Myasthenia gravis is a neuromuscular disease characterized by weakness and marked fatigability of skeletal muscle; exacerbations and partial remissions occur frequently. The defect in myasthenia gravis is in synaptic transmission at the neuromuscular junction, such that mechanical responses to nerve stimulation are not well sustained. Myasthenia gravis is caused by an autoimmune response primarily to the ACh receptor at the postjunctional endplate. These antibodies reduce the number of receptors detectable by receptor-binding assays and electrophysiological measurements of ACh sensitivity. The similarity of the symptoms of myasthenia gravis and curare poisoning suggested that physostigmine might be of therapeutic value; 40 years elapsed before this suggestion was tried, successfully.
In a subset of ~10% of patients with myasthenic syndrome, muscle weakness has a congenital rather than an autoimmune basis, with mutations in the ACh receptor that affect ligand-binding and channel-opening kinetics, or in a form of AChE tethered by a collagen-like tail. Administration of anti-ChE agents does not result in subjective improvement in most congenital myasthenic patients.
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