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Ahadova A, Stenzinger A, Seppälä T, Hüneburg R, Kloor M, Bläker H. A "Two-in-One Hit" Model of Shortcut Carcinogenesis in MLH1 Lynch Syndrome Carriers. Gastroenterology 2023; 165:267-270.e4. [PMID: 36907525 DOI: 10.1053/j.gastro.2023.03.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 02/24/2023] [Accepted: 03/05/2023] [Indexed: 03/14/2023]
Affiliation(s)
- Aysel Ahadova
- Department of Applied Tumor Biology, Institute of Pathology, Heidelberg University Hospital, Clinical Cooperation Unit Applied Tumor Biology, German Cancer Research Centre, Heidelberg, Germany
| | - Albrecht Stenzinger
- Institute of Pathology, Heidelberg University Hospital, German Cancer Consortium and German Cancer Research Center, Heidelberg, Germany
| | - Toni Seppälä
- Faculty of Medicine and Health Technology, Tampere University, Tays Cancer Center, Tampere University Hospital, Tampere, Finland; Applied Tumor Genomics Research Program, Department of Surgery, Abdominal Center, Helsinki University Hospital, Helsinki, Finland
| | - Robert Hüneburg
- National Center for Hereditary Tumor Syndromes, Department of Internal Medicine I, University Hospital Bonn, Bonn, Germany
| | - Matthias Kloor
- Department of Applied Tumor Biology, Institute of Pathology, Heidelberg University Hospital, Clinical Cooperation Unit Applied Tumor Biology, German Cancer Research Centre (DKFZ), Heidelberg, Germany.
| | - Hendrik Bläker
- Institute of Pathology, University Hospital Leipzig, Leipzig, Germany
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Kenyon J, Nickel-Meester G, Qing Y, Santos-Guasch G, Drake E, PingfuFu, Sun S, Bai X, Wald D, Arts E, Gerson SL. Epigenetic Loss of MLH1 Expression in Normal Human Hematopoietic Stem Cell Clones is Defined by the Promoter CpG Methylation Pattern Observed by High-Throughput Methylation Specific Sequencing. ACTA ACUST UNITED AC 2016; 3. [PMID: 27570841 PMCID: PMC4996274 DOI: 10.23937/2469-570x/1410031] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Normal human hematopoietic stem and progenitor cells (HPC) lose expression of MLH1, an important mismatch repair (MMR) pathway gene, with age. Loss of MMR leads to replication dependent mutational events and microsatellite instability observed in secondary acute myelogenous leukemia and other hematologic malignancies. Epigenetic CpG methylation upstream of the MLH1 promoter is a contributing factor to acquired loss of MLH1 expression in tumors of the epithelia and proximal mucosa. Using single molecule high-throughput bisulfite sequencing we have characterized the CpG methylation landscape from −938 to −337 bp upstream of the MLH1 transcriptional start site (position +0), from 30 hematopoietic colony forming cell clones (CFC) either expressing or not expressing MLH1. We identify a correlation between MLH1 promoter methylation and loss of MLH1 expression. Additionally, using the CpG site methylation frequencies obtained in this study we were able to generate a classification algorithm capable of sorting the expressing and non-expressing CFC. Thus, as has been previously described for many tumor cell types, we report for the first time a correlation between the loss of MLH1 expression and increased MLH1 promoter methylation in CFC derived from CD34+ selected hematopoietic stem and progenitor cells.
