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 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.
Take the Testing
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 prive 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 pring 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 s 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 of the disease, and at thc time, IVA was not included in newborn screening. The Monacos had no warning whatsoever.
Not Take the Testing
Genetic testing, exciting as it may seem, isn’t always the answer. When Wendy Uhlmann, a genetic counselor at the University of Michigan, teaches medical students, she flashes two slides on a screen side by side. One says ignorance is bliss (福佑). The other: knowledge is power. That’s because the value of testing becomes especially ambiguous- and ethically complicated-- when there is no way to pr or treat disease, as in the case of early-onset Alzheimer’s, which often strikes before the age of 50. or Huntington’s.
Today only about 5 Percent of people who are at risk for Huntington’s--which is caused by a single gene and leads to a progressive loss of physical control and mental acuity--take the test. Many are worried that genetic testing will put their health insurance or job security at risk. While there have been few documented cases of discrimination, nobody can say for sure what will happen as more disease genes are discovered and more Americans sign on for predictive testing. States have a patchwork of regulations in place, but what needs to happen now, experts say, is for Congress to pass the Genetic Information Nondiscrimination Act, which would put a federal stamp of approval on keeping genetic information safe.
Moreover, some people can’t live with uncertainty. Stephanie Vogt knew Huntington’s ran in her family-her grandfather and his three brothers all died of complications of the disease--and she wanted to find out where she stood. "As soon as 1 found out there was a test. I just had to do it," she says. In August 2000, after comprehensive genetic counseling, Stephanie, her sister, Victoria, and their mother, Gayle Smith, learned her results: positive. "It was like a scene out of ’The Matrix’, where everything freezes and struts again," says Stephanie, now 35 and single.
Scientific revolutions must be tempered by reality. Genes aren’t the only factors involved in complex diseases--lifestyle and environmental influences, such as diet or smoking, are too. And predictions about new tests and treatments may not come to pass as fast as researchers hope--they may not come at all. Still, it’s hard not to get excited about the future, especially when you consider the medical competition now underway.
How many people with breast cancer are inherited from family tree