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How Common is Myasthenia Gravis?

Reviewed by: HU Medical Review Board | Last reviewed: August 2020

Myasthenia gravis (MG) is an autoimmune condition that causes certain muscles to become weak. The muscles most often affected are the ones that control:1

  • Facial expressions
  • Eye movements
  • Talking
  • Swallowing and chewing
  • Breathing
  • Arm and leg movements

With an autoimmune condition, the body creates proteins that attack healthy tissue instead of germs. With MG, the body attacks places where nerves and muscles communicate and cause contraction. This causes the muscles to feel weak or uncoordinated. This weakness often gets better after rest.1

How common is MG?

Between 36,000 and 60,000 people in the United States have been diagnosed with MG. Doctors believe many people live with the condition while being misdiagnosed or undiagnosed.2,3

The number of people diagnosed with MG has been increasing worldwide. This is probably due to better diagnosis that leads to better treatment and longer lives.2

While MG is the most common disorder of neuromuscular transmission, it is still a rare disease. Other autoimmune conditions like rheumatoid arthritis, lupus, and multiple sclerosis are much more common than MG.3,4

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Who gets it?

Doctors once thought that women developed MG more than men. However, doctors now believe that men and women get MG at similar rates. MG is found in all racial and ethnic groups.5-7

However, the age at which symptoms begin can be quite different between the sexes. MG most often appears in women under age 40 and in men after age 60. However, it can occur at any age. About 1 in 10 people with MG are children or teens.1,5

Some babies born to women with MG will show signs of the disorder for the first few days or weeks of life. This is called transient neonatal myasthenia gravis, and symptoms usually go away in a few weeks with treatment. It is not a true autoimmune condition.6

Men are more likely to have ocular MG. MuSK (muscle-specific receptor tyrosine kinase) myasthenia gravis is more common in women.7

Is it genetic?

Most people with MG have no family history of the disease. Only 3 to 5 percent of people with MG have a family member with MG or another autoimmune condition. Like many autoimmune conditions, research shows that people who develop MG may have inherited genes that make them more likely to develop an autoimmune condition.8

For instance, some studies show that about 3 out of 4 people with MG have certain problems with their thymus gland. The thymus lies just behind the breastbone between the lungs, and it plays an important role in the immune system. People with MG often have a thymus that is too big or overactive. Some people develop tumors on their thymus gland. These tumors are called thymomas. These tumors can be harmless, but also can turn into cancer or cause lasting health issues. These conditions can cause an autoimmune reaction, which means the body attacks itself.7-9

People with MG are at higher risk of developing other autoimmune conditions such as lupus or autoimmune thyroid disease. This could be another sign that genes play a role in who develops myasthenia gravis.6

What to expect over the lifespan

Myasthenia gravis is a chronic disease, meaning it generally lasts a person’s whole life. Because of better treatments, most people with MG have a normal life expectancy. The symptoms usually can be controlled with treatment. Some people even have a remission of some or all their symptoms.1,6

About 1 out of every 5 people with MG will have what is called a myasthenic crisis. This life-threatening condition happens when the muscles used for breathing become very weak and the person may need a machine to help them breathe. This machine is called a ventilator.10