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Affiliation(s)
- Jonathan Kenyon
- Department of Pathology, Case Western Reserve University, Cleveland, OH, 44106, USA; Division of Hematology and Oncology, Case Western Reserve University, Cleveland, OH, 44106, USA; Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Gabrielle Nickel-Meester
- Division of Infectious Disease, Department of Medicine, Case School of Medicine and the Center for AIDS Research, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Yulan Qing
- Division of Hematology and Oncology, Case Western Reserve University, Cleveland, OH, 44106, USA; Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Gabriela Santos-Guasch
- Division of Hematology and Oncology, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Ellen Drake
- Division of Hematology and Oncology, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - PingfuFu
- Department of Epidemiology & Biostatistics, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Shuying Sun
- Department of Mathematics, Texas State University, San Marcos, TX, 78666, USA
| | - Xiaodong Bai
- RNA Center, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - David Wald
- Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, OH, 44106, USA; Center for Stem Cell and Regenerative Medicine, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, OH, 44106, USA
| | - Eric Arts
- Division of Infectious Disease, Department of Medicine, Case School of Medicine and the Center for AIDS Research, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Stanton L Gerson
- Department of Pathology, Case Western Reserve University, Cleveland, OH, 44106, USA; Division of Hematology and Oncology, Case Western Reserve University, Cleveland, OH, 44106, USA; Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, OH, 44106, USA; Center for Stem Cell and Regenerative Medicine, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, OH, 44106, USA; Seidman Cancer Center, University Hospitals of Cleveland, Cleveland, OH, 44106, USA
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Sijmons RH, Greenblatt MS, Genuardi M. Gene variants of unknown clinical significance in Lynch syndrome. An introduction for clinicians. Fam Cancer 2014; 12:181-7. [PMID: 23525798 DOI: 10.1007/s10689-013-9629-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Clinicians referring patients for genetic testing for Lynch syndrome will sooner or later receive results for DNA Mismatch Repair (MMR) genes reporting DNA changes that are unclear from a clinical point of view. These changes are referred to as variants of unknown, or unclear, clinical significance (VUS). In contrast to clearly pathogenic mutations, VUS do not firmly diagnose Lynch syndrome at the molecular level and cannot be used to identify with certainty any of the patients' asymptomatic relatives as Lynch syndrome mutation carriers. The International database that collects MMR gene variants ( www.insight-group.org/mutations ) already lists more than 1,000 different VUSs and these variants are likely the tip of the iceberg. This paper aims at introducing non-geneticist clinicians to the topic of clinical MMR gene variant interpretation. Many lines of evidence are being used to classify VUS. Some are already familiar to clinicians and others may be less familiar but are expected to become important in clinical genetics in the coming years. Clinicians can play an important role in collecting the data needed to interpret the MMR variants detected in their patients.
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Affiliation(s)
- Rolf H Sijmons
- Department of Genetics, University Medical Center Groningen, University of Groningen, Hanzeplein 1, Groningen, The Netherlands.
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Functional analysis in mouse embryonic stem cells reveals wild-type activity for three MSH6 variants found in suspected Lynch syndrome patients. PLoS One 2013; 8:e74766. [PMID: 24040339 PMCID: PMC3769292 DOI: 10.1371/journal.pone.0074766] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2011] [Accepted: 08/06/2013] [Indexed: 02/02/2023] Open
Abstract
Lynch syndrome confers an increased risk to various types of cancer, in particular early onset colorectal and endometrial cancer. Mutations in mismatch repair (MMR) genes underlie Lynch syndrome, with the majority of mutations found in MLH1 and MSH2. Mutations in MSH6 have also been found but these do not always cause a clear cancer predisposition phenotype and MSH6-defective tumors often do not show the standard characteristics of MMR deficiency, such as microsatellite instability. In particular, the consequences of MSH6 missense mutations are challenging to predict, which further complicates genetic counseling. We have previously developed a method for functional characterization of MSH2 missense mutations of unknown significance. This method is based on endogenous gene modification in mouse embryonic stem cells using oligonucleotide-directed gene targeting, followed by a series of functional assays addressing the MMR functions. Here we have adapted this method for the characterization of MSH6 missense mutations. We recreated three MSH6 variants found in suspected Lynch syndrome families, MSH6-P1087R, MSH6-R1095H and MSH6-L1354Q, and found all three to behave like wild type MSH6. Thus, despite suspicion for pathogenicity from clinical observations, our approach indicates these variants are not disease causing. This has important implications for counseling of mutation carriers.
