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

Global, regional, and national burden and trends of early-onset tracheal, bronchus, and lung cancer from 1990 to 2019

BACKGROUND

Tracheal, bronchus, and lung cancer (TBL) is one of the main cancer health problems worldwide, but data on the burden and trends of early-onset tracheal, bronchus, and lung cancer (EO-TBL) are sparse. The aim of the present study was to provide the latest and the most comprehensive burden estimates of the EO-TBL cancer from 1990 to 2019.

METHODS

Overall, we used data from the Global Burden of Disease (GBD) study in EO-TBL cancer from 1990 to 2019. Evaluation metrics included incidence, mortality, and disability-adjusted life years (DALYs). The joinpoint regression model was used to analyze the temporal trends. Decomposition analysis was employed to analyze the driving factors for EO-TBL cancer burden alterations. Bayesian age-period-cohort (BAPC) analysis was used to estimate trends in the next 20 years.

RESULTS

The global age-standardized incidence rate (ASIR), age-standardized mortality rate (ASMR), and age-standardized DALYs rate (ASDR) for EO-TBL cancer decreased significantly from 3.95 (95% uncertainty interval [UI]: 3.70-4.24), 3.41 (95% UI: 3.19-3.67), 158.68 (95% UI: 148.04-170.92) in 1990 to 2.82 (95% UI: 2.54-3.09), 2.28 (95% UI: 2.07-2.49), 106.47 (95% UI: 96.83-116.51) in 2019 with average annual percent change (AAPC) of -1.14% (95% confidence interval [CI]: -1.32 to -0.95), -1.37% (95% CI: -1.55 to -1.18), and - 1.35% (95% CI: -1.54 to -1.15) separately. The high and high-middle sociodemographic index (SDI) region had a higher burden of EO-TBL cancer but demonstrated a downward trend. The most prominent and significant upward trends were Southeast and South Asia, Africa, and women in the low SDI and low-middle SDI quintiles. At the regional and national level, there were significant positive correlations between ASDR, ASIR, ASMR, and SDI. Decomposition analysis showed that population growth and aging have driven the increase in the number of incidence, mortality, and DALYs in the global population, especially among the middle SDI quintile and the East Asia region. The BAPC results showed that ASDR, ASIR, and ASMR in women would increase but the male population remained relatively flat over the next 20 years.

CONCLUSIONS

Although global efforts have been the most successful and effective in reducing the burden of EO-TBL cancer over the past three decades, there was strong regional and gender heterogeneity. EO-TBL cancer need more medical attention in the lower SDI quintiles and in the female population.

DNA Mismatch Repair Gene Variants in Sporadic Solid Cancers

The phenotypic effects of single nucleotide polymorphisms (SNPs) in the development of sporadic solid cancers are still scarce. The aim of this review was to summarise and analyse published data on the associations between SNPs in mismatch repair genes and various cancers. The mismatch repair system plays a unique role in the control of the genetic integrity and it is often inactivated (germline and somatic mutations and hypermethylation) in cancer patients. Here, we focused on germline variants in mismatch repair genes and found the outcomes rather controversial: some SNPs are sometimes ascribed as protective, while other studies reported their pathological effects. Regarding the complexity of cancer as one disease, we attempted to ascertain if particular polymorphisms exert the effect in the same direction in the development and treatment of different malignancies, although it is still not straightforward to conclude whether polymorphisms always play a clear positive role or a negative one. Most recent and robust genome-wide studies suggest that risk of cancer is modulated by variants in mismatch repair genes, for example in colorectal cancer. Our study shows that rs1800734 in MLH1 or rs2303428 in MSH2 may influence the development of different malignancies. The lack of functional studies on many DNA mismatch repair SNPs as well as their interactions are not explored yet. Notably, the concerted action of more variants in one individual may be protective or harmful. Further, complex interactions of DNA mismatch repair variations with both the environment and microenvironment in the cancer pathogenesis will deserve further attention.

