DNA repair XRCC1 Arg399Gln polymorphism alone, and in combination with CYP2E1 polymorphisms significantly contribute to the risk of development of childhood acute lymphoblastic leukemia

DNA repair pathways as guardians of the genome: Therapeutic potential and possible prognostic role in hematologic neoplasms

DNA repair pathways, which are also identified as guardians of the genome, protect cells from frequent damage that can lead to DNA breaks. The most deleterious types of damage are double-strand breaks (DSBs), which are repaired by homologous recombination (HR) and non-homologous end joining (NHEJ). Single strand breaks (SSBs) can be corrected through base excision repair (BER), nucleotide excision repair (NER), and mismatch repair (MMR). Failure to restore DNA lesions or inappropriately repaired DNA damage culminates in genomic instability and changes in the regulation of cellular functions. Intriguingly, particular mutations and translocations are accompanied by special types of leukemia. Besides, expression patterns of certain repair genes are altered in different hematologic malignancies. Moreover, analysis of mutations in key mediators of DNA damage repair (DDR) pathways, as well as investigation of their expression and function, may provide us with emerging biomarkers of response/resistance to treatment. Therefore, defective DDR pathways can offer a rational starting point for developing DNA repair-targeted drugs. In this review, we address genetic alterations and gene/protein expression changes, as well as provide an overview of DNA repair pathways.

Modulatory role of GSTM1 null genotype on the frequency of micronuclei in pesticide-exposed agricultural workers

In this study, we aimed to investigate the extent of genotoxic risk and the association between null GSTM1/GSTT1 and GSTP1 Ile105Val variants and cellular DNA damage, as measured by micronucleus (MN) assay in a group of agricultural workers from Denizli, Turkey. Peripheral blood samples were collected from 116 subjects, including 58 workers who were occupationally exposed to pesticides and 58 healthy unexposed controls. The MN frequencies of each individual were assessed by cytokinesis-blocked micronuclei assays on lymphocytes. Genotypes for different GST variants were determined using polymerase chain reaction-based methods. A significant 3.4-fold increase in MN frequency was observed in workers compared with the controls ( p < 0.001). Among the GST genotypes, only the GSTM1 null genotype was found to be significantly associated with an increased MN frequency in workers ( p = 0.01). Individuals with a concomitant null GSTM1/GSTT1 genotype demonstrated a significant ( p = 0.01) increase in MN frequency compared with those with functional isozymes in the exposed worker group. The association of the GSTM1 null genotype with higher MN frequency suggests that it may be a modifier of genotoxic risk in individuals exposed to pesticides and may thus be a candidate susceptibility biomarker for human biomonitoring studies.

The association between XRCC1 Arg399Gln polymorphism and risk of leukemia in different populations: a meta-analysis of case-control studies

Background

Associations between Arg399Gln single-nucleotide polymorphism (SNP) in the XRCC1 gene and leukemia susceptibility have been studied extensively, however, the results are inconsistent. The aim of this study was to determine these associations using meta-analytical methods.

Methods

A meta-analysis was performed to examine the associations between XRCC1 Arg399-Gln SNP and leukemia risk. A literature search of PubMed and Web of Science databases was conducted to identify relevant studies published up to March 10, 2015. The references of the retrieved articles were also screened. All the statistical analyses were conducted using Review Manager software.

Results

The XRCC1 Arg399Gln SNP was found to be associated with increased childhood risk of acute lymphoblastic leukemia among Asians under the dominant (odds ratio [OR] 2.11, 95% confidence interval [CI] 1.50–2.97, P<0.0001), allele contrast (OR 1.72, 95% CI 1.33–2.23, P<0.0001), and homozygote contrast (OR 2.34, 95% CI 1.25–4.36, P=0.008) models. However, no association was found in Caucasians between the SNP and risk of either chronic myeloid leukemia or chronic lymphocytic leukemia under any contrast model.

Conclusion

The findings of the current meta-analysis indicate that the XRCC1 Arg399Gln SNP is a risk factor for childhood lymphoblastic leukemia in Asians.

