MG is the most common primary disorder of neuromuscular transmission. The usual cause is an acquired immunological abnormality, but some cases result from genetic abnormalities at the neuromuscular junction. Much has been learned about the pathophysiology and immunopathology of MG during the past 20 years. What was once a relatively obscure condition of interest primarily to neurologists is now the best characterized and understood autoimmune disease. A wide range of potentially effective treatments are available, many of which have implications for the treatment of other autoimmune disorders.

EPIDEMIOLOGY
The prevalence of MG in the United States is estimated at 14/100,000 population, approximately 36,000 cases in the United States. However, MG is probably under diagnosed and the prevalence is probably higher. Previous studies showed that women are more often affected than men. The most common age at onset is the second and third decades in women and the seventh and eighth decades in men. As the population ages, the average age at onset has increased correspondingly, and now males are more often affected than females, and the onset of symptoms is usually after age 50.