Myasthenia gravis is an autoimmune disease characterised by muscular weakness. In order to move at will, voluntary muscles receive chemical messages (neurotransmitters) from nerves (motor neurones) at special structures called neuromuscular junctions, where the nerve joins the muscle fibre. The neurotransmitter passes to a receptor, which is activated and causes the muscle to contract.
In myasthenia gravis, the immune system stops the action of the neurotransmitter by blocking or destroying the receptor in the neuromuscular junction - this prevents the muscle from contracting. This blocking of the chemical messages causes the muscular weakness. Usually, a person affected by this disease has a worsening of symptoms after physical exertion and feels better after resting. The disease usually targets the eyes first. Sometimes, the disease progresses further and interferes with swallowing, chewing and talking. Myasthenia gravis is rarely fatal unless the muscles of respiration are impaired. Around three in every 10,000 people are thought to have the disease. Women are twice as likely as men to develop myasthenia gravis, although anyone of any age or either sex can have the disease. There is no cure, but treatment can ease the symptoms.