Genotyping possible polymorphic variants of human mismatch repair genes in healthy Korean individuals and sporadic colorectal cancer patients

Micronuclei Formation upon Radioiodine Therapy for Well-Differentiated Thyroid Cancer: The Influence of DNA Repair Genes Variants

Radioiodine therapy with ¹³¹I remains the mainstay of standard treatment for well-differentiated thyroid cancer (DTC). Prognosis is good but concern exists that ¹³¹I-emitted ionizing radiation may induce double-strand breaks in extra-thyroidal tissues, increasing the risk of secondary malignancies. We, therefore, sought to evaluate the induction and 2-year persistence of micronuclei (MN) in lymphocytes from 26 ¹³¹I-treated DTC patients and the potential impact of nine homologous recombination (HR), non-homologous end-joining (NHEJ), and mismatch repair (MMR) polymorphisms on MN levels. MN frequency was determined by the cytokinesis-blocked micronucleus assay while genotyping was performed through pre-designed TaqMan^® Assays or conventional PCR-restriction fragment length polymorphism (RFLP). MN levels increased significantly one month after therapy and remained persistently higher than baseline for 2 years. A marked reduction in lymphocyte proliferation capacity was also apparent 2 years after therapy. MLH1 rs1799977 was associated with MN frequency (absolute or net variation) one month after therapy, in two independent groups. Significant associations were also observed for MSH3 rs26279, MSH4 rs5745325, NBN rs1805794, and tumor histotype. Overall, our results suggest that ¹³¹I therapy may pose a long-term challenge to cells other than thyrocytes and that the individual genetic profile may influence ¹³¹I sensitivity, hence its risk-benefit ratio. Further studies are warranted to confirm the potential utility of these single nucleotide polymorphisms (SNPs) as radiogenomic biomarkers in the personalization of radioiodine therapy.

Combinatorial approach of in silico and in vitro evaluation of MLH1 variant associated with Lynch syndrome like metastatic colorectal cancer

Colorectal cancer (CRC) is the third most developing cancer worldwide and Lynch syndrome (LS) accounts for 3–4% of CRC. Genetic alteration in any of DNA mismatch repair (MMR) gene is the major cause of LS that disrupt the normal upstream and downstream MMR events. Germline mutation of MLH1 in heterozygous state have an increased risk for CRC. Defective MMR pathway mostly results in microsatellite instability (MSI) that occurs in high percentage of CRC associated tumors. Here, we reported a patient with LS like metastatic CRC (mCRC) associated with other related cancers. Whole exome sequencing (WES) of the proband was performed to identify potential causative gene. Genetic screening validated by Sanger sequencing identified a heterozygous missense mutation in exon 12 of MLH1 (c.1151T>A, p.V384D). The clinical significance of identified variant was elucidated on the basis of clinicopathological data, computational predictions and various in vitro functional analysis. In silico predictions classified the variant to be deleterious and evolutionary conserved. In vitro functional studies revealed a significant decrease in protein expression because of stability defect leading to loss of MMR activity. Mutant residue found in MutL transducer domain of MLH1 that localized in the nucleus but translocation was not found to be significantly disturbed. In conclusion, our study give insight into reliability of combinatorial prediction approach of in silico and in vitro expression analysis. Hence, we highlighted the pathogenic correlation of MLH1 variant with LS associated CRC as well as help in earlier diagnosis and surveillance for improved management and genetic counselling.

Relevance of hMLH1 -93G>A, 655A>G and 1151T>A polymorphisms with colorectal cancer susceptibility: a meta-analysis based on 38 case-control studies

OBJECTIVE

There has been increasing interest in the study of the association between human mutL homolog 1 (hMLH1) gene polymorphisms and risk of colorectal cancer (CRC). However, results from previous studies are inconclusive. Thus, a meta-analysis was conducted to derive a more precise estimation of the effects of this gene.

METHODS

A comprehensive search was conducted in the PubMed, EMBASE, Chinese Biomedical Literature databases until January 1, 2018. Odds ratio (OR) with 95% confidence interval (CI) was used to assess the strength of the association.

RESULTS

Finally, 38 case-control studies in 32 publications were identified met our inclusion criteria. There were 14 studies with 20668 cases and 19533 controls on hMLH1 -93G>A, 11 studies with 5,786 cases and 8,867 controls on 655A>G and 5 studies with 1409 cases and 1637 controls on 1151T>A polymorphism. The combined results showed that 655A>G and 1151T>A polymorphisms were significantly associated with CRC risk, whereas -93G>A polymorphism was not significantly associated with CRC risk. As for ethnicity, -93G>A and 655A>G polymorphisms were associated with increased risk of CRC among Asians, but not among Caucasians. More interestingly, subgroup analysis indicated that 655A>G might raise CRC risk in PCR-RFLP and HB subgroups.

CONCLUSION

Inconsistent with previous meta-analyses, this meta-analysis shows that the hMLH1 655A>G and 1151T>A polymorphisms might be risk factors for CRC. Moreover, the -93G>A polymorphism is associated with the susceptibility of CRC in Asian population.

Lifestyle chemical carcinogens associated with mutations in cell cycle regulatory genes increases the susceptibility to gastric cancer risk

In the present study, we correlated the various lifestyle habits and their associated mutations in cell cycle (P21 and MDM2) and DNA damage repair (MLH1) genes to investigate their role in gastric cancer (GC). Multifactor dimensionality reduction (MDR) analysis revealed the two-factor model of oral snuff and smoked meat as the significant model for GC risk. The interaction analysis between identified mutations and the significant demographic factors predicted that oral snuff is significantly associated with P21 3'UTR mutations. A total of five mutations in P21 gene, including three novel mutations in intron 2 (36651738G > A, 36651804A > T, 36651825G > T), were identified. In MLH1 gene, two variants were identified viz. one in exon 8 (37053568A > G; 219I > V) and a novel 37088831C > G in intron 16. Flow cytometric analysis predicted DNA aneuploidy in 07 (17.5%) and diploidy in 33 (82.5%) tumor samples. The G2/M phase was significantly arrested in aneuploid gastric tumor samples whereas high S-phase fraction was observed in all the gastric tumor samples. This study demonstrated that environmental chemical carcinogens along with alteration in cell cycle regulatory (P21) and mismatch repair (MLH1) genes may be stimulating the susceptibility of GC by altering the DNA content level abnormally in tumors in the Mizo ethic population.

