Myasthenia Gravis

In 1890, German medical professor Wilhelm Erb and other physicians had been observing several cases of a neuromuscular disease that they believed was affecting how nerve impulses were transmitted to muscle at the neuromuscular junction. The patient’s experienced a "grave muscular weakness" and Wilhelm named it myasthenia gravis. Through further research, the physicians discovered whether it affected the eye muscles first, or created difficulty in talking, chewing and swallowing, or in using the arms and legs it was neither hereditary nor contagious. Their discoveries lead to more detailed research.

In the early 1970s when Muscular Dystrophy Association, using snake venom, observed that patients with the disease had decreased numbers of acetylcholine receptors. Thus, discovering that the disease affected acetylcholine receptors of the skeletal muscles. The Muscular Dystrophy Association also found that, in rabbits, an immune attack against the acetylcholine receptors resulted in muscle membrane damage that is similar to that seen in human myasthenia gravis. This rabbit experiment was responsible for a large portion of what scientists now know about myasthenia gravis.

Myasthenia gravis causes a progressive and abnormally rapid fatigue of the voluntary muscles. It is known as an autoimmune disease, in which the body generates an immune system attack against its own skeletal muscles. This arises when lymphocytes in the blood produce antibodies that destroy muscle-cell receptors for acetylcholine molecules, preventing muscle contractions. The antibodies have been shown to decrease the usefulness of acetylcholine receptors through accelerated endocytosis and blockade of the receptor. Endocytosis is when extracellular substances are being incorporated into the cell by vesicles forming inward through budding of the plasma membrane. Researchers have been able to demonstrate the effect of antibodies on acetylcholine receptor by using radioactively labeled alpha bungaroo toxin, a snake poison, to follow the rate of degradation. Antibodies from patients with myasthenia gravis cause an increase in the rate of degradation of acetylcholine receptors. Blockade of acetylcholine receptors is another form of autoimmune attack from myasthenia gravis. Antibodies from these patients have been shown to block the acetylcholine binding sites preventing acetylcholine from binding to its receptor and opening the ion channel. The antibodies may bind near the acetylcholine binding site rather than directly on it, because the acetylcholine binding site is so small. In this case, the antibodies would prevent acetylcholine from binding at the receptor by interfering with the acetylcholine molecule as it moves towards its receptor.

Symptoms for some one with myasthenia gravis include a flattened smile and droopy eyes, with slow pupillary light responses.