Gut Microbiome of Parkinson’s and Healthy Twins Largely Similar

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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Among pairs of genetically identical twins, one with Parkinson’s disease and the other twin without it, minimal variation is evident in the makeup of bacteria living in the digestive tract, according to a new study.

This finding highlights the role of person-to-person variability in influencing the gut microbiome, which researchers say needs to be accounted for in studies hoping to understand how the makeup of gut bacteria influence the development of Parkinson’s.

The study, “Gut microbiota in monozygotic twins discordant for Parkinson’s disease,” was published in the Annals of Neurology.

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The human digestive tract is home to billions of bacteria and other microorganisms, collectively referred to as the gut microbiome. An emerging body of research suggests this microbiome is dysregulated in people with Parkinson’s compared to those without the disease.

A complicating factor in this kind of research, however, is that the composition of the gut microbiome varies substantially from person to person, making it difficult to say with certainty whether given variations are truly connected to Parkinson’s. A person’s genetic makeup, as well as exposures during early life, are known to influence the gut microbiome. But most research to date has not been able to control for these factors.

A team of scientists in Italy conducted a study of monozygotic twins, colloquially called “identical” twins, who have the exact same genetic makeup and generally have similar early life exposures.

Gut microbiome and Parkinson’s

“Twins, particularly monozygotic ones, offer a unique model for controlling confounders contributing to interpersonal variation, as they share the genetic background as well as many important early life events and life-course factors (e.g. delivery, feeding, major dietary pattern, geography, etc…),” the researchers wrote.

The analysis included 20 pairs of twins (40 people in total); men made up 11 of the pairs, and the group’s average age was 67.8. In each pair, one twin had Parkinson’s disease, while the other twin was healthy.

For each twin pair, the content of the gut microbiome was assessed via genetic analyses of a stool sample. Researchers then conducted a battery of statistical tests comparing the microbiome profiles of twins with and without Parkinson’s.

Results showed some small, but statistically significant, differences in bacterial composition and metabolic pathways. Specifically, Parkinson’s patients had relatively higher amounts of the bacterial species Bacteroides pectinophilus and Bifidobacterium catenulatum, and more activity in metabolic pathways related to making bile acid.

Aside from these minor differences, however, each twin pair “showed a substantial comparability in general features, including dietary pattern, and detected minimal differences in bacterial taxa [groups] abundance at species level … and in predicted metabolic pathways,” the researchers wrote.

Among the small differences identified, it was not clear whether or how they might influence the development of Parkinson’s, the researchers wrote, noting a need for further research. Broadly, study findings highlight the need to account for person-to-person variability in the makeup of the gut microbiome when comparing people with or without Parkinson’s.

“Large prospective studies addressing incident [Parkinson’s] and accounting for all potential confounders are still warranted to further investigate a cause-effect relationship between variability in gut microbiota” and Parkinson’s, the scientists concluded.

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