The relationship between human muth homolog 1 gene mutation at site 415 and sporadic colon cancers in Chinese Han population

Background: The genetic factors of colon cancer play an important role in the tumor development and growth. The incidence of colon cancers has greatly increased in China. However, few data is available for the relationship between human muth homolog 1 (hMLH1) gene mutation at site 415 and sporadic colon cancers in Chinese population. Objective: Investigate the relationship between G→C mutation in hMLH1 gene at site 415 and sporadic colon cancers in Chinese Han population. Methods: Using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and DNA sequencing techniques, the genotype of the hMLH1 gene was analyzed at site 415 in 97 cases of sporadic colon cancer patients and 138 controls. Reverse-transcription (RT)-PCR was used to determine the level of hMLH1 mRNA expression in normal colonic mucosa of patients with different genotype. Results: The frequency of genotype C/C at the 415 site of the hMLH1 gene was significantly higher in colon cancer patients than in controls. The expression levels of hMLH1 mRNA in normal colonic mucosa were similar in colon cancer patients with different genotypes. Conclusion: G’!C mutation in hMLH1 gene at site 415 may represent a genetic factor that is associated with sporadic colon cancer in a small group of Chinese Han population.

Pooling-analysis on hMLH1 polymorphisms and cancer risk: evidence based on 31,484 cancer cases and 45,494 cancer-free controls

To elucidate the veritable relationship between three hMLH1 polymorphisms (rs1800734, rs1799977, rs63750447) and cancer risk, we performed this meta-analysis based on overall published data up to May 2017, from PubMed, Web of knowledge, VIP, WanFang and CNKI database, and the references of the original studies or review articles. 57 publications including 31,484 cancer cases and 45,494 cancer-free controls were obtained. The quality assessment of six articles obtained a summarized score less than 6 in terms of the Newcastle-Ottawa Scale (NOS). All statistical analyses were calculated with the software STATA (Version 14.0; Stata Corp, College Station, TX). We found all the three polymorphisms can enhance overall cancer risk, especially in Asians, under different genetic comparisons. In the subgroup analysis by cancer type, we found a moderate association between rs1800734 and the risk of gastric cancer (allele model: OR = 1.14, P = 0.017; homozygote model: OR = 1.33, P = 0.019; dominant model: OR = 1.27, P = 0.024) and lung cancer in recessive model (OR = 1.27, P = 0.024). The G allele of rs1799977 polymorphism was proved to connect with susceptibility of colorectal cancer (allele model: OR = 1.21, P = 0.023; dominate model: OR = 1.32, P <0.0001) and prostate cancer (dominate model: OR = 1.36, P <0.0001). Rs63750447 showed an increased risk of colorectal cancer, endometrial cancer and gastric cancer under all genetic models. These findings provide evidence that hMLH1 polymorphisms may associate with cancer risk, especially in Asians.

The hMLH1 -93G>A Polymorphism and Risk of Ovarian Cancer in the Chinese Population

Background

As a mismatch repair (MMR) gene, hMLH1 plays an important role in the maintenance of chromosomal integrity. Several studies have investigated the associations of hMLH1 -93G>A (rs1800734) and Ile219Val (rs1799977) in diverse tumor types with discordant results, but their roles in ovarian cancer in the Chinese population remains to be elucidated.

Methods

In a case-control analysis, we assessed the association between these two polymorphisms and ovarian cancer risk in 421 ovarian cancer patients and 689 control subjects in the Chinese population using logistic regression.

Results

We found that the variant hMLH1 genotypes (-93AA and AG) are associated with risk of ovarian cancer (adjusted odds ratio [OR] = 2.02, 95% confidence interval [CI] = 1.42–2.89) compared with the -93GG genotype. The A allele increases the risk of ovarian cancer in a dose-dependent manner (P<10⁻⁴). Functional test showed that -93A allele increased hMLH1 promoter transcriptional activity and the luciferase activity. However, no significant difference was found in the genotype frequencies at the Ile219Val site between the cases and controls.

Conclusions

These findings indicate that the -93G>A polymorphism in hMLH1 may affect ovarian cancer susceptibility in the Chinese population.

Association between MutL homolog 1 polymorphisms and the risk of colorectal cancer: a meta-analysis

PURPOSE

As one of the most essential components of mismatch repair system, MutL homolog 1 (MLH1) plays an increasingly implicated role in initiation and promotion of colorectal carcinogenesis, with germ-line mutations in different loci. However, whether a single genetic variant in MLH1 could predict the risk of cancer was still under doubt and recent studies yielded inconsistent results. Therefore, this meta-analysis aimed at investigating the association between MLH1 single-nucleotide polymorphisms (SNPs) and colorectal cancer (CRC) risks.

METHODS

A systematic literature search of PubMed, MEDLINE, Web of Science and BIOSIS databases was performed to obtain all available SNPs and studies. We focused on three SNPs (rs1800734, rs1799977 and rs63750448) with the most included studies and conducted overall and subgroup analyses after data extraction.

RESULTS

A total of 37,347, 29,114 and 2722 patients in case and control groups were meta-analyzed in four genetic models (AA vs. BB, AB vs. BB, AA+AB vs. BB and AA vs. BB+AB) for each SNP. The overall results suggested that the mutation in rs63750447 predicted a higher CRC risk (AB vs. BB: OR 2.283, 95 % CI 1.612-3.232, P = 0.000; AA+AB vs. BB: OR 2.291, 95 % CI 1.618-3.244, P = 0.000), while rs1800734 and rs1799977 were not associated with CRC risks. Subgroup analysis according to study area, quality score and genotyping technique revealed the similar results.

CONCLUSIONS

As the first meta-analysis reporting the association between rs63750448 and CRC risk, the A allele substitution might be a risk factor for CRC. Additionally, there was no persuasive evidence showing that SNPs of rs1800734 and rs1799977 were related to CRC susceptibility.

