Association between maternal COMT gene polymorphisms and fetal neural tube defects risk in a Chinese population

Maternal tea consumption was reported to increase the risk of fetal neural tube defects (NTDs). Catechol‐O‐methyltransferase (COMT) may be involved in the metabolism of polyphenolic methylation of tea, thus influence the risk of fetal NTDs. Methods: A total of 576 fetuses or newborns with NTDs and 594 healthy newborns were included in the case–control study. Information on maternal tea consumption, sociodemographic characteristics, reproductive history, and related behavior was collected through face‐to‐face interviews. Maternal blood samples were collected to examine polymorphisms in COMT, and the possible interaction of COMT and tea consumption was analyzed. RESULTS: After controlling for potential confounders, homozygotes of rs737865 showed an elevated risk for total NTDs (odds ratio [OR] = 2.04, 95% confidence interval [CI], 1.24–3.35) and for the anencephaly subtype (OR = 1.99, 95% CI, 1.17–3.39). The CC genotype of rs4633 was positively associated with the overall risk of NTDs (OR = 3.66, 95% CI, 1.05–12.83). Heterozygotes for rs4680 were associated with a decreased risk of spina bifida (OR = 0.71, 95% CI, 0.51–0.98). The COMT rs4680 A allele was negatively related with the risk of spina bifida, with adjusted OR = 0.64 (95% CI, 0.45–0.89). An interaction between tea consumption (1 to 2 cups/day) and the rs4680AA/AG genotype was found in the spina bifida subtype (P_interaction = .08). Conclusion: Several COMT variants were associated with elevated risk of NTDs in a Chinese population. Maternal tea consumption may be associated with an increased risk for fetal NTDs in genetically susceptible subgroups. Birth Defects Research (Part A) 100:22–29, 2014. © 2013 Wiley Periodicals, Inc.     

Reduced folate carrier gene is a risk factor for neural tube defects in a Chinese population

BACKGROUND: There is a considerable body of data demonstrating that periconceptional supplementation of folic acid can prevent a significant proportion of neural tube defects (NTDs). At present, the mechanism by which folic acid exerts its beneficial effect remains unknown. Folate transporter genes, including the reduced folate carrier gene (RFC1), have been proposed as NTD risk factors. METHODS: The study population included 104 nuclear families with NTDs and 100 nonmalformed control families. We investigated the possible association between a common RFC1 polymorphism (A80G) and NTD risk among offspring, as well as potential gene-environment interactions between the infant RFC1 genotype and maternal periconceptional use of folic acid through a population-based case-control study. RESULTS: We observed that the infants of the GG genotype were associated with a 2.56-fold increased risk of NTDs when compared to the AA genotype (odds ratio [OR], 2.56; 95% confidence interval [CI], 1.04-6.36) in our study population. Among mothers who did not utilize folic acid supplements, the risk for having a child with an NTD was 3.30 (95% CI, 1.15-9.65) for offspring with the GG genotype, compared to the reference (AA) genotype. Children who had the GG genotype and whose mothers did not take folic acid had an elevated risk for NTDs (OR, 8.80; 95% CI, 2.83-28.69), compared to offspring with the AA and GA genotypes whose mothers utilized folic acid supplements. CONCLUSIONS: Our findings suggest that the RFC1 G allele is likely to be an important genetic factor in determining folate transport and subsequently may be a risk factor for NTDs in this Chinese population.     

Maternal PCMT1 gene polymorphisms and the risk of neural tube defects in a Chinese population of Lvliang high-risk area

Protein-L-isoaspartate (D-aspartate) O-methyltransferase 1 (PCMT1) gene encodes for the protein repair enzyme L-isoaspartate (D-aspartate) O-methyltransferase (PIMT), which is known to protect certain neural cells from Bax-induced apoptosis. Previous study has shown that PCMT1 polymorphisms rs4552 and rs4816 of infant are associated with spina bifida in the Californian population. The association between maternal polymorphism and neural tube defects is still uncovered. A case-control study was conducted to investigate a possible association between maternal PCMT1 and NTDs in Lvliang high-risk area of Shanxi Province in China, using a high-resolution DNA melting analysis genotyping method. We found that increased risk for anencephaly in isolated NTDs compared with the normal control group was observed for the G (vs. A) allele (p=0.034, OR=1.896, 95% CI, 1.04-3.45) and genotypes GG+GA (p=0.025, OR=2.237, 95% CI, 1.09-4.57). Although the significance was lost after multiple comparison correction, the results implied that maternal polymorphisms in PCMT1 might be a potential genetic risk factor for isolated anencephaly in this Chinese population.     

