MEDICINE

Family ties

Tracing the genetic link to a deadly cancer

MARK NICHOLS May 17 1993
MEDICINE

Family ties

Tracing the genetic link to a deadly cancer

MARK NICHOLS May 17 1993

Family ties

MEDICINE

Tracing the genetic link to a deadly cancer

In 1990, doctors sent two patients from northeastern Newfoundland who had suffered from colon cancer to see Jane Green, a medical geneticist at Memorial University in St. John’s. Both patients knew that cancer was prevalent in their family backgrounds and, recalled Green, “were especially concerned” that their children might develop it. After studying medical records, Green realized that the two patients were members of the same extended family in which an inherited disorder appeared to cause colon cancer. She also knew, Green said, that the family could be a valuable medical resource because researchers could study the history of a large number of family members who re mained in the same remote region through successive generations. Green’s belief was vindicated last week when researchers in the United States and Finland reported a dramatic discovery: after studies involving the Newfoundland family and another in New Zealand,

they had come close to identifying a gene that causes some cases of colon cancer and other forms of cancer.

Experts said that the finding would eventually open the way for new screening techniques to identify potential victims and allow early treatment of colon cancer. The gene in question is not the only cause of colon cancer. Doctors involved in the study said that the gene they have pinpointed probably causes about 14 per cent of

all cases of colon cancer, -

while other genes, diet and aging play a role in the remaining cases. In 1990, the most recent year for which figures are available, 4,431 Canadians died of colon cancer.

Members of the research team led by Dr. Bert Vogelstein of Johns Hopkins University Oncology Center in Baltimore, Md., and Dr. Albert de la Chapelle of the University of Helsinki, revealed another, unusual, finding. In articles published in the May 7 issue of Science, a Washington-based weekly, the researchers also reported that the gene under study may function differently from other known cancer-causing genes. Usually, defective genes trigger cancer by causing cells to begin proliferating wildly. But Vogelstein said

that the new gene may cause cancer by mutating other genes in the patient’s cells.

A chance conversation at a New England summer school led to the Newfoundland family’s crucial role in the study. Green said that in 1991, when she attended a course on medical genetics in Bar Harbor, Me., a colleague of Vogelstein’s “mentioned the difficulties they

were having finding families with a history of colon cancer to study. I said that I knew of a couple of families.” Green, 49, said that she spent the next six months ar-

ranging for the collection of blood samples from 35 members of the extended family. Green passed along the blood samples, with coded information on the family’s history, to Vogelstein’s team. Researchers in Baltimore and Helsinki then extracted genetic material from the blood samples. Using molecular genetics techniques, researchers hunted for telltale “markers”—unique portions of genetic material that act as signposts. Their goal: to find a marker that was shared by all the family members with cancer.

Vogelstein told Maclean’s that at one point, after team members had unsuccessfully searched for about 250 markers, “we were getting frustrated and were even thinking of giving up. But, he added: “A member of the Newfoundland family contracted colon cancer. He was a 27-year-old man and seeing colon cancer in someone that young convinced us that we were on the right track. So we tried another 100 or so markers—and we hit pay dirt.” Vogelstein said that the defective gene is on chromosome number 2, one of the 23 pairs of chromosomes that contain the approximately 100,000 genes found in every human cell.

The next step, Vogelstein said, will be to identify the gene and the defect in it that causes cancer. Once that has been done, tests will be able to detect which people carry the defective gene. They can then be screened for the presence of cancer in its early stages. When colon cancers are caught soon enough, added Vogelstein, they can be surgically removed with a high rate of success—a prospect that could significantly diminish the ravages of a deadly disease.

MARK NICHOLS