ALLELES OF THE APC GENE - AN ATTENUATED FORM OF FAMILIAL POLYPOSIS

An attenuated form of familial adenomatous polyposis coli, AAPC, cause s relatively few colonic polyps, but still carries a significant risk of colon cancer. The mutant alleles responsible for this attenuated ph enotype have been mapped in several families to the adenomatous polypo sis coli (APC) locus on human chromosome 5q. Four distinct mutations i n the APC gene have now been identified in seven AAPC families. These mutations that predict truncation products, either by single base pair changes or frameshifts, are similar to mutations identified in famili es with classical APC. However, they differ in that the four mutated s ites are located very close to one another and nearer the 5' end of th e APC gene than any base substitutions or small deletions yet discover ed in patients with classical APC.