Becker muscular dystrophy (BMD) is a disease that causes the muscles to deteriorate. It is one of several muscular dystrophies, which are genetic (or inherited) diseases of the voluntary muscles or the muscles used to move parts of the body. Although BMD may affect all of the voluntary muscles, patients tend to maintain the function of the smooth, or involuntary muscles, such as those of the bladder and bowel.
BMD is caused by a mutation, or defect, in the DMD gene. This gene provides instructions for making the protein known as dystrophin. This protein helps to keep muscle cells intact, and proper levels of dystrophin are critical for muscle function. People with BMD are deficient in dystrophin; the dystrophin may be produced in low quantities or produced in a form that does not function properly.
BMD may affect all races and ethnicities. However, it primarily affects males and occurs in about one in 30,000 male births. BMD is similar to a more common disease called Duchenne muscular dystrophy (DMD), which affects about one in 3,500 male births. Both conditions are caused by mutations in the DMD gene and both tend to affect more males than females. However, the mutations in the DMD gene are slightly different in each disease. Furthermore, the symptoms of BMD tend to be milder, more variable, typically occur later in life, and they progress more slowly than DMD.
Onset of BMD is generally in adolescence or adulthood. Symptoms usually appear around 10 years of age, but can occur between the ages of two and 21. The disease progresses slowly and may vary from patient to patient but all voluntary muscles may be affected, especially those of the hips, pelvis, thighs, and shoulders. Muscle shrinking tends to be more severe in the lower body.
By the age of 30, the muscle degeneration in BMD becomes so severe that most patients cannot walk. As the muscles of the heart are affected by the disease, heart problems occur between age 20 and 40. Patients with BMD usually die of heart failure. In BMD, the average age of death is 42 years.
Although there is no known cure for BMD, many treatments are available to improve symptoms and maximize quality of life. With proper treatment, many individuals with BMD survive well into mid or late adulthood and have normal life expectancies.
Because Becker muscular dystrophy (BMD) is an inherited disorder, risk factors include having a family history of the disease. BMD is a recessive inherited genetic condition. Normal individuals have two copies of most genes (one inherited from the father and one from the mother). In a recessive genetic disorder, both copies of a certain gene need to be defective for the condition to manifest itself. It has been shown that mutations in the dystrophin gene, which is located on the X chromosome, may cause BMD.
Females have two copies of the X chromosome, but males have one X chromosome and one Y chromosome. Males inherit an X chromosome from the mother and a Y chromosome from the father, so a male can only inherit the dystrophin gene from the mother. Daughters inheriting the defective gene will be carriers while sons inheriting the gene will have BMD.
General: Becker muscular dystrophy (BMD) is caused by a defect, or mutation, in the DMD gene, which provides the instructions for making a protein called dystrophin. The mutation prevents the full-length protein from being produced. This protein normally helps maintain the structure and function of muscle cells. Individuals with BMD have lower than normal levels of this protein, so it cannot function fully. Although the reasons are not clearly understood, muscle cells lacking dystrophin eventually die.
Inheritance: Because Becker muscular dystrophy (BMD) is an inherited disorder, risk factors include having a family history of the disease. BMD is a recessive inherited genetic condition. Normal individuals have two copies of most genes (one inherited from the father and one from the mother). In a recessive inherited disorder, both copies of a certain gene need to be defective for the condition to occur. Mutations in the dystrophin gene DMD may cause BMD. This gene is located on the X chromosome, which is one of the sex chromosomes.
Females have two X chromosomes, while males have an X and a Y chromosome. If a female has one copy of the defective gene, the second X chromosome with a working copy of the gene can compensate. This is why women with the condition tend to experience milder symptoms. If a male has one copy of the defective gene, there is no other copy to compensate, which is why males experience more severe symptoms. Interestingly, males cannot pass on a defective X chromosome in X-linked recessive conditions.
A female who has a mutant DMD gene on one X chromosome has a 50% risk of passing the mutant gene to a son. Therefore, if the mother has one mutated gene, each son will have a 50% chance of being affected with BMD.
