation twin model, we decomposed the covariation between N and MD into (a) genetic and environmental factors that are common to both traits, as well as specific to each one and (b) direct causal effects of N at time 1 on subsequent MD, as well as between MD and subsequent N.
  
  
  RESULTS
  E was negatively correlated with lifetime and one-year prevalence of MD. N predicted the new onset of MD, and was predicted by both current and past MD. It did not predict the time to onset of MD. All of the covariation between N and MD was due to additive genetic and individual-specific environmental factors shared by both traits and a direct causal path between MD and N assessed later. No genetic factors were unique to either trait.
  
  
  CONCLUSIONS
  In men, N may be a vulnerability factor for MD but does not cause it directly. However, MD may have a direct causal effect on N. The genetic overlap between N and MD in men may be greater than in women.
authors.affiliation: Washington VA Medical Center, Washington, DC 20422, USA. ayman.fanous@med.va.gov
authors.forename: Ayman H
authors.initials: AH
authors.lastname: Fanous
authors.forename: Michael C
authors.initials: MC
authors.lastname: Neale
authors.forename: Steven H
authors.initials: SH
authors.lastname: Aggen
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Kendler
mesh_terms: D000328:Adult; D015984:Causality; D003865:Major Depressive Disorder / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics; D004200:Diseases in Twins / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics; D005120:Extraversion, Psychological; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009497:Neurotic Disorders / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics; D010555:Personality Inventory; D010641:Phenotype; D012042:Registries; D012737:Sex Factors; D012931:Social Environment; D013694:Temperament; D014768:Virginia