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Colas C, Coulet F, Svrcek M, Collura A, Fléjou JF, Duval A, Hamelin R. Lynch or not Lynch? Is that always a question? Adv Cancer Res 2012; 113:121-66. [PMID: 22429854 DOI: 10.1016/b978-0-12-394280-7.00004-x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The familial cancer syndrome referred to as Lynch I and II was renamed hereditary nonpolyposis colorectal cancer (HNPCC) only to revert later to Lynch syndrome (LS). LS is the most frequent human predisposition for the development of colorectal cancer (CRC), and probably also for endometrial and gastric cancers, although it has yet to acquire a consensus name. Its estimated prevalence ranges widely from 2% to 7% of all CRCs due to the fact that tumors from patients with LS are difficult to recognize at both the clinical and molecular level. This review is based on two assumptions. First, all LS patients inherit a predisposition to develop CRC (without polyposis) and/or other tumors from the Lynch spectrum. Second, all LS patients have a germline defect in one of the DNA mismatch repair (MMR) genes. When a somatic second hit inactivates the relevant MMR gene, the consequence is instability of DNA repeat sequences such as microsatellites and the tumors are referred to as having the microsatellite instability (MSI) phenotype. However, some of the inherited predisposition to develop CRC without concurrent polyposis, termed HNPCC, is found in non-LS patients, while not all MSI tumors are from LS cases. LS tumors are therefore at the junction of inherited and MSI cases. We describe here the defining characteristics of LS tumors that differentiate them from inherited non-MSI tumors and from non-inherited MSI tumors.
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Affiliation(s)
- Chrystelle Colas
- INSERM, UMRS 938, Centre de Recherche Saint-Antoine, Equipe Instabilité des Microsatellites et Cancers, Paris, France
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Funkhouser WK, Lubin IM, Monzon FA, Zehnbauer BA, Evans JP, Ogino S, Nowak JA. Relevance, pathogenesis, and testing algorithm for mismatch repair-defective colorectal carcinomas: a report of the association for molecular pathology. J Mol Diagn 2012; 14:91-103. [PMID: 22260991 DOI: 10.1016/j.jmoldx.2011.11.001] [Citation(s) in RCA: 132] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2011] [Revised: 10/04/2011] [Accepted: 11/09/2011] [Indexed: 02/06/2023] Open
Abstract
Loss-of-function defects in DNA mismatch repair (MMR), which manifest as high levels of microsatellite instability (MSI), occur in approximately 15% of all colorectal carcinomas (CRCs). This molecular subset of CRC characterizes patients with better stage-specific prognoses who experience no benefit from 5-fluorouracil chemotherapy. Most MMR-deficient (dMMR) CRCs are sporadic, but 15% to 20% are due to inherited predisposition (Lynch syndrome). High penetrance of CRCs in germline MMR gene mutation carriers emphasizes the importance of accurate diagnosis of Lynch syndrome carriers. Family-based (Amsterdam), patient/family-based (Bethesda), morphology-based, microsatellite-based, and IHC-based screening criteria do not individually detect all germline mutation carriers. These limitations support the use of multiple concurrent tests and the screening of all patients with newly diagnosed CRC. This approach is resource intensive but would increase detection of inherited and de novo germline mutations to guide family screening. Although CRC prognosis and prediction of 5-fluorouracil response are similar in both the Lynch and sporadic dMMR subgroups, these subgroups differ significantly with regard to the implications for family members. We recommend that new CRCs should be classified into sporadic MMR-proficient, sporadic dMMR, or Lynch dMMR subgroups. The concurrent use of MSI testing, MMR protein IHC, and BRAF c.1799T>A mutation analysis would detect almost all dMMR CRCs, would classify 94% of all new CRCs into these MMR subgroups, and would guide secondary molecular testing of the remainder.
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Affiliation(s)
- William K Funkhouser
- Mismatch Repair-Defective CRC Working Group of the Association for Molecular Pathology Clinical Practice Committee, University of North Carolina, Chapel Hill, North Carolina, USA.
