A novel mouse model of PMS2 founder mutation that causes mismatch repair defect due to aberrant splicing

AbstractHereditary non-polyposis colorectal cancer, now known as Lynch syndrome (LS) is one of the most common cancer predisposition syndromes and is caused by germline pathogenic variants (GPVs) in DNA mismatch repair (MMR) genes. A common founder GPV in PMS2 in the Canadian Inuit population, NM_000535.5: c.2002A>G, leads to a benign missense (p.I668V) but also acts as a de novo splice site that creates a 5 bp deletion resulting in a truncated protein (p.I668*). Individuals homozygous for this GPV are predisposed to atypical constitutional MMR deficiency with a delayed onset of first primary malignancy. We have generated mice with an equivalent germline mutation (Pms2c.1993A>G) and demonstrate that it results in a splicing defect similar to those observed in humans. Homozygous mutant mice are viable like the Pms2 null mice. However, unlike the Pms2 null mice, these mutant mice are fertile, like humans homozygous for this variant. Furthermore, these mice exhibit a significant increase in microsatellite instability and intestinal adenomas on an Apc mutant background. Rectification of the splicing defect in human and murine fibroblasts using antisense morpholinos suggests that this novel mouse model can be valuable in evaluating the efficacy aimed at targeting the splicing defect in PMS2 that is highly prevalent among the Canadian Inuits.

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Determining the frequency of de novo germline mutations in DNA mismatch repair genes

Journal of Medical Genetics ◽

10.1136/jmedgenet-2011-100082 ◽

2011 ◽

Vol 48 (8) ◽

pp. 530-534 ◽

Cited By ~ 26

Author(s):

A. K. Win ◽

M. A. Jenkins ◽

D. D. Buchanan ◽

M. Clendenning ◽

J. P. Young ◽

...

Keyword(s):

Mismatch Repair ◽

De Novo ◽

Dna Mismatch Repair ◽

Germline Mutations ◽

Mismatch Repair Genes ◽

Dna Mismatch ◽

Dna Mismatch Repair Genes ◽

Repair Genes

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OMIC-08. COMPOUND HETEROZYGOSITY OF POLE AND PMS2 LEADS TO CMMRD-LIKE PHENOTYPE- “POLYNCH” SYNDROME

Neuro-Oncology ◽

10.1093/neuonc/noab090.155 ◽

2021 ◽

Vol 23 (Supplement_1) ◽

pp. i38-i39

Author(s):

Orli Michaeli ◽

Hagay Ladany ◽

Yosef E Maruvka ◽

Ayelet Erez ◽

Shay Ben Shachar ◽

...

Keyword(s):

Brain Tumors ◽

Lynch Syndrome ◽

Mismatch Repair ◽

De Novo ◽

Clinical Manifestations ◽

Dna Polymerase Epsilon ◽

Pathogenic Variants ◽

Repair Deficiency ◽

Mutation Burden ◽

Desmoplastic Medulloblastoma

Abstract Mono-allelic germline pathogenic variants (PV) in one of the mismatch repair (MMR) system genes cause Lynch syndrome, associated mainly with colon and endometrial cancer in adults. Germline PVs in DNA polymerase epsilon (POLE) are associated with a dominantly inherited syndrome which confers risk for polyposis and colon cancer. Brain tumors have been described as part of Lynch syndrome and POLE associated syndrome, mostly in adults. Constitutional mismatch repair deficiency (CMMRd) is caused by bi-allelic mutations in the MMR genes, associated with multiple café au lait macules (CAMs) and high incidence of pediatric cancer, including brain tumors. Both MMRD and POLE associated tumors have high tumor mutation burden (TMB), however, microsatellite status is usually unstable in MMR tumors, and stable in POLE. Germline POLE and CMMRd tumors have different mutational signatures, as is signature of MMR tumors with secondary somatic POLE. We describe a 4.5 y/o male who presented with a grossly metastatic SHH-activated, TP53-wildtype desmoplastic medulloblastoma. Physical examination was noted for CAMs. Family history was positive for a heterozygous POLE variant with variable clinical manifestations. Immunohistochemistry of the tumor showed loss of nuclear expression of the MMR gene PMS2, specifically in tumor cells. Analysis showed exceptionally high TMB (up to 276 Mut/Mb) and both the MMR and the POLE signatures. Germline analysis detected the familial POLE variant as well as a de novo heterozygous PMS2 PV. The phenotype of the patient together with the tumor’s features, led us to classify this case as a CMMRd-like. The patient had a partial response to intensive chemotherapy and is currently on immunotherapy without radiation. Collectively, our data suggest that heterozygous simultaneous germline mutations in MMR and polymerase genes can lead to novel “POLYNCH syndrome” that manifests with an ultra-hypermutant aggressive tumor and requires appropriate treatment and surveillance.

