Larrie Stone

Larrie Stone

Muscular dystrophy is a group of genetically transmitted diseases characterized by progressive atrophy — deterioration — of muscle tissue somewhere in the body.

There are nine distinct types of this disease that are recognized. Each form of muscular dystrophy includes an insidious loss of strength with increasing disability and deformity. However, each type differs somewhat in the muscle groups affected, the age of onset, the rate of progression and the mode of genetic inheritance.

Duchene muscular dystrophy (DMD) is inherited as a sex-linked recessive trait. This means that the flawed or mutated gene responsible for DMD is located on the X-chromosome. Males have only one X-chromosome and a Y-chromosome, while females have two X-chromosomes. A few females in the human population can have an X-chromosome bearing the mutated DMD gene and are called carriers. They are usually normal, although a minority of them do suffer some degree of muscular weakness. However, they have the probability of passing the DMD gene on to half of their male offspring.

DMD affects about 1/5,000 males at birth and in approximately two-thirds of these cases, the gene is inherited from their mother while the other third of cases are due to a new mutation in either the egg or sperm they received at conception.

The DMD gene is responsible for the production of the muscle protein dystrophin. This protein is necessary for maintaining muscle cell integrity. Without this protein, the muscle cells and eventually the muscles themselves collapse.

Early in childhood, boys with the mutant gene begin to have muscle atrophy leading to disability which gets progressively worse. These children typically die in their teens or early twenties as a result of respiratory failure.

Thanks to advances in cardiac care and respiratory care, life expectancy is increasing and many young adults with DMD now attend college, have careers, and get married. Survival into the early 30s is becoming more common, and there are cases of men living into their 40s and 50s.

Another column will describe some very promising research on a possible cure for this debilitating genetic disease.

Larrie Stone is a retired Dana College science professor.

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