Function of the Acetylcholine Receptor (AChR) Antibody test:
This is the primary diagnostic test for myasthenia gravis.
What is myasthenia gravis (MG)?
The name myasthenia gravis, which is Latin and Greek in origin, means “grave, or serious, muscle weakness”.
Myasthenia gravis is an autoimmune disease usually caused by antibodies that block or destroy receptors for the neurotransmitter acetylcholine, leading to muscle weakness and fatigue.
The hallmark of myasthenia gravis is muscle weakness that worsens after periods of activity and improves after periods of rest.
There is no known cure but with current therapies most cases of myasthenia gravis are not as “grave” as the name implies.
Available treatments can control symptoms and often allow people to have a relatively high quality of life.
Most individuals with the condition have a normal life expectancy.
What do Acetylcholine Receptor (AChR) Antibodies do?
At the normal neuromuscular junction, a nerve cell tells a muscle cell to contract by releasing the chemical acetylcholine (ACh). ACh attaches to the ACh receptor — a pore or “channel” in the surface of the muscle cell — twisting it open and allowing an inward flux of electrical current that triggers muscle contraction. These contractions enable someone to move a hand, for example.
The Acetylcholine Receptor (AChR) antibodies may cause blocks in neuromuscular transmission by interfering with the binding of acetylcholine (ACh) to ACh receptor (AChR) sites on the muscle membrane and thereby preventing muscle contraction.
It is this phenomenon that characterizes Myasthenia gravis.
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The presence of these antibodies is virtually diagnostic of Myasthenia gravis. In an individual patient with MG, however, antibody levels are particularly useful in monitoring response to immunosuppressive therapy. As the patient improves, antibody titer decreases.
What causes MG?
Researchers suspect viruses or bacteria might trigger the autoimmune response; the thymus gland also seems sometimes to play a role in the disease. Although MG is not hereditary, genetic susceptibility appears to play a role in it and other autoimmune diseases.
References:
Myasthenia Gravis Fact Sheet https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Myasthenia-Gravis-Fact-Sheet
Aarli JA, Lefvert AK, Tonder O. Thymoma specific antibodies in sera from patients with myasthenia gravis demonstrated by indirect haemagglutination. J Neuroimm. 1981;1:421–427.
Conroy WG, Saedis MS, Lindstrom J. TE671 cells express an abundance of a partially mature acetylcholine receptor α subunit which has characteristics of an assembly intermediate. J Biol Chem. 1990;265:21642-21651.
Drachman DB, Adams RN, Josifek LF, et al. Functional activities of autoantibodies to acetylcholine receptors and the clinical severity of myasthenia gravis. N Engl J Med. 1982;307:769-775.
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