Amerindian genetic ancestry and INDEL polymorphisms associated with susceptibility of childhood B-cell Leukemia in an admixed population from the Brazilian Amazon

Acute lymphoblastic leukemia (ALL) is a malignant tumor common in children. Studies of genetic susceptibility to cancer using biallelic insertion/deletion (INDEL) type polymorphisms associated with cancer development pathways may help to clarify etymology of ALL. In this study, we investigate the role of eight functional INDEL polymorphisms and influence of genetic ancestry to B-cell ALL susceptibility in children of Brazilian Amazon population, which has a high degree of inter-ethnic admixture. Ancestry analysis was estimated using a panel of 48 autosomal ancestry informative markers. 130 B-cell ALL patients and 125 healthy controls were included in this study. The odds ratios and 95% confidence intervals were adjusted for confounders. The results indicated an association between the investigated INDEL polymorphisms in CASP8 (rs3834129), CYP19A1 (rs11575899) e XRCC1 (rs3213239) genes in the development of B-cell ALL. The carriers of Insertion/Insertion (Ins/Ins) genotype of the polymorphism in CASP8 gene presented reduced chances of developing B-cell ALL (P=0.001; OR=0.353; 95% CI=0.192-0.651). The Deletion/Deletion (Del/Del) genotype of the polymorphism in CYP19A1 gene was associated to a lower chance of developing B-cell ALL (P=3.35×10-6; OR=0.121; 95% CI=0.050-0.295), while Del/Del genotype of the polymorphism in XRCC1 gene was associated to a higher chance of developing B-cell ALL (P=2.01×10-4; OR=6.559; 95% CI=2.433-17.681). We also found that Amerindian ancestry correlates with the risk of B-cell ALL. For each increase of 10% in the Amerindian ancestry results in 1.4-fold chances of developing B-cell ALL (OR=1.406; 95% IC=1.123-1.761), while each increase of 10% in the European ancestry presents a protection effect in the development of B-cell ALL (OR=0.666; 95% IC=0.536-0.827). The results suggest that genetic factors influence leukemogenesis and might be explored in the stratification of B-cell ALL risk in admixed populations.

Genetic susceptibility in childhood acute leukaemias: a systematic review

Acute leukaemias (AL) correspond to 25-35% of all cancer cases in children. The aetiology is still sheltered, although several factors are implicated in causality of AL subtypes. Childhood acute leukaemias are associated with genetic syndromes (5%) and ionising radiation as risk factors. Somatic genomic alterations occur during fetal life and are initiating events to childhood leukaemia. Genetic susceptibility has been explored as a risk factor, since environmental exposure of the child to xenobiotics, direct or indirectly, can contribute to the accumulation of somatic mutations. Hence, a systematic review was conducted in order to understand the association between gene polymorphisms and childhood leukaemia risk. The search was performed in the electronic databases PubMed, Lilacs, and Scielo, selecting articles published between 1995 and 2013. This review included 90 case-control publications, which were classified into four groups: xenobiotic system (n = 50), DNA repair (n = 16), regulatory genes (n = 15), and genome wide association studies (GWAS) (n = 9). We observed that the most frequently investigated genes were: NQO1, GSTM1, GSTT1, GSTP1, CYP1A1, NAT2, CYP2D6, CYP2E1, MDR1 (ABCB1), XRCC1, ARID5B, and IKZF1. The collected evidence suggests that genetic polymorphisms in CYP2E1, GSTM1, NQO1, NAT2, MDR1, and XRCC1 are capable of modulating leukaemia risk, mainly when associated with environmental exposures, such as domestic pesticides and insecticides, smoking, trihalomethanes, alcohol consumption, and x-rays. More recently, genome wide association studies identified significant associations between genetic polymorphisms in ARID5B e IKZF1 and acute lymphoblastic leukaemia, but only a few studies have replicated these results until now. In conclusion, genetic susceptibility contributes to the risk of childhood leukaemia through the effects of gene-gene and gene-environment interactions.

