Cytoplasmic 5′-nucleotidase autoantibodies in inclusion body myositis: Isotypes and diagnostic utility


  • Steven A. Greenberg MD

    Corresponding author
    1. Department of Neurology, Brigham and Women's Hospital and Children's Hospital Informatics Program, Harvard Medical School and Harvard-MIT Division of Health Sciences and Technology, Boston, Massachusetts, USA
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Introduction: Recent studies have identified circulating immunoglobulin (Ig) G autoantibodies against cytoplasmic 5′-nucleotidase 1A (cN1A; NT5C1A) in patients with inclusion body myositis (IBM), whose detection provides for an IBM blood diagnostic test. Whether or not anti-cN1A autoantibody isotypes other than IgG are present in IBM has not previously been reported. Methods: Plasma and serum samples from 205 patients (50 with and155 without IBM) were studied for the presence of IgM and IgA, in addition to IgG, anti-cN1A autoantibodies using immunoblots and enzyme-linked immunoassays (ELISAs). Results: IgM, IgA, and IgG anti-cN1A autoantibodies were detected by ELISA with similar sensitivities (49–53%) and specificities (94–96%), but with differing patterns of autoantibody isotype presence. Combination assays of all 3 autoantibody levels improved diagnostic sensitivity to 76%. Conclusions: In addition to previously recognized IgG anti-cN1A autoantibodies, IBM patients have circulating IgM and IgA anti-cN1A autoantibodies. Differing patterns of these isotypes may be present and useful for diagnosis. Muscle Nerve 50: 488–492, 2014