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Lefevre JH, Colas C, Coulet F, Bonilla C, Mourra N, Flejou JF, Tiret E, Bodmer W, Soubrier F, Parc Y. MYH biallelic mutation can inactivate the two genetic pathways of colorectal cancer by APC or MLH1 transversions. Fam Cancer 2011; 9:589-94. [PMID: 20640893 DOI: 10.1007/s10689-010-9367-0] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
MYH associated polyposis is a hereditary syndrome responsible for early colorectal cancer with a distinct genetic pathway from the Familial Adenomatous Polyposis or the Hereditary Non Polyposis Colorectal Cancer syndrome. We have studied a family with three members bearing a biallelic mutation in MYH at c.1185_1186dup. One patient who developed colon cancer had loss of expression of MLH1 on tumoral tissue and microsatellite instability (MSI) phenotype. Analysis of MLH1 based on his blood sample revealed no germline mutation or large genomic deletion. No methylation of the promoter was identified in tumoral DNA. No transversion mutations were identified in APC or KRAS in tumor DNA of this patient. Loss of expression of MLH1 was due to a transversion in intron 7 at position +5 (c.588 + 5G > T) leading to a complete deletion of exon 7 at the RNA level. This observation demonstrates that MLH1 can be a target of MYH transversions leading to MSI phenotype.
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Affiliation(s)
- Jérémie H Lefevre
- Department of Digestive Surgery, Hôpital Saint-Antoine AP-HP, University Pierre et Marie Curie Paris VI, 184 rue du Faubourg Saint-Antoine, 75571 Paris, France.
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Borràs E, Pineda M, Blanco I, Jewett EM, Wang F, Teulé A, Caldés T, Urioste M, Martínez-Bouzas C, Brunet J, Balmaña J, Torres A, Ramón y Cajal T, Sanz J, Pérez-Cabornero L, Castellví-Bel S, Alonso A, Lanas A, González S, Moreno V, Gruber SB, Rosenberg NA, Mukherjee B, Lázaro C, Capellá G. MLH1 founder mutations with moderate penetrance in Spanish Lynch syndrome families. Cancer Res 2010; 70:7379-91. [PMID: 20858721 DOI: 10.1158/0008-5472.can-10-0570] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The variants c.306+5G>A and c.1865T>A (p.Leu622His) of the DNA repair gene MLH1 occur frequently in Spanish Lynch syndrome families. To understand their ancestral history and clinical effect, we performed functional assays and a penetrance analysis and studied their genetic and geographic origins. Detailed family histories were taken from 29 carrier families. Functional analysis included in silico and in vitro assays at the RNA and protein levels. Penetrance was calculated using a modified segregation analysis adjusted for ascertainment. Founder effects were evaluated by haplotype analysis. The identified MLH1 c.306+5G>A and c.1865T>A (p.Leu622His) variants are absent in control populations and segregate with the disease. Tumors from carriers of both variants show microsatellite instability and loss of expression of the MLH1 protein. The c.306+5G>A variant is a pathogenic mutation affecting mRNA processing. The c.1865T>A (p.Leu622His) variant causes defects in MLH1 expression and stability. For both mutations, the estimated penetrance is moderate (age-cumulative colorectal cancer risk by age 70 of 20.1% and 14.1% for c.306+5G>A and of 6.8% and 7.3% for c.1865T>A in men and women carriers, respectively) in the lower range of variability estimated for other pathogenic Spanish MLH1 mutations. A common haplotype was associated with each of the identified mutations, confirming their founder origin. The ages of c.306+5G>A and c.1865T>A mutations were estimated to be 53 to 122 and 12 to 22 generations, respectively. Our results confirm the pathogenicity, moderate penetrance, and founder origin of the MLH1 c.306+5G>A and c.1865T>A mutations. These findings have important implications for genetic counseling and molecular diagnosis of Lynch syndrome.