X-ray repair cross-complementing group 1(XRCC1) genetic polymorphisms and thyroid carcinoma risk: a meta-analysis

A number of studies have been conducted to explore the association of XRCC1 polymorphisms with thyroid cancer risk, but the results have been inconsistent. Thus we performed the present meta-analysis to clarify this issue based on all of the evidence available to date. Relevant studies were retrieved by searching PubMed and statistical analysis conducted using Stata software. Nine studies were included in this meta-analysis (1,620 cases and 3,557 controls). There were 6 studies (932 cases and 2,270 controls) of the Arg194Trp polymorphism, 7 studies (1432 cases and 3356 controls) of the Arg280His polymorphism and 9 studies (1,620 cases and 3,557 controls) for the Arg399Gln polymorphism. No association of XRCC1 Arg194Trp, Arg280His and Arg399Gln polymorphism with thyroid cancer risk was observed in the overall analysis. However, subgroup analysis revealed: 1) an elevated risk in aa vs AA analysis (OR=2.03, 95%CI= 1.24-3.31) and recessive genetic model analysis (OR=1.93, 95%CI= 1.20-3.08) in the larger sample size trials for XRCC1 Arg194Trp polymorphism; 2) a decreased thyroid cancer risk on subgroup analysis based on ethnicity in Aa vs AA analysis (OR=0.84, 95%CI= 0.72-0.98) and in a dominant genetic model (OR=0.84, 95%CI= 0.72-0.97) in Caucasian populations for the XRCC1 Arg399Gln polymorphism; 3) a decreased thyroid cancer risk on subgroup analysis based on design type in Aa vs AA analysis (OR=0.72, 95% CI= 0.54-0.97) among the PCC trials for the Arg399Gln polymorphism. Our results suggest that the XRCC1 Arg399Gln polymorphism may be associated with decreased thyroid cancer risk among Caucasians and XRCC1 Arg194Trp may be associated with a tendency for increased thyroid cancer risk in the two larger sample size trials.

Association between the XRCC1 Arg194Trp polymorphism and risk of cancer: evidence from 201 case-control studies

The Arg194Trp polymorphism in the X-ray cross-complementing group 1 (XRCC1) had been implicated in cancer susceptibility. The previous published data on the association between XRCC1 Arg194Trp polymorphism and cancer risk remained controversial. Hence, we performed a meta-analysis to investigate the association between cancer susceptibility and XRCC1 Arg194Trp (59,227 cases and 81,587 controls from 201 studies) polymorphism in different inheritance models. We used odds ratios with 95 % confidence intervals to assess the strength of the association. Overall, significantly increased cancer risk was found (recessive model: (odds ration [OR] = 1.18, 95% confidence interval [CI] = 1.09-1.27; homozygous model: OR = 1.21, 95% CI = 1.10-1.33; additive model: OR = 1.05, 95% CI = 1.01-1.09) when all eligible studies were pooled into the meta-analysis. In further stratified and sensitivity analyses, significantly increased glioma risk was found among Asians, significantly decreased lung cancer risk was found among Caucasians, and significant increased breast cancer risk was found among hospital-based studies. In summary, this meta-analysis suggests that Arg194Trp polymorphism may be associated with increased breast cancer risk, Arg194Trp polymorphism is associated with increased glioma risk among Asians, and Arg194Trp polymorphism is associated with decreased lung cancer risk among Caucasians. In addition, our work also points out the importance of new studies for Arg194Trp association in some cancer types, such as gastric, pancreatic, prostate, and nasopharyngeal cancers, where at least some of the covariates responsible for heterogeneity could be controlled, to obtain a more conclusive understanding about the function of the XRCC1 Arg194Trp polymorphism in cancer development (I (2) > 75%).

Genetic polymorphisms of XRCC1 and leukemia risk: a meta-analysis of 19 case-control studies

Objective

Three common X-ray repair cross-complementing groups 1 (XRCC1) polymorphisms, Arg399Gln, Arg194Trp, and Arg280His, have been reported to be implicated in the development of leukemia. However, previous results from different studies were inconsistent. Consequently, we performed a meta-analysis in order to accurately evaluate the association between XRCC1 Arg399Gln, Arg194Trp, and Arg280His polymorphisms and leukemia risk.

