MUSK and myasthenia gravis: Myasthenia gravis (MG) is an autoimmune disease characterized by fatigable weakness of cranial and skeletal muscles with elevated titers of acetylcholine receptor (AChR), muscle-specific receptor tyrosine kinase (MuSK) autoantibodies, or other AChR-related proteins that affect the postsynaptic membrane at the neuromuscular junction [1].