Nuclear Matrix Protein Antibody In Idiopathic Inflammatory Myopathies Resistance Distribution And Clinical Significance

Objective:To determine the serum levels of anti-NXP-2antibodies and their clinical association in patients with idiopathic inflammatory myopathies(IIM).Methods:Serum from198Chinese patients with IIM including15Juvenile dermatomyositis(JDM),133dermatomyositis(DM) and50polymyositis(PM), other connective tissue diseases including70systemic lupus erythematosus(SLE),60rheumatoid arthritis(RA),25systemic sclerosis(SSc),46primary Sjogren’s syndrome(PSS),10mixed connective tissue disease(MCTD) and60healthy controls were measured by enzyme linked immunosorbent assay. Positive serums were further examined by immunoprecipitation assays. We analyzed the distribution of these autoantibodies in each groups and evaluated the association between autoantibodies and clinical features of IIM.Results:Serum anti-NXP-2antibodies positive rate in IIM were5%. Patients with JDM were20%, with dermatomyositis3.7%, with polymyositis4%, respectively. There were Statistical differences of positive rate withinJDM, DM and PM(P=0.043). No patients with other CTD patients as well as healthy controls were positive for this autoantibody.Anti-NXP2-positive IIM patients had significantly younger age than anti-NXP2-negative IIM patients(t=-2.09, P<0.05). The incidence of calcinosis was significantly higher in the anti-NXP2positive group than anti-NXP2negative group(P<0.01).There was no significant difference between the sex ratio, arthritis, rash, dysphagia, myalgia, myasthenia, Raynaud phenomenon, interstitial lung disease and incidence of cancer(P>0.05). In laboratory examination, the levels of aspartate aminotransferase, IgA, C3of anti-NXP2-positive IIM patients were significantly higher than anti-NXP2-negative patients(P<0.05). However there was no significant difference in serum creatine kinase, lactate dehydrogenase, hydroxybutyrate dehydrogenase, alanine aminotransferase, γ-glutamyltranspeptidase, erythrocyte sedimentation rate, C-reactive Proteinand the positive rate of tumor markers(P>0.05). Among the3anti-NXP-2positive JDM patients, two patients showed calcinosis, oneof them who died later had myasthenia and rapid progress.Conclusion:This study first reported the serum levels of anti-NXP-2antibodies in Chinese patients with IIM and other connective tissue diseases. We found that anti-NXP2-antibody only exists in patients with IIM. Anti-NXP2-antibodies were associated with young onset of IIM and calcinosis.