Hereditary Nonpolyposis Colorectal Cancer Mutations Research Articles

The Early Detection of Pancreatic Cancer: Whom and How?

The 5-year survival rate of pancreatic cancer is extremely low till now, because resectable cases are less than 20% and 5-year survival rate after surgical resection is only 10-20%. Early detection and curative surgery are important to prolong the survival which was well proved by colon cancer screening test in general population. However, screening test for general population can not prove the survival benefit in pancreatic cancer. So, many studies were performed for the development of screening strategies in high-risk groups of pancreatic cancer. The following were current candidates for screening: first-degree relatives of patients with pancreatic cancer from a familial pancreatic cancer kindred with at least two affected firstdegree relatives; patients with Peutz-Jeghers syndrome; and p16, BRCA2 and hereditary non-polyposis colorectal cancer mutation carriers with ≥ 1 affected firstdegree relative. The recommended screening tests are endoscopic ultrasonography and magnetic resonance cholangiopancreatography. Screening is recommended at age 50 or 10 year earlier than the onset age of pancreatic cancer among family. However, the screening interval is not established and there is great disagreement as to which screening abnormalities were of sufficient concern to for surgery to be recommended. Korean J Pancreatobiliary 2015;20(4):198-203

Copy Number Variation in Hereditary Non-Polyposis Colorectal Cancer

Hereditary non-polyposis colorectal cancer (HNPCC) is the commonest form of inherited colorectal cancer (CRC) predisposition and by definition describes families which conform to the Amsterdam Criteria or reiterations thereof. In ~50% of patients adhering to the Amsterdam criteria germline variants are identified in one of four DNA Mismatch repair (MMR) genes MLH1, MSH2, MSH6 and PMS2. Loss of function of any one of these genes results in a failure to repair DNA errors occurring during replication which can be most easily observed as DNA microsatellite instability (MSI)—a hallmark feature of this disease. The remaining 50% of patients without a genetic diagnosis of disease may harbour more cryptic changes within or adjacent to MLH1, MSH2, MSH6 or PMS2 or elsewhere in the genome. We used a high density cytogenetic array to screen for deletions or duplications in a series of patients, all of whom adhered to the Amsterdam/Bethesda criteria, to determine if genomic re-arrangements could account for a proportion of patients that had been shown not to harbour causative mutations as assessed by standard diagnostic techniques. The study has revealed some associations between copy number variants (CNVs) and HNPCC mutation negative cases and further highlights difficulties associated with CNV analysis.

Purification, crystallization and preliminary X-ray diffraction analysis of the human mismatch repair protein MutSβ.

MutSβ is a eukaryotic mismatch repair protein that preferentially targets extrahelical unpaired nucleotides and shares partial functional redundancy with MutSα (MSH2-MSH6). Although mismatch recognition by MutSα has been shown to involve a conserved Phe-X-Glu motif, little is known about the lesion-binding mechanism of MutSβ. Combined MSH3/MSH6 deficiency triggers a strong predisposition to cancer in mice and defects in msh2 and msh6 account for roughly half of hereditary nonpolyposis colorectal cancer mutations. These three MutS homologs are also believed to play a role in trinucleotide repeat instability, which is a hallmark of many neurodegenerative disorders. The baculovirus overexpression and purification of recombinant human MutSβ and three truncation mutants are presented here. Binding assays with heteroduplex DNA were carried out for biochemical characterization. Crystallization and preliminary X-ray diffraction analysis of the protein bound to a heteroduplex DNA substrate are also reported.

