Motor Function Linked to Cognitive Differences for SMA Type 3 Adults

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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Among adults with spinal muscular atrophy (SMA) type 3, those with greater motor impairment tend to score better on some cognitive measures, but worse on others, a new study reports.

Among those with SMA, “patients with greater motor difficulties had lower performance in attention, but higher performance in measures of language, verbal fluency, and memory,” the researchers wrote.

The study, “Cognitive profiles and clinical factors in type III Spinal Muscular Atrophy: a preliminary study,” was published in the journal Neuromuscular Disorders.

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SMA is a neuromuscular disorder characterized by the loss of motor neurons, the nerve cells responsible for coordinating muscle movement. Other neuromuscular diseases like amyotrophic lateral sclerosis and Duchenne muscular dystrophy are known to sometimes cause cognitive impairment.

SMA is not generally associated with cognitive problems, but how the disease affects cognition remains incompletely understood. In addition to direct effects of SMA on the nervous system, an emerging body of research is suggesting that SMA may prompt cognitive differences in part because patients live with different physical limitations from their peers, so they have to find different strategies to navigate daily life.

In this study, led by scientists at the University of Padova in Italy, 22 adults with SMA type 3 (ages 18–56) underwent a battery of neuropsychological tests, as well as measures of motor function.

“We used an extensive battery that allowed us to accurately examine performance in multiple cognitive domains,” the researchers wrote.

For comparison, the study also included adults without SMA (controls). The two groups were similar in terms of age and sex, though the controls had more formal education. The researchers accounted for this difference in statistical analyses, but still acknowledged it as a limitation of the study, as well as noting the small number of participants.

Compared with the controls, the SMA patients scored markedly lower in measures of language ability, visuospatial skills (telling where objects are based on sight), and executive function (the cognitive process of controlling your own behavior).

Statistical analyses showed that, among the SMA patients, those with worse scores on assessments of motor function or disease severity tended to score lower on measures of attention, but higher on measures of language, verbal fluency, and memory. Sex-stratified analyses generally showed similar trends, though more pronounced for males.

The association between motor symptoms and reduced scores in measures of attention “may suggest the presence [of] structural or functional brain changes in SMA type III,” according to the researchers, since this connection implies that some cognitive problems tend to worsen as other SMA symptoms worsen. However, they cautioned that wide-sweeping conclusions cannot be drawn from this preliminary study.

“Studies with larger sample [sizes] are needed to understand the frequency of cognitive ‘impairments’ and what factors can mediate cognitive functions trajectories,” the researchers wrote. They also noted that future studies should assess whether cognitive problems are associated with visible changes in the brain or with psychological challenges like depression and anxiety.

The fact that worse motor scores were associated with better scores in some areas of cognition adds to the growing body of evidence suggesting that people with SMA tend to experience cognitive changes to compensate for physical limitations that come with the disease, the researchers said.

“Together, our results partially support previous findings, and as a whole, this may point to possible compensational mechanism or coping strategies in SMA which may have a positive impact on cognitive development,” the team concluded.