RÉSUMÉ
Signs of myasthenia gravis developed by age 3 years in 11 children. Six of these patients had persistent neonatal myasthenia gravis, a familial abnormality of neuromuscular transmission that is not immunologically mediated. Five patients had juvenile onset myasthenia gravis, an autoimmune disorder similar to myasthenia gravis in adults. Autoimmune myasthenia has rarely been recognized by age 3 years, but the presence of five cases in our series suggests that the disorder may be more common in young children than once believed. The development of anti-acetylcholine receptor antibody assays makes it easier to distinguish autoimmune myasthenia gravis from the congenital forms. This distinction is important, because the prognosis, treatment, and risk of recurrence in family members is different for each type of myasthenia.