A Revolution in Medicine: The Search for Cures: From Oncology to Infectious Disease, Genetic Science Is Transforming Medical Practice. the Dream of Outfitting People with Therapeutic Genes May Still Be Decades Away, but Scientists Are Finding Simpler Ways to Harness the Power of DNA

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Ann Miscoi had seen her father and her uncle die of organ failure in their mid-40s, so she figured she was lucky to be living when she turned 50 last year. The trouble was, she felt half dead. Her joints ached, her hair was falling out and she was plagued by unrelenting fatigue. Her doctor assured her that nothing was seriously wrong, even after a blood test revealed unusually high iron levels, but Miscoi wasn't so sure. Scanning the Internet, she learned about a hereditary condition called hemochromatosis, in which the body stores iron at dangerous concentrations in the blood, tissues and organs. Hemochromatosis is the nation's most common genetic illness, and probably the most underdiagnosed. As Miscoi read about it, everything started making sense--her symptoms, her blood readings, even her relatives' early deaths. So she found a doctor who would take her concerns more seriously.

Until recently, diagnosing the condition required a liver biopsy--not a procedure you'd undertake lightly. But Miscoi didn't have to go that route. Scientists isolated the gene for hemochromatosis a few years ago, and developed a test that can spot it in a drop of blood. Miscoi tested positive, and the diagnosis may well have saved her life. Through a regimen of weekly blood lettings, she was able to reduce her iron level before her organs sustained lasting damage. She's now free of symptoms, and as long as she gives blood every few months she should live a normal life span. "Without the DNA test," she says, "I would have had a hard time convincing any doctor that I had a real problem."

Hemochromatosis testing could save millions of lives in coming decades. And it's just one early hint of the changes that the sequencing of the human genome, now in its final stages, could bring. By 2010, says Dr. Francis Collins of the National Human Genome Research Institute, screening tests will enable anyone to gauge his or her unique health risks, down to the body's tolerance for cigarettes and cheeseburgers. Meanwhile, genetic discoveries will trigger a flood of new pharmaceuticals--drugs aimed at the causes of disease rather than the symptoms--and doctors will start prescribing different treatments for different patients, depending on their genetic profiles. The use of genes as medicine is probably farther off, but Collins believes even that will be routine within a few decades. "By 2050," he said recently, "many potential diseases will be cured at the molecular level before they arise."

That may be a bit optimistic, but the trends Collins foresees are already well in motion. Clinical labs now perform some 4 million genetic tests each year in the United States. Newborns are routinely checked for sickle cell anemia, congenital thyroid disease and phenylketonuria, a metabolic disorder that causes mental retardation. Like hemochromatosis, these conditions are catastrophic if they go undetected, but highly manageable when they're spotted early. Newer tests can help people from cancer-prone families determine whether they've inherited the culpable mutation. "My mother died of colon cancer at age 47," says Dr. Bert Vogelstein, an oncologist at Johns Hopkins and the Howard Hughes Medical Institute. "If we'd known she was [genetically] at risk, we could have screened for the disease and caught it early."

Early detection is just the beginning. Genes help determine not only whether we get sick but also how we respond to various treatments. "In the past," says Dr. William Evans of St. Jude Children's Research Hospital in Memphis, Tenn., "the questions were, 'How old are you and how much do you weigh?' " Now, thanks to recent genetic discoveries, physicians can sometimes determine who stands to benefit from a given drug, and who might be harmed by it. At St. Jude, doctors gauge the aggressiveness of children's leukemia cells before settling on chemotherapy or bone-marrow transplantation. And kids who qualify for chemo receive additional gene tests to gauge their tolerance. …