Sequencing can be very useful in assessing the risk of rare diseases triggered by a single faulty gene, such as the brain disorder known as Huntington's disease. With more common and more complex ailments affected by many genes and the interactions between them, the picture gets fuzzier. The study suggests, for instance, that whole-genome tests aren't especially helpful in predicting cancer in most people who don't have a strong family history of the disease.
This is more or less what I said in an earlier post. The study examined "data from thousands of twins in five countries" for 24 diseases. It found that for 23 of those diseases, gene mapping produced negative results, providing a false sense of security.