Anyone can get MG. Statistics vary about the frequency of the disease, but according to the Myasthenia Gravis Foundation of America, the prevalence is about 1 in 5,000. MG occurs in all ethnic groups, in both genders, and can strike at any age. It is not clear why an individual develops MG, but some researchers believe the cause could be a genetic defect.

By Ethnic Group
No studies show one ethnic group being more or less susceptible to MG than another. Cases of MG have been documented in countries throughout the world.

By Sex
When MG affects young adults, women are twice as likely to be affected as men of the same age group (5).

By Age Group
While individuals are susceptible at any age, the vast majority of cases are attributed to an acquired disorder of the immune system that appears in adulthood. MG most commonly affects young adult women (under age 40) and older men (over age 55). The most common age of onset is between 20 and 30 years in women and about 50 years in men.

By Genes
In rare cases, MG is caused by a defective gene in infants born to non-myasthenic mothers. This is called congenital myasthenia gravis, and infants have MG symptoms based on a genetic abnormality in neuromuscular transmission.

Twelve percent of babies born to myasthenic mothers have received the mother’s antibodies. The baby will exhibit MG symptoms such as a feeble cry, weak sucking or respiratory distress which can be reversed by anticholinesterase medication or blood exchange. These signs of neonatal MG spontaneously disappear within the first few weeks or months of life.

Rarely, infants exhibit symptoms of MG. However, the symptoms usually disappear within the first few weeks or months of life – sometimes with treatment and sometimes spontaneously.

MG is not strictly hereditary, but people who inherit a tendency to develop autoimmune disease are at an increased risk of developing MG.

Close relatives of an affected person have a slightly higher chance of developing MG than average, however, this risk increases as the relative gets closer.