July 24, 2016
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Definition of MG (myasthenia gravis)

MG (myasthenia gravis): An autoimmune neuromuscular disorder characterized by fatigue and exhaustion of muscles. It is caused by a mistaken immune response to the nicotinic acetylcholine receptors (AChR), which are found in junctions between muscles and the nervous system. The body produces antibodies that attack these AChR receptors, preventing signals from reaching the muscles. Proof that the anti-AChR antibodies are responsible for myasthenia comes from the effect these antibodies can have on the unborn and the newborn.

Pregnancy: During pregnancy in a woman with myasthenia, the anti-AChR antibodies can cross the placenta and block the function of the fetal form of AChR leading to fetal paralysis. Fetal and neonatal death is a common consequence. Babies who survive often have arthrogryposis multiplex congenita (nonprogressive congenital contractures) due to lack of fetal muscle movement before birth. Transient signs of MG are seen in 10-15% of babies born to MG mothers. These problems are potentially preventable if the mother is effectively treated during pregnancy.

Treatment: There is currently no cure for myasthenia gravis, but today at least 90 percent of patients with MG survive. A number of treatments are available that help, including steroids and other immunosuppressive medications and cholinergic medications.

Source: MedTerms™ Medical Dictionary
Last Editorial Review: 5/13/2016

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