Methionine synthase reductase MTRR 66A > G has no effect on total homocysteine, folate, and Vitamin B12 concentrations in renal transplant patients

Association of maternal methionine synthase reductase gene polymorphisms with the risk of congenital heart disease in offspring: a hospital-based case-control study

BACKGROUND

Evidence suggests that periconceptional folic acid supplementation may prevent congenital heart disease (CHD). Methionine synthase reductase (MTRR) is one of the key regulatory enzymes in the folate metabolic pathway. This study aimed to comprehensively evaluate the association of single nucleotide polymorphisms (SNPs) in the maternal MTRR gene with CHD risk in offspring.

METHODS

A hospital-based case-control study involving 740 mothers of CHD cases and 683 health controls was conducted.

RESULTS

The study showed that maternal MTRR gene polymorphisms at rs1532268 (C/T vs. C/C: aOR = 1.524; T/T vs. C/C: aOR = 3.178), rs1802059 (G/A vs. G/G: aOR = 1.410; A/A vs. G/G: aOR = 3.953), rs2287779 (G/A vs. G/G: aOR = 0.540), rs16879334 (C/G vs. C/C: aOR = 0.454), and rs2303080 (T/A vs. T/T: aOR = 0.546) were associated with the risk of CHD. And seven haplotypes were observed to be associated with the risk of CHD, T-G-A haplotype (OR = 1.298), C-A-C-C (OR = 4.824) and A-G haplotype (OR = 1.751) were associated with increased risk of CHD in offspring; A-A-A (OR = 0.773), T-A-A (OR = 0.557), G-A-C-C (OR = 0.598) and G-C (OR = 0.740) were associated with decreased risk of CHD in offspring.

CONCLUSIONS

Maternal MTRR gene polymorphisms were associated with CHD in offspring, and its haplotypes have affected the occurrence of CHD. Furthermore, given the complexity and heterogeneity of CHD, the mechanisms by which these factors influence offspring cardiac development remain unknown, and studies in larger samples in an ethnically diverse population are needed.

Associations between Genetic Variants and Blood Biomarkers of One-Carbon Metabolism in Postmenopausal Women from the Women's Health Initiative Observational Study

BACKGROUND

Genetic variation in one-carbon metabolism may affect nutrient concentrations and biological functions. However, data on genetic variants associated with blood biomarkers of one-carbon metabolism in US postmenopausal women are limited, and whether these associations were affected by the nationwide folic acid (FA) fortification program is unclear.

OBJECTIVES

We investigated associations between genetic variants and biomarkers of one-carbon metabolism using data from the Women's Health Initiative Observational Study.

METHODS

In 1573 non-Hispanic White (NHW) and 282 Black/African American, American Indian/Alaska Native, Asian/Pacific Islander, and Hispanic/Latino women aged 50-79 y, 288 nonsynonymous and tagging single-nucleotide variants (SNVs) were genotyped. RBC folate, plasma folate, pyridoxal-5'-phosphate (PLP), vitamin B-12, homocysteine, and cysteine concentrations were determined in 12-h fasting blood. Multivariable linear regression tested associations per variant allele and for an aggregated genetic risk score. Effect modifications before, during, and after nationwide FA fortification were examined.

RESULTS

After correction for multiple comparisons, among NHW women, 5,10-methylenetetrahydrofolate reductase (MTHFR) rs1801133 (677C→T) variant T was associated with lower plasma folate (-13.0%; 95% CI: -17.3%, -8.6%) and higher plasma homocysteine (3.5%; 95% CI: 1.7%, 5.3%) concentrations. Other associations for nonsynonymous SNVs included DNMT3A rs11695471 (T→A) with plasma PLP; EHMT2 rs535586 (G→A), TCN2 rs1131603 (L349S A→G), and TCN2 rs35838082 (R188W G→A) with plasma vitamin B-12; CBS rs2851391 (G→A) with plasma homocysteine; and MTHFD1 rs2236224 (G→A) and rs2236225 (R653Q G→A) with plasma cysteine. The influence of FA fortification on the associations was limited. Highest compared with lowest quartiles of aggregated genetic risk scores from SNVs in MTHFR and MTRR were associated with 14.8% to 18.9% lower RBC folate concentrations. Gene-biomarker associations were similar in women of other races/ethnicities.

CONCLUSIONS

Our findings on genetic variants associated with several one-carbon metabolism biomarkers may help elucidate mechanisms of maintaining B vitamin status in postmenopausal women.

