Imagine visiting your doctor for an annual exam—only this time the checkup begins not with a physical but with a routine sequencing of your genome. Using information from the test, your physician not only diagnoses the diseases you are most susceptible to but also selects the types and doses of medication best suited to help you combat the maladies. It's called personalized medicine. And no, it doesn't mean your doctor will be extra kind or personable. The term broadly refers to the detection, treatment, and prevention of diseases based on a person's unique genetic makeup, and many people believe it will revolutionize health care. "When you go to your physician ten years from now virtually all the decisions about diagnosis and treatment will be based on individual information about your particular circumstance as opposed to a more general kind of approach to lots of other people in your general circumstance," said genome expert Francis Collins. Collins led the international effort to sequence the human genome, which was completed in 2003. That effort was followed by the creation of a map of human genetic variation. The genome contains tens of thousands of genes, which code for proteins and other molecules that make life possible. Although there are some three billion "letters" in the human DNA code, 99.9 percent are identical between any two people. The small remaining differences hold clues about why people tend to develop particular diseases. 'We now have the technology to assess in people with disease, versus those who don't have the disease, which of those [genetic] variances seem to be overrepresented," Collins said. "We are on the brink of discovering what are the hereditary factors in diabetes, heart disease, in the common cancers, high blood pressure, asthma, mental illness—virtually any disease you can think of that tends to run in families.