Diseases of the neuromuscular junction.

The neuromuscular junction is a prototype synapse and it is also the site of well-characterised autoimmune and hereditary disorders. In the presynaptic terminal, voltage-gated potassium channels and voltage-gated calcium channels are subtly altered in genetic disorders and mutations in the enzyme that synthesises acetylcholine have been demonstrated in a particular form of hereditary myasthenia syndrome. Recent advances have revealed agrin, muscle-specific kinase (MuSK) and rapsyn as important signalling elements in the development and maintainance of the molecular architecture of the postsynaptic membrane. This is proving relevant to seronegative myasthenia gravis, with the discovery of anti-MuSK antibodies, and to a type of congenital myasthenic syndrome, in which acetylcholine receptor deficiency is due to mutations in rapsyn.