The Effects of Polymorphisms in One-carbon Metabolism Genes on Manifestation of Ichthyosis Vulgaris

BACKGROUND: Ichthyosis vulgaris is the most common type of Mendelian disorders of cornification, caused by loss-of-function mutations in the gene encoding epidermal protein filaggrin (FLG), namely R501X and 2282del4. FLG 2282del4 mutation in heterozygotes is incompletely penetrant. Polymorphisms in one-carbon metabolism genes could be associated with clinical manifestation of ichthyosis vulgaris. AIM: The purpose of the present study was to analyze the effects of MTHFR, MTR and MTRR polymorphisms in patients with ichthyosis vulgaris. METHODS: 31 patients with ichthyosis vulgaris, 7 their FLG heterozygous relatives without symptoms of disorder, and 150 healthy controls were enrolled in study. FLG null mutations —R501X (rs61816761) and 2282del4 (rs558269137) — and one-carbon metabolism gene polymorphisms — MTHFR C677T (rs1801133), MTHFR A1298C (rs1801131), MTR A2756G (rs1805087) and MTRR A66G (rs1801394) — were analyzed by a polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) assay. RESULTS: Among patients with ichthyosis, heterozygous for FLG 2282del4 mutation, the distributions of genotypes for folate metabolism genes were: MTHFR C677T CC:CT:TT —29.4%:70.6%:0.0%; MTHFR A1298C AA:AC:CC — 52.9%:47.1%:0.0%; MTR A2756G AA:AG:GG — 70.3%:23.5%:5.9%; MTRR A66G AA:AG:GG — 23.4%:52.9%:23.5%. The frequencies of MTR 2756AA and MTRR 66GG genotypes were 1.4–1.6 times higher in affected individuals heterozygous for 2282del4 than in patients with other FLG genotypes. In affected 2282del4 heterozygotes, the frequency of MTR 2756AA genotype was 1.6 times greater than in healthy controls (p<0.01). The strongest association was found between MTHFR 677CT/MTHFR 1298AA/MTR 2756AA/MTRR 66AG genotype and ichthyosis — OR=11.23 (95% CI 2.51−50.21, p=0.002). CONCLUSIONS: Various genotypes of one-carbon metabolism genes increase the risk of ichthyosis in heterozygotes for the FLG 2282del4 mutation (OR 2.799‑11.231). The most probable predisposing genotype is 677CT/1298AA/2756AA+AG/66AG.

Effect of MTHFR A1298C and MTRR A66G Genetic Mutations on Homocysteine Levels in the Chinese Population: A Systematic Review and Meta-analysis

Background and Objectives

The Chinese population typically has inadequate folate intake and no mandatory folic acid fortification. Methylenetetrahydrofolate reductase (MTHFR) and methionine synthase reductase (MTRR) are the two key regulatory enzymes in the folate/homocysteine (Hcy) metabolism. Hcy has been implicated in the pathogenesis of cardiovascular disease. We conducted a meta-analysis to assess whether the MTHFR gene A1298C and the MTRR gene A66G polymorphisms affect Hcy levels in the Chinese population.

Methods

This analysis included 13 studies with Hcy levels reported as one of the study measurements. Summary estimates of weighted mean differences and 95% confidence intervals (CIs) were obtained using random-effect models.

Results

Overall, there were no significant differences in Hcy concentrations between participants with the MTHFR 1298 CC (12 trials, n = 129), AA (n = 2166; β, -0.51 μmol/L; 95%CI: -2.14, 1.11; P = 0.53), or AC genotype (n = 958; β, 0.55 μmol/L; 95%CI: -0.72, 1.82; P = 0.40). Consistently, compared to those with the MTRR 66 GG genotype (6 trials, n = 156), similar Hcy concentrations were found in participants with the AA (n = 832; β, -0.43 μmol/L; 95%CI: -1.04, 0.17; P = 0.16) or AG (n =743; β, -0.57 μmol/L; 95%CI: -1.46, 0.31; P = 0.21) genotype. Similar results were observed for the dominant and recessive models.

Conclusions

Neither the MTHFR A1298C polymorphism nor the MTRR A66G polymorphism affects Hcy levels in the Chinese population.

Screening of six polymorphisms related with folate metabolism in parents of individuals with Down syndrome

OBJECTIVE

The study aim to investigate MTHFR C677T, MTHFR A1298C, RFC1 A80G, MTR A2756G, CBS 844ins68, MTRR A66G polymorphisms in Down syndrome (DS) parents.

METHODS

Polymorphisms were evaluated in 35 mothers and 24 fathers of individuals with free trisomy of chromosome 21 confirmed by karyotype. The control group included 26 mothers and 26 fathers who had no children with DS. The molecular analysis was performed by polymerase chain reaction and restriction fragment length polymorphism (reaction chain polymerase restriction fragment length polymorphism) or polymerase chain reaction. The χ² test (chi-square) was used to compare allele's differences among the study and the control group. Hardy-Weinberg equilibrium model was performed by χ² testing. Multiple logistic regression models and binary logistic regression used to determine the association between polymorphisms and parental DS risk.

RESULTS

This study did not reveal any significant difference in frequencies of polymorphisms. The haplotype analysis did not reveal linkage disequilibrium. The logistic regression analysis did not demonstrate differences between the groups. However, the binary logistic regression showed a higher frequency of the polymorphic homozygote genotype in DS parent group to codominant and dominant model in the RFC1 A80G.

