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What is Duchenne muscular dystrophy and Becker muscular dystrophy?
These types of muscle diseases are caused when a gene fails to make the protein dystrophin, which helps connect the moving part of muscle to the tissue that holds the body together.
In Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD), the absence of dystrophin leads to progressive muscle weakness. Eventually, the heart and respiratory muscles are also affected. Some children may also have problems with attention, intellect, and behavior or even autism, as some forms of this disease can affect the brain.
DMD is the most common form of muscular dystrophy. BMD is a variation of DMD. In BMD, muscles typically function better than they do in DMD, due to a small level of dystrophin being produced.
Both DMD and BMD usually affects only males as the affected gene is on the X-chromosome. It occurs in one out of 3,500-5,000 live male births. This disease rarely affects girls, but when it does, the condition is normally not as severe.
What causes muscular dystrophy?
DMD is a genetic disease, which means it is inherited. Our genes determine our traits, such as eye color and blood type. Genes are contained in the cells of our bodies on stick-like structures called chromosomes. There are normally 46 chromosomes in each cell of our body, or 23 pairs. The first 22 pairs are shared in common between males and females, while the last pair determine gender and are called the sex chromosome pair: females have two X chromosomes, while males have one X and one Y chromosome.
DMD is caused by an X-linked recessive gene. "X-linked" means that the gene causing the trait or the disorder is located on the X chromosome. Genes on the X chromosome can be recessive or dominant, and their expression in females and males is not the same because the genes on the Y chromosome do not exactly pair up with the genes on the X. X-linked recessive genes are expressed in females only if there are two copies of the gene (one on each X chromosome). However, for males there only needs to be one copy of an X-linked recessive gene in order for the trait or disorder to be expressed. For example, a woman can carry a recessive gene on one of the X chromosomes unknowingly, and pass it on to a son, who will express the trait or disease.
In Duchenne's muscular dystrophy (DMD), one-third of all cases are thought to be new mutations in the family (not inherited from the mother).
What are the symptoms of muscular dystrophy?
Muscular dystrophy is usually seen in children before the age of 5, with weakness typically affecting the shoulder and hipmuscle as one of the initial symptoms. The following are the most common symptoms of muscular dystrophy. However, each child may experience symptoms differently. Symptoms may include:
- Clumsy movement
- Difficulty climbing stairs
- Frequently trips and falls
- Unable to jump or hop normally
- Tip toe walking
A telltale clinical characteristic for DMD is Gowers' sign. Children with DMD find it very hard to get up from a sitting or lying position on the floor. They first pull up to their hands and knees. The child walks his/her hands up their legs to brace themselves as they rise to a standing position.
Another classic symptom of muscular dystrophy is known as the "slip through" symptom. Your child's physician puts his/her hands around the sides of the child's chest, right up under the arms. As the child is lifted up, the shoulders weaken and move upward, almost allowing the child to slip through your child's physician's hands.
In addition, children with BMD and DMD often have very large calf muscles due to the large amounts of fatty deposits that are replacing muscle.
The symptoms of muscular dystrophy may resemble other conditions or medical problems. Always consult your child's physician for a diagnosis.
How are DMD and BMD diagnosed?
The diagnosis of muscular dystrophy is made with a physical examination and diagnostic testing by your child's physician. During the examination, your child's physician obtains a complete prenatal and birth history of the child and asks if other family members are known to have muscular dystrophy. Often, we are able to diagnosis children with some blood tests including a genetic test to confirm the diagnosis.
Diagnostic tests for muscular dystrophy may include:
- Blood tests
- Muscle biopsy - the primary test used to confirm diagnosis. A small sample of muscle tissue is taken and examined under a microscope.
- Electromyogram (EMG) – a test to check if the muscle weakness is a result of destruction of muscle tissue rather than nerve damage.
- Electrocardiogram (ECG or EKG) - a test that records the electrical activity of the heart, shows abnormal rhythms (arrhythmias or dysrhythmias), and detects heart muscle damage.
Treatment for muscular dystrophy:
Specific treatment for muscular dystrophy will be determined by your child's physician based on:
- Your child's age, overall health, and medical history
- The extent of the condition
- The type of condition
- Your child's tolerance for specific medications, procedures, or therapies
- Expectations for the course of the condition
- Your opinion or preference
To date, there is no known cure for Duchenne or Becker muscular dystrophy. However, there are medications and treatments which can help slow the progression of heart, lung and muscle symptoms.
Since muscular dystrophy is a life-long condition that is not correctable, management includes focusing on preventing or minimizing deformities and maximizing the child's functional ability at home and in the community.
The care for children with this disease requires many different specialties including neuromuscular, pulmonary, cardiology, physical medicine & rehabilitation, physical therapy, orthopedics, and more. As such, patients who are seen in a multidisciplinary clinic have access to most of their doctors in one visit.
In some patients, there is a mutation which can be treated to help slow the progression of the disease. Exondys 51 (eteplirsen) is a drug that was recently approved by the FDA for the treatment of a particular type of DMD. For almost all patients, the use of steroids has been shown to slow the progression of disease, allowing a longer period before needing a wheelchair as well as to slow the heart and lung weakening.
Long-term outlook for a child with muscular dystrophy:
Muscular dystrophy is a progressive condition that needs life-long management to prevent deformity and complications. Walking and sitting often becomes more difficult as the child grows. Usually by the age of 12, the child needs a wheelchair because the leg muscles are too weak to work. Heart or lung problems often occur by the late teenage years or into the early 20s.
The interdisciplinary healthcare team will work with your family to improve your child's functional outcomes and to provide support as you learn to care for your child's needs.
The Muscular Dystrophy Association (MDA) can be an important resource, both financially and emotionally, for parents of children with muscular dystrophy.
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