An investigation on the polymorphisms of two DNA repair genes and susceptibility to ESCC and GCA of high-incidence region in northern China. Mol Biol Rep. 2009;36:357-364. [PMID: 18046624 DOI: 10.1007/s11033-007-9187-y]

XRCC2 knockdown effectively sensitizes esophageal cancer to albumin-paclitaxel in vitro and in vivo

Esophageal cancer (EC), a prevalent malignancy, has a high incidence and mortality. X-ray repair cross complementing 2 (XRCC2) functions on DNA damage and repair that works the progression of various cancers. Nevertheless, the role and mechanism of XRCC2 remain unknown in EC. The XRCC2 expression was examined by reverse transcription quantitative polymerase chain reaction and western blot. The function of XRCC2 in EC were investigated through cell counting kit-8, colony formation, transwell, flow cytometry, chromatin immunoprecipitation, luciferase, and western blot experiments. Besides, the role of XRCC2 in EC was assessed by western blot and immunohistochemistry experiments after nude mice were injected with EC109 cells and treated with nab-paclitaxel. The XRCC2 expression was upregulated in EC. Knockdown of XRCC2 diminished cell viability, and the number of colonies, migration cells and invasion cells of KYSE150 and EC109 cells. Silencing of XRCC2 diminished the cell viability of both two cells with a lower IC50, whereas boosted the apoptosis rate of both cells with the treatment of albumin-paclitaxel. All these outcomes were reverse with the upregulation of XRCC2 in both two cells. Mechanically, XRCC2 was transcriptionally regulated by specificity protein 1 (SP1), and silencing of SP1 inhibited the cell growth of EC. In vivo, transfection of shXRCC2 with or without albumin-paclitaxel treatment both decreased the tumor size and weight, as well as the expression of XRCC2 and Ki-67 in xenografted mice. XRCC2 transcriptionally regulated by SP2 promoted proliferation, migration, invasion, and chemoresistance of EC cells.

Identification of key genes controlling cancer stem cell characteristics in gastric cancer

BACKGROUND

Self-renewal of gastric cancer stem cells (GCSCs) is considered to be the underlying cause of the metastasis, drug resistance, and recurrence of gastric cancer (GC).

AIM

To characterize the expression of stem cell-related genes in GC.

METHODS

RNA sequencing results and clinical data for gastric adenoma and adenocarcinoma samples were obtained from The Cancer Genome Atlas database, and the results of the GC mRNA expression-based stemness index (mRNAsi) were analyzed. Weighted gene coexpression network analysis was then used to find modules of interest and their key genes. Survival analysis of key genes was performed using the online tool Kaplan-Meier Plotter, and the online database Oncomine was used to assess the expression of key genes in GC.

RESULTS

mRNAsi was significantly upregulated in GC tissues compared to normal gastric tissues (P < 0.0001). A total of 16 modules were obtained from the gene coexpression network; the brown module was most positively correlated with mRNAsi. Sixteen key genes (BUB1, BUB1B, NCAPH, KIF14, RACGAP1, RAD54L, TPX2, KIF15, KIF18B, CENPF, TTK, KIF4A, SGOL2, PLK4, XRCC2, and C1orf112) were identified in the brown module. The functional and pathway enrichment analyses showed that the key genes were significantly enriched in the spindle cellular component, the sister chromatid segregation biological process, the motor activity molecular function, and the cell cycle and homologous recombination pathways. Survival analysis and Oncomine analysis revealed that the prognosis of patients with GC and the expression of three genes (RAD54L, TPX2, and XRCC2) were consistently related.

CONCLUSION

Sixteen key genes are primarily associated with stem cell self-renewal and cell proliferation characteristics. RAD54L, TPX2, and XRCC2 are the most likely therapeutic targets for inhibiting the stemness characteristics of GC cells.

