Just saw this Scientific American article about two recent studies that found a link between gut bacteria and multiple sclerosis.
https://www.scientificamerican.com/a...ple-sclerosis/
They have a disclaimer, though: "It’s too soon to know how important the microbiome is in increasing the risk of MS compared to the 200 genetic variants that have been linked to the disease, or compared to the Epstein-Barr virus, smoking, and low levels of vitamin D, which also seem to play a role."