Esophageal cancer genetics in South Africa

Esophageal cancer (EC) is an extremely aggressive cancer with one of the highest mortality rates. The cancer is generally only diagnosed at the later stages and has a poor 5-year survival rate due to the limited treatment options. China and South Africa are two countries with a very high prevalence rate of EC. EC rates in South Africa have been on the increase, and esophageal squamous cell carcinoma is the predominant subtype and a primary cause of cancer-related deaths in the black and male mixed ancestry populations in South Africa. The incidence of EC is highest in the Eastern Cape Province, especially in the rural areas such as the Transkei, where the consumption of foods contaminated with Fusarium verticillioides is thought to play a major contributing role to the incidence of EC. China is responsible for almost half of all new cases of EC globally. In China, the prevalence of EC varies greatly. However, the two main areas of high prevalence are the southern Taihang Mountain area (Linxian, Henan Province) and the north Jiangsu area. In both countries, environmental toxins play a major role in increasing the chance that an individual will develop EC. These associative factors include tobacco use, alcohol consumption, nutritional deficiencies and exposure to environmental toxins. However, genetic polymorphisms also play a role in predisposing individuals to EC. These include single-nucleotide polymorphisms that can be found in both protein-coding genes and in non-coding sequences such as miRNAs. The aim of this review is to summarize the contribution of genetic polymorphisms to EC in South Africa and to compare and contrast this to the genetic polymorphisms observed in EC in the most comprehensively studied population group, the Chinese.

A modifier of Huntington's disease onset at the MLH1 locus

Huntington's disease (HD) is a dominantly inherited neurodegenerative disease caused by an expanded CAG repeat in HTT. Many clinical characteristics of HD such as age at motor onset are determined largely by the size of HTT CAG repeat. However, emerging evidence strongly supports a role for other genetic factors in modifying the disease pathogenesis driven by mutant huntingtin. A recent genome-wide association analysis to discover genetic modifiers of HD onset age provided initial evidence for modifier loci on chromosomes 8 and 15 and suggestive evidence for a locus on chromosome 3. Here, genotyping of candidate single nucleotide polymorphisms in a cohort of 3,314 additional HD subjects yields independent confirmation of the former two loci and moves the third to genome-wide significance at MLH1, a locus whose mouse orthologue modifies CAG length-dependent phenotypes in a Htt-knock-in mouse model of HD. Both quantitative and dichotomous association analyses implicate a functional variant on ∼32% of chromosomes with the beneficial modifier effect that delays HD motor onset by 0.7 years/allele. Genomic DNA capture and sequencing of a modifier haplotype localize the functional variation to a 78 kb region spanning the 3'end of MLH1 and the 5'end of the neighboring LRRFIP2, and marked by an isoleucine-valine missense variant in MLH1. Analysis of expression Quantitative Trait Loci (eQTLs) provides modest support for altered regulation of MLH1 and LRRFIP2, raising the possibility that the modifier affects regulation of both genes. Finally, polygenic modification score and heritability analyses suggest the existence of additional genetic modifiers, supporting expanded, comprehensive genetic analysis of larger HD datasets.

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 clinicopathological significance of hMLH1 hypermethylation in non-small-cell lung cancer: a meta-analysis and literature review

The hMLH1 gene plays an essential role in DNA repair. Methylation of the hMLH1 gene is common in many types of cancer and can lead to the loss of hMLH1 expression. However, the association and clinicopathological significance between hMLH1 promoter hypermethylation and non-small-cell lung cancer (NSCLC) is elusive. Here, we investigated the correlation of hMLH1 promoter hypermethylation and NSCLC using 13 studies by comprising 1,056 lung cancer patients via a meta-analysis. We observed that 1) loss of hMLH1 protein expression was significantly associated with its promoter hypermethylation, 2) hMLH1 gene inactivation through hypermethylation contributed to the tumorigenesis of NSCLC, which could be a decisive factor for the pathogenesis of NSCLC due to its high occurrence in NSCLC tissues compared to normal lung tissues, 3) a correlation exists between histologic subtypes/disease stages (TNM I+II vs III+IV) and hypermethylation status of hMLH1 gene, and 4) NSCLC patients with hMLH1 hypermethylation and subsequent low expression levels of hMLH1 have a short overall survival period than those patients with normal expression of hMLH1 gene. hMLH1 mRNA predicts patient survival in lung cancer, and this was confirmed by using a public database. We then discussed the tumor suppressor function of hMLH1 and the clinicopathological significance of hMLH1 in NSCLC. We concluded that hMLH1 hypermethylation should be an early diagnostic marker for NSCLC and also a prognostic index for NSCLC. hMLH1 is an interesting therapeutic target in human lung cancers.

