Prenatal diagnosis of congenital myasthenia with arthrogryposis in a myasthenic mother.

We studied two children born to a myasthenic mother. The first child, a female, had multiple flexion contractures. She died 1 h after birth. In the second pregnancy, 3 years later, ultrasonographic examination at 20 weeks showed decreased fetal movements and multiple flexion contractures. The pregnancy was interrupted. Eight other cases of congenital myasthenia with arthrogryposis are known; four of them are siblings. The recurrence risk may be as high as 100 per cent. Our second case demonstrates that prenatal diagnosis is possible early enough to allow termination of pregnancy.