More About Muscular Dystrophy
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 may also 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.
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.
Duchenne
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. Soon, 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.
Nearly all children with DMD lose the ability to walk sometime between ages 7 and 12. In the teen years, activities involving the arms, legs or trunk require assistance or mechanical support.
Becker
Often, the diagnosis of Becker muscular dystrophy isn't made until adolescence or even adulthood, possibly when a young man finds he can't keep up in physical education classes or military training. To compensate for his weakening muscles, the young man begins walking with a waddling gait, walking on his toes or sticking out his abdomen.
As with Duchenne, the pattern of muscle loss in BMD usually begins with the hips and pelvic area, the thighs and the shoulders. But in BMD, the rate of muscle degeneration varies a great deal from one person to another. Some men require wheelchairs by their 30s or later, while some manage for many years with minor aids, such as canes.
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. 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.
Usually, the origin of the weakness can be pinpointed by a physical exam. Occasionally, special tests called electromyography or nerve conduction studies are done. In these tests, the electrical activity of the muscles is measured and nerves are stimulated to see whether the problem lies in the muscles or the nerves.
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 an 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.
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 inadequate dystrophin). An MR (magnetic resonance) scan may also be ordered. These painless scans allow doctors to visualize what's going on inside weakening muscles.
The availability of DNA diagnostic tests, using either blood cells or muscle cells to get precise genetic information, is expanding rapidly. 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 can also be tested to find out whether they're carriers of the disease, meaning they could have children with the disorder.
To learn more about the various forms of Muscular Dystrophy or to help with donations, or maybe even volunteering please visit the national Muscular Dystrophy Association's web site to locate the nearest office. Click here to go there now!
