Myasthenia gravis (MG) is an autoimmune disease that causes certain muscles to become weak. Autoimmune means the body attacks healthy cells instead of invaders like germs.
Antibodies are chemicals the body’s immune system makes to target germs and unhealthy cells like cancer. In myasthenia gravis, antibodies begin to block, change, or destroy places where nerves and muscles communicate. This area is called the neuromuscular junction.1-4
A neuromuscular junction includes areas on the muscle that “read” nerve signals, telling the muscle to move. These areas are called receptors because they receive nerve signals. With MG, when the nerves send out their message using a chemical called acetylcholine, the acetylcholine receptor on the muscle cannot “read” the signal. This causes the muscles to become weak and tire easily.
There are no known risk factors for myasthenia gravis.
Does MG run in families?
Doctors do not know why myasthenia gravis causes the body to turn on itself. One theory is that autoimmune diseases seem to run in some families, which may mean that certain genes are involved.
HLA genes are important in immune system function and changes in these genes are tied to many autoimmune diseases. The HLA-DR3, HLA-B8, and non-HLA genes are linked to early-onset MG. The HLA-2, HLA-B7, and HLA-DRB115.01 genes are linked to late-onset MG. However, doctors do not understand yet how changes in these genes lead to MG.4
There are a few rare myasthenic syndromes caused by genetic mutations, but these are different diseases that also cause muscle weakness.1-4
Can it be prevented?
Today, there are no known ways to prevent someone from getting MG. However, MG drugs help with nerve and muscle signaling and help control the antibodies that attack the neuromuscular junction. This means that finding the right diagnosis and getting treatment as early as possible can help manage the symptoms. Some things that may make MG worse include:2
- Being tired
- Being sick with a cold or other infection
- Stress
- Pregnancy
- Menstrual period
People with myasthenia gravis also are told to avoid certain drugs that can make MG worse, such as:2
- Beta-blockers
- Quinidine gluconate
- Quinidine sulfate
- Quinine
- Phenytoin
- Some antibiotics
- Some anesthetics
Doctors also know that the thymus gland in people with MG may cause the immune system to go into overdrive. However, doctors do not understand the exact role the thymus gland plays in MG.
Research into causes of MG
Doctors are working to find answers to what causes myasthenia gravis. Better understanding of the causes MG would help doctors find treatments customized to each person’s unique case.