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.We remain captivated by idea of genes for this or that -- homosexuality, alcoholism, left-handedness. But it seems that these and almost all other interesting traits are the result, not of single genes, but the interactions of dozens or hundreds of genes. For medical conditions you also have to factor in the environment: you may have a genetic predisposition to lung cancer, but you still probably won't get it if you never smoke and stay away from wood fires.
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.
I'm not sure why Obama wants to throw a few hundred million at "precision medicine" -- I assume it polls well and he wants to remind people that Democrats are the party of science. But it is a foolish boondoggle all the same.