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The large majority of germline alterations identified in the DNA mismatch repair (MMR) gene PMS2, a low-penetrance gene for the cancer predisposition Lynch syndrome, represent variants of uncertain significance (VUS). The inability to classify most VUS interferes with personalized healthcare. The complete in vitro MMR activity (CIMRA) assay, that only requires sequence information on the VUS, provides a functional analysis-based quantitative tool to improve the classification of VUS in MMR proteins. To derive a formula that translates CIMRA assay results into the odds of pathogenicity (OddsPath) for VUS in PMS2 we used a set of clinically classified PMS2 variants supplemented by inactivating variants that were generated by an in cellulo genetic screen, as proxies for cancer-predisposing variants. Validation of this OddsPath revealed high predictive values for benign and predisposing PMS2 VUS. We conclude that the OddsPath provides an integral metric that, following the other, higher penetrance, MMR proteins MSH2, MSH6 and MLH1 can be incorporated as strong evidence type into the upcoming criteria for MMR gene VUS classification of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP).

POLE mutations identified in endometrial cancers in the observation arm of the PORTEC-1 trial

Fluorescent In Situ Hybridization of Pole on metaphase spreads of Pole-mutant cell line

Supplementary Methods

Purpose: Pathogenic POLE proofreading domain mutations are found in many malignancies where they are associated with ultramutation and favorable prognosis. The extent to which this prognosis depends on their sensitivity to adjuvant treatment is unknown, as is the optimal therapy for advanced-staged or recurrent POLE-mutant cancers.Experimental Design: We examined the recurrence-free survival of women with POLE-mutant and POLE–wild-type endometrial cancers (EC) in the observation arm of the randomized PORTEC-1 endometrial cancer trial (N = 245 patients with stage I endometrial cancer for analysis). Sensitivity to radiotherapy and selected chemotherapeutics was compared between Pole-mutant mouse-derived embryonic stem (mES) cells, generated using CRISPR-Cas9 (Pole mutations D275A/E275A, and cancer-associated P286R, S297F, V411L) and isogenic wild-type cell lines.Results: In the observation arm of the PORTEC-1 trial (N = 245), women with POLE-mutant endometrial cancers (N = 16) had an improved recurrence-free survival (10-year recurrence-free survival 100% vs. 80.1% for POLE–wild-type; HR, 0.143; 95% confidence interval, 0.001–0.996; P = 0.049). Pole mutations did not increase sensitivity to radiotherapy nor to chemotherapeutics in mES cells. In contrast, Pole-mutant cells displayed significantly increased sensitivity to cytarabine and fludarabine (IC50 Pole P286R–mutant vs. wild-type: 0.05 vs. 0.17 μmol/L for cytarabine, 4.62 vs. 11.1 μmol/L for fludarabine; P < 0.001 for both comparisons).Conclusions: The favorable prognosis of POLE-mutant cancers cannot be explained by increased sensitivity to currently used adjuvant treatments. These results support studies exploring minimization of adjuvant therapy for early-stage POLE-mutant cancers, including endometrial and colorectal cancers. Conversely, POLE mutations result in hypersensitivity to nucleoside analogues, suggesting the use of these compounds as a potentially effective targeted treatment for advanced-stage POLE-mutant cancers. Clin Cancer Res; 24(13); 3197–203. ©2018 AACR.

