MS

NPR: Researchers Find A Web Of Factors Behind Multiple Sclerosis

Even so, genes don't explain it all. MS occurs more frequently at higher latitudes, suggesting that vitamin D deficiency might play a role in disease risk (the vitamin's production in the body is dependent on sun exposure). Smoking also increases risk for the disease, as does obesity.

And while the tale of the Faroe Islands is disputed – large scale retroactive epidemiological studies are notoriously hard to pull off – it is for the most part accepted that microbes play some role in MS given that dozens of microbes, including the Epstein-Barr virus, have been tied to MS.