Duchenne muscular dystrophy
Duchenne muscular dystrophy is the most common fatal genetic disorder diagnosed in childhood, affecting approximately 1 in every 3,500 live male births (about 20,000 new cases each year worldwide). Because the Duchenne gene is found on the X-chromosome, it primarily affects boys; however, it occurs across all races and cultures.
Duchenne can be passed from parent to child, but approximately 35% of cases occur because of a random spontaneous mutation. In other words, it can affect anyone. Although there are medical treatments that may help slow its progression, there is currently no cure for Duchenne.
Progressive muscle weakness is the main feature of muscular dystrophy. Each separate form of muscular dystrophy varies a bit in terms of the age at which the signs and symptoms usually begin and the sequence in which different muscle groups are affected.
Listed below are the common signs of Duchenne. If a boy has a combination of these traits, he should be tested for Duchenne:
- Has a hard time lifting his head or has a weak neck
- Is not walking by 15 months
- Has a hard time walking, running, or climbing stairs
- Is not speaking as well as other kids his age
- Needs help getting up from the floor or walks his hands up his legs in order to stand
- Has calves that look bigger than normal (pseudohypertophy)
- Walks with his legs apart
- Walks on his toes and waddles
- Walks with his chest pointed out (or has a sway back, saddle back, or hollow back)
One of our largest known genes, dystrophin is an important muscle protein that acts as a kind of anchor, holding muscles together by maintaining the structure of muscle cells.
Dystrophin is also believed to carry signals between the inside and outside of muscle fibers. Without dystrophin, muscles are unable to operate properly, and eventually suffer progressive damage.
The dystrophin gene is carried on the X-chromosome. As males have only one X-chromosome, this makes them more susceptible to dystrophin damage, as they lack a second X-chromosome to make up for the damaged gene.
When a male’s body is not able to produce any dystrophin at all, he is diagnosed with Duchenne.
Duchenne is usually passed from parent to child, but many cases are the result of random spontaneous genetic mutations, which can occur during any pregnancy. In fact, about one out of every three cases occurs in families with no previous history of Duchenne.
Genetic counseling is advised if there is a family history of the disorder. Duchenne muscular dystrophy can be detected with about 95% accuracy by genetic studies performed during pregnancy.
Duchenne muscular dystrophy (DMD) is suspected and diagnosed when the following clinical findings are found: a positive family history of DMD, more men affected that women in a family, progressive muscle weakness which is usually greater in the proximal muscles (closest to the trunk of the body) than distal muscles (those farthest away from the hips and shoulders such as those in the hands, feet, lower arms or lower legs), symptoms before the age of 5 years old and wheel chair dependency before age 13.
In addition to a medical history review and physical examination, your doctor may suggest some of the following tests:There are reliable tests to help doctors diagnose a boy with Duchenne. The following tests are typically used to confirm a preliminary diagnosis of Duchenne:
- Creatine Kinase: Creatine phosphate kinase (also known as CPK or CK) is an enzyme that normally lives inside muscles. Males with Duchenne often have CK levels 10 to 100 times the normal range. Elevated CK levels indicate muscle damage, although a high CK does not confirm a diagnosis of Duchenne.
- Genetic Testing: Genetic testing (using blood cells or muscle cells) is the best way to obtain exact genetic information for a conclusive Duchenne diagnosis. The field of genetic testing is rapidly evolving, and there are several types of testing that provide accurate genetic diagnosis.
Duchenne results in progressive loss of strength and is caused by a mutation in the gene that encodes for dystrophin. Because dystrophin is absent, the muscle cells are easily damaged. Eventually, increasing difficulty in breathing due to respiratory muscle dysfunction requires ventilation support, and cardiac dysfunction can lead to heart failure. The progressive muscle weakness leads to serious medical problems, particularly issues relating to the heart and lungs. Young men with Duchenne typically live into their late twenties.
Corticosteroids, such as prednisone, may help improve muscle strength and delay the progression of certain types of muscular dystrophy.
The U.S. Food and Drug Administration (FDA) has granted accelerated approval for eteplirsen (EXONDYS 51) as a once weekly intravenous infusion of 30 milligrams per kilogram for the treatment of Duchenne muscular dystrophy (DMD) in patients who have a confirmed mutation in the DMD gene that is amenable to exon 51 skipping. Though, clinical benefit of EXONDYS 51 has not been established. Continued approval for this indication may be contingent upon verification of a clinical benefit in confirmatory trials.
Several different types of therapy and assistive devices can improve quality and sometimes length of life in people who have muscular dystrophy. Examples include:
- Range-of-motion exercises. Muscular dystrophy can restrict the flexibility and mobility of joints. Limbs often draw inward and become fixed in that position. One goal of physical therapy is to provide regular range-of-motion exercises to keep joints as flexible as possible.
- Mobility aids. Braces can provide support for weakened muscles and help keep muscles and tendons stretched and flexible, slowing the progression of contractures. Other devices — such as canes, walkers and wheelchairs — can help maintain mobility and independence.
- Breathing assistance. As respiratory muscles weaken, a sleep apnea device may help improve oxygen delivery during the night. Some people with severe muscular dystrophy may need to rely on a ventilator — a machine that forces air in and out of their lungs.
Surgical and other procedures:
Surgical remedies are an option for several of the problems common to muscular dystrophy, such as:
- Contractures. Tendon surgery can loosen joints drawn inward by contractures.
- Scoliosis. Surgery may also be needed to correct a sideways curvature of the spine that can make breathing more difficult.
- Heart problems. Some people who have heart problems related to muscular dystrophy may be helped by the insertion of a pacemaker, which prompts the heart to beat more regularly.
Activity is encouraged:
Inactivity (such as bed rest) can worsen the muscle disease. Physical therapy may be helpful to maintain muscle strength and function. Orthopedic appliances (such as braces and wheelchairs) may improve mobility and the ability to care for yourself.
You can ease the stress of illness by joining a support group where members share common experiences and problems. See muscular dystrophy - support group. The Muscular Dystrophy Association is an excellent source of information on this disease.