Maternal Folate Polymorphisms and the Etiology of Human Nondisjunction

Attempts to identify genetic contributors to human meiotic nondisjunction have met with little, if any, success. Thus, recent reports linking Down syndrome to maternal polymorphisms at either of two folate metabolism enzymes, methylenetetrahydrofolate reductase (MTHFR) and methionine synthase reductase (MTRR), have generated considerable interest. In the present report, we asked whether variation at MTHFR (677C-->T) or MTRR (66A-->G) might be associated with human trisomies other than trisomy 21. We analyzed maternal polymorphisms at MTHFR and MTRR in 93 cases of sex-chromosome trisomy, 44 cases of trisomy 18, and 158 cases of autosomal trisomies 2, 7, 10, 13, 14, 15, 16, 18, or 22, and compared the distributions of genotypes to those of control populations. We observed a significant increase in the MTHFR polymorphism in mothers of trisomy 18 conceptuses but were unable to identify any other significant associations. Overall, our observations suggest that, at least for the sex chromosomes and for a combined set of autosomal trisomies, polymorphisms in the folate pathway are not a significant contributor to human meiotic nondisjunction.     

年轻母亲叶酸代谢基因多态性与唐氏综合征发生的关系

为探讨年轻母亲叶酸代谢相关基因MTHFR 677C>T、MTRR 66A>G、RFC-1 80G>A和MTR 2756A>G多态性与唐氏综合征(Down syndrome, DS)发生的关系, 采用随机病例-对照研究设计, 应用PCR-RFLP方法检测60例DS患儿的母亲与68例正常生育女性的基因型。经χ² 检验, MTHFR基因T等位基因频率在病例组和对照组中差异有统计学意义(P<0.05), 而MTRR、MTR和 RFC-1等位基因频率差异无统计学意义。Logistic回归分析显示: 携带MTHFR TT基因型的母亲孕育DS患儿的风险显著增加(OR=3.51, 95% CI=1.30~9.46, P<0.05), 而杂合子CT以及CT合并TT基因型与DS发生风险无显著关联; 携带MTRR GG基因型的母亲孕育DS患儿的风险增加3.16倍(OR=3.16, 95% CI=1.20~8.35, P<0.05), 而RFC-1和MTR突变基因型与DS发生风险无显著关联; MTHFR(CT+TT)/MTRR GG、MTHFR (CT+TT)/ RFC-1 AA、MTHFR CC / MTR (AG +GG)、 MTHFR (CT+TT)/MTR AA、MTRR GG/MTR AA和RFC-1 AA / MTR AA联合基因型与DS发生风险显著相关。结果表明, 年轻女性MTHFR 677C>T、MTRR 66A>G位点变异是孕育DS患儿的独立风险因子, 尚不能认为RFC-1 80G>A、MTR 2756A>G多态性与DS发生相关, 而基因与基因多态位点之间存在交互和修饰效应。     

MTHFR、MTRR和MTR基因多态性与唐氏综合征发生的相关性研究

应用PCR-RFLP方法分析31例唐氏综合征（Down＇s syndrome, DS）患儿母亲和68例正常生育女性叶酸代谢相关基因：MTHFR 677C〉T、MTRR 66A〉G和MTR 2756A〉G多态性,探讨其与唐氏综合征DS发生的关系。采用Pearson χ^2 检验基因和基因型频率分布,并分析各基因之间的相互作用,计算比值比评价相对危险度。MTHFR基因T等位基因频率在病例组和对照组中具有显著性差异（P〈0.05）,而MTRR和MTR基因G等位基因频率在病例组和对照组中的差异无显著性。MTHFR TT基因型母亲生育DS风险显著增加（OR=3.51,95 %CI=1.04-11.85,P〈0.05）。MTRR GG基因型生育DS的风险增加3.57倍（OR=3.57,95 %CI=1.19-10.73,P〈0.05）。MTR突变基因型AG和GG与生育DS的风险无显著关系。MTHFR （CT＋TT）/MTRR GG、MTHFR （CT＋TT）/MTR AA和MTRR GG/MTR AA联合基因型与DS发生风险显著相关。结果表明,MTHFR 677C〉T、MTRR 66A〉G位点变异是生育DS的独立风险因子,尚不能认为MTR 2756A〉G多态与DS发生相关。基因与基因多态位点之间存在交互和修饰效应。     

