Duchenne muscular dystrophy
What is Duchenne muscular dystrophy?
Duchenne muscular dystrophy (DMD) is an inherited disorder caused by a mutation in the gene that helps create the protein dystrophin, which stabilizes muscle membranes. Boys with DMD have very little to no dystrophin in their bodies. Without enough dystrophin, the muscle cells become leaky and die.
DMD appears in young boys, usually between ages 2 and 5. Over time, boys with DMD are unable to regenerate their muscles. Instead, their bodies replace muscle tissue with scar tissue and fat. Boys with DMD have progressive weakness. They often lose the ability to walk around 10 to 12 years of age. Muscles in boys with DMD also become harder and shorter (contractures).
Why does DMD usually affect boys?
DMD generally affects boys because the dystrophin gene is on the X chromosome. Chromosomes are the parts of your cells that contain your genes. Boys only have one X chromosome. Girls have two X chromosomes, one from each parent. Boys get one X chromosome from their mother and one Y chromosome from their father. The condition only rarely affects girls.
Because a boy only has one copy of the dystrophin gene, a DMD mutation means that he will not have enough dystrophin to keep his muscles working well. For this reason, DMD is called an X-linked condition. When a girl inherits a DMD mutation on one of her X chromosomes, she usually gets enough dystrophin from a healthy gene on the other X chromosome. But some girls don’t have quite enough dystrophin. This causes mild to moderate DMD symptoms and disease of the heart muscle (cardiomyopathy).
How will DMD affect my child?
Because the diaphragm is a muscle, boys with DMD have progressive breathing problems. Contractures and spinal problems like scoliosis can make this worse. These issues can lead to a pattern of restrictive lung disease.
The heart is also a muscle and so it is also affected. Over time, the heart muscle weakens as scar tissue replaces heart cells. This process usually happens later than weakness of skeletal muscles.
DMD has no cure, but some persons with DMD can live into their 40s and 50s.
Muscle weakness begins in young children. It affects the hips and thighs before spreading to the arms and the rest of the body. First signs and symptoms of DMD in preschoolers may include
- Trouble with running, jumping, and climbing stairs
- Using hands to get up from sitting or squatting. This is a movement called Gower’s sign.
- Enlarged calves
- Leg pain
- Learning problems
As the disease gets worse, DMD can lead to
- Broken bones from falling
- Greater need for a wheelchair
- Curving of the spine (scoliosis)
- Stiff joints that can’t move (contractures)
- Tiredness (fatigue) and weakness
- Shortness of breath or other breathing problems
- Irregular heartbeat or other heart problems
How is DMD diagnosed?
Your child’s healthcare provider will take a full health history and ask about current symptoms and past health conditions. He or she will ask about related conditions in the family. He or she usually does a physical exam and lab tests. Your child may need tests that include
- Blood tests, for muscle enzymes such as creatine kinase
- DNA blood tests, for dystrophin changes
- Dystrophin analysis, a blood test that looks at your dystrophin
- Muscle biopsy, to look at the muscle cells or confirm a diagnosis
Your child may first see his or her main healthcare provider and then be diagnosed by a neurologist. Some neurologists have special training to treat nerve and muscle diseases such as DMD. Your child may also need care from other providers such as cardiologists, pulmonologists, and physical therapists.
How we treat Duchenne muscular dystrophy
DMD has no cure, but many supportive treatments can help manage the condition.
We recommend that all boys with DMD see a cardiologist and pulmonologist soon after diagnosis. We use tests such as echocardiograms, electrocardiograms and cardiac MRIs to learn how diseased the heart has become and to help guide our therapies. We use medications to help prevent damage to the heart. Cardiologist visits will take place annually in younger children and every 6 months in older children or children with more progressive disease.
The pulmonologist will help optimize lung function. This can include help with improving the effectiveness of their cough, non-invasive ventilatory techniques such as CPAP and BiPAP, or even tracheostomy. Pulmonologist visits should take place six months once the child loses the ability to walk.
Some possible treatments for children with DMD include
- Steroid medicine. This may help slow loss of muscle and improve heart function.
- Heart medicines. These can help treat cardiomyopathy.
- Pacemakers or other heart devices. These can help keep the heartbeat regular or make the work of the heart less difficult.
- Breathing devices. These can help your child get enough air. Many people with DMD sleep with a breathing machine mask at night. Your child may also need a tracheostomy device.
- Range-of-motion exercises. These can help your child stay flexible and limit contractures of the joints. Gentle exercise like water exercises may be safe. Your child’s healthcare team can help design a safe exercise program for your child.
Surgery can ease contractures or straighten a curved spine. But children with DMD have extra risks with anesthesia.
Advances in care have improved the life expectancy for people with DMD. Researchers are working on developing new medicines.