Duchenne muscular dystrophy, usually abbreviated to DMD, is one of the most common types of muscular dystrophy. It is a severe genetic disease characterized by muscle weakness from a young age, and it affects approximately 1 in 5000 males.
DMD is caused by an alteration in the dystrophin gene (also known as the DMD gene). When this gene is faulty, the body cannot produce an important protein called ‘dystrophin’.
This dystrophin gene is located on the X chromosome. DMD is a recessive disorder, meaning that so long as there is at least one working copy of the dystrophin gene, the individual should not be affected. This is why females are rarely affected; they have two X chromosomes, so though one X chromosome may have the altered dystrophin gene, the other working X chromosome will compensate for this. Females with one altered dystrophin gene are called “carriers” – they are usually unaffected by the disease, but can pass on this to their children. In extremely rare cases, females can also be affected by DMD.
As a result, almost all DMD patients are male, due to the fact they have one X chromosome and one Y chromosome. If their X chromosome has the faulty dystrophin gene, they do not have any compensatory working copy, and thus will be have DMD.