Manifesting Carriers of DMD or BMD

What is a Manifesting Carrier?

A manifesting carrier is a female who displays symptoms of a condition that usually only affects males such as Becker and Duchenne Muscular Dystrophy. Although it is a commonly held belief that carriers merely pass on the disease and are unaffected, female carriers can have similar muscular weakness as affected males and for this reason are termed Manifesting Carriers. This condition can occur with no known family history of BMD or DMD so all females who are suspected of having any form of muscular dystrophy should be tested to determine if they could be Manifesting Carriers because of the genetic implications.

Genetic Aspects

All females inherit two copies of the X chromosome - one from each parent. Each body cell needs only one functional X chromosome. This is randomly determined, so that all females have a mixture of cells in which the active X is either the maternal or the paternal.

All carriers of DMD have some cells in which the active X carries the defect and problems arising from them will obviously depend on the proportion of such cells and their distribution. There is a theory that a compensatory mechanism could cause the 'normal' cells to produce enough dystrophin to make up the deficiency - this has yet to be demonstrated. In very rare cases, when the active X carrying the DMD gene is in the cast majority of muscles cells the female carrier will have DMD as severely as affected males. At the other end of the scale the carrier can be unaffected. It is estimated that at least 10% of carriers may have problems, which can vary from a mild generalized weakness to an inability to walk, depending on how many muscles are affected. The weakness can be asymmetric. There is also growing evidence that the heart muscle can be affected in isolation which may not become apparent until later in life. (sourced from 4/4/14). For more information on Manifesting Carriers click here. 

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