Myasthenia gravis (MG) is a neuromuscular disease that presents with fluctuating muscle weaknessA condition characterised by varying degrees of muscle weakness that can change in intensity over time, often seen in neuromuscular disorders like myasthenia gravis
and fatigue.1,2 This is caused by the body’s own defence mechanism, the immune systemThe body’s defence system that protects against disease and infection (e.g. bacteria and viruses), mistakenly attacking and disrupting the communication between the nerves and muscles at the place where they connect, or what is known as the neuromuscular junction.3
The normal function of the immune system is to fight off infections when foreign microorganisms, such as bacteria and viruses, enter the body.4 In MG, the immune system is mistakenly activated to attack the body’s own cells, which is why MG is characterised as an autoimmune diseaseA condition in which the immune system mistakenly attacks and damages healthy cells and tissues.1,4
The term myasthenia gravis comes from a combination of Greek (mys = muscle, asthenia = weakness) and Latin (gravis = severe) terms meaning “severe muscle weakness”.
MG affects approximately 150–250 individuals for every 1 million people worldwide.1 Though rare, MG is very well characterised and is one of the most common diseases affecting the neuromuscular junction.1,6
About 85% of patients with MG experience gMG1
In individuals younger than 50 years of age, MG is three times more common in females than in males.1 In individuals older than 50 years of age, MG is slightly more common in males than in females.1
The nerves normally control the muscles by sending electrical signals, so-called nerve impulsesThe electrical signals sent by the nerves to control the muscles, to the muscles.3 As a result of the impulses, the nerve cells release specific molecules at the neuromuscular junctionThe place where nerves and muscles connect.3 The released molecules are called acetylcholine. Acetylcholine molecules bind to proteins called acetylcholine receptors on the muscle surface. This binding activates the muscles and leads to muscle contractionThe tightening or shortening of muscle fibres, leading to movement or muscle tension.3
In individuals with MG, the body's immune systemThe body’s defence system that protects against disease and infection (e.g. bacteria and viruses)
produces specific proteins, known as autoantibodiesAntibodies produced by the immune system that mistakenly target and attack the body’s own tissues or cells
, that mistakenly block or alter the function of the acetylcholine receptors, causing muscles to be unable to contract.3,6 These autoantibodies can also lead to activation of the complement systemProteins in the blood that help to fight infections and are part of the immune system
1 – a part of our immune system that normally helps fight disease by clearing up foreign molecules and damaged cells.7,8 However, in MG, the complement activation instead causes damage to the body’s own muscle cells.1,6
Though both genetic and environmental factors play a role in the development of MG,1 in most cases MG is not genetically inherited and occurs in people with no history of disease in their family.9 Who’s at risk for MG may also be influenced by sex hormones, which could explain the differences seen in the frequency of MG between females and males.1
gMG, generalised myasthenia gravis; MG, myasthenia gravis.