Scientists Discover A Cancer Trigger

BOSTON Scientists have discovered a mutant bit of geneticmaterial that may help trigger more than 50,000 cases of cancer ayear, including leukemia and breast tumors.

They estimate that these genetic variations are somehow involvedin one out of 11 cases of cancer of the breast, colon and bladder,and probably a substantial proportion of leukemia and lung andprostate cancer, too.

The mutations they found appear to roughly double the risk ofcancer. Twenty percent of all people with the common forms of cancercarry them, as do 10 percent of all healthy people.

The discovery gives important clues for cancer research, butthere's no reason - at least yet - to search people's geneticmaterial for the mutations, said Dr. Theodore G. Krontiris of NewEngland Medical Center, whose finding builds on earlier work by histeam and other researchers.

For years, the search for the genetic underpinnings of cancerhas focused on specific genes that lead to cancer when they becomemutated. But recently, scientists have begun to look at theseemingly meaningless code that fills up chromosomes between genes.

Of particular interest are multiple copies of short stretches ofgenetic code. These bits, called minisatellites, might repeat agenetic sequence 50 or 100 times.

Minisatellites are scattered through the human library of genes,and many appear to be closely linked with genes that contain the codeto manufacture essential proteins.

One gene, called H-ras, is well known to cause cancer when itbecomes mutated. In the latest work, the scientists found thaterrant forms of a minisatellite somehow seems to interfere with theworkings of normal versions of the H-ras gene, triggering cancer in acompletely different way.

Krontiris said he suspects that the mutant minisatellite messesup the normal control of the H-ras gene so it manufactures proteinimproperly.

"We are excited about the possibility that this influence mightextend to other minisatellites and other genes and therefore the riskof other types of common diseases," such as diabetes, he said.

Another kind of genetic repeat has been linked to some inheriteddiseases. Scientists have found that Huntington's disease andmyotonic dystrophy, among others, occur when a tiny piece of geneticcode inside a gene repeats itself over and over.

Genetic repeats vary from person to person. Because they are sounique, forensic specialists use them for genetic fingerprinting, thetask of matching suspects' genetic patterns with those left at crimescenes in blood and semen.