What are Duchenne and Becker Muscular Dystrophies?
Muscular dystrophies are genetic disorders characterized by progressive muscle wasting and weakness that begin with microscopic changes in the muscle. As muscles degenerate over time, the person’s muscle strength declines.
Duchenne muscular dystrophy (DMD) was first described by the French neurologist Guillaume Benjamin Amand Duchenne in the 1860s. Becker muscular dystrophy (BMD) is named after the German doctor Peter Emil Becker, who first described this variant of DMD in the 1950s.
In DMD, boys begin to show signs of muscle weakness as early as age 3. The disease gradually weakens the skeletal, or voluntary, muscles, those in the arms, legs and trunk. By the early teens or even earlier, the boy’s heart and respiratory muscles also may be affected.
BMD is a much milder version of DMD. Its onset is usually in the teens or early adulthood, and the course is slower and far less predictable than that of DMD.
(Though DMD and BMD affect boys almost exclusively, in rare cases they can affect girls. See “Does It Run in the Family?”)
What causes Duchenne and Becker muscular dystrophies?
Until the 1980s, little was known about the cause of any kind of muscular dystrophy. In 1986, MDA-supported researchers identified the gene that, when flawed — a problem known as a mutation — causes DMD. In 1987, the protein associated with this gene was identified and named dystrophin.
Genes contain codes, or recipes, for proteins, which are very important biological components in all forms of life. DMD occurs when a particular gene on the X chromosome fails to make the protein dystrophin. BMD results from different mutations in the same gene. People with BMD have some dystrophin, but it’s not enough or it’s poor in quality. Having some dystrophin protects the muscles of those with Becker from degenerating as badly or as quickly as those of people with Duchenne.
By the way, eating or not eating food with protein can’t replace lost dystrophin.
The course of DMD is fairly predictable. Children with the disorder are often late in learning to walk. In toddlers, parents may notice enlarged calf muscles, or pseudohypertrophy.
A preschooler with DMD may seem clumsy and fall often. Parents also may note that he has trouble climbing stairs, getting up from the floor or running.
By school age, the child may walk on his toes or the balls of his feet, with a slightly rolling gait. He has a waddling and unsteady gait and can easily fall over. To try to keep his balance, he sticks his belly out and puts his shoulders back. He also has difficulty raising his arms.
Many children with DMD lose the ability to walk some time between ages 7 and 12. In the teen years, activities involving the arms, legs or trunk may require assistance or mechanical support.
In diagnosing any form of muscular dystrophy, a doctor usually begins by taking a patient and family history and performing a physical examination. Much can be learned from these, including the pattern of weakness. The history and physical go a long way toward making the diagnosis, even before any complicated diagnostic tests are done.
It’s important to get a formal diagnosis because other diseases have some of the same symptoms as DMD and BMD. Becker MD has often been overlooked or misdiagnosed as limb-girdle muscular dystrophy or spinal muscular atrophy. For this reason, it’s important to have both genetic testing and a muscle biopsy before assuming that the problem is actually BMD.
The doctor also wants to determine whether the patient’s weakness results from a problem in the muscles themselves or in the nerves that control them. Problems in the muscle-controlling nerves, or motor neurons, originating in the spinal cord and brain and reaching out to all the muscles, can cause weakness that looks like a muscle problem but really isn’t.
Early in the diagnostic process doctors often order a special blood test called a CK level. CK stands for creatine kinase, an enzyme that leaks out of damaged muscle. When elevated CK levels are found in a blood sample, it usually means muscle is being destroyed by some abnormal process, such as a muscular dystrophy or inflammation. Therefore, a high CK level suggests that the muscles themselves are the likely cause of the weakness, but it doesn’t tell exactly what the muscle disorder might be.
Boys with DMD often have enlarged calf muscles.
The availability of DNA diagnostic tests, using either blood cells or muscle cells to get precise genetic information, has expanded. You can ask your MDA clinic physician or genetic counselor what tests are available. Since many men with BMD (and some with DMD) become fathers, it’s important to know for certain which inherited disease an individual has. Sisters of people with DMD or BMD also can be tested to find out whether they’re carriers of the disease, meaning they could have children with the disorder.