Males who have a mutant DMD gene on their X chromosome are affected by BMD. However, they are not at risk for passing the mutation to their sons. Therefore, BMD is a condition that is genetically inherited by individuals from their mother.
On the other hand, a male with BMD may pass the defective clotting factor gene to his daughters. Because males only pass X chromosomes to their daughters, each daughter of a male with BMD will carry one defective DMD gene.
Random occurrence: About 30% of known cases of males with BMD do not have the genetic mutation or defect associated with the disease. This may occur because of a mutation in the egg or developing embryo.
SIGNS AND SYMPTOMS
General: Becker muscular dystrophy (BMD) is a disease that causes the muscles to deteriorate. It is a disease of the voluntary muscles, which are the muscles used to move parts of the body. Although BMD may affect all of the voluntary muscles, patients tend to maintain the function of the smooth or involuntary muscles, such as those of the bladder and bowel.
The most common symptoms of the muscle breakdown that BMD patients experience are weakness and fatigue. By the age of 30, the muscle degeneration in BMD becomes so severe that most patients cannot walk.
Cognitive dysfunction: Some but not all patients with BMD have some degree of cognitive dysfunction. Researchers believe that cognitive dysfunction seen in BMD is caused by the defective dystrophin gene. Studies have found that the frequencies of learning disabilities, behavioral problems, and autism are higher among individuals with BMD than among the general population. These conditions do not appear to worsen with time. Although little is known about the incidence of intellectual disabilities in BMD, it is estimated that about one-third of patients with Duchenne muscular dystrophy have some cognitive disabilities.
Lack of coordination: BMD may affect the development of motor skills during childhood. Children with BMD may take longer than other children to learn to crawl or walk. Children with BMD also tend to be clumsy and may walk unsteadily, fall often, and have difficulty getting up from the floor.
Heart disorders: While muscular weakness is typically the first sign of BMD, some cases of the disease are not diagnosed until the patient develops a heart condition known as dilated cardiomyopathy. In dilated cardiomyopathy, the heart is not able to pump blood efficiently. Symptoms may include irregular heart beat, fatigue, and shortness of breath.
Muscular disorders: Muscle weakness in BMD progresses slowly. Over time, this leads to difficulty walking and frequent falls among those with BMD. Most patients with BMD are unable to walk unassisted by age 30.
Muscle damage tends to be more severe in the lower body. Among the muscles that are most affected by the disease are those of the hips, pelvis, thighs, and shoulders. Muscles in the arms, neck, and other areas are also affected in BMD.
Early in the progression of the disease, the muscles in the calves may grow larger. This is a form of compensation known as pseudohypertrophy that is temporary as the muscle is eventually replaced with cartilage and fatty tissue.
To compensate for weakening muscles, a person in the early stages of BMD may walk with a "waddling" gait, walk in his or her toes, or stick out the abdomen while walking.
The Gower sign, in which a person needs to "walk up" his or her body with the hands in order to assume a standing position, is commonly seen in BMD. While this sign is not specific to BMD, it does indicate weakness in the hip muscles.
Contracture, which is shortening of the muscles in a way that restricts mobility and movement, is another common muscular symptom of BMD. Contractures may be seen in the elbows, heels, and legs.
Respiratory problems: People with BMD may develop breathing problems as a result of wasting of the muscles that control inhaling and exhaling. In the early stages of breathing problems, symptoms may include headaches, difficulty concentrating, difficulty staying awake, and nightmares.
Skeletal disorders: People with BMD may have skeletal conditions in the chest and back. Scoliosis, or curvature of the spine, is often seen in patients with BMD. This is generally due to the weakening of the muscles that support the spine.
TYPES OF THE DISEASE
Becker muscular dystrophy (BMD) is one of several muscular dystrophies, which are genetic (or inherited) diseases of the voluntary muscles, or the muscles used to move parts of the body. While much variation among individuals with Becker muscular dystrophy has been observed, there are no specified different types of the disease.
General: Symptoms of Becker muscular dystrophy (BMD) are typically apparent by 11 years of age but may appear between the ages of two and 21. BMD is generally suspected when a patient experiences muscle weakness and continues to become weaker.
