Cytosolic 5′-nucleotidase 1A autoimmunity in sporadic inclusion body myositis

Authors

  • H. Benjamin Larman PhD,

    1. Department of Genetics, Harvard University Medical School, Boston, MA
    2. Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Boston, MA
    3. Howard Hughes Medical Institute, Chevy Chase, MD
    4. Division of Health Sciences and Technology, Harvard–Massachusetts Institute of Technology, Cambridge, MA
    5. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA
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    • H. Benjamin Larman and Mohammad Salajegheh are co-first authors

  • Mohammad Salajegheh MD,

    1. Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA
    2. Children's Hospital Informatics Program, Harvard Medical School, Boston, MA
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    • H. Benjamin Larman and Mohammad Salajegheh are co-first authors

  • Remedios Nazareno BS,

    1. Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA
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  • Theresa Lam BA,

    1. Children's Hospital Informatics Program, Harvard Medical School, Boston, MA
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  • John Sauld,

    1. Proteomics Center at Children's Hospital, Boston, Harvard Medical School, Boston, MA
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  • Hanno Steen PhD,

    1. Proteomics Center at Children's Hospital, Boston, Harvard Medical School, Boston, MA
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  • Sek Won Kong MD,

    1. Children's Hospital Informatics Program, Harvard Medical School, Boston, MA
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  • Jack L. Pinkus PhD,

    1. Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA
    2. Children's Hospital Informatics Program, Harvard Medical School, Boston, MA
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  • Anthony A. Amato MD,

    1. Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA
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  • Stephen J. Elledge PhD,

    1. Department of Genetics, Harvard University Medical School, Boston, MA
    2. Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Boston, MA
    3. Howard Hughes Medical Institute, Chevy Chase, MD
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  • Steven A. Greenberg MD

    Corresponding author
    1. Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA
    2. Children's Hospital Informatics Program, Harvard Medical School, Boston, MA
    • Department of Genetics, Harvard University Medical School, Boston, MA
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Address correspondence to Dr Greenberg, Department of Neurology, Brigham and Women's Hospital, Harvard Medical School, 75 Francis Street, Boston, MA 02115. E-mail: sagreenberg@partners.org

Abstract

Objective

We previously identified a circulating autoantibody against a 43 kDa muscle autoantigen in sporadic inclusion body myositis (IBM) and demonstrated the feasibility of an IBM diagnostic blood test. Here, we sought to identify the molecular target of this IBM autoantibody, understand the relationship between IBM autoimmunity and muscle degeneration, and develop an IBM blood test with high diagnostic accuracy.

Methods

IBM blood samples were screened using mass spectrometry and a synthetic human peptidome. Plasma and serum samples (N=200 patients) underwent immunoblotting assays, and results were correlated to clinical features. Muscle biopsy samples (n=30) were examined by immunohistochemistry and immunoblotting. Exome or whole genome sequencing was performed on DNA from 19 patients.

Results

Both mass spectrometry and screening of a 413,611 human peptide library spanning the entire human proteome identified cytosolic 5′-nucleotidase 1A (cN1A; NT5C1A) as the likely 43 kDa IBM autoantigen, which was then confirmed in dot blot and Western blot assays using recombinant cN1A protein. Moderate reactivity of anti-cN1A autoantibodies was 70% sensitive and 92% specific, and high reactivity was 34% sensitive and 98% specific for the diagnosis of IBM. One to 3 major cN1A immunodominant epitopes were identified. cN1A reactivity by immunohistochemistry accumulated in perinuclear regions and rimmed vacuoles in IBM muscle, localizing to areas of myonuclear degeneration.

Interpretation

Autoantibodies against cN1A are common in and highly specific to IBM among muscle diseases, and may provide a link between IBM's dual processes of autoimmunity and myodegeneration. Blood diagnostic testing is feasible and should improve early and reliable diagnosis of IBM. Ann Neurol 2013;73:408–418

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