Understanding Patterns of Health Communication in Families at Risk for Hereditary Nonpolyposis Colorectal Cancer: Examining the Effect of Conclusive Versus Indeterminate Genetic Test Results

In families meeting criteria for hereditary nonpolyposis colorectal cancer (HNPCC), genetic testing may or may not identify a mutation. Communication about genetic testing and risk in families with identified HNPCC mutations is associated with individual and relational factors. Similar communication patterns would be expected in families with similar clinical and pathological characteristics, but without an identified HNPCC mutation; however, previous studies have not included such families. Social network analysis was used to compare communication networks and associated individual and relational factors in families with and without identified HNPCC mutations. Respondents from families without identified mutations communicated about genetic counseling and testing and risk for HNPCC with a significantly smaller proportion of network members, compared to respondents from mutation-positive families. Members of families without identified mutations were also more likely to share thoughts about risk for HNPCC with network members whose advice they take, compared to members of families with known mutations. These findings extend our knowledge of communication in families at risk of HNPCC to include the many families in which a causative mutation has not yet been identified. Differences in the breadth of communication about genetics and risk for HNPCC, and the possibility that members of families without identified mutations may seek advice from those with whom they communicate about risk, provide new avenues for future research. Understanding existing communication patterns could help improve education and counseling processes, and facilitate the development of interventions designed to assist in family discussions of risk.

A systematic review of gynecological cancer surveillance in women belonging to hereditary nonpolyposis colorectal cancer (Lynch syndrome) families

We performed a systematic review of studies that evaluate the role of gynecological cancer surveillance in women who carry a hereditary nonpolyposis colorectal cancer (HNPCC) mutation or belong to a family that fulfills the criteria for HNPCC. The PubMed database and a clinical trials database were used to identify relevant studies. We included studies that reported results of gynecological cancer surveillance in women who carry a HNPCC mutation, belong to a family in which a HNPCC mutation was detected or belong to a family fulfilling the Amsterdam II criteria. Number and stage of cancers, interval cancers and cancer precursor states detected at screening. Five studies fulfilled our review criteria. Surveillance modalities for endometrial cancer included transvaginal ultrasound combined with endometrial sampling when indicated, or transvaginal ultrasound with a routine endometrial biopsy, and, in certain studies, the tumor marker CA-125. The highest yield of pathological findings in surveillance visits, from 5 to 6.5%, occurred in studies that included routine endometrial biopsies. Without a routine sampling, 7/14 cancers and 11/18 hyperplasias would have been missed. One case of advanced ovarian cancer was detected at surveillance. Currently available published studies on gynecological cancer surveillance in women with HNPCC do not adequately allow for evidence-based clinical decisions. Detection of endometrial cancer or hyperplasia in nonsymptomatic women belonging to an HNPCC family is improved by adding routine endometrial sampling along with transvaginal ultrasound for surveillance visits. No benefit was shown for ovarian cancer surveillance.

Explanations of Risk in Families Without Identified Mutations for Hereditary Nonpolyposis Colorectal Cancer

Genetic testing for hereditary forms of cancer does not always identify a causative mutation. Little is known about personal or family response to these indeterminate results when a hereditary form of cancer is suspected. This study explored thoughts about and responses to risk for hereditary nonpolyposis colorectal cancer (HNPCC) when a family member has received indeterminate genetic test results. In this qualitative study, data were gathered from index cases who received indeterminate genetic test results through a longitudinal study offering genetic counseling and testing for HNPCC. First-degree relatives of these indeterminate index cases were also invited to participate in the qualitative interview. Semistructured telephone interviews were conducted with index cases and their at-risk first-degree relatives. Data were analyzed using the within- and across-case method. The across-case analysis led to the development of the Awareness and Surveillance Trajectory, which describes individual interpretations of and responses to risk, based on personal and family history. Explanations of risk addressed the meaning of cancer in the family and provided context for individual interpretations. They were identified using within-case analysis and organized into a typology: innate, exceptional, idiosyncratic, and undeveloped explanations. Members of families without identified HNPCC mutations vary in their explanations for, interpretations of, and responses to indeterminate genetic test results. Explanations of family risk and interpretations of individual risk offer healthcare providers valuable information. In combination with the Awareness and Surveillance Trajectory, assessment of these beliefs can facilitate development of individualized recommendations and strategies for possible preventive actions.

