Genetic Testing
Genetic testing is transforming medicine and the way families think about their health. As science uncovers the complicated secrets of DNA, we face difficult choices and new challenges. About Genetic Testing
The year was 1895 and Pauline Gross, a young actress, was scared. Gross knew nothing about the human-genome (基因组，染色体组) project--such medical triumphs, but she did know about a nasty disease called cancer, and it was running through her family. "I'm healthy now," she often told Dr. Aldred Warthin a pathologist at the University of Michigan, "but I fully expect to die an early death."
At the time, Gross's prediction was based solely on observation: family members had died of cancer; she would, too. Today, more than 100 years later, Gross's relatives have a much more clinical option: genetic testing. With a simple blood test, they can peer into their own DNA, learning--while still perfectly healthy--whether they carry an inheritable gene mutation (突变) that has dogged their family for decades and puts them at serious risk.
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Testing is just one piece of the genomic revolution. A major goal is to create new sophisticated therapies that home in on a disease's biological source, then fix the problem. Already, genes are helping to predict a patient's response to existing medications. A prime example, taken by Dr. Wylie Burke of the University of Washington, is a variant of a gene called TPMT, which can lead to life-threatening reactions to certain doses of chemotherapy (化学疗法). A genetic test can guide safe and appropriate treatment. Two genes have been identified that influence a person's response to some anti-blood-clotting drug. And scientists are uncovering genetic differences in the way people respond to other widely used medications, like antidepressants (搞抑郁药).
Knowing a patient's genotype, or genetic profile, may also help researchers uncover new preventive therapies for sticky diseases. At Johns Hopkins University School of Medicine, Dr. Christopher Ross has tested several compounds shown to slow the progression of Huntington's in mice. Now he wants to test them in people who are positive for the Huntington's mutation but have not developed symptoms--a novel approach to clinical drug trials, which almost always involve sick people seeking cures. "We're using genetics to move from treating the disease after it happens," he says, "to preventing the worst symptoms of the disease before it happens."
It's not just their own health that people care about. There is also the desire to get rid of disease from the family tree. Therefore, the future is what drives many adults to the clinic. The gene tests currently offered for certain diseases, like breast cancer, affect only a small percentage of total cases. Inherited mutations contribute to just 5 to 10 percent of all breast cancers. But the impact on a single life can be huge. The key: being able to do something to ward off disease. "Genetic testing offers us profound insight," says Dr. Stephen Gruber, of the University of Michigan. "But it has to be balanced with our ability to care for these patients."
Genetic testing today starts at the earliest stages of life. Couples planning to have children can be screened prior to conception to see if they are carriers of genetic diseases; prenatal (产前) tests are offered during pregnancy, and states now screen newborns for as many as 29 conditions, the majority of them genetic disorders. For Jana and Tom Monaco, of Woodbridge, Va. , early testing has made an enormous difference in the lives of their children. Their journey began in 2001, when their seemingly healthy third child, 3-year-old Stephen, developed a life-threatening stomach virus that led to severe brain damage. His diagnosis: a rare but treatable disease called isovaleric acidemia (IVA). Unknowingly, Jana and her husband were carriers

A. stroke
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C. SARS
D. AIDS