To determine which disorder is causing a problem, a doctor may order a muscle biopsy, the surgical removal of a small sample of muscle from the patient. By examining this sample, doctors can tell a great deal about what’s actually happening inside the muscles. Modern techniques can use the biopsy to distinguish muscular dystrophies from inflammatory and other disorders as well as between different forms of dystrophy.
Other tests on the biopsy sample can provide information about which muscle proteins are present in the muscle cells, and whether they’re present in the normal amounts and in the right locations. This can determine whether the disease is DMD (with no dystrophin) or BMD (with some dystrophin).
What can be done to treat DMD or BMD?
Thanks to advances in many areas of medicine, there are very good therapies available to assist with all the effects of Duchenne and Becker muscular dystrophies. These interventions are being improved all the time. MDA clinic physicians can provide referrals to specialists and therapists for these forms of care. The use of available therapies can help maintain comfort and function and prolong life expectancy.
Contractures
The impact of DMD and BMD can be minimized significantly by keeping the body as flexible, upright and mobile as possible. There are several ways to do this.
Contractures can affect the knees, hips, ankles, elbows, wrists and fingers.
As muscle deteriorates, a person with muscular dystrophy often develops fixations of the joints, known as contractures. If not treated, these will become severe, causing discomfort and restricting mobility and flexibility. Contractures can affect the knees, hips, feet, elbows, wrists and fingers.
However, there are many ways to minimize and postpone contractures. Range-of-motion exercises, performed on a regular schedule, help delay contractures by keeping tendons from shortening prematurely. It’s important that a physical therapist show you how to do range-of-motion exercises correctly.
Braces on the lower legs also can help keep the limbs stretched and flexible, delaying the onset of contractures.
When contractures have advanced, surgery may be performed to relieve them. A tendon release procedure, also called heel cord surgery, is often done to treat ankle and other contractures while the child is still walking. Usually the boy will need to wear lower leg braces after this.
Spinal curvatures
In young men with DMD, the spine can be gradually pulled into a curved shape. The spine may curve from side to side (scoliosis) or forward in a “hunchback” shape (kyphosis). Scoliosis usually appears after a boy has started using a wheelchair full time. The “swayback” curvature sometimes seen in those who are still walking is called lordosis.
Range-of-motion exercises help delay contractures.
Severe scoliosis can interfere with sitting, sleeping and even breathing, so measures should be taken to try to prevent it. Exercises to keep the back as straight as possible and advice about sitting and sleeping positions can be obtained from a physical therapist.
Spine-straightening surgery involves inserting metal rods with hooks into the spine. Surgery for youngsters with DMD is usually performed in adolescence.
Medications
Medications belonging to a group known as corticosteroids have been found effective in slowing the course of DMD. (Data for or against corticosteroids in BMD are lacking.)
In 2005 the American Academy of Neurology released recommendations about the use of these drugs in DMD. It concluded that:
•Prednisone (available in the United States) and deflazacort (not usually available in the United States) are beneficial in the treatment of DMD. Seven high-quality studies showed a significant increase, with these medications, in strength, timed muscle function (such as time it took a boy to climb stairs) and pulmonary function.
•Effective initial treatments are: 0.75 milligrams per kilogram of body weight per day for prednisone, or 0.9 milligrams per kilogram per day for deflazacort.
•The dose should be reduced if excessive side effects, such as significant weight gain, cataracts, thinning of the bones (osteoporosis) or behavioral problems, occur. The most frequent side effects are weight gain and the development of a rounded, puffy face.
•Researchers don’t yet know whether deflazacort has fewer side effects than prednisone.
The optimal age to begin treatment with corticosteriods has not been determined. Some physicians believe corticosteroids should be started as soon as the diagnosis is made, while others prefer to wait until a boy is having difficulty walking. Before starting treatment with corticosteriods, the physician and the family should have a balanced discussion about anticipated benefits and potential side effects.
