Animal models of antimuscle-specific kinase myasthenia.

Antimuscle-specific kinase (anti-MuSK) myasthenia (AMM) differs from antiacetylcholine receptor myasthenia gravis in exhibiting more focal muscle involvement (neck, shoulder, facial, and bulbar muscles) with wasting of the involved, primarily axial, muscles. AMM is not associated with thymic hyperplasia and responds poorly to anticholinesterase treatment. Animal models of AMM have been induced in rabbits, mice, and rats by immunization with purified xenogeneic MuSK ectodomain, and by passive transfer of large quantities of purified serum IgG from AMM patients into mice. The models have confirmed the pathogenic role of the MuSK antibodies in AMM and have demonstrated the involvement of both the presynaptic and postsynaptic components of the neuromuscular junction. The observations in this human disease and its animal models demonstrate the role of MuSK not only in the formation of this synapse but also in its maintenance.