Methods

Through computerized searching of PubMed, ISI Web of Knowledge, Cochrane, EBSCO, and OpenGrey databases, and manually searching relevant references, a total of 19 studies with 3387 cases and 6168 controls for Arg399Gln (G>A) polymorphism, 12 studies with 2043 cases and 4550 controls for Arg194Trp (C>T), and 6 studies with 1445 cases and 1905 controls for Arg280His (G>A) were collected to perform meta-analysis and stratified analysis to explore the associations between these variants and leukemia susceptibility. Based on three genetic models, the codominant model, dominant model and recessive model, odds ratios (ORs) as well as their 95% confidence intervals (CIs) were used to evaluate the association strength between XRCC1 genotypes and leukemia risk.

Results

With respect to overall leukemia susceptibility, no association was detected. In stratified analyses by tumor type, Arg399Gln was associated with higher acute lymphoblastic leukemia (ALL) risk (AA vs. GG, OR  =  1.50, 95% CI: 1.11-2.02; AA+GA vs. GG, OR  =  1.35, 95% CI: 1.02-1.78). Additionally, Arg399Gln, Arg194Trp, and Arg280His may influence the susceptibilities of some leukemia type and race populations.

Conclusion

This meta-analysis indicates these three polymorphisms of XRCC1 do not associate with overall leukemia risks but could be associated with the risks for some specific subgroups.

Inhibitory Effects of Spirulina platensis on Carcinogen-Activating Cytochrome P450 Isozymes and Potential for Drug Interactions

Spirulina platensis (SP) has been considered as potential food source of 21st century due to its remarkable nutrient profile and therapeutic benefits. However, the cytochrome P450 (CYP)-mediated drug/chemical interaction potential of SP has not yet been pursued. We investigated the effects of SP on the expressions and enzymatic activities of main CYP isozymes. After the rats were orally administered with SP daily for 5 consecutive weeks, there were significant downregulations in hepatic expression levels and inhibition in enzymatic activities of CYP1A2 and CYP2E1 compared to controls. In addition, a significant decrease was observed in CYP2C6-associated enzyme activity with no remarkable changes in messenger RNA (mRNA)/protein levels. The SP application resulted in significant increases in mRNA/protein levels of both CYP2B1 and CYP3A1 without a significant change in enzyme activities. These findings partly explain the chemopreventive properties of SP toward various organ toxicities, mutagenesis, and carcinogenesis; however, its coadministration with some CYP substrates may lead to undesirable drug interactions.

DNA repair gene XRCC1 polymorphisms and susceptibility to childhood acute lymphoblastic leukemia: a meta-analysis

OBJECTIVE

To estimate the relationship between genetic polymorphisms of X-ray repair cross-complementing group 1 (XRCC1) and the susceptibility to childhood acute lymphoblastic leukemia (ALL).

METHODS

Relevant case-control studies were enrolled in the meta-analysis. We applied Rev Man 4.2 software to pool raw data and test studies' heterogeneity and to calculate the incorporated odds ratio (OR) and 95% confidence interval (95% CI).

RESULTS

Our data showed that the OR for the Gln allele of the Arg399Gln polymorphism, compared with the Arg allele, was 1.35 (95% CI, 1.16-1.57; P<0.0001) for childhood ALL patients. Similarly, the homozygous genotype Gln/Gln and heterozygous genotype Arg/Gln both significantly increased the risk of childhood ALL compared with the wild genotype Arg/Arg (OR =1.58; 95% CI, 1.13-2.21; P=0.008; OR =1.51; 95% CI, 1.21-1.87; P=0.0002). The dominant model of Arg399Gln was associated with childhood ALL risk (OR =1.54; 95% CI, 1.25-1.89; P<0.0001). The ethnic subgroup analysis demonstrated that the Gln allele in all five ethnic groups was prone to be a risk factor for childhood ALL just with different degrees of correlation while Arg194Trp SNP showed a protective or risk factor or irrelevant thing in different races.

CONCLUSIONS

XRCC1 399 polymorphism may increase the risk of childhood ALL. Different ethnic groups with some gene polymorphism have different disease risks.

