• Duchenne muscular dystrophy (DMD) is a rare neuromuscular disease caused by changes in the dystrophin gene.
• DMD causes progressive muscle weakness leading to mobility issues, along with learning and developmental delays.
• Treatments for DMD focus on boosting dystrophin levels and improving the quality of life of those living with the disease.

Duchenne muscular dystrophy is a rare genetic disorder that causes muscle weakness and degeneration over time. According to the Muscular Dystrophy Association (MDA), it affects 1 in 5,000 males, with symptoms appearing as early as ages 2 to 3. The condition is significantly less common in females. An estimated 20,000 children are diagnosed with DMD globally each year.

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.

What Causes Duchenne Muscular Dystrophy?

DMD is a rare disease 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.

Children and adults with DMD have progressive muscle weakness because their bodies don’t make enough dystrophin protein to hold together and protect their 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 responsible for causing DMD are often passed down through family members. Children inherit one set of chromosomes from each of their parents — these chromosomes control their characteristics, like eye and hair color and sex. Females inherit two X chromosomes from their parents, 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 do not have DMD, they can still pass it along to their children.

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 more males (1 out of 3,500 to 6,000 births) develop DMD as compared to females (1 in 50,000,000 births).

Symptoms of Duchenne Muscular Dystrophy

Signs and symptoms of DMD typically start appearing in early childhood, between the ages of 3 and 5. Children with DMD tend to miss major developmental milestones as they age. They may have a harder time holding their heads up, walking, or speaking as compared to 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. This is called Gowers’ sign and indicates weakness in the proximal muscles of the lower limbs.

Other physical signs of DMD include:

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

Children with DMD also have learning and behavior difficulties that can affect their performance in school and their overall quality of life. Behavioral signs and symptoms of DMD include:

• Attention-deficit/hyperactivity disorder (ADHD)
• Autism
• Trouble focusing
• Social challenges, such as making friends at school, which leads 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 levels of liver enzymes like creatine kinase or alanine transaminase.

Diagnosing 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 health care team can run several tests to make a final 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 control inflammation and help muscle cells make more dystrophin. 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.

Many children with DMD start taking heart medications by age 10 to prevent the progression of heart disease. Examples include blood pressure medications that relax blood vessels and take stress off of the heart muscle.

Exon-Skipping Therapies

Exon-skipping drugs for DMD correct mutations in the dystrophin gene so it can provide the correct instructions for making the dystrophin protein. These therapies treat certain genetic mutations, meaning only 30 percent of children and adults with DMD are eligible to receive this treatment.

There are currently four FDA-approved exon-skipping therapies:

• Amondys 45, a formulation of casimersen
• Exondys 51, a formulation of eteplirsen
• Viltepso, a formulation of vitolarsen
• Vyondys 53, a formulation of golodirsen

Gene Therapy

Gene therapy is another type of treatment in development for DMD. This approach works to replace dystrophin genes that have missing or damaged exons with functional versions of the gene.

Mobility Aids

Children and adults with DMD may also use mobility aids to help them move around and walk more easily. Walkers, braces, and wheelchairs may all be appropriate, depending on their needs. Respiratory treatments and devices are often needed to help your child or loved one breathe better.

Physical Therapy

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

Conditions Related to Duchenne Muscular Dystrophy

If your child has an unrelated condition alongside DMD, it’s 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 in those with DMD. Nearly all children with DMD will develop a type of heart disease known as dilated cardiomyopathy by the age of 18. 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 spans of people living with DMD. When doctors and researchers talk about life expectancy and survival, they use the term median overall survival (OS). This refers to the amount of time after which half of people with DMD continue to live.

A 2021 meta-analysis of several studies found that the median OS for people living with DMD is 22 years. However, they found that there’s a large difference in life expectancy, depending on a person’s age. People born after 1990 living with DMD had a median OS of just over 28 years — this is compared to a median OS of 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 for those with DMD in the coming years.

Talk With Others Who Understand

On myDMDcenter, people with Duchenne muscular dystrophy and their loved ones come together to gain a new understanding of DMD and share their stories with others who understand.

Does your child or loved one live with DMD? Share your experiences in the comments below.