Genetic Testing for Hereditary Nonpolyposis Colorectal Cancer (HNPCC)

AbstractHereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant cancer syndrome that confers an elevated risk of early‐onset colorectal cancer (CRC) and increased lifetime risk for other cancers of the endometrium, stomach, small intestine, hepatobiliary system, kidney, ureter, and ovary. HNPCC accounts for up to 5% of all CRC, making it the most common hereditary colorectal cancer syndrome. Germline mutations in methyl‐directed mismatch repair (MMR) genes give rise to microsatellite instability (MSI) in tumor DNA. HNPCC is most often associated with mutations in the MLH1 gene on 3p21, the MSH2 gene on 2p21, and to a lesser extent MSH6 on 2p16. This unit presents a comprehensive molecular and genetic screening strategy for HNPCC mutations in the MLH1, MSH2, and MSH6 genes, including analysis of MSI, mutation scanning by denaturing high‐pressure liquid chromatography (DHPLC), and DNA sequencing analysis. Curr. Protoc. Hum. Genet. 61:10.12.1‐10.12.28. © 2009 by John Wiley & Sons, Inc.

Revised Bethesda Guidelines vs. MSI Testing for the Detection of HNPCC Mutations

Identification of hereditary nonpolyposis colorectal cancer (HNPCC) gene carriers is currently suboptimal, even in cancer patients and their family

Functional analysis of HNPCC-related missense mutations in MSH2

Hereditary nonpolyposis colorectal cancer (HNPCC) is associated with germline mutations in the human DNA mismatch repair (MMR) genes, most frequently MSH2 and MLH1. The majority of HNPCC mutations cause truncations and thus loss of function of the affected polypeptide. However, a significant proportion of MMR mutations found in HNPCC patients are single amino acid substitutions and the functional consequences of many of these mutations in DNA repair are unclear. We have examined the consequences of seven MSH2 missense mutations found in HNPCC families by testing the MSH2 mutant proteins in functional assays as well as by generating equivalent missense mutations in Escherichia coli MutS and analyzing the phenotypes of these mutants. Here we show that two mutant proteins, MSH2-P622L and MSH2-C697F confer multiple biochemical defects, namely in mismatch binding, in vivo interaction with MSH6 and EXO1, and in nuclear localization in the cell. Mutation G674R, located in the ATP-binding region of MSH2, appears to confer resistance to ATP-dependent mismatch release. Mutations D167H and H639R show reduced mismatch binding. Results of in vivo experiments in E. coli with MutS mutants show that one additional mutant, equivalent of MSH2-A834T that do not show any defects in MSH2 assays, is repair deficient. In conclusion, all mutant proteins (except for MSH2-A305T) have defects; either in mismatch binding, ATP-release, mismatch repair activity, subcellular localization or protein–protein interactions.

Biallelic PMS2 Mutations and a Distinctive Childhood Cancer Syndrome

Biallelic mutations in PMS2, a gene usually associated in heterozygous form with hereditary nonpolyposis colorectal cancer (HNPCC), results in a recently described childhood cancer syndrome. The tumor spectrum encompasses atypical brain cancers, hematologic malignancies, and colonic polyposis and cancer. Cutaneous stigmata resembling café-au-lait macules with more diffuse margins are frequently seen. Onset is as young as 2 years. The risk of second malignancy is high. Evidence exists for surveillance for bowel cancer, but surveillance for the wider tumor spectrum is of uncertain benefit. We report a consanguineous Australian-Lebanese family with multiple affected individuals shown to be homozygous for a PMS2 exon 7 deletion. We also review published cases of biallelic mutations in HNPCC-related genes. Early recognition of this familial cancer syndrome is critical, and should prompt investigation for familial HNPCC mutations.

Immune Response Against Frameshift-Induced Neopeptides in HNPCC Patients and Healthy HNPCC Mutation Carriers

