title: Family history of psychiatric illness as a risk factor for schizoaffective disorder: a Danish register-based cohort study.
abstract: BACKGROUND
  Schizoaffective disorder may be related to both schizophrenia and bipolar disorders, but no population-based studies, to our knowledge, have investigated this association in families.
  
  
  OBJECTIVE
  To determine whether a psychiatric history of schizoaffective disorder, bipolar disorder, or schizophrenia among parents and siblings is a risk factor for developing a schizoaffective disorder, and whether a specific pattern of family history of psychiatric illness exists in persons with schizoaffective disorder compared with persons with bipolar disorder or schizophrenia.
  
  
  METHODS
  Register-based cohort study.
  
  
  METHODS
  Denmark.
  
  
  METHODS
  The 2.4 million persons born in Denmark after 1952.
  
  
  METHODS
  Relative risks of the 3 illnesses estimated by Poisson regression.
  
  
  RESULTS
  In total, 1925 persons had a schizoaffective disorder, 3721 had a bipolar disorder, and 12 501 had schizophrenia. The relative risk of schizoaffective disorder was 2.76 (95% confidence interval, 2.49-3.06) if a first-degree relative had a history of mental illness compared with a person with no first-degree relatives with such a history. There was an additional risk (95% confidence interval) of 2.57 (2.11-3.13), 3.23 (2.63-3.95), or 1.92 (1.43-2.57) if the first-degree relative had schizophrenia, bipolar disorder, or schizoaffective disorder, respectively, compared with other psychiatric admissions. When bipolar disorder was the outcome, bipolar disorder in first-degree relatives was by far the significantly strongest risk factor. When schizophrenia was the outcome, the significantly strongest risk factor was schizophrenia among first-degree relatives.
  
  
  CONCLUSIONS
  Schizoaffective disorder is not simply a subgroup of either bipolar disorder or schizophrenia but may be genetically linked to both, with schizoaffective disorder being a subtype of each or a genetic intermediate form.
authors.affiliation: National Centre for Register-Based Research, University of Aarhus, Taasingegade 1, DK-8000 Aarhus C, Denmark. tml@ncrr.dk
authors.forename: Thomas Munk
authors.initials: TM
authors.lastname: Laursen
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Labouriau
authors.forename: Rasmus W
authors.initials: RW
authors.lastname: Licht
authors.forename: Aksel
authors.initials: A
authors.lastname: Bertelsen
authors.forename: Trine
authors.initials: T
authors.lastname: Munk-Olsen
authors.forename: Preben Bo
authors.initials: PB
authors.lastname: Mortensen
mesh_terms: D001714:Bipolar Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005192:Family Health; D005260:Female; D005500:Follow-Up Studies; D020022:Genetic Predisposition to Disease / Q000453:epidemiology / Q000235:genetics; D006801:Humans; D038801:International Classification of Diseases; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D001523:Mental Disorders / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics*; D008875:Middle Aged; D010375:Pedigree; D016012:Poisson Distribution; D011618:Psychotic Disorders / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics; D012042:Registries; D012306:Risk; D012307:Risk Factors; D012559:Schizophrenia / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics