title: Myositis-specific autoantibodies are specific for myositis compared to genetic muscle disease.
abstract: OBJECTIVE
  To determine the specificity of myositis-specific autoantibodies (MSAs) for autoimmune myopathy compared with inherited muscle diseases.
  
  
  METHODS
  Serum samples from 47 patients with genetically confirmed inherited muscle diseases were screened for the most common MSAs, including those recognizing TIF1γ, NXP2, Mi2, MDA5, Jo1, SRP, and HMGCR. We compared these results with the findings in a cohort of patients with dermatomyositis (DM) previously screened for anti-TIF1γ, -NXP2, -Mi2, -MDA5, and -Jo1.
  
  
  RESULTS
  Overall, the presence of anti-TIF1γ, -NXP2, -Mi2, -MDA5, or -Jo1 was 96% specific and 67% sensitive for DM compared to patients with genetic muscle diseases. No patients with inherited muscle disease had anti-SRP or anti-HMGCR autoantibodies. Only 2 patients with genetic muscle disease had a MSA. One patient with anti-Mi2 autoantibodies had both genetically confirmed facioscapulohumeral dystrophy and dermatomyositis based on a typical skin rash and partial response to immunosuppressive medications. A second patient with anti-Jo-1 autoantibodies had both genetically defined limb-girdle muscular dystrophy type 2A (i.e., calpainopathy) and a systemic autoimmune process based on biopsy-confirmed lupus nephritis, sicca symptoms, and anti-Ro52 autoantibodies.
  
  
  CONCLUSIONS
  The MSAs tested for in this study are highly specific for autoimmune muscle disease and are rarely, if ever, found in patients who only have genetic muscle disease. In patients with genetic muscle disease, the presence of a MSA should suggest the possibility of a coexisting autoimmune process.
authors.affiliation: National Institute of Arthritis and Musculoskeletal and Skin Diseases (A.L.M.), NIH, Bethesda; the Departments of Neurology (A.L.M., L.C.-S., T.E.L., K.R.W.), Medicine (L.C.-R., L.C.-S.), and Neuroscience (T.E.L., K.R.W.), Johns Hopkins University School of Medicine, Baltimore; and The Hugo W. Moser Research Institute (K.R.W.), Kennedy Krieger, Baltimore, MD.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Mammen
authors.affiliation: National Institute of Arthritis and Musculoskeletal and Skin Diseases (A.L.M.), NIH, Bethesda; the Departments of Neurology (A.L.M., L.C.-S., T.E.L., K.R.W.), Medicine (L.C.-R., L.C.-S.), and Neuroscience (T.E.L., K.R.W.), Johns Hopkins University School of Medicine, Baltimore; and The Hugo W. Moser Research Institute (K.R.W.), Kennedy Krieger, Baltimore, MD.
authors.forename: Livia
authors.initials: L
authors.lastname: Casciola-Rosen
authors.affiliation: National Institute of Arthritis and Musculoskeletal and Skin Diseases (A.L.M.), NIH, Bethesda; the Departments of Neurology (A.L.M., L.C.-S., T.E.L., K.R.W.), Medicine (L.C.-R., L.C.-S.), and Neuroscience (T.E.L., K.R.W.), Johns Hopkins University School of Medicine, Baltimore; and The Hugo W. Moser Research Institute (K.R.W.), Kennedy Krieger, Baltimore, MD.
authors.forename: Lisa
authors.initials: L
authors.lastname: Christopher-Stine
authors.affiliation: National Institute of Arthritis and Musculoskeletal and Skin Diseases (A.L.M.), NIH, Bethesda; the Departments of Neurology (A.L.M., L.C.-S., T.E.L., K.R.W.), Medicine (L.C.-R., L.C.-S.), and Neuroscience (T.E.L., K.R.W.), Johns Hopkins University School of Medicine, Baltimore; and The Hugo W. Moser Research Institute (K.R.W.), Kennedy Krieger, Baltimore, MD.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Lloyd
authors.affiliation: National Institute of Arthritis and Musculoskeletal and Skin Diseases (A.L.M.), NIH, Bethesda; the Departments of Neurology (A.L.M., L.C.-S., T.E.L., K.R.W.), Medicine (L.C.-R., L.C.-S.), and Neuroscience (T.E.L., K.R.W.), Johns Hopkins University School of Medicine, Baltimore; and The Hugo W. Moser Research Institute (K.R.W.), Kennedy Krieger, Baltimore, MD.
authors.forename: Kathryn R
authors.initials: KR
authors.lastname: Wagner