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Affiliation(s)
- Ester Borràs
- Laboratori de Recerca Translacional, Institut Català d'Oncologia, IDIBELL, Hospitalet de Llobregat, Barcelona, Spain
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De Grassi A, Segala C, Iannelli F, Volorio S, Bertario L, Radice P, Bernard L, Ciccarelli FD. Ultradeep sequencing of a human ultraconserved region reveals somatic and constitutional genomic instability. PLoS Biol 2010; 8:e1000275. [PMID: 20052272 PMCID: PMC2794366 DOI: 10.1371/journal.pbio.1000275] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2009] [Accepted: 11/24/2009] [Indexed: 12/27/2022] Open
Abstract
Ultradeep sequencing of genomes permits the detection of very low-level genomic instability in non-neoplastic tissues of patients with the most common form of inherited colorectal cancer. Early detection of cancer-associated genomic instability is crucial, particularly in tumour types in which this instability represents the essential underlying mechanism of tumourigenesis. Currently used methods require the presence of already established neoplastic cells because they only detect clonal mutations. In principle, parallel sequencing of single DNA filaments could reveal the early phases of tumour initiation by detecting low-frequency mutations, provided an adequate depth of coverage and an effective control of the experimental error. We applied ultradeep sequencing to estimate the genomic instability of individuals with hereditary non-polyposis colorectal cancer (HNPCC). To overcome the experimental error, we used an ultraconserved region (UCR) of the human genome as an internal control. By comparing the mutability outside and inside the UCR, we observed a tendency of the ultraconserved element to accumulate significantly fewer mutations than the flanking segments in both neoplastic and nonneoplastic HNPCC samples. No difference between the two regions was detectable in cells from healthy donors, indicating that all three HNPCC samples have mutation rates higher than the healthy genome. This is the first, to our knowledge, direct evidence of an intrinsic genomic instability of individuals with heterozygous mutations in mismatch repair genes, and constitutes the proof of principle for the development of a more sensitive molecular assay of genomic instability. In hereditary non-polyposis colorectal cancer (HNPCC), a germline mutation in one allele of a gene responsible for repairing DNA damage predisposes the host to cancer, because subsequent somatic inactivation of the one wild-type allele leads to genomic instability that favours tumourigenesis. Nonneoplastic tissues of HNPCC individuals are believed to repair DNA normally, as they are heterozygous and thus are thought to be genomically stable. However, methods used to date are known to be incapable of detecting very low levels of genome instability. Here, we present a more sensitive procedure based on the resequencing of a HNPCC genomic region using next-generation sequencing technology. With this approach, we show that genomic instability is in fact detectable in nonneoplastic tissues of HNPCC patients compared with healthy donors. This constitutional instability may predispose them to acquiring the second somatic mutation event needed for cancer development.
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Affiliation(s)
- Anna De Grassi
- Department of Experimental Oncology, European Institute of Oncology, Milan, Italy
| | - Cinzia Segala
- Department of Experimental Oncology, European Institute of Oncology, Milan, Italy
| | - Fabio Iannelli
- Department of Experimental Oncology, European Institute of Oncology, Milan, Italy
| | - Sara Volorio
- IFOM, Fondazione Istituto FIRC di Oncologia Molecolare, IFOM-IEO Campus, Milan, Italy
| | - Lucio Bertario
- Hereditary Colorectal Tumor Registry; Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy
| | - Paolo Radice
- IFOM, Fondazione Istituto FIRC di Oncologia Molecolare, IFOM-IEO Campus, Milan, Italy
- Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy
| | - Loris Bernard
- Department of Experimental Oncology, European Institute of Oncology, Milan, Italy
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Zavodna K, Krivulcik T, Bujalkova MG, Slamka T, Martinicky D, Ilencikova D, Bartosova Z. Partial loss of heterozygosity events at the mutated gene in tumors from MLH1/MSH2 large genomic rearrangement carriers. BMC Cancer 2009; 9:405. [PMID: 19930554 PMCID: PMC2788582 DOI: 10.1186/1471-2407-9-405] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2009] [Accepted: 11/20/2009] [Indexed: 11/24/2022] Open
Abstract
Background Depending on the population studied, large genomic rearrangements (LGRs) of the mismatch repair (MMR) genes constitute various proportions of the germline mutations that predispose to hereditary non-polyposis colorectal cancer (HNPCC). It has been reported that loss of heterozygosity (LOH) at the LGR region occurs through a gene conversion mechanism in tumors from MLH1/MSH2 deletion carriers; however, the converted tracts were delineated only by extragenic microsatellite markers. We sought to determine the frequency of LGRs in Slovak HNPCC patients and to study LOH in tumors from LGR carriers at the LGR region, as well as at other heterozygous markers within the gene to more precisely define conversion tracts. Methods The main MMR genes responsible for HNPCC, MLH1, MSH2, MSH6, and PMS2, were analyzed by MLPA (multiplex ligation-dependent probe amplification) in a total of 37 unrelated HNPCC-suspected patients whose MLH1/MSH2 genes gave negative results in previous sequencing experiments. An LOH study was performed on six tumors from LGR carriers by combining MLPA to assess LOH at LGR regions and sequencing to examine LOH at 28 SNP markers from the MLH1 and MSH2 genes. Results We found six rearrangements in the MSH2 gene (five deletions and dup5-6), and one aberration in the MLH1 gene (del5-6). The MSH2 deletions were of three types (del1, del1-3, del1-7). We detected LOH at the LGR region in the single MLH1 case, which was determined in a previous study to be LOH-negative in the intragenic D3S1611 marker. Three tumors displayed LOH of at least one SNP marker, including two cases that were LOH-negative at the LGR region. Conclusion LGRs accounted for 25% of germline MMR mutations identified in 28 Slovakian HNPCC families. A high frequency of LGRs among the MSH2 mutations provides a rationale for a MLPA screening of the Slovakian HNPCC families prior scanning by DNA sequencing. LOH at part of the informative loci confined to the MLH1 or MSH2 gene (heterozygous LGR region, SNP, or microsatellite) is a novel finding and can be regarded as a partial LOH. The conversion begins within the gene, and the details of conversion tracts are discussed for each case.
