title: The relative influence of environment and genes in episodic tension-type headache.
abstract: OBJECTIVE
  To examine the relative importance of genetic and environmental influence for the development of tension-type headache by analyses of twins.
  
  
  METHODS
  The authors screened by questionnaire a population of 5,360 twins born during 1953 to 1960 from the general population for migraine and headache symptoms. The response rate of the questionnaire was 87%. All twin pairs with at least one twin of the pair reporting migraine or headache symptoms were interviewed by telephone by a physician. Correlation of liability and structural equation modeling were applied on tension-type headache.
  
  
  RESULTS
  A total of 1,417 subjects had tension-type headache equivalent to a 1-year prevalence of 62%. The male: female ratio was 1:1.24. Chronic tension-type headache was found in 49 twins corresponding to a prevalence of 2% with a male:female ratio of 1:1.21. The prevalence, pain characteristics, frequency, and duration of tension-type headache were similar to what has been found in the general Danish population. The correlation of liability of tension-type headache was low and not significantly different in monozygotic and dizygotic twin pairs: 0.21 (0.03 to 0.39), 0.08 (0 to 0.24). The best fitting model of phenotypic variation consisted of 81% non-shared environmental effects and of 19% additive genetic effects.
  
  
  CONCLUSIONS
  Environmental influence is of major importance for episodic tension-type headache and a genetic factor, if it exits, is minor. In chronic tension-type headache the genetic factor may be more important. These data clearly separate episodic tension-type headache from migraine without aura where the phenotypic variation consists of non-shared environmental effects of 39% and of 61% additive genetic effects.
authors.affiliation: Department of Neurology, Glostrup Hospital, University of Copenhagen, Denmark. ulrich@post1.tele.dk
authors.forename: Vibeke
authors.initials: V
authors.lastname: Ulrich
authors.forename: Morten
authors.initials: M
authors.lastname: Gervil
authors.forename: Jes
authors.initials: J
authors.lastname: Olesen
mesh_terms: D000328:Adult; D002908:Chronic Disease; D003718:Denmark / Q000453:epidemiology; D004200:Diseases in Twins / Q000453:epidemiology / Q000209:etiology* / Q000235:genetics; D004777:Environment; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D015995:Prevalence; D018781:Tension-Type Headache / Q000453:epidemiology / Q000209:etiology* / Q000235:genetics; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic