title: Cytosolic 5'-nucleotidase 1A autoimmunity in sporadic inclusion body myositis.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Genetics, Harvard University Medical School, Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA.
authors.forename: H Benjamin
authors.initials: HB
authors.lastname: Larman
authors.forename: Mohammad
authors.initials: M
authors.lastname: Salajegheh
authors.forename: Remedios
authors.initials: R
authors.lastname: Nazareno
authors.forename: Theresa
authors.initials: T
authors.lastname: Lam
authors.forename: John
authors.initials: J
authors.lastname: Sauld
authors.forename: Hanno
authors.initials: H
authors.lastname: Steen
authors.forename: Sek Won
authors.initials: SW
authors.lastname: Kong
authors.forename: Jack L
authors.initials: JL
authors.lastname: Pinkus
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Amato
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Elledge
authors.forename: Steven A
authors.initials: SA
authors.lastname: Greenberg
mesh_terms: D015720:5'-Nucleotidase / Q000097:blood* / Q000276:immunology*; D000368:Aged; D001323:Autoantibodies / Q000097:blood; D001324:Autoantigens / Q000378:metabolism; D015551:Autoimmunity / Q000276:immunology*; D003600:Cytosol / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D004268:DNA-Binding Proteins / Q000378:metabolism; D003882:Dermatomyositis; D018604:Epitope Mapping; D005260:Female; D016678:Genome / Q000235:genetics / Q000276:immunology; D006801:Humans; D047468:Immunoprecipitation; D008297:Male; D013058:Mass Spectrometry; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D009188:Myelitis, Transverse; D018979:Myositis, Inclusion Body / Q000097:blood* / Q000276:immunology* / Q000473:pathology; D017285:Polymyositis; D017422:Sequence Analysis, DNA; D014617:Vacuoles / Q000276:immunology / Q000378:metabolism / Q000473:pathology
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D004268:DNA-Binding Proteins; D015720:5'-Nucleotidase; C552626:NT5C1A protein, human