Speculation about the cause of multiple sclerosis includes genes and environmental factors. A study published Thursday supplies strong evidence that environmental factors play a critical role.
Multiple sclerosis is a disease in which the immune system goes awry and attacks healthy tissue in the body. Researchers at UC San Francisco conducted the most advanced gene analysis ever on identical twins in which one twin has MS and the other does not. The analysis did not yield evidence for genetic differences that could explain why one sibling had the disease and the other did not. Nor did researchers find any differences in the epigenome -- mechanisms that change the way genes are expressed apart from changes in DNA -- to explain the disease in one twin.
Exactly what environmental factors contribute to causing MS is still unknown, however. The leading theory is that a virus triggers the immune system reaction that leads to the disease. Smoking and vitamin D deficiency have also been suggested as possible environmental contributors. But, "the results put us a step closer to teasing out the relative contributions of genetic and environmental factors on multiple sclerosis," the lead author of the study, Sergio Baranzini, said in a news release.
The findings do not mean genes don't play a role in the disease. When one identical twin has MS, there is 30% increased risk that the identical sibling will develop it. That compares with an increased risk of only 5% for a nonidentical twin.
The study is in the current issue of the journal Nature.
-- Shari Roan
Photo: A doctor uses a fluorescent microscope to view a brain section of a patient with MS. Credit: Julia Malakie / Associated Press