Gut bacteria can differ among MS patients by genetic disease risk

Small study finds microbiome of mostly lower risk group similar to controls

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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People with a higher genetic risk for multiple sclerosis (MS) were seen to have detectable differences in their gut bacteria in a small study.

“There seems to be an association between genetic risk score and [changes in gut bacteria] in triggering the disease in a small cohort of MS patients,” its researchers, whose analyses covered 117 people with relapsing-remitting MS (RRMS), wrote.

The study, “Genetic risk score in multiple sclerosis is associated with unique gut microbiome,” was published in Scientific Reports.

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Changes in the gut microbiome are thought to contribute to diseases like MS

It’s not clear exactly what causes MS — both biological factors like genetics, as well as environmental factors like infections and lifestyle choices, are thought to play a role. While genetics don’t cause MS outright, prior studies have associated a number of genetic variants with an increased disease risk. Analyzing these variants can be used to calculate genetic risk scores for MS.

The human gut is home to billions of bacteria and other microscopic organisms, collectively called the gut microbiome. The microbiome plays vital roles in regulating human health, and its thought that abnormalities in the microbiome can contribute to disease.

The role of the microbiome in MS remains poorly understood, however.

Researchers at various U.S. institutes analyzed the gut microbiome composition of 117 people with RRMS, as well as 26 control subjects with no known disease. All of these patients identified as white,  and about two-thirds were on active MS treatments.

The scientists conducted clustering analyses to group participants based on similarities in their gut microbiome. This resulted in two distinct groups: cluster A, which included 98 MS patients and all of the controls, and cluster B, which included 19 MS patients.

These two groups did not significantly differ in terms of age, type of MS treatment, number of lesions, or other concomitant diseases, including gastrointestinal ones.

Study’s two RRMS groups mainly defined by differences in gut bacteria

Rather, what truly distinguished them were differences in gut microbiota — cluster B had a higher relative abundance of Bifidobacterium and a lack of Phascolarctobacterium genera, while cluster A lacked both Clostridium and Megasphaera genera and had a higher abundance of the Akkermansia genus.

Researchers then calculated an MS genetic risk score for each participant, using a validated method, and compared scores between the two groups. MS patients in general had higher genetic risk scores than controls, but patients in cluster B tended to have the highest scores, results showed.

“An interesting trend was observed where the gut-microbiome of subjects of Cluster A, which included a significant number of both [patient] cases and controls, tended to have a lower genetic risk scores compared to cluster B (higher genetic risk score) which consisted of cases only,” the researchers wrote.

“Surprisingly, we found that patients exhibiting the highest genetic risk score are the patients who had a distinct microbiome,” they added.

The scientists highlighted their study’s small size and the fact that gut microbiome composition varies a lot from person to person, noting larger studies are needed to verify these findings.

Likewise, it’s not clear why MS patients with a higher genetic risk score might differ from other patients in their gut bacteria.