Mutations In DNA Mismatch Repair Genes Research Articles

Report From the Jerusalem Workshop on Lynch Syndrome-Hereditary Nonpolyposis Colorectal Cancer

A Workshop was held in Jerusalem, Israel, on October 26 and 27, 2009 to discuss the management of Lynch syndrome-hereditary nonpolyposis colorectal cancer (CRC), with the primary goal to develop consensus for the optimal management of this disease. A second goal was to identify areas of research with the potential to advance the clinical management of Lynch syndrome. The perspectives and recommendations from the workshop are meant to be a platform for discussion and deliberation. The Workshop was organized by Moshe Shike (Memorial Sloan Kettering Cancer Center, New York) and sponsored by The Colon Cancer Foundation. More details of each presentation are available in an on-line supplement.

Abstract 2975: Two putative founder MSH6 mutations associated with inherited cancer susceptibility in Ashkenazi Jewish population

Abstract Background Inherited mutations in DNA mismatch-repair genes are the cause of several cancers associated with Lynch syndrome. The most common mutations affect MLH1 and MSH2 genes, while the MSH6 gene is less commonly involved. Furthermore, MSH6 mutations have been observed to result in an attenuated form of the syndrome. We report here case-control studies of two putative MSH6 founder mutations in the Ashkenazi Jewish (AJ) population. Methods Case-control studies were performed using DNA extracted from the blood of individuals of AJ descent presenting cancers compatible with Lynch syndrome and AJ individuals unaffected by cancer as controls. The DNA samples were screened for the presence of the two mutations in exon 9. The frequency of the mutations and the range of malignancies were analyzed. Results Among 2104 population-based AJ colorectal cancer cases (CRC), 8 carried a 4 bp duplication mutation, c.3984_3987dupl (0.38%), and 3 carried a 4 bp deletion mutation, c.3959_3962del (0.14%), in the exon 9 of the MSH6 gene. In comparison, 1 duplication (0.06%) and no deletions were observed in 1813 control individuals. The odds ratio for the c.3984_3987dupl and the c.3959_3962del in this population are OR = 8.64 (exact 95%CI 1.23-375, Fisher's exact test two-sided P = 0.04) and OR = NA, P = 0.25, respectively. Notably, the one control found to carry the duplication was, during the course of follow-up, diagnosed with both cecal and endometrial cancer. In a hospital-based series of 78 CRC, one individual carried the deletion, but no duplications were seen. Among 136 hospital-based AJ endometrial cancer cases, 2 carried the duplication, leading to an OR of 27.0 (95%CI: 1.39-1596, P = 0.014) when compared with the 1813 controls. In a series of 61 hospital-based AJ pancreas cancer cases, no duplication carriers were seen, but 1 individual carried the deletion (OR NA, P = 0.033). Notably, this individual developed 3 independent primary cancers - pancreas cancer, CRC and rhabdomyosarcoma. Testing for microsatellite instability and loss of MSH6 protein is in progress in these samples. Conclusion These rare, probable founder, MSH6 truncating mutations reported here are of great importance for the screening, genetic counseling and follow-up of Ashkenazi Jewish families presenting malignant tumors compatible with Lynch syndrome. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2975.

Risks of Lynch syndrome cancers for MSH6 mutation carriers.

Germline mutations in MSH6 account for 10%-20% of Lynch syndrome colorectal cancers caused by hereditary DNA mismatch repair gene mutations. Because there have been only a few studies of mutation carriers, their cancer risks are uncertain. We identified 113 families of MSH6 mutation carriers from five countries that we ascertained through family cancer clinics and population-based cancer registries. Mutation status, sex, age, and histories of cancer, polypectomy, and hysterectomy were sought from 3104 of their relatives. Age-specific cumulative risks for carriers and hazard ratios (HRs) for cancer risks of carriers, compared with those of the general population of the same country, were estimated by use of a modified segregation analysis with appropriate conditioning depending on ascertainment. For MSH6 mutation carriers, the estimated cumulative risks to ages 70 and 80 years, respectively, were as follows: for colorectal cancer, 22% (95% confidence interval [CI] = 14% to 32%) and 44% (95% CI = 28% to 62%) for men and 10% (95% CI = 5% to 17%) and 20% (95% CI = 11% to 35%) for women; for endometrial cancer, 26% (95% CI = 18% to 36%) and 44% (95% CI = 30% to 58%); and for any cancer associated with Lynch syndrome, 24% (95% CI = 16% to 37%) and 47% (95% CI = 32% to 66%) for men and 40% (95% CI = 32% to 52%) and 65% (95% CI = 53% to 78%) for women. Compared with incidence for the general population, MSH6 mutation carriers had an eightfold increased incidence of colorectal cancer (HR = 7.6, 95% CI = 5.4 to 10.8), which was independent of sex and age. Women who were MSH6 mutation carriers had a 26-fold increased incidence of endometrial cancer (HR = 25.5, 95% CI = 16.8 to 38.7) and a sixfold increased incidence of other cancers associated with Lynch syndrome (HR = 6.0, 95% CI = 3.4 to 10.7). We have obtained precise and accurate estimates of both absolute and relative cancer risks for MSH6 mutation carriers.