Ethnic Variation in the Thymidylate Synthase Enhancer Region Polymorphism among Caucasian and Asian Populations

Thymidylate synthase (TS) regulates the production of DNA synthesis precursors and is an important target of cancer chemotherapy. A tandem repeat sequence in a TS promoter enhancer region (TSER) was recently identified. Polymorphic variation affected in vitro expression levels of the gene. We evaluated the influence of ethnicity on TSER genotype. Allele frequency was similar in Caucasian and Southwest Asian subjects. However, homozygous triple repeat subjects were twice as common in Chinese subjects (67%) than in Caucasian subjects (38%). This demonstrates significant ethnic variation in a TS gene regulatory element which may have significant impact on pyrimidine homeostasis and drug therapy.     

Evaluation of transcobalamin II polymorphisms as neural tube defect risk factors in an Irish population

BACKGROUND: Decreased maternal folate levels are associated with having a child with a neural tube defect (NTD), and periconceptual folic acid supplementation reduces this risk by >50%. Vitamin B(12) (as methylcobalamin) is a cofactor for methionine synthase, an enzyme that plays a key role in folate metabolism. Alterations in vitamin B(12) metabolism may influence the development of NTDs. Low levels of maternal plasma vitamin B(12) and reduced binding of vitamin B(12) by transcobalamin II (TCII) are independent risk factors for NTDs. TCII levels are altered in the amniotic fluid of pregnancies affected by NTDs. Given this evidence, inherited variants in genes involved in vitamin B(12) trafficking such as TCII are candidate NTD risk factors. METHODS: We used case/control and family-based association methods to investigate whether six common polymorphisms in the TCII gene influence NTD risk. TCII genotypes were determined for more than 300 Irish NTD families and a comparable number of Irish controls. RESULTS: Allele and genotype frequencies for each polymorphism did not differ between family members and controls. CONCLUSIONS: These six TCII polymorphisms do not strongly influence NTD risk in the Irish population. The Supplementary Material for this article can be found on the Birth Defects Research (Part A) website: http://www.mrw.interscience.wiley.com/suppmat/1542-0752/suppmat/2005/73/v73.4.swanson.html     

A1298C polymorphism of the MTHFR gene and neural tube defects in the state of Yucatan, Mexico

BACKGROUND: Methylenetetrahydrofolate reductase (MTHFR) of the folate metabolism pathway is a candidate gene for neural tube defects (NTDs). Frequency of the second common polymorphism, A1298C, in the MTHFR gene is not well known in Mexico. Conflicting results exist regarding the association of A1298C-MTHFR with NTDs. One explanation for this controversy might be that alleles are differently distributed among various populations. The aim of the study was to determine the frequency of the A1298C-MTHFR polymorphism and its association with NTDs in a population of Yucatan, Mexico. METHODS: Genotyping was performed by use of polymerase chain reaction with restriction fragment length polymorphisms using MbOII endonuclease (PCR-RFLPs MbOII). Allele and genotype frequencies were compared between cases with NTDs, their mothers and fathers with matched controls based on an association analysis using EpiInfo software. RESULTS: A1298C genotypes were distributed according to Hardy-Weinberg expectations for all studied groups. Frequencies of allele C and heterozygous AC genotype were significantly higher in males (p = .006 and p = .011, respectively) in control group. Significant differences were not observed between cases and controls, except in mothers of NTD cases compared with mothers of healthy offspring for both allele C and heterozygous AC genotype (p = .009 and p = .01, respectively). CONCLUSIONS: The polymorphism A1298C-MTHFR is not associated with NTDs, except for mothers, suggesting only a maternal association with having NTD-affected offspring in the Yucatan population. The frequency of allele C in the control population was 10%, which is significantly lower than in other reported control populations worldwide (p < .01).     