The polymorphisms in methylenetetrahydrofolate reductase, methionine synthase, methionine synthase reductase, and the risk of colorectal cancer

Polymorphisms in genes involved in folate metabolism may modulate the risk of colorectal cancer (CRC), but data from published studies are conflicting. The current meta-analysis was performed to address a more accurate estimation. A total of 41 (17,552 cases and 26,238 controls), 24(8,263 cases and 12,033 controls), 12(3,758 cases and 5,646 controls), and 13 (5,511 cases and 7,265 controls) studies were finally included for the association between methylenetetrahydrofolate reductase (MTHFR) C677T and A1289C, methione synthase reductase (MTRR) A66G, methionine synthase (MTR) A2756G polymorphisms and the risk of CRC, respectively. The data showed that the MTHFR 677T allele was significantly associated with reduced risk of CRC (OR = 0.93, 95%CI 0.90-0.96), while the MTRR 66G allele was significantly associated with increased risk of CRC (OR = 1.11, 95%CI 1.01-1.18). Sub-group analysis by ethnicity revealed that MTHFR C677T polymorphism was significantly associated with reduced risk of CRC in Asians (OR = 0.80, 95%CI 0.72-0.89) and Caucasians (OR = 0.84, 95%CI 0.76-0.93) in recessive genetic model, while the MTRR 66GG genotype was found to significantly increase the risk of CRC in Caucasians (GG vs. AA: OR = 1.18, 95%CI 1.03-1.36). No significant association was found between MTHFR A1298C and MTR A2756G polymorphisms and the risk of CRC. Cumulative meta-analysis showed no particular time trend existed in the summary estimate. Probability of publication bias was low across all comparisons illustrated by the funnel plots and Egger's test. Collectively, this meta-analysis suggested that MTHFR 677T allele might provide protection against CRC in worldwide populations, while MTRR 66G allele might increase the risk of CRC in Caucasians. Since potential confounders could not be ruled out completely, further studies were needed to confirm these results.     

Maternal <Emphasis Type="Italic">MTHFR</Emphasis> polymorphism (677 C–T) and risk of Down’s syndrome child: meta-analysis

Methylenetetrahydrofolate reductase (MTHFR) is the most important gene that participates in folate metabolism. Presence of valine instead of alanine at position 677 and elevated levels of homocystein causes DNA hypomethylation which in turn favours nondisjunction. In this study, we conducted a meta-analysis to establish link between maternal single-nucleotide polymorphism (SNP) and birth of Down’s syndrome (DS) child. A total of 37 case–control studies were selected for analysis including our own, in which we investigated 110 cases and 111 control mothers. Overall, the result of meta-analysis showed significant risk of DS affected by the presence of maternal SNP (MTHFR 677 C–T OR = 0.816, 95% CI = 0.741–0.900, P<0.0001). Heterogeneity of high magnitude was observed among the studies. The chi-square value suggested a highly significant association between homozygous mutant TT genotype and birth of DS child (χ²=23.63, P=0.000). Genetic models suggested that ‘T’ allele possesses high risk for DS whether present in dominant (OR = 1.23, 95% CI = 1.13–1.34); codominant (OR = 1.17, 95% CI = 1.10–1.25) or recessive (OR = 1.21, 95% CI = 1.05–1.38) form. The analysis from all 37 studies combined together suggested that MTHFR 677 C–T is a major risk factor for DS birth.     

