IntroductionAutoantibodies in patients with polymyositis/dermatomyositis (PM/DM) are associated with unique subsets, clinical course and outcome. Anti-MJ antibodies, which recognize the nuclear protein NXP-2/MORC3, are reported in ~25% of juvenile DM. Prevalence and clinical significance of anti-MJ antibodies in adult Italian PM/DM patients were studied.MethodsSera from 58 consecutive adult Italian PM/DM patients were analyzed by immunoprecipitation of 35S-labeled K562 cells extract, ELISA (anti-MJ, Jo-1), Western blot and indirect immunofluorescence. Clinical associations were analyzed using information from medical charts.ResultsAnti-MJ antibodies were the most prevalent specificity (17%) found mainly in DM (30%, 8 cases) vs 8% of PM (2 cases, P = 0.02). Comparing 10 anti-MJ (+) vs 48 anti-MJ (-) cases, DM was more common (P = 0.03), and age at onset was younger in anti-MJ (+) (P = 0.0006). In anti-MJ (+), heliotrope rash (P = 0.01) and calcinosis (P = 0.09) were more frequent. None of them had heart or lung involvement, or malignancy. Myopathy in anti-MJ (+) patients responded well to therapy and none of them had elevated CPK at last visit (0% vs 25% in anti-MJ (-)). Only 60% of anti-MJ (+) showed immunofluorescent nuclear dots staining, despite PML localization of NXP-2/MORC3.ConclusionsAnti-MJ antibodies are the most frequent specificity in our cohort of adult Italian PM/DM. Anti-MJ (+) were associated with young onset DM, calcinosis, no internal organ involvement and good response of myopathy to therapy. Anti-MJ reported in juvenile DM is also found in adult PM/DM, and could be a new useful biomarker.

We retrospectively analysed the prevalence and clinical features associated to anti-Ku antibodies in patients affected by different autoimmune diseases. Anti-Ku antibodies are detected in 147 sera out of 7239 anti-ENA positive sera (2%). They are found in 2% of patients with systemic sclerosis (SSc) (8 out of 379), 1.8% of systemic lupus erythematosus (SLE) (7 out of 372) and 1.8% of undifferentiated connective tissue disease (UCTD) (9 out of 496) and more rarely in Sjögren Syndrome and rheumatoid arthritis. Most of anti-Ku positive patients were affected by UCTD and overlap syndromes, including polymyositis, SSc and SLE. Interstitial lung disease, myositis, articular symptoms, Raynaud's phenomenon and sicca represents the main clinical features detected in our cohort. The rate and severity of pulmonary disease is similar to those found in other SSc patients. Isolated anti-Ku were detected in about 47% of sera. No clinical differences were observed between these patients and subjects with multiple anti-nuclear specificities. However, anti-Ku are usually detected in association with other serological markers in SLE and Sjögren Syndrome, while they occurred isolated in SSc and polymyositis.

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Our study shows that antibodies to cellular antigens more rarely found in SLE are detectable in more than 15% of patients with anti-ENA antibodies. Most of them are found as single anti-ENA specificity. Anti-Ki and anti-Ku are found in a subset of disease, characterized by male gender and African origin, respectively. Clinical features of scleroderma were found only in patients with anti-Topo I.