Muscular dystrophy (MD) is a group of rare inherited muscle diseases in which muscle fibers are unusually susceptible to damage. Muscles, primarily your 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.

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

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

Signs and symptoms

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 fixation of the muscles around your joints (contractures) and loss of mobility

Many specific signs and symptoms vary from form to form 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.

Duchenne's muscular dystrophy
The types of muscular dystrophy that are due to a genetic deficiency of the protein dystrophin are called dystrophinopathies. Duchenne's 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's 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's 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's MD may exhibit curvature of their spine (scoliosis).

Becker's muscular dystrophy
This type of 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's. The onset of the signs and symptoms is generally later, from age 2 to 16.

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, as well as the muscle weakness of the other forms of muscular dystrophy.

The inability to relax muscles at will (myotonia) is found only in this type 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.

• Clouding of the lenses of the eyes (cataracts).

• Mild diabetes.

• Cataract

• Diarrhea

• Fatigue

• constipation

• Pneumonia

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 include:

• Severe muscle weakness

• Difficulty suckling and swallowing

• Difficulty breathing

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

• Limb-girdle muscular dystrophy

• Facioscapulohumeral 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 usually begins in the teen or early adult years.

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.

Congenital muscular dystrophy
Signs of congenital MD may include:

• General muscle weakness

• Joint deformities

This form is apparent at birth and progresses slowly. A more severe form of congenital MD called Fukuyama type congenital muscular dystrophy 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 rare form of muscular dystrophy usually begins in the muscles of the:

• Shoulders

• Upper arms

• Shins

Emery-Dreifuss MD usually begins in the childhood to early teen years and progresses slowly.

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