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Background & Aims: Germline variants in mismatch repair genes MLH1, MSH2 (EPCAM), MSH6, or PMS2 cause Lynch syndrome. Patients with these variants have an increased risk of developing colorectal cancers (CRCs) that differ from sporadic CRCs in genetic and histologic features. It has been a challenge to study CRCs associated with PMS2 variants (PMS2-associated CRCs) because these develop less frequently and in older patients than CRCs with variants in other mismatch repair genes., Methods: We analyzed 20 CRCs associated with germline variants in PMS2, 22 sporadic CRCs, 18 CRCs with germline variants in MSH2, and 24 CRCs from patients with germline variants in MLH1. Tumor tissue blocks were collected from Dutch pathology departments in 2017. After extraction of tumor DNA, we used a platform designed to detect approximately 3,000 somatic hotspot variants in 55 genes (including KRAS, APC, CTNNB1, and TP53). Somatic variant frequencies were compared using the Fisher exact test., Results: None of the PMS2-associated CRCs contained any somatic variants in the catenin-β 1 gene (CTNNB1), which encodes β-catenin, whereas 14 of 24 MLH1-associated CRCs (58%) contained variants in CTNNB1. Half the PMS2-associated CRCs contained KRAS variants, but only 20% of these were in hotspots that encoded G12D or G13D. These hotspot variants occurred more frequently in CRCs associated with variants in MLH1 (37.5%; P = .44) and MSH2 (71.4%; P = .035) than in those associated with variants in PMS2., Conclusions: In a genetic analysis of 84 colorectal tumors, we found tumors from patients with PMS2-associated Lynch syndrome to be distinct from colorectal tumors associated with defects in other mismatch repair genes. This might account for differences in development and less frequent occurrence., (Copyright © 2018 AGA Institute. Published by Elsevier Inc. All rights reserved.)

We investigated the presence and patterns of mosaicism in the APC gene in patients with colon neoplasms not associated with any other genetic variants; we performed deep sequence analysis of APC in at least 2 adenomas or carcinomas per patient. We identified mosaic variants in APC in adenomas from 9 of the 18 patients with 21 to approximately 100 adenomas. Mosaic variants of APC were variably detected in leukocyte DNA and/or non-neoplastic intestinal mucosa of these patients. In a comprehensive sequence analysis of 1 patient, we found no evidence for mosaicism in APC in non-neoplastic intestinal mucosa. One patient was found to carry a mosaic c.4666dupA APC variant in only 10 of 16 adenomas, indicating the importance of screening 2 or more adenomas for genetic variants., (Copyright © 2017 AGA Institute. Published by Elsevier Inc. All rights reserved.)

Background & Aims: Biallelic mutations in the base excision DNA repair gene MUTYH lead to MUTYH-associated polyposis (MAP) and predisposition to colorectal cancer (CRC). Functional studies have demonstrated significant differences in base recognition and glycosylase activity between various MUTYH mutations, notably for the 2 mutations most frequently reported in MAP patients: Y179C and G396D (previously annotated as Y165C and G382D). Our goal was to establish correlations between genotypes and colorectal phenotype of patients with MAP., Methods: In this multicenter study, we analyzed genotype and phenotype data from 257 MAP patients. Data included age at presentation of MAP, polyp count, and the occurrence, location, and age at presentation of CRC., Results: Patients with a homozygous G396D mutation or compound heterozygous G396D/Y179C mutations presented later with MAP and had a significantly lower hazard of developing CRC than patients with a homozygous Y179C mutation (P < .001). The mean ages of CRC diagnosis in patients were 58 years (homozygous G396D) and 52 years (compound heterozygous G396D/Y179C) versus 46 years (homozygous Y179C; P = .001, linear regression)., Conclusions: Our study identified the phenotypic effects of Y179C as relatively severe and of G396D as relatively mild. These clinical data are in accord with findings from in vitro functional assays. Genotypic stratification may become useful in the development of guidelines for counseling, surveillance, and management of families with MAP.

Background & Aims: Recent genome-wide association studies have identified common low-risk variants for colorectal cancer (CRC). To assess whether these influence CRC risk in the Lynch syndrome, we genotyped these variants in a large series of proven mutation carriers., Methods: We studied 675 individuals from 127 different families from the Dutch Lynch syndrome Registry whose mutation carrier status was known. We genotyped 8q24.21, 8q23.3, 10p14, 11q23.1, 15q13.3, and 18q21.1 variants in carriers of a mismatch repair gene mutation. Univariate and multivariate analysis was used to analyse the association between the presence of a risk variant and CRC risk., Results: A significant association was found between CRC risk and rs16892766 (8q23.3) and rs3802842 (11q23.1). For rs16892766, possession of the C-allele was associated with an elevated risk of CRC in a dose-dependent fashion, with homozygosity for CC being associated with a 2.16-fold increased risk. For rs3802842, the increased risk of CRC associated with the C-allele was only found among female carriers, while CRC risk was substantially higher among homozygous (hazard ratio [HR] 3.08) than among heterozygous carriers of the C-allele (HR 1.49). In an additive model of both variants, the risk was significantly associated with the number of risk alleles (HR 1.60 for carriers of 2 or more risk alleles). The effects were stronger in female carriers than in male carriers., Conclusion: We have identified 2 loci that are significantly associated with CRC risk in Lynch syndrome families. These modifiers may be helpful in identifying high-risk individuals who require more intensive surveillance.