An important gene that predisposes people to various kinds of cancer as well as causing a rare genetic disease has been isolated after an intensive search lasting more than a decade.
The discovery has aroused intense interest among researchers because, unlike other cancer-related genes, the defective form of this gene is relatively common in the population, suggesting it may be a significant cause of many cancers.
The gene is also the cause of a dreaded genetic disease. Children who inherit the defective form of the gene from both parents suffer from a disease of movement that strikes at an early age and is usually fatal by age 20.
Why the defect should cause this disease as well as cancer is still unknown.
Identification of the gene will not lead immediately to any therapy, but it affords insight into the nature of cancer, which eventually may lead to the development of practical ways of reversing the gene's damage.
As many as 1 percent of Americans, or more than two million people, carry the defective form of the gene, which is thought to increase their risk of getting any of a variety of cancers three to eight fold.
The cancers associated with the gene, called the ATM (for ataxia telangiectasia mutated), include those of the breast, lung, stomach, skin and pancreas.
"It's extremely important," said Dr. Bert Vogelstein, a molecular biologist at the Johns Hopkins University School of Medicine.
Dr. Vogelstein said that, for breast cancer alone, there are twice as many patients with the ATM gene as with the BrCa1 gene, the recently discovered cancer gene that received a torrent of publicity.
Dr. David Housman, a molecular biologist at the Massachusetts Institute of Technology, said that compared to the retinoblastoma gene, which causes tumors in 90 percent of those who carry it, the ATM gene was relatively ineffective in causing cancer.
But, he said, what makes the ATM gene so important is the number of people who have it. Although it increases cancer risk by just several fold, the numbers soon add up, making it a major cause of cancer.
For cancer researchers, who have been looking for ways to find particularly susceptible groups to test new ways of preventing cancer, the ATM gene could be an important new lead.
Dr. John Minna, director of the cancer center at the University of Texas Southwestern Medical Center at Dallas, said the discovery of the gene was "fantastic" and could give a huge boost to his studies and those of others who are testing ways to prevent lung cancer.
But the discovery also gives rise to questions of how the information will be used, and by whom. Once again, while basic research leaps ahead, society is faced with the dilemma of whether to tell people they have the gene and, if so, what to tell them.
While scientists hope to go slowly, using the gene to investigate the molecular biology of cancer and to select participants for studies on new ways to prevent cancer, companies are already anticipating selling a genetic screening test that would inform people of their cancer risk.
A troublesome problem raised by the ATM gene is that although it increases a woman's chances of developing breast cancer, it also may raise her risk of having cancer induced by radiation in mammograms.