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.

Expression of the mismatch repair gene hMLH1 is enhanced in non-small cell lung cancer with EGFR mutations

Mismatch repair (MMR) plays a pivotal role in keeping the genome stable. MMR dysfunction can lead to carcinogenesis by gene mutation accumulation. HMSH2 and hMLH1 are two key components of MMR. High or low expression of them often mark the status of MMR function. Mutations (EGFR, KRAS, etc) are common in non-small cell lung cancer (NSCLC). However, it is not clear what role MMR plays in NSCLC gene mutations. The expression of MMR proteins hMSH2 and hMLH1, and the proliferation markers PCNA and Ki67 were measured by immunohistochemistry in 181 NSCLCs. EGFR and KRAS mutations were identified by high resolution melting analysis. Stronger hMLH1 expression correlated to a higher frequency of EGFR mutations in exon 19 and 21 (p<0.0005). Overexpression of hMLH1 and the adenocarcinoma subtype were both independent factors that related to EGFR mutations in NSCLCs (p=0.013 and p<0.0005). The expression of hMLH1, hMSH2 and PCNA increased, while Ki67 expression significantly decreased (p=0.030) in NSCLCs with EGFR mutations. Overexpression of hMLH1 could be a new molecular marker to predict the response to EGFR-TKIs in NSCLCs. Furthermore, EGFR mutations might be an early event of NSCLC that occur before MMR dysfunction.

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.

High prevalence of mucosa-associated E. coli producing cyclomodulin and genotoxin in colon cancer

Some Escherichia coli strains produce toxins designated cyclomodulins (CMs) which interfere with the eukaryotic cell cycle of host cells, suggesting a possible link between these bacteria and cancers. There are relatively few data available concerning the colonization of colon tumors by cyclomodulin- and genotoxic-producing E. coli. We did a qualitative and phylogenetic analysis of mucosa-associated E. coli harboring cyclomodulin-encoding genes from 38 patients with colorectal cancer (CRC) and 31 with diverticulosis. The functionality of these genes was investigated on cell cultures and the genotoxic activity of strains devoid of known CM-encoding gene was investigated. Results showed a higher prevalence of B2 phylogroup E. coli harboring the colibatin-producing genes in biopsies of patients with CRC (55.3%) than in those of patients with diverticulosis (19.3%), (p<0.01). Likewise, a higher prevalence of B2 E. coli harboring the CNF1-encoding genes in biopsies of patients with CRC (39.5%) than in those of patients with diverticulosis (12.9%), (p = 0.01). Functional analysis revealed that the majority of these genes were functional. Analysis of the ability of E. coli to adhere to intestinal epithelial cells Int-407 indicated that highly adherent E. coli strains mostly belonged to A and D phylogroups, whatever the origin of the strains (CRC or diverticulosis), and that most E. coli strains belonging to B2 phylogroup displayed very low levels of adhesion. In addition, 27.6% (n = 21/76) E. coli strains devoid of known cyclomodulin-encoding genes induced DNA damage in vitro, as assessed by the comet assay. In contrast to cyclomodulin-producing E. coli, these strains mainly belonged to A or D E. coli phylogroups, and exhibited a non significant difference in the distribution of CRC and diverticulosis specimens (22% versus 32.5%, p = 0.91). In conclusion, cyclomodulin-producing E. coli belonging mostly to B2 phylogroup colonize the colonic mucosa of patients with CRC.

