Duchenne muscular dystrophy (DMD) is a rare genetic disorder that causes muscle weakness and degeneration over time. Each year, an estimated 20,000 children are diagnosed with DMD globally.

In recent years, new treatment options and support devices have helped children and adults with DMD live longer, healthier lives. This article will provide an overview of what causes DMD, how it’s diagnosed, and what therapies are currently available.

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What Causes Duchenne Muscular Dystrophy?

DMD is a rare disease caused when the body doesn’t make a protein called “dystrophin.” Why don’t people with DMD make dystrophin? DMD is caused by mutations (changes) in the dystrophin gene, which provides instructions for producing the protein dystrophin. This protein acts like an anchor that holds muscle cells together, keeping them strong and protecting them from injury. Dystrophin is found in skeletal muscle cells that are responsible for controlling movement and in heart muscle cells.

People with DMD have progressive muscle weakness because their bodies don’t make enough dystrophin protein to hold together and protect muscle cells.

People with DMD have progressive muscle weakness because their bodies don’t make enough dystrophin protein to hold together and protect muscle cells. As a result, the cells can’t properly attach to nearby tissues, causing them to tear. The damaged muscle fibers are replaced by scar tissue or fat, causing more muscle loss.

The Dystrophin Gene Is Passed From Parents to Children

The gene mutations that cause DMD are often passed down through family members. Children inherit one set of chromosomes, which control characteristics, like eye color, hair color, and sex, from each parent. Females inherit two X chromosomes from their parents, according to the National Human Genome Research Institute, whereas males inherit one X chromosome from their mother and one Y chromosome from their father.

DMD is known as an “X-linked disease.” The dystrophin gene is found on the X chromosome. If females inherit one X chromosome with a mutated dystrophin gene, they likely have a healthy gene on the other chromosome that provides instructions to make enough dystrophin protein. Females with one defective gene and one healthy gene are called “carriers” because, even though they don’t have DMD, they can still pass it along to their children.

Is DMD More Common in Males or Females?

Males inherit only one X chromosome — if they inherit a copy with a mutated gene, there isn’t another one to compensate. This is why Duchenne muscular dystrophy prevalence is higher among males (1 out of 3,500 to 6,000 births) than females (1 in 50,000,000 births), according to research cited in the journal Sleep Science.

Symptoms of Duchenne Muscular Dystrophy

Signs and symptoms of DMD typically start appearing in early childhood. Children with DMD tend to miss major developmental milestones. A child with DMD may have a harder time holding their head up, walking, or speaking than other children their age.

The most obvious signs of DMD are motor or movement symptoms. Muscle weakness in the legs and hips is often the first sign of DMD, which then moves to the neck and arms. Your child may also waddle when they walk (known as a “waddling gait”) or walk on their toes. Children with DMD tend to fall more often and have a difficult time walking up stairs.

When trying to stand from a prone or squatting position, a child with DMD may first assume a hands-and-knees position, then walk their hands up their shins, knees, and thighs until they’re upright. Called Gowers’ sign, this indicates weakness in the hips, thighs, and other leg muscles. Gowers’ sign in adults may also be seen, but it’s usually observed in early childhood.

Other physical signs of DMD include:

• Enlarged calf muscles
• Scoliosis (a change in the curvature of the spine)
• Contractures (short or stiffened muscles)

Many children with DMD start taking heart medications by age 10 to help prevent heart disease.

Children with DMD may also have learning or behavioral conditions that can affect school performance and quality of life. Behavioral signs and symptoms of DMD include:

• Attention-deficit/hyperactivity disorder (ADHD)
• Autism spectrum disorder
• Trouble focusing
• Social challenges, such as making friends at school, leading them to spend most of their time alone
• Anxiety
• Difficulty adapting to changes in plans or routines
• Academic performance difficulties

Your child or loved one may also have unusual blood test results early in life. Children with DMD often have high blood levels of liver and muscle enzymes, like creatine kinase or alanine transaminase.

Diagnosis of Duchenne Muscular Dystrophy

If your child or loved one has shown DMD symptoms, you’ll want to talk to their doctor about testing. They may refer you to a doctor who specializes in muscle disorders in children, such as a neurologist. Together, your child’s healthcare team can run several tests to make a final DMD diagnosis. Examples of tests used to diagnose DMD include:

• Physical exam — Through this test, a doctor learns more about your child’s symptoms and any other illnesses or injuries they’ve had in the past.
• Neurological and muscle exams — These test your child’s nerve and muscle function, including how they walk and how well their reflexes respond.
• Blood tests — This test measures your child’s creatine kinase levels to check for inflammation and tissue damage caused by DMD.
• Genetic testing — This looks for genetic changes that cause DMD. It’s recommended that other family members undergo this testing to see if they carry the same mutation.
• Muscle biopsy — This test is used if genetic testing can’t find a cause for DMD. It entails removing a small sample of muscle tissue for examination to see if the muscle cells are missing dystrophin protein.
• Electrocardiogram — This measures the heart’s electrical activity to check for any heart-related problems. Many children with DMD go on to develop heart disease.

