Though ten million Americans carry an abnormal copy of the cystic fibrosis (CF) gene, hardly any of them know it or realize that they risk having children with the disease. And until very recently, widespread population screening has not been practical.

In 1990, when the test that was available identified only 70 to 75 percent of carriers, an NIH panel decided that widespread screening should wait until the test could detect at least 90 to 95 percent of carriers.

That goal is now a reality. It turns out that by taking into account ethnic origins and including the appropriate mutations in the test, one can greatly increase its ability to detect carriers—especially since new, moderately prevalent mutations have been uncovered.

Many questions remain, however: Who should be screened? Should everyone be tested, including African-Americans (whose incidence of CF is only one-tenth that of whites) and Asians (who almost never have the disease)? Or should CF screening be limited to whites, as the President's ethics commission recommended in 1983? At what age should people be screened?

In 1997 a national panel of scientists recommended that all expectant couples and those planning to have children be offered the option to test for gene mutations that cause CF. Most important, people with a family history of the disease and their partners should be included. The panel further recommended that the cost of these tests be covered by insurance.

Meanwhile, there is a growing movement to have laws in place to prevent health insurers from denying people insurance, or employers from refusing people jobs, on the basis of their test results. Discrimination of this sort will grow unless new laws ensure that genetic information is confidential, warns Paul Billings, a medical ethicist at Pacific Presbyterian Medical Center in San Francisco.

Many states are far ahead of the federal government in enacting such laws. Forty-one states have passed legislation prohibiting health insurers from certain acts of discrimination based on the results of genetic tests, and thirty-one states have passed laws to protect people against discrimination from employers. A spate of new bills dealing with these issues is likely to surface in Congress soon.

While CF carrier testing in the schools might have some advantages, as students are a captive audience mostly in the pre-pregnancy state, geneticists fear that confusion about the tests' results might lead to stigma. They remember what happened in the early 1970s, when the nation embarked on an energetic program of screening for sickle cell anemia, which affects 1 in 400 African-Americans.

At that time, many of the people who learned they were carriers of the sickle cell defect mistakenly thought they had the disease (which requires inheriting two copies of the defective gene) and might die of it. Some were denied jobs or health insurance. And since no prenatal test was available then—it exists today—some carrier couples were told that the only way to prevent the disease was to avoid having children, advice that led to charges of racism. When screening programs are not properly introduced or explained and don't include individual counseling, they run the risk of being counter productive.

The most reasonable time to screen for CF might well be when a couple gets a marriage license, suggests Francis Collins. Testing at this stage would reduce the likelihood that the test results would influence a person's choice of marriage partners. But it would miss the large number of unmarried couples who have children. On the other hand, it would be a mistake to wait until the first prenatal visit to the obstetrician because that would limit a couple's options. "Most couples would like to have this information prior to conception," Collins says.

Everyone agrees that screening for genetic diseases should be voluntary and confidential and that counselors should not impose their own values. What counselors can do is explain the options. "There is still no cure for CF at this stage," Lap-Chee Tsui points out. "So if it is possible to avoid the disease, one should be given the chance."

— Maya Pines

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Scientists can test for the disease directly in patients (blue box) and prenatally. They can identify healthy carries of the faulty gene (light blue boxes) in the general population—not just among members of an affected family.

Illustration: Stansbury Ronsaville Wood, Inc.

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