Calcinosis and malignancy are rare in Chinese adult patients with myositis and nuclear matrix protein 2 antibodies identified by an unlabeled immunoprecipitation assay.

Autoantibodies in patients with myositis may associate with specific clinical manifestations. This study aimed to identify a subset of patients with myositis carrying antinuclear matrix protein 2 (anti-NXP-2) antibodies using an unlabeled immunoprecipitation (IP) assay, and clarify the features of these patients in a Chinese cohort. We developed novel methods for unlabeled protein IP and immunoblotting of Myc-tagged truncated NXP-2 fragments for anti-NXP-2 detection. The sera of 120 Chinese adult patients with myositis were screened for anti-NXP-2 by IP and immunoblot. Anti-NXP-2 antibodies were detected in 10 of the 120 patients (8.3%) using the established unlabeled protein IP and immunoblotting, with 70% (7/10) exhibiting either heliotrope rash or Gottron's papules. All 10 anti-NXP-2-positive patients exhibited myopathy and 60% complained of dysphagia. Severe diffuse calcinosis (10%) and nasopharyngeal carcinoma (10%) were each only present in single anti-NXP-2-positive patients with myositis. Antibodies against Ro-52 were found in four living but not in three deceased anti-NXP-2-positive patients. A comprehensive review of 13 anti-NXP-2 studies demonstrated markedly lower anti-NXP-2 prevalence among adult patients with myositis and lower association of anti-NXP-2 with calcinosis in Japan, China, and Hungary than in the USA and Italy. Anti-NXP-2 antibody association with internal malignancy in adult patients varied from 0 to 50% across different studies. A novel IP assay was developed to detect patients with myositis expressing anti-NXP-2. Calcinosis and malignancy are rare in Chinese adult patients with myositis positive for anti-NXP-2. Literature review indicated highest anti-NXP-2 prevalence and association of anti-NXP-2 with calcinosis in US and Italian myositis cohorts.