Researchers summoned a Baltimore County woman to an office at the Johns Hopkins School of Public Health last spring to tell her the bad news. They had found a genetic threat lurking in her 7-year-old son's DNA -- a mutant gene that almost always triggers a rare form of colon cancer.
It was the same illness that led surgeons to remove her colon in 1979.
While the boy, Michael, now 8, is still perfectly healthy, without surgery he is almost certain to develop cancer by age 40.
"I didn't think he was going to have it, I really didn't," Susan B., 43, recalled last week, her green eyes welling with tears. (She asked that her last name not be used to protect her family's privacy).
"But God answers prayers the way He has to. I accepted it. And we're going to work with it."
This genetic fortune-telling was no parlor trick. It was the product of astonishing advances in recent decades in understanding how genes build and regulate our bodies. And as scientists pinpoint new genes and learn to forecast the onset of more inherited disorders, millions of people are likely to demand their medical prognoses.
Some genetic specialists are worried. Gene tests can be powerful tools for the diagnosis, study or treatment of disease. But if they are casually prescribed, botched by laboratories or not understood by those who take them, tests could do more harm than good.
"I think this technology has enormous promise to benefit people," said Dr. Francis Collins, director of the National Center for Human Genome Research, which is leading the United States' $3 billion attempt to identify the 60,000 to 80,000 human genes.
"But it's also powerful information which, if used incorrectly, could injure people," Dr. Collins warned.
To prevent abuse, genome project officials picked Dr. Neil A. Holtzman, a Johns Hopkins pediatrician and genetics specialist, to lead a task force on genetic testing.
The 21-member task force, which held its first meeting in Hunt Valley last month, is expected to recommend ways the Food and Drug Administration can regulate these tests. Their report is due in two years.
Dr. Holtzman, 61, led the first pediatric genetics unit at Hopkins in the early 1970s. He worked on a study of one of the earliest genetic screening efforts, the testing of newborns for a condition known as phenylketonuria, or PKU. Today, the number of tests is multiplying as scientists around the country race to track the genetic roots of illnesses.
"Once you identify a genetic mutation, as part of that discovery you also have a test to see if other people also carry that mutation," Dr. Holtzman explained. "That has really blown the lid off genetic testing, in that many of the scientific and technological restraints are rapidly disappearing. The question is, will we use these tests in a responsible way?"
Take someone whose relatives have a fatal inherited disease. Testing negative for the gene could have the impact of a pardon on a death row inmate. A positive test could help a person cope by, for example, signaling the need to make financial or other plans for long-term care.
But a positive test might also stigmatize someone whose results become public -- making it harder for that person to get married, land a job, go to college or buy insurance.
Knowledge that a person is likely to die or be disabled by illness, of course, might create a crushing psychological burden.
The genetic disorder Huntington's disease, which strikes in late middle age, rapidly erodes its victims' bodies and minds. There is no effective treatment. While a test for the Huntington's gene has been around for a decade, many young adults who first ask about testing decide -- after counseling -- that they don't want to know.
But attitudes toward testing vary according to the disease.
"Colon cancer is very different from Huntington's disease; people are very willing to be tested," said Dr. Gloria Petersen, a Hopkins anthropologist who is studying the psychological and social effects of genetic testing. She gave Susan the news of her son's test results last spring.
Don Pardoe, a 23-year-old supermarket employee, said his mother died of familial adenomatous polyposis, or FAP, in 1974. All four of his sisters and brothers developed the disease. So he knew he was at grave risk in 1993, when he was told he carried the gene.
"It didn't really shock me," he said. "After seeing how much I take after my mother, I expected it. I just took it in stride, another thing I had inherited from her. I said, 'OK. What do we do next?' "
At the time, he showed no signs of illness. But the discovery of the gene prompted him to schedule more frequent examinations. That may have saved his life.
Within a year, precancerous polyps appeared. He underwent intestinal surgery last year.