MUSK and myasthenia gravis: Myasthenia gravis (MG) is a rare autoimmune neuromuscular disorder characterized by fatigable weakness of voluntary muscles, primarily due to autoantibodies either to acetylcholine receptors (AChR Abs), muscle-specific kinase antibodies (MuSK-Abs), low density lipoprotein receptor-related protein 4 (LRP-4-Abs), or titin antibodies [1,2,3,4].