Myasthenia gravis is an autoimmune neuromuscular disorder caused by the immune system attacking the muscles. Although doctors and researchers understand how myasthenia gravis develops, they’re not quite sure why it occurs in some people and not others. Unfortunately, not much is known about the exact cause of myasthenia gravis, but a handful of risk factors play a role.

Read on to learn about five factors associated with an increased risk of developing myasthenia gravis.

Myasthenia Gravis and the Immune System

Antibodies provide one strategy that your body’s immune system uses to protect you from infections. Antibodies are specialized immune proteins that tag invading viruses and bacteria for destruction, preventing you from getting sick. In autoimmune disorders like myasthenia gravis, the immune system malfunctions and produces abnormal antibodies targeted to attack your own cells or tissues. These abnormal antibodies are known as autoantibodies — “auto” means “self.”

People with myasthenia gravis have at least one autoantibody targeting the neuromuscular junction (NMJ). Nerve cells and skeletal muscle cells communicate with one another by sending the chemical messenger acetylcholine through the NMJ. In myasthenia gravis, different autoantibodies target different parts of the NMJ, including:

• Acetylcholine receptors (AChRs)
• Muscle-specific kinase (MuSK)
• Lipoprotein-related protein 4 (LRP4)

Without enough acetylcholine in the NMJ, the muscles can’t contract. This leads to muscle weakness, a key symptom of myasthenia gravis. Some people have ocular myasthenia gravis, which affects the eye muscles and can lead to drooping eyelids or double vision. Others may experience muscle weakness in the neck, arms, hands, and legs.

Autoantibodies are detected via blood tests, and the results help your neurologist determine which type of myasthenia gravis you have.

Although it’s known that autoantibodies are involved in myasthenia gravis, the reason they develop in the first place is less clear. Doctors and researchers believe certain risk factors — including genetics, age, gender, and environment — may all contribute to developing myasthenia gravis.

1. Genetics

Myasthenia gravis and other autoimmune diseases aren’t hereditary (directly passed down from parents to children), but genetics still seem to play a factor. Everyone has genes known as human leukocyte antigen (HLA) genes, and some types seem to increase the chances of developing myasthenia gravis. HLA genes identify which cells belong to your body and which are foreign invaders, letting your immune system know which to attack.

HLA genes can also play a role in the type of autoantibodies you develop in myasthenia gravis. One study found that people who inherit certain pairs of HLA genes are more likely to have myasthenia gravis caused by MuSK antibodies. The type of autoantibody you have can affect your myasthenia gravis symptoms and treatment plans.

It’s also worth noting that most people who develop myasthenia gravis don’t have a family medical history of the disorder. Researchers believe that between 3 percent and 5 percent of those with myasthenia gravis have a family member with myasthenia gravis or another autoimmune disorder.

2. Age and Gender

Your age and gender can also influence your chances of developing myasthenia gravis. One report notes that myasthenia gravis is considered “a disease of young women and old men.” This is because it most commonly affects women between ages 20 and 39 and men between ages 50 and 70.

Generally speaking, women are more likely than men to develop an autoimmune disorder, according to the journal Cureus. This is especially true for myasthenia gravis — a study in the Journal of Medicine and Life (JML) notes that for early-onset myasthenia gravis (diagnosed under age 40), the female-to-male ratio is 3:1.

Infants and children may also develop myasthenia gravis, although much less often than adults do. Neonatal myasthenia gravis occurs when a mother with myasthenia gravis passes along antibodies to their infant. These congenital symptoms are temporary and typically go away on their own after a few months.

Juvenile myasthenia gravis is a form of myasthenia gravis that affects children under 18 years of age. Myasthenia gravis is a rare disorder and affects 10 in every 1 million people. Juvenile myasthenia gravis is even more rare, accounting for just 10 percent of those with myasthenia gravis.

3. Race and Ethnicity

Another known risk factor for myasthenia gravis is race or ethnicity. Studies show that people from certain racial and ethnic groups are more likely than others to develop this condition. For example, African American women have a higher risk of myasthenia gravis compared to Caucasian men and women and African American men, according to the JML study.

Your racial and ethnic background can also influence your type of myasthenia gravis. Researchers have found that Black men and women tend to develop ocular myasthenia gravis, and Caucasian women are more likely to have generalized disease.

People in Asian populations are more likely to develop early-onset myasthenia gravis and less likely to develop the late-onset type. Up to 30 percent of myasthenia gravis cases in Asian populations are an infantile-onset form that affects children up to 4 years old.

4. Abnormal Thymus Gland

Your thymus gland is an important part of your immune system — it’s responsible for making and training immune cells to protect you. Roughly three-quarters of people with myasthenia gravis have an overactive or abnormally large thymus (known as thymic hyperplasia). According to the Muscular Dystrophy Association, doctors think that a thymus with abnormalities can’t properly train your immune cells to correctly identify foreign invaders. As a result, they’re more likely to mistakenly attack your tissues and cause myasthenia gravis.

An abnormally large thymus can also collect immune cells and lead to a thymoma, or thymic tumor. Around 15 percent of people with myasthenia gravis have a thymoma, per the Muscular Dystrophy Association. Most of these tumors are harmless, but they have the potential to become cancerous.

If you have a thymoma, your doctor may suggest surgery to remove your thymus (known as a thymectomy). People often see an improvement in their symptoms after having the surgery.

5. Environmental Triggers

Researchers believe that exposure to certain environmental factors can trigger myasthenia gravis in people with underlying genetic risk factors. This means that if you have certain HLA genes, other factors in your environment may cause you to develop myasthenia gravis. These possibly triggering environmental factors include:

• Physical trauma
• Emotional stress
• Bacterial or viral infection
• Overactive thyroid (hyperthyroidism)
• Thyroid hormone therapy
• Pregnancy
• Certain medications
• Surgery
• Allergic reactions

Doctors have also found that some of these triggers can worsen symptoms in people already diagnosed with myasthenia gravis.

Find Your Team

On MGteam, the social network for people living with myasthenia gravis and their loved ones, members come together to ask questions, give advice, and share their stories with others who understand life with myasthenia gravis.

Do you have any risk factors for myasthenia gravis? Do certain situations make your symptoms worse? Share your experience in the comments below, or start a conversation by posting on your Activities page.