Cognitive Impairments May Affect DMD Boys Regardless of IQ Scores, Study Suggests

Researchers have found that cognitive function, including the ability to multitask and solve problems, may be impaired in boys with Duchenne muscular dystrophy (DMD) — even in those with normal and above average IQs.

Their study, “Cognitive profile in Duchenne muscular dystrophy boys without intellectual disability: The role of executive functions,” appeared in the journal Neuromuscular Disorders.

Most studies assessing cognitive function in DMD have been performed in boys with moderate to severe intellectual disability or psychiatric disorders.

In this study, researchers in Italy aimed to assess this function in DMD boys that presented no intellectual and behavior disabilities. They performed a prospective observational study of 40 boys aged 6 to 11.

The researchers used the Wechsler Intelligence Scale for Children – a comprehensive cognitive ability test that includes verbal comprehension, perceptual reasoning, working memory, and processing speed for children between the ages of 6 and 16 – and additional tests, focusing on working memory and executive functions. These included the Tower of London test that assesses planning and problem-solving capacity. In the test, colored disks or balls on pegs are moved individually from an initial state to match a goal state. An optimal performance involves forming, retaining and implementing a plan to make as few moves as possible.

“We were also interested in determining the correlation between neuropsychological data and mutations site in the DMD gene,” they wrote.

Of the 40 patients analyzed, 45 percent had IQ scores in the normal range, 37 percent had above-average IQs and 17 percent had below-average IQs.

The analyses showed that some aspects of cognitive function were often impaired in DMD boys with no intellectual disability. Patients performed poorly on the digit span and letter-number sequencing, leading to a low average working memory index. Also, 80 percent of the DMD boys who took the Tower of London test had low average scores on “rules and moves,” revealing impairments in working memory and planning.

“A significant impairment was found also in other two basic components of Executive Functioning (inhibition and response switch),” researchers wrote.

The impairments were detected in all three groups – low, normal and above average IQ groups – in similar trends. Also, the analysis revealed no significant correlation between the tests performance and patients genotype.

Overall, these findings suggest that key aspects of cognitive function, including multitasking, problem solving, and working memory – all required for goal oriented behavior – are often impaired in DMD boys.

“Our results support the hypothesis that DMD boys are at risk of impairment of some aspects of cognitive function even in the absence of a global intellectual disability,” researchers wrote. “Further studies, using neuroimaging functional techniques may help to better understand the role of the network involving cerebellum and cortex on the cognitive profile of these patients.”