CONCLUSION

In conclusion, although the screening results were significant only to the RFC1 A80G polymorphism, the other determinations of the genetic factors associated with abnormal chromosome segregation could be helpful in future studies, including other polymorphisms involved in folate metabolism.

Homocysteine Metabolism Gene Polymorphisms (MTHFR C677T, MTHFR A1298C, MTR A2756G and MTRR A66G) Jointly Elevate the Risk of Folate Deficiency

Folate deficiency is strongly associated with cardiovascular disease. We aimed to explore the joint effect of the methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C, methionine synthase (MTR) A2756G, and methionine synthase reductase (MTRR) A66G polymorphisms on folate deficiency in a Chinese hypertensive population. A total of 480 subjects aged 28–75 were enrolled in this study from September 2005–December 2005 from six hospitals in different Chinese regions. Known genotypes were detected by PCR-RFLP methods and serum folate was measured by chemiluminescence immunoassay. Our results showed that MTHFR 677TT and MTR 2756AG + GG were independently associated with a higher risk of folate deficiency (TT vs. CC + CT, p < 0.001 and AG + GG vs. AA p = 0.030, respectively). However, the MTHFR A1298C mutation may confer protection by elevating the serum folate level (p = 0.025). Furthermore, patients carrying two or more risk genotypes showed higher odds of folate deficiency than null risk genotype carriers, especially those carrying four risk genotypes. These findings were verified by generalized multifactor dimensionality reduction (p = 0.0107) and a cumulative effects model (p = 0.001). The results of this study have shown that interactions among homocysteine metabolism gene polymorphisms lead to dramatic elevations in the folate deficiency risk.

Analysis of methionine synthase reductase polymorphism (A66G) in Indian Muslim population

BACKGROUND AND OBJECTIVES:

Methionine synthase reductase (MTRR) is a vital enzyme of homocysteine/methionine metabolic pathway and is required for the conversion of inactive form of methionine synthase (MTR) to its active form. A clinically important allelic variant of MTRR A66G, with less enzymatic activity is reported with worldwide prevalence rate of ~ 30%. The present study was designed to determine the frequency of MTRR A66G polymorphism in rural Sunni Muslim population of Eastern Uttar Pradesh.

MATERIALS AND METHODS:

Total 56 subjects were analyzed for MTRR A66G polymorphism. A66G mutation analysis was carried out according to the polymerase chain reaction-restriction fragment length polymorphism method of Wilson et al. [1] amplification with MTRR specific primers followed by amplicon digestion with NdeI enzyme was used for the identification of different MTRR genotypes in subjects.

RESULTS AND DISCUSSION:

The AA genotype was found in 5 subjects, AG in 23 subjects, and GG genotype in 28 subjects. Genotype frequencies of AA, AG, and GG were 0.089, 0.41, and 0.5 respectively. The allele frequency of A allele was found to be 0.298 and G allele was 0.705.

CONCLUSION:

It is evident from the present study that the percentage of homozygous genotype GG and frequency of G allele is high in the target Muslim population.

Investigation of homocysteine-pathway-related variants in essential hypertension

Hyperhomocysteinemia (hHcy) has been associated with an increased risk of cardiovascular disease and stroke. Essential hypertension (EH), a polygenic condition, has also been associated with increased risk of cardiovascular related disorders. To investigate the role of the homocysteine (Hcy) metabolism pathway in hypertension we conducted a case-control association study of Hcy pathway gene variants in a cohort of Caucasian hypertensives and age- and sex-matched normotensives. We genotyped two polymorphisms in the methylenetetrahydrofolate reductase gene (MTHFR C677T and MTHFR A1298C), one polymorphism in the methionine synthase reductase gene (MTRR A66G), and one polymorphism in the methylenetetrahydrofolate dehydrogenase 1 gene (MTHFD1 G1958A) and assessed their association with hypertension using chi-square analysis. We also performed a multifactor dimensionality reduction (MDR) analysis to investigate any potential epistatic interactions among the four polymorphisms and EH. None of the four polymorphisms was significantly associated with EH and although we found a moderate synergistic interaction between MTHFR A1298C and MTRR A66G, the association of the interaction model with EH was not statistically significant (P = 0.2367). Our findings therefore suggest no individual or interactive association between four prominent Hcy pathway markers and EH.

Genetic and clinical determinants of early, acute calcineurin inhibitor-related nephrotoxicity: results from a kidney transplant consortium

BACKGROUND

Calcineurin inhibitor (CNI)-related acute nephrotoxicity is a common complication of transplantation. Clinical factors and elevated CNI levels are associated with nephrotoxicity; however, they do not fully explain the risk. Genetic factors may also predispose individuals to nephrotoxicity.

METHODS

We enrolled 945 kidney recipients into a multicenter, prospective study. DNA was genotyped for 2724 single-nucleotide polymorphisms (SNPs) using a customized chip. Cox models, unadjusted and adjusted for clinical factors, examined the association between SNPs and time to early CNI-related acute nephrotoxicity in the first 6 months posttransplant.

