title: Relative importance of genetic effects in rheumatoid arthritis: historical cohort study of Danish nationwide twin population.
abstract: OBJECTIVE
  To determine the relative importance of environmental and genetic effects in the development of rheumatoid arthritis.
  
  
  METHODS
  Historical cohort study with record linkage between a twin registry and the Danish discharge registry as well as the Danish national registry of deaths used to estimate completeness.
  
  
  METHODS
  Two population based nationwide twin birth cohorts.
  
  
  METHODS
  37 338 twins were sent a questionnaire about rheumatic diseases. Self reported rheumatoid arthritis was verified by clinical examination and from medical records.
  
  
  METHODS
  The probandwise concordance rate of rheumatoid arthritis in monozygotic and dizygotic twins.
  
  
  RESULTS
  The response rate was 84.7%. Rheumatoid arthritis was verified in 13 monozygotic and 36 dizygotic twins. There were no concordant monozygotic twin pairs and two concordant dizygotic twin pairs. Based on capture-recapture methods the probability of ascertainment was 78.3%. The probandwise concordance rate was 0 (95% confidence interval 0 to 24.7) in monozygotic twins and 8.8 (1.9 to 23.7) in dizygotic twins.
  
  
  CONCLUSIONS
  Genes are of minor importance in the development of rheumatoid arthritis.
authors.affiliation: Department of Rheumatology, Odense University Hospital, 5000 Odense C, Denmark. a.svendsen@winsloew.ou.dk
authors.forename: Anders J
authors.initials: AJ
authors.lastname: Svendsen
authors.forename: Niels V
authors.initials: NV
authors.lastname: Holm
authors.forename: Kirsten
authors.initials: K
authors.lastname: Kyvik
authors.forename: Per Hyltoft
authors.initials: PH
authors.lastname: Petersen
authors.forename: Peter
authors.initials: P
authors.lastname: Junker
mesh_terms: D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000235:genetics*; D015331:Cohort Studies; D003718:Denmark; D004200:Diseases in Twins / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D012042:Registries; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic