Myasthenia gravis is a disorder of neuromuscular transmission in which the acetycholine receptors are blocked by autoantibodies. As a result, there is weakness of muscles, initially the extra-ocular muscles leading to diplopia, later the respiratory muscles and muscles for movement. Inheritance is usually sporadic. In 1 to 4% of cases there is apparently a familial tendency to get the disease, but there is not an easily discernable pattern of inheritance.