In the past, disease diagnosis was based on symptoms that might be indicative of several diseases. Nowadays, diagnosis of some diseases has become more accurate because we are able to test for genes known to be associated with the disease. This method not only clearly identifies the presence of a particular disease; it can also precisely determine the subtype of the disease. Throughout history, the practice of medicine has largely been reactive. Even now days, we have to wait until the onset of diseases and then try to treat or cure them. As we don’t fully understand the genetic and environmental factors that cause major diseases such as cancer, Alzheimer’s and diabetes, our efforts to treat them are often imprecise, unpredictable and ineffective.In addition, the drugs and treatments we devise are tested on broad populations and are prescribed using statistical averages.