Clinical expression of myotonic dystrophy: the predictive role of DNA diagnosis.

Myotonic dystrophy (DM), the most common muscular dystrophy of adult life, presents with a variety of clinical and genetic challenges to all involved; patients, their families, and clinicians. The clinical picture is extremely variable and may range from mild adult onset myotonia to severe congenital hypotonia associated with respiratory distress. An infant born to a mother with DM had remarkable hypotonia, expressionless face, respiratory difficulties, and club feet. Direct molecular genetic testing of the newborn and the mother showed trinucleotide repeat expansion mutations. Genetic counseling issues as well as the value of prenatal diagnosis are presented.