Test Spots 76% of Cystic Fibrosis Carriers

A new test can spot three-quarters of all adults who risk having children with cystic fibrosis, and more accurate versions should soon allow routine screening of everyone in the United States for this common genetic defect, researchers report.

The screening can help parents avoid having children with cystic fibrosis. But experts say it also raises ethical and practical questions about who should get the test and what should be done with the information it provides.

Cystic fibrosis is the most common fatal genetic disease of young Americans. It occurs most often among whites, striking about one of every 2,500 white newborns in the United States.

“People for years have realized that, if we had a good carrier test for cystic fibrosis, there would be the potential to test everyone before reproduction to see if they were a carrier or not,” Dr. Arthur L. Beaudet said. “The evidence is at hand that such a carrier test will soon be available.”

One in every 25 white Americans carries one copy of the cystic fibrosis gene. They are healthy, but if they marry another carrier there is a 1-in-4 chance that their children will have cystic fibrosis.

The disease causes a variety of symptoms, including abnormal mucous secretion that results in lung infections. Although doctors can ease many of the symptoms and extend lives, there is no treatment for the underlying disease.

Last summer, scientists pinpointed the precise genetic error or mutation responsible for most cases of cystic fibrosis. The latest study found that checking people’s genes for this defect can identify 76% of all carriers.

That research, conducted by Beaudet and his colleagues at Baylor College of Medicine in Houston, was published in today’s New England Journal of Medicine. Drs. Lap-Chee Tsui of the Hospital for Sick Children in Toronto and Francis S. Collins of the University of Michigan, who discovered the cystic fibrosis gene, were co-authors of the report.

Although Lap-Chee and Collins pinpointed the mutated gene that accounts for about three-quarters of all cystic fibrosis cases, scientists at about 40 other laboratories are cooperating to track down the half-dozen or so other mutations that also can cause the disease.

Collins predicted that these mutations will be identified within the next year. Then doctors should be able to offer screening tests that will identify 95% of all carriers.

Experts hope that adults will use the test results for family planning. If couples learn that both are carriers, some might decide to adopt rather than run the risk of having a child with cystic fibrosis. Others might opt to have artificial insemination with sperm from a donor who is not a carrier.

If a couple chooses pregnancy, the test can be performed on the fetus, the researchers said. If the fetus turns out to have the disease, parents can then decide whether to have the baby or to get an abortion.