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Muscular dystrophy (MD) is a group of rare inherited muscle diseases in which muscle fibers are unusually susceptible to damage. Muscles, primarily voluntary muscles, become progressively weaker. In the late stages of muscular dystrophy, fat and connective tissue often replace muscle fibers. In some types of muscular dystrophy, heart muscles, other involuntary muscles and other organs are affected.

The most common types of muscular dystrophy appear to be due to a genetic deficiency of the muscle protein dystrophin.

There's no cure for muscular dystrophy, but medications and therapy can slow the course of the disease.

Signs and symptoms vary according to the type of muscular dystrophy. In general, they may include:

• Muscle weakness
• Apparent lack of coordination
• Progressive crippling, resulting in contractures of the muscles around your joints and loss of mobility

Many specific signs and symptoms vary from among the different forms of MD. Each type is different in the age of onset, what parts of the body the symptoms primarily affect and how rapidly the disease progresses.

Dystrophinopathies
These types of muscular dystrophies are due to a genetic deficiency of the protein dystrophin.

Duchenne muscular dystrophy is the most severe form of dystrophinopathy. It occurs mostly in young boys and is the most common form of MD that affects children. Signs and symptoms of Duchenne MD may include:

• Frequent falls
• Large calf muscles
• Difficulty getting up from a lying or sitting position
• Weakness in lower leg muscles, resulting in difficulty running and jumping
• Waddling gait
• Mild mental retardation, in some cases

Signs and symptoms of Duchenne usually appear between the ages of 2 and 5. It first affects the muscles of the pelvis, upper arms and upper legs. By late childhood, most children with this form of muscular dystrophy are unable to walk. Most die by their late teens or early 20s, often from pneumonia, respiratory muscle weakness or cardiac complications. Some people with Duchenne MD may exhibit curvature of their spine (scoliosis).

Becker's muscular dystrophy is a milder form of dystrophinopathy. It generally affects older boys and young men, and progresses more slowly, usually over several decades. Signs and symptoms of Becker's MD are similar to those of Duchenne. The onset of the signs and symptoms is generally later, and those affected by Becker's MD usually are able to walk until at least age 15, and often well into adulthood.

Myotonic dystrophy
Also known as Steinert's disease, this form of muscular dystrophy produces stiffness of muscles and an inability to relax muscles at will (myotonia), as well as the muscle weakness of the other forms of muscular dystrophy.

Although this form of MD can affect children, it often doesn't affect people until adulthood. It can vary greatly in its severity. Muscles may feel stiff after using them. Progression of this form of MD is slow. Besides myotonia, signs and symptoms of adult-onset myotonic dystrophy may include:

• Weakening of voluntary muscles that control your arms and legs, usually beginning with the limb muscles farthest from the torso — the muscles of the feet, hands, lower legs and forearms.
• Weakening of head, neck and face muscles, which may result in the face having a hollow, drooped appearance.
• Weakening of muscles involved in breathing and swallowing. Weaker breathing muscles may result in less oxygen intake and fatigue. Weaker swallowing muscles increase the risk of choking.
• Fainting or dizziness, which may indicate that the disease is interfering with the conduction of electrical signals that keep the heart rate normal.
• Weakening of muscles of hollow internal organs such as those in the digestive tract and the uterus. Depending on which part of the digestive tract is affected, you may experience problems with swallowing as well as constipation and diarrhea. Weakness of the uterine walls may cause problems during childbirth.
• Difficulty sleeping well at night and daytime sleepiness, and inability to concentrate because of the effect of the disease on the brain.
• Frontal balding in men.
• Clouding of the lenses of the eyes (cataracts).
• Mild diabetes.

Rarely, infants have this form of muscular dystrophy, in which case it's called congenital myotonic dystrophy. The infant form is more severe, although infants with myotonic dystrophy don't experience myotonia. Signs in infants may include:

• Severe muscle weakness
• Difficulty sucking and swallowing
• Difficulty breathing
• Cognitive impairment

Facioscapulohumeral muscular dystrophy
Also known as Landouzy-Dejerine disease, this form involves progressive muscle weakness, usually in this order:

• Face
• Shoulders
• Abdomen
• Feet
• Upper arms
• Pelvic area
• Lower arms

When someone with facioscapulohumeral MD raises his or her arms, the shoulder blades may stick out like wings. Progression of this form is slow, with some spurts of rapidly increasing weakness. Onset usually occurs during the teen to early adult years.

