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A multilocus test of genetic association is proposed, which can account for genetic effects that might be modified by variants in other genes or by environmental factors. The powerful advantages of this method is demonstrated both in analysis of data from a case-control study of the association between colorectal adenoma and DNA variants in the NAT2 genomic region that are well known to be related to a common biological phenotype and under different models of gene-gene interactions with use of simulated data.

Familial adenomatous polyposis (FAP) classification is a diagnosis nightmare. A colon-cancer-prone family with a tendency to form small, right-sided adenomas was described in 1988 and eventually the problem was linked to the APC gene with mutations nearer the 5' end. Three classes of APC mutations exist in kindreds having an attenuated phenotype. The range of numbers of adenomas found in those with mutations is very large. Those in practice must be aware of the broad range of signs and symptoms that FAP can present clinically and be aware that classical prophylactic and surveillance practices are not adequate for all cases of FAP. Early upper endoscopy is needed for some families. Those classified as attenuated familial adenomatous polyposis (AFAP) patients should have colonoscopy and polypectomy and if the number of colonic adenomas is so large that they cannot be followed by that means, prophylactic subtotal colectomy with continued follow-up of the rectal segment by endoscopy should be used.