Abstract A124: Genome-wide association identified susceptibility loci as modifiers of colorectal cancer risk in Lynch syndrome

Abstract Purpose: The purpose of this study was to determine whether 5 common low-penetrance variants identified in recent genome-wide association studies (GWAS) for colorectal cancer modify colorectal cancer risk in people with Lynch syndrome. People with Lynch syndrome are genetically predisposed to colorectal cancer owing to an inherited DNA mismatch repair (MMR) gene mutation; however, disease expression varies, pointing to the role of modifying factors. A study of Dutch Lynch syndrome families (Wijnen et al., 2009) examined 6 GWAS-identified markers and found that 2 of them—rs16892766 (8q23.3) and rs3802842 (11q23.1)—were associated with colorectal cancer risk. However, other risk variants have yet to be characterized in Lynch syndrome. A replication study of 3 markers in subjects enrolled irrespective of whether they were MMR gene mutation carriers (Poynter et al., 2007) found that 2 risk variants in the 8q24 region (rs10505477 and rs6983267) and 1 variant in the 9p24 region (rs719725) were associated with colorectal cancer risk. Methods: In a retrospective cohort study, we analyzed 278 people with Lynch syndrome and a confirmed MMR gene mutation from the M. D. Anderson Lynch syndrome registry. We genotyped the 5 aforementioned risk variants—rs16892766, rs3802842, rs10505477, rs6983267, and rs719725—and analyzed the association between each risk variant and colorectal cancer using Cox proportional hazards regression while adjusting for sex, MMR gene mutation status, and familial correlation. Results: Of the 278 subjects from 128 families with 11,702 person years of follow-up, 146 subjects had colorectal cancer, and the remaining subjects were unaffected. In a codominant model, rs16892766 was significantly associated with colorectal cancer (hazard ratio [HR]: 1.61; 95% confidence interval [CI]: 1.10–2.35). Similarly, rs3802842 exhibited a marginally significant trend in an additive model (Ptrend = 0.07), and the association was most clearly evident among carriers of mutations in the MLH1 MMR gene in a codominant model (HR: 1.98; 95% CI: 1.18–3.33). Conclusion: Our study replicates the previous finding of an association between 2 GWAS-identified susceptibility loci and risk of colorectal cancer in people with Lynch syndrome. Although people with Lynch syndrome have a strong predisposition to colorectal cancer due to the underlying MMR mutation, these common genetic variants may further modify their colorectal cancer risk, particularly in carriers of multiple risk alleles. These and other low-penetrance susceptibility loci are likely to have future application in personalized risk prediction in identifying individuals who are most susceptible so that they can be provided more rigorous cancer-prevention strategies. Citation Information: Cancer Prev Res 2010;3(1 Suppl):A124.

8. How effective is DNA mismatch repair enzyme immunohistochemistry performed on colorectal cancer biopsies compared with resection material?