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Affiliation(s)
- Katarina Zavodna
- Laboratory of Cancer Genetics, Cancer Research Institute of Slovak Academy of Sciences, Vlarska 7, 833 91 Bratislava, Slovak Republic.
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Abstract
Colorectal cancers (CRC)--and probably all cancers--are caused by alterations in genes. This includes activation of oncogenes and inactivation of tumor suppressor genes (TSGs). There are many ways to achieve these alterations. Oncogenes are frequently activated by point mutation, gene amplification, or changes in the promoter (typically caused by chromosomal rearrangements). TSGs are typically inactivated by mutation, deletion, or promoter methylation, which silences gene expression. About 15% of CRC is associated with loss of the DNA mismatch repair system, and the resulting CRCs have a unique phenotype that is called microsatellite instability, or MSI. This paper reviews the types of genetic alterations that can be found in CRCs and hepatocellular carcinoma (HCC), and focuses upon the epigenetic alterations that result in promoter methylation and the CpG island methylator phenotype (CIMP). The challenge facing CRC research and clinical care at this time is to deal with the heterogeneity and complexity of these genetic and epigenetic alterations, and to use this information to direct rational prevention and treatment strategies.
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Affiliation(s)
- Clement Richard Boland
- Division of Gastroenterology, Department of Internal Medicine, Sammons Cancer Center, Baylor Research Institute, Baylor University Medical Center, 3500 Gaston Avenue, Dallas, TX 75246, USA.
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12
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Hofstra RMW, Spurdle AB, Eccles D, Foulkes WD, de Wind N, Hoogerbrugge N, Hogervorst FBL. Tumor characteristics as an analytic tool for classifying genetic variants of uncertain clinical significance. Hum Mutat 2008; 29:1292-303. [PMID: 18951447 DOI: 10.1002/humu.20894] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
It is important to identify a germline mutation in a patient with an inherited cancer syndrome to allow mutation carriers to be included in cancer surveillance programs, which have been proven to save lives. Many of the mutations identified result in premature termination of translation, and thus in loss-of-function of the encoded mutated protein. However, the significance of a large proportion of the sequence changes reported is unknown. Some of these variants will be associated with a high risk of cancer and have direct clinical consequence. Many criteria can be used to classify variants with unknown significance; most criteria are based on the characteristics of the amino acid change, on segregation data and appearance of the variant, on the presence of the variant in controls, or on functional assays. In inherited cancers, tumor characteristics can also be used to classify variants. It is worthwhile to examine the clinical, morphological and molecular features of a patient, and his or her family, when assessing whether the role of a variant is likely to be neutral or pathogenic. Here we describe the advantages and disadvantages of using the tumor characteristics of patients carrying germline variants of uncertain significance (VUS) in BRCA1, BRCA2, or in one of the mismatch repair (MMR) genes, MLH1, MSH2, or MSH6, to infer pathogenicity.
