Muscular dystrophy (MD) refers to a group of genetic diseases that cause progressive muscle weakness and loss. More than 30 forms of MD exist, all with different causes and symptoms. Though the most common types appear during childhood, other forms affect only adults.
MD is generally caused by a mutation in the genes that encode for essential muscle proteins. People typically inherit these mutations from their parents. MD currently has no cure, but available treatments can reduce symptoms and slow progress of the disease.
Common muscular dystrophy types
Duchenne is the most common form of MD, accounting for about a third of all muscular dystrophies. It affects about one in every 3,500 male births. Duchenne patients have a mutation in the DMD gene that causes a lack of dystrophin protein. Dystrophin maintains the structure of muscle fibers, so without dystrophin, a patient’s muscles gradually degrade.
The first signs of Duchenne usually occur between ages 1 to 3. As they grow, boys start to show difficulty running, jumping or standing, and most of them need a wheelchair by their teen years. Muscle degradation can be severe enough to shorten life expectancy, though modern treatments can generally slow muscle deterioration, so it is not uncommon for patients to live into their 30s and 40s.
Like Duchenne, Becker MD is also caused by a mutation in the DMD gene. However, Becker is much milder. Patients typically don’t develop symptoms until after age 10, or even into adulthood. Symptoms may include issues with the heart, lungs, joints and skeletal muscles. Most patients are able to maintain an active lifestyle without wheelchair assistance.
Facioscapulohumeral MD (FSHD) generally appears in the teen years or early adulthood. Severity differs among patients, but most FSHD patients experience muscle weakness in the face and shoulders. They usually have difficulty raising their arms, whistling and making certain facial expressions such as closing their eyes tightly.
Myotonic dystrophy typically does not develop until adulthood. Two types of myotonic dystrophy exist, depending on which gene is mutated. Patients with myotonic MD have difficulty contracting and then relaxing muscles at will. Symptoms typically appear first in neck and facial muscles. Myotonic MD also has an early childhood form known as Steinert’s disease.
Limb-girdle MD (LGMD) is associated with a weakening of both the shoulder and upper-arm muscles and the central hip muscles. LGMD can appear as early as childhood and as late as middle age, and it usually progresses very slowly. Muscle degradation linked to LGMD can result in a waddle-like gait and trouble reaching overhead. In advanced stages of LGMD, heart and breathing muscles may also be affected.
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