Genome vs Enviroment: the twin match.

"What fraction of the population would benefit from genome sequencing? “Benefit” in this context is defined as receiving information indicating that the risk of disease is increased or decreased to a degree that would alter an individual's lifestyle or medical management." This is the starting question that Roberts et al. wanted to answer to. Right now this seems an unsuccessfully effort, an impossible challange given the millions of variants that could contribute to the risk of a disease. However there is a field in which this challenge becomes easier: the genome of twins. Infact, as the authors wrote in their article published on Science Translational Medicine, in a pair of twins in which at least one is affected by a disease, the probability of the other twin developing a disease is dependent on the genome whenever that disease has some genetic component. The study was conducted on 53,666 twin pairs, analyzing 24 disease. The researchers, given the affected status of one of the two twins, used the prevalence of the disease in the second twin to calculate the genetic risk of a given disease for that genome. The results, elaborated without any type of sequencing effort, reveal that the majority of the twins would have tested negative for risk for 23 of the 24 diseases, substantially their risk was below the risk of the general population. This article received many critical comments, here you can find a series of them posted on the Nature blog, the main critics focused on the low novelty of the study. It is well known that twins could get sick of different diseases and also die for different causes that don't depend on their common genome.

What emerges from this work is that our genome, and its whole sequencing, is valuable and instrumental for the identification of the basis of many genetic disease, primarily for those with a family history. On the other hand, enviroment has the main role in many medical conditions, especially in complex diseases such as cancer. This is not a bad news because, indipendently of our genetic starting conditions, the match against complex diseases is open, and weapons such as diet, sports, and lifestyle, could make us the winners.