MLH1 polymorphisms and cancer risk: a meta-analysis based on 33 case-control studies

OBJECTIVE

Cumulative evidence suggests that MLH1, the key component in the mismatch pathway, plays an important role in human cancers. Two potential functional polymorphisms (-93G>A and I219V) of MLH1 have been implicated in cancer risk. The aim of this meta-analysis was to summarize the evidence for associations.

METHODS

Eligible studies were identified by searching the electronic literature PubMed, ScienceDirect and Embase databases for relevant reports and bibliographies. Studies were included if of case-control design investigating MLH1 polymorphisms (-93G>A and I219V) and cancer risk with sufficient raw data for analysis. Odds ratios (OR) and 95% confidence intervals (95% CI) were used to evaluate the strength of associations.

RESULTS

Our meta-analysis from 33 published case-control studies showed the variant A allele of -93G>A polymorphism to be associated with increased risk in all genetic models (AA vs. GG: OR = 1.22, 95% CI: 1.03-1.44), especially among non-Asians (AA vs. GG: OR = 1.28, 95% CI: 1.04-1.58). For the I219V polymorphism, however, there was no main effect associated with overall cancer risk in any genetic model.

CONCLUSIONS

The meta-analysis suggested that the MLH1 -93G>A polymorphism may be a biomarker of cancer susceptibility. Large sample association studies and assessment of gene-to-gene as well as gene-to-environment interactions are required to confirm these findings.

Human mismatch repair protein hMutLα is required to repair short slipped-DNAs of trinucleotide repeats

Mismatch repair (MMR) is required for proper maintenance of the genome by protecting against mutations. The mismatch repair system has also been implicated as a driver of certain mutations, including disease-associated trinucleotide repeat instability. We recently revealed a requirement of hMutSβ in the repair of short slip-outs containing a single CTG repeat unit (1). The involvement of other MMR proteins in short trinucleotide repeat slip-out repair is unknown. Here we show that hMutLα is required for the highly efficient in vitro repair of single CTG repeat slip-outs, to the same degree as hMutSβ. HEK293T cell extracts, deficient in hMLH1, are unable to process single-repeat slip-outs, but are functional when complemented with hMutLα. The MMR-deficient hMLH1 mutant, T117M, which has a point mutation proximal to the ATP-binding domain, is defective in slip-out repair, further supporting a requirement for hMLH1 in the processing of short slip-outs and possibly the involvement of hMHL1 ATPase activity. Extracts of hPMS2-deficient HEC-1-A cells, which express hMLH1, hMLH3, and hPMS1, are only functional when complemented with hMutLα, indicating that neither hMutLβ nor hMutLγ is sufficient to repair short slip-outs. The resolution of clustered short slip-outs, which are poorly repaired, was partially dependent upon a functional hMutLα. The joint involvement of hMutSβ and hMutLα suggests that repeat instability may be the result of aberrant outcomes of repair attempts.

The cumulative effects of polymorphisms in the DNA mismatch repair genes and tobacco smoking in oesophageal cancer risk

The DNA mismatch repair (MMR) enzymes repair errors in DNA that occur during normal DNA metabolism or are induced by certain cancer-contributing exposures. We assessed the association between 10 single-nucleotide polymorphisms (SNPs) in 5 MMR genes and oesophageal cancer risk in South Africans. Prior to genotyping, SNPs were selected from the HapMap database, based on their significantly different genotypic distributions between European ancestry populations and four HapMap populations of African origin. In the Mixed Ancestry group, the MSH3 rs26279 G/G versus A/A or A/G genotype was positively associated with cancer (OR = 2.71; 95% CI: 1.34–5.50). Similar associations were observed for PMS1 rs5742938 (GG versus AA or AG: OR = 1.73; 95% CI: 1.07–2.79) and MLH3 rs28756991 (AA or GA versus GG: OR = 2.07; 95% IC: 1.04–4.12). In Black individuals, however, no association between MMR polymorhisms and cancer risk was observed in individual SNP analysis. The interactions between MMR genes were evaluated using the model-based multifactor-dimensionality reduction approach, which showed a significant genetic interaction between SNPs in MSH2, MSH3 and PMS1 genes in Black and Mixed Ancestry subjects, respectively. The data also implies that pathogenesis of common polymorphisms in MMR genes is influenced by exposure to tobacco smoke. In conclusion, our findings suggest that common polymorphisms in MMR genes and/or their combined effects might be involved in the aetiology of oesophageal cancer.