Because BMD is an inherited disorder, a family history of the disease may indicate performing a complete physical exam. The clinician will ask about muscle weakness, fatigue, clumsiness, and falls. He or she will perform tests to determine whether the source of muscular weakness is from the muscles themselves or from the nerves that control them. Because BMD is less severe than Duchenne muscular dystrophy, neck muscle strength is often maintained for a longer period of time. This may help a clinician to distinguish between the two diseases.
Biopsy: A biopsy is the surgical removal of a small piece of tissue for examination. For BMD, the sample is generally taken from the thigh muscle. A laboratory technician can determine whether dystrophin is present in the muscle cells and in what amount.
Blood tests: Tests that measure an enzyme called creatine kinase (CK, also known as creatine phosphokinase or CPK) in the blood can be used to identify muscle defects. CK is an enzyme that helps carry out a chemical reaction on creatine, a substance used by muscle for energy. Because CK may leak out of damaged muscle cells, the CK levels rise in the blood in patients with BMD. CK levels may also rise due to other factors, such as a heart attack or normal exercise. Therefore, the serum CK test may not be able to diagnose a patient specifically with BMD because other diseases that affect the muscles, as well as normal exercise, also result in increased levels of serum CK.
A blood test may also measure the level of transaminases in the blood. Transaminases are enzymes that allow amino acids to be broken down. High levels of transaminases are usually associated with liver disease. However, a high level of transaminases may also be due to the breakdown of muscle tissue, such as in BMD.
Electrocardiogram: An electrocardiogram (ECG or EKG) observes and records the electrical waves that cause the heart muscles to pump. When performing this test, the clinician will be looking especially for cardiomyopathy, a type of heart disease in which the heart doesn't work effectively.
Electromyogram: An electromyogram measures electrical impulses in muscle tissue. These tend to be diminished in BMD.
Genetic testing: Genetic testing looks specifically for mutations in the dystrophin gene. There are advanced methods of genetic testing available, including direct genomic sequence analysis.
Imaging: X-rays may be done on the spine to diagnose the severity and follow the progress of scoliosis. This is particularly important during adolescence when the development of scoliosis typically occurs. However, scoliosis is not specific to BMD.
Pulmonary function: Pulmonary function tests may be done to determine how effectively the individual is breathing and whether the muscles that control breathing are being affected. Poor results from pulmonary functions tests may indicate that the muscles that cause an individual to inhale and exhale are being affected by BMD.
General: General complications of Becker muscular dystrophy (BMD) are largely due to muscle degeneration. Complications may include progressive disability, decreased mobility, decreased ability to care for one's self, and deformities.
Cognitive: People with BMD may have some cognitive impairment, including learning disabilities. These tend to fall into three categories: attention focusing, verbal learning and memory, and emotional interaction. Researchers believe that cognitive dysfunction seen in BMD is caused by the defective dystrophin gene.
Developmental: BMD may affect the development of motor skills during childhood.
Gastrointestinal: As people with BMD lose muscle mass and tone, the digestive system may be affected. Complications that may arise include dysphagia, which includes swallowing problems and the risk for entry of foods or liquids into the lungs (pulmonary aspiration), and constipation.
Heart: Dilated cardiomyopathy is a common complication of BMD in which the heart cannot pump blood effectively. In this condition, the muscles of the heart become weakened or the heart may become enlarged. If left untreated, cardiomyopathy may become serious or even fatal.
Muscles: Muscular complications of BMD may include joint contractures in which joints lose mobility and flexibility because the muscles, tendons, and ligaments become shortened and/or stiffened. Contractures most often affect the knees, hands, feet, elbows, wrists, and fingers. If not treated, contractures may become severe. Other complications may include muscle cramps.
Respiratory: The degeneration of muscle mass in BMD affects the diaphragm and other muscles that control breathing. This can lead to several breathing problems, including pneumonia and respiratory failure. In the early stages of breathing problems, symptoms may include headaches, difficulty concentrating, difficulty staying awake, and nightmares. Decreased respiratory function also increases the risk of infection.
Skeletal: People with BMD may develop skeletal abnormalities such as scoliosis, in which the spine curves to the side, or lordosis, in which the spine curves forward creating a swayback. This is generally due to the weakening of the muscles that support the spine.