Colorectal cancers (CRC) associated with the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome display high-level microsatellite instability (MSI-H) as a consequence of mismatch repair deficiency. HNPCC-associated CRC frequently show features of a pronounced immune response, most likely resulting from the MSI-induced generation of novel tumor-specific carboxy-terminal frameshift peptides (FSPs). However, the role of FSP-specific immune surveillance mechanisms in HNPCC are unknown at present. The efficacy of tumor-infiltrating T cells isolated from MSI-H CRCs (n = 3) was examined by in vitro killing assays. FSP-specific T-cell responses were measured by enzyme-linked immunospot in the peripheral blood from patients with MSI-H CRC (n = 32), healthy HNPCC mutation carriers (n = 16), patients with microsatellite stable (MSS) CRC (n = 17), and healthy donors (n = 22). Tumor-infiltrating T cells isolated from MSI-H CRCs specifically recognized MSI-induced FSPs and showed cytotoxic activity against MSI-H but not MSS CRC cells. FSP-specific T-cell responses were detected in the majority of peripheral blood samples from patients with MSI-H but not MSS CRC. Interestingly, FSP-specific T-cell reactivity was already detectable in the peripheral blood of healthy HNPCC family members with germline mutations but without history of tumor development. These data suggest that FSPs presented by DNA mismatch repair-deficient CRC cells are effectively recognized by the patient's immune system and may explain the characteristic clinicopathologic features of HNPCC-associated but also sporadic MSI-H CRCs. These observations are of high relevance for the development of FSP-based vaccination approaches, particularly for the preventive application in HNPCC mutation carriers.

531 POSTER Questionable usefulness of Braf-V600E mutation to distinguish between sporadic and hereditary colorectal tumors with microsatellite instability in young patients

Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal-dominant disorder characterized by predisposition to colorectal cancer and extracolonic malignancies, frequent multiple primary tumors in the same patient, and early age of cancer onset. A main clinical variant of Lynch syndrome, Muir–Torre syndrome (MTS) is characterized by the association between one or more visceral malignancies, with at least one sebaceous skin tumor or keratoacanthoma. In our study, we have screened a cohort of 538 HNPCC patients, related to 57 HNPCC families, to detect sebaceous skin tumors and keratoacanthomas and the role of mismatch repair (MMR) genes, MLH1, MSH2, and MSH6, in their pathogenesis. Among the 57 HNPCC families, we have identified four MTS families and one suspected MTS family, in which sebaceous carcinoma was found in one HNPCC mutation carrier subject who did not show visceral malignancy. In four of these families, linked to two MLH1 mutations and to two MSH2 mutations, biomolecular characterization showed concordance among immunohistochemistry analysis and gene mutations. The evidences of our investigations show that MLH1 and MSH2 gene mutations have an equivalent etiopathological role both for Lynch syndrome and for MTS; hence, we propose a broadened clinical criteria for definition of Lynch syndrome that will include sebaceous adenoma, carcinoma, and keratoacanthoma.

Discrepancies Between Estimated and Perceived Risk of Cancer among Individuals with Hereditary Nonpolyposis Colorectal Cancer

Communicating cancer risk and recommending adequate control programs is central for genetic counseling. Individuals affected by hereditary nonpolyposis colorectal cancer (HNPCC) are at about 80% life-time risk of colorectal cancer and for female carriers 40-60% risk of endometrial cancer and 10-15% risk of ovarian cancer. The perceived risk among mutation carriers may, however, deviate from the risk communicated and has been demonstrated to influence adherence to control programs. We investigated the perceived cancer risk among HNPCC mutation carriers (n = 47) and correlated the findings to individual characteristics. A perceived risk of colorectal cancer above 60% was reported by 22/45 individuals, and only one out of five mutation carriers reported a perceived risk > 80%. Female mutation carriers, individuals below age 50, and individuals who received their oncogenetic counseling within 1 year prior to the study reported higher, albeit not significantly, perceived risks of colorectal cancer. Higher perceived risks were also reported by individuals who had lost a parent to HNPCC-related cancer at early age, whereas individuals with a personal history of cancer did not report a higher perceived risk. Regarding gynecological cancer, 6/18 females reported a perceived risk of 40-60% for endometrial cancer, whereas the remaining women both underestimated and overestimated their risk, and none of the women referred to the risk of ovarian cancer. We conclude that despite educational efforts and an increasing amount of data on the cancer risk in HNPCC, a minority of the mutation carriers report a perceived risk at the same level as that communicated during oncogenetic counseling.

