Congenital myasthenic syndromes

By the mid-1970s the autoimmune origin of myasthenia gravis had been well established. Once this feat had been accomplished, it also became apparent that myasthenic disorders occurring in a genetic or congenital setting had a different etiology. As a result, a number of distinct myasthenic syndromes have been recognized and investigated by electrophysiological and ultrastructural methods. The newly recognized disorders are conditioned by divergent causes, such as a failure of acetylcholine resynthesis or packaging, absence of acetylcholinesterase from the neuromuscular junction, abnormal gating properties of the acetylcholine receptor-associated ion channel, or an abnormality in the regulation of the density of acetylcholine receptor molecules in the postsynaptic membrane. These genetic defects either impair neuromuscular transmission directly or result in secondary derangements that eventually compromise the safety margin of neuromuscular transmission.