In Duchenne muscular dystrophy (DMD), the age when symptoms start and how quickly they get worse can be very different from person to person, according to a recent study published in the Journal of Neuromuscular Diseases.
The study included 376 patients with DMD, averaging 7.1 years old. About 78% of patients began the study with a North Star Ambulatory Assessment (NSAA) score above 16, indicating they had a lower risk of losing their ability to walk within the next two years.
Researchers identified a subgroup of patients — known as the “centrally representative sample” — whose disease progression closely followed a typical pattern seen in DMD, particularly in terms of the average age when walking ability is lost. By comparing this group to the overall patient population, they aimed to explore the differences between a common disease course and the more varied experiences of all patients, helping to better understand typical versus broader disease patterns.
In the centrally representative subgroup of 34 patients, walking ability improved between ages 4 and 7 but then declined sharply, with patients losing the ability to walk by age 13.
In the overall group, walking ability remained stable between the ages of 4 and 6, declined more gradually and reached zero around age 15 instead of 13.
Read more about the prognosis of DMD
The study also identified patterns in how specific skills improved or declined over time. Some skills — like standing on one leg, lifting the head, jumping, running, standing on the heels and hopping on one foot — got better in early childhood. Other skills — like standing, walking, climbing stairs and rising from a chair or floor — declined with age. These patterns were more clear and pronounced in the centrally representative group but were also observed in the larger group.
This study shows that DMD progression varies significantly: while some patients lose walking ability rapidly, others decline more gradually.
Factors like age, current NSAA score, steroid use, and genetics all influence how quickly someone’s mobility will decline.
“This study highlights that rates of functional decline in DMD can be understated (and for some patients, overstated) when looking at population averages,” the study’s authors said.
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