The impact of predictive genetic testing for hereditary nonpolyposis colorectal cancer: three years after testing

BackgroundTo fully assess predictive genetic testing programs, it is important to assess outcomes over periods of time longer than the 1-year follow-up reported in the literature. MethodsWe conducted a 3-year study of individuals who received predictive genetic test results for previously identified familial mutations in Australian Familial Cancer Clinics. Questionnaires were sent before attendance at the familial cancer clinic and 2 weeks, 4 months, 1 year, and 3 years after receiving test results. Psychological measures were included each time, and preventive behaviors were assessed at baseline and 1 and 3 years. Psychological measures were adjusted for age, gender, and baseline score. ResultsThe study included 19 carriers and 54 non-carriers. We previously reported an increase in mean cancer-specific distress in carriers at 2 weeks with a return to baseline levels by 12 months. This level was maintained until 3 years. Non-carriers showed sustained decreases after testing with a significantly lower level at 3 years compared with baseline (P < 0.001). These scores tended to be lower than those for carriers at 3 years (P = 0.09). Mean depression and anxiety scores did not differ between carriers and non-carriers and, at 3 years, were similar to baseline. All carriers and 7% of non-carriers had had a colonoscopy by 3 years, and 69% of 13 female carriers had undergone gynecological screening in the previous 2 years. Prophylactic surgery was rare. ConclusionThis report of long-term data indicates appropriate screening and improved psychological measures for non-carriers with no evidence of undue psychological distress in carriers of hereditary nonpolyposis colorectal cancer mutations.

Value of MLH1 and MSH2 Mutations in the Appearance of Muir–Torre Syndrome Phenotype in HNPCC Patients Presenting Sebaceous Gland Tumors or Keratoacanthomas

Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal-dominant disorder characterized by predisposition to colorectal cancer and extracolonic malignancies, frequent multiple primary tumors in the same patient, and early age of cancer onset. A main clinical variant of Lynch syndrome, Muir-Torre syndrome (MTS) is characterized by the association between one or more visceral malignancies, with at least one sebaceous skin tumor or keratoacanthoma. In our study, we have screened a cohort of 538 HNPCC patients, related to 57 HNPCC families, to detect sebaceous skin tumors and keratoacanthomas and the role of mismatch repair (MMR) genes, MLH1, MSH2, and MSH6, in their pathogenesis. Among the 57 HNPCC families, we have identified four MTS families and one suspected MTS family, in which sebaceous carcinoma was found in one HNPCC mutation carrier subject who did not show visceral malignancy. In four of these families, linked to two MLH1 mutations and to two MSH2 mutations, biomolecular characterization showed concordance among immunohistochemistry analysis and gene mutations. The evidences of our investigations show that MLH1 and MSH2 gene mutations have an equivalent etiopathological role both for Lynch syndrome and for MTS; hence, we propose a broadened clinical criteria for definition of Lynch syndrome that will include sebaceous adenoma, carcinoma, and keratoacanthoma.

