Coexistence of anti-HMGCR and anti-MDA5 identified by an unlabeled immunoprecipitation assay in a chinese patient cohort with myositis

Myositis-specific autoantibodies are important diagnostic and prognostic markers. The aim of our study is to detect anti-3-hydroxy 3-methylutaryl coenzyme A reductase (anti-HMGCR) antibody using novel unlabeled immunoprecipitation (IP) assay and immunoblotting in Chinese patients with myositis and to clarify the features of anti-HMGCR-positive patients. In the present study, we established novel unlabeled IP assay and immunoblotting of HMGCR C-terminus for anti-HMGCR detection. The presence of anti-HMGCR was screened in 181 Chinese patients with myositis. The sera from 12 of 181 patients were positive for anti-HMGCR. The prevalence of anti-HMGCR autoantibody in our cohorts is about 6.6%. Unexpected, coexistence of anti-HMGCR and anti-melanoma differentiation-associated protein (anti-MDA5) were identified in 4 patients with characteristic rash and interstitial lung disease (ILD), but without myasthenia and elevated serum creatine kinase (CK) levels. Other anti-HMGCR positive patients without anti-MDA5 presented with severe proximal muscle weakness. Mean serum CK levels and lactate dehydrogenase (LDH) were significantly higher in anti-HMGCR-positive patients than in antibody-negative patients (P <.05). Muscle biopsies available from 6 anti-HMGCR-positive patients were characterized with prominent myofiber necrosis and regeneration, little or none of inflammatory cell infiltrates. None of anti-HMGCR positive patients in our cohort was exposed to statins. Our data suggested that anti-HMGCR were found to coexist frequently with anti-MDA5 identified by the established unlabeled IP assay and statin exposure is rare in Chinese myositis patients with anti-HMGCR.