Duchenne Muscular Dystrophy: An X-linked Recessive Genetic Disorder

Duchenne Muscular Dystrophy (DMD) is a type of muscular dystrophy that primarily affects males. The genetic culprit is the DMD gene that makes a muscle protein called dystrophin. The correct form of DMD is essential for proper muscle functioning and development. In people with this genetic disorder the dystrophin protein is not made at all. It is estimated that 1 in 3,500 to 5,000 newborn males are affected by DMD on a worldwide basis.

In patients with the genetic disorder DMD muscle weakness appears in early childhood and progresses rapidly as they age. Children show delayed motor skills and usually cannot perform simple tasks such as sitting, standing and walking. By puberty, DMD patients are frequently dependent on a wheelchair.

There is also a severe heart condition that can be associated with Duchenne Muscular Dystrophy; dilated cardiomyopathy. This causes the heart to enlarge and results in blood not being properly pumped round the body.

To date the DMD gene (also known by the names of BMD, DMD_HUMAN, and Dystrophin) is the largest known human gene. It's located on the short arm of the X chromosome. More specifically, it's located at position at position 21.2 from base pair 31,047,265 to base pair 33,267,646 on the X chromosome.

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The DMD genetic disorder is inherited following an X-linked recessive pattern. In males, one mutated copy of the gene is enough to produce the DMD symptoms. As women have two X chromosomes the mutation of the DMD gene must be present in both sex chromosomes for the gene to cause the disorder. If it's present in just one, a woman is usually asymptomatic because of the presence of a correct version of the gene on the other X chromosome.

It has been estimated that 66.6% of DMD male patients receive the mutated gene from their mother. The other 33.3% seem to be affected by “naturally” occurring genetic mutations.

Currently there is no cure or treatment for Duchenne Muscular Dystrophy. All that can be done for patients is to manage the disease through physical therapy and certain drugs. There are also several labs around the world looking for a gene therapy treatment and several trials are underway.

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