AFTER 4 years of hot pursuit, a us biotech company has won the race to isolate the much sought-after breast cancer gene called BRCA I. Close on the heels of this discovery, an international group has reported mapping of another breast cancer gene called BRCA2. Together, the pair probably accounts for about two- thirds of breast cancer cases running in families, or roughly 5 per cent of all cases.

BRCA1, localised in chromosome 11 four years ago by Mary-Claire King, a geneticist at the University of California at Berkeley, has been nabbed by an international consortium working for the Myriad Genetics Inc. The group analysed more than 200 families on its way to the finish line. A woman who inherits this gene, say scientists, has a 60 per cent risk of breast cancer by the age of 50, and a 90 per cent lifetime risk (Nature, Vol 371, No 6495).

The second cancer gene - BRCA2 -has been mapped by a group based in the International Breast Cancer Linkage Consortium, under the leadership of the Institute of Cancer Research in Sutton, the UK, and from Utah. Now with BRCA1 identified, the isolation Of BRCA2 is next in line.

The immediate practical implication of this discovery is for genetic testing. But there are problems here. For one, experience with other adult-onset inherited disorders has shown that a negative DNA does not rule out the occurrence of the disease. Also, the gene is large, and the link between mutations of BRCA1 and the occurrence of breast cancer in families carrying it is far from clear. Moreover, it is not yet clear how widely the mutations are scattered, and how easy or costly large-scale testing will be.

Despite these grey areas, the company has been granted a patent for the discovery. The patenting has reopened the debate about how best to commercialise results from the human genome project, and whether patents should be granted on individual genes.