title: A subset of systemic sclerosis but not of systemic lupus erythematosus is defined by isolated anti-Ku autoantibodies.
abstract: OBJECTIVE
  We aimed to analyse the annual incidence of anti-Ku antibodies and to study their clinical associations in patients mainly affected by systemic sclerosis (SSc) and systemic lupus erythematosus (SLE) overlap diseases.
  
  
  METHODS
  Anti-Ku were detected by counterimmunoelectrophoresis in a total of 203 sera during 14 years of anti-ENA detection. Anti-Ku+ sera belong to 46 patients, mostly affected by UCTD (12 cases), SSc spectrum diseases (13 cases), including SSc/PM, SSc/DM and SSc; and SLE spectrum diseases (9 cases), including SLE, SLE/APS, SLE/SS, SLE/PM.
  
  
  RESULTS
  Anti-Ku antibodies represent 2% of all anti-ENA positive sera, and are found in 1.3-3% of anti-ENA positive sera per year. Anti-Ku+ SSc represents 2% of all SSc patients. All anti-Ku+ SSc spectrum diseases showed a limited cutaneous disease; myositis, dysphagia and isolated anti-Ku in more than 70% of cases. Interstitial lung disease (ILD) was found in 54% of SSc patients, frequently with mild functional impairment. When compared with other limited SSc cases, anti-Ku+ SSc showed a higher rate of male patients, arthritis, myositis and ILD. A lower rate of digital ulcers was found, although both groups showed the same rate of SSc pattern at nailfold capillaroscopy. Anti-Ku+ SLE patients (representing 1.5% of all SLE) showed cutaneous features, Raynaud's phenomenon, multiple autoantibodies, without major organ manifestations. Isolated anti-Ku+ patients significantly show a diagnosis within SSc spectrum diseases, with arthralgias, Raynaud's phenomenon, dysphagia, ILD, myositis and sclerodactyly.
  
  
  CONCLUSIONS
  In SLE spectrum diseases, anti-Ku are found associated with other autoantibodies, without a peculiar clinical profile, except for Raynaud's phenomenon and severe alterations of capillary bed. In SSc anti-Ku are frequently associated with myositis and ILD, mostly found as isolated autoantibodies.
authors.affiliation: Rheumatology and Clinical Immunology Unit, Spedali Civili, piazzale Spedali Civili 1, 25100 Brescia, Italy. ilariacava@virgilio.it
authors.forename: Ilaria
authors.initials: I
authors.lastname: Cavazzana
authors.forename: Micaela
authors.initials: M
authors.lastname: Fredi
authors.forename: Mara
authors.initials: M
authors.lastname: Taraborelli
authors.forename: Marzia
authors.initials: M
authors.lastname: Quinzanini
authors.forename: Angela
authors.initials: A
authors.lastname: Tincani
authors.forename: Franco
authors.initials: F
authors.lastname: Franceschini
mesh_terms: D000328:Adult; D000368:Aged; D001323:Autoantibodies / Q000097:blood / Q000276:immunology*; D004265:DNA Helicases / Q000276:immunology*; D005260:Female; D006801:Humans; D000072200:Ku Autoantigen; D008180:Lupus Erythematosus, Systemic / Q000453:epidemiology* / Q000276:immunology*; D008297:Male; D020678:Microscopic Angioscopy; D008875:Middle Aged; D009220:Myositis / Q000453:epidemiology / Q000276:immunology; D011928:Raynaud Disease / Q000453:epidemiology / Q000276:immunology; D012307:Risk Factors; D012595:Scleroderma, Systemic / Q000453:epidemiology* / Q000276:immunology*; D016036:Seroepidemiologic Studies; D055815:Young Adult
chemical_list: D001323:Autoantibodies; D004265:DNA Helicases; C106893:XRCC5 protein, human; D000072200:Ku Autoantigen