The coexistence of myasthenia gravis and myotonic dystrophy in one family

We are reporting the unique coexistence of two distinct neuromuscular diseases, myotonic dystrophy and the juvenile form of myasthenia gravis, occurring in one family. A 16-month-old previously healthy female presented with a two month history of bilateral varying drooping of both eyelids and bilateral external ophthalmoparesis. The acetylcholine receptor antibodies were elevated, and there was a dramatic response to edrophonium confirming the clinical impression of myasthenia gravis. Spontaneous remission of the ptosis was noted after six months with no specific treatment. Many other family members were examined; none of them had clinical or laboratory evidence of myasthenia gravis. The clinical examination of the mother and the maternal grandmother, neither of whom had any complaints, resulted in a definite diagnosis of myotonic dystrophy. The proband's father and a 3-year-old sister were examined and found to be normal. We studied the HLA antigens of all of the available family members; none were found to have the HLA antigens most commonly associated with myasthenia gravis. Secretor gene studies were not helpful in providing additional genetic identification. The question generated by the coexistence of these two uncommon disorders in one family is if there is a genetic or other relationship between them or if this was merely a coincidental occurrence. At this point in time the question remains unanswered and must await demonstration of additional similar circumstances.