LRP4 and myasthenia gravis: Rare forms of MG are due to autoantibodies targeting other postsynaptic membrane components such as the muscle-specific kinase (MuSK) protein, which is essential for NMJ formation and clustering of AChRs, and the lipoprotein receptor-related protein 4 (LRP4) a receptor that binds to neuronal agrin to activate MuSK (5, 9).