Abstract
BackgroundFamilial adenomatous polyposis (FAP) is an autosomal dominant condition that predisposes patients to colorectal cancer. FAP is the result of a loss of APC function due to germline pathogenic variants disrupting gene expression. Genotype-phenotype correlations are described for FAP. For example attenuated forms of the disease are associated with pathogenic variants at the 5’ and 3’ ends of APC whilst severe forms of the disease appear to be linked to variants occurring in the mutation cluster region (MCR) of the gene. Variants occurring in the MCR are phenotypically associated with hundreds to thousands of adenomas carpeting the colon and rectum and patients harbouring changes in this region have a high propensity to develop colorectal cancer. Not all patients who carry pathogenic variants in this region have severe disease which may be a result of environmental factors. Alternatively, phenotypic variation observed in these patients could be due to modifier genes that either promote or inhibit disease expression. Mouse models of FAP have provided several plausible candidate modifier genes, but very few of these have survived scrutiny. One such genetic modifier that appears to be associated with disease expression is CD36. We previously reported a weak association between a polymorphism in CD36 and a later age of disease onset on a relatively small FAP patient cohort.MethodsIn the current study, we enlarged the FAP cohort. 395 patients all carrying pathogenic variants in APC were tested against three CD36 Single Nucleotide Polymorphisms (SNP)s (rs1049673, rs1761667 rs1984112), to determine if any of them were associated with differences in the age of disease expression.ResultsOverall, there appeared to be a statistically significant difference in the age of disease onset between carriers of the variant rs1984112 and wildtype. Furthermore, test equality of survivor functions for each SNP and mutation group suggested an interaction in the Log Rank, Wilcoxon, and Tarone-Ware methods for rs1049673, rs1761667, and rs1984112, thereby supporting the notion that CD36 modifies disease expression.ConclusionsThis study supports and strengthens our previous findings concerning CD36 and an association with disease onset in FAP, AFAP and FAP-MCR affected individuals. Knowledge about the role CD36 in adenoma development may provide greater insight into the development of colorectal cancer.
Highlights
Familial adenomatous polyposis (FAP) is an autosomal dominant condition that predisposes patients to colorectal cancer
We have previously reported tentative evidence that polymorphisms in Cluster of differentiation 36 (CD36) influence the age at which polyposis expression occurs [25], based on a relatively small population of patients with confirmed adenomatous polyposis coli (APC) pathogenic variants
Patient groups were divided according to the pathogenic variant site within APC, which correlated with phenotype: severe (FAP-mutation cluster region (MCR) bounded by codons 1250– 1513); attenuated (AFAP = 5’end spanning exons 3 to 5; 3’distal end and those in exon 9); and intermediate (FAP = the rest of the gene)
Summary
Familial adenomatous polyposis (FAP) is an autosomal dominant condition that predisposes patients to colorectal cancer. FAP is the result of a loss of APC function due to germline pathogenic variants disrupting gene expression. Variants occurring in the MCR are phenotypically associated with hundreds to thousands of adenomas carpeting the colon and rectum and patients harbouring changes in this region have a high propensity to develop colorectal cancer. Mouse models of FAP have provided several plausible candidate modifier genes, but very few of these have survived scrutiny. One such genetic modifier that appears to be associated with disease expression is CD36. After the identification of APC, the phenotype expanded to include variant forms of the disease, which ranged from very mild disease (reduced expressivity) to allelic variants that did not display overt polyposis [6,7,8,9,10,11]
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