Prevalence and Heritability of Duchenne Muscular Dystrophy
DR. P. MICHAEL CONNEALLY: Duchenne muscular dystrophy is inherited as an X-linked recessive disorder. The lesion seems to be in the middle of the short arm of the X chromosome. There is also an autosomal recessive condition which is very akin to Duchenne and is relatively common among the Amish (1). For practical purposes, Duchenne dystrophy occurs only in males. Although cases of females with Duchenne muscular dystrophy have been reported (2), the majority are Turner’s syndrome (XO) or structural abnormalities of the X. In fact, you will see stated in textbooks that the frequency of Duchenne muscular dystrophy in Turner’s is the same as the frequency in males because they only have one X chromosome. This is not quite true. If, for example, all of the nondisjunction occurs in the male, then the stated frequency in Turner’s syndrome would be correct. If, on the other hand, all of the nondisjunction occurred in the female, then all of the X’s would come from the male; in this case you would have no Duchenne since it is an X- linked lethal. There is also a possibility of extreme lyonization which could also cause Duchenne in females if, by chance, all or the vast majority of their normal X’s are inactivated (2).
KeywordsCreatine Kinase Muscular Dystrophy Duchenne Dystrophy Duchenne Muscular Dystrophy Fragile Site
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