Diagnosis & Genetic Testing
Duchenne muscular dystrophy is a genetic disease that happens in about 1 in 3,500 births. Children with Duchenne have muscles that weaken as they grow older. Duchenne is caused by a genetic mutation in the dystrophin gene, which is found on the X-chromosome. Most, but not all, people with Duchenne are males. People with Duchenne cannot make a protein called dystrophin. As muscles are used naturally (running, walking, etc.), they become injured and build back up in a normal process. Without the dystrophin, injured muscles are unable to repair themselves and the muscle is replaced by fat and scar tissue, or fibrosis. As more of the muscles become replaced by fat and scar tissue, the muscle becomes weak.
Diagnosis Facts to Remember
1. Getting an early diagnosis is an important step so that you and your medical team can make plans for your child’s care.
|2. Creatine kinase (CK) is an enzyme that is released from muscle when it is damaged and cannot repair itself. Doctors cannot diagnosis Duchenne with only a CK test. If your child has elevated CK levels, your doctor will need to confirm the diagnosis using genetic testing.
|3. You are not alone. There are many people who can help you, and PPMD can help you find them. Your doctor can also help. Reach out to your doctor to answer your questions. You should also talk to a genetic counselor.
What signs should I look for?
If your child has any of these signs, talk to his doctor about whether you needs to see a specialist with experience treating children who have neuromuscular disorders.
- Someone in your family has or had Duchenne, or someone is a carrier.
- Your child is at least 18 months old but still cannot walk: 50% of boys who have Duchenne cannot walk at 18 months.
- Trouble getting off the floor (Gower’s maneuver): To stand up, your child puts his feet apart, pushes up his bottom, and pushes off the floor. He then walks his hands up his knees and thighs to stand upright.
- Trouble running and jumping: Very few children who have Duchenne can run well or jump with both feet together.
- Walks with the stomach forward and shoulders back, causing your child to have a sway back (lordosis), or has trouble moving his neck.
- Enlarged calf muscles (pseudohypertrophy). Pseudohypertrophy of the calf muscle is caused by fat and scar tissue collecting the calf muscle.
Some children with Duchenne have speech or language delays. Many waddle when they walk, or walk on their toes or the balls of their feet. Many fall easily for no reason. Many have trouble climbing stairs. These issues are common in Duchenne but also can happen for many other reasons. Talk to your child’s doctor.
A diagnosis is helpful because it explains the reason for developmental delays, helps the family adjust, allows families to make informed choices about having children, and allows the medical team to make plans for treatment. A diagnosis of Duchenne is made using the following steps:
- Step 1: Have a clinical exam.
A clinical exam of the child is the first step in diagnosis. The clinical exam checks the child’s muscles and development. The doctor will also ask if anyone in the family has had Duchenne, or if any women are known to be carriers. A carrier is a (usually healthy) woman who carries a mutation in the dystrophin gene. If there is a family history of Duchenne, the child should have more testing, even if he is younger than 5.
- Step 2: Check his creatine kinase level.
If your child’s doctor suspects that Duchenne, the doctor will draw blood to test his creatine kinase (CK or CPK) level. Creatine kinase is an enzyme that is released from muscle when it is damaged. The normal range for a CK is 60 to 400 units/liter. Children with Duchenne have a CK level that is 10 – 200 times higher than normal. A very high CK will tell the doctor that the child has a muscular disease (myopathy). To find out if that muscle disease is Duchenne, the doctor has to do another test—either a genetic test or a muscle biopsy. Genetic testing is the better choice.
- Step 3: Have genetic testing.
If the child has a high CK level, the doctor should use genetic testing to look for the genetic changes (called mutations) that cause Duchenne. Genetic testing is usually done on a blood sample. There are many different types of genetic tests that the doctor can use. It may take a few weeks or months to get the results. If the genetic test finds a mutation that causes Duchenne, then the child is diagnosed with Duchenne. Learn more about genetic testing on PPMD’s DuchenneConnect site.
Decode Duchenne provides free genetic testing and counseling to people with Duchenne or Becker muscular dystrophy who have been unable to access genetic testing in the past due to financial barriers. The program is administered by PPMD through DuchenneConnect, our registry that connects people living with Duchenne or Becker to clinical trials. Learn more about Decode Duchenne.
- Step 4: Muscle biopsy.
If the child has a high CK level and signs of Duchenne, but the lab did not find a genetic mutation using genetic testing, the child may need to have a muscle biopsy. During this minor surgery, the doctor will remove a small sample of the child’s muscle. The muscle sample is sent to a lab to be reviewed for dystrophin. If the child’s muscle sample has no dystrophin, then he is diagnosed with Duchenne. Not all people with Duchenne need a muscle biopsy. Parents should encourage the doctor to do genetic testing first, and to use a genetic testing plan that reduces the chance that the child will need a muscle biopsy.
What you can do to care for yourself and your family
Finding out that you have a child with Duchenne can be overwhelming. As you begin your journey, it’s important to know that you are not alone. Look for help and support for you and your family. Ask your doctor to send you to see a genetic counselor to learn about more about the cause of Duchenne in your family, and the chance that it could happen again. It is also very important that you take an active role in managing your child’s care.
The Care Team
Register with Parent Project Muscular Dystrophy
DuchenneConnect: Understand Genetic Testing