A dietary mutagen induces loss of the wild-type allele in mismatch repair gene-heterozygous cells. This results in impaired DNA damage signaling and in compound hypermutagenesis. These findings provide insights into the etiology of colorectal carcinogenesis in Lynch syndrome.The prevalent cancer predisposition Lynch syndrome (LS, OMIM #120435) is caused by an inherited heterozygous defect in any of the four core DNA mismatch repair (MMR) genes MSH2, MSH6, MLH1 or PMS2. MMR repairs errors by the replicative DNA polymerases in all proliferating tissues. Its deficiency, following somatic loss of the wild-type copy, results in a spontaneous mutator phenotype that underlies the rapid development of, predominantly, colorectal cancer (CRC) in LS. Here, we have addressed the hypothesis that aberrant responses of intestinal stem cells to diet-derived mutagens may be causally involved in the restricted cancer tropism of LS. To test this we have generated a panel of isogenic mouse embryonic stem (mES) cells with heterozygous or homozygous disruption of multiple MMR genes and investigated their responses to the common dietary mutagen and carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Our data reveal that PhIP can inactivate the wild-type allele of heterozygous mES cells via the induction of either loss of heterozygosity (LOH) or intragenic mutations. Moreover, while protective DNA damage signaling (DDS) is compromised, PhIP induces more mutations in Msh2, Mlh1, Msh6 or Pms2-deficient mES cells than in wild-type cells. Combined with their spontaneous mutator phenotypes, this results in a compound hypermutator phenotype. Together, these results indicate that dietary mutagens may promote CRC development in LS at multiple levels, providing a rationale for dietary modifications in the management of LS.

The large majority of germline alterations identified in the DNA mismatch repair (MMR) gene PMS2, a low-penetrance gene for the cancer predisposition Lynch Syndrome (LS, OMIM 120435), represent variants of unknown significance (VUS). The inability to assess pathogenicity of such VUS interferes with personalized healthcare. The complete in vitro MMR activity (CIMRA) assay, that only requires sequence information on the VUS, provides a functional analysis-based tool suited for VUS classification. To derive a formula that translates CIMRA assay results for PMS2 VUS into the odds of pathogenicity (OddsPath), we used a set of clinically classified PMS2 variants, supplemented by inactivating variants generated by an in cellulo genetic screen, as proxies for pathogenic variants. Validation of this OddsPath revealed very high predictive values for PMS2 VUS. We conclude that this OddsPath provides an integral metric that, similar to the other, higher penetrance, MMR proteins MSH2, MLH1 and MSH6, can be incorporated into the upcoming criteria for MMR gene VUS classification of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP). This will represent a seminal step forward in enabling personalized healthcare for individuals suspected of LS and their relatives.

PURPOSE:To enhance classification of variants of uncertain significance (VUS) in the DNA mismatch repair (MMR) genes in the cancer predisposition Lynch syndrome, we developed the cell-free in vitro MMR activity (CIMRA) assay. Here, we calibrate and validate the assay, enabling its integration with in silico and clinical data.METHODS:Two sets of previously classified MLH1 and MSH2 variants were selected from a curated MMR gene database, and their biochemical activity determined by the CIMRA assay. The assay was calibrated by regression analysis followed by symmetric cross-validation and Bayesian integration with in silico predictions of pathogenicity. CIMRA assay reproducibility was assessed in four laboratories.RESULTS:Concordance between the training runs met our prespecified validation criterion. The CIMRA assay alone correctly classified 65% of variants, with only 3% discordant classification. Bayesian integration with in silico predictions of pathogenicity increased the proportion of correctly classified variants to 87%, without changing the discordance rate. Interlaboratory results were highly reproducible.CONCLUSION:The CIMRA assay accurately predicts pathogenic and benign MMR gene variants. Quantitative combination of assay results with in silico analysis correctly classified the majority of variants. Using this calibration, CIMRA assay results can be integrated into the diagnostic algorithm for MMR gene variants.KEYWORDS:Lynch syndrome; assay calibration; functional assay; variant classification; variants of uncertain significance

We describe a family severely affected by colorectal cancer (CRC) where whole‐exome sequencing identified the coinheritance of the germline variants encoding MSH6 p.Thr1100Met and MUTYH p.Tyr179Cys in, at least, three CRC patients diagnosed before 60 years of age. Digenic inheritance of monoallelic MSH6 variants of uncertain significance and MUTYH variants has been suggested to predispose to Lynch syndrome‐associated cancers; however, cosegregation with disease in the familial setting has not yet been established. The identification of individuals carrying multiple potential cancer risk variants is expected to rise with the increased application of whole‐genome sequencing and large multigene panel testing in clinical genetic counseling of familial cancer patients. Here we demonstrate the coinheritance of monoallelic variants in MSH6 and MUTYH consistent with cosegregation with CRC, further supporting a role for digenic inheritance in cancer predisposition.

