Deviations from the norm of germline APC allele-specific expression associate with colorectal cancer

Background and Aims - Germline variation in allele-specific expression (ASE) is associated with highly penetrant familial cancers, but its role in common sporadic cancers is unclear. ASE of the adenomatous polyposis coli (APC) gene plays a role in familial adenomatous polyposis coli. We hypothesized that moderate ASE variation in APC contributes to common forms of colorectal cancer (CRC). Patients and Methods - Denaturing high performance liquid chromatography (DHPLC) was employed for germline APC ASE analysis in CRC cases (n=53) and controls (n=68). Means, medians, and variances of ASE were compared. Mutation analysis and SNP genotyping were performed. Results - ASE distributions differed significantly between groups; cases had a significantly larger variance than controls (p = 0.0004). Importantly, CRC risk increased proportionally with the degree of deviation from the mean. Individuals with ASE deviating more than 1 SD from the mean had an odds ratio (OR) of 3.97 (1.71, 9.24 95% CI; p = 0.001); those deviating more than 1.645 SDs had an OR of 13.46 (1.76, 609.40 95% CI; p = 0.005). In support of these findings, sequence analysis revealed that a patient with marked ASE, who was negative for CRC family history, carried a nonsense APC mutation (p.Arg216X). Furthermore, APC genotyping showed that multiple SNPs were associated with ASE values and/or ASE variance in cases, but not in controls. Thus, cis variants may explain at least some of the ASE results. Conclusion - Our results indicate that imbalanced germline ASE of APC is more frequent in CRC patients than controls, and represents an indicator of risk for common forms of CRC.