The specificity of MuSK ELISA was 0.95 (95% CI 0.87–0.99) based on the results from 63 serum samples of disease control which consisted of 45 patients diagnosed with a disease other than MG in the initial cohort (MND 30, LEMS 5, Myopathy 4, Others 6) and 18 patients with RIPA-AChR Ab-positive MG. This evidence concerns the gene MUSK and myopathy.