Monoallelic PMS2 germline mutations cause 5-15% of Lynch syndrome, a midlife cancer predisposition, whereas biallelic PMS2 mutations cause approximately 60% of constitutional MMR deficiency (CMMRD), a rare childhood cancer syndrome. Recently improved DNA and RNA-based strategies are applied to overcome problematic PMS2 mutation analysis due to the presence of pseudogenes and frequent gene conversion events. Here, we determined PMS2 mutation detection yield and mutation spectrum in a nationwide cohort of 396 probands. Furthermore, we studied concordance between tumor IHC/ MSI (immunohistochemistry/ microsatellite-instability) profile and mutation carrier state. Overall, we found 52 different pathogenic PMS2 variants explaining 121 Lynch syndrome and nine CMMRD patients. In vitro MMR assays suggested pathogenicity for three missense variants. Ninety-one PMS2 mutation carriers (70%) showed isolated loss of PMS2 in their tumors, for 31 (24%) no or inconclusive IHC was available, and eight carriers (6%) showed discordant IHC (presence of PMS2 or loss of both MLH1 and PMS2). Ten cases with isolated PMS2 loss (10%; 10/97) harbored MLH1 mutations. We confirmed that recently improved mutation analysis provides a high yield of PMS2 mutations in patients with isolated loss of PMS2 expression. Application of universal tumor pre-screening methods will however miss some PMS2 germline mutation carriers. This article is protected by copyright. All rights reserved.

Purpose: Pathogenic POLE proofreading domain mutations are found in many malignancies where they are associated with ultramutation and favorable prognosis. The extent to which this prognosis depends on their sensitivity to adjuvant treatment is unknown, as is the optimal therapy for advanced-staged or recurrent POLE-mutant cancers. Experimental Design: We examined the recurrence-free survival of women with POLE-mutant and POLE–wild-type endometrial cancers (EC) in the observation arm of the randomized PORTEC-1 endometrial cancer trial (N = 245 patients with stage I endometrial cancer for analysis). Sensitivity to radiotherapy and selected chemotherapeutics was compared between Pole-mutant mouse-derived embryonic stem (mES) cells, generated using CRISPR-Cas9 (Pole mutations D275A/E275A, and cancer-associated P286R, S297F, V411L) and isogenic wild-type cell lines. Results: In the observation arm of the PORTEC-1 trial (N = 245), women with POLE-mutant endometrial cancers (N = 16) had an improved recurrence-free survival (10-year recurrence-free survival 100% vs. 80.1% for POLE–wild-type; HR, 0.143; 95% confidence interval, 0.001–0.996; P = 0.049). Pole mutations did not increase sensitivity to radiotherapy nor to chemotherapeutics in mES cells. In contrast, Pole-mutant cells displayed significantly increased sensitivity to cytarabine and fludarabine (IC50 Pole P286R–mutant vs. wild-type: 0.05 vs. 0.17 μmol/L for cytarabine, 4.62 vs. 11.1 μmol/L for fludarabine; P < 0.001 for both comparisons). Conclusions: The favorable prognosis of POLE-mutant cancers cannot be explained by increased sensitivity to currently used adjuvant treatments. These results support studies exploring minimization of adjuvant therapy for early-stage POLE-mutant cancers, including endometrial and colorectal cancers. Conversely, POLE mutations result in hypersensitivity to nucleoside analogues, suggesting the use of these compounds as a potentially effective targeted treatment for advanced-stage POLE-mutant cancers. Clin Cancer Res; 24(13); 3197–203. ©2018 AACR.

