Some Patients with CMTX Show Cognitive Deficits, Study Suggests
Some patients with Charcot-Marie-Tooth Disease type X (CMTX) exhibit cognitive deficits, such as difficulties with executive function and reading, a recent study shows.
The study, “Evidence for Cognitive Deficits in X-Linked Charcot-Marie-Tooth Disease,” was published in the Journal of the International Neuropsychological Society.
CMTX, also called X-linked CMT, is caused by mutations in the GJB1 gene, which provides instructions for making a protein that is expressed primarily by glia — the “support cells” of the nervous system. Previous studies have identified nervous system abnormalities in people with CMTX, such as irregular MRI imaging scans of the brain.
“Such anatomical abnormalities are expected to reflect on cognitive functions … It is, therefore, highly plausible that cognitive function may be affected in these patients,” the researchers wrote. Despite this, no study to date has systematically assessed cognitive function in people with CMTX.
In this study, 24 people (13 male, age range 19–61 years) underwent a battery of neuropsychological tests, evaluating executive function, reading ability, and memory. Based on the scores on those tests, researchers divided the participants into three groups.
The first group included seven (29%) of the participants and was characterized by lower-than-normal scores on tests of executive function (the ability to plan complex tasks), such as the Trail Making Task.
The second group also included seven (29%) of the participants, and it was characterized by low reading scores. More specifically, deficits were seen in decoding written stimuli, but not in word recognition. That is, people in this group had normal scores in tests where they had to read a number of real words. But, in tests where they had to sound out a series of made-up words, their scores were significantly below average.
Importantly, in a random sample of the population, it would be expected that around 7% would perform significantly worse than average. The frequency of low scores in the two above groups was significantly higher, meaning that these differences aren’t due to random chance.
The third group included the remaining 10 participants. Three of these participants had low scores on one assessment – one for comprehension of instructions, one for oral word fluency, and one for visual working memory. The remaining seven participants in this group had no evidence of any cognitive deficit.
“The present data provide evidence for cognitive deficits in CMTX,” the researchers concluded.
There were no significant differences between these three groups in terms of age, sex, specific GJB1 mutation, or years of formal education.
There was a trend toward some differences in degree of neuropathy (nerve damage); however, this did not reach statistical significance. Future studies could explore this further, and investigate whether there are links between cognitive deficits and the aforementioned brain structure abnormalities sometimes seen in CMTX, which were not investigated in this study.
“In future studies, it would be important to combine cognitive assessment with [brain] imaging parameters in the same subjects with CMTX,” the researchers wrote.
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