Calcium supplements and vitamin D are often prescribed with prednisone to counteract the effects on the bones.
A low-calorie, low-sodium diet is usually recommended to help offset the weight gain and fluid retention seen with corticosteroids.
Medications that lessen the workload on the heart are sometimes prescribed for DMD or BMD. (See "In what other ways do DMD and BMD affect the body?")
Braces, standing frames and wheelchairs
Braces, also called orthoses, support the ankle and foot or extend over the knee. Ankle-foot orthoses are sometimes prescribed for night wear to keep the foot from pointing downward and keep the Achilles tendon stretched while the child is sleeping.
Standing for a few hours each day, even with minimal weight bearing, promotes better circulation, healthier bones and a straight spine. A standing walker or standing frame can assist people with DMD and BMD to stand. Some wheelchairs will tilt into a standing position.
Sooner or later, all boys with DMD need wheelchairs. Many at first use wheelchairs at school or the mall, continuing to walk some at home. In Duchenne, it’s typical for a child to be using a wheelchair full time by about age 12. Although the child and parents may dread the wheelchair as a symbol of disability, most users find they are actually more mobile, energetic and independent than when trying to walk on very weak legs.
Other mobility and positioning aids can help those who care for people with DMD or BMD. Among the simplest is a transfer board for helping the person move in and out of the wheelchair. Mechanical lifts, shower chairs and electronic beds also may be used.
In what other ways do DMD and BMD affect the body?
Pain and sensation
Braces, or “orthoses,” can add support when muscles are weak.
You may be relieved to know that the muscle deterioration in Duchenne and Becker isn’t usually painful in itself. Some people report muscle cramps at times; these can usually be treated with over-the-counter pain relievers.
Also, since muscular dystrophy doesn’t affect nerves directly, those who have the disorders retain normal sensations of touch and other senses. They also usually have control over the smooth, or involuntary, muscles of the bladder and bowel, and have normal sexual functions.
The heart
Like muscles in the limbs, heart muscles also can be weakened by lack of dystrophin. Over time, sometimes as early as the teen years, the damage done by DMD to the heart can become life-threatening. This system should be monitored closely, usually by a pediatric cardiologist.
People with DMD and BMD often develop cardiomyopathy — heart muscle weakness — because of a deficiency of dystrophin. The muscle layer (myocardium) of the heart deteriorates, just as the skeletal muscles do, putting the person at risk of fatal heart failure.
Some people with BMD have mild skeletal muscle involvement but severe cardiac problems.
In 2005, the American Academy of Pediatrics released its recommendations for people with DMD and BMD and carriers of these diseases.
Ankle-foot orthoses keep the front of the foot from flopping down and tripping the child.
The academy recommends that those with DMD have a complete cardiac evaluation by a specialist beginning in early childhood and again at least every other year until age 10. After that, the evaluations should be done every year or at the onset of symptoms of heart weakness, such as fluid retention or shortness of breath.
For those with BMD, it recommends evaluations at least every other year beginning at age 10.
Carriers of DMD and BMD are at higher-than-average risk of developing cardiomyopathy. The academy suggests that carriers should undergo a complete cardiac evaluation in late adolescence or early adulthood, or sooner if symptoms occur, and that they should be evaluated every five years starting at age 25 to 30.
There’s some preliminary evidence that treatment with angiotensin converting enzyme (ACE) inhibitors and beta blockers can slow the course of cardiac muscle deterioration in DMD and BMD if the medications are started as soon as abnormalities on an echocardiogram (ultrasound imaging of the heart) appear but before symptoms occur.
Some people with BMD who have severe heart problems but generally good health have been successfully treated with heart transplants.
Respiratory function
Boys with DMD should have regular echocardiograms.
After a boy with DMD is about 10 years old, the diaphragm and other muscles that operate the lungs may weaken, making them less effective at moving air in and out. Boys and young men with DMD may not complain of shortness of breath. Problems that may indicate poor respiratory function include headaches, mental dullness, difficulty concentrating or staying awake, and nightmares.