Thymidylate synthase polymorphisms and risks of human orofacial clefts

OBJECTIVE: Underlying mechanisms are unknown by which folic acid use in early pregnancy may reduce risks of orofacial clefts. Thymidylate synthase (TYMS) is a folate‐dependent enzyme that catalyzes reductive methylation of deoxyuridylate to thymidylate, thereby playing a central role in DNA synthesis and repair. We investigated two TYMS functional variants (a 28‐bp tandem repeat in the promoter enhancer region of the 5′‐UTR; and TYMS 1494del6 (rs16430): a 6‐bp deletion in the 3′‐UTR) for their risk of cleft palate (CP) and of cleft lip with/without CP (CLP). We investigated effect measure modification between these variants and maternal folate intake for cleft risk. DESIGN: This case‐control study included deliveries from July 1999 to June 2003 from select areas of California. Case groups included CLP or CP alone. Nonmalformed, liveborn controls were randomly selected. Maternal interviews provided information on vitamin use and dietary folate intake. DNA was derived from newborn bloodspots. RESULTS: Data were available for 304 CLP cases, 123 CP cases, and 581 controls. 1496del6 variants did not appear to influence risk of CP or CLP. Homozygosity for the 28‐bp VNTR variant influenced CP risk (odds ratios, OR = 1.8, 95% confidence interval, 1.1–3.1), particularly among Hispanic infants, OR 2.1 (1.0–4.6). Effect measure modification was observed between the 28‐bp VNTR and combined folate intake for CP with an OR of 10.0 (1.6–60.9). CONCLUSION: Although these findings are consistent with biological mechanisms, they were based on relatively small sample sizes and may represent false‐positive discoveries. Replication is warranted in other populations. Birth Defects Research (Part A) 97:95–100, 2013. © 2013 Wiley Periodicals, Inc.     

Length Polymorphism of Thymidylate Synthase Regulatory Region in Chinese Populations and Evolution of the Novel Alleles

The tandemly repeated 28-bp sequence in the 5-terminal regulatory region of human thymidylate synthase (TSER), which has been reported to be polymorphic in different populations, was surveyed in 668 Chinese from 9 Han groups, 8 ethnic populations, and 36 individuals representing a three-generation pedigree. Amplified fragments were separated by electrophoresis on 4% agarose gel. In addition to the reported double and triple repeats of the 28-bp sequence in TSER, we also detected a novel quintuple repeat in this region. The transient expression activity of TSER with the quintuple repeat is almost the same as that of the reported TSER with the triple repeat. All three alleles of the repeat type (2, 3, and 5) were further confirmed by sequencing. The frequencies of the TSER allele 2 and 3 were 18.82 and 81% in totally unrelated Chinese samples, respectively, while the frequency of allele 3 was variable in different Chinese populations with a range from 62 to 95%. On the basis of the sequences of the different alleles, the existence of the tandem repeats in each allele might be explained by slipped-strand mispairing during DNA replication.     

Association between MTR A2756G and MTRR A66G polymorphisms and maternal risk for neural tube defects: A meta-analysis

Background

Methionine synthase (MTR) and methionine synthase reductase (MTRR) genes have been considered to be implicated in the development of neural tube defects (NTDs). However, the results are inconsistent. Accordingly, we conducted a meta-analysis to further investigate such an association.

Methods

Published literature from PubMed and Embase databases was retrieved. All studies evaluating the association between MTR A2756G or MTRR A66G polymorphism and maternal risk for NTDs were included. Pooled odds ratio (OR) with 95% confidence interval (CI) was calculated using the fixed- or random-effects model.

