Duchenne Muscular Dystrophy

To screen for DMD, a health care provider uses a small amount of blood collected from your baby’s heel. To learn more about this process, visit the Blood Spot Screening page.

During screening, a special machine measures the level of an enzyme called creatine kinase (CK) in your baby’s blood. CK is released when muscle cells are damaged. Newborn screening looks for a type of CK called CK-MM.

CK-MM is found mostly in the skeletal muscles. Babies with high levels of CK-MM might have DMD, BMD, or a different neuromuscular disorder. Newborn screening cannot always tell whether a baby will have DMD or whether the result is a false positive.

If your baby’s blood spot screening result for DMD is out-of-range, your baby’s health care provider will contact you. Together, you will discuss next steps and follow-up plans.

An out-of-range screening result does not mean that your baby definitely has the condition. It does mean that your baby needs more follow-up testing. To learn more about screening results, visit the Blood Spot Screening Results page.

Your baby may need the following tests after an out-of-range screening result:

• Blood tests
• Genetic testing using a blood sample
• A muscle biopsy (removing and viewing a small portion of muscle tissue) – this is rare

You should complete any recommended follow-up testing as soon as possible. Without diagnosis and treatment, babies with this condition can have serious health problems.

False-positive newborn screening results for this condition can happen. Some situations can affect screening results for DMD, including:

• Screening samples that were collected too early (before the baby is 24 hours old)
• Babies who experienced birth trauma

False negative newborn screening results for this condition can also happen. In some cases, babies with DMD have normal levels of CK-MM on screening and don’t get picked up by screening. Babies who were born early (premature) or had a low birth weight may be at higher risk for false negative results.

Newborn screening helps babies lead healthier lives. If your baby has an out-of-range result, follow up with your health care provider quickly. It is important to follow their instructions. Your baby may need to get treatment right away, even if they aren’t showing signs or symptoms. In some cases, your baby’s health care provider may decide it is best to watch (monitor) your baby to decide next steps. Careful monitoring and early treatment will help your baby stay as healthy as possible.

Signs and symptoms of DMD most often appear before age 6 years but may start in a baby’s first year. Most babies will not show symptoms in the first few years of life.

First signs of the condition may include:

• Fatigue (extreme tiredness)
• Developmental delay, or not reaching milestones
• Speech delay
• Behavioral problems
• Large calves
• Muscle weakness, usually starting in the legs
• Trouble getting up from the floor and frequent falls
• Shortness of breath or problems breathing
• Hypotonia (low muscle tone, or “floppiness”)

A change in the DMD gene causes DMD. The DMD gene gives your body instructions for making the dystrophin protein that helps muscles work properly and stay strong.

Without a working DMD gene, the body can’t make enough working dystrophin protein. Without dystrophin, muscles can’t repair themselves properly. This eventually causes muscle weakness.

DMD is a genetic condition that babies typically inherit from their biological mother. Mothers may be a carrier. This means they have the changed gene but don’t have the condition. DMD can also occur for the first time in a family when the mother is not a carrier (de novo DMD). Almost all children with DMD are male. To learn more about genetic conditions, visit MedlinePlus Genetics.

• DMD is inherited in an X-linked recessive pattern. This means babies inherit this condition on their X chromosome.
  • Most baby girls have two X-chromosomes. If they have a nonworking DMD gene on one of the two X-chromosomes, they typically have a working copy of the DMD gene on the other. This is enough to reduce the risk of symptoms.
  • Most baby boys only have one X-chromosome. All boys with one nonworking DMD gene (on their only X-chromosome) have a risk for DMD.
• Girls with one working copy and one nonworking copy of the DMD gene are called carriers.
  • Carriers for DMD may also have symptoms of the condition, but often not until adulthood.
  • Carriers may pass down a nonworking copy of the gene to their children.
• When a boy is diagnosed with DMD, the mother needs to be tested to find out if she is a carrier. A carrier mother has a 1 in 2, or 50%, chance of having another son born with DMD or having another daughter who is a carrier. A boy with DMD will pass the variant on to all of their biological daughters.
• Genetic counselors and medical geneticists can help families learn about this condition and the chance of having children with it. Visit the National Society of Genetic Counselors to find a genetic counselor and the American College of Medical Genetics and Genomics to find a medical geneticist.