No clear link between gut microbiome, Parkinson’s MCI: Study

Unique pattern of gut microbiome not found to differ between patient groups

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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An illustration shows a close-up view of the human digestive system.

There appears to be no link between a unique pattern of the gut microbiome — the genetic material carried by all of the microorganisms, such as bacteria, living in the gut — and mild cognitive impairment in people with Parkinson’s disease, a study found.

The study, “Gut microbiome is not associated with mild cognitive impairment in Parkinson’s disease,” was published as a brief communication in npj Parkinson’s Disease by researchers with the National Centre of Excellence in Research on Parkinson’s consortium.

There’s growing evidence that the gut may have a role to play in how Parkinson’s develops. Changes in the gut microbiome may cause toxic clumps of the alpha-synuclein protein to form in the gut before they spread to the brain, where they contribute to symptom development.

Mild cognitive impairment (MCI), a nonmotor symptom, is characterized by a subtle yet noticeable decline in cognitive abilities such as thinking, memory, and reasoning skills. Although individuals with mild cognitive impairment experience these declines, the changes are not severe enough to interfere with daily activities or significantly affect independence. However, it’s a risk factor and often precedes the onset of dementia, in which cognitive changes become severe enough to impact day-to-day life.

“While gut microbial community differences between people with PD and individuals without parkinsonism are well established, only a single publication has investigated the gut microbiome in PD with MCI, suggesting significant differences in … PD with MCI to PD with unimpaired cognition or to control subjects,” the researchers wrote.

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Checking diversity

They aimed to confirm those findings in a larger group of patients from a geographically distinct cohort using data from the Luxembourg Parkinson’s Study.

The study involved 58 patients with mild cognitive impairment, with a mean age of 73.1, and 60 patients with normal cognition with a mean age of 71.3. It also included 90 healthy individuals with normal cognition who were younger and didn’t experience constipation as frequently as Parkinson’s patients.

Their gut microbiome showed no differences in alpha diversity, a measure of how diverse a sample is based on its richness (number of species) and evenness (abundance of each of those species), between patients with or without mild cognitive impairment and healthy individuals.

An analysis of beta diversity, which compares samples to assess the degree of variation in microbial community structures, showed differences between patients and healthy individuals, but not between patients with or without mild cognitive impairment.

Some groups of bacteria differed significantly between patients and healthy individuals. Bacteria of the family Lachnospiraceae, Clostridiaceae, and Butyricicoccaceae were decreased in PD patients, whereas those of the Enterobacteriaceae family and the genera Hungatella and DTU089 were increased.

However, there were no significant differences between the two groups of patients, leading the researchers to conclude the “results did not support a specific microbiome signature related to MCI in PD.”