Clinical and Serologic Characterization of an Argentine Pediatric Myositis Cohort: Identification of a Novel Autoantibody (anti-MJ) to a 142-kDa Protein

Abstract

Objective.Autoantibodies are frequently found in adult patients with polymyositis (PM), dermato-myositis (DM), and overlap myositis disorders. They are less common in pediatric patients with myositis. We investigated the autoantibody pattern in a pediatric Argentine Caucasian cohort to characterize novel autoantibodies.Methods.Sera from children that satisfied published criteria for idiopathic inflammatory myopathy were analyzed for autoantibodies by RNA and protein immunoprecipitation and immunoblotting techniques. Routine myositis-specific and myositis-associated autoantibodies as well as autoantibody specificities were determined.Results.We tested sera from 64 consecutive pediatric myositis patients, including 40 with juvenile DM, 7 with juvenile PM, and 17 with overlap myositis syndromes. Sixteen (25%) patients were found to have anti-MJ autoantibody exclusively, which appears to identify a subset of pediatric myositis patients with severe disease characterized by muscle contractures and atrophy and significant compromise of functional status. Fourteen (22%) patients were found to have an antibody targeting 2 proteins of 155 and 140 kDa. Other myositis-specific autoantibodies were uncommon in this pediatric cohort.Conclusion.A newly recognized autoantibody, anti-MJ, was the most common antibody found in this Argentine pediatric cohort. The clinical features indicated that this antibody is distinct from other reported antibodies in pediatric patients with myositis.