Lynch syndrome (HNPCC) and microsatellite instability analysis guidelines

The “International Workshop on Diagnostic Guidelines for Hereditary Non-Polyposis Colorectal Cancer and Microsatellite Instability” represents the third workshop in this series. In November 1996, NCI’s DCP convened a workshop entitled “Intersection of Pathology and Genetics in HNPCC Syndrome.” In December 1997, another workshop, “International Workshop on Microsatellite Instability and Replication Error Phenotypes in Cancer Detection and Familial Predisposition,” was sponsored by the NCI. Recommendations developed at these two workshops included the Bethesda Guidelines and panel of five specific microsatellite markers that have broad utility in several experimental and diagnostic settings. However, recent findings warranted a re-examination of the current guidelines for HNPCC diagnosis. MSI and immunohistochemistry (IHC) detection are other molecular tests that have been developed for detecting DNA mismatch repair (MMR) defects and were not included in previous HNPCC diagnostic guidelines. The “International Workshop on Diagnostic Guidelines for Hereditary Non-Polyposis Colorectal Cancer and Microsatellite Instability,” held in December 2002, brought together experts in the areas of hereditary nonpolyposis colorectal cancer (HNPCC) and microsatellite instability (MSI). Participants were charged with reviewing, evaluating, and updating existing criteria for HNPCC and MSI, as well as with providing recommendations to the NCI based on new insights into the disease and its manifestations. The workshop’s primary goal was to generate recommendations on appropriate strategies for: (1) evaluating MSI, (2) diagnosing HNPCC, and (3) identifying HNPCC mutation carriers. In applying the results of new research on HNPCC, workshop participants were asked to consider the previous recommendations for MSI testing, refined these recommendations, and identify the most effective screening approaches. First case of Lynch syndrome (HNPCC) may have been reported by Albert Warthin, who first suspected and documented the disorder in his affected seamstress (she died of endometrial cancer), in 1895. Dr. Warthin published the woman’s family history, characterized by a pattern of gynecologic cancer – specifically endometrial cancer – and many other gastrointestinal cancers. In 1961, Dr. Lynch documented a similar experience, with a patient whose family was riddled with colon and endometrial cancers. Dr. Lynch and colleagues subsequently identified other families with the same pattern of cancers, noting that in addition to colon and endometrial cancers, gastric, small bowel, and other cancers occurred significantly more often in these families [1– 4]. It was observed that there was a significantly marked 70–80% excess of proximal colon cancers in these patients. Cutaneous manifestations such as Muir Torre features [5,6], sebaceous adenomas, and sebaceous carcinomas also were found to be associated with the disorder. Aside from colorectal cancers (CRC), endometrial cancers were identified as the second-leading cancer associated with the syndrome. With current detection and treatment options, it is felt that no one with HNPCC should die from colorectal cancer, assuming that the patient has been identified, has a dedicated physician, and has been referred to a gastroenterologist

Age of diagnosis of colorectal cancer in HNPCC patients is more complex than that predicted by R72P polymorphism in TP53

Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominantly inherited cancer syndrome associated with germline mutations in DNA mismatch repair (MMR) genes. Recently a polymorphism at codon 72 (R72P) in the tumour suppressor gene TP53 has been implicated in the age of disease onset in HNPCC. In this report we have studied a large cohort of HNPCC patients to assess the impact of this polymorphism on disease expression and age of diagnosis of colorectal cancer (CRC). DNA samples from 218 HNPCC mutation positive patients from Australia and Poland were genotyped for the arginine to proline change at codon 72 in the TP53 gene. The association between the polymorphism and disease characteristics (mutation status, disease expression and age of diagnosis of CRC) was tested using Pearson's Chi-square and Kaplan-Meier survival analysis. Our study of Australian and Polish HNPCC patients does not provide evidence for an association between the Arg/Pro (GC) genotype of the R72P polymorphism and age of diagnosis of CRC. The R72P polymorphism was examined in HNPCC patients and found to be not associated with disease development in either the Australian or Polish populations. When gene mutation status (hMLH1 or hMSH2) was included in the analysis some evidence of an affect was observed. The genotyping revealed in the Australian population that the R72P polymorphism was under-represented in the hMSH2 group whereas it was over-represented in the Polish hMSH2 group. A similar trend was observed for hMLH1 in both groups but was not significant. Age of diagnosis of CRC in HNPCC patients is therefore more complex than that predicted by the R72P TP53 polymorphism alone, suggesting an inter-relationship with other genetic and/or environmental factors.

Occult endometrial cancer and decision making for prophylactic hysterectomy in hereditary nonpolyposis colorectal cancer patients

