Microbiome varies between multiple sclerosis subtypes

Variations in the composition of the microbiota are associated with different multiple sclerosis (MS) phenotypes, according to a new study published in Annals of Clinical and Translational Neurology. the findings demonstrate the importance of patient stratification in studies of the microbiota in MS and also identify potential therapeutic targets for some patients.

Accumulating evidence suggests that alterations in the microbiota are important in MS, but the results of studies to date have varied. However, in most of these previous studies, patients with relapsing-remitting MS (RRMS) that had been exposed to various MS treatments were compared with healthy controls. In the new study, led by Marie D'hooghe and Jeroen Raes, the microbiome profiles of patients with different Ms phenotypes were compared.

The study included 98 patients with MS and 120 healthy controls, 98 of whom were participants in the existing Flemish Gut Flora Project. Patients with MS were divided into five subgroups on the basis of their clinical phenotypes: untreated RRMS, untreated RRMS during a relapse, untreated benign MS, interferon-treated RRMS and non-active primary progressive MS.

Stool samples from the patients and controls were analysed to determine the composition of their microbiota.

No measures of microbiota composition differed through the significantly between all patients with MS and healthy controls. However, measures of microbial richness microbiome and the abundance of several microbial taxa did differ between MS phenotypes.

Patients were also classified into one of four enterotypes - groups defined by specific clusters of bacterial species that make up the microbiota. An enterotype known as Bacteroides2 (Bact2) was enriched among patients with interferon-treated RRMS and untreated RRMS during a relapse.

"The Bact2 enterotype is considered dysbiotic and has previously been found enriched in inflammatory diseases, such as ulcerative colitis, Crohn's disease and primary sclerosing cholangitis," explains Raes. "Its presence is correlated with increased systemic and intestinal inflammation, even in the healthy population, and it's exactly the patients with more 'inflammatory' MS - those experiencing a relapse - in whom we find enriched Bact2."

The findings provide important information for the development of disease modifying strategies that target the microbiota.