Duchenne muscular dystrophy or DMD is the most common of the muscular dystrophies, affecting approximately 1 in every 3,500 newborn boys. It is caused by a fault in a gene called the dystrophin or DMD gene. A fault in this gene stops the body making a protein called dystrophin. This protein is important in muscle fibres, and its absence results in muscle weakness that gets worse over time because muscle cells break down and are gradually lost.
Because the dystrophin gene is on the X chromosome, Duchenne muscular dystrophy affects only boys. Girls have two X chromosomes, so if one of these is unaffected it can usually compensate for the faulty one, while boys have one X and one Y chromosome, so if their single copy of the dystrophin gene is faulty, they have the symptoms of DMD, while girls with one affected gene and one normal one usually won't show symptoms but can be "carriers". This means that the disease can be passed on in families - a mother who is a carrier has a 50:50 chance of having a son who is affected. But in up to about a third of cases, the mutation arises spontaneously in the boy.
Most affected boys develop the first signs of difficulty in walking at the age of 1 to 3 years. They often walk later than other boys their own age, have enlarged calf muscles and have trouble running, jumping or climbing stairs. They fall easily and may have a tendency to walk on their toes. They may also have a speech delay. One of the classic signs of DMD is what is known as the "Gowers’" manoeuvre or sign, where the boy has to use his hands and arms to "walk" up his body in order to push himself to an upright position. This is due to weakness in the hips and thigh muscles. Some boys also have learning and or behavioural difficulties.
Typically, boys with Duchenne lose their ability to walk between the ages of ten and fourteen. By their late teens, they lose the strength in their upper bodies, including the ability to move their arms. The disease also affects the heart and breathing muscles, so around this time they also usually need help with breathing at night. Over time, their respiratory systems weaken, and they require constant support. Young men with Duchenne do have a shorter life expectancy but advances in management of the condition have increased life span significantly and enabled young men to lead much more independent lives than was previously possible.
While there is still no cure for DMD, it is one of the conditions where there is substantial active research and where several potential new therapies are currently being tested in clinical trials. It is also a condition for which experts have established internationally approved care guidelines that can make a big difference to the quality of life and life expectancy of a boy with the disease.