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Duchenne muscular dystrophy
medical conditions

Duchenne muscular dystrophy

Explore the available health information, treatment context, and integrative evidence for Duchenne muscular dystrophy.

Background
  • Duchenne muscular dystrophy (DMD) is an inherited genetic condition that affects about two out of every 10,000 people. Due to the inheritance pattern of DMD, males are more frequently affected with the disease than females (about 1 in 3,500 males is affected with DMD). DMD is part of a group of hereditary muscle diseases called muscular dystrophies.
  • Patients with DMD experience a progressive degeneration of muscle function beginning in infancy or early childhood. The loss of muscle function usually starts in the pelvis and the legs and eventually spreads to all parts of the body. Patients with DMD first lose the ability to walk, and eventually they lose the ability to move other parts of their bodies, such as the arms.
  • DMD is caused by a defect, or mutation, in a gene that contains instructions for making dystrophin, a protein that normally helps to maintain the structure and function of muscle. Individuals with DMD have reduced levels of this protein, so the muscles cannot carry out normal functions. Becker muscular dystrophy is another type of muscular dystrophy that is caused by a different type of mutation in the dystrophin gene.
  • Many patients with DMD eventually experience heart and/or lung complications, due to deterioration of muscles in these organs. This may lead to an inability to pump blood or breathe normally.
  • Most individuals with DMD do not survive past 30 due to the complications of muscle deterioration.
  • There is currently no known cure for DMD. However, some treatments exist that may help manage the symptoms, such as the use of walking devices to assist with moving and ventilators to assist with breathing.
Risk Factors and Causes
  • DMD 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 DMD.
  • 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. Therefore, a female needs to inherit two mutant copies of dystrophin to develop DMD (one from each parent), whereas a male only needs to inherit one mutant copy of dystrophin to develop the condition.
  • Because females need to inherit two mutant copies of dystrophin to develop the condition, whereas males only need to inherit one mutant copy, DMD is more common in males than females. An estimated one out of 10,000 people is affected with DMD, whereas one out of 3,500 males is affected with the disease. Females who inherit only one mutant copy of dystrophin are called "carriers." Females who are carriers may exhibit some mild symptoms.

