ABIOTROPHY of skeletal muscle — that is, degeneration and atrophy after a latent period of apparently normal development and function — is the most obvious common denominator in the group of disorders called the muscular dystrophies. It should be realized, however, that systems other than skeletal muscle are frequently involved in these diseases. Striking examples of this are the cataract, frontal baldness, skeletal anomalies, gonadal atrophy and personality change seen in myotonic dystrophy. The relation between the changes in skeletal muscle and those in other tissues is uncertain except that they behave as single mendelian traits genetically. Although the several . . .