Very young boys with Duchenne muscular dystrophy (DMD) have measurable differences in motor skills, which could have implications for the early detection of DMD and for evaluating how treatments affect their development as opposed to the natural course of the disease, a study shows.
Findings of the study, “Early signs of gross motor delay in very young boys with Duchenne muscular dystrophy,” were presented in a poster session at the 2019 American Academy of Neurology (AAN) annual meeting, taking place through May 10 in Philadelphia.
As therapies and treatments for DMD continue to evolve, it’s becoming increasingly clear that early diagnosis and earlier treatment can lead to better outcomes. Typically, DMD is diagnosed in children at between 3 and 5 years of age.
“The differentiation between healthy infants and those with DMD has not been established in infants and young children,” the researchers wrote.
It’s also important to have measurements that are actually reflective of the state of disease — that is, clinicians and researchers need to be sure that the tests they use to measure, for example, motor skills, are actually assessing this in a way that allows both distinguishing between children with and without DMD and tracking how treatments improve (or don’t improve) these skills in children with DMD.
To this end, researchers recruited 114 boys with DMD (ages from about 10 months to nearly 8 years old) and gave them three different tests of motor skills: the motor function part of the Bayley Scales of Infant and Toddler Development (third edition), the North Star Ambulatory Assessment (NSAA), and the 100-meter timed test.
All of these tests involve testing motor skills — for example, the time it takes for a child to run around some cones or climb a set of stairs. Since there is published data for what a “normal” score is for each of these tests, the researchers were able to compare the scores in their DMD group with these normal ones.
Their goal was both to determine whether these tests were effective measurements in DMD and to find out what score or range of scores in each test might be indicative of DMD.
All three tests were found to be effective at differentiating between boys with DMD and normally developing boys, with lower scores for DMD patients. For example, in the 100-meter timed test, the scores of boys with DMD were, on average, about half of the normal value.
“Difficulty with key skills were indicative of early gross motor involvement. The delay in gross motor skills remained present over time,” the authors wrote.
They also compared the results of patients on steroids with those of patients not on steroids, showing that patients treated with steroids had significantly higher scores on all outcomes.
“Clinicians can use the expected trajectories [Bayley-III, NSAA and 100 meter] to better counsel families on disease course,” the poster read. “The Bayley-III, NSAA and 100 m can be successfully implemented in the young DMD cohort and may be useful tools for clinical use and as trial outcome measures.”