title: The prevalence and incidence of mixed connective tissue disease: a national multicentre survey of Norwegian patients.
abstract: OBJECTIVE
  Mixed connective tissue disease (MCTD) is an immune-mediated, systemic disorder of unknown aetiology. As the epidemiology of the disease is largely unknown, the authors performed a nationwide cross-sectional retrospective study to assess the prevalence and incidence of MCTD in Norway.
  
  
  METHODS
  Every adult patient (≥ 18 years) with MCTD seen at one of the departments of rheumatology was reviewed for inclusion. Only patients who satisfied the following four criteria were included: clinical diagnosis of MCTD verified by a rheumatologist; positive serum anti-ribonucleoprotein antibody test; fulfilment of at least one of three of following criteria sets: the modified Sharp's criteria, the criteria of Alarcón-Segovia and Villareal and those of Kasukawa; and exclusion of other connective tissue diseases.
  
  
  RESULTS
  The four inclusion criteria were fulfilled by 147 adult Caucasian patients. The female to male ratio was 3.3 and the mean age at diagnosis of adult-onset MCTD was 37.9 years (95% CI 35.3 to 40.4 years). At the end of 2008, the point prevalence of living adult MCTD patients in Norway was 3.8 (95% CI 3.2 to 4.4) per 100,000 adults. The incidence of adult-onset MCTD in Norway during the period from 1996 to 2005 was 2.1 (95% CI 1.7 to 2.5) per million per year.
  
  
  CONCLUSIONS
  MCTD has a female predominance and the incidence and prevalence of MCTD is low, and lower than reported figures for polymyositis, dermatomyositis, systemic sclerosis and systemic lupus erythematosus. The prevalence estimates were similar across the three criteria sets of MCTD.
authors.affiliation: Department of Rheumatology, Oslo University Hospital Rikshospitalet, Oslo, Norway. ragunnar@gmail.com
authors.forename: Ragnar
authors.initials: R
authors.lastname: Gunnarsson
authors.forename: Oyvind
authors.initials: O
authors.lastname: Molberg
authors.forename: Inge-Margrethe
authors.initials: IM
authors.lastname: Gilboe
authors.forename: Jan Tore
authors.initials: JT
authors.lastname: Gran
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000367:Age Factors; D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D000974:Antibodies, Antinuclear / Q000097:blood; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008947:Mixed Connective Tissue Disease / Q000453:epidemiology* / Q000276:immunology; D009664:Norway / Q000453:epidemiology; D012261:Ribonucleoproteins / Q000276:immunology; D055815:Young Adult
chemical_list: D000974:Antibodies, Antinuclear; D012261:Ribonucleoproteins