The presence of anti-cytosolic-5′-nucleotidase 1A (cN1A) autoantibodies has been reported in 33 to 72% of IBM patients in previous studies (4–8); it has a high sensitivity for IBM because it is only rarely detected in other types of idiopathic inflammatory myopathies (IIM) (9) and also in other autoimmune diseases such as Sjogren’s syndrome and systemic lupus erythematosus (10). The gene discussed is NT5C1A; the disease is inclusion body myositis.