Anyone with a weakened respiratory system is also subject to more infections and difficulty in coughing. A simple cold can quickly progress to pneumonia. During infections, it’s important to get prompt treatment before a respiratory emergency occurs.
Noninvasive ventilation can improve sleep quality.
As breathing ability declines, the family can get a cough assist device or learn procedures to assist with coughing and keep the bronchial system free from secretions. A respiratory therapist or pulmonologist can be consulted for the needed information.
At some point, assisted ventilation may be needed to help provide sufficient air flow into and out of the lungs.
The first step in using assisted ventilation is usually a noninvasive device, meaning one that doesn’t require any surgical procedures. The person receives air under pressure through a mask, nosepiece or mouthpiece. If round-the-clock ventilatory support becomes necessary, it’s possible to use noninvasive ventilation full time, under the care of a doctor knowledgeable in this practice. Some young men choose to switch to an invasive system, which means that a surgical opening called a tracheostomy is performed, allowing air to be delivered directly into the trachea (windpipe).
MDA’s booklet “Breathe Easy: Respiratory Care in Neuromuscular Disorders” gives detailed information on this topic.
Intellectual effects
About a third of boys with DMD have some degree of learning disability, although few are seriously retarded. Doctors believe that dystrophin abnormalities in the brain may cause subtle cognitive and behavioral deficits. The learning problems seen in some people with DMD and BMD occur in three general areas: attention focusing, verbal learning and memory, and emotional interaction.
Children suspected of having a learning disability can be evaluated by a developmental or pediatric neuropsychologist through the school system’s special education department or with a referral from the MDA clinic. If a learning disability is diagnosed, educational and psychological interventions can begin right away. The specialist may prescribe exercises and techniques that can help improve these deficits, and the school also can provide special help with learning.
Can special diets or exercises help in DMD and BMD?
Diet
Many people, when they hear the words “lack of a protein,” logically ask, “Should I eat more protein?” Unfortunately, eating more protein has no effect on any of the proteins missing in muscular dystrophy.
About a third of boys with DMD have a learning disability.
No special dietary restrictions or additions are known to help in DMD or BMD. Most doctors recommend a diet similar to that for any growing boy, but with a few modifications.
A combination of immobility and weak abdominal muscles can lead to severe constipation, so the diet should be high in fluid and fiber, with fresh fruits and vegetables dominant.
For boys who use power wheelchairs, take prednisone or who aren’t very active, caloric intake should probably be somewhat restricted to keep weight down. Obesity puts greater stress on already weakened skeletal muscles and the heart. Doctors have found that a low-calorie diet doesn’t have any harmful effect on the muscles.
Those on prednisone and those with heart problems also may need a sodium-restricted diet.
Exercise
Some experts recommend swimming and water exercises.
Exercise can help build skeletal muscle, keep the cardiovascular system healthy, and contribute to feeling better. But in muscular dystrophy, too much exercise could damage muscle. Consult with your doctor about how much exercise is best. A person with DMD or BMD can exercise moderately but shouldn’t go to the point of exhaustion.
Some experts recommend swimming and water exercises (aquatic therapy) as a good way to keep muscles as toned as possible without causing undue stress on them. The buoyancy of the water helps protect against certain kinds of muscle strain and injury. Before undertaking any exercise program, make sure you’ve had a cardiac evaluation.
Physical and occupational therapy
A physical therapy program is usually part of the treatment for DMD and BMD. Your MDA clinic physician will refer you to a physical therapist for a thorough evaluation and recommendations.
The primary goals of physical therapy are to allow greater motion in the joints and to prevent contractures and scoliosis.
Occupational therapy focuses on specific activities and functions, while physical therapy emphasizes mobility and, where possible, strengthening of large muscle groups. Occupational therapy can help with tasks for work, recreation or daily living, such as driving, dressing or using a computer.
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