title: The relative role of genetic and environmental factors in migraine without aura.
abstract: OBJECTIVE
  To clarify the relative role of genetic and environmental factors in the etiology of migraine without aura (MO).
  
  
  METHODS
  The study population consisted of 5,360 twins, 1,013 monozygotic (MZ) and 1,667 same-gender dizygotic (DZ) twin pairs, from the population-based Danish Twin Registry. A total of 87% completed a simple validated questionnaire screening for migraine. All twin pairs, in whom at least one twin had self-reported migraine or severe headache with accompanying symptoms, were interviewed via telephone by a physician. Ninety percent of the eligible twins were interviewed. Probandwise concordance rates and correlations in liability were calculated, and structural equation model-fitting analyses were applied to quantitate the relative role of genetic and environmental factors in the etiology of MO.
  
  
  RESULTS
  The probandwise concordance rate was higher in MZ than DZ twin pairs (0.43 versus 0.31; 95% CI, 0.36 to 0.49 versus 0.26 to 0.36). The correlation in liability was higher in MZ than in DZ twin pairs (0.62 versus 0.41; 95% CI, 0.50 to 0.74 versus 0.29 to 0.53). Structural equation model fitting indicated a highly significant genetic component, because a model with both genetic and environmental components fitted significantly better than a model with only environmental components. The best fitting model implied that the liability to MO resulted from additive genetic effects (61%; 95% CI, 49 to 71%)) and individual-specific environmental effects (39%; 95% CI, 29 to 51%).
  
  
  CONCLUSIONS
  This study indicates that genetic factors play a role in the etiology of migraine without aura. The genetic variability is additive, with a negligible contribution of nonadditive genetic effects. The genetic contributions were similar in men and women despite a higher prevalence in women. Environmental factors are equally important and these factors are individual to the migraineurs.
authors.affiliation: Department of Neurology, Glostrup Hospital, University of Copenhagen, Glostrup, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Gervil
authors.forename: V
authors.initials: V
authors.lastname: Ulrich
authors.forename: J
authors.initials: J
authors.lastname: Kaprio
authors.forename: J
authors.initials: J
authors.lastname: Olesen
authors.forename: M B
authors.initials: MB
authors.lastname: Russell
mesh_terms: D000293:Adolescent; D000328:Adult; D003718:Denmark; D004200:Diseases in Twins; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008881:Migraine Disorders / Q000235:genetics* / Q000503:physiopathology*; D008959:Models, Neurological; D011795:Surveys and Questionnaires