RESULTS

Cyclosporine was associated with a 1.49 hazard (95% confidence interval, 1.04-2.14) of acute nephrotoxicity relative to tacrolimus. Acute nephrotoxicity occurred in 22.6% of cyclosporine and 19.8% of tacrolimus recipients. The median (interquartile range) daily dose and trough concentration at time of nephrotoxicity were 400 mg (400-500 mg) and 228 ng/mL (190-272 ng/mL) in the cyclosporine group, and 6 mg (4-8 mg) and 12.6 ng/mL (10.2-15.9 ng/mL) in the tacrolimus group, respectively. In single-SNP adjusted analysis, nine SNPs in the XPC, CYP2C9, PAX4, MTRR, and GAN genes were associated with cyclosporine nephrotoxicity. In a multi-SNP analysis, SNPs from the same genes remained significant after adjusting for the clinical factors, showing that the SNPs are jointly and independently predictive of cyclosporine nephrotoxicity. No SNPs were associated with tacrolimus nephrotoxicity.

CONCLUSION

We identified SNPs that were potentially associated with early, acute cyclosporine-related nephrotoxicity. Identifying risk SNPs before transplantation provides an opportunity for personalization of immunosuppression by identifying those who may benefit from CNI-avoidance or minimization, or assist in selecting CNI type. These SNPs require independent validation.

Genetic and environmental determinants of plasma total homocysteine levels: impact of population-wide folate fortification

OBJECTIVES

Folate metabolism is an important target for drug therapy. Drug-induced inhibition of folate metabolism often causes an elevation of plasma total homocysteine (tHcy). Plasma tHcy levels are influenced by several nongenetic (e.g. folate intake, age, smoking) as well as genetic factors. Over the last decade, several countries have implemented a nationwide folate fortification program of all grain products. This investigation sought to determine the impact of folate fortification on the relative contribution of environmental and genetic factors to the variability of plasma tHcy.

METHODS

Two cohorts were compared in this study, one from the United States (with folate fortification, n=281) and one from Austria (without folate fortification, n=139). Several environmental factors as well as previously identified gene variants important for tHcy levels (MTHFR C677T, MTHFR A1298C, MTRR A66G) were examined for their ability to predict plasma tHcy in a multiple linear regression model.

RESULTS

Nongenetic, environmental factors had a comparable influence on plasma tHcy between the two cohorts (R: approximately 0.19). However, after adjusting for other covariates, the tested gene variants had a substantially smaller impact among patients from the folate-fortified cohort (R=0.021) compared with the nonfolate-fortified cohort (R=0.095). The MTHFR C677T polymorphism was the single most important genetic factor. Male sex, smoking, and folate levels were important predictors for nonfolate-fortified patients; age was for folate-fortified patients.

CONCLUSION

Population wide folate fortification had a significant effect on the variability of plasma tHcy and reduced the influence of genetic factors, most importantly the MTHFR 677TT genotype, and may be an important confounder for a personalized drug therapy.

Methionine synthase reductase A66G polymorphism contributes to tumor susceptibility: evidence from 35 case-control studies

Methionine synthase reductase (MTRR) gene is involved in tumorigenesis by regulating DNA methylation through activation of methionine synthase (MTR). MTRR is polymorphic at nucleotide 66 (A-to-G) and the resulting variant enzyme has a lower affinity for MTR. The reported associations of MTRR A66G polymorphism with cancer risk are contradictory. Therefore, we performed a meta-analysis to better assess the associations, including 18,661 cases and 27,678 controls from 35 studies. Crude ORs with 95% CIs were used to assess the strength of association between the MTRR A66G polymorphism and cancer risk. The pooled ORs were performed for homozygote model (GG vs. AA), heterozygote model (GG vs. GA), recessive genetic model (GG vs. GA + AA), and dominant genetic model (GG + GA vs. AA), respectively. Overall, results indicated that the G allele and GG variant genotypes were associated with a significantly increased cancer risk (G vs. A: OR, 1.039; 95% CI, 1.009-1.078; homozygote model: OR, 1.094; 95% CI, 1.006-1.191). In subgroup analysis by ethnicity, significant increased risks were found among Asians with G allele (G vs. A: OR, 1.063; 95% CI, 1.011-1.119; homozygote model: OR, 1.189; 95% CI, 1.055-1.341; recessive model: OR, 1.197; 95% CI, 1.068-1.341). For stratification analysis, the cancer types with fewer than three studies were categorized into "other cancers", and the results indicated that there was a significant elevated cancer risk in "other cancers" in all genetic models, not in colorectal cancer, lymphoid leukemia or breast cancer. In summary, our study suggests that the MTRR A66G polymorphism is a potential biomarker for cancer risk.

