MUSK and myasthenia gravis: Pathogenic mechanisms of serum or purified IgG from MG patients with AChR or MuSK autoantibodies have been identified, the passive transfer of patient serum or purified IgG has reproduced myasthenic weakness in experimental animals, and clinical cues for the autoimmune nature of the disease is the improvement of the symptoms after immunosuppression and after the removal of antibodies by plasmapheresis or B-cell depletion (discussed below in detail).