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Yield of Lynch Syndrome Surveillance for Patients With Pathogenic Variants in DNA Mismatch Repair Genes

Clinical Gastroenterology and Hepatology ◽

10.1016/j.cgh.2019.08.043 ◽

2020 ◽

Vol 18 (5) ◽

pp. 1112-1120.e1 ◽

Cited By ~ 4

Author(s):

Anne Goverde ◽

Ellis L. Eikenboom ◽

Ellemieke L. Viskil ◽

Marco J. Bruno ◽

Michael Doukas ◽

...

Keyword(s):

Lynch Syndrome ◽

Mismatch Repair ◽

Dna Mismatch Repair ◽

Mismatch Repair Genes ◽

Dna Mismatch ◽

Pathogenic Variants ◽

Dna Mismatch Repair Genes ◽

Syndrome Surveillance ◽

Repair Genes

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Oligonucleotide-directed mutagenesis screen to identify pathogenic Lynch syndrome-associated MSH2 DNA mismatch repair gene variants

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1520813113 ◽

2016 ◽

Vol 113 (15) ◽

pp. 4128-4133 ◽

Cited By ~ 19

Author(s):

Hellen Houlleberghs ◽

Marleen Dekker ◽

Hildo Lantermans ◽

Roos Kleinendorst ◽

Hendrikus Jan Dubbink ◽

...

Keyword(s):

Lynch Syndrome ◽

Mismatch Repair ◽

Dna Mismatch Repair ◽

Embryonic Stem ◽

Mismatch Repair Gene ◽

Missense Mutations ◽

Repair Gene ◽

Dna Mismatch ◽

Mmr Genes ◽

Pathogenic Variants

Single-stranded DNA oligonucleotides can achieve targeted base-pair substitution with modest efficiency but high precision. We show that “oligo targeting” can be used effectively to study missense mutations in DNA mismatch repair (MMR) genes. Inherited inactivating mutations in DNA MMR genes are causative for the cancer predisposition Lynch syndrome (LS). Although overtly deleterious mutations in MMR genes can clearly be ascribed as the cause of LS, the functional implications of missense mutations are often unclear. We developed a genetic screen to determine the pathogenicity of these variants of uncertain significance (VUS), focusing on mutator S homolog 2 (MSH2). VUS were introduced into the endogenous Msh2 gene of mouse embryonic stem cells by oligo targeting. Subsequent selection for MMR-deficient cells using the guanine analog 6-thioguanine allowed the detection of MMR-abrogating VUS. The screen was able to distinguish weak and strong pathogenic variants from polymorphisms and was used to investigate 59 Msh2 VUS. Nineteen of the 59 VUS were identified as pathogenic. Functional assays revealed that 14 of the 19 detected variants fully abrogated MMR activity and that five of the detected variants attenuated MMR activity. Implementation of the screen in clinical practice allows proper counseling of mutation carriers and treatment of their tumors.

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Do non-pathogenic variants of DNA mismatch repair genes modify neurofibroma load in neurofibromatosis type 1?