MTRR A66G polymorphism and breast cancer risk: a meta-analysis

Methionine synthase reductase (MTRR) is one of the important enzymes involved in the folate metabolic pathway and its functional genetic polymorphisms may be associated with breast cancer risk. However, this relationship remains inconclusive. For better understanding the effect of MTRR A66G polymorphism on breast cancer risk, a meta-analysis was performed. By searching PubMed and EMBASE, a total of six case-control studies, containing 6,084 cases and 6,756 controls, were included. The strength of association between MTRR A66G polymorphism and breast cancer risk was assessed by odds ratio (OR) with the corresponding 95% confidence interval (95% CI). The results strongly suggested that there was no significant association between MTRR A66G polymorphism and breast cancer susceptibility in overall comparisons in all genetic models (additive model: OR 1.00, 95% CI 0.89-1.11, P = 0.943; dominant model: OR 1.00, 95% CI 0.91-1.10, P = 0.989; recessive model: OR 1.00, 95% CI 0.91-1.09, P = 0.926). Similarly, in subgroup analyses for ethnicity (Caucasian, Asian and mixed population) and folate intake status (high and low folate intake), the results were negative. Sensitivity analysis demonstrated that omitting any study did not perturb the results. In conclusion, this meta-analysis strongly suggests that MTRR A66G polymorphism is not associated with breast cancer risk, especially in Caucasians and Asians.

A common gene variant in methionine synthase reductase is not associated with peak homocysteine concentrations after nitrous oxide anesthesia

OBJECTIVES

Oxidation of vitamin B12 by nitrous oxide leads to the inactivation of methionine synthase resulting in elevated plasma total homocysteine concentrations. Methionine synthase reductase is the only human enzyme that is able to reverse the oxidation of vitamin B12, which also occurs naturally by reactive oxygen species. A common polymorphism in methionine synthase reductase, MTRR 66A>G, is associated with reduced enzyme activity. Thus, we hypothesized that patients with this gene variant develop higher plasma total homocysteine concentrations after nitrous oxide anesthesia than wild-type patients.

METHODS

In this follow-up investigation of a previous gene association study, we prospectively included 140 healthy individuals undergoing elective surgery under general anesthesia that included 66% nitrous oxide. Peak postoperative plasma total homocysteine was the main outcome variable and was measured within 2 h after the end of anesthesia. The MTRR 66A>G genotype was determined after completion of the study. The association between genotype and peak postoperative total homocysteine was modeled with a general linear model.

RESULTS

No association between MTRR 66A>G and immediate postoperative plasma total homocysteine after nitrous oxide anesthesia was detected. All three groups, stratified by genotype (MTRR 66AA, AG, GG), shared similar baseline characteristics and increases in plasma total homocysteine. The average increase in plasma homocysteine was 2.4 mumol/l (+28%) in all three groups indicating the expected inactivation of methionine synthase by nitrous oxide through oxidation of vitamin B12, but no genetic effect.

CONCLUSION

In conclusion, this study showed that the MTRR 66A>G gene variant is not associated with peak elevated postoperative plasma total homocysteine after nitrous oxide anesthesia. Whether the gene influences the rate of recovery of methionine synthase remains to be determined.

Genetic and environmental influences on total plasma homocysteine and coronary artery disease (CAD) risk among South Indians

BACKGROUND

Hyperhomocysteinemia, a documented risk factor for CAD is highly prevalent in Indians. The rationale behind the current study is to explore the genetic and environmental causes for such high prevalence as there are limited studies in this context.

METHODS

A total of 108 CAD cases and 108 controls were analyzed for tHcy and 4 folate pathway genetic polymorphisms [methylene tetrahydrofolate reductase (MTHFR) C677T, 5-methyltetrahydrofolate homocysteine methyl transferase (MTR) A2756G, methionine synthase reductase (MTRR) A66G and glutamate carboxypeptidase II (GCPII) C1561T] using reverse phase HPLC and PCR-RFLP methods respectively.

RESULTS

MTHFR 677T, MTRR 66A, GCPII 1561T, male gender, alcohol intake, smoking, diabetes, creatinine and hypertension were found to influence tHcy. After controlling for confounding factors, Hyperhomocysteinemia and two of its genetic determinants i.e. MTHFR C677T [OR: 1.96, 95% CI: 1.06-3.61] and GCP II C1561T [OR: 2.09, 95% CI: 1.09-3.97] were found to be associated with risk for CAD. Significant epistatic interactions were observed between MTHFR 677T/MTR 2756G and GCP II 1561T/MTRR 66G. Alcohol intake in subjects with MTR 2756G allele was found to inflate the risk for CAD [OR: 4.15, 95% CI: 1.35-12.69].

CONCLUSION

Hyperhomocysteinemia, C677T MTHFR and C1561T GCPII are risk factors for CAD. Potential gene--gene and gene--environment interactions indicate the need for multi-variate analyses for risk prediction.

One-carbon metabolism enzyme polymorphisms and uteroplacental insufficiency

OBJECTIVES

This study was undertaken to test novel genetic polymorphisms involved in 1-carbon metabolism for a potential association with increased risk of developing pregnancy complications associated with uteroplacental insufficiency.