  • DMD 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 DMD have an absence of this protein, so it can't carry out its normal function. Although the reasons are not clearly understood, muscle cells lacking dystrophin eventually die.
  • About two-thirds of cases of DMD are inherited, meaning that a defective DMD gene was transmitted from a parent to the child. However, about one third of cases of DMD are not inherited, but instead result from a random mutation in the egg or sperm or in early embryonic development.
  • DMD is a recessive X-linked condition, meaning that the dystrophin gene is located on the X chromosome and that all copies of the dystrophin gene need to be defective for an individual to develop the condition. Because females have two X chromosomes, they need to have two mutant copies of dystrophin to develop DMD. If a female has one mutant copy and one normal copy, the normal copy will make enough dystrophin to compensate for the mutant copy and any symptoms will be very mild. Because a male has one X chromosome and one Y chromosome, males only need to have one mutant copy of the dystrophin gene to develop the condition. This is because males don't have a second dystrophin gene that can serve as a backup.
Signs and Symptoms
  • Muscle deterioration: Patients with DMD experience a progressive degeneration of muscle function starting in infancy or in early childhood (around age six). The loss of muscle function usually starts in the pelvis and the legs, but eventually spreads to all parts of the body. An infant or child may stumble, waddle, or have difficulty climbing stairs due to impaired leg function. The ability to sit or stand is often affected too. It may be difficult to diagnose DMD just based on these symptoms, so if DMD is suspected, additional tests may be needed.
  • In patients with DMD, the muscles may become enlarged and eventually the muscle tissue is replaced with fat and connective tissue, a process called pseudohypertrophy. Muscle enlargement is especially noticeable in the calf muscles. This causes the muscle to progressively waste away and by age 12 most patients lose the ability to walk. Many patients experience loss of strength and endurance. As a patient gets older, other muscles throughout the body become affected, such as the arms, back, neck, and shoulders. Eventually, patients may completely lose the ability to move and become paralyzed.
  • Contractures: Many patients experience joint contractures, which is a stiffening of muscles around joints that can make it difficult and painful to move or lock the joints in positions.
  • Mental defects: For unknown reasons, about one-third of patients with DMD have learning disabilities or exhibit mental defects.
  • Carrier females: Females who are "carriers" (they have one normal copy of the dystrophin gene and one mutant copy) for DMD may exhibit some mild symptoms, including some muscle weakness or cramping. However, complete loss of muscle function typically doesn't occur in carrier females, and symptoms are generally milder than in males. Carrier females may exhibit symptoms early in life, and in some cases, symptoms may grow progressively worse.
Diagnosis
  • Physical signs: The first step in diagnosing DMD typically begins with a clinical exam in which a doctor looks for physical signs of the condition, especially weakened muscles or loss of muscle function. If DMD is suspected, other tests may be used to confirm a diagnosis.
  • Serum CK test: Tests that measure an enzyme called creatine kinase (CK), or creatine phosphokinase, 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. CK levels rise in the blood in patients with DMD when muscle cells deteriorate and CK leaks out. 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 DMD because other diseases that affect the muscles, as well as normal exercise, also result in increased levels of serum CK.
  • Biopsy: A doctor may surgically remove a small piece of muscle from patients in order to examine the muscle for signs of deterioration. A muscle biopsy may also be used to check for abnormal levels of the protein dystrophin. Patients with DMD are known to have reduced levels of this protein.
  • Genetic testing: Mutations in the dystrophin gene are known to cause DMD. Genetic tests can be used to check for these mutations and diagnose DMD. These tests may be used to confirm a diagnosis if there is a family history of DMD or if symptoms of DMD are present.
  • Gowers' sign: Some individuals with DMD may exhibit Gowers' sign, which may be useful in diagnosing the condition. Patients with Gowers' sign need to use their hands and arms to push themselves up when sitting (generally by moving the hands along the thighs). This is because patients with DMD may have difficulty standing due to weakness in leg muscles.
Complications
  • Infection: An infection of the lungs, especially pneumonia, is common in patients with DMD. This may be due to a weakness of respiratory muscles that reduces the ability of a patient to cough and leads to mucus buildup in the lungs.
  • Scoliosis: If the muscles of the back become weakened, they may become unable to hold the spine upright. This may lead to an abnormal curvature of the spine, called scoliosis. Individuals with scoliosis may have difficulty sitting in chairs and usually have back pain.
  • Respiratory muscles: In DMD, muscles in the lungs and diaphragm eventually deteriorate. This interferes with breathing, and difficulty breathing is the most common cause of death in patients with DMD. Most individuals with DMD do not survive past 30.
  • Cardiomyopathy: In some individuals with DMD, the muscles of the heart become enlarged and weakened. This may lead to an impaired ability to pump blood and may be life-threatening.
Treatment
  • Currently, there is no known cure for DMD. Treatment generally focuses on managing the symptoms.
  • Assistive devices: Most patients with DMD lose the ability to walk. Leg braces or wheelchairs may be used to assist in moving.
  • Drugs: Experimental drugs are being tested in patients with DMD. These drugs may help treat the disease by allowing patients with DMD to make full-length dystrophin proteins. One drug that has been tested (called gentamicin) was found to be toxic to patients at high doses. Another similar drug currently being evaluated is PTC124, which may be less toxic and more effective at treating patients with DMD.
  • Physical therapy: Children with DMD may benefit from seeing a physical therapist. A physical therapist can help patients maintain muscle tone and keep muscles strong and flexible through performing different exercises.
  • Steroids: A steroid drug called prednisone, which can slow the rate of muscle deterioration, may be prescribed to patients with DMD. Prednisone has some side effects, including weight gain and loss of bone density.
  • Surgery: Some patients with DMD exhibit a deformity in the spine called scoliosis, in which the spine is abnormally curved. Surgery may be performed to partially correct this problem and reduce the extent of the abnormal curvature.
  • Transplantation: A heart transplant may be performed in some cases, if the deterioration of heart muscle is so severe that the heart is unable to pump enough blood.
  • Ventilator: Because many patients with DMD develop respiratory problems, a mechanical ventilator may be recommended by a doctor to assist with breathing. A mechanical ventilator is a machine that sends air into the lungs. Based on the severity of the respiratory problems, a ventilator may only be required during the night, or both during the day and at night.
Prevention
  • There are currently no known ways to prevent DMD. However, genetic counseling for parents is available.
References
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