Lung cancer in never smokers

Lung cancer in never smokers (LCINS) is the seventh leading cause of death among solid tumors. The main risk factor for lung cancer is smoking; however, approximately 15% of lung cancer patients have never smoked. LCINS is more frequent in women, irrespective of geographical location, nevertheless, the highest incidence has been found in South-East Asia. The histological incidence of adenocarcinoma is higher in the group of never smokers than squamous cell carcinoma. There is a familial clustering of lung cancer that is more pronounced in never smokers, where the family history was associated with an increased risk. Genome-wide association studies identified certain chromosomal aberrations in LCINS. Furthermore, the oncogenic mutation pattern is distinct in nonsmoking patients: activating mutations of EGFR or anaplastic lymphoma kinase are more frequent. The etiology of LCINS includes several environmental factors as well, such as environmental tobacco smoke, viral and hormonal factors, a variety of pulmonary diseases and certain occupational exposures. It is now established that EGFR-tyrosine kinase inhibitor treatment (erlotinib and geftinib) in lung cancer is more effective in LCINS, owing to the higher incidence of EGFR mutation in nonsmokers. Despite the growing body of information on LCINS in recent years there is a need to further investigate the pathogenesis of this particular lung cancer. Future studies on LCINS should try to tackle the issues of prevention, early diagnosis and the exploration of novel therapeutic targets to combat lung cancer disease.

Interaction between polymorphisms of DNA repair genes significantly modulated bladder cancer risk

DNA repair is a primary defense mechanism against damage caused by exogenous and endogenous sources. We examined the associations between bladder cancer and 7 polymorphisms from 5 genes involved in the maintenance of genetic stability (MMR: MLH1-93G>A; BER: XRCC1--77T>C and Arg399Gln; NER:XPC Lys939Gln and PAT +/-; DSBR:ATM G5557A and XRCC7 G6721T) in 302 incident bladder cancer cases and 311 hospital controls. Genotyping was done using a polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) technique. The homozygous variant of XRCC7 G6721T (Odds Ratio [OR]: 2.36; 95% Confidence Interval [CI]: 1.13-4.92) was associated with increased bladder cancer risk. In an analysis of combined genotypes, the combination of XRCC1Arg399Gln (Gln allele) with XRCC1-77 T/T led to an increase in risk (OR: 1.61; 95% CI: 1.10-2.36). Moreover, when the XPCLys939Gln (Gln allele) (nucleotide excision repair [NER]) was present together with XRCC7 (T allele) (double strand break repair [DSBR]), the bladder cancer risk dramatically increased (OR: 4.42; 95% CI: 1.23-15.87). Our results suggest that there are multigenic variations in the DNA repair pathway involved in bladder cancer susceptibility, despite the existence of ethnic group differences.

Polymorphisms of mismatch repair gene hMLH1 and hMSH2 and risk of gastric cancer in a Chinese population

