- The most common form of MG is a chronic autoimmune neuromuscular disorder characterized by fluctuating weakness of the voluntary muscle groups.
- The prevalence of MG in the U.S. is estimates that approximately 20 in 100,000 are affected
- MG can occur regardless of race, gender and age
- MG is not thought to be directly inherited nor contagious, but may occur in more than one member of the same family
- MG is not transmitted via intimate or any form of contact
- There is no known cure for MG, but there are many effective treatments that can make managing life with MG easier
Myasthenia gravis, or MG, is not the only medical condition referred to as MG. There is a venereal infection caused by bacteria, Mycoplasma genitalium, that is also referred to as MG. Myasthenia gravis has nothing to do with Mycoplasma genitalium. Myasthenia gravis is not transmitted via intimate, sexual or any other form of contact.
What happens in the body when someone has MG?
The voluntary muscles of the entire body are controlled by nerve impulses that arise in the brain. These impulses travel down the nerves to the place where the nerves meet the muscle fibers. Nerve fibers do not actually connect with muscle fibers. There is a space between the nerve ending and muscle fiber, called the neuromuscular junction. When the nerve impulse originating in the brain arrives at the nerve ending, it releases a chemical called acetylcholine. Acetylcholine travels across the space to the muscle fiber side of the neuromuscular junction where it attaches to many receptor sites. The muscle contracts when enough of the receptor sites have been activated by the acetylcholine.
For someone with MG, there can be as much as an 80% reduction in the number of these receptor sites. The reduction in the number of receptor sites is caused by an antibody that destroys or blocks the receptor site. Antibodies are proteins that play an important role in the immune system. They are normally directed at foreign proteins called antigens that attack the body. Such foreign proteins include bacteria and viruses. Antibodies help the body to protect itself from these foreign proteins.
While it is not still fully understood why, the immune system of the person with MG makes antibodies against the receptor sites of the neuromuscular junction. The antibodies destroy the receptor sites more rapidly than the body can replace them. Muscle weakness occurs when acetylcholine cannot activate enough receptor sites at the neuromuscular junction.
When it comes to diagnosing MG, abnormal antibodies can be measured in the blood of most people with MG, but not all.