Results

A total of 11 studies (1005 cases and 2098 controls) on MTR A2756G polymorphism and 10 studies (1211 cases and 2003 controls) on MTRR A66G polymorphism were included. Overall, this meta-analysis revealed no significant association between maternal MTR A2756G polymorphism and NTD susceptibility in either genetic model. A significant association between MTRR A66G polymorphism and maternal risk for NTDs was observed for GG vs. AA (OR = 1.31, 95% CI 1.03–1.67) among Caucasians.

Conclusion

The present meta-analysis indicated that MTRR A66G polymorphism, but not MTR A2756G, is significantly associated with maternal risk for NTDs in Caucasians.     

Crystal structure and enzymatic characterization of thymidylate synthase X from Helicobacter pylori strain SS1

Thymidylate synthase X (ThyX) catalyzes the methylation of dUMP to form dTMP in bacterial life cycle and is regarded as a promising target for antibiotics discovery. Helicobacter pylori is a human pathogen associated with a number of human diseases. Here, we cloned and purified the ThyX enzyme from H. pylori SS1 strain (HpThyX). The recombinant HpThyX was discovered to exhibit the maximum activity at pH 8.5, and K_m values of the two substrates dUMP and CH₂H₄folate were determined to be 15.3 ± 1.25 μM and 0.35 ± 0.18 mM, respectively. The analyzed crystal structure of HpThyX with the cofactor FAD and the substrate dUMP (at 2.31 Å) revealed that the enzyme was a tetramer bound to four dUMP and four FAD molecules. Different from the catalytic feature of the classical thymidylate synthase (ThyA), N5 atom of the FAD functioned as a nucleophile in the catalytic reaction instead of Ser84 and Ser85 residues. Our current work is expected to help better understand the structural and enzymatic features of HpThyX thus further providing valuable information for anti‐H. pylori inhibitor discovery.     

Methionine synthase polymorphisms (MTR 2756 A>G and MTR 2758 C>G) frequencies and distribution in the Jordanian population and their correlation with neural tube defects in the population of the northern part of Jordan

BACKGROUND:

The human methionine synthase gene (MTR) is located on chromosome 1q43; it is of 105.24 kb and is made up of 33 exons. Methionine synthase is a cytoplasmic enzyme that requires methylcobalamin for activity and catalyzes the remethylation of homocysteine to methionine. In this reaction, the methyl group of 5-methyltetrahydrofolate is transferred to the enzyme bond cob(I) alamin to generate methylcobalamin, followed by the transfer of the methyl group to homocysteine to reform methionine.

MATERIALS AND METHODS:

The frequencies of the polymorphisms of MTR 2756A>G and MTR 2758C>G have been determined in this study in a sample of 491 individuals collected from all regions of Jordan and representing the Jordanian population. The different alleles and genotypes at the two polymorphic sites were identified using the Polymerase Chain Reaction - Restriction Fragment Length Polymorphism (PCR-RFLP) analysis.

RESULTS:

Showed that the percentages of the polymorphic alleles at the MTR 2756 position in the north, middle and south regions were 90.38, 92.65 and 83.69%, respectively, for the MTR 2756A allele, and were 9.61, 7.34 and 16.30%, respectively, for the MTR 2756G allele, with overall percentages in the whole Jordanian population of 90.73 and 9.27% for the MTR 2756A and MTR 2756G alleles, respectively. The percentages of the genotype MTR 2756AA were 82.90% in the northern region, 86.72% in the middle region and 71.73% in the southern region, and an overall percentage of MTR 2756AA in the whole Jordanian population was 83.50%. The frequencies of MTR 2756AG genotype in the northern, middle and southern regions were 14.95, 11.84 and 23.91%, respectively, with an overall percentage of 14.46% in the whole Jordanian population. The percentages of the genotype MTR 2756GG in the northern, middle and southern regions were 2.13, 1.42 and 4.34%, respectively, with an overall percentage of 2.04% in the whole Jordanian population. Only the wild type allele (C) of the MTR 2758C>G polymorphism was detected in this study. In addition, the association of MTR 2756A>G and MTR 2758C>G polymorphisms with the development of neural tube defects (NTDs) was examined using 17 cases of mothers from the northern part of Jordan, who gave birth to NTD affected children during the period of this study. Results showed no association between these two examined polymorphisms and the increase in maternal risk for giving birth to NTD children.