The genotype of MLH1 identifies a subgroup of follicular lymphoma patients who do not benefit from doxorubicin: FIL-FOLL study

Though most follicular lymphoma biomarkers rely on tumor features, the host genetic background may also be relevant for outcome. Here we aimed at verifying the contribution of candidate polymorphisms of FCγ receptor, DNA repair and detoxification genes to prognostic stratification of follicular lymphoma treated with immunochemotherapy. The study was based on 428 patients enrolled in the FOLL05 prospective trial that compared three standard-of-care regimens (rituximab-cyclophosphamide-vincristine-prednisone versus rituximab-cyclophosphamide-doxorubicin-vincristine-prednisone versus rituximab-fludarabine-mitoxantrone) for the first line therapy of advanced follicular lymphoma. Polymorphisms were genotyped on peripheral blood DNA samples. The primary endpoint was time to treatment failure. Polymorphisms of FCGR2A and FCGR3A, which have been suggested to influence the activity of rituximab as a single agent, did not affect time to treatment failure in the pooled analysis of the three FOLL05 treatment arms that combined rituximab with chemotherapy (P=0.742, P=0.252, respectively). These results were consistent even when the analysis was conducted by intention to treat, indicating that different chemotherapy regimens and loads did not interact differentially with the FCGR2A and FCGR3A genotypes. The genotype of MLH1, which regulates the genotoxic effect of doxorubicin, significantly affected time to treatment failure in patients in the rituximab-cyclophosphamide-doxorubicin-vincristine-prednisone arm (P=0.001; q<0.1), but not in arms in which patients did not receive doxorubicin (i.e., the rituximab-cyclophosphamide-vincristine-prednisone and rituximab-fludarabine-mitoxantrone arms). The impact of MLH1 on time to treatment failure was independent after adjusting for the Follicular Lymphoma International Prognostic Index and other potential confounding variables by multivariate analysis. These data indicate that MLH1 genotype is a predictor of failure to benefit from rituximab-cyclophosphamide-doxorubicin-vincristine-prednisone treatment in advanced follicular lymphoma and confirm that FCGR2A and FCGR3A polymorphisms have no impact when follicular lymphoma is treated with rituximab plus chemotherapy (clinicaltrials.gov identifier: NCT00774826).

Clinical evaluation of a multiple-gene sequencing panel for hereditary cancer risk assessment

PURPOSE

Multiple-gene sequencing is entering practice, but its clinical value is unknown. We evaluated the performance of a customized germline-DNA sequencing panel for cancer-risk assessment in a representative clinical sample.

METHODS

Patients referred for clinical BRCA1/2 testing from 2002 to 2012 were invited to donate a research blood sample. Samples were frozen at -80° C, and DNA was extracted from them after 1 to 10 years. The entire coding region, exon-intron boundaries, and all known pathogenic variants in other regions were sequenced for 42 genes that had cancer risk associations. Potentially actionable results were disclosed to participants.

RESULTS

In total, 198 women participated in the study: 174 had breast cancer and 57 carried germline BRCA1/2 mutations. BRCA1/2 analysis was fully concordant with prior testing. Sixteen pathogenic variants were identified in ATM, BLM, CDH1, CDKN2A, MUTYH, MLH1, NBN, PRSS1, and SLX4 among 141 women without BRCA1/2 mutations. Fourteen participants carried 15 pathogenic variants, warranting a possible change in care; they were invited for targeted screening recommendations, enabling early detection and removal of a tubular adenoma by colonoscopy. Participants carried an average of 2.1 variants of uncertain significance among 42 genes.

CONCLUSION

Among women testing negative for BRCA1/2 mutations, multiple-gene sequencing identified 16 potentially pathogenic mutations in other genes (11.4%; 95% CI, 7.0% to 17.7%), of which 15 (10.6%; 95% CI, 6.5% to 16.9%) prompted consideration of a change in care, enabling early detection of a precancerous colon polyp. Additional studies are required to quantify the penetrance of identified mutations and determine clinical utility. However, these results suggest that multiple-gene sequencing may benefit appropriately selected patients.

The hMLH1 promoter polymorphisms and cancer susceptibility in Asian populations: a meta-analysis

BACKGROUND

A variety of studies have evaluated the associations between polymorphisms in the promoter regions of the hMLH1 and cancer risk. However, the results remain inconclusive. To better understand the roles of the hMLH1 polymorphisms and cancer risk, we conducted a comprehensive meta-analysis to investigate the association between the hMLH1 -93G/A and 1151T/A (Val384Asp) polymorphisms and cancer risk in Asian population.

METHODS

We performed a meta-analysis by conducting searches of the published studies in Pub Med, CNKI, CBM, ISI web of knowledge and Google scholar search databases. Finally, 12 studies were included into our meta-analysis. Overall and subgroup analyses were performed. Odds ratio (OR) and 95% confidence interval (CI) were used to evaluate the associations between hMLH1 polymorphisms and cancer risk. Statistical analysis was performed with Review Manager 5.0.

RESULTS

Twelve studies addressing two hMLH1 polymorphisms were analyzed among a total of 4128 cancer cases and 4678 controls. For hMLH1 -93G/A, there was no evidence that the hMLH1 -93G/A polymorphism was significantly associated with an increased cancer risk (P>0.05) in Asian populations (heterozygote comparison: OR=0.89 [95% CI (0.75, 1.060)] P=0.20; dominant model comparison: OR=0.98 [95% CI (0.83, 1.15)] P=0.79). In subgroup analysis based on cancer types and the sources of control, no associations were found in colorectal cancer, gastric cancer and "other cancers" under the any gene model except for lung cancer (recessive model comparison: OR=1.69 [95% CI (1.30, 2.19)] P<0.0001). For hMLH1 1151T/A, the polymorphism significantly associated with an increased cancer risk in Asians: OR=1.88 [95% CI (1.49, 2.25)], P<0.0001, and OR=1.87 [95% CI (1.49, 2.25)], P<0.0001.

CONCLUSIONS

Our investigations demonstrated that the hMLH1 -93G/A polymorphism is not a candidate for susceptibility to overall cancers, and that the hMLH1 1151T/A polymorphism is significantly associated with higher cancer risk in Asian populations. Further studies with large sample size for hMLH1 should be conducted.

