title: Prevalence, concordance, and heritability of Scheuermann kyphosis based on a study of twins.
abstract: BACKGROUND
  The purpose of this study was to establish a cohort of symptomatic twins with Scheuermann kyphosis to provide estimates of prevalence, concordance, odds ratio, and heritability. These estimates indicate to what extent genetic factors contribute to the etiology of this disease.
  
  
  METHODS
  The Odense-based Danish Twin Registry is unique in that it contains data on all 73,000 twin pairs born in Denmark over the last 130 years. For the present study, all 46,418 twins born from 1931 through 1982 received a seventeen-page questionnaire, in which one question was "Have you been diagnosed with Scheuermann disease by a doctor"? The prevalence of self-reported Scheuermann disease was calculated, with the total number of answers used as the general population. Pairwise and probandwise concordance, odds ratio, tetrachoric correlations, and heritability were calculated.
  
  
  RESULTS
  We found that the overall prevalence of Scheuermann disease was 2.8%, with a prevalence of 2.1% among women and 3.6% among men (p < 0.0001). The pairwise concordance for monozygotic twins was 0.19 compared with 0.07 for dizygotic twins. The probandwise concordance was 0.31 for monozygotic twins and 0.13 for dizygotic twins. The odds ratios were 32.92 and 6.25 in the monozygotic and dizygotic twins, respectively. These differences were significant (p < 0.01). Heritability was 74%.
  
  
  CONCLUSIONS
  In a large cohort of twins that included almost 35,000 individuals, the self-reported overall prevalence of Scheuermann disease was 2.8% and the male-to-female ratio was close to 2:1. Because the pairwise and probandwise concordance and the odds ratio were two to three times higher in monozygotic than in dizygotic twins and the heritability was high, we concluded that there is a major genetic contribution to the etiology of Scheuermann disease.
authors.affiliation: Department of Orthopaedic Surgery, The Spine Section, University Hospital of Odense, Soender Boulevard 29, DK-5000 Odense, Denmark. Damborg@Dadlnet.dk
authors.forename: Frank
authors.initials: F
authors.lastname: Damborg
authors.forename: Vilhelm
authors.initials: V
authors.lastname: Engell
authors.forename: Mikkel
authors.initials: M
authors.lastname: Andersen
authors.forename: Kirsten Ohm
authors.initials: KO
authors.lastname: Kyvik
authors.forename: Karsten
authors.initials: K
authors.lastname: Thomsen
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D015897:Comorbidity; D003718:Denmark / Q000453:epidemiology; D004200:Diseases in Twins / Q000453:epidemiology* / Q000235:genetics*; D005260:Female; D006801:Humans; D007738:Kyphosis / Q000453:epidemiology* / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D015995:Prevalence; D012544:Scheuermann Disease / Q000453:epidemiology* / Q000235:genetics*