Overview

In the early stages, Duchenne MD affects the shoulder and upper arm muscles and the muscles of the hips and thighs. These weaknesses lead to difficulty in rising from the floor, climbing stairs, maintaining balance and raising the arms.

What is Duchenne muscular dystrophy?

Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by progressive muscle degeneration and weakness. It is one of nine types of muscular dystrophy.

DMD is caused by an absence of dystrophin, a protein that helps keep muscle cells intact. Symptom onset is in early childhood, usually between ages 3 and 5. The disease primarily affects boys, but in rare cases it can affect girls.

What are the symptoms of DMD?

Muscle weakness can begin as early as age 3, first affecting the muscles of the hips, pelvic area, thighs and shoulders, and later the skeletal (voluntary) muscles in the arms, legs and trunk. The calves often are enlarged. By the early teens, the heart and respiratory muscles also are affected. For more about DMD symptoms, see Signs and Symptoms.

Becker muscular dystrophy (BMD) is a milder version of DMD. Its onset is usually in the teens or early adulthood, and the course is slower and less predictable than that of DMD.

What causes DMD?

Duchenne muscular dystrophy was first described by the French neurologist Guillaume Benjamin Amand Duchenne in the 1860s, but until the 1980s, little was known about the cause of any kind of muscular dystrophy. In 1986, MDA-supported researchers identified a particular gene on the X chromosome that, when flawed (mutated), leads to DMD. In 1987, the protein associated with this gene was identified and named dystrophin. Lack of the dystrophin protein in muscle cells causes them to be fragile and easily damaged.

DMD has an X-linked recessive inheritance pattern and is passed on by the mother, who is referred to as a carrier. For more about the way gene mutations cause Duchenne dystrophy, see Causes/Inheritance.

What are DMD 'carriers'?

DMD carriers are females who have a normal dystrophin gene on one X chromosome and an abnormal dystrophin gene on the other X chromosome. Most carriers of DMD do not themselves have signs and symptoms of the disease, but a minority do. Symptoms can range from mild skeletal muscle weakness or cardiac involvement to severe weakness or cardiac effects and can begin in childhood or adulthood. For more, read Females and DMD in Causes/Inheritance.

What is the life expectancy in DMD?

Until relatively recently, boys with DMD usually did not survive much beyond their teen years. Thanks to advances in cardiac and respiratory care, life expectancy is increasing and many young adults with DMD attend college, have careers, get married and have children. Survival into the early 30s is becoming more common, and there are cases of men living into their 40s and 50s. For more about living with DMD, see Medical Management.

What is the status of DMD research?

MDA-supported researchers are actively pursuing several exciting strategies in DMD, such as gene therapy, exon skipping, stop codon read-through and gene repair. Human clinical trials are under way for some of these strategies. For an overview of DMD research strategies and the latest research news, see Research.



Signs and Symptoms

boy with enlarged calf muscles
Boys with DMD often have enlarged calf muscles.

Children with Duchenne muscular dystrophy (DMD) are often late walkers.

In toddlers, parents may notice enlarged calf muscles (see image at right). This enlargement is known as pseudohypertrophy, or "false enlargement," because the muscle tissue is abnormal and may contain scar tissue.

A preschooler with DMD may seem clumsy and fall often. Parents also may note that children have trouble climbing stairs, getting up from the floor or running.

By school age, children may walk on their toes or the balls of their feet with a slightly waddling gait, and fall frequently. To try to keep their balance, they may stick out their bellies and pull back their shoulders. Children also have difficulty raising their arms.

Many children with DMD begin using a wheelchair sometime between ages 7 and 12. Transition to a wheelchair usually is a gradual process; at first, the chair may be required only to conserve the child's energy when covering long distances. (Children often experience renewed independence once they fully transition to a power wheelchair.)

In the teen years, activities involving the arms, legs or trunk may require assistance or mechanical support.

Boy performing Gowers maneuver Boy performing Gowers maneuver Boy performing Gowers maneuver
Boy performing Gowers maneuver Boy performing Gowers maneuver

Because of weakened leg muscles, boys with DMD have a distinctive way of rising from the floor, called a Gowers’ maneuver.