Single Nucleotide Polymorphisms (SNPs) of RAD51-G172T and XRCC2-41657C/T Homologous Recombination Repair Genes and the Risk of Triple- Negative Breast Cancer in Polish Women

Double strand DNA breaks are the most dangerous DNA damage which, if non-repaired or misrepaired, may result in genomic instability, cancer transformation or cell death. RAD51 and XRCC2 encode proteins that are important for the repair of double-strand DNA breaks by homologous recombination. Therefore, genetic variability in these genes may contribute to the occurrence and progression of triple-negative breast cancer. The polymorphisms of the XRCC2 gene -41657C/T (rs718282) and of the RAD51 gene, −172G/T (rs1801321), were investigated by PCR-RFLP in 70 patients with triple-negative breast cancer and 70 age- and sex matched non-cancer controls. The obtained results demonstrated a significant positive association between the RAD51 T/T genotype and TNBC, with an adjusted odds ratio (OR) of 4.94 (p = 0.001). The homozygous T/T genotype was found in 60 % of TNBC cases and in 14 % of the used controls. Variant 172 T allele of RAD51 increased cancer risk (OR = 2.81 (1.72–4.58), p < .0001). No significant associations were observed between -41657C/T genotype of XRCC2 and the incidence of TNBC. There were no significant differences between the distribution of XRCC2 -41657C/T genotypes in the subgroups assigned to histological grades. The obtained results indicate that the polymorphism of RAD51, but not of XRCC2 gene, may be positively associated with the incidence of triple-negative breast carcinoma in the population of Polish women.

An association between the -41657 C/T polymorphism of X-ray repair cross-complementing 2 (XRCC2) gene and ovarian cancer

X-ray repair cross-complementing group 2 (XRCC2) gene is important for the repair of double-strand DNA breaks (DSB) by homologous recombination (HR). XRCC2 polymorphisms may be associated with the development of certain types of cancers, but little is known about their association with ovarian carcinoma. XRCC2 -41657C/T (rs718282) polymorphisms were genotyped by the PCR-RFLP (restriction fragment length polymorphism) method in 608 patients with ovarian cancer and in 400 cancer-free women, who served as controls. In the present work, a relationship was identified between XRCC2 -41657C/T polymorphism and the incidence of ovarian cancer. An association was observed between ovarian carcinoma occurrence and the presence of T/T genotype [OR = 3.50 (2.46-4.97), p < 0.0001]. A tendency for an increased risk of ovarian cancer was detected with the occurrence of T allele of XRCC2 polymorphism. There were no significant differences between the distribution of XRCC2 -41657C/T genotypes in the subgroups assigned to histological grades. We suggest that the -41657C/T polymorphism of the XRCC2 gene may be risk factors for ovarian cancer development.

XRCC2 gene polymorphisms and its protein are associated with colorectal cancer susceptibility in Chinese Han population

XRCC2 is an essential part of the homologous recombination repair pathway. However, relatively little is known about the effect of XRCC2 gene C41657T and G4234C polymorphisms on the individual susceptibility to colorectal cancer (CRC). The purpose of this study was to investigate the association between XRCC2 gene C41657T and G4234C polymorphisms and CRC and to explore the relationship among the polymorphisms and clinicopathologic parameters and protein expression levels of XRCC2. A hospital-based case-control study was conducted with 246 CRC cases and 262 healthy controls. The genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism. XRCC2 protein was analyzed by immunohistochemistry for the paraffin sections of 120 CRC cases. The study data showed that the C41657T genotypes were associated with the risk of CRC. The CT/TT genotypes and T allele were overrepresented among the CRC cases. Compared with CC, CT/TT enhanced the risk of CRC (odds ratio = 1.646, 95 % confidence interval = 1.127-2.404, P = 0.010). XRCC2 protein expression of CRC patients with CT/TT genotypes was significantly higher than that of the patients with CC genotype (χ (2) = 4.887, P = 0.027). XRCC2 gene G4234C polymorphisms have no relevance to the risk of CRC. Our findings suggest that XRCC2 C41657T polymorphism may adjust the XRCC2 expression and might influence susceptibility of CRC.

Downregulation of MLL3 in esophageal squamous cell carcinoma is required for the growth and metastasis of cancer cells

The mixed lineage leukemia 3 (MLL3), a member of the mixed lineage leukemia (MLL) family, has been reported to be mutated in multiple cancer types. However, its function in esophageal squamous cell carcinoma (ESCC) remains poorly understood. Here, we found that the expression of MLL3 was downregulated in ESCC tissues. Moreover, over-expression of MLL3 in ESCC cells inhibited cell proliferation and migration, while the knockdown expression of MLL3 promoted the tumorigenicity of ESCC cells. Mechanistically, MLL3 regulated the expression of multiple growth-related and migration-related genes. Taken together, our study suggested that downregulation of MLL3 was very important in the progression of ESCC.