STUDY DESIGN

This was a prospective cohort study consisting of 50 women at low risk and 93 women at high risk for having a pregnancy complication develop. Maternal and fetal DNA samples were genotyped for methionine synthase (MTR) A2756G, methionine synthase reductase (MTRR) A66G and methylenetetrahydrofolate dehydrogenase (MTHFD1) G1958A. A chi squared or chi(2) analysis was used to compare genotypes and pregnancy outcome, 1-way analysis of variance and linear regression were used to compare genotype with continuous variables.

RESULTS

The fetal MTR 2756 G allele was associated with uteroplacental insufficiency (P = .022, likelihood ratio = 10.4) and maternal homocysteine (P = .017). The maternal MTR A2756G polymorphism was associated with uteroplacental insufficiency (P = .049, likelihood ratio = 6.0), but only in mothers not supplementing with high-dose B-vitamins. The maternal MTHFD1 AA genotype was associated with intrauterine growth restriction (P = .047, likelihood ratio = 5.8).

CONCLUSION

This study suggests the maternal and fetal MTR 2756 G allele is an important risk factor in the development of uteroplacental insufficiency. In addition, the maternal MTHFD1 1958 AA genotype may be associated with intrauterine growth restriction.

Relation between plasma homocysteine, gene polymorphisms of homocysteine metabolism-related enzymes, and angiographically proven coronary artery disease

BACKGROUND

Hyperhomocyteinemia (HHcy) is a risk factor for coronary artery disease (CAD), and methylenetetrahydrofolate reductase (MTHFR), methionine synthase (MTR), and methionine synthase reductase (MTRR) polymorphisms may contribute to plasma total homocysteine (tHcy) variation. We investigated the association of polymorphisms 1298A-->C in the MTHFR gene, 2756A-->G in the MTR gene, and 66A-->G in the MTRR gene with tHcy levels and with CAD in patients undergoing coronary angiography.

METHODS

CAD patients (n=151) and control subjects (n=79) were compared regarding the prevalence of the polymorphisms, risk factors, and biochemical parameters.

RESULTS

The mean tHcy concentration was significantly higher in CAD patients than in control subjects (P<0.001). HHcy (tHcy>/=15 mumol/l) conferred an OR of CAD of 4.1 (95% CI 2.2-7.5, P<0.001). In both cases and controls, smokers had a higher tHcy level than non-smokers and demonstrated a markedly increased risk for CAD (OR=2.5, 95% CI 1.7-3.3, P<0.001). The allele frequencies of the MTHFR 1298A-->C, MTR 2756A-->G, and MTRR 66A-->G mutations were 36.7%, 15.7%, and 36.6%, respectively. The 1298C allele frequency was significantly higher in the CAD group than in controls (P<0.05) and showed a significant association with CAD in heterozygote carriers. There was no statistically significant difference between cases and controls in the frequencies of the A2756G alleles/genotypes in the MTR gene and of the A66G alleles/genotypes in the MTRR gene. The contributions to tHcy levels of the three common mutations were statistically significant. The heterozygosity of the MTHFR 1298AC genotype, MTR 2756G allele, and MTRR 66G allele yielded an OR of 3.4, 2.0, and 2.1, respectively, for having HHcy.

CONCLUSION

We suggest that HHcy confers a risk for CAD, and smokers with tHcy are at a greatly increased risk. Our finding supports an important role of the MTHFR gene in CAD and provides evidence of polygenic regulation of tHcy.

No association between MTHFR A1298C and MTRR A66G polymorphisms, and MS in an Australian cohort

Multiple sclerosis (MS) is a complex neurological disease that affects the central nervous system (CNS) resulting in debilitating neuropathology. Pathogenesis is primarily defined by CNS inflammation and demyelination of nerve axons. Methionine synthase reductase (MTRR) is an enzyme that catalyzes the remethylation of homocysteine (Hcy) to methionine via cobalamin and folate dependant reactions. Cobalamin acts as an intermediate methyl carrier between methylenetetrahydrofolate reductase (MTHFR) and Hcy. MTRR plays a critical role in maintaining cobalamin in an active form and is consequently an important determinant of total plasma Hcy (pHcy) concentrations. Elevated intracellular pHcy levels have been suggested to play a role in CNS dysfunction, neurodegenerative, and cerebrovascular diseases. Our investigation entailed the genotyping of a cohort of 140 cases and matched controls for MTRR and MTHFR, by restriction length polymorphism (RFLP) techniques. Two polymorphisms: MTRR A66G and MTHFR A1298C were investigated in an Australian age and gender matched case-control study. No significant allelic frequency difference was observed between cases and controls at the alpha = 0.05 level (MTRR chi2 = 0.005, P = 0.95, MTHFR chi2 = 1.15, P = 0.28). Our preliminary findings suggest no association between the MTRR A66G and MTHFR A1298C polymorphisms and MS.

