Cystic fibrosis marker.

A first step toward identifying the gene responsible for cystic fibrosis was reported last week by two biotechnology companies. The work is expected to lead to a screening test for carriers of the disease and eventually to new treatments.

Cystic fibrosis is the most common lethal genetic disease in the United States. Approximately one in every 2,000 U.S. Caucasian babies is born with the disease; most do not survive beyond their early twenties.

Two genetic markers for cystic fibrosis were described in Salt Lake City by independent research groups at the meeting of the American Society for Human Genetics. A genetic market is a segment of DNA identified by scientists that is located near an unidentified gene of interest. By following inheritance of the market within a family, scientists can determine who is likely to inherit the gene. The marker also indicates where within the chromosomes a gene is located.

One genetic marker for cystic fibrosis is located on chromosome 21, reports Integrated Genetics of Framingham, Mass. In collaboration with scientists at the University of Rochester and Yale University, company researchers determined there is a 94 percent probability that the marker and cystic fibrosis gene will be inherited together.

Another genetic marker for cystic fibrosis was reported by scientists at Collaborative Research, Inc., of Lexington, Mass., and at the Hospital for Sick Children in Toronto. The chromosomal location of this genetic marker is still being determined, but it appears to be inherited with the cystic fibrosis gene 85 percent of the time.

The two new cystic fibrosis markers appear to be linked to different genes, says Thomas O. Oesterling of Collaborative Research. He suggests that there are two genes that cause the disease in different families, and that the marker discovered by Collaborative Research is linked to the major gene. The companies are planning an exchange of markers to test on different families.