Q: My neighbor’s son was just diagnosed with muscular dystrophy. Is there a cure for this yet?
A: There are multiple different types of muscular dystrophy (MD); all are diseases that compromise the normal proteins needed to create and maintain healthy muscle tissue. MD affects about 1 in every 4,000 boys, but is less common in girls. Most of these cases are inherited, but a spontaneous gene mutation (one that is not inherited) is thought to occur in up to one-third of cases.
MD causes a progressive disruption in normal muscle function, manifesting as muscle weakness. The patient’s symptoms, including which muscle groups are compromised and at what age they manifest, depend on many factors, including the amount and type of muscle proteins affected. This depends on the specific genetic defect; different types of MD manifest differently.
Most commonly the voluntary muscles (such as the muscles that move the arms and legs) are affected, but depending on the specific type of MD essentially any of the body’s muscles can be compromised, including the swallowing muscles, the heart, the breathing muscles and others. In some MD patients other organ systems may be involved (for example the proteins involved in some types of MD may play a role in brain nerve cell junctions).
Complications of MD may cause significant morbidity and mortality. For example, if the breathing muscles are compromised the patient may not be able to get enough oxygen (and expel enough carbon dioxide) to keep the cells of other body organs healthy. If the swallowing muscles become affected, maintaining adequate nutrition may be a challenge, and if the heart is adversely affected the patient may not be able to supply adequate blood to the body. The skeletal muscles (that help move the arms, legs, etc.) pull the joints in different directions in a balanced and coordinated manner to finely control movement. Compromise of the skeletal muscles can corrupt this balance, and so patients with MD may develop joint stiffness, looseness and/or contractures, curvature of the spine, and/or other skeletal problems.
The most common type of MD is Duchenne MD (DMD, accounting for about half of all cases), which is due to a problem with the muscle protein dystrophin. The gene for this protein is on the X chromosome, and since boys have XY sex chromosomes, and so only one copy of the X chromosome, they are affected much more commonly than girls. Girls have XX sex chromosomes, so if only one X is abnormal there will typically be minimal symptoms, although she will be a “carrier” who can pass the condition on to her children, especially sons since mom is the source of the X chromosome in sons.
DMD typically compromises the muscles of the shoulder, arm ,hip and upper leg between the ages of 3 and 5; the muscle weakness may begin by causing frequent falls, difficulty standing from a seated position or other symptoms. Its effects are often rapidly progressive, and most kids with DMD are unable to walk on their own by their tween years.
Becker MD is also due to a problem with the protein dystrophin, but it is due to a different genetic defect which causes it to manifest symptoms later in life, typically in the patient’s teen or early adult years. It typically progresses more slowly that DMD, although this is variable from patient to patient.
MD is suspected based on the clinical symptoms, and then blood tests to look for abnormally elevated muscle breakdown enzymes and other tests (for example an ultrasound, and in some cases an electromyogram) may be indicated. A muscle biopsy may be carried out to verify the diagnosis, although nowadays genetic testing to identify the specific genetic defect and confirm the diagnosis is often done.
Although specific screening for MD is presently not recommended, the periodic checkups that children get will often identify delayed achievement of “milestones,” ages when children usually begin to be able to do certain things like walk, tall, etc., and that, in addition to a detailed history and physical, may raise suspicion of the condition.
Presently there is no cure for any of the types of MD, although there has been significant improvement in treatments. Patients with MD should be followed by a team of clinicians with experience and expertise treating this condition.
Treatment for MD focuses on minimizing symptoms and complications, so is individualized for each patient. It may include medications, for example, steroid medications may slow muscle degeneration and improve symptoms and functionality, mobility assist devices such as braces, crutches, wheelchairs, surgery (for example, if needed to address joint contractures), and other supportive care to improve nutrition, respiration, physical therapy, occupational therapy, etc. The patient and their family/loved ones may benefit from support groups and/or counseling.
These treatments have improved survival and quality of life for MD patients. Years ago a patient with DMD usually died in their teens, but today many DMD patients survive to their thirties and even longer.
The first medication to modify MD disease progression (eteplirsen) in certain patients with DMD (those with a specific type of gene mutation) was recently (September 2016) approved by the FDA. Many other treatments are being researched, as are many treatment techniques (for example gene therapy approaches), so there is hope for even better therapies in the future.
Jeff Hersh Ph.D., M.D., can be reached at DrHersh@juno.com