Muscular dystrophy (MD) is the name for a group of disorders in which muscle size and strength gradually decrease over time. Nine different forms of the disorder have been discovered.
The nine different forms of muscular dystrophy are usually distinguished by the part of the body they affect. They include the following:
All forms of muscular dystrophy are caused by wasting of muscle tissue. Muscle cells die, and muscles become weaker and unable to perform their normal functions. Researchers are still uncertain how this loss of muscle function takes place. They believe that cells may lose their ability to produce certain muscle proteins. Proteins are essential chemicals that occur in all cells and have many different functions. For example, they act as building blocks for cells and as enzymes. Enzymes are special kinds of proteins that control the rate at which chemical reactions take place in cells.
Researchers believe that some forms of MD occur because some muscle proteins are absent or present in smaller-than-average amounts. In such cases, muscle tissue becomes weak. Other muscle proteins may be needed to repair damage in muscle tissue. If those proteins are absent, muscles that are damaged cannot be repaired. In most cases, the connection between absent muscle proteins or reduced amounts of proteins and various forms of MD is simply not yet known.
What scientists do know is that MD is almost entirely a genetic disorder. A genetic disorder is a medical problem caused by defects in a person's genes. Genes are chemical units found within cells that carry essential information telling the cell what functions it should perform. Every person gets two sets of genes, one from each parent. Under most circumstances, the two sets of genes merge to produce a normal set of instructions. A cell follows those instructions to perform a normal set of functions.
Occasionally, a person inherits faulty genes from one or both of his or her parents. In such cases, the instructions provided to a cell can be incorrect and the cell is unable to perform its normal functions.
In the case of MD, a person may receive a single faulty gene from one parent or a pair of faulty genes, one from each parent. A single faulty gene may cause no problem at all. In that case, the person is said to be a carrier. A carrier can transmit the faulty gene to his or her own children. But it will not interfere with the person's own health.
In other cases, one faulty gene is all it takes to cause some form of MD. For example, DMD, FSH, OPMD, and some forms of LGMD and DD are thought to be caused by a single faulty gene. The faulty gene may make it impossible for muscle cells to function as they should. Muscle tissues weaken, and some form of muscular dystrophy results.
Other forms of MD require the presence of two faulty genes, one from each parent. CMD and some forms of LGMD and DD are thought to be caused by this mechanism. Again, the two faulty genes carry incorrect information to a cell and the cell does not function normally. It produces faulty muscle protein, an insufficient amount of the protein, or no protein at all. Muscle tissue weakens and dies, and MD results.
All forms of MD have one characteristic in common—muscular weakness. Other symptoms differ, however, depending on the type of MD involved.
The first symptoms of DMD appear during preschool years. The disorder affects the legs first. A boy has trouble walking and maintaining balance. In most cases, he begins walking three to six months later than average. As his calf muscles begin to weaken, he may change the way he walks. He places his legs farther apart in order to maintain balance. Walking this way produces a waddling effect that is characteristic of DMD.
Contractures usually begin at about the age of five or six. They affect the calf muscles most severely, pulling the foot down and back. This forces a boy to walk on his tiptoes. Balance becomes more of a problem. As a result, falls and broken bones become common at this age. By the age of nine or ten, a boy with DMD might not be able to climb stairs or stand by himself. Most DMD patients have to use a wheelchair by the age of twelve.
Sometimes faulty genes occur on the Y chromosome but not the X chromosome. Chromosomes are structures in cells that contain many genes. Women have two X chromosomes and no Y chromosomes. Men have one X chromosome and one Y chromosome. Faulty genes that occur in Y chromosomes are only present in men. This explains why some forms of muscular dystrophy affect men only. Men inherit those faulty genes, but women do not.
Muscles in other parts of the body are also weakened. When muscles in the upper body are affected, scoliosis (see scoliosis entry), or curvature of the spine, may result. The most serious problem, however, affects the muscles of the diaphragm. The diaphragm provides the in-and-out force that allows a person to breathe and to cough. As the diaphragm weakens, breathing becomes more difficult and patients will have less energy and stamina. They also become more subject to infection because they cannot cough up infectious agents that get into their lungs. Young men with DMD can live into their twenties provided they have mechanical aids to help with their breathing and good respiratory (breathing system) hygiene.