The purpose of this study was to determine the genotype and allele frequencies of hMLH1 (-93G>A and I219V) and hMSH2 (-118T>C and IVS12-6T>C) polymorphisms in patients with gastric carcinoma and normal controls, and to evaluate the association between these polymorphisms and the risk of gastric cancer in a hospital-based Chinese population. Genomic DNA was extracted from peripheral blood lymphocytes. A TaqMan assay was used to determine the genotype and allele frequencies of hMLH1 and hMSH2 polymorphisms in data obtained from 554 gastric cancer cases and 592 controls. Unconditional logistic regression was used to assess the association between the four single nucleotide polymorphisms (SNPs) and gastric carcinoma risk. No evidence of an association among any of the four polymorphisms and the risk of gastric cancer was observed. However, when gastric cancer patients were further stratified by age, gender, smoking status, alcohol use and clinicopathological characteristics, and compared with the control populations, the combined variant genotype hMSH2 -118T>C (TC+CC) was not only associated with an increased risk of gastric cancer in subgroups of younger subjects [ages ≤63years; adjusted odds ratio (OR)=1.51, 95% confidence interval (CI), 1.05-2.16], but also with diffuse tumors (adjusted OR=1.41, 95% CI, 1.01-1.96). These data indicate that the polymorphisms of -93G>A, I219V and IVS12-6T>C are not associated with the risk of gastric cancer. However, hMSH2-118T>C combined with variant genotypes (TC+CC) may confer a potential risk of gastric cancer in the Chinese population.

The MLH1 2101C>A (Q701K) variant increases the risk of gastric cancer in Chinese males

Background

Gastric cancer is one of the most common cancers affecting East Asians, and MLH1 could play a critical role during tumorigenesis in this condition.

Methods

Samples from 236 Chinese patients suffering from gastric cancer were screened for MLH1 germline mutations. Carrier frequencies of the mutations were compared between gastric cancer patients and 240 cancer-free controls. Bioinformatic analysis was used to predict the effect of these mutations on protein function and mRNA splicing.

Results

Six MLH1 sequence alterations were identified in gastric cancer patients including two promoter region substitutions, -93G>A and -28A>G, and four missense mutations 649C>T (R217C), 655A>G (I219V), 1151T>A (V384D) and 2101C>A (Q701K). Compared with the MLH1 2101CC genotype, the 2101CA genotype was associated with a risk of gastric cancer (OR = 8.42, 95% CI = 1.04-68.06) in males. Furthermore, the MLH1 2101C>A mutant was predicted by in silico analysis to affect exon splicing ability. Immunohistochemistry of one index patient carrying the MLH1 2101C>A mutation demonstrated a loss of MLH1 protein and normal expression of MSH2 and E-cadherin. No significant differences were demonstrated between cases and controls for the other five MLH1 variants but the data indicated an ethnic difference in the frequency of these variations between Eastern Asians and Western populations.

Conclusions

An ethnic-specific MLH1 mutation spectrum occurred in Chinese gastric cancer patients. The MLH1 2101C>A mutation could be a marker for susceptibility to gastric cancer, particularly in males.

DNA repair gene polymorphisms and risk of early onset colorectal cancer in Lynch syndrome

DNA repair plays a pivotal role in maintaining genomic integrity with over 130 genes involved in various repair pathways that include base excision repair, nucleotide excision repair, double strand break repair and DNA mismatch repair. Polymorphisms within genes that are involved in these processes have been widely reported to be associated with cancer susceptibility in an extensive range of malignancies that include colorectal cancer (CRC). Lynch syndrome is caused by inherited germline mutations in DNA mismatch repair genes, predominantly in MLH1 and MSH2, that predispose to a variety of epithelial malignancies, most notably CRC. Despite being a relatively well understood hereditary cancer syndrome there remain several questions in relation to genetic influences on disease expression. Since Lynch syndrome is associated with a breakdown in DNA mismatch repair variation in other DNA repair genes may influence disease expression. In this report we have genotyped 424 Australian and Polish Lynch syndrome participants for eight common DNA repair gene polymorphisms to assess any association with the age of CRC onset. The DNA repair gene SNPs included in the study were: BRCA2 (rs11571653), MSH3 (rs26279), Lig4 (rs1805386), OGG1 (rs1052133), XRCC1 (rs25487), XRCC2 (rs3218536 and rs1799793) and XRCC3 (rs861539). Cox multi-variant regression modelling failed to provide any convincing evidence of an effect in any of the polymorphisms analysed. The data suggest that polymorphisms in DNA repair genes do not contribute to cancer risk in a population of CRC patients who are at increased risk of disease as a result in a deficiency of DNA mismatch repair.

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.

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.

