Executive skills in DMD boys dip around age 8, improve by teens
Results of new study suggest a developmental delay, not steady decline
In boys with Duchenne muscular dystrophy (DMD), executive skills — essentially the brain’s self-management tools, such as self-control, emotional regulation, and working memory — appear largely typical at age 5, begin to lag around age 8, and show signs of partial catch-up by early adolescence.
Those are the findings of a new Swedish study that examined how executive functions — both those dubbed hot and cold — develop across childhood and adolescence in boys with DMD. So-called cold executive functions involve more purely cognitive skills, such as working memory and flexible thinking. Those called hot are more closely tied to emotion and motivation, such as risky decision-making.
Overall, the researchers found “age-related differences in executive functions for boys with Duchenne.” However, the results suggest a developmental delay rather than a steady decline in these skills, according to the team.
“Clinically, these findings highlight the importance of adopting a proactive, individualized approach that considers the complex developmental trajectory of boys with DMD, addressing [differences] in both … hot and cold [executive function] skills,” the researchers wrote.
The study, “Age-related differences in hot and cold executive functions in boys with Duchenne muscular dystrophy: longitudinal individual changes and age-group comparisons across childhood and adolescence,” was published in the journal Neuromuscular Disorders.
While DMD is best known for progressive muscle weakness, dystrophin — the protein missing in these patients — also plays a role in the central nervous system, comprising the brain and spinal cord.
Examining executive function in DMD boys from age 5 to 14
Earlier research has often assumed that cognitive abilities in boys with DMD remain stable over time. However, the impact of DMD on executive functions — the mental skills used to plan, focus attention, regulate behavior, and manage emotions — as these children grow older remains unknown.
To learn more, researchers from the University of Gothenburg in Sweden examined the development of executive functions in boys with DMD ages 5 to 14. The team looked at both hot and cold executive functions, noting that, “while these categories are conceptually distinct, they frequently overlap in real-life tasks.”
According to the investigators, “hot EF [executive function] typically mature later than cold EF, particularly during adolescence, when decision-making in emotionally charged situations may develop at a slower pace compared to more cognitively oriented abilities.”
The main analysis involved 70 boys with DMD who were assessed at ages 5, 8, 11, or 14. A smaller group of 13 boys was tested on two occasions: Six were assessed at 5 and 8 years of age; five at ages 8 and 11; and two at ages 11 and 14.
Executive function was measured in two ways. Performance-based tests focused on attention, behavioral regulation, and cognitive flexibility analyzed the children’s cold executive function. In the Minnesota Executive Function Scale, children completed a card-sorting game in which they matched cards to target boxes based on color, size, or shape, with progressive levels of difficulty.
Parents, meanwhile, completed questionnaires designed to capture how executive difficulties were manifested in everyday life. These questionnaires assessed areas such as behavior regulation, which is more likely to measure hot executive function. They also featured the metacognitive index, which measures both hot and cold executive function and has subscales of task completion, working memory, and planning and organizing.
No clear impairments seen in boys at age 5
Overall, the findings suggested that executive function differences become more noticeable as children with DMD grow older. At age 5, the study did not find clear impairments. By age 8, however, scores showed emerging difficulties in hot executive function.
By age 11, the difficulties were most pronounced. Both cold and hot executive functions were rated as most problematic, and performance was the poorest relative to age-matched population norms.
But then, at age 14, executive function trended toward catching up to age-related norms, the researchers noted.
“This raises a compelling question,” the investigators wrote. “Could a possible developmental delay in both hot and cold EF during this period increase the risk of behavioural problems? And can EF training for boys or compensation for EF skills minimize the outcome of behavioural problems?”
[The] age-related differences [identified] could guide proactive, tailored interventions that support strategies helping boys and their parents address delays in hot EF skills around 8 years of age and, subsequently, delays in cold EF skills around 11 years of age.
The team also noted that half of the participants showed better behavior regulation between 5 and 8 years of age while the other half showed worse control. Likewise, large individual differences were seen in working memory between ages 8 and 11.
“These results underscore the importance of monitoring EF across a wider age range in this population,” the researchers wrote.
Among the study’s limitations, the team noted that the number of boys participating was relatively small.
Still, “[the] age-related differences [identified] could guide proactive, tailored interventions that support strategies helping boys and their parents address delays in hot EF skills around 8 years of age and, subsequently, delays in cold EF skills around 11 years of age,” the scientists wrote.
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