Autoantibodies to ion channels at the neuromuscular junction.

Autoantibodies directed against voltage- or ligand-gated ion channels and their associated proteins at the neuromuscular junction give rise to a family of neurological autoimmune diseases. Antibodies to acetylcholine receptors or muscle-specific kinase present on the postsynaptic muscle membrane are associated with different forms of myasthenia gravis (MG). Antibodies to the presynaptic voltage-gated potassium and calcium channels are responsible for acquired neuromyotonia and Lambert-Eaton myasthenic syndrome (LEMS), respectively. The patients respond to immunotherapies and their plasma can transfer defects in neuromuscular transmission to mice, indicating that these are antibody-mediated conditions. In a small proportion of cases, ion channel antibodies have also been implicated in neurological dysfunction in the central nervous system. In these conditions, a proportion of the patients have an underlying tumour, thymoma in both MG and neuromyotonia and small cell lung carcinoma in LEMS, emphasising the putative role of autoimmunity to tumour antigens as a cause of neurological disease.