MuSK antibodies in AChR Ab-seropositive MG vs AChR Ab-seronegative MG

Hoch et al.1 recently reported a novel specific target antigen, the muscle-specific receptor tyrosine kinase (MuSK), for the autoantibodies in acetylcholine receptor antibody (AChR-Ab)-seronegative myasthenia gravis (MG) patients. MuSK is expressed at the postsynaptic membrane of neuromuscular junctions and has multiple roles in the clustering of AChR by the agrin secreted from motoneuron terminus. Therefore, autoantibodies against MuSK may cause severe inhibition of AChR clustering, leading to reduced numbers, altered distribution of AChRs in mature muscle, or both. MuSK antibodies are found in ∼37.5 to 70% of patients with AChR-Ab-seronegative MG but not in those with AChR-Ab-seropositive MG, a clear differentiation of the two forms of disease.1–5⇓⇓⇓⇓ Furthermore, a lack of detectable MuSK antibodies was reported in MG patients with thymoma. To evaluate MuSK antibodies clinically in patients with MG, we developed a …