Novel DNA variants and mutation frequencies of hMLH1 and hMSH2 genes in colorectal cancer in the Northeast China population

Research on hMLH1 and hMSH2 mutations tend to focus on Lynch syndrome (LS) and LS-like colorectal cancer (CRC). No studies to date have assessed the role of hMLH1 and hMSH2 genes in mass sporadic CRC (without preselection by MSI or early age of onset). We aimed to identify novel hMLH1 and hMSH2 DNA variants, to determine the mutation frequencies and sites in both sporadic and LS CRC and their relationships with clinicopathological characteristics of CRC in Northeast of China. 452 sporadic and 21 LS CRC patients were screened for germline and somatic mutations in hMLH1 and hMSH2 genes with PCR–SSCP sequencing. We identified 11 hMLH1 and seven hMSH2 DNA variants in our study cohort. Six of them were novel: four in hMLH1 gene (IVS8-16 A>T, c.644 GAT>GTT, c.1529 CAG>CGG and c.1831 ATT>TTT) and two in hMSH2 gene (−39 C>T, insertion AACAACA at c.1127 and deletion AAG at c.1129). In sporadic CRC, germline and somatic mutation frequencies of hMLH1/hMSH2 gene were 15.59% and 17.54%, respectively (p = 0.52). Germline mutations present in hMLH1 and hMSH2 genes were 5.28% and 10.78%, respectively (p<0.01). Somatic mutations in hMLH1 and hMSH2 genes were 6.73% and 11.70%, respectively (p = 0.02). In LS CRC, both germline and somatic mutation frequencies of hMLH1/hMSH2 gene were 28.57%. The most prevalent germline mutation site in hMSH2 gene was c.1168 CTT>TTT (3.90%), a polymorphism. Somatic mutation frequency of hMLH1/hMSH2 gene was significantly different in proximal, distal colon and rectal cancer (p = 0.03). Our findings elucidate the mutation spectrum and frequency of hMLH1 and hMSH2 genes in sporadic and LS CRC, and their relationships with clinicopathological characteristics of CRC.

Dimovski A. Molecular profile of the Lynch Syndrome in the Republic of Macedonia

The most frequent type of hereditary colorectal cancer, the one occurring in the setting of the Lynch syndrome (LS) is considered a phenotypic manifestation of a germline defect in the mismatch repair mechanism i.e. in the MLH1, MSH2, MSH6 or PMS2 gene. Aiming towards establishment of a standardized protocol involving molecular analyses for diagnosis of this syndrome and developing a unique national register of families with hereditary colorectal cancer syndromes in the Republic of Macedonia, we began a prospective study to reveal the genetic defects among Macedonian patients with colorectal cancer (CRC) and identifying families with hereditary CRC. A total of 53 patients fulfilling the revised Bethesda criteria for MSI-genetic testing were compared to 350 patients with sporadic CRC. The results reveal significant differences in age at diagnosis (p=0.03), involvement of microsatellite instability (p<0.0001) and localization of the tumor in respect to flexura lienalis (p=0.009) and suggest affiliation of the majority of the “Bethesda+” CRCs to the so called Familial Colorectal cancer Type X group. The molecular characterization of LS suspects identified the novel MLH1 c.392C>G nonsense mutation with a possible founder effect in the Macedonian population, the MLH1 ex.3-12 deletion, as well as the c.244A>G mutation, IVS14- 19A>G and IVS4+65A>C changes in MLH1 without confirmed pathological significance. The observed high frequency (87.5%) of the Ile219Val (c.655A>G) variant in MLH1 among the LS suspects prompts further analyses to evaluate its involvement in the development of hereditary CRC by itself or as a risk modifying factor among the patients from the Republic of Macedonia.

MLH1 and XRCC1 polymorphisms in Mexican patients with colorectal cancer

DNA repair proteins maintain DNA integrity; polymorphisms in genes coding for these proteins can increase susceptibility to colorectal cancer (CRC) development. We analyzed a possible association of MLH1 -93G>A and 655A>G and XRCC1 Arg194Trp and Arg399Gln polymorphisms with CRC in Mexican patients. Genomic DNA samples were obtained from peripheral blood of 108 individuals with CRC (study group) at diagnosis and 120 blood donors (control group) from Western Mexico; both groups were mestizos. The polymorphisms were detected by PCR-RFLP. Association was estimated by calculating the odds ratio (OR). We found that the MLH1 and XRCC1 polymorphisms were in Hardy- Weinberg equilibrium. The MLH1 655A>G polymorphism in the 655G allele was associated with a 2-fold increase risk for CRC (OR = 2.04 and 95% confidence interval (95%CI) = 1.12-3.69; P < 0.01), while the MLH1 -93G>A polymorphism allele was associated with a protective effect (OR = 0.60, 95%CI = 0.40-0.89; P = 0.01 in the -93A allele and OR = 0.32, 95%CI = 0.13-0.79; P = 0.01 in the AA genotype). The XRCC1 Arg194Trp and Arg399Gln polymorphisms did not show any significant associations. In conclusion, we found that MLH1 -93G>A and 655A>G polymorphisms are associated with CRC in Mexican patients.

High-throughput mutation profiling identifies frequent somatic mutations in advanced gastric adenocarcinoma

Background

Gastric cancer is one of the leading cancer types in incidence and mortality, especially in Asia. In order to improve survival, identification of a catalogue of molecular alterations underlying gastric cancer is a critical step for developing and designing genome-directed therapies.

Methodology/Principal Findings

The Center for Cancer Genome Discovery (CCGD) at the Dana-Farber Cancer Institute (DFCI) has adapted a high-throughput genotyping platform to determine the mutation status of a large panel of known cancer genes. The mutation detection platform, termed OncoMap v4, interrogates 474 “hotspot” mutations in 41 genes that are relevant for cancer. We performed OncoMap v4 in formalin-fixed paraffin-embedded (FFPE) tissue specimens from 237 gastric adenocarcinomas. Using OncoMap v4, we found that 34 (14.4%) of 237 gastric cancer patients harbored mutations. Among mutations we screened, PIK3CA mutations were the most frequent (5.1%) followed by p53 (4.6%), APC (2.5%), STK11 (2.1%), CTNNB1 (1.7%), and CDKN2A (0.8%). Six samples harbored concomitant somatic mutations. Mutations of CTNNB1 were significantly more frequent in EBV-associated gastric carcinoma (P = 0.046). Our study led to the detection of potentially druggable mutations in gastric cancer which may guide novel therapies in subsets of gastric cancer patients.