Child s Nervous System ◽

10.1007/s00381-021-05436-w ◽

2022 ◽

Author(s):

Anja Harder

Keyword(s):

Mismatch Repair ◽

Neurofibromatosis Type 1 ◽

Neurofibromatosis Type ◽

Tumour Suppressor Genes ◽

Gene Variants ◽

Single Nucleotide Variants ◽

Dna Mismatch ◽

Pathogenic Variants ◽

Patients At Risk

AbstractNon-pathogenic mismatch repair (MMR) gene variants can be associated with decreased MMR capacity in several settings. Due to an increased mutation rate, reduced MMR capacity leads to accumulation of somatic sequence changes in tumour suppressor genes such as in the neurofibromatosis type 1 (NF1) gene. Patients with autosomal dominant NF1 typically develop neurofibromas ranging from single to thousands. Concerning the number of neurofibromas NF1 patients face a situation that is still not predictable. A few studies suggested that germline non-pathogenic MMR gene variants modify the number of neurofibromas in NF1 and by this mechanism may promote the extent of neurofibroma manifestation. This review represents first evidence that specific non-pathogenic single nucleotide variants of MMR genes act as a modifier of neurofibroma manifestation in NF1, highlighting MSH2 re4987188 as the best analysed non-pathogenic variant so far. In summary, besides MSH2 promotor methylation, specific non-pathogenic germline MSH2 variants are associated with the extent of neurofibroma manifestation. Those variants can serve as a biomarker to facilitate better mentoring of NF1 patients at risk.

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Mismatch Repair Universal Screening of Endometrial Cancers (MUSE) in a Canadian Cohort

Current Oncology ◽

10.3390/curroncol28010052 ◽

2021 ◽

Vol 28 (1) ◽

pp. 509-522

Author(s):

Jessica Lawrence ◽

Lara Richer ◽

Jocelyne Arseneau ◽

Xing Zeng ◽

George Chong ◽

...

Keyword(s):

Mismatch Repair ◽

Screening Program ◽

Cost Effective ◽

Promoter Hypermethylation ◽

University Hospital ◽

Screening Criteria ◽

Cancer Predisposition Syndrome ◽

Dna Mismatch ◽

Pathogenic Variants ◽

Endometrial Cancers

Background: Approximately 2–6% of endometrial cancers (ECs) are due to Lynch Syndrome (LS), a cancer predisposition syndrome caused by germline pathogenic variants (PVs) affecting the DNA mismatch repair (MMR) pathway. Increasingly, universal tissue-based screening of ECs has been proposed as an efficient and cost-effective way to identify families with LS, though few studies have been published on Canadian cohorts. The purpose of this study was to evaluate the feasibility and overall performance of a universal immunohistochemistry (IHC) screening program for women with EC within a single Canadian university hospital centre. Methods and Results: From 1 October 2015 to 31 December 2017, all newly diagnosed ECs (n = 261) at our centre were screened for MMR protein deficiency by IHC. MMR deficiency was noted in 69 tumours (26.4%), among which 53 had somatic MLH1 promoter hypermethylation and were considered “screen-negative”. The remaining MMR-deficient cases (n = 16) were considered “screen-positive” and were referred for genetic counselling and testing. Germline PVs were identified in 12/16 (75%). One additional PV was identified in a screen-negative individual who was independently referred to the Genetics service. This corresponds to an overall LS frequency of 5.0% among unselected women with EC, and 6.4% among women diagnosed under age 70 years. Our algorithm detected MMR gene pathogenic variants in 4.6% and 6.2% of unselected individuals and individuals under age 70 years, respectively. Four germline PVs (30.8%) were identified in individuals who did not meet any traditional LS screening criteria. Conclusions: Universal IHC screening for women with EC is an effective and feasible method of identifying individuals with LS in a Canadian context.

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Potential drug cost impact of nivolumab (N) in Canada in patients with DNA mismatch repair deficient (dMMR) metastatic colorectal cancer (mCRC).

