LRP4 and myasthenia gravis: Multiple antibodies against the acetylcholine receptor (AChR) or other related proteins, such as muscle-specific kinase (MuSK) and lipoprotein receptor-related protein 4 (LRP4) in the postsynaptic membrane of the neuromuscular junction can be detected in the serum of most MG patients, which are applied to classify subgroups (e.g., anti-AChR, anti-MuSK, anti-LRP4, seronegative).