Conclusions/Significance

Using high throughput mutation screening platform, we identified that PIK3CA mutations were the most frequently observed target for gastric adenocarcinoma.

RACIAL DIFFERENCES IN MLH1 AND MSH2 MUTATION: AN ANALYSIS OF YELLOW RACE AND WHITE RACE BASED ON THE INSIGHT DATABASE

MLH1 and MSH2 mutations underlie 90% of hereditary nonpolyposis colorectal cancer (HNPCC) mutations. The International Society of Gastrointestinal Hereditary Tumors (InSiGHT) has established an international database of mutations associated with HNPCC. Based on the InSiGHT database and the original references that reported the mutations, we analyzed the distributions of MLH1 and MSH2 mutations in yellow race and white race respectively and compared them subsequently. We found: (1) the distributions of mutation individuals in exon 1, 17 and 19 of MLH1 gene and in exon 2 of MSH2 gene showed significant differences between the two race groups (p < 0.05); (2) the distributions of mutation types in exon 2, 7 and 18 of MLH1 and exon 10 and 16 of MSH2 showed significant differences (p < 0.05); and (3) three mutations (c.649C > T, c.1625A > T and c.1721T > C) in MLH1 and five mutations (c.23C > T, c.187dupG, c.505A > G, c.1168C > T and c.2211-6T > C) in MSH2 have much higher frequency in yellow race than those in white race. Furthermore, three mutations (c.1453G > C, c.1742C > T and c.1758dupC) in MLH1 and two mutations (c.1255C > A and c.1886A > G) in MSH2 were only found in yellow race, which implies that specific mutations in yellow race need more attention when screening mutations in these two genes.

Distinct mutations in MLH1 and MSH2 genes in hereditary non-polyposis colorectal cancer (HNPCC) families from China

Hereditary non-polyposis Colorectal Cancer (HNPCC) is an autosomal dominant inheritance syndrome. HNPCC is the most common hereditary variant of colorectal cancer (CRC), which accounts for 2-5% CRCs, mainly due to hMLH1 and hMSH2 mutations that impair DNA repair functions. Our study aimed to identify the patterns of hMSH2 and hMLH1 mutations in Chinese HNPCC patients. Ninety-eight unrelated families from China meeting Amsterdam or Bethesda criteria were included in our study. Germline mutations in MLH1 and MSH2 genes, located in the exons and the splice-site junctions, were screened in the 98 probands by direct sequencing. Eleven mutations were found in ten patients (11%), with six in MLH1 (54.5%) and five in MSH2 (45.5%) genes. One patient had mutations in both MLH1 and MSH2 genes. Three novel mutations in MLH1 gene (c.157_160delGAGG, c.2157dupT and c.-64G>T) were found for the first time, and one suspected hotspot in MSH2 (c.1168C>T) was revealed.

Association between the hMSH2 IVS12-6 T>C polymorphism and cancer risk: A meta-analysis

The hMSH2 gene, a member of the mismatch repair (MMR) pathway, plays a key role in the maintenance of genomic integrity. The common sequence variation in hMSH2, IVS12-6 T>C, has been implicated in cancer risk. However, the results of published studies on this polymorphism remain conflicting. Hence, we conducted a meta-analysis to clarify the role of the hMSH2 IVS12-6 T>C polymorphism in cancer. We performed a comprehensive literature search updated to March 2011 of studies on the associations between the hMSH2 IVS12-6 T>C polymorphism and cancer risk. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to assess the strength of the associations. Thirteen studies involving 7,527 patients and 8,762 control subjects were included in this meta-analysis. The overall results indicated no major influence of the polymorphism on cancer risk. However, stratified analysis by cancer types showed that the hMSH2 IVS12-6 polymorphism increased the risk for non-Hodgkin's lymphomas (heterozygote comparison: OR=1.62; 95% CI 1.06-2.47). When stratified by the source of controls, significant associations were observed in hospital-based populations (heterozygote comparison: OR=1.28; 95% CI 1.02-1.61). These results indicate that the polymorphism of hMSH2, IVS12-6, may cause a different effect in different types of cancers. To draw more comprehensive conclusions, further prospective studies with larger numbers of participants worldwide are required to examine the associations between this polymorphism and cancer risk.

The association between MLH1 -93 G>A polymorphism of DNA mismatch repair and cancer susceptibility: a meta-analysis

DNA mismatch repair, known as a fundamentally biological pathway, plays key roles in maintaining genomic stability, eliminating mismatch bases and preventing both mutagenesis in the short term and cancerogenesis in the long term. Polymorphisms of MLH1 in individuals may have an effect on the DNA repair capacity and therefore on cancer risk. Recently, emerging studies have been done to evaluate the association between MLH1 -93 G/A polymorphism and cancer risk in diverse populations. However, the results remain conflicting rather than conclusive. In this meta-analysis, we assessed reported studies of association between the MLH1 -93 G/A polymorphism and cancer risk including 13 691 cancer cases and 14 068 controls from 17 published studies. A borderline significant association between the MLH1 -93 G/A polymorphism and cancer risk was observed in overall analysis [heterozygote: odds ratio (OR) = 1.15; 95% confidence interval (CI) 1.05-1.26; homozygote: OR = 1.21; 95% CI, 1.04-1.40; dominant model: OR = 1.13; 95% CI 1.01-1.26; recessive model: OR = 1.21; 95% CI 1.07-1.35, respectively]. In subgroup analysis by ethnicity, significantly increased risks were found in Asian population and mixed population but not in Caucasian population. After stratified analysis according to the quality of literature, increased cancer risks were observed in the studies of lower quality but not in the studies of higher quality. Similarly, elevated cancer risks were observed in hospital-based studies but not in population-based studies. These findings showed no persuasive evidence that MLH1 -93 G/A polymorphism was associated with an increased risk of cancer. On the conservative standpoint, well-designed population-based studies with larger sample size in different ethnic groups should be performed to further confirm these results.

