But for most common diseases, hundreds of genetic risk variants with small effects have been identified, and it is hard to develop a clear picture of who is really at risk for what. This was actually one of the major and unexpected findings of the Human Genome Project. In the 1990s and early 2000s, it was thought that a few genetic variants would be found to account for a lot of disease risk. But for widespread diseases like diabetes, heart disease and most cancers, no clear genetic story has emerged for a vast majority of cases.
Age, sex, body weight and a few simple blood tests are much better predictors of Type 2 diabetes, for example, than a genetic score based on how many snippets of “risky” DNA you have. And the advice for those at risk to exercise more and eat more healthfully remains the same.