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Becker Muscular Dystrophy (BMD)
Saturday, 13 September 2003
Tuesday, 23 November 2004
Additional entries in our database that you might find useful:   Duchenne Muscular Dystrophy

What

Becker Muscular Dystrophy (BMD) is a rare genetic disorder that causes muscles to deteriorate over time. As there is more and more muscle wasting, there is more and more loss in muscle strength. BMD is very similar to Duchenne Muscular Dystrophy (DMD), except the symptoms are milder in Becker Muscular Dystrophy. Progression of symptoms is slower and less predictable than those associated with Duchenne Muscular Dystrophy.

Who

BMD mostly affects males, but may also affect females (see explanation of female carrier and X-linked genetic disorder below). In southern Italy, BMD occurs in 3.2 per 100,000 people. It should be noted that this number may actually be higher because some individuals are so mildly affected that they go undiagnosed and unidentified.

Signs and Symptoms

The onset of symptoms is usually in the teens or early twenties. The symptoms vary greatly between individuals. Males: BMD affects the muscles of the body. This causes cramps when he exercises and decreasing stamina and tolerance for exercise. Because muscle is lost in the hips, pelvis, thighs, and shoulders, he tends to waddle when he walks, walks on his toes, or thrusts his stomach forward. This helps to compensate for his weak muscles. BMD also affects the muscles of the heart (cardiomyopathy). This may cause feeling like he is out of breath, cause fluid to accumulate in the lungs, or cause swelling of the feet and lower legs. BMD may affect muscles in the chest such as the diaphragm. Because this is where the lungs are, it may cause him to be more prone to respiratory infections or have difficulty coughing. BMD can cause other symptoms such as headaches, mental dullness, difficulty concentrating or staying awake, and/or nightmares. Intellectually, males with BMD may have learning difficulties such as verbal learning and difficulty with memory. They may have attention difficulties and cannot focus. They may also have emotional interactions that are inappropriate. Females: As in males, BMD also affects the muscles of the body in females. About 5 to 10% of female carriers of this X-linked genetic disorder demonstrate muscle weakness. It is common for these women to have weakness of the hips, pelvis, thighs, and shoulders. The weakness can be more on one side of the body than the other (asymmetric). Their calves may even become enlarged. If muscles of the heart are affected (cardiomyopathy), they may feel like they are out of breath, get fluid in their lungs, or have swelling of their feet and lower legs. One difference between the disease in males and females is that in females, there is slow or no progression of symptoms.

Possible Causes

Cells, the building blocks of the human body, are home to the genetic information, or “blueprints”, that determine all of our physical characteristics. These genes are organized into chromosomes, of which there are 23 pairs. Each pair is made up of one chromosome from the mother’s egg and one from the father’s sperm. One of these pairs is very special because it determines the sex of the baby. The sex chromosome can come either in the form of an X or a Y. Girls usually inherit two X chromosomes, one from her mother’s egg and one from her father’s sperm. Boys usually inherit one X chromosome from his mother’s egg, and one Y chromosome from his father’s sperm. An X-linked disorder, such as BMD, is a disease that is inherited via the X chromosome. A girl has two copies of the X chromosome, so if she inherits a defect in one X chromosome (i.e. an X-linked disease) she should still have one good copy of the chromosome to compensate. This is why women can be asymptomatic (show no symptoms) or be mildly affected “carriers” of a genetic disease. If a carrier female has a daughter, her daughter has a 50% chance of also being a carrier and a 50% chance of being completely normal (assuming that the X chromosome she inherits from her father is normal). If this carrier female has a son, that son has a 50% chance of inheriting her normal X chromosome and a 50% chance of inheriting the one with the defect. When male babies inherit the X with the defect, they do not have another X chromosome to provide the correct “blueprints” and override the defect. Some of the necessary genetic information may, therefore, be missing or incorrect, and could lead to a health problem. This is why we usually only see X-linked diseases in males. In BMD, a portion of the X chromosome contains a mistake (mutation). The gene with the mutation normally has directions on how to make a protein called “dystrophin”. Dystrophin is a molecule that is essential for muscle cells to work normally. In DMD, this mutation is very large which causes little or no dystrophin to be made. In BMD, the mutation is not as severe and so there is still some dystrophin protein made, but it is not enough or it is poor in quality. Having some dystrophin, albeit flawed, protects muscles from degenerating as severely or as rapidly as muscles in individuals affected with DMD.

