Inherited variants of MYH associated with somatic G:C-->T:A mutations in colorectal tumors.

Inherited defects of base excision repair have not been associated with any human genetic disorder, although mutations of the genes mutM and mutY, which function in Escherichia coli base excision repair, lead to increased transversions of G:C to T:A. We have studied family N, which is affected with multiple colorectal adenomas and carcinoma but lacks an inherited mutation of the adenomatous polyposis coli gene (APC) that is associated with familial adenomatous polyposis. Here we show that 11 tumors from 3 affected siblings contain 18 somatic inactivating mutations of APC and that 15 of these mutations are G:C-->A transversions--a significantly greater proportion than is found in sporadic tumors or in tumors associated with familial adenomatous polyposis.

Different combinations of biallelic APC mutation confer different growth advantages in colorectal tumours.

New facets to Knudson's [corrected] "two-hit" hypothesis have been proposed recently in relation to adenomatous polyposis coli (APC): protein inactivation may be selected weakly, and the two hits may be interdependent. We reviewed published data on 165 sporadic and 102 familial adenomatous polyposis-associated colorectal tumors with two characterized mutations. Using a Poisson model, we redefined the mutation cluster region (MCR) to residues 1281-1556 and confirmed that the locations of pairs of APC mutations are interdependent (P < 0.