Overexpression of WRAP53 is associated with development and progression of esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is a highly aggressive cancer whose underlying molecular mechanisms are poorly understood. The natural antisense transcript (NAT) WRAP53 regulates p53 expression and WRAP53 protein is a component of telomerase. NATs play key roles in carcinogenesis, and although WRAP53 is known to increase cancer cell survival, its role in ESCC clinicopathology is unknown. The aim of this study was to investigate WRAP53 expression in ESCC and to correlate it with clinicopathological characteristics.

METHODS

WRAP53 mRNA and protein expression was measured by quantitative PCR (qRT-PCR) and western blotting, respectively, in 4 ESSC cells lines and in 45 paired ESCC and non-neoplastic esophageal mucosa tissues. To correlate WRAP53 protein expression with clinicopathological characteristics, immunohistochemistry (IHC) was performed on 134 ESCC and 85 non-neoplastic esophageal mucosa tissues.

RESULTS

Expression of WRAP53 was detected in all ESCC cell lines and was upregulated in the ESCC tissues compared with the corresponding non-neoplastic tissues (P<0.01). More cells expressed WRAP53 protein in the ESCC tissues than in the non-neoplastic tissues (P<0.01). Overexpression of WRAP53 was significantly correlated with tumor infiltration depth (P = 0.000), clinical stage (P = 0.001), and lymph node metastasis (P = 0.025). Wrap53 expression was not correlated with age, gender, or tumor differentiation.

CONCLUSION

This report indicates increased expression of WRAP53 in ESCC and that WRAP53 overexpression is correlated with tumor progression. WRAP53 may play a significant role in ESCC; accordingly, WRAP53 could be a useful biomarker for ESCC.

Polymorphism of the DNA repair genes RAD51 and XRCC2 in smoking- and drinking-related laryngeal cancer in a Polish population

INTRODUCTION

Cigarette smoke and alcohol can generate reactive oxygen species, which may induce DNA double-strand breaks (DSBs), the most serious DNA lesion. In humans, DSBs are repaired mainly by non-homologous end joining and homologous recombination repair (HRR). Several polymorphisms in the DNA repair gene have been extensively studied in the association with various human cancers. In the present work we investigated the association between polymorphisms of two HRR genes, XRCC2 and RAD51, and tobacco- and alcohol-related larynx cancer in a Polish population.

MATERIAL AND METHODS

Two polymorphisms of the XRCC2 gene, -41657C > T (rs718282) and 31479G > A (rs3218536), as well as one polymorphism of the RAD51 gene, -135G > C (rs1801320), were investigated by PCR-RFLP in 253 patients with larynx cancer and 253 age- and sex-matched non-cancer controls.

RESULTS

Analysis of the gene-smoking and -drinking interactions revealed a weak association between larynx cancer and the -41657C > T polymorphisms of the XRCC2 gene among the moderate alcohol drinkers. The C allele of the -135G > C polymorphism of RAD51 increased cancer risk in the smoker group. Increased risk was also found for heavy drinkers. Additionally, there were no significant differences between distributions of genotypes in subgroups assigned to different TNM stages and grades.

CONCLUSIONS

The results indicated that the -135G > C polymorphism of the RAD51 gene may be associated with smoking- and drinking-related larynx cancer in Poland.

PLC-ε1 gene polymorphisms significantly enhance the risk of esophageal squamous cell carcinoma in individuals with a family history of upper gastrointestinal cancers

BACKGROUND AND AIMS

Phospholipase C epsilon 1 (PLCε1) may regulate cell growth, differentiation, apoptosis and angiogenesis and play an important role in carcinogenesis and the progression of several cancers. This study was designed to validate the association of the PLCε1 rs2274223 single nucleotide polymorphism (SNP) with esophageal squamous cell carcinoma (ESCC) as identified by genome-wide association studies (GWAS) and further assess whether the rs11599672 SNP could affect an individual's susceptibility to ESCC.

METHODS

These two SNPs were genotyped by polymerase chain reaction ligase detection reaction (PCR-LDR) in 527 ESCC patients and 527 controls.

RESULTS

Compared with the rs2274223 SNP AA genotype, other genotypes or combined genotypes all enhanced the risk of ESCC. Further analyses showed that AG/GG genotype carriers with a family history of upper gastrointestinal cancers (UGIC) had an increased risk of ESCC than those AA genotype carriers without UGIC family history (OR = 2.10, 95% CI = 1.46-3.10). Overall, rs11599672 SNP had no influence on ESCC susceptibility. However, UGIC family history elevated the risk of ESCC for subjects with the TT genotype (OR = 1.59, 95% CI = 1.13-2.24).

