Magazine article Science News

Genetic Markers Improve Colorectal Screen

Magazine article Science News

Genetic Markers Improve Colorectal Screen

Article excerpt

Genetic markers improve colorectal screen

A rare genetic defect causes tiny polyps -- sometimes hundreds of them -- to grow in the large intestine. Without surgery to remove the polyp-ridden section of the colon, cancer eventually results. Now researchers have developed a genetic test to predict a person's risk of developing the precancerous condition, known as familial adenomatous polyposis (FAP).

People who have a parent with FAP run a 50-50 chance of inheriting the gene and developing the disorder, which often emerges during adolescence. To detect FAP in time to stop its progression to cancer, physicians typically begin checking for polyps when youngsters in families carrying the gene reach their teens, repeating the exams annually and watching for additional symptoms such as bony growths on the head.

Used in conjunction with standard diagnostic methods, the new genetic screen for members of FAP-prone families should reduce the need for frequent colorectal exams among those who don't inherit the gene while increasing the chance of identifying those who do, says study leader Malcolm G. Dunlop of the Medical Research Council Human Genetics Unit in Edinburgh, Scotland.

Scientists have yet to find the gene for FAP, but they have founds a number of DNA probes, or "markers," positioned on the chromosome very close to it. Dunlop and his colleagues, who describe their work in the Feb. 9 LANCET, used six previously identified markers to screen blood samples from 41 members (including children, teens and adults) of seven families with a history of FAP.

The screen revealed a high risk of FAP in four adults who had stopped having annual colon exams in their 30s or late 20s because their results had consistently come up negative. Upon subsequent examination, one showed cancerous growths and the other three showed polyps that probably would have progressed to cancer if not detected, Dunlop says. All four underwent colorectal surgery. …

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