Background and Aim Microsatellite instability (MSI) due to DNA mismatch repair (MMR) gene mutations characterises Lynch syndrome. Deficient MMR also occurs in ~15% of sporadic colorectal carcinoma (CRC) due to promoter methylation. MSI may be predicted using MMR protein (MMRP) immunohistochemistry (IHC), allowing focussed therapeutic intervention and genetic investigations. Most laboratories perform IHC on resections. IHC is highly sensitive to degree of tissue fixation. Biopsy material may produce superior staining based on faster and more thorough fixation. Furthermore, if neo-adjuvant chemotherapy is given prior to surgical resection, MMRP expression maybe altered in subsequent resections, but not preceding biopsies. This study aims to determine if IHC for DNA MMRP expression in CRC is as reliable on biopsy material as on resection specimens. Methods 112 CRC cases with biopsy and resection material had IHC performed for MLH1, PMS2, MSH2 and MHS6. The strength and distribution of staining in cancerous and normal tissue was examined, blindly, by a single observer, validated by consultant pathologist review of randomly selected cases. Results were cross-tabulated and statistically analysed. Results There was excellent agreement of definitive MMRP expression between biopsy and resection material: MLH1 (κ = 1), PMS2 (κ = 0.906), MSH2 (κ = 1.00), MSH6 (κ = 0.663), p p Conclusion Biopsy specimens are easier to interpret and provide an equally accurate evaluation of MMRP expression as resection specimens. Informed, significant management decisions maybe made prior to definitive therapy.

Molecular Analysis of Endometrial Tumorigenesis: Importance of Complex Hyperplasia Regardless of Atypia

Endometrial carcinoma (EC) is common in the population and the most frequent extracolonic malignancy in hereditary nonpolyposis colorectal carcinoma (HNPCC)/Lynch syndrome. We characterized precursor lesions of endometrioid EC to identify markers of malignant transformation and tumor progression. Serial specimens of normal endometrium, simple hyperplasia, complex hyperplasia without atypia, complex hyperplasia with atypia, and endometrial carcinoma obtained during a 10-year surveillance of DNA mismatch repair (MMR) gene mutation carriers (together 110 samples) were molecularly profiled and compared with a sporadic reference series of endometrial specimens taken for nonmalignant reasons (62 samples). Among MMR gene mutation carriers, decreased MMR protein expression was present in 7% in normal endometrium, 40% in simple hyperplasia, 100% in complex hyperplasia without atypia, 92% in complex hyperplasia with atypia, and 100% in endometrial carcinoma. Microsatellite instability frequencies were lower (6%, 17%, 67%, 38%, and 64%, respectively). Among 24 tumor suppressor genes, the number of methylated loci increased from normal endometrium to simple hyperplasia to complex hyperplasia (complex hyperplasia without atypia/complex hyperplasia with atypia) in both Lynch syndrome and reference series. The most frequently methylated genes were CDH13, RASSF1A, and GSTP1. In MMR gene mutation carriers, MMR and methylation defects appeared up to 12 years before endometrial carcinoma. Molecular changes in endometrial tissue are detectable several years before endometrial carcinoma in genetically predisposed individuals. Abnormal MMR and methylation classify normal endometrium and simple hyperplasia into one category and complex hyperplasia without atypia, complex hyperplasia with atypia, and endometrial carcinoma into another, suggesting that, contrary to a traditional view, complex hyperplasia without atypia and complex hyperplasia with atypia are equally important as precursor lesions of endometrial carcinoma.

Ten Years After Mutation Testing for Lynch Syndrome: Cancer Incidence and Outcome in Mutation-Positive and Mutation-Negative Family Members

Colonoscopies with polypectomies and endometrial biopsies with transvaginal ultrasonography, repeated at 2- to 3-year intervals, are performed for prevention or early detection of cancer in patients with DNA mismatch repair gene mutation causing Lynch syndrome. The long-term effectiveness of surveillance was evaluated in Lynch syndrome family members tested approximately 10 years ago. Cancer incidence and survival were determined after an 11.5-year follow-up in 242 mutation-positive and 367 mutation-negative participants. These participants in 57 Lynch syndrome families with 14 different mutations were at 50% risk. The median age was 36 years (range, 18 to 72 years) in mutation carriers and 42 years (range, 18 to 72 years) in mutation-negative participants, and none had had cancer of the Lynch syndrome type. Compliance was 95.9% for the colonic surveillance and 97.1% for the gynecologic surveillance. Colorectal cancer (CRC) occurred in 30 mutation-positive participants, and 74 participants had adenomas removed. Three patients died of CRC. Endometrial cancer (EC) occurred in 19 of 103 women at risk, and 48 women had prophylactic hysterectomy. Six of 112 women at risk had ovarian cancer. The overall cancer risk ratio (RR) in mutation carriers was 5.80 (95% CI, 3.4 to 9.5). Cancer mortality rate (RR = 2.28; 95% CI, 0.82 to 6.31) and overall death rate (RR = 1.26; 95% CI, 0.65 to 2.46) were not significantly increased. Long-term compliance in surveillance for CRC and EC exceeded 95% in Lynch syndrome. All CRC deaths were not prevented as a result of noncompliance or missed lesions. Still, after 10 years of surveillance, no significant increase in mortality had occurred compared with mutation-negative relatives.