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Affiliation(s)
- Robert M W Hofstra
- Department of Genetics, University Medical Center Groningen and University of Groningen, Groningen, the Netherlands.
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13
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Genome-wide copy neutral LOH is infrequent in familial and sporadic microsatellite unstable carcinomas. Fam Cancer 2008; 7:319-30. [DOI: 10.1007/s10689-008-9194-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2008] [Accepted: 04/01/2008] [Indexed: 01/05/2023]
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Imai K, Yamamoto H. Carcinogenesis and microsatellite instability: the interrelationship between genetics and epigenetics. Carcinogenesis 2008; 29:673-80. [PMID: 17942460 DOI: 10.1093/carcin/bgm228] [Citation(s) in RCA: 301] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
DNA mismatch repair (MMR) deficiency results in a strong mutator phenotype and high-frequency microsatellite instability (MSI-H), which are the hallmarks of tumors arising within Lynch syndrome. MSI-H is characterized by length alterations within simple repeated sequences, microsatellites. Lynch syndrome is primarily due to germline mutations in one of the DNA MMR genes; mainly hMLH1 or hMSH2 and less frequently hMSH6 and rarely hPMS2. Germline hemiallelic methylation of MLH1, termed epimutation, has been reported to be a new cause of Lynch syndrome. MSI-H is also observed in approximately 15% of colorectal, gastric and endometrial cancers and in lower frequencies in a minority of other tumors, where it is associated with the hypermethylation of the promoter region of hMLH1. MSI-H underlies a distinctive tumorigenic pathway because cancers with MSI-H exhibit many differences in genotype and phenotype relative to cancers without MSI-H, irrespective of their hereditary or sporadic origins. Genetic, epigenetic and transcriptomic differences exist between cancers with and those without the MSI-H. The BRAF V600E mutation is associated with sporadic MSI-H colorectal cancers (CRCs) harboring hMLH1 methylation but not Lynch syndrome-related CRCs. The differences in genotype and phenotype between cancers with and those without MSI-H are likely to be causally linked to their differences in biological and clinical features. Therefore, the diagnosis of MSI-H in cancers is thus considered to be of increasing relevance, because MSI-H is a useful screening marker for identifying patients with Lynch syndrome, a better prognostic factor and could affect the efficacy of chemotherapy. This review addresses recent advances in the field of microsatellite instability research.
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Affiliation(s)
- Kohzoh Imai
- Sapporo Medical University, South 1, West 17, Chuo-ku, Sapporo 060-8556, Japan.
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Yan H, Jin H, Xue G, Mei Q, Ding F, Hao L, Sun SH. Germline hMSH2 promoter mutation in a Chinese HNPCC kindred: evidence for dual role of LOH. Clin Genet 2007; 72:556-61. [PMID: 17894833 DOI: 10.1111/j.1399-0004.2007.00911.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Hereditary non-polyposis colorectal cancer (HNPCC) is a dominantly inherited cancer predisposition syndrome that is caused by germline mutations in mismatch repair genes. By screening the core promoters of hMSH2, hMLH1, and hMSH6 in 37 Chinese suspected HNPCC families, a novel germline mutation c.-78_-79delGT was found in the hMSH2 promoter. Its pathogenic effects were supported by the following findings: (a) it co-segregated with HNPCC-related cancers and was not present in the 220 control subjects, (b) tumors harboring the mutation lacked the expression of hMSH2 and showed high microsatellite instability, (c) it significantly decreased the promoter activity, and (d) it abolished the binding ability of the transcription factor E1A-F. Loss of heterozygosity (LOH) was found in three of the tumors studied. Intriguingly, in the tumors from patients II:1 and III:1, LOH occurred in the wild-type allele and agreed well with the traditional 'two-hit' model. In contrast, in the tumor from patient III:3, LOH occurred in the mutant allele. A pathogenic somatic mutation (c.2210+1G>A) was also found in this tumor; therefore, we proposed that the 'second hit' was inactivated by somatic mutation, and the mutant allele was lost during tumor progression; this provided evidence for the new hypothesis for the dual role of LOH.
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Affiliation(s)
- H Yan
- Department of Medical Genetics, College of Basic Medical Sciences, Second Military Medical University, Shanghai, 200433, China
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