Congenital myotonic dystrophy
Incidence
It is seen only in offspring of women who are themselves affected with myotonic dystrophy.
Clinical Characteristics
Congenital myotonic dystrophy was first recognized in 1960, and it has since become clear that it is a distinctive, frequently fatal, and far from rare form of myotonic dystrophy. It is seen only in offspring of women who are themselves affected with myotonic dystrophy. These mothers are often only mildly affected but almost invariably show some neuromuscular abnormalities. The relationship between the congenital and the commoner adult-onset form of the disease is still not fully understood, although molecular analysis is now providing evidence on this topic. The major clinical features of this disorder are: bilateral facial weakness, feeding difficulties, hypotonia, talipes, delayed motor development, hydramnios in later pregnancy, mental retardation, neonatal respiratory distress and reduced fetal movements. The facial appearance is highly distinctive, largely owing to the combination of bilateral facial palsy with marked jaw weakness. The early, often intrauterine onset of muscle weakness helps to mold the facial features by creating the characteristic tented upper lip. Decreased intrauterine muscle action plays a role in many of the other features, such as the high incidence of respiratory inadequacy and pulmonary hypoplasia (caused by underdeveloped diaphragm and intercostal muscles), the occurrence of talipes and other joint contractures, the development of polyhydramnios (owing to lack of intrauterine swallowing), and the generally poor fetal movements. By contrast to the adult disorder, myotonia is inconspicuous or absent in affected infants, though it becomes more prominent as affected individuals reach later childhood. The relationship to adult myotonic dystrophy is important to recognize, since the discovery of a typical adult case in the family, usually the mother or another maternal relative, will confirm the diagnosis in the infant. It has been recognized for many years that this form is not only clinically very different from the disease in adult life but, also, is exclusively transmitted by affected females, even though these mothers are often not severely affected themselves.
Precipitants
no
Provocation Tests
no
Diagnostic Procedures
DB-W. Molecular analysis, is proving particularly helpful in the diagnosis of congenital myotonic dystrophy, since affected individuals show a large expansion (3 to 6 kb) of the unstable DNA sequence, which should be readily recognizable. Absence of this specific abnormality would strongly suggest that another form of congenital myopathy is the cause of the problem. Detection of the molecular defect also now can be used for specific prenatal diagnosis.