Myaesthenia Gravis is a wasting neuromuscular disease. There is no known cause, and there is no known cure. It attacks approximately one person in twenty- thousand. That makes it rather common. More common than, say, Muscular Dystrophy or Multiple Sclerosis, or several of the other, rather, better-known diseases of the same family of wasting neuro muscular diseases, which include polio and stroke.
Stroke is the same, in that it ends up with the same result.
You end up paralyzed. And I travel all over the country for them. And generally, I can recognize a myasthenic at a hundred yards. They have an identifying look. Which, anyone trained can spot immediately.