title: Environmental and familial risk factors for psychotic and non-psychotic severe depression.
abstract: BACKGROUND
  Severe unipolar depression can be classified as either psychotic depression (PD) or non-psychotic depression (non-PD). A number of biological and clinical differences have been detected between PD and non-PD, but it remains unknown whether risk factors for the two subtypes also differ. The aim of the present study was therefore to investigate whether a number of potential risk factors influenced the risk of developing PD and non-PD to different extents.
  
  
  METHODS
  This is a register-based historical prospective cohort study following all 2.4 million individuals born in Denmark between 1955 and 1990. During follow-up 2183 and 9101 individuals were registered in the Danish Psychiatric Central Research Register with PD and non-PD respectively. The association between risk factors and the development of PD and non-PD was estimated by survival analysis (Poisson regression) and expressed as incidence rate ratios (IRR).
  
  
  RESULTS
  The most consistent finding of the study was that of a general overlap in familial and environmental risk factors for PD and non-PD. However, a parental history of bipolar disorder was a risk factor for PD (mother, IRR=1.66, p=0.003. Father, IRR=1.56, p=0.040) and not for non-PD (mother, IRR=0.92, p=0.430. Father, IRR=1.08, p=0.552). Conversely, a positive family history of schizophrenia was associated with neither PD nor non-PD LIMITATIONS: Diagnoses were assigned as part of routine clinical practice.
  
  
  CONCLUSIONS
  Our findings justify the distinction between PD and non-PD in the current diagnostic manuals. Furthermore, the fact that parental bipolar disorder and not schizophrenia was a risk factor for PD supports the Kraepelinian dichotomy.
authors.affiliation: Unit for Psychiatric Research, Aalborg Psychiatric Hospital, Aarhus University Hospital, Aalborg, Denmark. sdo@rn.dk
authors.forename: Søren Dinesen
authors.initials: SD
authors.lastname: Ostergaard
authors.forename: Berit Lindum
authors.initials: BL
authors.lastname: Waltoft
authors.forename: Preben Bo
authors.initials: PB
authors.lastname: Mortensen
authors.forename: Ole
authors.initials: O
authors.lastname: Mors
mesh_terms: D000328:Adult; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D003865:Major Depressive Disorder / Q000453:epidemiology* / Q000235:genetics*; D004777:Environment; D005260:Female; D006801:Humans; D008297:Male; D011618:Psychotic Disorders / Q000453:epidemiology / Q000235:genetics; D012307:Risk Factors