They first get on hands and knees, then elevate the posterior, then “walk” their hands up the legs to raise the upper body.

Pain and sensation

The muscle deterioration in Duchenne MD isn’t usually painful in itself. Some people report muscle cramps at times; these usually can be treated with over-the-counter pain relievers.

Because muscular dystrophy doesn’t affect nerves directly, touch and other senses are normal, as is control over the smooth, or involuntary, muscles of the bladder and bowel, and sexual functions.

The heart

Lack of dystrophin can weaken the muscle layer in the heart (myocardium), resulting in a condition called cardiomyopathy. Over time, sometimes as early as the teen years, the damage done by DMD to the heart can become life-threatening. The heart should be monitored closely, usually by a pediatric cardiologist. See Medical Management for more on cardiomyopathy in DMD.

Respiratory function

Beginning at about 10 years of age, the diaphragm and other muscles that operate the lungs may weaken, making the lungs less effective at moving air in and out. Although the child may not complain of shortness of breath, problems that indicate poor respiratory function include headaches, mental dullness, difficulty concentrating or staying awake, and nightmares.

Weakened respiratory muscles make it difficult to cough, leading to increased risk of serious respiratory infection. A simple cold can quickly progress to pneumonia. It's important to get flu shots, and when infections occur, to get prompt treatment. See Medical Management for more on respiratory care in DMD.

Learning

About a third of boys with DMD have some degree of learning disability, although few have serious mental retardation. Doctors believe that dystrophin abnormalities in the brain may have subtle effects on cognition and behavior. Learning problems in DMD occur in three general areas: attention focusing, verbal learning and memory, and emotional interaction.

Children suspected of having a learning disability can be evaluated by a developmental or pediatric neuropsychologist through the school system’s special education department or with a referral from the MDA clinic.

If a learning disability is diagnosed, educational and psychological interventions can begin right away. The specialist may prescribe exercises and techniques that can help improve these areas, and the school also can provide special help with learning. See Medical Management for more about learning disabilities in DMD.




Diagnosis

In diagnosing any form of muscular dystrophy, a doctor usually begins by taking a patient and family history, and performing a physical examination. Much can be learned from these, including the pattern of weakness. The history and physical go a long way toward making the diagnosis, even before any complicated diagnostic tests are done.

CK level

Early in the diagnostic process, doctors often order a blood test called a CK level. CK stands for creatine kinase, an enzyme that leaks out of damaged muscle. When elevated CK levels are found in a blood sample, it usually means muscle is being destroyed by some abnormal process, such as a muscular dystrophy or inflammation. A very high CK level suggests that the muscles themselves (and not the nerves that control them) are the likely cause of the weakness, although it doesn’t tell exactly what the muscle disorder might be.

Genetic testing

Genetic testing involves analyzing the DNA of any cells (usually blood cells are used) to see whether there is a mutation in the dystrophin gene, and if so, exactly where it occurs. Such DNA testing for dystrophin mutations is widely available in the United States. Ask your MDA clinic physician or genetic counselor for more information. And, for more on getting a definitive genetic diagnosis, see The Genie's Out of the Bottle: Genetic testing in the 21st century.

Female relatives of men and boys with DMD can undergo DNA testing to see if they are carriers of the disease. Women who are DMD carriers can pass on the disease to their sons and their carrier status to their daughters. In a minority of cases, girls and women who are DMD carriers may themselves show symptoms of DMD, such as muscle weakness and heart problems. These symptoms may not show up until adulthood. (See Causes/Inheritance.)

Several experimental drugs currently in development to treat DMD require knowledge of the person's precise genetic mutation, so genetic testing has become important not only for diagnosis but possibly for future treatments.

Muscle biopsy

To obtain more information, the doctor may order a muscle biopsy, the surgical removal of a small sample of muscle from the patient. By examining this sample, doctors can tell a great deal about what’s actually happening inside the muscles.

Modern techniques can use the biopsy to distinguish muscular dystrophies from inflammatory and other disorders, and also to distinguish among different forms of muscular dystrophy. For instance, the amount of functional dystrophin protein found in a muscle biopsy sample sheds light on whether the disease course is likely to be DMD (with no dystrophin present) or the milder Becker muscular dystrophy (with some partially functional dystrophin present).