Variants that disrupt the translation initiation sequences in cancer predisposition genes are generally assumed to be deleterious. However, few studies have validated these assumptions with functional and clinical data. Two cancer syndrome gene variants likely to affect native translation initiation were identified by clinical genetic testing: MLH1:c.1A>G p.(Met1?) and BRCA2:c.67+3A>G. In vitro GFP-reporter assays were conducted to assess the consequences of translation initiation disruption on alternative downstream initiation codon usage. Analysis of MLH1:c.1A>G p.(Met1?) showed that translation was mostly initiated at an in-frame position 103 nucleotides downstream, but also at two ATG sequences downstream. The protein product encoded by the in-frame transcript initiating from position c.103 showed loss of in vitro mismatch repair activity comparable to known pathogenic mutations. BRCA2:c.67+3A>G was shown by mRNA analysis to result in an aberrantly spliced transcript deleting exon 2 and the consensus ATG site. In the absence of exon 2, translation initiated mostly at an out-of-frame ATG 323 nucleotides downstream, and to a lesser extent at an in-frame ATG 370 nucleotides downstream. Initiation from any of the downstream alternative sites tested in both genes would lead to loss of protein function, but further clinical data is required to confirm if these variants are associated with a high cancer risk. Importantly, our results highlight the need for caution in interpreting the functional and clinical consequences of variation that leads to disruption of the initiation codon, since translation may not necessarily occur from the first downstream alternative start site, or from a single alternative start site.

Lynch syndrome (LS) is a common cancer predisposition caused by an inactivating mutation in one of four DNA mismatch repair (MMR) genes. Frequently a variant of uncertain significance (VUS), rather than an obviously pathogenic mutation, is identified in one of these genes. The inability to define pathogenicity of such variants precludes targeted healthcare. Here, we have modified a cell-free assay to test VUS in the MMR gene PMS2 for functional activity. We have analyzed nearly all VUS in PMS2 found thus far and describe loss of MMR activity for five, suggesting the applicability of the assay for diagnosis of LS.

The year 1964 marks the birth of two lines of genetic research that converged nearly thirty years later, providing a prime example of the cross-fertilization between molecular genetics, biophysics, biochemistry, medical genetics, and medicine.

In clinical genetic diagnostics, it is difficult to predict whether genetic mutations that do not greatly alter the primary sequence of the encoded protein causing unknown functional effects on cognate proteins lead to development of disease. Here, we report the clinical identification of c.2038 T>C missense mutation in exon 18 of the human MLH1 gene and biochemically characterization of the p.Cys680Arg mutant MLH1 protein to implicate it in the pathogenicity of the Lynch syndrome (LS). We show that the mutation is deficient in DNA mismatch repair and, therefore, contributing to LS in the carriers.

Genetic testing of an Irish kindred identified an exonic nucleotide substitution c.1664T>C (p.Leu555Pro) in the MLH1 mismatch repair (MMR) gene. This previously unreported variant is classified as a “variant of uncertain significance” (VUS). Immunohistochemical (IHC) analysis and microsatellite instability (MSI) studies, genetic testing, a literature and online MMR mutation database review, in silico phenotype prediction tools, and an in vitro MMR activity assay were used to study the clinical significance of this variant. The MLH1 c.1664T>C (p.Leu555Pro) VUS co-segregated with three cases of classic Lynch syndrome-associated malignancies over two generations, with consistent loss of MLH1 and PMS2 protein expression on IHC, and evidence of the MSI-High mutator phenotype. The leucine at position 555 is well conserved across a number of species, and this novel variant has not been reported as a normal polymorphism in the general population. In silico and in vitro analyses suggest that this variant may have a deleterious effect on the MLH1 protein and abrogate MMR activity. Evidence from clinical, histological, immunohistochemical, and molecular genetic data suggests that MLH1 c.1664T>C (p.Leu555Pro) is likely to be the pathogenic cause of Lynch syndrome in this family.

