Congenital muscular dystrophies.

The congenital muscular dystrophies are a group of genetic myopathies characterized by hypotonia, weakness, or arthrogryposis at birth. Classification is inadequate and based entirely upon phenotypic expression, because a genetic marker has not been identified in any of these disorders. Some have only muscle disease, whereas others have cerebral disturbances (hypomyelination and/or disturbances of neuronal migration) as well. Ocular malformation may also be present. The outcome is variable, and it is difficult to provide an accurate prognosis soon after birth.