CONCLUSIONS

These results highlighted the role of a genetic factor in ESCC and suggested that the PLCε1 rs2274223 SNP might be an effective genetic marker to assess the risk of ESCC in individuals with a UGIC family history from a region of high incidence in northern China.

Expression and clinical significance of the DNA repair enzyme MYH in esophageal squamous cell carcinoma

MYH is an important enzyme in combating DNA oxidative stress in the occurrence and development of various types of tumors. To investigate the correlation between expression of the DNA repair enzyme MYH in esophageal squamous cell carcinoma and 8-oxoguanine (8-oxoG) oxidative damage, as well as the clinical significance of altered MYH expression, tissues from 175 esophageal carcinoma cases were investigated in the present study. MYH expression and 8-oxoG oxidative damage in squamous cell carcinoma and adjacent normal tissue were assessed by immunohistochemistry and Western blotting. In 82.9% (145/175) of the cases, MYH protein expression in esophageal squamous cell carcinoma was lower than that of adjacent normal tissue (t=4.24, P<0.001). Additionally, 8-oxoG staining was higher in the tumors than in the normal tissue. Lower expression of MYH in esophageal squamous cell carcinoma was associated with depth of invasion, venous invasion, TNM stage and lymph node metastasis (P<0.05). In conclusion, a lower MYH expression level in esophageal cell carcinoma tissue was inversely associated with more severe 8-oxoG oxidative damage, suggesting that changes in MYH activity correspond to increased DNA damage in tumor cells. The use of MYH expression as a postoperative index for esophageal squamous cell carcinoma may guide the formulation of individualized chemotherapy for patients after surgery.

Analysis of the polymorphisms XRCC1Arg194Trp and XRCC1Arg399Gln in gliomas

XRCC genes (X-ray cross-complementing group) were discovered mainly for their roles in protecting mammalian cells against damage caused by ionizing radiation. Studies determined that these genes are important in the genetic stability of DNA. Although the loss of some of these genes does not necessarily confer high levels of sensitivity to radiation, they have been found to represent important components of various pathways of DNA repair. To ensure the integrity of the genome, a complex system of DNA repair was developed. Base excision repair is the first defense mechanism of cells against DNA damage and a major event in preventing mutagenesis. Repair genes may play an important role in maintaining genomic stability through different pathways that are mediated by base excision. In the present study, we examined XRCC1Arg194Trp and XRCC1Arg399Gln polymorphism using PCR-RFLP in 80 astrocytoma and glioblastoma samples. Patients who had the allele Trp of the XRCC1Arg194Trp polymorphism had an increased risk of tumor development (OR = 8.80; confidence interval at 95% (95%CI) = 4.37-17.70; P < 0.001), as did the allele Gln of XRCC1Arg399Gln (OR = 1.01; 95%CI = 0.53-1.93; P = 0.971). Comparison of overall survival of patients did not show significant differences. We suggest that XRCC1Arg194Trp and XRCC1Arg399Gln polymorphisms are involved in susceptibility for developing astrocytomas and glioblastomas.

Role of microRNA let-7 and effect to HMGA2 in esophageal squamous cell carcinoma

To investigated the role of microRNA (miRNA) let-7 and its regulation on high mobility group A2 (HMGA2) protein expression in esophageal squamous cell carcinoma (ESCC). Let-7 expressions were detected in esophageal cancer cell line Eca109, and 45 paired of fresh ESCC and normal adjacent tissues (NAT) by real-time quantitative PCR (qRT-PCR). To evaluate the role of let-7 and HMGA2, cell proliferations were analyzed with synthetic let-7 mimics- or its inhibitor-transfected cells. Moreover, expressions of HMGA2 were performed by western blotting and further confirmed by 150 paired of formalin-fixed, paraffin-embeded (FFPE) ESCC and NAT by immunohistochemistry (IHC). In Eca109, when transfected with let-7 mimics, accumulation of let-7 was obviously suppressed cell proliferation with approximately 14%. Conversely, when Eca109 transfected with let-7 inhibitor, expression of let-7 was declined, which promoted cell proliferation with approximately 16%. Both of them had no effect on the level of HMGA2 mRNA. The transcription of let-7 inversely correlated with HMGA2 protein. Compared with the NAT, expression of let-7 was significantly lower in ESCC tissues (P < 0.05), and there was a significant correlation between low expression of let-7 and lymph node metastasis in ESCC (P < 0.05). Moreover, the protein expression of HMGA2 was significantly higher in ESCC compared with NAT (P < 0.05). However, mRNA expression of HMGA2 had no obvious significance between them. The present results demonstrated that let-7 and HMGA2 involved in ESCC carcinogenesis. Let-7 could inhibit cell proliferation and lower expressed in ESCC, and there was a correlation between let-7 lower expression and lymph node metastasis in ESCC patients. As well as, HMGA2 protein expression was significantly higher in ESCC than that in NAT, and HMGA2 may negatively regulated by let-7 at the post- transcriptional level in ESCC.