About a third of the boys with DMD also have learning disorders. These disorders can include problems with learning by ear and trouble paying attention to some tasks. Specialized educational problems can help compensate for these disorders.
The symptoms of BMD usually appear in late childhood to early adulthood. They are similar to those of DMD, but they are usually less severe. They may also develop at a different rate and in a different pattern. For example, young men with BMD can often walk on their own into their twenties or early thirties. Scoliosis may also develop, but it is less severe and develops more slowly. One symptom that is more serious in BMD than DMD involves heart problems. These problems include irregular heartbeats and congestive heart failure. Symptoms related to heart problems include fatigue, shortness of breath, chest pain, and dizziness. Respiratory problems may also develop, requiring the use of a mechanical device to help the patient breathe.
EDMD usually begins in early childhood. The first symptom is likely to be contractures, which is a permanent shortening of a muscle. Muscle weakness then appears in the shoulders, upper arms, and calves. Most men with EDMD survive into middle age. As with BMD, heart problems may develop and can cause death.
At least two forms of LGMD occur. One develops during childhood and the other in the teens or twenties. The major symptom is weakening of muscles in the center of the body. Contractures may occur, and most people lose the ability to walk about twenty years after their disorder is diagnosed. In some people, respiratory problems may require the use of a mechanical device to assist with breathing.
FSH varies in its severity and age of onset. Symptoms can begin anywhere from childhood to the early twenties. Symptoms tend to be more severe when the disorder appears earlier. The condition mostly affects muscles of the face, shoulders, and upper arms, although hips and legs may also be affected. Children with FSH often develop partial or complete deafness.
Symptoms of myotonic dystrophy include facial weakness, a slack (loose) jaw, drooping eyelids, and muscle wasting in the forearms and calves. A person with this dystrophy has difficulty letting go of an object, especially if it's cold. Myotonic dystrophy affects heart muscles, causing irregular heartbeats, and the muscles of the digestive system, leading to digestion problems and constipation.
Myotonic dystrophy can also affect other body systems. It can cause cataracts (see cataracts entry), destruction of the retina, mental retardation (see mental retardation entry), skin disorders (see skin disorders entry), wasting of the testicles, sleep problems (see insomnia entry), and diabetes-like problems (see diabetes mellitus entry). Most people with this type of dystrophy are severely disabled within twenty years of first diagnosis. They usually do not require a wheelchair, however.
OPMD usually begins when a person has reached his or her thirties or forties. The disorder affects muscles controlling the eyes and throat. Symptoms include drooping eyelids and difficulty swallowing. Muscle weakness later spreads to the face, neck, and sometimes the upper limbs. Difficulty in swallowing can result in problems of the upper respiratory system. Among the most serious of these problems is pneumonia (see pneumonia entry).
DD usually begins in the twenties or thirties. It first appears as a weakness in the hands, forearms, and lower legs. One of the first symptoms may be difficulty with fine movements, such as typing or fastening buttons. Symptoms usually progress slowly. The disorder seldom affects a person's normal life span.
CMD is marked by severe muscle weakness from birth. Infants with the disorder cannot control their muscles and tend to flop around. Nonetheless, children with CMD may learn to walk, with or without a supporting device, such as crutches. Many live into young adulthood and even beyond. Fukuyama CMD is a far more serious disorder, however. Children with this condition seldom learn to walk and suffer severe mental retardation. They generally die in childhood.
Diagnosis begins with a medical history and a complete physical examination. A medical history is important to find out if dystrophy has occurred in other family members. Since the disorder is hereditary, family patterns are helpful in diagnosing the condition. A physical examination is necessary to rule out conditions with similar symptoms.
A number of laboratory tests are available for diagnosing MD. These tests include:
Most doctors with experience in dealing with MD can diagnose the disorder quite easily. In some cases, however, MD can be confused with other diseases that have similar symptoms. For example, the disorder known as myasthenia gravis (pronounced MY-uhs-THEE-nee-uh GRA-vuhs) affects the site where nerves and muscles come together. Its symptoms are somewhat similar to those of some forms of MD.
