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  1. James Lilleker1,2,
  2. Anke Rietveld3,
  3. Stephen Pye2,
  4. Janine Lamb4,
  5. Mark Roberts1,
  6. Robert Cooper1,4,5,
  7. Ger Pruijn6,
  8. Hector Chinoy1,2,
  9. Baziel van Engelen3,
  10. MYONET Collaborators7
  1. 1Salford Royal NHS Foundation Trust
  2. 2Centre for Musculoskeletal Research, University of Manchester
  3. 3Radboud University Medical Center, Nijmegen, The Netherlands
  4. 4Centre for Integrated Genomic Medical Research, University of Manchester
  5. 5MRC/ARUK Institute of Ageing and Chronic Disease, University of Liverpool
  6. 6Department of Biomolecular Chemistry, Radboud University, Nijmegen, The Netherlands
  7. 7Full author list available on request


Background Inclusion Body Myositis (IBM) pathogenesis is incompletely understood. Anti-cytosolic 5′-nucleotidase 1A (cN1A/NT5c1A) autoantibodies have recently been identified in ∼1/3 of patients. We investigated the potential utility of anti-cN1A testing in IBM.

Methods Data from four European IBM registries (UK, Netherlands, France, Sweden) were pooled. Anti-cN1A serotyping by ELISA was performed. Cases were stratified by anti-cN1A serotype and associations investigated. Mortality analysis was performed using Cox proportional hazards regression.

Results Data from 311 IBM patients were analysed, 102 (32.8%) were anti-cN1A seropositive. At disease onset, fewer seropositive patients had proximal arm weakness (8.3% vs. 23.2%, OR 0.30, 95% CI=0.11–0.73, p=0.004). A higher proportion of seropositive patients had excess cytochrome oxidase deficient fibres on muscle biopsy (86.9% vs. 71.8%, OR 2.61, 95% CI=1.08–6.97, p=0.022). During follow-up, 70 patients died at a mean age of 77.8 years (SD=8.2). Adjusted mortality risk was higher in the seropositive group (HR 1.95, 95% CI=1.17–3.27, p=0.011)

Conclusions Anti-cN1A seropositivity was associated with an increased mortality risk, suggesting a more severe disease phenotype. Stratification of IBM by anti-cN1A serotype may prove important in future treatment decisions if disease modifying therapies for IBM become available.

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