Familial colorectal cancer type X: clinical, pathological and molecular characterization

Some families fulfilling the Amsterdam Criteria (AC) differ from the Lynch syndrome (LS) in that colorectal cancers (CRC) do not present microsatellite instability (MSI) and DNA mismatch repair gene mutations are not found. These families have been designated as Familial Colorectal Cancer type X (XS) and their genetic basis remains unknown. In families fulfilling AC for LS: 1) To perform MSI testing in CRC and to correlate it with clinical and pathological characteristics and with the mutational analysis in the DNA mismatch repair genes; 2) In cases suggestive of XS, to study the suppressor pathway (SP) of carcinogenesis. 45 patients with CRC, from 41 families fulfilling AC, were included. Clinical and pathological data were recorded. MSI testing was performed with the Bethesda marker panel and mutational analysis in MLH1, MSH2 and MSH6 genes was undertaken by DGGE, MLPA and direct sequencing. To study the SP, loss of heterozigoty was evaluated at the following loci: APC, p53, DCC and SMAD4 genes. 33/41 (80%) and 8/41 (20%) families presented high-grade microsatellite instability (MSI-H) and microsatellite stable (MSS) CRC, respectively. In families suggestive of XS, a smaller number of CRC and less frequent spectrum associated tumors were detected. In comparison with MSI-H CRC, MSS CRC were preferentially located at the distal colon/rectum and less often presented mucous production or lymphocytic infiltrate. In 70% of families with MSI-H CRC, a pathogenic mutation in one of the DNA mismatch repair genes was identified, as opposed to none in the group with MSS CRC. The SP was followed in 2 cases and an alternative one in other two. The remaining 4 cases were noninformative; however, 5/8 (63%) presented allelic losses in the APC gene. 1) Families fulfilling AC and harbouring MSS CRC presented particular characteristics, which reinforce the existence of a new entity, different from LS; 2) The designation of Familial Colorectal Cancer type X seems appropriate to classify an entity whose CRC follow an unclear carcinogenesis pathway and that presents an unknown genetic basis; 3) The designation of LS should be restricted to families with an identified pathogenic DNA mismatch repair gene mutation.

Prediction of Lynch Syndrome in Consecutive Patients With Colorectal Cancer

Lynch syndrome is caused by inherited mutations in DNA mismatch repair genes (primarily MSH2, MLH1, MSH6, and PMS2) and is one of the most prevalent inherited cancer syndromes. Several models have been developed to predict the occurrence of Lynch syndrome in high-risk patients and families, but it is not known how these models compare with one another or how they perform for colorectal cancer patients from the general population. We used data from such patients to test the ability of four models--Leiden, MMRpredict, PREMM(1,2), and MMRpro--to distinguish between those who did and did not carry DNA mismatch repair gene mutations. We studied a consecutive series of 725 patients who were younger than 75 years at colorectal cancer diagnosis and whose DNA mismatch repair gene mutation status was available; 18 of the 725 patients carried such a mutation. For each model, we calculated the risk score, compared the observed number of mutations with the expected number, and determined the receiver operating characteristics. All statistical tests were two-sided. Although all four models overestimated the probability of a mutation (range = 1.2- to 4.3-fold), especially in low-risk patients, they could discriminate between carriers and noncarriers of a mismatch repair mutation. The areas under the receiver operating characteristics curves from the four models ranged from 0.91 to 0.96. Carriers of mutations in the MSH6 or PMS2 genes had lower risk scores than carriers of MSH2 or MLH1 mutations. For example, the MMRpredict model gave median risk scores of 24% and 94% (P < .015) for MSH6-PMS2 and MSH2-MLH1 mutation carriers, respectively. For the Leiden, MMRpredict, and PREMM(1,2) models, correcting the risk scores for bias introduced by family size improved their power to discriminate between carriers and noncarriers. After correcting for family size, the best model was MMRpredict, which achieved a sensitivity of 94% (95% confidence interval [CI] = 73% to 99%) and a specificity of 91% (95% CI = 88% to 93%) and identified a smaller proportion of patients than the revised Bethesda criteria as those who should undergo additional molecular or immunohistochemical testing (11% vs 50%). MMRpredict was the best-performing model for identifying colorectal cancer patients who are at high risk of carrying a DNA mismatch repair gene mutation and thus should be screened for Lynch syndrome.

