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Germline variants affecting the exonuclease domains of POLE and POLD1 predispose to multiple colorectal adenomas and/or colorectal cancer (CRC). The aim of this study was to estimate the prevalence of previously described heterozygous germline variants POLE c.1270C>G, p.(Leu424Val) and POLD1 c.1433G>A, p.(Ser478Asn) in a Dutch series of unexplained familial, early onset CRC and polyposis index cases. We examined 1188 familial CRC and polyposis index patients for POLE p.(Leu424Val) and POLD1 p.(Ser478Asn) variants using competitive allele-specific PCR. In addition, protein expression of the POLE and DNA mismatch repair genes was studied by immunohistochemistry in tumours from POLE carriers. Somatic mutations were screened using semiconductor sequencing. We detected three index patients (0.25%) with a POLE p.(Leu424Val) variant. In one patient, the variant was found to be de-novo. Tumours from three patients from two families were microsatellite instable, and immunohistochemistry showed MSH6/MSH2 deficiency suggestive of Lynch syndrome. Somatic mutations but no germline MSH6 and MSH2 variants were subsequently found, and one tumour displayed a hypermutator phenotype. None of the 1188 patients carried the POLD1 p.(Ser478Asn) variant. POLE germline variant carriers are also associated with a microsatellite instable CRC. POLE DNA analysis now seems warranted in microsatellite instable CRC, especially in the absence of a causative DNA mismatch repair gene germline variant. [ABSTRACT FROM AUTHOR]

DNA methylation is a hallmark in a subset of right-sided colorectal cancers. Methylation-based screening may improve prevention and survival rate for this type of cancer, which is often clinically asymptomatic in the early stages. We aimed to discover prognostic or diagnostic biomarkers for colon cancer by comparing DNA methylation profiles of right-sided colon tumours and paired normal colon mucosa using an 8.5 k CpG island microarray. We identified a diagnostic CpG-rich region, located in the first intron of the protein-tyrosine phosphatase gamma gene (PTPRG) gene, with altered methylation already in the adenoma stage, that is, before the carcinoma transition. Validation of this region in an additional cohort of 103 sporadic colorectal tumours and 58 paired normal mucosa tissue samples showed 94% sensitivity and 96% specificity. Interestingly, comparable results were obtained when screening a cohort of Lynch syndrome-associated cancers. Functional studies showed that PTPRG intron 1 methylation did not directly affect PTPRG expression, however, the methylated region overlapped with a binding site of the insulator protein CTCF. Chromatin immunoprecipitation (ChIP) showed that methylation of the locus was associated with absence of CTCF binding. Methylation-associated changes in CTCF binding to PTPRG intron 1 could have implications on tumour gene expression by enhancer blocking, chromosome loop formation or abrogation of its insulator function. The high sensitivity and specificity for the PTPRG intron 1 methylation in both sporadic and hereditary colon cancers support biomarker potential for early detection of colon cancer. [ABSTRACT FROM AUTHOR]