title: Development and evaluation of a standardized ELISA for the determination of autoantibodies against cN-1A (Mup44, NT5C1A) in sporadic inclusion body myositis.
abstract: OBJECTIVE
  Sporadic inclusion body myositis (sIBM) is an autoimmune degenerative disease of the muscle, with inflammatory infiltrates and inclusion vacuoles. Its pathogenesis is not fully understood and the diagnosis is hampered by its imprecise characteristics, at times indistinguishable from other idiopathic inflammatory myopathies such as polymyositis and dermatomyositis. The diagnosis may be assisted by the detection of autoantibodies targeting Mup44, a skeletal muscle antigen identified as cytosolic 5'-nucleotidase 1A (cN-1A, NT5C1A). A novel standardized anti-cN-1A IgG ELISA was developed and its diagnostic performance was evaluated by two reference laboratories.
  
  
  METHODS
  Recombinant human full-length cN-1A was expressed and purified, and subsequently utilized to set up a standardized ELISA. To evaluate the novel assay, laboratory A examined sera from North American patients with clinically and pathologically diagnosed definite sIBM (n = 17), suspected sIBM (n = 14), myositis controls (n = 110), non-myositis autoimmune controls (n = 93) and healthy subjects (n = 52). Laboratory B analyzed a Dutch cohort of definite sIBM patients (n = 51) and healthy controls (n = 202).
  
  
  RESULTS
  Anti-cN-1A reactivity was most frequent in definite sIBM (39.2-47.1%), but absent in biopsy-proven classic polymyositis or dermatomyositis. Overall diagnostic sensitivity and specificity amounted to 35.5 and 96.1% (laboratory A) and 39.2 and 96.5% (laboratory B).
  
  
  CONCLUSIONS
  Anti-cN-1A autoantibodies were detected by ELISA with moderate sensitivity, but high specificity for sIBM and may therefore help diagnose this infrequent and difficult-to-diagnose myopathy. The novel anti-cN-1A IgG ELISA can improve and accelerate the diagnosis of sIBM using sera where muscle biopsy is delayed or unfeasible.
authors.affiliation: Institute for Experimental Immunology, Euroimmun AG, Seekamp 31, 23560, Lübeck, Germany.
authors.forename: Sabine L
authors.initials: SL
authors.lastname: Kramp
authors.affiliation: RDL Reference Laboratory Inc., 10755 Venice Blvd., Los Angeles, CA, 90034, USA.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Karayev
authors.affiliation: RDL Reference Laboratory Inc., 10755 Venice Blvd., Los Angeles, CA, 90034, USA.
authors.forename: Guo
authors.initials: G
authors.lastname: Shen
authors.affiliation: RDL Reference Laboratory Inc., 10755 Venice Blvd., Los Angeles, CA, 90034, USA.
authors.forename: Allan L
authors.initials: AL
authors.lastname: Metzger
authors.affiliation: RDL Reference Laboratory Inc., 10755 Venice Blvd., Los Angeles, CA, 90034, USA.
authors.forename: Robert I
authors.initials: RI
authors.lastname: Morris
authors.affiliation: RDL Reference Laboratory Inc., 10755 Venice Blvd., Los Angeles, CA, 90034, USA.
authors.forename: Eugene
authors.initials: E
authors.lastname: Karayev
authors.affiliation: RDL Reference Laboratory Inc., 10755 Venice Blvd., Los Angeles, CA, 90034, USA.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Lam
authors.affiliation: RDL Reference Laboratory Inc., 10755 Venice Blvd., Los Angeles, CA, 90034, USA.
authors.forename: Richard M
authors.initials: RM
authors.lastname: Kazdan
authors.affiliation: Department of Biomolecular Chemistry, Institute for Molecules and Materials and Radboud Institute for Molecular Life Sciences, Radboud University Nijmegen, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands.
authors.forename: Ger J M
authors.initials: GJ
authors.lastname: Pruijn
authors.affiliation: Institute for Experimental Immunology, Euroimmun AG, Seekamp 31, 23560, Lübeck, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Saschenbrecker
authors.affiliation: Institute for Experimental Immunology, Euroimmun AG, Seekamp 31, 23560, Lübeck, Germany.
authors.forename: Cornelia
authors.initials: C
authors.lastname: Dähnrich
authors.affiliation: Institute for Experimental Immunology, Euroimmun AG, Seekamp 31, 23560, Lübeck, Germany. w.schlumberger@euroimmun.de.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schlumberger
keywords: Anti-Mup44; Anti-cN-1A; Autoantibodies; Autoimmunity; ELISA; Myopathy; Sporadic inclusion body myositis