The host genetic background of DNA repair mechanisms is an independent predictor of survival in diffuse large B-cell lymphoma

Several drugs used for diffuse large B-cell lymphoma (DLBCL) treatment rely on DNA damage for tumor cell killing. We verified the prognostic impact of the host DNA repair genotype in 2 independent cohorts of DLBCL treated with R-CHOP21 (training cohort, 163 cases; validation cohort, 145 cases). Among 35 single nucleotide polymorphisms analyzed in the training series, MLH1 rs1799977 was the sole predicting overall survival. DLBCL carrying the MLH1 AG/GG genotype displayed an increased death risk (hazard ratio [HR] = 3.23; P < .001; q =0 .009) compared with patients carrying the AA genotype. Multivariate analysis adjusted for International Prognostic Index identified MLH1 AG/GG as an independent OS predictor (P < .001). The poor prognosis of MLH1 AG/GG was the result of an increased risk of failing both R-CHOP21 (HR = 2.02; P = .007) and platinum-based second-line (HR = 2.26; P = .044) treatment. Survival analysis in the validation series confirmed all outcomes predicted by MLH1 rs1799977. The effect on OS of MLH1, a component of the DNA mismatch repair system, is consistent with its role in regulating the genotoxic effects of doxorubicin and platinum compounds, which are a mainstay of DLBCL first- and second-line treatment.

Analysis of the hMSH2 gene variants in head and neck cancer

The hMSH2 (human MutS homolog 2) gene plays a central role in DNA mismatch repair. Structural variations in the gene may lead to protein instability and deficient mismatch repair. However, the role of polymorphic variants of the hMSH2 gene have not been defined in head and neck cancer. In this study, the roles of three polymorphic variants in the functional domains of the gene were investigated in 166 patients with head and neck cancer by allele-specific PCR, electronical array addressing, and PCR/RFLP (restriction fragment length polymorphism). This is the first study to investigate the gIVS12-6T --> C polymorphism in head and neck cancer. A significant association between the CC genotype and reduced risk of disease suggests that the gIVS12-6T --> C substitution at the splice-acceptor site may affect the risk of head and neck cancer. We did not observe an association between the Asn127Ser and Gly322Asp polymorphisms and cancer risk. A possible role of the gIVS12-6T --> C substitution warrants further validation in larger cohorts because of low allele frequency.

A new familial gastric cancer-related gene polymorphism: T1151A in the mismatch repair gene hMLH1

We designed to understand the effects of the T1151A gene polymorphism in the hMLH1 gene on the pathogenesis of familial gastric cancer. Peripheral blood DNA from 113 patients with familial gastric cancer or suspected familial gastric cancer that were newly identified in the same year, along with 180 healthy subjects, was subjected to polymerase chain reaction-denaturing high-performance liquid chromatography (PCR-DHPLC) and DNA sequencing of exon 12 in the hMLH1 gene. Our results as following, the T1151A detection rate was remarkably higher in patients with familial gastric cancer or suspected familial gastric cancer compared to normal control patients (P < 0.05). Stratified analysis showed that there was a significant difference in the detection rate between the control group and elderly patients whose age of onset was greater than 50 years old (P < 0.05). The detection rate of patients from high-risk families were relatively high (P < 0.05). An especially significant distribution was observed in patients who had suffered precancerous diseases related to gastric cancer (P < 0.01). In conclusion, familial gastric carcinoma families in China carrying the T1151A polymorphism may have a higher risk of suffering from gastric cancer. This gene polymorphism can be used as a candidate screening index for high-risk populations.

I219V polymorphism in hMLH1 gene in patients affected with ulcerative colitis

INTRODUCTION

hMLH1 gene, lying on chromosome 3p21-23, is a key factor of the mismatch repair (MMR) complex, which amends DNA replication errors. MMR alterations are involved in the development of both hereditary and sporadic forms of colorectal carcinoma related to ulcerative colitis (UC). I219V Polymorphism is located on exon 8 of hMLH1 and provides an aminoacidic substitution of isoleucine to valine, on the protein codon 219. This may affect the speed and fidelity of protein synthesis because of a tRNA paucity or changes in the mRNA secondary structure. Most of the hereditary nonpolyposis colon cancer-associated missense mutations of hMLH1 cause structural changes of the amino- or carboxy-terminal regions, involving the domains that interact with ATP and hPMS2.

AIMS AND METHODS

In this study, we analyzed the hMLH1 I219V polymorphism frequency in colectomized patients with UC. Venous blood from 100 ulcerative patients and 97 apparently healthy subjects has been collected. Out of 100 patients affected with UC, 75 noncolectomized showed an alternating course of disease, while 25 did not respond to the common drugs, and underwent colectomy. Genotyping was performed by polymerase chain reaction and following enzymatic digestion by BccI.

RESULTS

No significant differences were found between patients with UC and controls both for genotype and allele frequencies. However, our data show a significant association when colectomized and noncolectomized patients are compared. The frequencies of G homozygosity were 28% in colectomized and 10.7% in noncolectomized patients (p < 0.05, chi(2) = 4.4, Odds ratio = 3.3). The allele frequencies of allele A were 52% in colectomized and 68% in noncolectomized patients; while those of allele G were 48% and 32%, respectively.

CONCLUSIONS

I219V polymorphism in hMLH1 could influence the clinical course of the disease and lead to resistance to therapy.

Polymorphisms of MLH1 in benign prostatic hyperplasia and sporadic prostate cancer

Mismatch repair is one of several DNA repair pathways of which defects may lead to cancer. We hypothesize that polymorphisms of the MLH1 gene can be a risk factor for benign prostatic hyperplasia (BPH) and prostate cancer. The genetic distribution of MLH1 polymorphisms that lead to amino acid changes at codons 132, 219, 384, and 723 were analyzed in BPH and sporadic prostate cancer patients, and compared to healthy controls from an Asian population. These experiments demonstrate a protective role for the codon 384 variant allele against prostate cancer (P=0.031) but not BPH when compared to normal controls and furthermore, an inverse association was observed with stage (P=0.074) and grade (P=0.056) of cancer. This is the first report that demonstrates a protective effect for the race-related MLH1 polymorphism at codon 384 against prostate cancer and these results are important in understanding their role in this disease.

