When a team of US researchers compared the complete genomes of twin females with each other, they failed to find any genetic differences that might cause MS.
[Researchers] next looked for a difference in epigenetics-chemical modifications to DNA that affect gene expression but not genetic sequence- in the twins' immune cells and in cells of two other sets of similarly affected twins. But no differences were found in the expression levels of key genes, either.
This is really elegant work, and even though it's a negative, it shows the incredible depth that one can explore the issue with today's technology. It emphasizes the fact that we haven't really identified the smoking gun, so to speak. It still drives us to want to look harder.