Background and objective. Hereditary nonpolyposis colorectal cancer (HNPCC) is the most frequent form of hereditary colorectal cancer. In addition to the high lifetime risk for colorectal cancer in mutation carriers, there is also a remarkably increased risk for endometrial cancer (EC). Methods. In this retrospective study, clinical and molecular approach to the individual decision making as to whether or not to perform a prophylactic hysterectomy in a subset of HNPCC patients is discussed. 147 female patients meeting at least one criterion of the Bethesda guidelines were included in this analysis between 1995 and 2003. After clinical and genetic counseling, patients gave informed written consent and microsatellite analysis, immunohistochemistry and sequencing of the mismatch repair genes MLH1, MSH2 and MSH6 was performed. Results. 11 of the analyzed patients had a personal history of EC and had undergone previous hysterectomy at ages 26 to 62 years. Prophylactic hysterectomy with oophorectomy was considered in postmenopausal women meeting the Amsterdam criteria and/or carrying a disease causing mismatch repair gene mutation who were operated on because of diagnosed colorectal cancer in our center for hereditary cancer. This procedure was performed in 4 patients. None of them had shown any symptoms of a gynecologic malignancy. Preoperative gynecological examination showed no evidence for EC or ovarian cancer in these patients. Postoperative histological examination showed EC stage T1b N0 M0 in 2 patients. Conclusions. Since the efficiency of gynecological surveillance is uncertain, prophylactic hysterectomy could be an option for a subset of HNPCC patients and mutation carriers.

Long Term Follow-up of HNPCC Gene Mutation Carriers: Compliance with Screening and Satisfaction with Counseling and Screening Procedures

Hereditary non polyposis colorectal cancer (HNPCC) is a hereditary predisposition to colorectal and endometrial cancer, caused by mutations of the mismatch repair (MMR) genes MSH2, MLH1 and MSH6. Regular colonoscopy reduces the incidence of colorectal cancer in mutation carriers dramatically. The aim of this study was to evaluate the use of colonoscopy by proven HNPCC mutation carriers. We also evaluated the satisfaction with the counseling and screening procedures at the long term. A questionnaire survey was performed among 94 proven MMR gene mutation carriers. Data were analyzed using univariate and multivariate analysis. The average time of follow-up was 3,5 years (range 0.5-8.5 years). The response rate was 74%. The proportion of unaffected mutation carriers under colonoscopic screening increased from 31 to 88% upon genetic testing, and for gynecological screening from 17 to 69%. However, more than half of the responders experienced colonoscopy as unpleasant or painful. About 97% felt well informed during counseling, and 88% felt sufficiently supported. Ten percent of the responders reported a high cancer worry that was significantly (P = 0.007) associated with a high perceived cancer risk. Six responders (9%) regretted being tested. Remarkably, of 4 of these 6 a close relative died recently of cancer. Problems with obtaining a disability or life insurance or mortgage were experienced by 4 out 10 healthy carriers opting for these services. In conclusion, genetic testing for HNPCC considerably improves compliance for screening, which will result in a reduction of HNPCC-related cancer morbidity and mortality in mutation carriers. Most HNPCC gene mutation carriers cope well with their cancer susceptibility on the long term.

Functional Significance and Clinical Phenotype of Nontruncating Mismatch Repair Variants of

Germline mutations in mismatch repair genes are associated with hereditary nonpolyposis colorectal cancer. A significant proportion of mutations are nontruncating and associated with a variability of clinical phenotype and microsatellite instability and with occasional presence of residual protein in tumor tissue that suggests impaired functional activity but not total lack of mismatch repair. To address pathogenic significance and mechanism of pathogenicity, we studied the functionality of 31 nontruncating MLH1 mutations found in clinically characterized colorectal cancer families and 3 other variations listed in a mutation database. Mutations constructed by site-directed mutagenesis were studied for protein expression/stability, subcellular localization, protein-protein interaction, and repair efficiency. The genetic and biochemical data were correlated with clinical data. Finally, comparative sequence analysis was performed to assess the value of sequence homology as a tool for predicting functional results. Altogether, 22 mutations were pathogenic in more than one assay, 2 variants were impaired in one assay, and 10 variants acted like wild-type protein. Twenty of 34 mutations affected the quantity of MLH1 protein, whereas only 15 mainly amino-terminal mutations were defective in an in vitro repair assay. Comparative sequence analysis correctly predicted functional studies for 82% of variants. Pathogenic nontruncating alterations in MLH1 may interfere with different biochemical mechanisms but generally more than one. The severe biochemical defects are mirrored by phenotypic characteristics such as early age at onset and high microsatellite instability, whereas variants with no or mild defects in functionality are associated with variable clinical phenotypes.