title: Do risk factors for schizophrenia predispose to emigration?
abstract: OBJECTIVE
  Increased incidence rates of schizophrenia in immigrants still lack a satisfactory explanation. The aim of this study was to examine the hypothesis that risk factors for schizophrenia also increase the risk of emigration to a foreign country. If valid, Danes emigrating from Denmark carry a higher predisposition to develop schizophrenia compared to Danes living in Denmark.
  
  
  METHODS
  Utilizing data from the Danish Civil Registration System, we established a population-based cohort of 1.10 million native Danes. We assessed relative risks of emigration to a foreign country in relation to sex, age, urban birth, parental age, and a history of mental illness.
  
  
  RESULTS
  Urban birth in Denmark was a significant predictor of emigration to a foreign country. A maternal history of psychiatric contact during childhood and a parental history of bipolar affective disorder increased the risks of emigration. A personal history of mental illness decreased the risk of emigration, mostly for people diagnosed with schizophrenia.
  
  
  CONCLUSIONS
  Our study provided evidence that Danish emigrants residing in a foreign country have both a higher predisposition of schizophrenia due to differential exposure to birth in urban areas and a lower predisposition of schizophrenia due to differential exposure to a history of mental illness. Although competing selection mechanisms operate, the combined effect of these different selection mechanisms was limited, thus suggesting a potential role for yet to be identified adverse environmental effects operating either before or after emigration.
authors.affiliation: National Centre for Register-based Research, Aarhus University, Taasingegade 1, 8000 Aarhus C, Denmark. cbp@ncrr.dk
authors.forename: Carsten Bøcker
authors.initials: CB
authors.lastname: Pedersen
authors.forename: Preben Bo
authors.initials: PB
authors.lastname: Mortensen
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Cantor-Graae
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D003718:Denmark; D004641:Emigration and Immigration; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D015995:Prevalence; D012189:Retrospective Studies; D012307:Risk Factors; D012559:Schizophrenia / Q000453:epidemiology* / Q000208:ethnology / Q000209:etiology*; D012680:Sensitivity and Specificity; D012737:Sex Factors; D055815:Young Adult