New Discovery Shows Gut Bacteria May Trigger Multiple Sclerosis

Multiple sclerosis (MS) is a disease in which the immune system attacks the brain and spinal cord. In addition to genetic and environmental factors, scientists have discovered that gut bacteria can also influence the onset of the disease. A study of identical twins showed that certain gut bacteria, present in people with MS, can cause symptoms of the disease in mice. This helps to better understand MS and may lead to new treatments in the future.

Multiple sclerosis (MS) is a disease that affects the central nervous system, that is, the brain and spinal cord. It occurs when the body's own immune system attacks a part of the nerves called myelin, which acts as a “protective coating” for neurons. This causes problems with communication between the brain and the rest of the body.

The most common symptoms include intense fatigue, difficulty walking, muscle weakness, numbness or tingling in the arms and legs, vision problems (such as double or blurred vision), imbalance, dizziness and cognitive difficulties, such as memory and concentration problems.

Symptoms may appear in flare-ups and then partially improve, or progress more steadily over time.

Multiple sclerosis is considered a chronic inflammatory disease, and although the exact causes are not yet fully known, it is believed to occur in people who already have a genetic predisposition and who have been exposed to certain environmental factors.

These risk factors can include more than 200 common genetic alterations, as well as habits and conditions such as smoking, low levels of vitamin D, obesity and infection with a virus called Epstein-Barr.

In recent years, scientists have also begun to study the role of bacteria that live in the intestine, known as the gut microbiota, as possible causes or influences of multiple sclerosis.

Multiple sclerosis is considered a chronic inflammatory disease, and although the exact causes are not yet fully known, it is believed to occur in people who already have a genetic predisposition and who have been exposed to certain environmental factors.

These risk factors can include more than 200 common genetic alterations, as well as habits and conditions such as smoking, low levels of vitamin D, obesity and infection with a virus called Epstein-Barr.

In recent years, scientists have also begun to study the role of bacteria that live in the intestine, known as the gut microbiota, as possible causes or influences of multiple sclerosis.

In previous studies, scientists had already noted this link between the gut microbiota and the onset of multiple sclerosis, but they did not yet know exactly which bacteria were involved or where in the intestine they were located.

To address this issue, a new strategy was developed. The researchers studied identical twins (same DNA), where only one of them had multiple sclerosis. This helped to eliminate genetics as the cause of the observed differences.

They analyzed the bacteria in the guts of these twins and then transplanted these bacteria into genetically modified, germ-free mice.

The results showed that mice that received bacteria from people with multiple sclerosis were much more likely to develop the disease than those that received bacteria from healthy people.

In addition, it was discovered that two specific bacteria in the intestine, called Eisenbergiella tayi and Lachnoclostridium, both from the Lachnospiraceae family, may be directly linked to the increased occurrence of multiple sclerosis. These bacteria were found mainly in the final part of the small intestine, called the ileum.

Another interesting detail was that female mice became sicker than males, which may reflect what also happens in humans, since multiple sclerosis is more common in women.

This study is important because it shows that certain bacteria in the intestine can actually contribute to the onset of multiple sclerosis. Knowing this could help develop new forms of early diagnosis and even treatments that involve controlling or modifying the intestinal microbiota.

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Multiple sclerosis and gut microbiota: Lachnospiraceae from the ileum of MS twins trigger MS-like disease in germfree transgenic mice—An unbiased functional study

Hongsup Yoon, Lisa Ann Gerdes, Florian Beigel, and Anneli Peters 

PNAS. 122 (18) e2419689122. April 21, 2025.

https://doi.org/10.1073/pnas.2419689122

Abstract:

We developed a two-tiered strategy aiming to identify gut bacteria functionally linked to the development of multiple sclerosis (MS). First, we compared gut microbial profiles in a cohort of 81 monozygotic twins discordant for MS. This approach allowed to minimize confounding effects by genetic and early environmental factors and identified over 50 differently abundant taxa with the majority of increased taxa within the Firmicutes. These included taxa previously described to be associated with MS (Anaerotruncus colihominis and Eisenbergiella tayi), along with newly identified taxa, such as Copromonas and Acutalibacter. Second, we interrogated the intestinal habitat and functional impact of individual taxa on the development of MS-like disease. In an exploratory approach, we enteroscopically sampled microbiota from different gut segments of selected twin pairs and compared their compositional profiles. To assess their functional potential, samples were orally transferred into germfree transgenic mice prone to develop spontaneous MS-like experimental autoimmune encephalomyelitis (EAE) upon bacterial colonization. We found that MS-derived ileal microbiota induced EAE at substantially higher rates than analogous material from healthy twin donors. Furthermore, female mice were more susceptible to disease development than males. The likely active organisms were identified as Eisenbergiella tayi and Lachnoclostridium, members of the Lachnospiraceae family. Our results identify potentially disease-facilitating bacteria sampled from the ileum of MS affected twins. The experimental strategy may pave the way to functionally understand the role of gut microbiota in initiation of MS.