XRCC1 Arg399Gln variation and leukemia susceptibility: evidence from 2,647 cases and 5,518 controls

Previous reports implicate XRCC1 Arg399Gln polymorphism as a possible risk factor for several cancers. Increasing studies have been conducted on the association of XRCC1 Arg399Gln polymorphisms with susceptibility to leukemia. However, conflicting results have been generated. The goal of the present study was to derive a more precise estimation of the relationship. Meta-analyses assessing the association of XRCC1 Arg399Gln variation with leukemia were conducted, and subgroup analyses on ethnicity and clinical types were further performed. Eligible studies were identified for the period up to February 2013. Consequently, 16 publications including 17 case-control studies with 2,647 cases and 5,518 controls were selected for analysis. The overall data indicated a significant association of XRCC1 Arg399Gln polymorphism with leukemia risk (Gln/Gln versus Arg/Arg: OR = 1.37, 95% confidence interval (CI) = 1.08-1.74; dominant model: OR = 1.23, 95%CI = 1.03-1.46; recessive model: OR = 1.23, 95%CI = 1.06-1.44). In the subgroup analysis by ethnicity, Gln allele may increase leukemia susceptibility among Asians (Gln/Gln versus Arg/Arg: OR = 1.82, 95%CI = 1.19-2.78; dominant model: OR = 1.53, 95%CI = 1.00-2.33; recessive model: OR = 1.51, 95%CI = 1.11-2.06), but not Caucasians or mixed ethnicities. In the subgroup analysis by clinical types, increased risk was observed in acute lymphocytic leukemia (ALL) subgroup (Gln/Gln versus Arg/Arg: OR = 1.45, 95%CI = 1.09-1.93; recessive model: OR = 1.30, 95%CI = 1.00-1.69), but not in acute myeloid leukemia, chronic lymphocytic leukemia, or chronic myeloid leukemia subgroups, respectively. Collectively, the results of the present study suggest that XRCC1 Arg399Gln polymorphism might be a low-penetrant risk factor for leukemia, particularly among Asians. Homozygous Gln/Gln alleles might have a correlation with increased ALL susceptibility.

Cytochrome P450 2E1: its clinical aspects and a brief perspective on the current research scenario

Research on Cytochrome P450 2E1 (CYP2E1), a key enzyme in alcohol metabolism has been very well documented in literature. Besides the involvement of CYP2E1 in alcohol metabolism as illustrated through the studies discussed in the chapter, recent studies have thrown light on several other aspects of CYP2E1 i.e. its extrahepatic expression, its involvement in several diseases and pathophysiological conditions; and CYP2E1 mediated carcinogenesis and modulation of drug efficacy. Studies involving these interesting facets of CYP2E1 have been discussed in the chapter focusing on the recent observations or ongoing studies illustrating the crucial role of CYP2E1 in disease development and drug metabolism.

Reprint of: gene susceptibility to oxidative damage: from single nucleotide polymorphisms to function

Oxidative damage to DNA can cause mutations, and mutations can lead to cancer. DNA repair of oxidative damage should therefore play a pivotal role in defending humans against cancer. This is exemplified by the increased risk of colorectal cancer of patients with germ-line mutations of the oxidative damage DNA glycosylase MUTYH. In contrast to germ-line mutations in DNA repair genes, which cause a strong deficiency in DNA repair activity in all cell types, the role of single nucleotide polymorphisms (SNPs) in sporadic cancer is unclear also because deficiencies in DNA repair, if any, are expected to be much milder. Further slowing down progress are the paucity of accurate and reproducible functional assays and poor epidemiological design of many studies. This review will focus on the most common and widely studied SNPs of oxidative DNA damage repair proteins trying to bridge the information available on biochemical and structural features of the repair proteins with the functional effects of these variants and their potential impact on the pathogenesis of disease.

Involvement of the XRCC1 Arg399Gln gene polymorphism in the development of cervical carcinoma

BACKGROUND

Although infection with the human papillomavirus (HPV) is crucial to the development of cervical cancer, it is not considered a sufficient isolated factor to cause this malignancy. The association of the XRCC1 Arg399Gln (rs25487) polymorphism with cervical cancer has been demonstrated in some populations.

METHODS

The XRCC1 Arg399Gln genetic variants were identified by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in patients with advanced cervical cancer (n=189) and controls (n=308).

