Myasthenia gravis (MG) is one of a number of autoimmune diseases that develop unexpectedly. It is not contagious — and except for a rare temporary form passed from a mother to a newborn, it isn’t passed down through families.
There are, however, genetic and environmental factors that can make individuals more susceptible to MG and other autoimmune disorders.
How does MG develop?
The cause of MG has not yet been identified. Researchers think some viral or bacterial proteins may resemble proteins produced by the body, triggering the production of auto-antibodies, but this isn’t know for certain. MG most often affects women under 40 and men over 60, but cases can occur at any age and across all racial and ethnic groups.
Symptoms of muscle weakness such as drooping eyelids, fatigue, and trouble chewing can come as a surprise, and often aren’t recognized as signs of a broader problem. When this is combined with the fact that MG symptoms mimic other conditions, such as chronic fatigue, thyroid disorders and multiple sclerosis, it often takes some time before patients receive the correct diagnosis.
Can you inherit MG?
MG is not hereditary — except in rare cases. When a woman who has MG is pregnant, it’s possible for her antibodies to cross the placenta. This can lead to transient neonatal MG, a temporary form of MG that develops a few days after birth and goes away two to four weeks later.
Transient neonatal MG only occurs in about 10% of pregnancies in women with MG. It generally doesn’t have any lasting effects, and doesn’t increase the chance that a baby will develop MG later in life.
Read more about MG causes and risk factors.
What are the factors that may contribute to the onset of MG?
Autoimmune disorders such as MG can be triggered by a combination of genetic mutations and susceptibility, as well as environmental factors. As a result, the body’s immune system mistakenly attacks healthy cells, tissues and organs, causing inflammation and dysfunction.
Genetic factors
Specific genetic factors that may make someone more susceptible to developing MG are:
- Genes for HLA-88, DRw3 and DQw2: These human leukocyte antigens (HLAs) are proteins on the surface of cells that are responsible for regulating the immune system.
- Haplotypes DR14 and DQ5: Haplotypes are clusters of genes that are inherited together. MuSK antibody-positive MG has shown links with haplotypes DR14 and DQ5.
These genes are more common in people who have MG and suggest a greater risk of developing the autoimmune disease. However, there is no certainty that the disease will occur.
Additionally, around 3.8% to 7.1% of people diagnosed with MG have a family member who has MG or another autoimmune condition. Researchers think genetic predisposition to autoimmune disease likely plays a role in these cases, but the exact cause isn’t known.
Environmental factors
Exposure to environmental factors may contribute to the onset of MG in people whose genetics make them more susceptible to the disease. These factors include:
- The presence of another autoimmune disease.
- Thymus gland abnormalities.
- Illness or infection.
- Stress.
- Some medications.
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