Diagnosis

A diagnosis is often made with the onset of symptoms in the teens or early twenties. It is common for a young man to first be diagnosed when he notices that he can no longer keep up with a physical education class or military training. Several tests can be performed to confirm a diagnosis of BMD. The first is called “electromyography” which tests the nerves within the muscles. Another test is a blood test to measure CK (creatine kinase) levels. CK is an enzyme from muscle cells and levels are high when muscle is destroyed, as it is in muscular dystrophy. The third test is a muscle biopsy. A biopsy takes a small piece of muscle for study under a microscope. Biopsies positive for BMD would show changes in the muscle that will ultimately lead to muscle wasting and weakness. DNA testing to look for mistakes in the gene for dystrophin is available. One should speak with a genetic counselor or a BMD specialist about the possibility of DNA testing. Genetic counseling is very important since many men with BMD become fathers. Sisters of men affected with BMD should be tested to check whether or not they are carriers. If they are carriers, they can pass the disorder onto their children.

Treatment

At this time, there is no cure for BMD. Treatments mainly focus on alleviating symptoms. Common problems associated with muscle deterioration is contractures of the joints such as the knees, elbows, hips, wrists, or fingers. Contractures may become uncomfortable and restrict flexibility and mobility. Regular physical therapy and range-of-motion exercises can reduce and delay contractures. Braces that keep joints stretched can also postpone the onset of contractures. When contractures become more severe, surgery can release the tension by cutting tendons. This procedure is called a “tendon release procedure” and is often performed to treat ankle contactures. Medications called steroids (such as prednisone) may help slow down the loss of muscle function and may even increase strength. While there are many benefits to taking prednisone, there are also many potentially dangerous side effects such as weight gain, osteoporosis or depression. Calcium supplements (for osteoporosis) or antidepressants are sometimes also prescribed to offset these side effects. As those with BMD age, many will need assistance with mobility. Braces, standing frames, and wheelchairs are common devices that may be used to maximize independence and quality of life. Those using power wheelchairs may want to restrict calories in their diet to keep their weight down. Weight gain puts additional stress on the heart and muscles of the body, muscles that are already weakened. It may also be helpful to eat a diet high in fiber, including fresh fruits and vegetables, and to drink plenty of fluids. This should help reduce constipation, a common problem for those who are immobile and have weak abdominal muscles. Physical therapy (PT) and exercise, such as water aerobics and swimming, can help build muscle and maintain cardiovascular health. Water activity allows exercise without excessive stress and strain. A personal exercise routine should be designed by both the physician and the physical therapist to ensure moderate exercise without over-exertion. An individual with BMD should not work out to the point of exhaustion. Occupational therapy (OT) is another component of health maintenance for someone with BMD. This type of therapy differs from physical therapy because instead of focusing on mobility and strength, occupational therapy focuses on specific tasks and maximization of abilities. OT helps with work-related tasks, leisure activities, and daily living, such as driving, grooming, or writing.

Prognosis

In BMD the rate and degree of muscle degeneration varies tremendously between individuals. While some men depend on wheelchairs by their 30s, others cope for several years with minor supports, such as canes. It is of comfort to many friends and family members to know that the muscle deterioration in BMD does not cause the individual pain. Muscle wasting only affects the muscle cells, not the nerve cells, so individuals maintain normal sensations of touch, pressure, vibration and temperature. Since it affects only voluntary muscle, they also retain control over the muscles of the bowel and bladder, and they have normal sexual function. BMD also causes weakness of the heart muscle (myocardium). The most serious side effect of BMD, cardiomyopathy, may put an individual at risk of heart failure. The impact of BMD usually progresses to fatal in the fourth or fifth decade of life.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Becker Muscular Dystrophy.org
This site provides an online, worldwide community for those affected by BMD. One can register, post health status, email address and personal comments on the site as well as communicate with other individuals suffering from BMD.

Muscular Dystrophy Association
The Muscular Dystrophy Association s website has numerous links to informative sites as well as Simply Stated reviews of related topics and information about research and ongoing clinical trials. Resources in Spanish are also available.

Parent Project Muscular Dystrophy
An organization founded by parents of children with muscular dystrophy aimed at providing information and support to all those affected by the disease.

Google Search for Becker Muscular Dystrophy (BMD)

References and Sources

www.ncbi.nlm.nih.gov/omim/ #300376 MUSCULAR DYSTROPHY, BECKER TYPE; BMD www.genetests.org Search GeneReviews for “becker muscular dystrophy”.