title: CLASSIFICATION OF ANXIETY DISORDERS COMORBID WITH MAJOR DEPRESSION: COMMON OR DISTINCT INFLUENCES ON RISK?
abstract: BACKGROUND
  Anxiety and depression display frequent comorbidity. Individuals with comorbid disorders also often have more extreme symptomatology than those with single disorders. This correlation between comorbidity and severity poses an interesting question: Are comorbid forms of anxiety and depression essentially just more severe versions of the pure disorders?
  
  
  METHODS
  In a large major depression (MD) case-control sample of individuals from the China, Oxford and VCU Experimental Research on Genetic Epidemiology project, we examined the patterns of lifetime anxiety comorbidity (including generalized anxiety disorder--GAD, panic disorder, and five phobia subtypes) among MD cases (N = 5,864) in this population. Binary and multinomial logistic regression was used to estimate associations between risk factors and outcomes including MD as well as latent class membership, which were compared using continuation ratios.
  
  
  RESULTS
  We found a five-class solution to fit best, and each resulting class had a distinct pattern of association with the tested risk factors. The use of continuation ratios suggests that a class characterized by high endorsement of GAD is comparable to a more severely affected "pure MD" group. The other three classes (characterized by agoraphobia, various specific phobias, and by high endorsement of all comorbid anxiety disorders, respectively) appear to differ meaningfully from MD alone.
  
  
  CONCLUSIONS
  Risk for MD resulting from environmental and psychosocial factors may also predispose individuals to GAD, and less consistently, other anxiety disorders. Presentations of MD with certain phobias display distinguishably different patterns of risk, however, and are therefore likely qualitatively distinct.
authors.affiliation: Department of Psychiatry, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Arden
authors.initials: A
authors.lastname: Moscati
authors.affiliation: Wellcome Trust Centre for Human Genetics, Oxford, UK.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Flint
authors.affiliation: Department of Psychiatry, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Kendler
mesh_terms: D000328:Adult; D001008:Anxiety Disorders / Q000145:classification* / Q000453:epidemiology; D002681:China / Q000453:epidemiology; D015897:Comorbidity; D003865:Major Depressive Disorder / Q000145:classification* / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012306:Risk
keywords: GAD/generalized anxiety disorder; anxiety/anxiety disorders; depressive disorder; panic attacks/agoraphobia; phobia/phobic disorders