Hereditary colorectal cancer: MYH-associated polyposis and other newly identified disorders

Historically, discussions of familial adenomatous polyposis and hereditary non-polyposis colon cancer have dominated lectures and writings on hereditary predisposition to colorectal cancer. In the last decade, the subject has grown well beyond the two entities. In this paper, five topics relevant to genetic risk assessment for colorectal cancer are reviewed. These include the autosomal recessive MYH-associated polyposis, hyperplastic polyposis and serrated pathway syndrome, the association of autosomal dominant juvenile polyposis with hereditary hemorrhagic telangiectasia, familial colorectal cancer type X, and the syndrome of biallelic DNA mismatch repair gene mutations. Knowledge of these entities may assist clinicians to recognize and manage cases that do not fit into the more common syndromes of colorectal cancer predisposition.

Microsatellite instability in the evaluation of hereditary nonpolyposis colorectal cancer

Hereditary nonpolyposis colorectal cancer (HNPCC) accounts for most hereditary colorectal cancers. The detection of families with HNPCC enables disease surveillance and clinical management, which significantly reduce morbidity and mortality. Mutations in DNA mismatch repair (MMR) genes underlie HNPCC and cause microsatellite instability (MSI). Although screening for pathogenic mutations in DNA MMR genes is time consuming and costly, MSI-based molecular diagnosis improves HNPCC diagnosis, which was once based on clinical characteristics and family history alone. Patients selected for MSI testing usually fulfill the Bethesda criteria. Tumor MSI status with tissue immunohistochemistry staining directs further genetic evaluation, including sequencing of MMR genes or methylation studies. This review outlines the importance of MSI status in disease diagnosis, prognosis, and treatment.

Mismatch repair gene mutations in Chinese HNPCC patients

To explore the characteristics of DNA mismatch repair gene mutations in Chinese patients with hereditary non-polyposis colorectal cancer (HNPCC) or Lynch syndrome, the MLH1 and MSH2 genes from probands of 76 HNPCC families were sequenced. By doing so, two frame-shift mutations, three splice-site mutations and fourteen missense mutations (thirteen missense mutations and one nonsense mutation) were identified in the MLH1 gene. In addition, one splice-site mutation and six missense mutations were detected in the MSH2 gene. None of these mutations were detected in 100 matched healthy controls. The remaining mutation-negative cases were subjected to large fragment deletion analysis using multiplex ligation-dependent probe amplification (MLPA). By doing so, five large fragment deletions were detected in the MSH2 gene. No large fragment deletions were detected in the MLH1 gene. We conclude that the MLH1 and MSH2 genes in Chinese HNPCC families exhibit broad mutation spectra.

Genetic Variation in Genes for the Xenobiotic-Metabolizing EnzymesCYP1A1, EPHX1, GSTM1, GSTT1, andGSTP1and Susceptibility to Colorectal Cancer in Lynch Syndrome

Individuals with Lynch syndrome are predisposed to cancer due to an inherited DNA mismatch repair gene mutation. However, there is significant variability observed in disease expression likely due to the influence of other environmental, lifestyle, or genetic factors. Polymorphisms in genes encoding xenobiotic-metabolizing enzymes may modify cancer risk by influencing the metabolism and clearance of potential carcinogens from the body. In this retrospective analysis, we examined key candidate gene polymorphisms in CYP1A1, EPHX1, GSTT1, GSTM1, and GSTP1 as modifiers of age at onset of colorectal cancer among 257 individuals with Lynch syndrome. We found that subjects heterozygous for CYP1A1 I462V (c.1384A>G) developed colorectal cancer 4 years earlier than those with the homozygous wild-type genotype (median ages, 39 and 43 years, respectively; log-rank test P = 0.018). Furthermore, being heterozygous for the CYP1A1 polymorphisms, I462V and Msp1 (g.6235T>C), was associated with an increased risk for developing colorectal cancer [adjusted hazard ratio for AG relative to AA, 1.78; 95% confidence interval, 1.16-2.74; P = 0.008; hazard ratio for TC relative to TT, 1.53; 95% confidence interval, 1.06-2.22; P = 0.02]. Because homozygous variants for both CYP1A1 polymorphisms were rare, risk estimates were imprecise. None of the other gene polymorphisms examined were associated with an earlier onset age for colorectal cancer. Our results suggest that the I462V and Msp1 polymorphisms in CYP1A1 may be an additional susceptibility factor for disease expression in Lynch syndrome because they modify the age of colorectal cancer onset by up to 4 years.

