title: Seasonal affective disorders: relevance of Icelandic and Icelandic-Canadian evidence to etiologic hypotheses.
abstract: OBJECTIVE
  This study tests the suggestion of earlier studies concerning the importance of genetic factors in the etiology of winter seasonal affective disorders (SADs) and subsyndromal winter SAD (S-SAD).
  
  
  METHODS
  Two study populations of Winnipeg, Manitoba residents were canvassed: 250 adults of wholly Icelandic descent and 1000 adults of non-Icelandic descent. We distributed the Seasonal Pattern Assessment Questionnaire by mail to these 2 populations, yielding 204 and 449 valid responses, respectively.
  
  
  RESULTS
  Rates of SAD and S-SAD proved markedly lower in the Icelandic population than those in the non-Icelandic population.
  
  
  CONCLUSIONS
  These differences seem unexplained by differences in ambient light or climate, thus indicating that genetic factors contribute to the expression of SADs. Compared with earlier findings from a group of adults of wholly Icelandic descent living in nearby rural Manitoba, the etiologic importance of as-yet-undetermined environmental factors unrelated to latitude or ambient light is also indicated.
authors.affiliation: Department of Physiology, University of Iceland, Vatnsmýrarvegur 16, IS-101 Reykjavík, Iceland. physicel@hi.is
authors.forename: Jóhann
authors.initials: J
authors.lastname: Axelsson
authors.forename: Jón G
authors.initials: JG
authors.lastname: Stefánsson
authors.forename: Andrés
authors.initials: A
authors.lastname: Magnússon
authors.forename: Helgi
authors.initials: H
authors.lastname: Sigvaldason
authors.forename: Mikael M
authors.initials: MM
authors.lastname: Karlsson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D005006:Ethnicity / Q000235:genetics*; D005260:Female; D005828:Genetics, Population; D006801:Humans; D007055:Iceland / Q000208:ethnology; D008297:Male; D008350:Manitoba / Q000453:epidemiology; D008875:Middle Aged; D016574:Seasonal Affective Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics* / Q000523:psychology