title: Major depression and associated impairment: same or different genetic and environmental risk factors?
abstract: OBJECTIVE
  Impairment was added as a diagnostic criterion for many psychiatric disorders in DSM-IV. Does the addition of impairment influence only prevalence rates, or does it also introduce new etiological factors into psychiatric diagnoses?
  
  
  METHODS
  A lifetime history of major depression and associated functional impairment was assessed by personal interview with 3,669 female and 4,377 male twins from the population-based Virginia Twin Registry. Structural equation modeling was used to estimate the correlation between risk factors for major depression and associated functional impairment.
  
  
  RESULTS
  While the risk factors for major depression and associated functional impairment are substantially correlated, they are not identical. The most parsimonious model suggests that over a quarter of the variance in associated functional impairment is due to factors unrelated to risk for major depression. Of the variance unique to associated functional impairment, approximately one-third is familial. The relationship between associated functional impairment and major depression did not differ significantly between men and women.
  
  
  CONCLUSIONS
  Risk factors for major depression and associated functional impairment are substantially but imperfectly correlated. The addition of associated functional impairment as a criterion for the diagnosis of major depression not only lowers prevalence estimates but also introduces a small set of new etiological factors into the diagnosis of major depression.
authors.affiliation: Virginia Institute for Psychiatric and Behavioral Genetics, Departments of Human Genetics and Psychiatry, Virginia Commonwealth University, USA.
authors.forename: Debra L
authors.initials: DL
authors.lastname: Foley
authors.forename: Michael C
authors.initials: MC
authors.lastname: Neale
authors.forename: Charles O
authors.initials: CO
authors.lastname: Gardner
authors.forename: Andrew
authors.initials: A
authors.lastname: Pickles
authors.forename: Carol A
authors.initials: CA
authors.lastname: Prescott
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Kendler
mesh_terms: D000203:Activities of Daily Living / Q000145:classification / Q000523:psychology*; D000293:Adolescent; D000328:Adult; D003865:Major Depressive Disorder / Q000453:epidemiology / Q000235:genetics* / Q000523:psychology; D004185:Disability Evaluation; D004200:Diseases in Twins / Q000453:epidemiology / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease / Q000453:epidemiology / Q000235:genetics* / Q000523:psychology; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D012307:Risk Factors; D012737:Sex Factors; D012931:Social Environment