Introduction

Questions and Answers
Part I
Part II

Characteristics of the 9 Muscular Dystrophies

MDA's Search for Causes

MDA's Search for Treatments and Cures

MDA is Ready to Help

MAJOR CHARACTERISTICS OF THE NINE (9) MUSCULAR DYSTROPHIES

MYOTONIC dystrophy (DM), also known as Steinert's disease, is the most common adult form of muscular dystrophy. Its name underscores an unusual symptom found only in this form of dystrophy—myotonia — which is similar to a spasm or stiffening of muscles after use.

Myotonic dystrophy results from a gene flaw on chromosome 19, one of the autosomes. The gene containing the defect is for an enzyme recently named myotonin protein kinase. Some researchers believe the defect may affect other nearby genes.

Read More:
	Facts about... Myotonic

The disease causes muscle weakness and affects the central nervous system, heart, gastrointestinal tract, eyes (causing cataracts) and endocrine (hormone-producing) glands. Although muscle weakness progresses slowly, this symptom can vary greatly, even among members of a single family. Most often muscle weakness doesn't hamper daily living for many years after symptoms first occur.

Many people with myotonic dystrophy seem to require more sleep than the average person. Mild mental retardation is present in some people with the disease, and a peculiar emotional and mental "indifference" has also been found to accompany myotonic dystrophy in some patients.

Congenital myotonic dystrophy is a rare form of the disorder occurring almost exclusively in infants of mothers with the adult form of the disease. At birth, infants can show symptoms of the disease, including severe weakness, difficulty in sucking and swallowing, and impaired breathing. Delayed motor development and mental retardation are common features of congenital myotonic dystrophy.

The cardiac problems in this disease can be serious and should be followed carefully by a physician. Drug therapy or a cardiac pacemaker may be necessary.

Adverse reactions to general anesthesia sometimes occur in people with myotonic dystrophy, so it's important to alert physicians to the presence of this disease in someone who is about to have surgery. A medical bracelet is advisable in case no one is around to "speak for" the patient.

Eye surgery can remove the cataracts associated with myotonic dystrophy, and ankle and wrist splints are helpful for some of the muscle weakness.

The gastrointestinal problems may need medical attention at times. Labor and delivery may be complicated by muscle abnormalities in the uterus, and the obstetrician should be informed about a patient's myotonic dystrophy status and care.

DUCHENNE muscular dystrophy (DMD) is the most common childhood form of muscular dystrophy. Early signs of Duchenne, which usually occur between the ages of 2 and 6,

Read More:
	Facts about... Duchenne & Becker

In Duchenne muscular dystrophy, posture changes as the child grows.

Progression varies somewhat from child to child. The use of orthopedic devices and physical therapy can prolong the ability to walk. Frequently, however, a wheelchair will be needed by age 12.

Mild mental retardation has been noted in some (by no means all) boys with Duchenne dystrophy.

Breathing becomes affected during the later stages of Duchenne, leading to respiratory infections. These are often successfully treated with antibiotics and respiratory therapy. Severe respiratory and heart problems mark the disease's final stages, usually in the boy's teens or early 20s.

In 1986, MDA-funded researchers identified the gene that, when defective, is responsible for Duchenne muscular dystrophy. They discovered that the gene's failure to make a working version of the muscle protein dystrophin is the cause of the disease. Most boys with Duchenne have little or no dystrophin in their muscles.

Further research has shown that dystrophin is attached to other proteins at the edge of muscle fibers and that it probably helps anchor the fibers to connective tissue surrounding them.

The signs, symptoms and course of BECKER muscular dystrophy (BMD) are very similar to those of Duchenne but generally appear later and progress more slowly. At one time, doctors thought Becker dystrophy might be an entirely different disease from Duchenne.

Read More:
	Facts about... Duchenne & Becker

Becker dystrophy can first appear much later than Duchenne, even as late as age 25. The progression is typically slower, with the ability to walk usually preserved into the 30s.

The severity of the disease varies, and boys and men with Becker dystrophy have a longer life expectancy than those with Duchenne.The severity and rate of progression of Becker dystrophy depends on how much dystrophin is made and how well it functions in the muscles.

The cardiac problems are similar to those in Duchenne and should be followed by a physician.

Most often, the onset of LIMB-GIRDLE muscular dystrophy (LGMD) is in adolescence or early adulthood. In the most common forms, the disease causes progressive weakness that starts in the hips and moves to the shoulders. The weakness progresses to include the arms and legs. Within 20 years of onset, walking is difficult, if not impossible.

Read More:
	Facts about... Limb-Girdle

Researchers have found that autosomal recessive limb-girdle dystrophy can result from gene defects on chromosomes 2, 13, 15 and 17, and that an autosomal dominant form can result from gene defects on chromosome 5. A gene on chromosome 15 that codes for the enzyme calpain 3 may play a role in some cases of limb-girdle dystrophy. A flawed gene on chromosome 17 for the muscle protein adhalin is also known to cause other cases. The other genes haven't yet been positively identified.

