DNA repeats associated with cancer.

In recent months, researchers have linked several genetic diseases to three-part bits of genetic code that repeat more often than normal (SN: 7/10/93, p.20).

Larger repeating bits, called minisatellites, can also cause problems, says Theodore G. Krontiris at Tufts University School of Medicine in B(7ston. Unusual variations in the number of one particular repeat are associated with one in 11 breast, colorectal, and bladder cancers, he and his colleagues report in the Aug. 19 NEW ENGLAND JOURNAL OF MEDICINE.

Krontiris and his colleagues examined a 28-base-pair repeat that occurs shortly aftera gene called HRASI. Nucleotide bases are the building blocks of a gene's DNA. HRAS1 codes for a protein that helps control the timing of cell division and differentiation. Tumors can develop when this gene doesn't work right, Krontiris says.

These 28 base pairs can repeat 30 to 100 times, creating at least 30 versions - or alleles - of this section of DNA. Earlier, Krontiris' group had shown that about 94 percent of all Caucasians possess one of four of these versions. In contrast, people with cancer are up to three times as likely as people without cancer to have different, rarer versions.

Krontiris and his colleagues have now strengthened the link between rare alieles and some cancers. They examined this part of the genetic code in 439 people with cancer and 390 people visiting the hospital for reasons other than cancer. In addition, they compiled and analyzed similar data from 22 other studies - 4,250 people all together - to assess the relationship between these rare alieles and cancer.

No single rare version correlates strongly with cancer, but taken together, rare alleles prove quite significant, says Krontiris. The association was strongest for bladder cancer.