Do polymorphisms and haplotypes of mismatch repair genes modulate risk of sporadic colorectal cancer?

The Czech Republic presents one of the highest incidences of colorectal cancer in the world. We genotyped 10 single nucleotide polymorphisms in five DNA mismatch repair genes in 614 colorectal cancer cases and 614 matched controls from this country. The carriers of T-allele of the hMSH6-556G>T polymorphism were at increased risk of colorectal cancer (OR 1.29; 95% CI 1.02-1.62). The stratification of data showed that risk associated with the polymorphism was confined to rectal cancer (OR 1.42; 95% CI 1.03-1.95). The A-allele of the Ex1-145G>A polymorphism in the hMSH6 gene was associated with a decreased risk of colorectal cancer (OR 0.76; 95% CI 0.60-0.98). The C-allele of the IVS4-101G>C polymorphism in hMSH6 was associated with an increased risk of colon cancer (OR 1.34; 95% CI 1.03-1.74). The carriers of the variant allele for the polymorphism IVS9-1406C>T in hMLH1 exhibited a decreased risk of rectal cancer (OR 0.71; 95% CI 0.51-0.98). We observed a differential distribution of haplotypes based on three hMSH6 polymorphisms (-556G>T-Ex1-145G>A-IVS4-101G>C) in the cases and controls (global P=0.02). The TAG haplotype was associated with a decreased risk of colorectal cancer (OR 0.74; 95% CI 0.59-0.92), whereas the most frequent haplotype GGG was associated with increased risk of rectal cancer (OR 1.32; 95% CI 1.05-1.65). However, multiple hypotheses testing diminishes a statistical significance of above associations. Our data suggest a limited role for the investigated individual variants in mismatch repair genes for the susceptibility to the disease. The haplotypes covering hMSH6 gene may, however, be involved in risk modulation in this population.

The association between genetic variants in hMLH1 and hMSH2 and the development of sporadic colorectal cancer in the Danish population

BACKGROUND

Mutations in the mismatch repair genes hMLH1 and hMSH2 predispose to hereditary non-polyposis colorectal cancer (HNPCC). Genetic screening of more than 350 Danish patients with colorectal cancer (CRC) has led to the identification of several new genetic variants (e.g. missense, silent and non-coding) in hMLH1 and hMSH2. The aim of the present study was to investigate the frequency of these variants in hMLH1 and hMSH2 in Danish patients with sporadic colorectal cancer and in the healthy background population. The purpose was to reveal if any of the common variants lead to increased susceptibility to colorectal cancer.

METHODS

Associations between genetic variants in hMLH1 and hMSH2 and sporadic colorectal cancer were evaluated using a case-cohort design. The genotyping was performed on DNA isolated from blood from the 380 cases with sporadic colorectal cancer and a sub-cohort of 770 individuals. The DNA samples were analyzed using Single Base Extension (SBE) Tag-arrays. A Bonferroni corrected Fisher exact test was used to test for association between the genotypes of each variant and colorectal cancer. Linkage disequilibrium (LD) was investigated using HaploView (v3.31).

RESULTS

Heterozygous and homozygous changes were detected in 13 of 35 analyzed variants. Two variants showed a borderline association with colorectal cancer, whereas the remaining variants demonstrated no association. Furthermore, the genomic regions covering hMLH1 and hMSH2 displayed high linkage disequilibrium in the Danish population. Twenty-two variants were neither detected in the cases with sporadic colorectal cancer nor in the sub-cohort. Some of these rare variants have been classified either as pathogenic mutations or as neutral variants in other populations and some are unclassified Danish variants.

CONCLUSION

None of the variants in hMLH1 and hMSH2 analyzed in the present study were highly associated with colorectal cancer in the Danish population. High linkage disequilibrium in the genomic regions covering hMLH1 and hMSH2, indicate that common genetic variants in the two genes in general are not involved in the development of sporadic colorectal cancer. Nevertheless, some of the rare unclassified variants in hMLH1 and hMSH2 might be involved in the development of colorectal cancer in the families where they were originally identified.

Polymorphism in the hMSH2 gene (gISV12-6T > C) is a prognostic factor in non-small cell lung cancer

Genetic polymorphisms at the genes involved in mismatch repair may determine individual's susceptibility to cancer initiation and progression. However, the prognostic significance of hMSH2 gIVS12-6T>C polymorphism (T-C substitution at the -6 intronic splice acceptor site of exon 13) in non-small cell lung cancer (NSCLC) remains unclear. Therefore, we investigated the frequency of hMSH2 gIVS12-6T>C polymorphism in 156 NSCLC patients and 235 cancer-free individuals matched for age, gender and smoking habit. The correlations between hMSH2 genotypes and protein expression and survival of the patients were also analyzed. The frequencies of hMSH2 genotypes T/T, T/C, and C/C were 37.4%, 43.0%, and 19.6%, respectively, and the variant (C) allele was represented at a significantly higher frequency in the general Taiwanese population than in non-Asian populations (P<0.0001, chi(2) test). No significant difference in hMSH2 genotype distribution was found between NSCLC patients and cancer-free controls (P=0.255, multivariate logistic regression). However, the homozygous wild-type T/T genotype was significantly associated with a poor prognosis (P=0.007, log-rank test). Our study showed that the frequency of the variant C allele was significantly higher in the general Taiwanese population than in non-Asian populations and the T/T genotype of hMSH2 gIVS12-6T>C polymorphism was a poor prognostic factor in NSCLC patients.