Other: Individuals with BMD are at an increased risk of malignant hyperthermia with the use of certain anesthetics. In this condition, an anesthetic, which is given to dull pain and to partially paralyze a person during surgery, causes muscles to become rigid and to break down. Additional symptoms include high fever, increased heart rate, and increased levels of acid in the body's tissues.
There is no known cure for Becker muscular dystrophy (BMD). The goal of treatment is to improve symptoms and maximize quality of life.
Assistive devices: As BMD progresses and the individual loses mobility, assistive devices such as braces, standing frames, walkers, and wheelchairs may be needed. Braces on the lower legs may also help to lengthen the muscles and prevent contractures, which are shortenings of the muscle fibers that limit range of motion and prevent mobility. A brace may be prescribed for wear at night to keep the foot from pointing downward and to keep the Achilles tendon stretched while the individual is sleeping. Other devices that may be helpful include a transfer board for helping the individual move in and out of the wheelchair, mechanical lifts, shower chairs, and adjustable beds.
Diet: While there are no known specific dietary prescriptions or restrictions for people with BMD, dietary approaches to manage constipation may be needed. The diet should therefore be high in fluid and fiber as well as fruits, vegetables, and whole grains. When mobility is limited, calorie needs decrease. Being overweight or obese may worsen the complications of BMD. Therefore, it is important that an individual eat a diet that helps to maintain a healthy weight.
Occupational therapy: Occupational therapy aims to improve function in specific activities and functions, such as aspects of self care, driving, and using a computer.
Pain relief: In most cases, BMD symptoms and complications do not cause pain. However, in some cases, patients may find muscle cramps painful and can find relief with over-the-counter pain relievers.
Physical activity: Swimming and water exercises may help individuals with BMD to keep muscles strong and toned without causing stress. Exercise should not be to the point of exhaustion.
Physical therapy: Because inactivity may worsen the condition of the muscles in BMD, activity is encouraged. The goals of physical therapy are to allow greater motion in the joints and to maintain muscle strength and tone. Physical therapy may also help to prevent, delay, or improve shortening of the muscle fibers known as contractures, and curvature of the spine known as scoliosis. Range-of-motion exercises, performed regularly, may also help to delay contracture. Exercises can be done to help correct spinal curvature or scoliosis.
Psychological support: Because the stress of a degenerative disease can be difficult, psychotherapy or a support group may be helpful for patients and families with BMD. Muscular dystrophy support groups, for example, provide a forum in which members can share experiences and problems.
Individuals with learning disabilities can also be evaluated by a mental health professional. Special exercises and educational therapies may be prescribed.
Respiratory support: If breathing problems become severe, respiratory assistance may be needed. A special mask worn while sleeping can deliver positive airway pressure. As breathing deteriorates, a cough assistance device can help the patient to cough and to keep the lungs clear.
Speech therapy: If speech and swallowing are affected by muscle wasting of BMD, a speech therapist may be helpful. Recommendations may include avoiding certain food textures and eating or drinking positions.
Surgery: Once contractures have set in, surgery may be the only option available to relieve them. A tendon release procedure, also known as a heel cord surgery, is often done to treat ankle and other contractures while the individual is still walking. After this surgery, a patient will often need lower leg braces. In severe scoliosis, surgery may be necessary. In this procedure, a metal rod with hooks is placed into the spine.
Transplantation: In cases of severe cardiomyopathy, a type of heart disease in which the heart is not able to pump blood efficiently, a heart transplant may be considered.
Note: Currently, there is insufficient evidence available on the safety and effectiveness of integrative therapies for the prevention or treatment of Becker muscular dystrophy (BMD). The integrative therapies listed below should be used only under the supervision of a qualified healthcare provider and should not be used in replacement of other proven therapies or preventive measures.
Good scientific evidence:
Vitamin D: Vitamin D deficiency has been associated with muscle weakness and pain in both adults and children. Limited research has reported vitamin D deficiency in patients with low back pain, and supplementation may lead to pain reduction in many patients.
