DMD Symptoms Show Up Early and Can Be Measured, Study Finds

Careful assessments of motor, cognitive and language function in very young children with Duchenne muscular dystrophy (DMD) show these children lag behind their age-matched peers well before obvious symptoms of the disease appear.

The findings of this new MDA-supported study are particularly important at this time. New treatments now in development may work best when given very early in life, but standardized measurements and understanding of disease progression in this age group have not been available.

Outcome measures needed

Reliable outcome measures — tools to determine the effects of a treatment — are available for older children with DMD but not for very young ones. An example of an outcome measure used in older children with DMD is the "six-minute walk test," which measures the distance a child can walk in six minutes.

Determining the effects of new treatments in boys with DMD who are younger than age 3 — the approximate lower limit for symptom-based diagnosis of the disease — will be necessary before such treatments can be widely prescribed.

To better understand the earliest stages of DMD and begin to develop outcome measures for infants and young children that can be used in future clinical trials of DMD drugs, U.S. and British doctors studied the disorder in 24 boys with genetically verified DMD who were at least 1 month old but less than 3 years old. None were taking corticosteroids.

Funded by MDA and the U.S. National Institutes of Health (NIH), the study was conducted at five U.S. medical centers belonging to the MDA DMD Clinical Research Network and at Newcastle University in Newcastle Upon Tyne, United Kingdom.

Early deficits apparent with specialized testing

The investigators, who published their findings online May 30, 2013, in the journal Neuromuscular Disorders, found there were clear differences between infants/young boys with DMD and typically developing children in several areas:

  • gross motor function, which refers to use of the large muscles in activities like sitting, crawling and walking;
  • fine motor function, which refers to use of small muscles in activities like using eating utensils and stacking blocks;
  • language skills, meaning a child's ability to understand and use words; and
  • cognitive skills, meaning a child's general ability to understand or remember ideas or information.

On measures of motor function, as well as cognitive and language development, they found the boys with DMD performed significantly less well than their unaffected, age-matched peers. (Cognitive and language functions, as well as motor functions, can be affected in DMD.)

The investigators administered the motor, cognitive, language and behavioral tests from the Bayley III Scales of Infant and Toddler Development; the Expanded Hammersmith Functional Motor Scale; and the North Star Ambulatory Assessment (for children old enough to walk). They found the Bayley III scales to be the most useful, although the others were informative as well.

On the Bayley scales, the investigators found the following:

  • Composite motor function (combined gross and fine motor scores): Boys with DMD had an average score of 82.2, compared to an average score of 100 in typically developing children of the same age.
  • Gross motor function: Boys with DMD had an average score of 6.1, compared to an average of 10 in typically developing children.
  • Fine motor function: Boys with DMD had an average score of 7.9, compared to an average of 10 in typically developing children.
  • Composite language function (combined measures of understanding and using language): Boys with DMD had a score of 85.8, compared with 100 for typically developing children.
  • Composite cognitive function (combined measures of thinking ability): Boys with DMD had a score of 89.5, compared with 100 for typically developing children.

The authors noted, "While [measuring] the very young, less-than-six-month, age group will remain challenging, developmental scales such as the Bayley III allow them to be studied."

For more information

To learn more, also see:

21 756