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Myasthenia Gravis and other Myasthenic syndromes
Background
Myasthenia gravis (MG) is an autoimmune disease, usually caused by antibodies that attack the acetylcholine receptors or a protein called MuSK on voluntary muscle (muscle that we consciously use to move parts of our body). The acetylcholine receptors bind a chemical called acetylcholine, which is an essential message signal released from the nerve ending when we want to tell our muscles to move, for example when we need to walk or open our hand to pick up a pencil or a cup. The loss of these receptors reduces communication between the nerve and the muscle and causes muscle weakness with fatigue.
Of the other myasthenic syndromes, Lambert-Eaton Myasthenic syndrome (LEMS) is also an autoimmune disease, caused by antibodies directed at the calcium channels at the nerve terminal on which acetylcholine release is dependent. This results in a decrease in the amount of acetylcholine released by the nerve impulse.
In the congenital myasthenic syndromes (CMS) the immunological system is not involved at all. These are inherited genetic conditions in which mutations in a number of genes responsible for producing proteins (currently at least 12) at different sites at the neuromuscular junction interfere with the signals sent from the nerve to the muscle.
Most adults have the autoimmune form of the condition, whereas this is much less common in childhood. Consequently, CMS accounts for a relatively greater proportion of children with myasthenia than among adults.