Avoid if allergic or hypersensitive to vitamin D or any of its components. Vitamin D is generally well-tolerated in recommended doses. Doses higher than recommended may cause toxic effects. Individuals with hyperparathyroidism (overactive thyroid), kidney disease, sarcoidosis, tuberculosis, or histoplasmosis are at a higher risk of experiencing toxic effects. Vitamin D is generally considered safe for pregnant women. It may be necessary to give infants vitamin D supplements along with breast milk. The recommended intake of vitamin D for normal infants, children, and adolescents is 200 International Units (IU) daily.
Unclear or conflicting scientific evidence:
Coenzyme Q10: Coenzyme Q10 (CoQ10) is produced by the human body and is necessary for the basic functioning of cells. CoQ10 levels are reported to decrease with age and to be low in patients with some chronic diseases such as muscular dystrophies. Early studies in patients with muscular dystrophy taking CoQ10 supplements describe improvements in exercise capacity, heart function, and overall quality of life. Additional research is needed in this area.
Avoid in patients with allergy or hypersensitivity to CoQ10. Although few side effects have been associated with CoQ10, there have been reports of nausea, stomach upset, or rash. Caution is advised in people who have bleeding disorders or who are taking drugs that increase the risk of bleeding. Caution is advised in patients with diabetes or hypoglycemia and in those taking drugs, herbs, or supplements that affect blood sugar. Use cautiously in patients with liver disease, as large doses of CoQ10 (greater than 300mg per day) may elevate aminotransferase levels. Use cautiously in patients with biliary obstruction or liver disease as these conditions may increase CoQ10 concentrations. CoQ10 may decrease blood pressure and caution is advised in patients with low blood pressure or taking blood pressure medications. Elevations of liver enzymes have been reported rarely, and caution is advised in people with liver disease or taking medications that may harm the liver. CoQ10 may lower blood levels of cholesterol or triglycerides. Based on limited human evidence, thyroid hormone levels may be altered. There is not enough scientific evidence to support the use of CoQ10 during pregnancy or breastfeeding.
Creatine: Creatine is naturally synthesized in the human body from amino acids primarily in the kidney and liver and transported in the blood for use by muscles. Creatine loss is suspected to cause muscle weakness and breakdown in Duchenne muscular dystrophy, a condition that is related to BMD. Further research of creatine supplementation for muscular dystrophy is needed before a recommendation can be made.
Avoid in patients with allergy or hypersensitivity to creatine. Use of creatine supplements has been associated with symptoms of asthma. There have been rare reports of loss of appetite, stomach upset, diarrhea, or nausea with creatine use. Avoid in patients with liver or kidney disease. Use cautiously in patients with diabetes or low blood sugar. Creatine may cause muscle cramps or muscle breakdown, leading to muscle tears or discomfort. Weight gain and increased body mass may occur. Heat intolerance, fever, dehydration, reduced blood volume, or electrolyte imbalances (and resulting seizures) may occur. Chronic administration of a large quantity of creatine is reported to increase the production of formaldehyde, which may potentially cause serious unwanted side effects. Creatine may increase the risk of compartment syndrome of the lower leg, a condition characterized by pain in the lower leg associated with inflammation and ischemia (diminished blood flow), which is a potential surgical emergency. Creatine cannot be recommended during pregnancy or breastfeeding due to a lack of safety information.
Fair negative scientific evidence:
Selenium: Early studies suggest that selenium supplementation is not helpful in muscular dystrophy.
Avoid if allergic or sensitive to products containing selenium. Avoid with a history of nonmelanoma skin cancer. Selenium is generally regarded as safe for pregnant or breastfeeding women. However, animal research reports that large doses of selenium may lead to birth defects.
There are currently no known methods of preventing Becker muscular dystrophy (BMD). If there is a family history of BMD, genetic counseling may help the family understand the risks of having a child with BMD. Genetic testing can determine whether an individual is a carrier of BMD.
Because men with BMD may become fathers, it is important to know what inherited disease an individual has (Duchenne muscular dystrophy or BMD). Sisters of people with BMD may also be tested for carrier status. Because fathers only pass X chromosomes to their daughters, all daughters of a father with BMD will have at least one mutated X chromosome.
This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).
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