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). 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.

BackgroundTranscript dosage imbalance may influence the transcriptome. To gain insight into the role of altered gene expression in hereditary colorectal polyposis predisposition, in the present study we analyzed absolute and allele-specific expression (ASE) of adenomatous polyposis coli (APC) and mutY Homolog (MUTYH) genes.MethodsWe analyzed DNA and RNA extracted from peripheral blood mononuclear cells (PBMC) of 49 familial polyposis patients and 42 healthy blood donors selected according similar gender and age. Patients were studied for germline alterations in both genes using dHPLC, MLPA and automated sequencing. APC and MUTYH mRNA expression levels were investigated by quantitative Real-Time PCR (qRT-PCR) analysis using TaqMan assay and by ASE assays using dHPLC-based primer extension.ResultsTwenty out of 49 patients showed germline mutations: 14 in APC gene and six in MUTYH gene. Twenty-nine patients did not show mutations in both genes. Results from qRT-PCR indicated that gene expression of both APC and MUTYH was reduced in patients analyzed. In particular, a significant reduction in APC expression was observed in patients without APC germline mutation vs control group (P < 0.05) while APC expression in the mutation carrier patients, although lower compared to control individuals, did not show statistical significance. On the other hand a significant reduced MUTYH expression was detected in patients with MUTYH mutations vs control group (P < 0.05). Altered ASE of APC was detected in four out of eight APC mutation carriers. In particular one case showed a complete loss of one allele. Among APC mutation negative cases, 4 out of 13 showed a moderate ASE. ASE of MUTYH did not show any altered expression in the cases analyzed. Spearman’s Rho Test analysis showed a positive and significant correlation between APC and MUTYH genes both in cases and in controls (P = 0.020 and P < 0.001).ConclusionsAPC and MUTYH showed a reduced germline expression, not always corresponding to gene mutation. Expression of APC is decreased in mutation negative cases and this appears to be a promising indicator of FAP predisposition, while for MUTYH gene, mutation is associated to reduced mRNA expression. This study could improve the predictive genetic diagnosis of at-risk individuals belonging to families with reduced mRNA expression regardless of presence of mutation.Electronic supplementary materialThe online version of this article (doi:10.1186/s13046-015-0244-4) contains supplementary material, which is available to authorized users.