Signs & Symptoms

Unless specifically tested for, Duchenne is rarely diagnosed at birth. The first noticeable symptoms of Duchenne may be a delay in the motor milestones of a young child. These milestones include sitting and standing independently. When looking for signs that a child may have Duchenne it is important to watch them running and getting up from the floor as muscle weakness is more noticeable during these activities.

Symptoms can include:

  • Delay in motor milestones of a young child
  • Enlarged calf muscles (pseudohypertrophy)
  • Trouble running and jumping
  • Unusual gait
  • Using the Gower's Manouevre to get off the floor (where the child has to use their hands and arms to "walk" up their own body from a squatting position due to lack of hip and thigh muscle strength)

Testing For Duchenne

Tests are needed to diagnose Duchenne. The first step is a blood test to measure the amount of a substance called creatine kinase. Children with Duchenne always have a very high level of creatine kinase in their blood (10-100 times above normal).

Creatine kinase is an enzyme that is found in muscle cells in the body. If muscles are damaged, the muscle cells are broken open and their contents find their way to the bloodstream. Elevated levels can be the result of an acute muscle injury, or to a chronic condition such as Duchenne.

If the creatine kinase level is found to be high further tests are needed to see if it is due to Duchenne or to another condition.

The next step in diagnosing Duchenne involves either genetic tests and/or a muscle biopsy:

Most cases of Duchenne can be diagnosed by genetic tests on a blood sample. The DNA in the blood is tested to look for changes in the DMD gene. The DMD gene makes the protein dystrophin which is essential for muscle function.

A muscle biopsy involves taking a small piece of muscle under local anaesthetic. The muscle is examined under a microscope to look at the amount of dystrophin protein in the muscle fibres. Someone with Duchenne has very little or no detectable dystrophin in their muscles.

Genetic testing (looking at the body's genetic instructions) on a blood sample for changes in the DMD gene can help establish the diagnosis of Duchenne. Genetic testing is constantly changing, but the methods currently being used look for large changes in the gene (deletion or duplication of whole exons). Another method looks at the letters of the code that spell out the instructions for making dystrophin that are found within the DMD gene (sequencing). Together these two methods can detect Duchenne in about 95% of patients.

There are a small number of patients who are not found to have a detected change in the DMD gene using a genetic testing method, but who are diagnosed with DMD by biopsy. These people still have a change in their gene but it is in an area of the gene that is not examined using the currently available genetic testing methods. The results of genetic testing may not be conclusive of a diagnosis of DMD, only the muscle biopsy can tell the level of dystrophin protein for sure.