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Myasthenia gravis and genetics

Myasthenia gravis is a disease that belongs to the group of neuromuscular diseases, described as disorders that affect the connection between muscles and nerves, resulting in muscle weakness, fatigue, and a range of other symptoms.

Millions of people worldwide suffer from it, and although it is not known in depth what causes it, genetics and myasthenia are related, playing a vital role in the predisposition to develop it

 

What is myasthenia?

Myasthenia or myasthenia gravis is a chronic autoimmune neuromuscular disease characterized by muscle weakness. Not all muscles in the body are affected, only those that are voluntarily controlled. 

The cardiac or intestinal musculature would not be affected [1], but the muscle groups most affected by myasthenia are those of the eyes, face, throat, neck, and limbs [2]. Weakness usually increases during periods of activity and decreases with rest [3]. 

The leading cause of myasthenia gravis is the communication breakdown between nerves and muscles. In a normal situation, the nerves communicate with the muscles by releasing a neurotransmitter that interacts with muscle receptors, stimulating muscular contraction.

In most cases of myasthenia gravis, the immune system produces antibodies that attack these receptors. As a result, communication stops. 

Although it’s unknown why this happens, several theories exist, including the relationship between genetics and myasthenia. Among the possible causes, the strongest is the one that relates this autoimmune phenomenon to a dysfunction of the thymus gland. Approximately 65% of people with myasthenia gravis suffer from an enlargement of this gland, and 10% usually present a tumor known as a thymoma. Half of these are generally cancerous [4].

Is myasthenia gravis hereditary?

Myasthenia is a disease of multifactorial origin in which environmental causes are also involved; genetics and epigenetics are enormously influential in predisposing people to develop myasthenia gravis.

Human leukocyte antigen (HLA) is one of the highest-known genetic risk factors so far associated with myasthenia [6]. In addition, it is also known that there are specific congenital forms of the disease of genetic origin, but with a different pathogenesis, known as Congenital Myasthenic Syndromes [7].

 

Signs and symptoms of myasthenia

The main symptoms of myasthenia gravis are related to the muscle weakness that characterizes the disease. In the first instance, about 40% of patients have their eye musculature affected, although, over time, 85% of those diagnosed with myasthenia will have this problem [4].

In addition to the eyes, where drooping of one or both eyelids and double vision occur, other frequently affected muscles and their symptoms are as follows:

  • Muscles of the face and throat: impaired speech, difficulty swallowing, fatigue when chewing, and changes in facial expressions.
  • Muscles of the neck and extremities: difficulty supporting the head, instability when walking, and weakness in the arms, hands, and fingers. This weakness in both arms and legs caused by myasthenia gravis is not symmetrical as in other neuromuscular diseases [5].

 

Symptoms usually improve with rest, so muscle weakness may appear at certain times and disappear at others. Despite this, the general symptomatology tends to evolve, reaching its worst stage a few years after diagnosis [2]. 

The good news is that, after this time, the progression of symptoms usually slows down, and some stabilization is achieved, although the severity of the disease may suddenly change [5].

One of the most severe problems of this disease occurs when weakness occurs in any of the muscles of the respiratory system. In these cases, a myasthenic crisis may occur, consisting of dyspnea and acute respiratory failure that may require hospital admission [4].

If we don’t treat a respiratory crisis immediately, myasthenia gravis can be fatal. However, with proper care, patients often have a completely average life expectancy [5].

Myasthenia is most often diagnosed in women in their 20s and 40s and men in their 50s and 80s. Although it rarely occurs in childhood, the disease may develop in people of any age [4]. There is no cure for myasthenia gravis, but with the correct treatment, symptom relief is achieved [2].

Myasthenia gravis genetics

24Genetics and genetic myasthenia

Some studies have shown that myasthenia gravis occurs commonly in people with other autoimmune disorders, such as rheumatoid arthritis, systemic lupus erythematosus, and other conditions that cause overstimulation of the thyroid gland, such as Hashimoto’s thyroiditis [4].

An excellent way to anticipate the diagnosis of these diseases and, in some way, to be forewarned before the appearance of the first symptoms is to know your genetic predisposition to develop them. At 24Genetics, we have the most complete health tests on the market, through which you will see if you are more or less prone to develop many diseases related to genetics, like myasthenia. So come in and get yours!

 

Bibliography

[1] Myasthenia gravis – Genetic and Rare Diseases Information Center [updated Mar. 2018 – accessed Mar. 2023] Available at: https://rarediseases.info.nih.gov/espanol/13037/miastenia-grave

[2] Myasthenia gravis – Mayo Clinic Staff [updated May 2019 – accessed Mar. 2023] Available at: https://www.mayoclinic.org/es-es/diseases-conditions/myasthenia-gravis/symptoms-causes/syc-20352036

[3] Myasthenia Gravis Fact Sheet…. National Institute of Neurological Disorders and Stroke (NINDS). [published 2017; accessed Mar. 2023] Available at: http://www.ninds.nih.gov/disorders/myasthenia_gravis/detail_myasthenia_gravis.htm.

[4] Myasthenia gravis -Michael Rubin , MDCM, New York Presbyterian Hospital-Cornell Medical Center [accessed Mar. 2023] Available at: https://www.msdmanuals.com/es-es/hogar/enfermedades-cerebrales,-medulares-y-nerviosas/trastornos-del-nervio-perif%C3%A9rico-y-trastornos-relacionados/miastenia-grave.

[5] Myasthenia gravis – Dr. Jaime Gállego Pérez De Larraya (specialist neurology department) [accessed Mar. 2023] Available at: https://www.cun.es/enfermedades-tratamientos/enfermedades/miastenia-gravis

[6] Genetic factors influencing familial and sporadic forms of autoimmune myasthenia gravis – María Salvadó Figueras [published Feb. 2020; accessed Mar. 2023] Available at: https://www.tdx.cat/handle/10803/669455#page=1

[7] Myasthenia gravis – Reviewed by Dr Sonia Berrih-Aknin – Pr Bruno Eymard [updated Nov. 2014; accessed Mar. 2023] Available at: https://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=ES&Expert=589

Written by Debora Pino García

Geneticist

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