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Autoantibodies to cytosolic 5′-nucleotidase 1A in inclusion body myositis

Authors

  • Helma Pluk PhD,

    1. Department of Biomolecular Chemistry, Institute for Molecules and Materials and Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen, Nijmegen, the Netherlands
    Current affiliation:
    1. Department of Biochemistry, Radboud University Nijmegen Medical Center, Nijmegen, the Netherlands
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  • Bas J. A. van Hoeve MD,

    1. Department of Neurology, Center for Neuroscience, Donders Institute for Brain, Cognition, and Behavior, Radboud, University Nijmegen Medical Center, Nijmegen, the Netherlands
    Current affiliation:
    1. Department of Neurology, VieCuri Medical Center, Venlo, the Netherlands
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  • Sander H. J. van Dooren PhD,

    1. Department of Biomolecular Chemistry, Institute for Molecules and Materials and Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen, Nijmegen, the Netherlands
    Current affiliation:
    1. Institute of Pharmacology and Toxicology, Biomedical Center, University of Bonn, Bonn, Germany
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  • Judith Stammen-Vogelzangs,

    1. Department of Biomolecular Chemistry, Institute for Molecules and Materials and Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen, Nijmegen, the Netherlands
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  • Annemarie van der Heijden,

    1. Department of Biomolecular Chemistry, Institute for Molecules and Materials and Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen, Nijmegen, the Netherlands
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  • Helenius J. Schelhaas MD, PhD,

    1. Department of Neurology, Center for Neuroscience, Donders Institute for Brain, Cognition, and Behavior, Radboud, University Nijmegen Medical Center, Nijmegen, the Netherlands
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  • Marcel M. Verbeek PhD,

    1. Department of Neurology, Center for Neuroscience, Donders Institute for Brain, Cognition, and Behavior, Radboud, University Nijmegen Medical Center, Nijmegen, the Netherlands
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  • Umesh A. Badrising MD, PhD,

    1. Department of Neurology, Leiden University Medical Center, Leiden, the Netherlands
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  • Snjolaug Arnardottir MD, PhD,

    1. Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden
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  • Karina Gheorghe,

    1. Rheumatology Unit, Department of Medicine, Karolinska University Hospital, Solna, Karolinska Institute, Stockholm, Sweden
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  • Ingrid E. Lundberg PhD,

    1. Rheumatology Unit, Department of Medicine, Karolinska University Hospital, Solna, Karolinska Institute, Stockholm, Sweden
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  • Wilbert C. Boelens PhD,

    1. Department of Biomolecular Chemistry, Institute for Molecules and Materials and Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen, Nijmegen, the Netherlands
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  • Baziel G. van Engelen MD, PhD,

    1. Department of Neurology, Center for Neuroscience, Donders Institute for Brain, Cognition, and Behavior, Radboud, University Nijmegen Medical Center, Nijmegen, the Netherlands
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  • Ger J. M. Pruijn PhD

    Corresponding author
    • Department of Biomolecular Chemistry, Institute for Molecules and Materials and Nijmegen Center for Molecular Life Sciences, Radboud University Nijmegen, Nijmegen, the Netherlands
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Address correspondence to Dr Pruijn, 271 Department of Biomolecular Chemistry, Radboud University Nijmegen, PO Box 9101, NL-6500 HB Nijmegen, the Netherlands. E-mail: G.Pruijn@ncmls.ru.nl

Abstract

Objective

Sporadic inclusion body myositis (sIBM) is an inflammatory myopathy characterized by both degenerative and autoimmune features. In contrast to other inflammatory myopathies, myositis-specific autoantibodies had not been found in sIBM patients until recently. We used human skeletal muscle extracts as a source of antigens to detect autoantibodies in sIBM and to characterize the corresponding antigen.

Methods

Autoantibodies to skeletal muscle antigens were detected by immunoblotting. The target antigen was immunoaffinity-purified from skeletal muscle extracts and characterized by mass spectrometry. A cDNA encoding this protein was cloned and expressed in vitro, and its recognition by patient sera was analyzed in an immunoprecipitation assay. Epitopes were mapped using microarrays of overlapping peptides.

Results

An Mr 44,000 polypeptide (Mup44) was frequently targeted by sIBM autoantibodies. The target protein was purified, and subsequent mass spectrometry analysis revealed that Mup44 is the cytosolic 5′-nucleotidase 1A (cN1A). By immunoprecipitation of recombinant cN1A, high concentrations of anti-Mup44 autoantibodies were detected in 33% of sIBM patient sera, whereas their prevalence in dermatomyositis, polymyositis, and other neuromuscular disorders appeared to be rare (4.2%, 4.5%, and 3.2%, respectively). Low concentrations of anti-Mup44 antibodies were found in myositis as well as other neuromuscular disorders, but not in healthy controls. Three major autoepitope regions of cN1A were mapped by using microarrays containing a set of overlapping peptides covering the complete cN1A amino acid sequence.

Interpretation

Anti-Mup44 autoantibodies, which are targeted to cN1A, represent the first serological biomarker for sIBM and may facilitate the diagnosis of this type of myositis. ANN NEUROL 2013;73:397–407

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