Evaluation of the Cognitive Impact of Spinal Muscular Atrophy Requires Validated Instruments

Spinal muscular atrophy (SMA) is a congenital motor neuron disease that causes progressive muscle weakness and disability. In studying SMA, researchers have focused mostly on the evaluation of motor function. The effects of this disorder on cognitive function remain largely unknown, with a handful of studies painting a heterogeneous picture.

A literature review designed to identify and evaluate instruments used to assess cognitive function in children and adolescents with SMA showed that, so far, very few studies have evaluated the cognitive impact of the disease. A literature review identified 37 studies in which 28 instruments were used to assess cognitive function in patients with SMA types 1, 2, or 3. Commonly used instruments included the Wechsler Intelligence Scale, Bayley Scales of Infant and Toddler Development, Child Behavior Checklist, eye tracking devices, Pediatric Quality of Life Inventory, and Raven text. The domains assessed most often were language abilities and memory, followed by verbal intelligence and non-verbal or performance intelligence.

The studies yielded conflicting results, which could be attributed to the inconsistent use of different instruments, as well as 6the use of different endpoints, said presenting author Omar Dabbous, MD, MPH. Some studies that used standard cognitive tests showed that patients with SMA have cognitive impairment, while other studies revealed that patients with SMA have normal cognitive function.

The authors noted that assessing cognitive function in children with SMA is challenging because physical symptoms and limited communication skills may prevent an accurate measurement of cognitive function based on standard cognitive tests typically used for infants, children, and young adults. Moreover, the lack of cognitive function tests designed specifically for patients with SMA further complicates evaluation.

“Assessment of cognition in the first years of life, when the neural foundations of cognition are forming, is inherently challenging,” the authors wrote. “While available instruments include domains related to cognitive function, no particular validated instrument is optimal for assessing cognition in patients with SMA. Development and validation of a new instrument for cognitive assessment tailored for patients with SMA may help address this unmet need.” The lack of validated instruments for the assessment of cognition in young patients with SMA may be a missed opportunity to understand SMA pathology and the effects of therapies, the authors concluded.