title: A twin study of rheumatoid arthritis in the Japanese population.
abstract: OBJECTIVE
  Rheumatoid arthritis (RA) is the most common immune-related inflammatory arthritis affecting 0.5-1.0% of the population. Both genetic and environmental factors are associated with RA onset. Twin studies reported from European countries estimated heritability of RA as 53-65%. However, no twin studies have been reported from Asian countries.
  
  
  METHODS
  We collected a total of 43 monozygotic and 43 dizygotic twins from 7550 patients with RA and obtained information of RA status in the twin pairs. We characterized RA patients whose twin siblings had RA. Variance components analysis was performed to estimate heritability in RA in the Japanese population.
  
  
  RESULTS
  Four and one patients with RA over 43 monozygotic (9.3%) and 43 dizygotic twins (2.3%), respectively, had twin siblings with RA. All the patients whose information of sero-positivity was available and whose twin siblings had RA were sero-positive. Heritability of RA was estimated as 62.2% and 56.1% in the AE and ACE models, respectively. The estimated heritability was comparable with those reported in the Europeans, compatible with previous overlap of RA susceptibility genes between Japanese and European populations.
  
  
  CONCLUSIONS
  Heritability of RA onset in the Japanese population is estimated to be comparable with that in European populations.
authors.affiliation: a Center for Genomic Medicine , Kyoto University Graduate School of Medicine , Kyoto , Japan .|b Center for the Promotion of Interdisciplinary Education and Research , Kyoto University , Kyoto , Japan .|c Division of Rheumatology, Immunology, and Allergy , Brigham and Women's Hospital, Harvard Medical School , Boston , MA , USA .|d Division of Genetics , Brigham and Women's Hospital, Harvard Medical School , Boston , MA , USA .|e Program in Medical and Population Genetics , Broad Institute , Cambridge , MA , USA .
authors.forename: Chikashi
authors.initials: C
authors.lastname: Terao
authors.affiliation: f Institute of Rheumatology, Tokyo Women's Medical University , Tokyo , Japan .
authors.forename: Katsunori
authors.initials: K
authors.lastname: Ikari
authors.affiliation: g First Department of Internal Medicine, School of Medicine , University of Occupational & Environmental Health , Kitakyushu , Japan .
authors.forename: Shingo
authors.initials: S
authors.lastname: Nakayamada
authors.affiliation: h Graduate School of Education , Kyoto University , Kyoto , Japan .
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Takahashi
authors.affiliation: a Center for Genomic Medicine , Kyoto University Graduate School of Medicine , Kyoto , Japan .
authors.forename: Ryo
authors.initials: R
authors.lastname: Yamada
authors.affiliation: i Department of Rheumatology and Clinical Immunology , Kyoto University Graduate School of Medicine , Kyoto , Japan , and.
authors.forename: Koichiro
authors.initials: K
authors.lastname: Ohmura
authors.affiliation: j Department of the Control for Rheumatic Diseases , Kyoto University Graduate School of Medicine , Kyoto , Japan.
authors.forename: Motomu
authors.initials: M
authors.lastname: Hashimoto
authors.affiliation: j Department of the Control for Rheumatic Diseases , Kyoto University Graduate School of Medicine , Kyoto , Japan.
authors.forename: Moritoshi
authors.initials: M
authors.lastname: Furu
authors.affiliation: j Department of the Control for Rheumatic Diseases , Kyoto University Graduate School of Medicine , Kyoto , Japan.
authors.forename: Hiromu
authors.initials: H
authors.lastname: Ito
authors.affiliation: j Department of the Control for Rheumatic Diseases , Kyoto University Graduate School of Medicine , Kyoto , Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Fujii
authors.affiliation: f Institute of Rheumatology, Tokyo Women's Medical University , Tokyo , Japan .
authors.forename: Shinji
authors.initials: S
authors.lastname: Yoshida
authors.affiliation: g First Department of Internal Medicine, School of Medicine , University of Occupational & Environmental Health , Kitakyushu , Japan .
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Saito
authors.affiliation: f Institute of Rheumatology, Tokyo Women's Medical University , Tokyo , Japan .
authors.forename: Atsuo
authors.initials: A
authors.lastname: Taniguchi
authors.affiliation: f Institute of Rheumatology, Tokyo Women's Medical University , Tokyo , Japan .
authors.forename: Shigeki
authors.initials: S
authors.lastname: Momohara
authors.affiliation: b Center for the Promotion of Interdisciplinary Education and Research , Kyoto University , Kyoto , Japan .
authors.forename: Hisashi
authors.initials: H
authors.lastname: Yamanaka
authors.affiliation: i Department of Rheumatology and Clinical Immunology , Kyoto University Graduate School of Medicine , Kyoto , Japan , and.
authors.forename: Tsuneyo
authors.initials: T
authors.lastname: Mimori
authors.affiliation: a Center for Genomic Medicine , Kyoto University Graduate School of Medicine , Kyoto , Japan .
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Matsuda
mesh_terms: D001172:Arthritis, Rheumatoid / Q000453:epidemiology / Q000235:genetics*; D004200:Diseases in Twins / Q000453:epidemiology / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D015995:Prevalence
keywords: Epidemiological study; Genetics and heritability; Rheumatoid arthritis