There are currently no cures for any form of muscular dystrophy. A few drugs have been found that slow the progress of some forms of MD. For example, prednisone (pronounced PRED-nih-zone), a corticosteroid (pronounced kor-tih-ko-STIHR-oid), slows the progress of DMD. Generally speaking, however, drugs have a limited and uncertain value in the treatment of MD.
The primary goal of treatment programs for MD is to prevent complications. The major complications are decreased ability to move on one's own, contractures, scoliosis, heart defects, and respiratory problems.
Regular stretching exercises help prevent or delay contractures. Braces may be used to help support ankles, feet, legs, and other body parts with weakened muscles. Patients can sometimes be taught to use another set of muscles in place of muscles damaged by MD. A program of regular, light exercise can help keep muscles in good condition.
Surgery may be necessary to correct some severe symptoms of MD. Contractures can be treated, for example, by cutting the damaged muscle. The muscle is then held in place until it grows back normally. In FSH, the shoulder blade can be braced to compensate for muscle weakness. For a person with OPMD, eyelids can be lifted by a surgical procedure to correct for drooping eyelids. Scoliosis can sometimes be corrected by back surgery. In this surgery, the vertebrae that make up the spine are fused (fixed) together. Steel rods are then inserted and attached to the vertebrae to keep the spine in a straight, stiff position.
The purpose of occupational therapy is to help patients find ways of making up for their loss of strength and dexterity. Strategies may include changes in the home environment, learning to use special utensils and dressing aids, and use of a wheelchair and communication devices, such as hearing aids.
Good nutrition helps promote general health in all forms of MD. No special diet is needed or has been shown to relieve any of its symptoms, however.
EDMD and BMD may require certain kinds of treatment for heart problems. For example, drugs such as nifedipine (pronounced nie-FED-uh-peen) help maintain a regular heartbeat. An artificial pacemaker may also need to be installed in patients with an irregular heartbeat.
Weakness in diaphragm muscles can be a very serious condition that may result in a person losing the ability to breathe on his or her own. In such cases, a mechanical device may be needed to help the patient breathe. For example, air may be administered through a face mask or mouthpiece. Or a tracheotomy (pronounced TRAY-kee-OT-uh-mee) may be necessary. In a tracheotomy, a tube is inserted through a hole cut in the throat. Air can then be provided directly to the person's respiratory system.
Good lung hygiene is always necessary. Without proper care, infections of the lungs are common. Such infections can easily lead to pneumonia and even death. Patients with MD may also need to learn techniques for coughing. The normal cough reaction is usually difficult because of damaged muscles. But coughing is necessary to expel foreign particles that can cause disease and infection.
Two experimental procedures may hold some promise for treating MD. One of these procedures is called myoblast transfer. In this procedure, millions of immature muscle cells are injected into a patient's damaged muscle. The goal of the procedure is to provide the person's body with normal, healthy cells that may be able to function in place of damaged ones. Thus far, there seems to be no evidence that this procedure is successful, although research continues in the hope of success in the future.
The second procedure is gene therapy. In gene therapy, a person with MD is injected with artificially produced genes that are correct copies of the faulty genes in their body. The hope is that the correct genes will function in cells the way the faulty genes are supposed to but don't. Gene therapy is a very difficult task complicated with many side effects. However, many researchers believe that it may be the most likely way of curing MD.
The expected lifetime for a male with DMD has increased significantly in the past two decades. Most young men will now live into their early or mid-twenties. The main cause of death is respiratory infection.
Prognosis for other forms of MD is highly variable. It depends very much on the age at which symptoms first appear and how severe those symptoms are. People with BMD, EDMD, and myotonic dystrophy may have normal life spans. The critical issue for people with these disorders is attention to and care for heart problems that may develop.
There is no way to prevent any form of MD. Some forms of the disorder can now be detected by genetic tests. Parents can have their unborn children tested for these forms of muscular dystrophy. They can then use that information for family planning purposes.
Bergman, Thomas. Precious Time: Children Living With Muscular Dystrophy (Don't Turn Away). Milwaukee, WI: Gareth Stevens, 1996.
Emery, Alan. Muscular Dystrophy: The Facts. Oxford Medical Publication, 1994.
The Muscular Dystrophy Association. 3300 East Sunrise Drive, Tucson, AZ 85718. (520) 529–2000; (800) 572–1717. http://www.mdausa.org.