In many individuals suspected of the common cancer predisposition Lynch syndrome, variants of unclear significance (VUS), rather than an obviously pathogenic mutations, are identified in one of the DNA mismatch repair (MMR) genes. The uncertainty of whether such VUS inactivate MMR, and therefore are pathogenic, precludes targeted healthcare for both carriers and their relatives. To facilitate the identification of pathogenic VUS, we have developed an in cellulo genetic screen-based procedure for the large-scale mutagenization, identification, and cataloging of residues of MMR genes critical for MMR gene function. When a residue identified as mutated in an individual suspected of Lynch syndrome is listed as critical in such a reverse diagnosis catalog, there is a high probability that the corresponding human VUS is pathogenic. To investigate the applicability of this approach, we have generated and validated a prototypic reverse diagnosis catalog for the MMR gene MutS Homolog 2 ( Msh2 ) by mutagenizing, identifying, and cataloging 26 deleterious mutations in 23 amino acids. Extensive in vivo and in vitro analysis of mutants listed in the catalog revealed both recessive and dominant-negative phenotypes. Nearly half of these critical residues match with VUS previously identified in individuals suspected of Lynch syndrome. This aids in the assignment of pathogenicity to these human VUS and validates the approach described here as a diagnostic tool. In a wider perspective, this work provides a model for the translation of personalized genomics into targeted healthcare.

Germline mutations in the human DNA mismatch repair (MMR) genes MSH2 and MLH1 are associated with the inherited cancer disorder Lynch syndrome (LS), also known as hereditary nonpolyposis colorectal cancer or HNPCC. A proportion of MSH2 and MLH1 mutations found in suspected LS patients give rise to single amino acid substitutions. The functional consequences in regard to pathogenicity of many of these variants are unclear. We have examined the functionality of a panel of MLH1 missense mutations found in LS families, by testing the variant proteins in functional assays, addressing subcellular localization, and protein-protein interaction with the dimer partner PMS2 and the MMR-associated exonuclease 1. We show that a significant proportion of examined variant proteins have functional defects in either subcellular localization or protein-protein interactions, which is suspected to lead to the cancer phenotype observed in patients. Moreover, the obtained results correlate well with reported MMR activity and with in silico analysis for a majority of the variants. Hum Mutat 33:1647-1655, 2012. © 2012 Wiley Periodicals, Inc.

Lynch syndrome (LS) is an autosomal dominant disorder that predisposes to colon, endometrial, and other cancers. LS is caused by a heterozygous germline mutation in one of the DNA mismatch repair (MMR) genes. A significant proportion of all mutations found in suspected LS patients comprises single amino acid alterations. The pathogenicity of these variants of uncertain significance (VUS) is difficult to assess, precluding diagnosis of carriers and their relatives. Here we present a rapid cell-free assay to investigate MMR activity of MSH2 or MSH6 VUS. We used this assay to analyze a series of MSH2 and MSH6 VUS, selected from the Leiden Open Variation Database. Whereas a significant fraction of the MSH2 VUS has lost MMR activity, suggesting pathogenicity, the large majority of the MSH6 VUS appears MMR proficient. We anticipate that this assay will be an important tool in the development of a comprehensive and widely applicable diagnostic procedure for LS-associated VUS. Hum Mutat 33:488494, 2012. (C) 2011 Wiley Periodicals, Inc.

The hereditary colon and endometrium cancer predisposition Lynch Syndrome (also called HNPCC) is caused by a germ-line mutation in one of the DNA mismatch repair (MMR) genes. A significant fraction of the gene alterations detected in suspected Lynch Syndrome patients is comprised of amino acid substitutions. The relevance for cancer risk of these variants is difficult to assess, as currently no time- and cost-effective, validated, and widely applicable functional assays for the measurement of MMR activity are available. Here we describe a rapid, cell-free, and easily quantifiable MMR activity assay for the diagnostic assessment of variants of the MLH1 MMR protein. This assay allows the parallel generation and functional analysis of a series of variants of the MLH1 protein in vitro using readily available, or preprepared, reagents. Using this assay we have tested 26 MLH1 variants and of these, 15 had lost activity. These results are in concordance with those obtained from first-generation assays and with in silico and pathology data. After its multifocal technical and clinical validation this assay could have great impact for the diagnosis and counseling of carriers of an MLH1 variant and their relatives.