Effects of selected genetic polymorphisms in xeroderma pigmentosum complementary group D on gastric cancer

DNA repair capacity (DRC) can be altered based on sequence variations in DNA repair genes, which may result in cancer susceptibility. The current study was to evaluate the association between genetic polymorphisms, including associated haplotypes of xeroderma pigmentosum complementary group D (XPD), and individual susceptibility to gastric cancer. Two-hundred-eight patients with gastric cancer and 339 healthy controls were enrolled in this study. Their genomic DNA was extracted from peripheral blood leukocytes. The genotypes at exon 6, 10 and 23 were identified by polymerase chain reaction (PCR). Unconditional logistic regression model was used to analyze the effects of the polymorphisms, including the corresponding haplotypes, on the susceptibility to develop gastric cancer. The proportion of genotypes GA or AA at exon 10 in cases was showed to be significantly higher than that in controls (P < 0.01, P < 0.01, respectively). The risk of genotype GA or AA carriers to develop gastric cancer was simultaneously much higher (OR = 3.38, 95% CI 2.30-4.95; OR = 6.13, 95% CI 2.45-15.31, respectively). The allele A at exon 10 was also observed to manifest a substantially higher frequency in cases compared to controls (P < 0.01), which might indicate an increased tendency to gastric cancer (OR = 2.40, 95% CI 1.81-3.17). No significant differences were found in the distribution of genotypes at exon 6 or 23 between the two groups (P = 0.23, P = 0.52; P = 0.44, P = 0.56, respectively). By haplotype analysis, haplotype AAA could individually increase incidence of gastric cancer (P < 0.01, OR = 3.39, 95% CI 2.21-5.21). In contrast, haplotypes CGA and AGA were showed a decline in gastric cancer susceptibility (OR = 0.67, 95% CI 0.46-0.97; OR = 0.58, 95% CI 0.41-0.83, respectively). The rest of haplotypes made no statistically significant difference between cases and controls. Taken together, this study demonstrates that the genetic variation at exon 10 and haplotype AAA may be contributing factors in developing gastric cancer.

Polymorphic DNA repair and metabolic genes: a multigenic study on gastric cancer

Risk factors for gastric cancer (GC) include inter-individual variability in the inflammatory response to Helicobacter pylori infection, in the ability of detoxifying DNA reactive species and repairing DNA damage generated by oxidative stress and dietary carcinogens. To evaluate the association between polymorphic DNA repair genes and GC risk, a case-control study including 314 histologically confirmed GC patients and 548 healthy controls was conducted in a GC high-risk area in Tuscany, Italy. Polymorphic variants of base excision repair (APE1-D148E, XRCC1-R194W, XRCC1-R399Q and OGG1-S326C), nucleotide excision repair (XPC-PAT, XPA-23G>A, ERCC1-19007T>C and XPD-L751Q), recombination (XRCC3-T241M) and alkylation damage reversal (MGMT-L84F) were tested for their potential role in the development of GC by using logistic regression models. The same population was also characterised for GSTT1 and GSTM1 variant alleles to search for possible functional interactions between metabolic and DNA repair genotypes by two-way interactions using multivariate logistic models. No significant association between any single DNA repair genotype and GC risk was detected with a borderline association with the XPC-PAT homozygous genotype [odds ratio (OR) =1.42; 95% confidence interval (CI) 0.94-2.17]. Gene-gene interaction analysis revealed combinations of unfavourable genotypes involving either multiple DNA repair polymorphisms or DNA repair and GST-specific genotypes. The combination of the XPC-PAT and the XPA variant alleles significantly increased GC risk (OR=2.15; 95% CI 1.17-3.93, P=0.0092). A significant interaction was also found between the APE1 wild-type genotype and either the single GSTT1 (OR=4.90; 95% CI 2.38-10.11, P=0.0079) or double GSTM1-GSTT1 null (OR=7.84; 95% CI 3.19-19.22, P=0.0169) genotypes or the XPA-mutant allele (OR=3.56; 95% CI 1.53-8.25, P=0.0012). These findings indicate that a complex interaction between host factors such as oxidative stress, antioxidant capacity and efficiency of multiple DNA repair pathways underlies the inter-individual variability in GC risk.

