Myasthenia gravis (MG) is caused by the failure of neuromuscular signal transmission and in the majority of patients this is caused by the presence of autoantibodies to the acetylcholine receptor (ARAb positive MG patients).
In 10-20 % of the patients with generalized MG, and in up to 50 % of the patients with ocular MG these autoantibodies can not be detected. In these cases the disease is commonly referred to as seronegative MG (SNMG). For a long time these seronegative patients posed a serious challenge for adequate diagnosis of MG。
Recent studies showed the presence of antibodies to the muscle-specific receptor tyrosine kinase (MuSK) in sera of patients with generalized seronegative MG (in about 50 % of putative seronegative MG patients). MuSK is part of an agrin receptor complex and mediates the agrin-induced clustering of acetylcholine receptors. MuSK MG patients are mostly female, have prominent cranial and bulbar involvement, and (when compared to ARAb positive MG patients) the onset of the disease tends to be earlier (third or fourth
decade). The measurement of MuSK antibodies will substantially aid diagnosis and clinical management of MG.