5. FACIOSCAPULOHUMERAL MUSCULAR DYSTROPHY

Wasting of the upper arm and shoulder muscles is typical in FSH muscular dystrophy. In people with FSH, the scapular bones (shoulder blades) look like wings when the arms are raised.

The word facioscapulohumeral refers to the muscles that move the face, scapula (shoulder blade) and humerus (upper arm bone). Common early signs of FACIOSCAPULOHUMERAL muscular dystrophy (FSH) are a forward sloping of the shoulders as well as difficulty raising the arms over the head and closing the eyes. Progression is slow, with long periods of stability interspersed with shorter periods of rapid muscle deterioration and increased weakness. The muscles of the face and shoulder area (shoulder "girdle") are the first affected. The weakness spreads to the muscles of the abdomen, feet, upper arms, pelvic area and lower arms, usually in that order. The disease ranges in severity from very mild to considerably disabling, with impairment of walking, chewing, swallowing and speaking. About half of those with the disorder retain the ability to walk throughout their lives.

Orthopedic supports can be helpful early in the progression of the disease, and surgery is sometimes done to improve function in the shoulder area.

6. CONGENITAL MUSCULAR DYSTROPHY

CONGENITAL muscular dystrophy (CMD) is really a group of diseases, not a single disease. These diseases are called "congenital" because symptoms can be noted from birth. One form that has been clearly described is Fukuyama congenital muscular dystrophy. This disorder involves severe weakness of the facial and limb muscles and a generalized lack of muscle tone, usually appearing before 9 months. Joint contractures are common. Brain abnormalities are also present, and most children have severe mental and speech problems. Seizures are often part of the disease, and medications are prescribed for these. Physical therapy is needed to minimize the contractures. The disease has been linked to a gene defect on chromosome 9, although the precise gene and its protein are so far unknown.

Another form of congenital dystrophy seems to be related to a deficiency or malfunction of the protein merosin, which normally lies outside muscle cells and links them to the surrounding tissue. The disorder is similar to Fukuyama dystrophy, with muscle weakness evident at birth or in the first few months of life, severe and early contractures and often joint deformities. This disorder has been tentatively named congenital muscular dystrophy with merosin deficiency and appears to be due to an as-yet-unidentified defect on chromosome 6.

OCULOPHARYNGEAL muscular dystrophy, (OPMD), meaning eye and throat, usually starts with drooping of the eyelids, most often in the 40s or 50s. This is followed by other signs of eye and facial muscle weakness, as well as by difficulty in swallowing. The later stages of this slowly progressive disease may include weakness in the pelvic and shoulder muscles. Swallowing problems can lead to choking and recurrent pneumonia.

Special glasses to prop up the eyelids can be worn, and surgery can be done to alleviate both the drooping eyelids and the swallowing difficulties.

The disease is linked to a gene defect on chromosome 14.

DISTAL muscular dystrophy (DD) is actually a group of rare muscle diseases, which have in common weakness and wasting of the distal (farthest from the center) muscles of the forearms, hands, lower legs and feet.

A type of distal dystrophy called Welander is inherited in an autosomal dominant pattern and affects the hands first. Another type, known as Markesbery-Griggs, is autosomal dominant in its inheritance and affects the front of the lower legs first, as does Nonaka dystrophy. Miyoshi dystrophy, caused by a gene defect on chromosome 2, is autosomal recessive and affects the back of the lower legs first.

In general, the distal dystrophies are less severe, progress more slowly and involve fewer muscles than the other dystrophies, although spread to other muscles can occur. Walking can be improved with orthopedic devices that support the foot.

EMERY-DREIFUSS (EDMD) is a rare form of muscular dystrophy. Muscle weakness and wasting generally start in the shoulders, upper arms and lower legs. Weakness may later spread to involve the muscles of the chest and pelvic area. Contractures appear early in the disease, usually involving the ankle and elbow. Unlike other forms of muscular dystrophy, contractures in Emery-Dreifuss dystrophy often appear before the person experiences significant muscle weakness. Physical therapy is beneficial in minimizing the contractures.

Life-threatening heart problems are a common part of this disorder. The heart problems are electrical (of the type known as "conduction defect") and can be treated with a cardiac pacemaker. These problems can even occur in females who don't have the disease but are carriers, so sisters and mothers of boys with Emery-Dreifuss should be examined.

The skeletal muscle weakness is less severe than it is in some other dystrophies, such as Duchenne.

Emery-Dreifuss dystrophy is caused by a defect in the gene on the X chromosome that codes for the protein called emerin. The function of this protein hasn't yet been identified.

Back to Disease Brochures