Downregulation of ornithine decarboxylase by pcDNA-ODCr inhibits gastric cancer cell growth in vitro

Ornithine decarboxylase (ODC), the first rate-limiting enzyme of polyamine biosynthesis, was found to be associated with cell growth, proliferation and transformation. ODC gene expression in gastric cancer was increased and its level was positively correlated with the degree of malignity of gastric mucosa and development of gastric lesions. In order to evaluate the therapeutic effects of antisense RNA of ODC on gastric cancer, an antisense RNA of ODC expressing plasmid pcDNA-ODCr which delivered a 120 bp fragment complementary to the initiation codon of ODC gene was constructed and transfected to gastric cancer cells SGC7901 and MGC803. Expression of ODC in gastric cancer cells was determined by western blot. Cell proliferation was assessed by MTS assay. Cell cycle was analyzed by flow cytometry and Matrigel assay was performed to assess the ability of gastric cancer cell invasiveness. The results showed that the ODC gene expression in gastric cancer cells transfected with the pcDNA-ODCr was downregulated efficiently. Tumor cell proliferation was suppressed significantly, and cell cycle was arrested at G1 phase. Gastric cancer cells had reduced invasiveness after gene transfer. Our study suggested that antisense RNA of ODC expressing plasmid pcDNA-ODCr had antitumor activity by inhibiting the expression of ODC, and downregulation of ODC expression using a gene therapy approach might be a novel therapeutic strategy for gastric cancer.

ARLTS1, MDM2 and RAD51 gene variations are associated with familial breast cancer

Genetic factors that contribute to the risk of breast cancer are largely not known and association studies have revealed several genes with low penetrance risk alleles for breast cancer. Analysis of these genes may provide important information on the risk factors affecting carcinogenesis. Variations in the ARLTS1, RAD51 and MDM2 genes have been associated with increased risk of different cancer types but for breast cancer the results are not consistent. In this study we investigated the role of the allelic variants in candidate genes acting in the tumor suppressor, DNA repair and p53 pathways as risk factors for familial breast cancer in 147 patients displaying characteristics of familial disease. Presence of the polymorphic variants were investigated by amplification of the corresponding regions and restriction fragment length polymorphism analysis. Genotype and allele frequencies in the patients were significantly different for all three variants. Our results indicate that the polymorphic variants might affect individual susceptibility towards breast cancer.

Genetic polymorphisms in double-strand break DNA repair genes associated with risk of oral premalignant lesions

Oral premalignant lesions (OPLs) are early genetic events en route to oral cancer. To identify individuals susceptible to OPL is critical to the prevention of oral cancer. In a case-control study consisting of 147 patients with histologically confirmed OPL and 147 matched controls, we evaluated the associations of 10 genetic variants in nine genes of the double-strand break (DSB) DNA repair pathway with OPL risk. The most notable finding was an intronic polymorphism (A17893G) of the XRCC3 gene. Compared with the homozygous wild-type AA genotype, the odds ratio (OR) (95% confidence interval [CI]) for the heterozygous AG and homozygous variant GG genotype was 0.85 (0.49-1.48) and 0.18 (0.07-0.47), respectively (P for trend=0.002). In addition, compared with the most common A-C haplotypes of XRCC3 (in the order of A17893G-T241M), the G-C haplotypes were associated with a significantly decreased risk of OPL (OR=0.40, 95% CI 0.23-0.68). Moreover, compared with individuals without the G-C haplotype, the OR was 1.04 (0.56-1.95) and 0.20 (0.08-0.51) for subjects with one copy and two copies of the G-C haplotypes, respectively (P for trend=0.005). Classification and regression tree (CART) analysis further revealed potential high-order gene-gene and gene-environmental interactions and categorised subjects into different risk groups according to their specific polymorphic signatures. Overall, our study provides the first epidemiological evidence supporting a connection between DSB gene variants and OPL development. Our data also suggest that the effects of high-order interactions should be taken into consideration when evaluating OPL predisposition.