title: Epidemiologic heterogeneity of common mood and anxiety disorders over the lifecourse in the general population: a systematic review.
abstract: BACKGROUND
  Clinical evidence has long suggested there may be heterogeneity in the patterns and predictors of common mood and anxiety disorders; however, epidemiologic studies have generally treated these outcomes as homogenous entities. The objective of this study was to systematically review the epidemiologic evidence for potential patterns of heterogeneity of common mood and anxiety disorders over the lifecourse in the general population.
  
  
  METHODS
  We reviewed epidemiologic studies examining heterogeneity in either the nature of symptoms experienced ("symptom syndromes") or in patterns of symptoms over time ("symptom trajectories"). To be included, studies of syndromes were required to identify distinct symptom subtypes, and studies of trajectories were required to identify distinct longitudinal patterns of symptoms in at least three waves of follow-up. Studies based on clinical or patient populations were excluded.
  
  
  RESULTS
  While research in this field is in its infancy, we found growing evidence that, not only can mood and anxiety disorders be differentiated by symptom syndromes and trajectories, but that the factors associated with these disorders may vary between these subtypes. Whether this reflects a causal pathway, where genetic or environmental factors influence the nature of the symptom or trajectory subtype experienced by an individual, or whether individuals with different subtypes differed in their susceptibility to different environmental factors, could not be determined. Few studies addressed issues of comorbidity or transitions in symptoms between common disorders.
  
  
  CONCLUSIONS
  Understanding the diversity of these conditions may help us identify preventable factors that are only associated with some subtypes of these common disorders.
authors.affiliation: Center for Urban Epidemiologic Studies, New York Academy of Medicine, New York, USA. anandi@hsph.harvard.edu
authors.forename: Arijit
authors.initials: A
authors.lastname: Nandi
authors.forename: John R
authors.initials: JR
authors.lastname: Beard
authors.forename: Sandro
authors.initials: S
authors.lastname: Galea
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D001008:Anxiety Disorders / Q000175:diagnosis / Q000453:epidemiology* / Q000523:psychology; D003625:Data Collection / Q000706:statistics & numerical data; D003866:Depressive Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology; D005260:Female; D006801:Humans; D008016:Life Change Events; D008137:Longitudinal Studies; D008875:Middle Aged; D019964:Mood Disorders / Q000175:diagnosis / Q000453:epidemiology* / Q000523:psychology; D011569:Psychiatric Status Rating Scales; D012307:Risk Factors; D012931:Social Environment; D013577:Syndrome