RESULTS

We observed that patients with advanced cervical cancer having the Gln/Gln or Gln/Arg vs Arg/Arg genotype displayed a 1.726-fold increased risk of cervical cancer (95% confidence interval [CI]=1.158-2.572, p=0.007). The odds ratio (OR) for Gln/Gln vs Gln/Arg or Arg/Arg was 1.742 (95% CI=1.073-2.827; p=0.0236). We also found a significantly higher frequency of the XRCC1 399Gln allele in patients with cancer than in controls, with OR=1.489 (95% CI=1.148-1.930, p=0.0026). The p value of the chi-square test for the trend observed for the XRCC1 Arg399Gln polymorphism was also statistically significant (ptrend=0.002). The statistical power of this study amounted to 78% for the Gln/Gln or Gln/Arg genotypes and 61% for the Gln/Gln genotype.

CONCLUSION

Although the statistical power of our study did not reach 80%, we found a statistically significant association between the XRCC1 399Gln variant and the incidence of cervical cancer.

X-ray repair cross-complementing group 1 (XRCC1) genetic polymorphisms and risk of childhood acute lymphoblastic leukemia: a meta-analysis

BACKGROUND

Recently, there have been a number of studies on the association between XRCC1 polymorphisms and childhood acute lymphoblastic leukemia (ALL) risk. However, the results of previous reports are inconsistent. Thus, we performed a meta-analysis to clarify the effects of XRCC1 variants on childhood ALL risk.

METHODS

A meta-analysis was performed to examine the association between XRCC1 polymorphisms (Arg399Gln, Arg194Trp, and Arg280His) and childhood ALL risk. We critically reviewed 7 studies with a total of 880 cases and 1311 controls for Arg399Gln polymorphism, 3 studies with a total of 345 cases and 554 controls for Arg280His polymorphism, and 6 studies with a total of 783 cases and 1180 controls for Arg194Trp polymorphism, respectively. Odds ratio (OR) and its 95% confidence interval (CI) were used.

RESULTS

Significant association between XRCC1 Arg399Gln polymorphism and childhood ALL risk was observed in total population analyses (OR(additive model) = 1.501, 95% CI 1.112-2.026, P(OR) = 0.008; OR(dominant model) = 1.316, 95% CI = 1.104-1.569, P(OR) = 0.002) and Asian subgroup analyses (OR(additive model) = 2.338, 95%CI = 1.254-4.359, P(OR) = 0.008; OR(dominant model) = 2.108, 95%CI = 1.498-2.967, P(OR) = 0.000). No association was detected in Caucasians, Metizo and mixed populations. Ethnicity was considered as a significant source of heterogeneity in the meta-regression model. For the other two XRCC1 polymorphisms, no association with childhood ALL risk was found.

CONCLUSIONS

The meta-analysis results suggested that XRCC1 Arg399Gln polymorphism might be associated with elevated childhood ALL risk among Asian population.

Gene susceptibility to oxidative damage: from single nucleotide polymorphisms to function

Oxidative damage to DNA can cause mutations, and mutations can lead to cancer. DNA repair of oxidative damage should therefore play a pivotal role in defending humans against cancer. This is exemplified by the increased risk of colorectal cancer of patients with germ-line mutations of the oxidative damage DNA glycosylase MUTYH. In contrast to germ-line mutations in DNA repair genes, which cause a strong deficiency in DNA repair activity in all cell types, the role of single nucleotide polymorphisms (SNPs) in sporadic cancer is unclear also because deficiencies in DNA repair, if any, are expected to be much milder. Further slowing down progress are the paucity of accurate and reproducible functional assays and poor epidemiological design of many studies. This review will focus on the most common and widely studied SNPs of oxidative DNA damage repair proteins trying to bridge the information available on biochemical and structural features of the repair proteins with the functional effects of these variants and their potential impact on the pathogenesis of disease.

XRCC1 Arg399Gln gene polymorphism and the risk of systemic lupus erythematosus in the Polish population

