Craig McDonald, MD, is a pediatric physical medicine and rehabilitation doctor at UC Davis Health. He’s also the director of the Neuromuscular Disease Clinic and a distinguished professor of pediatrics at UC Davis School of Medicine.
Muscular dystrophy is a group of diseases that causes your muscles to become weaker over time. Duchenne muscular dystrophy (DMD) is the most common type. It’s caused by a change in a gene that makes a protein needed for healthy muscles.
Duchenne muscular dystrophy is most common in boys. Although they’re born with the disease, symptoms usually appear between the ages of 3 to 5 years old. They may have a hard time standing up, walking, and climbing stairs. They may also develop heart and breathing problems.
It’s normal to feel overwhelmed if someone you know is diagnosed with DMD. There’s no cure, but medications and treatments can ease symptoms. We spoke to Craig McDonald, MD, is a pediatric physical medicine and rehabilitation doctor and director of the Neuromuscular Disease Clinic at the University of California Davis School of Medicine about who gets Duchenne muscular dystrophy, signs of the disease, how it’s treated, and more.
Q. Who gets Duchenne muscular dystrophy?
Although DMD is the most common neuromuscular disease in children, it’s still rare. It affects roughly 15,000 males in the United States, or 1 in every 3,500 to 5,000 boys. Because the DMD gene is found on the X chromosome, girls don’t usually have the disease. Here’s why:
- Girls have two X chromosomes (X from mom, X from dad)
- Boys have one X and one Y chromosome (X from mom, Y from dad)
If a girl inherits an X chromosome with the DMD gene change, she has another X chromosome that works properly. But she becomes a carrier of the disease. Some carriers may develop mild symptoms, such as muscle weakness or heart issues, as adults.
Duchenne muscular dystrophy runs in families. In 2 out of 3 cases, the genetic change is passed down by a carrier mother. The rest of the time, the mutation happens randomly. No one knows exactly why this change occurs.
Q. What are the symptoms of Duchenne muscular dystrophy?
The DMD gene tells your body how to make a protein called dystrophin. Dystrophin acts like a shock absorber for your muscles. It protects them from tearing or becoming injured from everyday activities. Without enough dystrophin, your muscle cells become damaged and die off. This weakens your muscles.
Duchenne muscular dystrophy affects how your child moves. Many parents notice that their child starts walking later than other kids their age. Most children are walking at 12 to 14 months, but those with DMD still may not walk at 18 months of age. They often have trouble standing up and climbing stairs. Kids with DMD can have large calves and tend to walk on their toes.
Dystrophin also plays a role in brain function, so children with Duchenne muscular dystrophy may have speech and cognitive delays. About 10% of DMD patients show signs of autism.
Q. What should I do if I think my child may have Duchenne muscular dystrophy? How is it diagnosed?
The earlier a child is treated for DMD, the better the outcomes. It’s important to get a diagnosis so he can see a specialized team for treatment as soon as possible. But there’s usually a two-year delay between the first signs of the disease and a diagnosis. Many doctors may not recognize the disease immediately.
If you see symptoms of Duchenne muscular dystrophy, ask your pediatrician about testing your child’s creatine kinase (CK) level. When damaged, muscles leak this enzyme. In children with the DMD, CK levels are as much as 10 to 20 times the normal amount.
Your pediatrician may refer you to a pediatric neurologist or specialist in neuromuscular medicine. They’ll perform physical and neurological exams and ask about your child’s medical history. A genetic test can confirm the change in the DMD gene. Your doctor may also request a muscle biopsy and electrocardiogram (EKG) to see DMD-related changes in your muscles and heart function.
Q. What kind of damage and complications does Duchenne muscular dystrophy cause?
DMD is a progressive disease, which means that it gets worse over time. Most boys with Duchenne muscular dystrophy use wheelchairs by the time they’re teenagers. DMD can also weaken the muscles in the lungs and heart. This can lead to breathing problems and heart problems. The main cause of death among DMD patients is heart failure.
A few decades ago, most boys with DMD only lived into their teen years. Thanks to scientific advances, the average life expectancy now stretches into the late 20s. Because of exciting new therapies, we’re seeing patients live well into their 30s and 40s.
Q. What are the treatments for Duchenne muscular dystrophy? What kind of health care providers will my child see?
Along with existing medicines, there are a number of exciting new therapies for DMD. Your doctor may prescribe one or a combination of the following:
- Steroid medicines: They may slow down muscle damage.
- Gene therapies: A one-time IV medication called Elevidys (delandistrogene moxeparvovec-rokl) delivers a replacement gene that makes a dystrophin-like protein.
- Exon-skipping drugs: This weekly infusion is a type of gene therapy. It allows your cells to skip the mutated section of your DMD gene. There are four types of Exon-skipping drugs that target specific mutations: Amondys 45, Exondys 51, Viltepso, and Vyondys 53.
- Duvyzat (givinostat): This medicine inhibits an enzyme that damages muscles. It also promotes muscle growth.
Your child’s main doctor will coordinate his care. It’s usually a pediatric neurologist or a physical medicine and rehabilitation specialist like myself. Duchenne muscular dystrophy has many symptoms, so your child will have a multidisciplinary team. This can include:
- Physical therapists teach exercises to preserve muscle and joint function. Those with DMD eventually need braces and wheelchairs.
- Occupational therapists can help patients maintain their daily tasks, like dressing themselves.
- Pediatric cardiologists monitor any DMD-related heart issues.
- Pediatric pulmonologists and respiratory therapists treat breathing problems. Some people with DMD need to use a ventilator some or all of the time to breathe.
- Development-behavioral pediatricians can address any cognitive or behavioral issues, such as autism.
- Dietitians can offer eating plans and advice. If your child takes steroids, he may be at risk for weight gain.
Q. What advice do you have for people who have a loved one with Duchenne muscular dystrophy?
We’ve seen tremendous advances over the last 10 to 15 years for DMD treatments and care management. There’s a lot of exciting, potentially transformative treatments in development, such as next-generation gene therapies. There’s a drug called deramiocel, which targets heart muscle, that’s shown promising data.
It’s a time of hope for those with Duchenne muscular dystrophy. We’ve learned a lot about how multidisciplinary care allows children to live much longer and have a better quality of life.