Can the bacteria living in your gut influence multiple sclerosis (MS) susceptibility and risk of relapse? That was the question Emmanuelle Waubant (University of California, San Francisco, USA) posed during her presentation at this year’s virtual ACTRIMS/ECTRIMS joint meeting.
The relationship between the gut and neurological conditions is well known; here at Brainwork we have previously covered migraine prevention through diet, and the role of the gut–brain axis in stroke recovery and MS. Prof. Waubant’s research focuses more specifically on the role of bacteria in the gut.
Pathogens in the gut lumen are involved in ‘training’ the immune response at a systemic level, so it would make sense that the gut microbiome could influence the disease course of MS. However, few studies have been performed on this topic, and those that have included relatively small numbers of patients, most of whom had relapsing–remitting MS (RRMS). Prof. Waubant gave an overview of the studies to give a bigger picture of the current research landscape.
How to measure the microbiome?
Most studies on the microbiome in MS focused on alpha diversity, that is the diversity within a single sample. In addition, some studied beta diversity, the diversity between samples. However, simple bacterial diversity is not the whole story: the relative abundance of certain species can also offer insights into the microbiome composition. However, even species abundance does not give the whole story: Prof. Waubant explained that “lots of the bacteria like to hang out together”, meaning that pathway analysis can be used to investigate whether certain groups of bacteria are over- or under-represented in MS. When used together, these different techniques can start to provide a holistic view of the microbiome.
Is the microbiome different in MS?
When comparing people with MS to controls, most studies did not find any significant difference in the alpha diversity of gut bacteria, which seems to argue against an effect of the microbiome on susceptibility to MS. More convincingly, a study of 34 pairs of twins, in which one twin had MS and the other did not, also found no difference in alpha and beta diversity between people with MS and their healthy twin.1
The relative abundance of certain species has been found to differ between people with MS and controls in a number of studies, although Prof. Waubant noted, “There’s a fair amount of variation across studies”. Regarding pathway analysis, of the 296 pathways identified in one study, two were found to be under-represented and four over-represented in samples from people with MS.2
But how does knowing which bacteria are present explain the potential effect on MS disease course? As Prof. Waubant explained, “From the composition of the gut microbiome we can go to the metabolic level.” Research has shown that the abundance of certain bacteria in stool samples correlated with metabolites in the blood. For example, Prof. Waubant’s team has found that four out of nine pathways that were associated with a risk of subsequent relapse were also involved in methane production or metabolism.
So, does the microbiome have a role in MS? Maybe, but further work is needed to determine exactly what is happening and how to exploit this for potential disease interventions.
For more coverage from ECTRIMS 2020, please click here.