Muir–Torre syndrome caused by partial duplication of MSH2 gene by Alu-mediated nonhomologous recombination

We describe a 54-year-old man with a pedicled tumour on the neck. The surgical specimen revealed a sebaceous carcinoma. He belonged to a cancer-prone family susceptible to gastrointestinal cancer. Systemic evaluation for latent malignancies revealed early-stage colonic adenocarcinoma. These findings were compatible with Muir-Torre syndrome (MTS). Microsatellite instability was detected in the sebaceous carcinoma, suggesting a DNA mismatch repair gene mutation. Moreover, duplication of exon 7 generated a nonsense codon at codon 427 of the MSH2 gene causing truncation of MSH2 protein. Immunohistochemical analysis showed diminished MSH2 protein levels in the sebaceous carcinoma and colonic adenocarcinoma. To date, there have been no reports showing duplication of exon 7 of the MSH2 gene in MTS or hereditary nonpolyposis colorectal cancer kindreds. Furthermore, the present case indicates that the dermatologist plays an important role in the diagnosis of MTS and evaluation for latent malignancies.

Assessment of the MMRpredict model for prediction of DNA mismatch repair gene mutations (Lynch Syndrome)

4127 Background: The MMRpredict model, developed at the University of Edinburgh, is a web-based model developed to predict which patients diagnosed with colorectal cancer (CRC) under age 55 years have germline mutations in a DNA mismatch repair (MMR) gene [Barnetson et al., NEngJMed 2006;354:2751–63]. Stage 1 MMRpredict estimates the carrier probability for MMR mutations from clinical parameters (age of diagnosis of colorectal cancer, proximal vs distal site, family history, multiple primary CRCs). We evaluated the performance of Stage 1 of this model in a well characterized cohort of colorectal cancer patients. Methods: Cases with CRC were identified through the Minnesota Cancer Surveillance System (MCSS), a population based registry and Mayo Clinic Rochester, a clinical practice. All were consented participants in the Mayo Colon Cancer Family Registry. Of 342 cases tested for MMR mutations (MLH1, MSH2, MSH6), 45 had insufficient information on colon site and 62 were older than 55 and could not be used in the study. The remaining 235 included 110 females/125 males; 90 cases with proximal site/145 with distal site; 229/235 were self-identified as White. Results: We defined 5 probability risk groups based on output from the MMRpredict web model Stage 1: 1–10%, 11–25%, 26–50%, 51–75%, and 76–100%. In our study, the number of cases in each of these groups was 60, 45, 65, 34, and 31, respectively. The corresponding number of mutations in each group was 1 (1.7%), 4 (8.9%), 9 (13.8%), 3 (8.8%), and 11 (35.5%). Overall, 28/235 patients were found to have mutations (11.9%), compared to predicted range of 62–107 (26–45%). Conclusion: MMRpredict Stage 1 over-estimated the probability of detecting a MMR gene mutation in this study. This may reflect ascertainment issues or genetics of different populations. No significant financial relationships to disclose.

Utility of computed tomographic colonography in surveillance for hereditary nonpolyposis colorectal cancer syndrome

Computed tomographic colonography (CTC) is suggested to be an alternative to colonoscopy as a surveillance tool in subjects with a high risk for colorectal cancer (CRC). To evaluate the utility of CTC we successively examined 78 subjects, all with a DNA mismatch repair gene mutation, by CTC and colonoscopy. We detected altogether 37 polyps or tumors in 28 subjects (prevalence 35.9%), adenomas in 13 subjects (16.7%), CRC in two (2.6%), and hyperplastic polyps in 13 (16.7%). A great majority of the polyps were diminutive. The per-patient sensitivity for detecting all lesions with CTC was 0.25 and 0.29 by two radiologists and the specificities 0.82 and 0.76. For lesions of 10 mm or larger the sensitivities were 0.6 and 1.0 and the specificities 0.96 by each examiner. Each diagnosed the two cancers correctly. We concluded that CTC has an acceptable accuracy for large lesions in the colon but the detection rate for small polyps is not comparable to that in colonoscopy. Therefore CTC remains a second choice in surveillance for use when colonoscopy for some reason is incomplete or unsuitable.

