title: Epidemiologic study of clinically amyopathic dermatomyositis and anti-melanoma differentiation-associated gene 5 antibodies in central Japan.
abstract: BACKGROUND
  Several reports have found the onset or activity of inflammatory myopathies to show spatial clustering and seasonal association. We recently detected autoantibodies against melanoma differentiation-associated gene 5 (MDA-5) in more than 20% of patients with dermatomyositis. Anti-MDA-5 antibodies were associated with the presence of rapidly progressive interstitial lung disease in clinically amyopathic dermatomyositis (CADM). The present study aims to assess the growing prevalence of CADM and the geographical incidence of anti-MDA-5-positive patients.
  
  
  METHODS
  We reviewed medical charts and examined the presence of anti-MDA-5 antibodies in 95 patients, including 36 CADM patients. Sera were obtained from 1994 through 2011. Statistical analyses were performed to assess whether CADM development and the presence of anti-MDA-5 antibodies were associated with various parameters, including age at disease onset, season of onset, annual positivity, and population of resident city.
  
  
  RESULTS
  Tertiles based on the year when the sera were collected showed increasing tendencies of CADM and anti-MDA-5-positive patients among all of the dermatomyositis patients. From 1994 to 2010, the relative prevalence of CADM and anti-MDA-5 antibody-positive patients significantly increased. Interestingly, the presence of anti-MDA-5 antibodies in 26 patients was inversely associated with the population of their city of residence.
  
  
  CONCLUSIONS
  This is the first study to examine the distribution of anti-MDA-5-positive dermatomyositis phenotypes in Japan. Regional differences in the incidences of these phenotypes would suggest that environmental factors contribute to the production of antibodies against MDA-5, which triggers innate antiviral responses.
authors.affiliation: Division of Connective Tissue Disease and Autoimmunity, Department of Dermatology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan. ymuro@med.nagoya-u.ac.jp
authors.forename: Yoshinao
authors.initials: Y
authors.lastname: Muro
authors.forename: Kazumitsu
authors.initials: K
authors.lastname: Sugiura
authors.forename: Kei
authors.initials: K
authors.lastname: Hoshino
authors.forename: Masashi
authors.initials: M
authors.lastname: Akiyama
authors.forename: Koji
authors.initials: K
authors.lastname: Tamakoshi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000097:blood / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D053487:DEAD-box RNA Helicases / Q000276:immunology*; D003882:Dermatomyositis / Q000097:blood / Q000453:epidemiology / Q000276:immunology*; D005260:Female; D005843:Geography; D006801:Humans; D015994:Incidence; D000072640:Interferon-Induced Helicase, IFIH1; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D012621:Seasons; D055815:Young Adult
chemical_list: D001323:Autoantibodies; C452815:IFIH1 protein, human; D053487:DEAD-box RNA Helicases; D000072640:Interferon-Induced Helicase, IFIH1