Twin study shows MS is more nurture than nature

Monozygotic - or identical - twins have provided science with the ideal platform for distinguishing between genetic and environmental influences for anything from personality, risk of cardiovascular disease or even voting habits.

But now a study in Nature on identical twins by researchers in the US has found that the autoimmune disease, MS, is more a mystery than we thought.

The researchers, led by Sergio Baranzini at the University of California, San Francisco, and Stephen Kingsmore of the National Center for Genome Resources in Santa Fe, New Mexico, sequenced the genomes of two identical twins, one with MS and one without, hoping to find a genetic difference that might explain why one of the twins had developed the disease.

However, to their surprise, they found no evidence of genetic, epigenetic or transcriptome differences that explain the disease discordance.

So, while it is known that one's predisposition to develop MS is dependent on their genes; if one identical twin develops MS, the other is 25 per cent likely to also develop it. But what was not known was whether there was a common genetic factor that determined whether one developed MS.

In this study, the researchers found no differences between the twins among around 3.6 million single nucleotide polymorphisms (SNPs) or around 200,000 insertion-deletion polymorphisms, which indicates that the twins were, indeed, genetically identical.

This rules out any specific genetic cause - such as a slight change in the genome between the twins - that might account for the disease discordance.

The researchers also looked at the one million odd SNPs in two other sets of identical twins, one with MS, focusing on the known regions of difference between two individuals, but also found the twins' genomes were the same.

This study is a very important negative result for MS researchers. It indicates that, while one might have a genetic predisposition towards developing MS, it takes a very specific environmental or stochastic trigger to initiate the disease.

However, there are still elements of the genome that could yet reveal the secrets of MS. Further epigenetic studies, or studies of particular types of cells, might give insights into the 'nature' side of MS.