Background/Purpose: To determine the sera levels of anti-NXP-2 antibodies and their clinical association in Chinese patients with idiopathic inflammatory myopathies(IIM).

Methods: Sera from 198 Chinese patients with IIM including 15 Juvenile dermatomyositis(JDM), 133 dermatomyositis(DM) and 50 polymyositis(PM), other connective tissue diseases(CTD) including 70 systemic lupus erythematosus(SLE), 60 rheumatoid arthritis(RA), 25 systemic sclerosis(SSc), 46 primary Sjogren’s syndrome(PSS), 10 mixed connective tissue disease(MCTD) and 60 healthy controls were measured by enzyme linked immunosorbent assay. The positive sera were further examined by immunoprecipitation assay. We analyzed the distribution of these autoantibodies in each groups and evaluated the association between autoantibodies and clinical features of IIM.

Results: The positive rate of anti-NXP-2 autoantibodies in IIM patients was 5%, patients with JDM 20%, DM 3.7% and PM 4%, respectively. The positive rate of anti-NXP-2 autoantibodies were statistical differences within JDM, DM and PM groups(P=0.043). There was no positive for the antibodies from patients with other CTD as well as healthy controls. Anti-NXP-2-positive patients had significantly younger age compared with anti-NXP-2-negative patients(t=-2.09,P<0.05). The incidence of calcinosis in the anti-NXP2-positive patients was significantly higher than that in the negative patients(P<0.01).There were no statistical differences between positive and negative groups for gender, duration, arthritis, rash, dysphagia, myalgia, myasthenia, Raynaud’s phenomenon, interstitial lung disease and concomitant with cancer(P>0.05). In laboratory examination, the sera levels of aspartate aminotransferase, IgA, complement C3 were significantly increased in anti-NXP-2-positive patients than those in anti-NXP-2-negative patients(P<0.05). However, there was no significantly statistical differences between two groups for sera levels of creatine kinase, lactate dehydrogenase, hydroxybutyrate dehydrogenase, alanine aminotransferase, γ-glutamyltranspeptidase, erythrocyte sedimentation rate, C-reactive Protein and the positive rate of tumor markers(P>0.05). Among the three anti-NXP-2-positive JDM patients, two patients showed calcinosis and myasthenia, one of them who died 10 months later had increasing level of anti-NXP-2 autoantidodies, severe myasthenia and rapid progress.

Conclusion: This study first reported the sera levels of anti-NXP-2 autoantibodies in Chinese patients with IIM and other CTD. We found that anti-NXP-2 autoantibodies only exist in patients with IIM. Anti-NXP-2 autoantibodies were associated with young-onset IIM and calcinosis.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-prevalence-and-clinical-usefulness-of-anti-nxp-2-autoantibodies-in-chinese-patients-with-idiopathic-inflammatory-myopathies/