Duchenne muscular dystrophy (DMD) is one of the most common types of inherited neuromuscular diseases, affecting about one in 3,500 boys.
DMD’s progression is relatively rapid compared with other types of muscular dystrophy. Boys typically begin showing signs of the disease between ages 1 and 6 and usually need to use a wheelchair before they reach their early teens.
DMD is caused by the lack of a protein called dystrophin. This protein provides structural support to muscle fibers. Without dystrophin, muscle fibers get damaged when they contract, and patients experience progressive muscle weakness.
Parents typically first notice signs of DMD when their toddler takes longer to reach developmental milestones, such as lifting their head, sitting, walking, and talking. A boy may also find it difficult to rise from the floor and walk their hands up their legs to stand from a sitting position. This is called the Gower maneuver, and it is a typical sign of DMD.
Boys usually experience muscle atrophy initially in muscles surrounding the hips and shoulder region. It is also common for boys with DMD to have enlarged calves. This is due to scar tissue build-up in muscles, and muscle tissue being replaced by fat and connective tissue.
Once boys with DMD do begin to walk, their movements may seem awkward. And they may walk on their toes or have a waddle-like gait. They often must extend their bellies and pull back their shoulders to maintain balance. Boys with DMD also tire noticeably faster than other children.
Most patients need a wheelchair for longer distances between ages 7 and 12 and become dependent on one by their early teens. Scoliosis, or curvature of the spine, commonly develops as patients spend more time in a wheelchair. Contractures, or tight and rigid joints, may also surface as the disease progresses, further limiting the patient’s range of motions.
Cardiac and respiratory issues
In addition to skeletal muscle atrophy, DMD patients also experience weakening of the heart and diaphragm muscles at later stages of the disease.
Symptoms of this damage start to be noticed in the teenage years. Cardiomyopathy, caused by muscle wasting of the heart, can result in an abnormal heartbeat and lead to heart failure.
The muscles that support breathing also weaken, increasing the risk of respiratory infections, and ultimately respiratory failure. In later stages of the disease, patients may need a ventilator to help them breathe.
About one in three DMD patients experiences some degree of cognitive impairment. This can lead to difficulties with learning and social interactions.
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