Why does MG happen?

What is the cause of Myasthenia Gravis?

Myasthenia Gravis (MG) occurs when the immune system mistakenly attacks the neuromuscular junction, where nerves and muscles communicate (1). This attack disrupts the normal transmission of messages from nerves to muscles (1). As a result, the muscles can’t work as they’re supposed to. 

To better understand why MG symptoms occur, let’s have a closer look to what triggers the disease.

 

Laboratory research on factors triggering Myasthenia Gravis

Autoimmune diseases in a nutshell

 

Autoimmune diseases occur when the immune system attacks the body's own components. These conditions are not contagious. Some people have an inherited predisposition, but in many cases the causes are still largely unknown.(2)

 How the muscle function normally 

Diagram of a healthy neuromuscular junction without Myasthenia Gravis

For a muscle to function normally, a neurotransmitter called acetylcholine attaches to acetylcholine receptors at the neuromuscular junction (where the nerve and muscle connect), producing a signal between the nerve and the muscle which causes the muscle to contract.(3)

 How MG causes muscle weakness 

Diagram of a neuromuscular junction affected by Myasthenia Gravis

In myasthenia gravis, abnormal autoantibodies are produced which block the attachment of acetylcholine to its receptors and the follow-on effects that affect the signals between the muscle and the nerve at the neuromuscular junction.(3)

Autoantibodies are produced by the immune system to help fight infection and disease. While the immune system is usually helpful in this manner, for people with myasthenia gravis there is a disruption to the balance of how the immune system works. This disruption causes the production of abnormal antibodies.(3)

These abnormal antibodies then affect the signals between the muscle and the nerves at the neuromuscular junction, causing the symptoms of myasthenia gravis, including muscle weakness.(3)

Another important part of our immune system is a pathway called the complement pathway. While the complement pathway is usually helpful, in people with myasthenia gravis this pathway can be overactive, causing changes to the neuromuscular junction. These changes reduce the number of acetylcholine receptors, meaning that there are fewer receptors for acetylcholine to bind which also affects the signals between the nerves and the muscles which results in muscle weakness. (3) ​

While there is no cure, MG symptoms can be treated

 

A treatment goal for people living with MG is to reduce symptoms or become symptom-free for a period of time. For this reason, you may want to have frequent conversations with your doctor about your MG symptoms. The MG-ADL scale is one tool used to measure MG symptoms, where symptoms are measured from 0-24, with a higher score meaning more severe MG.(4)

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REFERENCES :

1. Gilhus NE. N Engl J Med. 2016;375(26):2570-2581.

2. Myasthenia Gravis Fact Sheet. National Institute of Neurological Disorders and Stroke Website. Updated March 2020. Accessed May 2020. https://www.ninds.nih.gov/myasthenia-gravis-fact-sheet

3. Myasthenia Gravis Foundation of America. Overview of Myasthenia Gravis. 2020. https://myasthenia.org/understanding-mg/what-is-myasthenia-gravis.  Accessed Sept 2024.

4. Wolfe GI, et al. Neurology. 1999;52(7):1487-1489.

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argenx, a global immunology company, created MG United to support people living with MG and those who care for them. By providing information on MG United, argenx aims to help improve the lives of people suffering from this autoimmune disease. MG United does not offer medical advice; always consult your healthcare team for personalised medical guidance. The brands listed are the trademarks of their respective owners.