CORRELATION BETWEEN RELATIVES FOR COLORECTAL-CANCER MORTALITY IN FAMILIAL ADENOMATOUS POLYPOSIS

It has long been realized that age-specific cancer mortality in Famili al Adenomatous Polyposis (FAP) was bimodal, and a theory was proposed in which the involved locus was polymorphic in the general population. After the molecular cloning of the region 5q21. it has been suggested that the phenotypic variability in FAP may be due to the interaction of two loci, one of which is polymorphic. We show that these two hypot heses lead to different predictions of the correlation between relativ es for a phenotypic trait. and use colorectal cancer mortality data fr om the Italian Polyposes Registry to verify them. We conclude that the first of the two is more likely and suggest that the same variation t hat we observe among the affected subjects is present in the general p opulation, thus causing a significant difference between individuals f or colon cancer susceptibility.