MUSK and myasthenia gravis: Myasthenia gravis (MG) is a chronic autoimmune disorder of the neuromuscular junction characterized by autoantibodies against acetylcholine receptors (AChR-Ab), muscle-specific kinase (MuSK-Ab), lipoprotein-related protein 4, or agrin in the postsynaptic membrane at the neuromuscular junction [1].