A genetic vulnerability to carcinogens.

In the March 10 Parade magazine, Cornell University astronomer Carl Sagan recalls the harrowing bone-marrow transplant he underwent to check the ravages of myelodysplastic syndrome (MDS). Without a transplant, MDS victims often die of leukemia within a year. A new study suggests that a common genetic defect renders many people unusually vulnerable to this rare disease and perhaps to other cancers.

Douglas A. Bell of the National Institute of Environmental Health Sciences in Research Triangle Park, N.C., and his coworkers tested 92 MDS patients and 201 cancerfree volunteers for a gene that codes for a carcinogen-detoxifying enzyme (one of the glutathione S-transferases). In the Feb. 3 Lancet they report that those who failed to inherit a functional copy of this gene from either parent face four times the MDS risk of those who inherited even one such gene. In the United States, one in six persons lacks a working copy of this gene.

"This is the first disease strongly associated [with] the absence of this protective gene, but it certainly will not be the last," says Bell. However, he adds, it's important to point out that unless one is exposed to certain chemical carcinogens, "these gene defects have no adverse health impact."