Polymorphisms in hMLH1 and risk of early-onset lung cancer in a southeast Chinese population

DNA mismatch repair (MMR) plays an important role in maintaining genome stability. Defects in MMR genes have been involved in several types of sporadic and hereditary cancers. hMLH1 is considered one of central members of the MMR pathway. We conducted a hospital-based case-control study to investigate associations of common variations in the hMLH1 gene and risk of lung cancer. A total of 500 cases and 517 controls were genotyped for seven SNPs in hMLH1. Overall, the rs1799977 I219V polymorphism was marginally associated with the risk of lung cancer (P=0.055). This association was much stronger in younger patients (P=0.01; odds ratio, 5.28; 95% CI 1.45-19.21) and lung squamous cell carcinoma (P=0.006; odds ratio, 3.65; 95% CI 1.44-9.24). These findings indicate that the hMLH1 rs1799977 polymorphism may contribute to the etiology of early-onset lung cancer as well as some specific subtype of lung cancer. Larger association studies are warranted to validate our findings and mechanistic studies are needed to elucidate the underlying molecular mechanisms of the association.

Sporadic colorectal cancer and individual susceptibility: a review of the association studies investigating the role of DNA repair genetic polymorphisms

Mutations in one of the DNA repair genes are one of the most common reasons for cancer, and it may be assumed that the individual genetic background modulating the DNA repair capacity may affect the susceptibility to cancer. Numerous polymorphisms (mainly SNPs) have been identified for DNA repair genes, although their functional outcome and phenotypic effect is often unknown. The aim of the present review is to evaluate the studies investigating a possible influence of DNA repair polymorphisms in the risk of sporadic colorectal cancer and/or adenoma. Overall, no relevant common findings emerge among the studies, except for some statistically significant associations between polymorphisms in the XRCC1 and XPD genes, mainly for colorectal adenoma risk. Other individual associations remain to be confirmed. This inconclusive data may suggest that the modulation of cancer risk depends not only on a single gene/SNP, but also on a joint effect of multiple polymorphisms (or haplotypes) within different genes or pathways, in close interaction with environmental factors. The relevance of many low-penetrance genes in cancer susceptibility is supposed to be very subtle. Several reviewed association studies revealed weaknesses in their design. However, there has been a progressive improvement over the years in aspects such as simultaneous genotyping and combined analyses of different polymorphisms in larger numbers of patients and controls, as well as stratification of results by ethnicity, gender, and tumor localization. This gained experience shows that only carefully designed studies of a sufficient statistical power may resolve the relationships between polymorphisms and colorectal cancer risk.

Single-nucleotide polymorphisms of mismatch repair genes in healthy Chinese individuals and sporadic colorectal cancer patients

Mismatch repair (MMR) genes are among of the most important genes associated with colorectal cancer (CRC). Single-nucleotide polymorphisms (SNPs) are generally thought to provide important information across a wide spectrum of life sciences; however, no study of association between SNPs of MMR genes and Chinese sporadic colorectal cancer (SCRC) is available. We chose 29 reported single-nucleotide variants that have rarely been verified in a population-based study. We identified SNPs and the genotype-phenotype association in Chinese populations of 150 healthy individuals and 160 SCRC patients. We extracted the genomic DNA from the blood of these individuals and used sequencing to determine these SNPs. Three SNPs (MLH1 394G-->C, 655A-->G, 1151T-->A) occurred with a frequency of 8.8-11.2% in the Chinese population. These SNPs formed a series with combined effects. The haplotype of concurrent MLH1 655 and 1151 SNPs and the haplotype combinations of MLH1 1151, MLH1 394 occurred exclusively in SCRC. None of the other 26 variants were detected in the Chinese population.

A human cell-based assay to evaluate the effects of alterations in the MLH1 mismatch repair gene

We describe a new approach to investigate alterations in the human MLH1 mismatch repair (MMR) gene. This is based on complementation of the phenotype of a MLH1-defective subclone of the ovarian carcinoma A2780 cells by transfection of vectors encoding altered MLH1 proteins. Measurements of resistance (tolerance) to methylating agents, mutation rate at HPRT, microsatellite instability (MSI), and steady-state levels of DNA 8-oxoguanine were used to define the MMR status of transfected clones. The approach was validated by transfecting cDNA of wild-type (WT) MLH1, cDNAs bearing two previously identified polymorphisms (I219V and I219L) and two with confirmed hereditary nonpolyposis colorectal cancer (HNPCC) syndrome mutations (G224D and G67R). A low-level expression of two MLH1 polymorphisms partially reversed methylation tolerance and the mutator phenotype, including MSI. Higher levels of I219V resulted in full restoration of these properties to WT. Increased expression of I129L did not fully complement the MLH1 defect, because there was a simultaneous escalation in the level of oxidative DNA damage. The findings confirmed the important relationship between deficient MMR and increased levels of oxidative DNA damage. Mutations from Italian HNPCC families (G224D, G67R, N635S, and K618A) were all ineffective at reversing the phenotype of the MLH1-defective A2780 cells. One (K618A) was identified as a low penetrance mutation based on clinical and genetic observations.

Environmental genotoxicants/carcinogens and childhood cancer: Bridgeable gaps in scientific knowledge

Cancer in children is a major concern in many countries. An important question is whether these childhood cancers are caused by something, or are just tragic random events. Causation of at least some children's cancers is suggested by direct and indirect evidence, including epidemiological data, and animal studies that predict early life sensitivity of humans to carcinogenic effects. Candidate risk factors include genotoxic agents (chemicals and radiation), but also diet/nutrition, and infectious agents/immune responses. With regard to likelihood of risks posed by genotoxicants, there are pros and cons. The biological properties of fetuses and infants are consistent with sensitivity to preneoplastic genotoxic damage. Recent studies of genetic polymorphisms in carcinogen-metabolizing enzymes confirm a role for chemicals. On the other hand, in numerous epidemiological studies, associations between childhood cancers and exposure to genotoxicants, including tobacco smoke, have been weak and hard to reproduce. Possibly, sensitive genetic or ontogenetic subpopulations, and/or co-exposure situations need to be discovered to allow identification of susceptible individuals and their risk factors. Among the critical knowledge gaps needing to be bridged to aid in this effort include detailed tissue and cellular ontogeny of carcinogen metabolism and DNA repair enzymes, and associations of polymorphisms in DNA repair enzymes with childhood cancers. Perinatal bioassays in animals of specific environmental candidates, for example, benzene, could help guide epidemiology. Genetically engineered animal models could be useful for identification of chemical effects on specific genes. Investigations of interactions between factors may be key to understanding risk. Finally, fathers and newborn infants should receive more attention as especially sensitive targets.