A scientific and medical revolution has crept up on us. Twenty-one million Americans are affected by 6,000 so-called rare and orphan diseases, many of which are primarily attributable to misspelled genes. And virtually all diseases have a significant hereditary component. Diabetes, heart disease, the common cancers, mental illness, asthma, arthritis, Alzheimer's disease, and more are having their secrets unlocked through DNA. Families that faced common problems, without hope, are now discovering a new world of understanding, treatment, and prevention. You owe it to yourself to learn about your DNA: how it works, what it reveals, and the benefits and limits of this new knowledge.