Jim Kling
November 08, 2023
Cognitive issues in children with Duchenne muscular dystrophy (DMD) are linked to worse outcomes, but limited access to specialists and limited resources make this problem difficult to address. A new tool from the National Institutes of Health, called NIH Toolbox, could improve that outcome, according to Mathula Thangarajh, MD, PhD, who has conducted research in the field.
Dr Mathula Thangarajh
“When we talk to families and parents, they are able to identify that even during infancy that [children with DMD] have delayed cognitive function. This includes speech delay, but also language and adaptive skills. We also know that those children with speech delay, which is really a very commonly reported phenotype in up to 50%, go on to have school-based needs. They may repeat [grades] in elementary years, but they also use more resources at school,” said Dr. Thangarajh, who is an assistant professor of neurology at the Children’s Hospital of Richmond at Virginia Commonwealth University, Richmond, during a talk at the 2023 annual meeting of the American Association for Neuromuscular and Electrodiagnostic Medicine (AANEM).
A previous natural history study that utilized the Pediatric Quality of Life assessment also showed that DMD patients reported the lowest scores in brain health, including emotional health and school performance.
Other research has shown a correlation between cognitive function and survival in DMD. “This suggests that health maintenance may play an important role [in outcomes],” said Dr. Thangarajh. Another study found a correlation between psychomotor delay that required school-based interventions and earlier loss of ambulation, lower cardiac ejection fraction, and worse pulmonary function. The researchers also found that boys with cognitive delay were diagnosed at an earlier age, and yet had delays in diagnosis and worse motor function, pulmonary health, and cardiac health outcomes. On average, they lost ambulatory ability 2 years earlier.
A study by Dr. Thangarajh’s group showed that patients with speech delay and lower IQ had lower performance in timed tests, including 6-minute walk test distance and scored an average of 2 points lower on the North Star Ambulatory Assessment.
A tool for continuous cognitive assessment
The Centers for Disease Control and Prevention–supported DMD CARE guidelines only say that neuropsychological evaluations should be considered at diagnosis, but is essential if concerns arise about developmental progress. However, the Muscular Dystrophy Association has found barriers both in access to specialists, with an average wait time of 1-2 years, and burdensome out-of-pocket costs.
Those issues prompted Dr. Thangarajh to look for an alternative solution. At the time that she embarked on this work, the NIH was interested in technologies to assess neurobehavioral issues across different diseases. The resulting NIH Toolbox iPad app was driven largely by failed clinical trials in dementia, and the aim was to be able to provide continuous assessment over time. “It will allow for assessments across the lifespan, so you can use the same construct from age 3 to 80-plus,” said Dr. Thangarajh. It can also normalize population factors, such as annual household income and mother’s IQ.
She set out to validate the NIH Toolbox in children with DMD. The toolbox includes measures of crystalized cognition and fluid cognition. The former encompasses vocabulary and reading ability, which are strongly predicted by socioeconomic status and maternal IQ. On the other hand, fluid cognition includes cognitive features that develop across the lifespan and is directly related to academic underperformance in DMD patients.
Dr. Thangarajh’s group assessed 30 boys with DMD and found that crystallized cognition was normal, but they had a deficit in fluid cognition. They found deficits within several subdomains of fluid cognition. “This tells us that the NIH Toolbox was able to replicate what we had known in the literature, that these boys really have lower intellectual capacity, but they also have significant weakness in fluid cognition,” she said.
She also wanted to examine changes over time by testing the boys at a 1-year interview. “What we found was that they are not making as much gain in fluid cognition as we would like. They are just making marginal improvements over time. This has implications on how often we should screen them, but also not be over reliant on using school-based resources for them to get tested,” said Dr. Thangarajh.
Her group’s analysis of a dataset of 55 boys provided by PTC Therapeutics revealed a difference by age in a test of working memory. “What we found was that boys who are actually greater than 9 years, compared with those who are less than 9 years, they actually had a reversal of development-based improvement. The older they get, they were not making as much gains as you would expect,” said Dr. Thangarajh.
She went on to discuss psychosocial determinants of cognitive health in DMD. It is known that women who are carriers of the dystrophin mutation can underperform in cognitively stressful tasks, leading her to wonder if this could lead to transgenerational risk to offspring with DMD. Her group tested women who were carriers of the mutation with the NIH Toolbox and found that they had lower fluid cognition than noncarriers. They then tested 65 dyads of mothers and children, and found a correlation, but only when it came to inhibitory control, which required the individual to note the direction of an arrow while ignoring surrounding arrows pointing in various directions.
Next, the researchers examined neighborhoods and their impact on cognitive health, which can be affected by the presence of green spaces, access to public transportation and good nutrition, and other factors. There were significant deficits associated with residence zip codes. “We were pretty shocked. Someone who is not in a socially vulnerable region is scoring slightly below average, but someone who is in a very socially vulnerable neighborhood is only scoring 75 [age-adjusted score] on the NIH toolbox. So with this, we can conclude that carrier women are vulnerable in certain cognitive domains, but also children who come from socially vulnerable [situations] have poor cognitive control. This, again, has implications on how often we should screen and how much we should overly rely on school-based resources for these individuals,” said Dr. Thangarajh.
Overcoming a significant barrier
The NIH Toolbox has a lot of potential to improve DMD care, according to Dianna Quan, MD, who is the incoming president of AANEM, and professor of neurology at the University of Colorado at Denver, Aurora. “There’s this huge problem in terms of getting people in to see neuropsychologists and having formal evaluations. I think that’s a huge barrier. If we have people able to access this toolkit, which is simple and easily and universally accessible, how wonderful is that? I think that will be a really great improvement on what’s going on right now. It allows people to easily screen for these cognitive disabilities and make sure that we address them,” Dr. Quan said in an interview.
Asked how the tool could specifically improve care, Dr. Quan suggested that the first step is to understand the contributing factors to cognitive issues, whether they are biological, social, or a combination. “Some of them we can modify, potentially, through addressing the social environment. Some of those biologic factors may also be modifiable with many of the new drug studies that are coming.”
Dr. Thangarajh has received speaker honoraria from NS Pharma and PTC Therapeutics. Dr. Quan has received funding from Alnylam, Pfizer, Cytokinetics, Momenta, and Argenx.
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