CONCLUSION:

results of this study recommend that examination should be done on larger populations to arrive at better conclusions. Also, more studies on gene–gene interaction should be done to examine the associations with NTDs.     

DVL mutations identified from human neural tube defects and Dandy-Walker malformation obstruct the Wnt signaling pathway

Wnt signaling pathways,including the canonical Wnt/β-catenin pathway,planar cell polarity pathway,and Wnt/Ca~(2+) signaling pathway,play important roles in neural development during embryonic stages.The DVL genes encode the hub proteins for Wnt signaling pathways.The mutations in DVL2 and DVL3 were identified from patients with neural tube defects(NTDs),but their functions in the pathogenesis of human neural diseases remain elusive.Here,we sequenced the coding regions of three DVL genes in 176 stillborn or miscarried fetuses with NTDs or Dandy-Walker malformation(DWM) and 480 adult controls from a Han Chinese population.Four rare mutations were identified:DVL1 p.R558 H,DVL1 p.R606 C,DVL2 p.R633 W,and DVL3 p.R222 Q.To assess the effect of these mutations on NTDs and DWM,various functional analyses such as luciferase reporter assay,stress fiber formation,and in vivo teratogenic assay were performed.The results showed that the DVL2 p.R633 W mutation destabilized DVL2 protein and upregulated activities for all three Wnt signalings(Wnt/β-catenin signaling,Wnt/planar cell polarity signaling,and Wnt/Ca~(2+) signaling) in mammalian cells.In contrast,DVL1 mutants(DVL1 p.R558 H and DVL1 p.R606 C) decreased canonical Wnt/β-catenin signaling but increased the activity of Wnt/Ca~(2+)signaling,and DVL3 p.R222 Q only decreased the activity of Wnt/Ca~(2+) signaling.We also found that only the DVL2 p.R633 W mutant displayed more severe teratogenicity in zebrafish embryos than wild-type DVL2.Our study demonstrates that these four rare DVL mutations,especially DVL2 p.R633 W,may contribute to human neural diseases such as NTDs and DWM by obstructing Wnt signaling pathways.     

Association between the methionine synthase A2756G polymorphism and neural tube defect risk: A meta-analysis

Many studies have accessed the association between methionine synthase (MTR) A2756G polymorphism and neural tube defect (NTD). However, the conclusions are inconsistent. Our study aimed to clarify the nature of the genetic risks contributed by this polymorphism for NTD using meta-analysis. We searched electronic literature from the PubMed, EMBASE, and Medline databases, from which 10 articles were selected according to the inclusion criteria. The meta-analysis was conducted in 3 groups, namely, NTD patients, mothers with NTD offspring and fathers with NTD offspring. Pooled odds ratios (ORs) and 95% confidence intervals were used to evaluate the strength of the association and the result was corrected by multiple testing. To sum up, no associations between the MTR A2756G polymorphism and NTD risk were found among the 3 groups in all genetic models. However, as their sample size is not large enough, this result needs further research.     

Functional Inactivity and Mutations of p53 Differentially Affect Sensitivity to 5-Fluorouracil and Antifolate Inhibitors of Thymidylate Synthase (TS) by Altering TS Levels in Colorectal Cancer Cells

The role of p53 in altering TS expression and chemosensitivity was studied in colorectal cancer cells with wildtype, mutated, or functionally inactive p53. Cytotoxicity of TS inhibitors was studied by MTT, while PCR, Western blot, and activity assays assessed whether p53 status influenced TS expression. Lovo-175X2 cells showed increased resistance to TS inhibitors and significantly greater than wildtype expression and activity of TS. In contrast, Lovo-273X17 and Lovo-li were more sensitive to TS inhibitors and had reduced TS expression, due either to reduced TS mRNA or altered regulation of TS activity. Thus, functional inactivity and mutations of p53 differentially affect TS, potentially influencing response to TS inhibitor-based treatment.