Genetic variation in genes of folate metabolism and neural-tube defect risk

Neural-tube defects (NTD) are common congenital malformations that can lead to severe disability or even death. Periconceptional supplementation with the B-vitamin folic acid has been demonstrated to prevent 50-70% of NTD cases. Since the identification of the first genetic risk factor of NTD, the C677T single-nucleotide polymorphism (SNP) in the methylenetetrahydrofolate reductase (MTHFR) gene, and the observation that elevated plasma homocysteine levels are associated with NTD, research has focused on genetic variation in genes encoding for enzymes of folate metabolism and the closely-related homocysteine metabolism. In the present review relevant SNP in genes that code for enzymes involved in folate transport and uptake, the folate cycles and homocysteine metabolism are summarised and the importance of these SNP discussed in relation to NTD risk.

The methionine synthase reductase 66A>G polymorphism is a maternal risk factor for spina bifida

The methionine synthase reductase (MTRR) enzyme restores methionine synthase (MTR) enzyme activity and therefore plays an essential role in homocysteine remethylation. In some studies, the 66A>G polymorphism in the MTRR gene was associated with increased neural tube defect (NTD) risk. Using a case-control design, we studied the association between the MTRR 66A>G polymorphism and spina bifida risk in 121 mothers, 109 spina bifida patients, 292 control women, and 234 pediatric controls. Possible interactions between the MTRR 66A>G variant and the MTR 2756A>G polymorphism, the MTHFR 677C>T variant, plasma vitamin B12, and plasma methylmalonic acid (MMA) levels were examined in the 121 mothers and 292 control women. Meta-analyses were conducted to set the results of the case-control study in the context of eligible literature on the relation between the MTRR 66A>G variant and NTD risk. Finally, a transmission disequilibrium test was performed for 82 complete mother-father-child triads to test for preferential transmission of the MTRR risk allele. In our case-control study, the MTRR 66A>G polymorphism had no influence on spina bifida risk in children [odds ratio (OR) 0.6, 95% confidence interval (CI) 0.4-1.1]. The MTRR 66GG genotype increased maternal spina bifida risk by 2.1-fold (OR 2.1, 95% CI 1.3-3.3). This risk became more pronounced in combination with the MTHFR 677TT genotype (OR 4.0, 95% CI 1.3-12.5). Moreover, we demonstrate a possible interaction between the MTRR 66GG genotype and high plasma MMA levels (OR 5.5, 95% CI 2.2-13.5). The meta-analyses demonstrated that the maternal MTRR 66GG genotype was associated with an overall 55% (95% CI 1.04-2.30) increase in NTD risk and that the MTRR 66GG genotype did not increase NTD risk in children (OR 0.96, 95% CI 0.46-2.01). These data show that the MTRR 66GG genotype is a maternal risk factor for spina bifida especially when intracellular vitamin B12 status is low.

Maternal polymorphisms 677C-T and 1298A-C of MTHFR, and 66A-G MTRR genes: is there any relationship between polymorphisms of the folate pathway, maternal homocysteine levels, and the risk for having a child with Down syndrome?

This study was aimed at analyzing the effect of mutations in three non-synonymous SNP genes (677C > T and 1298A > C of the methylenetetrahydrofolate reductase (MTHFR) gene, and 66A > G in the MTRR gene) on total plasmatic homocysteine (Hcy), in 91 mothers of Down syndrome (DS) infants and 90 control mothers. The comparison of both groups of mothers is a new way to determine if those mutations and their interactions increase the risk for DS. Material came from the case-control network of the Spanish Collaborative Study of Congenital Malformations (ECEMC). Using a general lineal model in a backwards step, we performed the analyses including the different mutations, maternal age, the fact that each mother had a DS or a control infant, and all possible interactions of these variables, in the models, being maternal Hcy the continuous dependent variable. In another model, maternal folic acid intake during the third trimester of pregnancy was added. The results from both models were essentially the same: Hcy levels variability differs from case mothers to control ones, the presence of the MTHFR1298A > C polymorphism also affects significantly the Hcy variance, as it does the statistical interaction between the mutations MTRR66A > G and MTHFR1298A > C in the mother. In this sense, the interaction between different polymorphisms may totally modify their individual effects, and some of those effects are different in mothers of DS children and in controls' mothers. For instance, only two mutations in MTRR66 (GGAA) in mothers of control infants increase the reference maternal Hcy level in 4.66 units, and the individual effect of the genotype with only two mutations in the MTHFR1298 gene (AACC) increases the reference Hcy level in 12.74 units. However, the presence of the four mutations (GGCC) interacts giving a statistically significant decrease in 6.00 units in the level of Hcy in control mothers. On the contrary, in mothers of DS infants, the sole presence of two mutations in one of these two genes decreases the levels of Hcy (-2.31 units for GGAA genotype, and -3.43 units for AACC genotype), while the presence of the four mutations (GGCC) increases Hcy in 9.53 units. Taking into consideration that in the one-carbon metabolism cystathionine beta-synthase (CBS) catalyzes Hcy in an irreversible way, and that CBS gene is located in chromosome 21, fetuses and infants with DS have functional folate deficiency due to overexpression of CBS. This fact, as well as others influencing Hcy levels (such as nutrients interactions and lifestyle), together with the fetal genotype, suggest that their relationship with DS could be through an effect on fetal survival up to birth. Three possible mechanisms are considered by evaluating the results in the light of the present knowledge on cytology and molecular biology.

