Muscular dystrophy

Definition
The term muscular dystrophy (MD) refers to a group of inherited muscle disorders that cause muscles to become progressively smaller and weaker.

Causes/associated factors
Muscular dystrophy is most common in males. Each type of muscular dystrophy is caused by a genetic abnormality. These genetic abnormalities are known to cause a defect in muscle protein that's needed for normal muscle function. As muscle function decreases, they become progressively weaker. Other tissue replaces the lost muscle, and muscles may appear bigger. Rarely, muscular dystrophy can occur in people with no family history of the disease.
Muscular dystrophy can be passed to a child in one of three ways.

Autosomal dominant transmission occurs when one parent with the disorder passes the abnormal gene to his or her biological children. A parent who has one abnormal dominant gene and a corresponding normal gene has a 50 percent chance of passing on the abnormal gene to his or her children. If the parent has two abnormal dominant genes for MD, the abnormal gene will be passed on and all the children will develop the disorder.

Autosomal recessive transmission occurs when both parents pass a recessive gene for MD to their child, who will then develop MD. Because neither parent is usually affected, they're known as carriers. If a child receives one normal gene and one abnormal gene, the normal gene is dominant and the child will not develop MD, but will become a carrier. If both parents are carriers, their children have a 25 percent risk of developing MD and a 50 percent risk of becoming carriers.

X-linked recessive transmission occurs when the abnormal gene for MD is recessive and located on the X chromosome, one of the chromosomes that helps determine the child's sex. Mothers are carriers of this type of MD and can pass it on to their sons. Daughters who receive the abnormal gene are usually not affected, but become carriers. When a mother is a carrier, her sons have a 50 percent chance of developing MD and her daughters have a 50 percent change of becoming carriers.

Signs/symptoms
Often, the first symptom of muscular dystrophy is muscle weakness. Other signs vary depending on the type of muscular dystrophy. Here are details on the most common forms of MD.
Duchenne's muscular dystrophy
Duchenne's muscular dystrophy is the most common form of childhood MD, usually appearing between ages 2 and 6. An X-linked recessive disorder, Duchenne's MD typically affects the muscles of the pelvis, upper arms and upper legs. It progresses rapidly. Children with this type of MD often need wheelchairs by age 12.

Duchenne's muscular dystrophy causes frequent falling, changes in walking that produce a "waddling" motion, and problems getting up from a sitting or lying position. A collection of fat and connective tissue often makes the calves appear larger than normal. As muscles weaken, deformities of the spine and feet also appear.

Breathing may become weaker as the disease progresses, which can lead to respiratory infections such as pneumonia. Duchenne's MD often leads to significant respiratory and heart problems. People who have Duchenne's MD and their families often eventually face a decision about whether to use a ventilator. Most children who have Duchenne's MD live until the teens or early 20s.

Becker's muscular dystrophy
Becker's muscular dystrophy usually appears in children ages 2 to 16, but it may develop as late as age 25. An X-linked recessive disorder, Becker's MD progresses slowly and is less severe than Duchenne's MD, but symptoms are similar. This type of MD also affects the muscles of the pelvis, upper arms and upper legs. Walking is often possible until the mid-30s. People with Becker's MD may experience heart problems similar to those caused by Duchenne's MD.

Myotonic muscular dystrophy
Myotonic muscular dystrophy is the most common form of MD for adults. An autosomal dominant disorder, myotonic MD generally progresses slowly and may appear anytime from early childhood through adulthood. The muscles in the face, feet, hands and front of the neck are usually affected first. Myotonic MD causes cataracts (a cloudy area in the lens of the eye, the clear structure that focuses light rays onto the retina) and stiffness and/or muscle spasms. It also affects the central nervous system, heart, gastrointestinal tract and endocrine glands (glands that produce hormones).

Facioscapulohumeral dystrophy
An autosomal dominant disorder, facioscapulohumeral dystrophy commonly appears in the teens or early adulthood. This type of MD progresses slowly and varies in severity. The muscles in the face and shoulders are often affected first. Shoulders may slope forward, and the person may have difficulty raising his or her arms overhead and closing the eyelids. Muscle weakness eventually moves to the abdomen, feet, upper and lower arms, and pelvis. This form of MD sometimes causes problems with pursing the lips or kissing, chewing, swallowing and speaking.


Diagnosis
After asking questions about your medical history and symptoms, the doctor will do a physical exam. The doctor may take a biopsy of the muscle tissue (taking a sample for microscopic examination) or do muscle testing with electromyography (EMG, a test that records the electrical activity within a muscle). Nerve conduction studies may be done to evaluate nerve function. The doctor may also analyze urine and blood samples or do genetic testing.

Treatment
There is no cure for muscular dystrophy, and treatment cannot stop the progression of the disease. The goal of treatment is to maintain mobility and independence through physical therapy, exercise, orthopedic devices, and sometimes medication or surgery. A team of health care professionals, including neurologists, physiatrists, primary care physicians, orthopedists, physical and occupational therapists, and social workers, often work together to provide this care. Counseling and support groups can be helpful in learning how to cope with the disabilities caused by muscular dystrophy. Vocational guidance may also be helpful.

Complications
Complications from muscular dystrophy may include:
fractures or injuries due to falls
spinal curvature
contractures (muscle shortening)
pressure sores
respiratory infections or even respiratory failure for some types of MD
heart problems for some types of MD

Pregnancy-specific information
Some forms of muscular dystrophy affect women of childbearing age. Successful pregnancy is possible, but complications such as premature labor, prolonged labor, cesarean delivery and postpartum bleeding occur more often. During pregnancy, the weakness and muscle spasms of MD may worsen. Your doctor will follow you closely throughout your pregnancy.

Senior-specific information
Although muscular dystrophy is often a disease of children and younger adults, some forms can affect older adults as well. Be sure to report any symptoms to your doctor.

Prevention
If you have a family history of muscular dystrophy, consider genetic counseling before starting your own family. If you're already pregnant, your doctor may recommend an amniocentesis. This test can help the doctor determine the sex of the fetus and the possibility of disease. In some cases, genetic testing of the fetus can detect the abnormal gene that causes muscular dystrophy. As with all tests, discuss the possibility of false negative or false positive results with your doctor.