It has been shown that DNA repair is reduced in patients with systemic lupus erythematosus (SLE) and that the X-ray repair cross-complementing (XRCC1) Arg399Gln (rs25487) polymorphism may contribute to DNA repair. We evaluated the frequency of the XRCC1 Arg399Gln substitution in patients with SLE (n=265) and controls (n=360) in a sample of the Polish population. The odds ratio (OR) for SLE patients with the Gln/Gln versus Gln/Arg or Arg/Arg genotypes was 1.553 (95% confidence interval [CI]=0.9573-2.520; p=0.0729). OR for the Gln/Gln or Gln/Arg versus Arg/Arg genotype was 1.551 (95% CI=1.122-2.144, p=0.0077). The OR for the 399 Gln allele in patients with SLE was 1.406 (95% CI=1.111-1.779, p=0.0045). There was also a statistically significant p-value of the χ(2) test for the trend observed in the XRCC1 Arg399Gln polymorphism (ptrend=0.0048). We also found a significant contribution of the Gln/Gln or Arg/Gln versus Arg/Arg genotype to the presence of either the malar rash or photosensitivity manifestations of SLE OR=2.241 (1.328-3.781, p=0.0023, pcorr=0.0414). Moreover, the meta-analysis of Taiwanese Han Chinese, Brazilian, and Polish populations showed that the Gln/Gln or Gln/Arg genotype and Gln allele were associated with SLE incidence. OR for the Gln/Gln or Gln/Arg versus Arg/Arg genotype was 1.440 (95% CI=1.15-1.80, p=0.0019) and OR for the Gln allele was 1.27 (95% CI=1.08-1.51, p=0.0051). Our studies may confirm that the XRCC1 Arg399Gln polymorphism may increase the risk of incidence of SLE and the occurrence of some SLE manifestations.

Polymorphism in the DNA repair enzyme XRCC1: utility of current database and implications for human health risk assessment

Genetic polymorphisms are increasingly recognized as sources of variability not only in toxicokinetic but also in toxicodynamic response to environmental agents. XRCC1 is involved in base excision repair (BER) of DNA; it has variant genotypes that are associated with modified repair function. This analysis focuses on four polymorphisms: three in the coding region that affect protein structure and one in an upstream regulatory sequence that affects gene expression. The Arg399Gln variant is the most widely studied with evidence supporting a quantitative effect of genotype on phenotype. The homozygous variant (Gln/Gln) can have 3-4-fold diminished capacity to remove DNA adducts and oxidized DNA damage. This variant is relatively common in Caucasians and Asians where approximately 10% are homozygous variant. In contrast, the Arg194Trp variant appears to protect against genotoxic effects although the degree to which DNA repair is enhanced by this polymorphism is uncertain. The homozygous variant is rare in Caucasians and African Americans but it is present at 7% in Asians. A third coding region polymorphism at codon 280 appears to decrease repair function but additional quantitative information is needed and the homozygous variant is rare across populations studied. A polymorphism in an upstream promoter binding sequence (-77T>C) appears to lower XRCC1 levels by decreasing gene expression. Based upon genotype effect on phenotype and allele frequency, the current analysis finds that the codon 399 and upstream (-77) polymorphisms have the greatest potential to affect the toxicodynamic response to DNA damaging agents. However, the implications for risk assessment are limited by the likelihood that polymorphisms in multiple BER genes interact to modulate DNA repair.

Genetic instability in inherited and sporadic leukemias

Genetic instability due to increased DNA damage and altered DNA repair is of central significance in the initiation and progression of inherited and sporadic human leukemias. Although very rare, some inherited DNA repair insufficiency syndromes (e.g., Fanconi anemia, Bloom's syndrome) have added substantially to our understanding of crucial mechanisms of leukemogenesis in recent years. Conversely, sporadic leukemias account for the main proportion of leukemias and here DNA damaging reactive oxygen species (ROS) play a central role. Although the exact mechanisms of increased ROS production remain largely unknown and no single pathway has been detected thus far, some oncogenic proteins (e.g., the activated tyrosine kinases BCR-ABL1 and FLT3-ITD) seem to play a key role in driving genetic instability by increased ROS generation which influences the disease course (e.g., blast crisis in chronic myeloid leukemia or relapse in FLT3-ITD positive acute myeloid leukemia). Of course other mechanisms, which promote genetic instability in leukemia also exist. A newly emerging mechanism is the genome-wide alteration of epigenetic marks (e.g., hypomethylation of histone H3K79), which promotes chromosomal instability. Taken together genetic instability plays a critical role both in inherited and sporadic leukemias and emerges as a common theme in both inherited and sporadic leukemias. Beyond its theoretical impact, the analysis of genetic instability may lead the way to the development of innovative therapy strategies.