The connection between autoimmune inflammation and the gut microbiome has sparked great interest in the MS community in recent years. There is now interesting news on this topic: The Institute for Clinical Neuroimmunology at the Ludwig-Maximilians-University (LMU) Munich published a fascinating article in the renowned US-American scientific journal PNAS in May 2025 about the relationship between gut microbiota and multiple sclerosis (MS) (Yoon et al. Multiple sclerosis and gut microbiota: Lachnospiraceae from the ileum of MS twins trigger MS-like disease in germfree transgenic mice. PNAS 2025; 22(18):e2419689122).
The aim of the study was to identify specific gut bacteria that play a causative role in the development of MS. This has been attempted many times in the past, but the results of the studies were mostly inconsistent. This was partly because the cohorts examined were uneven and insufficiently controlled.
Twin Study
To minimize these problems, the Munich colleagues used a large cohort of twins. In this cohort, 81 monozygotic discordant twin pairs were identified. Discordant means that one twin has MS and the other does not. The advantage of studying monozygotic twins is that they are genetically identical and have shared the same environmental conditions. Therefore, by studying discordant monozygotic twins, both genetic and environmental confounding factors can be minimized. This is a unique feature of this new study.
The stool samples from 81 twin pairs were examined using so-called 16S rRNA sequencing, and the microbiome of the sick and not sick twin pairs were compared. Here, the twins suffering from MS showed a different bacterial composition, especially an increase in Lachnospiraceae (especially Eisenbergiella tayi and Lachnoclostridium).
In a further step, ileum samples (the ileum is the lower part of the small intestine) were taken from selected MS twins and their healthy siblings. The gut bacteria obtained from these samples were then transferred to germ-free transgenic mice that are genetically predisposed to develop an MS-like autoimmune disease. Notably, the microbiota from the ileum of the MS twins (not from the stool) triggered an MS disease (EAE = experimental autoimmune encephalomyelitis) in the mice. It is also worth mentioning that female mice reacted more sensitively and developed an EAE more frequently.
The study provides important evidence that certain types of bacteria, particularly in the ileum of MS patients, could play a disease-triggering role. The study also emphasizes the vital role of the ileum as a key region for the interaction between gut microbiota and the immune system in MS. This study raises hopes that microbiome-based therapies or prevention strategies could be available in the future.
Despite all the enthusiasm about this study, however, I believe that a lot of research work is still necessary until these basic scientific results can be translated into concrete medical strategies.
This post was translated from German to English with the help of AI.