Homocysteine metabolism, hyperhomocysteinaemia and vascular disease: an overview

Hyperhomocysteinaemia has been regarded as a new modifiable risk factor for atherosclerosis and vascular disease. Homocysteine is a branch-point intermediate of methionine metabolism, which can be further metabolised via two alternative pathways: degraded irreversibly through the transsulphuration pathway or remethylated to methionine by the remethylation pathway. Both pathways are B-vitamin-dependent. Plasma homocysteine concentrations are determined by nongenetic and genetic factors. The metabolism of homocysteine, the role of B vitamins and the contribution of nongenetic and genetic determinants of homocysteine concentrations are reviewed. The mechanisms whereby homocysteine causes endothelial damage and vascular disease are not fully understood. Recently, a link has been postulated between homocysteine, or its intermediates, and an alterated DNA methylation pattern. The involvement of epigenetic mechanisms in the context of homocysteine and atherosclerosis, due to inhibition of transmethylation reactions, is briefly overviewed.

Effects of single-nucleotide polymorphisms in MTHFR and MTRR on mortality and allograft loss in kidney transplant recipients

BACKGROUND

Plasma total homocysteine (tHcy) is associated with cardiovascular outcomes in kidney transplant recipients (KTR). The methylenetetrahydrofolate-reductase (MTHFR) 677C>T polymorphism, an important determinant of plasma tHcy concentrations, could therefore constitute an important prognostic marker.

METHODS

We prospectively followed 710 KTR over >6 years. The MTHFR677C>T, MTHFR1298A>C, MTHFR1793G>A, and MTRR66A>G polymorphisms were analyzed. Demographic, clinical, and transplant-related information was obtained, and patients were followed-up using the Austrian Dialysis and Transplant Registry. Using Cox regression, we established the independent relations of each genotype to the risk of death from any cause, and/or kidney allograft loss.

RESULTS

During a median follow-up of 6.1 years, 154 participants died and 260 kidney allografts were lost. Compared to patients with the MTHFR677CC genotype, patients with MTHFR677CT had an adjusted relative mortality risk of 1.02 (95%CI 0.70-1.47), and those with MTHFR677TT of 0.98 (95%CI 0.52-1.85). Compared to MTHFR677CC, the relative risks of kidney allograft loss were 0.93 (95%CI 0.70-1.23; MTHFR677CT) and 0.78 (95%CI 0.47-1.30; MTHFR677TT), respectively. None of the other genotypes were associated with the risks studied, either. These findings did not depend on whether we controlled for tHcy levels.

CONCLUSION

This study does not support the routine use of MTHFR or MTRR genotyping for prognostic evaluation or risk-stratification in kidney transplant recipients.

Associations between MTHFR 1793G>A and plasma total homocysteine, folate, and vitamin B12 in kidney transplant recipients

BACKGROUND

Currently, no evidence is available on the putative associations between a novel single nucleotide polymorphism of the 5,10-methylenetetrahydrofolate reductase gene MTHFR 1793G>A and plasma levels of vitamin B(12), folate, or total homocysteine (tHcy).

METHODS

In a cross-sectional study of 730 kidney allograft recipients, patients were categorized by MTHFR 1793G>A genotype. In univariate and multivariate linear regression models that allowed the outcome variables vitamin B(12), folate, and tHcy plasma levels to follow a gamma distribution, we tested for possible associations of allelic variants of MTHFR 1793G>A and these three dependent variables. As hypothesized in previous work, we specifically evaluated possible effect modification between the MTHFR 1793G>A and 1298A>C mutations on these outcomes.

RESULTS

The allele frequency for MTHFR 1793G>A was 0.052. Heterozygosity (N= 72) or homozygosity (N= 2) for MTHFR 1793G>A was not independently associated with plasma levels of vitamin B(12) (P= 0.33) or tHcy (P= 0.70), but a borderline association with higher folate concentrations was detected (Deltafolate = 1.91 nmol/L) (95% CI -0.03 to 3.86 nmol/L) (P= 0.05). Further, we found strong and significant positive interactions between the MTHFR 1793G>A and 1298A>C mutations on vitamin B(12) concentrations.

CONCLUSION

Higher folate concentrations in kidney transplant recipients with MTHFR 1793GA or 1793AA and markedly higher concentrations of vitamin B(12) in patients with combined MTHFR 1793G>A and 1298A>C mutations may contribute to the survival advantage that has been postulated for such patients showing these genotypes.