The other major types of muscular dystrophy are rare. They include:

• Limb-girdle muscular dystrophy
• Congenital muscular dystrophy
• Oculopharyngeal muscular dystrophy
• Distal muscular dystrophy
• Emery-Dreifuss muscular dystrophy

Limb-girdle muscular dystrophy
Muscles usually affected first by this form of muscular dystrophy include:

• Hips
• Shoulders

This form then progresses to the arms and legs, though progression is slow. Limb-girdle MD may begin from early childhood to adulthood.

Congenital muscular dystrophy
Signs of congenital MD may include:

• General muscle weakness
• Joint deformities

This form is apparent at birth and progresses slowly. More severe forms of congenital MDs may involve severe mental and speech problems as well as seizures.

Oculopharyngeal muscular dystrophy
The first sign of this type of muscular dystrophy is usually drooping of the eyelids, followed by weakness of the muscles of the eye, face and throat, resulting in difficulty swallowing. Progression is slow. Signs and symptoms first appear in adulthood, usually in a person's 40s, 50s or 60s.

Distal muscular dystrophy
This group involves the muscles farthest away from the center of the body — those of the hands, forearms, feet and lower legs. The severity is generally less than for other forms of MD, and this form tends to progress slowly. Distal MD generally begins in adulthood between the ages of 40 and 60.

Emery-Dreifuss muscular dystrophy
This form of muscular dystrophy usually begins in the muscles of the:

• Shoulders
• Upper arms
• Shins

Cardiac arrhythmias, stiffness of the spine and muscle contractures are other features of Emery-Dreifuss MD. Emery-Dreifuss MD usually begins in the childhood to early teen years and progresses slowly.

"Muscular dystrophy" is a general term for a group of inherited diseases involving a defective gene. Each form of muscular dystrophy is caused by a genetic mutation that's particular to that type of the disease.

Duchenne and Becker's muscular dystrophies are passed from mother to son through one of the mother's genes in a pattern called X-linked recessive inheritance. Boys inherit an X chromosome from their mothers and a Y chromosome from their fathers. The X-Y combination makes them male. Girls inherit two X chromosomes, one from their mothers and one from their fathers. The X-X combination determines that they are female.

The defective gene that causes Duchenne and Becker's muscular dystrophies is located on the X-chromosome. Women who have only one X-chromosome with the defective gene that causes these muscular dystrophies are carriers and sometimes develop heart muscle problems (cardiomyopathy) and mild muscle weakness. The disease can "skip" a generation until another son inherits the defective gene on the X-chromosome. In some cases of Duchenne and Becker's muscular dystrophies, the disease arises from a new mutation in a gene rather than from an inherited defective gene.

Patterns differ for other types of MD
Myotonic dystrophy is passed along in a pattern called autosomal dominant inheritance. If either parent carries the defective gene for myotonic dystrophy, there's a 50 percent chance the disorder will be passed along to a child.

Some of the less common types of muscular dystrophy are passed along in the same inheritance pattern that marks Duchenne and Becker's muscular dystrophies. Other types of muscular dystrophy can be passed on from generation to generation and affect males and females equally. Still others require a defective gene from both parents.

Duchenne muscular dystrophy occurs almost exclusively in boys, although it can occur in girls. Your young child may have difficulty walking, running, rising from the floor or climbing the stairs, or may appear clumsy and fall often. These may be early indications of muscular dystrophy. A child with MD may learn to walk later than other children do and may exhibit signs of muscle weakness between the ages of 2 and 5. By school age, a child with MD may walk unsteadily and on the toes or balls of the feet. Duchenne MD usually results in children losing the ability to walk by age 12.

If you're concerned about your child's motor abilities, clumsiness, or muscle strength and development, see your doctor. Once muscular dystrophy is diagnosed, medications and physical therapy can help slow its progression.

Because muscular dystrophies are inherited disorders, genetic counseling may be helpful if you're considering having children and to assess the risk of the disease in other family members.