Identification and Survival of Carriers of Mutations in DNA Mismatch-Repair Genes in Colon Cancer

Identification and Survival of Carriers of Mutations in DNA Mismatch-Repair Genes in Colon Cancer

Heritable germline epimutation of MSH2 in a family with hereditary nonpolyposis colorectal cancer

Epimutations in the germline, such as methylation of the MLH1 gene, may contribute to hereditary cancer syndrome in human, but their transmission to offspring has never been documented. Here we report a family with inheritance, in three successive generations, of germline allele-specific and mosaic hypermethylation of the MSH2 gene, without evidence of DNA mismatch repair gene mutation. Three siblings carrying the germline methylation developed early-onset colorectal or endometrial cancers, all with microsatellite instability and MSH2 protein loss. Clonal bisulfite sequencing and pyrosequencing showed different methylation levels in different somatic tissues, with the highest level recorded in rectal mucosa and colon cancer tissue, and the lowest in blood leukocytes. This mosaic state of germline methylation with different tissue distribution could act as the first hit and provide a mechanism for genetic disease inheritance that may deviate from the mendelian pattern and be overlooked in conventional leukocyte-based genetic diagnosis strategy.

Novel hMSH2, hMSH6 and hMLH1 gene mutations and microsatellite instability in sporadic colorectal cancer

To detect the hMSH2, hMSH6 and hMLH1 DNA mismatch repair gene mutations and microsatellite instability in somatic colorectal cancer. The mutations of hMSH2, hMSH6, and hMLH1 genes, including microsatellite instability of BAT-26, BAT-40, D2S123, D5S346 and D17S250 were analyzed in 31 patients with colorectal. The results revealed that eight cases (25.8%) harbored mutations in DNA mismatch repair genes. Of these, five novel mutations including I237V in exon 4 of hMSH2, ins T at codon 1196 in exon 7 of hMSH6, and ins G at codon 154 in exon 6, N158H in exon 6, and del A at codon 257 in exon 9 of hMLH1 were identified. Moreover, several intronic polymorphisms, including c-g transversion at IVS-1 nt211 + 9 of hMSH2, del T in poly T track at IVS-6 nt3559-5, ATCT duplicate in IVS-7 nt 3642 + 35 and t-g transversion at IVS-10 nt4080 + 185 of hMSH6 were demonstrated in these patients. In addition, seven cases (22.5%) exhibited microsatellite instability (MSI). These results suggested that the inactivation of DNA mismatch repair genes and microsatellite instability may play a minor role in somatic colorectal cancer development.

Identification and Survival of Carriers of Mutations in DNA Mismatch-Repair Genes in Colon Cancer

The identification of mutations in germ-line DNA mismatch-repair genes at the time of diagnosis of colorectal cancer is important in the management of the disease. Without preselection and regardless of family history, we recruited 870 patients under the age of 55 years soon after they received a diagnosis of colorectal cancer. We studied these patients for germ-line mutations in the DNA mismatch-repair genes MLH1, MSH2, and MSH6 and developed a two-stage model by multivariate logistic regression for the prediction of the presence of mutations in these genes. Stage 1 of the model incorporated only clinical variables; stage 2 comprised analysis of the tumor by immunohistochemical staining and tests for microsatellite instability. The model was validated in an independent population of patients. We analyzed 2938 patient-years of follow-up to determine whether genotype influenced survival. There were 38 mutations among the 870 participants (4 percent): 15 mutations in MLH1, 16 in MSH2, and 7 in MSH6. Carrier frequencies in men (6 percent) and women (3 percent) differed significantly (P<0.04). The addition of immunohistochemical analysis in stage 2 of the model had a sensitivity of 62 percent and a positive predictive value of 80 percent. There were 35 mutations in the validation series of 155 patients (23 percent): 19 mutations in MLH1, 13 in MSH2, and 3 in MSH6. The performance of the model was robust among a wide range of cutoff probabilities and was superior to that of the Bethesda and Amsterdam criteria for hereditary nonpolyposis colorectal cancer. Survival among carriers was not significantly different from that among noncarriers. We devised and validated a method of identifying patients with colorectal cancer who are carriers of mutations in DNA repair genes. Survival was similar among carriers and noncarriers.