Myotonic dystrophy. Part I. A genealogical study in the northern Transvaal.

Myotonic dystrophy is a disabling multisystem disorder which appears to be more common in South Africa than is generally recognized. Twenty white kindreds with the disease were studied; of these 4 large kindreds had a common ancestry. Genealogical data for 1 527 individuals were acquired. The minimum prevalence of myotonic dystrophy in the northern Transvaal was found to be 14,3/100 000 of the population. Recognition of the disorder is important since some of its complications are preventable and others potentially treatable.