A careful review of your family's history of muscle disease can help your doctor reach a diagnosis. In addition to a medical history review and physical examination, your doctor may rely on the following in diagnosing muscular dystrophy:

• Blood tests. Damaged muscles release enzymes such as creatine kinase (CK) into the blood. High blood levels of CK suggest a muscle disease such as muscular dystrophy.
• Electromyography. A thin-needle electrode is inserted through your skin into the muscle to be tested. Electrical activity is measured as you relax and as you gently tighten the muscle. Changes in the pattern of electrical activity can confirm a muscle disease. The distribution of the disease can be determined by testing different muscles.
• Ultrasonography. High-frequency sound waves are used to produce precise images of tissues and structures within your body. An ultrasound is a noninvasive way of detecting certain muscle abnormalities, even in the early stages of the disease.
• Muscle biopsy. A small piece of muscle is taken for laboratory analysis. The analysis distinguishes muscular dystrophies from other muscle diseases. Special tests can identify dystrophin and other markers associated with specific forms of muscular dystrophy.
• Genetic testing. Blood samples are examined for mutations in the gene that produces dystrophin. Standard tests examine just the portions of the dystrophin gene responsible for most cases of Duchenne and Becker's muscular dystrophies. These tests identify deletions or duplications on the dystrophin gene in about two-thirds of people with Duchenne and Becker's MDs. The genetic defects responsible for Duchenne and Becker's muscular dystrophies are harder to identify in other cases of those affected, but new tests that examine the entire dystrophin gene are making it possible to pinpoint tiny, less common mutations.

There's currently no cure for any form of muscular dystrophy. Research into gene therapy may eventually provide treatment to stop the progression of some types of muscular dystrophy. Current treatment is designed to help prevent or reduce deformities in the joints and the spine and to allow people with MD to remain mobile as long as possible. Treatments may include various types of physical therapy, medications, assistive devices and surgery.

Physical therapy
As muscular dystrophy progresses and muscles weaken, fixations (contractures) can develop in joints. Tendons can shorten, restricting the flexibility and mobility of joints. Contractures are uncomfortable and may affect the joints of your hands, feet, elbows, knees and hips.

One goal of physical therapy is to provide regular range-of-motion exercises to keep your joints as flexible as possible, delaying the progression of contractures, and reducing or delaying curvature of your spine. Using hot baths (hydrotherapy) also can help maintain range of motion in joints.

Medications
Doctors prescribe medications to treat some forms of muscular dystrophy:

• For myotonic dystrophy. The medications mexiletine (Mexitil), phenytoin (Dilantin, Phenytek), carbamazepine (Tegretol, Carbatrol), quinine and procainamide (Procanbid, Pronestyl) may be used to treat the delayed muscle relaxation that occurs in myotonic dystrophy.
• For Duchenne muscular dystrophy. The anti-inflammatory corticosteroid medication prednisone may help improve muscle strength and delay the progression of Duchenne MD.

Assistive devices
Braces can both provide support for weakened muscles of your hands and lower legs and help keep muscles and tendons stretched and flexible, slowing the progression of contractures. Other devices such as canes, walkers and wheelchairs can help maintain mobility and independence. If respiratory muscles become weakened, using a ventilator may become necessary.

Surgery
To release the contractures that may develop and that can position joints in painful ways, doctors can perform a tendon release surgery. This may be done to relieve tendons of your hip and knee and on the Achilles tendon at the back of your foot. Surgery may also be needed to correct curvature of the spine.

Other treatments
Because respiratory infections may become a problem in later stages of muscular dystrophy, it's important to be vaccinated for pneumonia and to keep up-to-date with influenza shots.

For family members of people with muscular dystrophy, coping with the illness involves a major commitment of physical, emotional and financial effort. The disease presents challenges in the classroom, in the home and in all aspects of life.

In dealing with a disease such as muscular dystrophy, support groups can be a valuable part of a wider network of social support that includes health care professionals, family, friends and a place of religious worship.

Support groups bring together people, family and friends who are coping with the same kind of physical or mental health challenge. Support groups provide a setting in which people can share their common problems and provide ongoing support to one another.

Ask your doctor about self-help groups that may exist in your community. Your local health department, public library, telephone book and the Internet also may be good sources to locate a support group in your area.