Polymorphisms of MLH1 and MSH2 genes and the risk of lung cancer among never smokers

Mismatch repair (MMR) plays an important role in repairing nucleotide mismatches during DNA replication. Defects in MMR genes are associated with some sporadic tumors. MLH1 and MSH2 are two of the MMR genes. We conducted a case-control study to investigate the associations between the risk of lung cancer and genetic polymorphisms in the MLH1 and MSH2 genes. The SNP genotypes were determined in 730 lung cancer patients and 730 healthy controls that were frequency matched for the age, gender, and smoking status. Among the SNP polymorphisms, -93A>G (rs1800734), which is located in the promoter region of MLH1, was significantly associated with the risk of lung cancer. The GG genotype for MLH1 -93A>G was associated with a significantly increased risk of lung cancer compared with the AA genotype among the never-smoking group (adjusted OR=1.64, 95% CI=1.10-2.44; P=0.013). Consistently, the haplotype of MLH1 with one -93G risk allele was associated with the risk of lung cancer compared with the AA haplotype among the never-smoking group. Furthermore, the risk of MLH1 -93A>G polymorphism in the never-smoking group related to lung adenocarcinoma was modulated by environmental tobacco smoke (ETS) exposure status, with a significant gene-ETS interaction (P=0.042). No evidence was found of the association between MSH2 and the lung cancer risk. In conclusion, our data suggest that the MLH1 -93A>G polymorphism may contribute to the etiology of lung cancer, particularly in never smokers. This study also suggests that MLH1 -93A>G polymorphisms and ETS exposure have a role in the tumorigenesis of lung adenocarcinoma among never smokers.

MLH1 Differential allelic expression in mutation carriers and controls

Germline defects in the MLH1 gene are associated with Lynch syndrome. A substantial proportion of these mutations leads to premature termination codons and can induce nonsense mediated decay (NMD) of the corresponding transcript. Resulting allelic expression differences represent a fast and inexpensive method to identify patients carrying MLH1 mutations. In patients and controls, we show that allelic expression imbalance (AEI) can be readily detected in RNA extracted from whole blood from patients carrying mutations expected to elicit NMD using mass spectrometry. Mutations closer to the 5' end of the gene tend to show smaller imbalances. AEI can also be detected in normal controls. Analysis of allelic expression in controls and individuals with mutations not expected to exhibit NMD revealed that MLH1 expression is influenced by sequence variation acting in cis. A maximum likelihood framework was used to identify two SNPs, rs1799977 (c.655G>A; p.I219V) and rs1800734 (c.-93 G>A) that are independently associated with expression. These influences are, however, small compared to the differences associated with pathological variants.

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.

Association between polymorphisms in the GSTA4 gene and risk of lung cancer: a case-control study in a Southeastern Chinese population

GST Alpha 4 (GSTA4) has an important role in the protection against oxidative stress induced by carcinogens such as tobacco smoke. However, few studies investigated the association between GSTA4 polymorphisms and lung cancer risk. We genotyped three selected GSTA4 SNPs (rs182623 - 1718:T > A, rs3798804 + 5034:G > A and rs316141 + 13984:C > T) in a case-control study of 500 lung cancer patients and 517 cancer-free controls and evaluated the association between these SNPs and risk of lung cancer in this Han Chinese population. We found that there was a significant difference in genotype and allele frequency distributions of GSTA4 -1718 between the cases and the controls (P = 0.006 and P = 0.003, respectively). Compared with the GSTA4 -1718TT genotype, individuals with the TA + AA genotypes had a significantly decreased risk of lung cancer (adjusted OR, 0.63; 95% CI, 0.47-0.84; P = 0.006). Although there were no such statistical differences between the cases and controls at the loci +5034 and +13984, nor for histological types, individuals carrying the genotypes of -1718TA, +5034GG and +13984CT had a significantly decreased lung cancer risk (OR, 0.37; 95% CI, 0.23-0.61; P < 0.0001), especially for those smokers who smoked </=25 pack-years (P < 0.000001). These results need to be confirmed in larger studies with different ethnic groups.