Journal of Clinical Oncology ◽

10.1200/jco.2018.36.4_suppl.797 ◽

2018 ◽

Vol 36 (4_suppl) ◽

pp. 797-797

Author(s):

Kiran Virik ◽

James Joseph Biagi ◽

Robert B Wilson

Keyword(s):

Mismatch Repair ◽

Drug Cost ◽

De Novo ◽

Dna Mismatch Repair ◽

Treated Patient ◽

Immune Checkpoints ◽

First Line ◽

Budgetary Impact ◽

Dna Mismatch ◽

The Cost

797 Background: The overall 5 year survival for mCRC remains poor (14%) despite the sequential use of chemotherapy and biologic agents. Immunotherapy is a promising treatment option in tumors with a high mutational burden. This includes mCRC DNA mismatch repair deficient tumors (dMMR). These have upregulation of immune checkpoints and a poorer prognosis. The CheckMate 142 phase II trial in pretreated dMMR mCRC patients showed durable responses and disease control across a number of subgroups including BRAF mutant tumors. The use of immunotherapy has an anticipated budgetary impact on health care systems within the context of this potentially funded utilization of N. Methods: An estimation of the N drug cost alone for new cases diagnosed in 2017 and treated upon relapse in Canada was undertaken. A cost estimate for N treatment in the first line of dMMR mCRC in relapses and de novo was undertaken should this be a future option. N cost per patient was calculated based on treatment indication, median number of cycles, standard dose/schedule. The analysis was performed in Canadian dollars ($) and assumed complete drug delivery and uncomplicated cycles. The cost of N was obtained from the pan Canadian Oncology Drug Review (pCODR) cost for N in lung cancer. The number of target patients and N utilization was derived from constructed schema to give a budget impact estimate. Results: Estimated N cost per treated patient is $91,667. The N drug cost for prior second line and third line relapsed chemotherapy treated patients respectively ranges from $23.6 Million (M) – $36.4M and $12.7M – $17.7M. For 1st line N: the cost of treating early stage dMMR CRC which subsequently recurs would be $49.1M and the cost for treatment of dMMR de novo mCRC would be $24.6M. A sensitivity analysis was performed. Conclusions: Immunotherapy drug costs in dMMR mCRC potentially add a substantial cost burden to the publicly funded Canadian healthcare system. As data evolves, longer duration of therapy and potential first line use will add further to the estimated budgetary impact.

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Escherichia coli mutator mutD5 is defective in the mutHLS pathway of DNA mismatch repair.

Genetics ◽

10.1093/genetics/121.2.205 ◽

1989 ◽

Vol 121 (2) ◽

pp. 205-212 ◽

Cited By ~ 3

Author(s):

R M Schaaper

Keyword(s):

Escherichia Coli ◽

Mismatch Repair ◽

Patch Repair ◽

Wild Type ◽

Mutator Strain ◽

Dna Mismatch ◽

Repair Deficiency ◽

In The Wild ◽

Mutator Strains ◽

Repair Defect

Abstract We have previously reported that the Escherichia coli mutator strain mutD5 was defective in the correction of bacteriophage M13mp2 heteroduplex DNA containing a T.G mismatch. Here, this defect was further investigated with regard to its interaction with the mutHLS pathway of mismatch repair. A set of 15 different M13mp2 heteroduplexes was used to measure the mismatch-repair capability of wild-type, mutL and mutD5 cells. Throughout the series, the mutD5 strain proved as deficient in mismatch repair as the mutL strain, indicating that the repair defect is similar in the two strains in both extent and specificity. [One exception was noted in the case a T.G mispair that was subject to VSP (Very Short Patch) repair. VSP repair was abolished by mutL but not by mutD.] Variation in the dam-methylation state of the heteroduplex molecules clearly affected repair in the wild-type strain but had no effect on either the mutD or mutL strain. Finally, mutDmutL or mutDmutS double-mutator strains were no more deficient in mismatch repair as were the single mutator strains. The combined results strongly argue that the mismatch-repair deficiency of mutD5 cells resides in the mutH,L,S-dependent pathway of mismatch repair and that the high mutation rate of mutD strains derives in part from this defect.

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