Treatment Options for Duchenne Muscular Dystrophy

The U.S. Food and Drug Administration (FDA) has approved several treatments for DMD that help control inflammation, slow muscle damage, and improve strength and function. Other supportive therapies help improve mobility and quality of life.

Corticosteroids

Corticosteroids are laboratory-made hormones that work similarly to the natural hormone cortisol to dampen inflammation. Studies have found that prednisone, prednisolone, and deflazacort (Emflaza) can improve muscle strength, lower the risk of scoliosis, and improve lung function. Vamorolone (Agamree) is a drug that works similarly to steroids to help treat DMD symptoms in people ages 2 and up.

In recent years, new therapies have helped extend the life expectancy of people living with DMD.

Many children with DMD start taking heart medications by age 10 to help prevent heart disease. For example, blood pressure medications relax blood vessels and take stress off the heart muscle.

Nonsteroidal Medication

Givinostat (Duvyzat) is a nonsteroidal medication and histone deacetylase inhibitor that may help reduce inflammation and delay muscle loss in people 6 and older with DMD.

Exon-Skipping Therapies

Exon-skipping drugs correct mutations in the dystrophin gene so it can provide the right instructions for making the dystrophin protein. These therapies treat certain genetic mutations, meaning only some children and adults with DMD are eligible, depending on which exon is affected. The FDA has approved four exon-skipping therapies:

• Casimersen (Amondys 45)
• Eteplirsen (Exondys 51)
• Golodirsen (Vyondys 53)
• Viltolarsen (Viltepso)

Gene Therapy

Gene therapy is another type of treatment being studied for DMD. This approach delivers instructions for making a shorter, functional version of dystrophin to help support muscle cells.

The gene therapy delandistrogene moxeparvovec-rokl (Elevidys) is approved for people with DMD ages 4 and older who are ambulatory, meaning they can still walk. It’s not currently approved for people who are nonambulatory. Elevidys isn’t a cure, but it may improve movement in some people. The FDA added a boxed warning for a rare risk of serious liver injury, including acute liver failure. Doctors monitor liver tests closely after treatment, and families may be asked to stay near a hospital for a period of time.

Mobility Aids

Children and adults with DMD may use mobility aids to help them move around and walk more easily. Walkers, braces, and wheelchairs may all be appropriate, depending on the person’s needs. Respiratory treatments and devices are often needed to help improve breathing.

Physical Therapy

Physical therapy can help boost your child’s or loved one’s quality of life, strengthening their muscles and enhancing their flexibility. Daily exercises can also help prevent atrophy or muscle wasting.

Conditions Related to Duchenne Muscular Dystrophy

An unrelated condition that occurs alongside DMD is known as a comorbidity. Children and adults with DMD are more likely to have comorbid conditions such as:

• Epilepsy
• Bowel movement difficulties, such as constipation
• Obesity
• Kidney problems
• Hormonal imbalances, such as adrenal insufficiency
• Hyperglycemia (high blood sugar levels)
• Dyslipidemia (imbalanced cholesterol levels)
• Hypertension (high blood pressure)
• Acid reflux or heartburn

Respiratory and heart problems are also common. By age 18, nearly all children with DMD will develop a type of heart disease known as dilated cardiomyopathy. They may also have breathing difficulty from weakened lung muscles.

What Is the Prognosis for Duchenne Muscular Dystrophy?

In recent years, exon-skipping therapies and respiratory support devices have helped extend the life expectancy of people living with DMD. When doctors and researchers talk about life expectancy and survival, they use the term median overall survival. This refers to the amount of time after which half of the people with DMD continue to live.

A 2021 meta-analysis of several studies found that the median overall survival for people with DMD is 22 years. However, researchers noted a large difference in life expectancy, depending on a person’s age. People born after 1990 living with DMD had a median overall survival of just over 28 years, compared with just over 18 years for people born before 1970. Heart failure is the usual cause of death for people with DMD.

The study showed that the life expectancy of children and adults living with DMD has improved by 10 years over the past few decades. These results are promising, and doctors and researchers hope to keep improving survival rates for those with Duchenne muscular dystrophy.

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