MTHFR and MTRR genotype and haplotype analysis and colorectal cancer susceptibility in a case-control study from the Czech Republic

Polymorphic variants in genes involved in one-carbon metabolism, in particular of dietary folate, may modulate the risk for colorectal cancer through aberrant DNA-methylation and altered nucleotide synthesis and repair. In the present study, we have assessed the association of six polymorphisms and relative haplotypes in the MTHFR gene (rs1801133 and rs1801131) and in the MTRR gene (rs1801394, rs1532268, rs162036, and rs10380) with the risk for colorectal cancer in 666 patients and 1377 controls from the Czech Republic. We found that the 677 C>T polymorphism in the MTHFR gene significantly decreased the risk for colorectal cancer in homozygous carriers of the variant allele (OR, 0.58; 95% CI, 0.39-0.87). Also, we noted a significantly different distribution of genotypes between cases and controls for the 66A>G polymorphism in the MTRR gene. In particular, homozygous carriers of the G-containing allele of this polymorphism were at an increased risk for colorectal cancer (OR, 1.39; 95% CI, 1.04-1.85). Haplotype analysis of the two MTHFR polymorphisms showed a moderate difference in the distribution of the TA haplotype between cases and controls. In comparison to the most common haplotype (CA), the TA haplotype was associated with a decreased risk for colorectal cancer (OR, 0.84; 95% CI, 0.71-0.99). No difference in the distribution between cases and controls was observed for the haplotypes based on the four polymorphisms in the MTRR gene. The present study suggests that the 677TT genotype and the TA haplotype in the MTHFR gene may also have a role in colorectal cancer risk in the Czech population, indicating the importance of genes involved in folate metabolism with respect to cancer risk. For MTRR, additional studies on larger populations are needed to clarify the possible role of variation in this gene in colorectal carcinogenesis.     

Genetic polymorphisms involved in folate metabolism and elevated plasma concentrations of homocysteine: maternal risk factors for Down syndrome in Brazil

The aim of the present study was to investigate the effect of polymorphisms C677T and A1298C in the methylenetetrahydrofolate reductase (MTHFR) gene, A2756G in methionine synthase reductase (MTR) gene and A80G in reduced folate carrier 1 (RFC1) gene, and plasma homocysteine (Hcy), on the maternal risk for Down syndrome (DS). Seventy-two DS mothers and 194 mothers who had no children with DS were evaluated. The investigation of the MTHFR C677T, MTR A2756G and RFC1 A80G polymorphisms was performed by polymerase chain reaction and enzyme digestion and the MTHFR A1298C polymorphism by allele-specific polymerase chain reaction. Hcy quantification was carried out by liquid chromatography-tandem mass spectrometry. The median number of polymorphic alleles for the four loci tested was greater in DS mothers compared to the control group, and the presence of three or more polymorphic alleles increased the risk for having a child with DS 1.74 times. Elevated maternal risk for DS was also observed when plasma Hcy concentration was higher than 4.99 micromol/L. In conclusion, the presence of three or more polymorphic alleles for MTHFR C677T, MTHFR A1298C, MTR A2756G, and RFC1 A80G, and plasma Hcy concentrations higher than 4.99 micromol/L are maternal risk factors for DS.     

Methylenetetrahydrofolate reductase 677C-->T polymorphism affects DNA methylation in response to controlled folate intake in young women

DNA methylation is critical for normal genomic structure and function and is dependent on adequate folate status. A polymorphism (677C-->T) in a key folate enzyme, methylenetetrahydrofolate reductase (MTHFR), may impair DNA methylation when folate intake is inadequate and may increase the risk of reproductive abnormalities. The present study was designed to evaluate the effect of the MTHFR 677C-->T polymorphism on changes in global DNA methylation in young women consuming a low folate diet followed by repletion with the current Recommended Dietary Allowance (RDA). Women (age 20-30 years) with the TT (variant; n = 19) or CC (n = 22) genotype for the MTHFR 677C-->T polymorphism participated in a folate depletion-repletion study (7 weeks, 115 microg DFE/day; 7 weeks, 400 microg DFE/day). DNA methylation was measured at baseline, week 7, and week 14 using a [3H]methyl acceptance assay and a novel liquid chromatography tandem mass spectrometry assay of the DNA bases methylcytosine and cytosine. [3H]Methyl group acceptance tended to increase (P = 0.08) during depletion in all subjects, indicative of a decrease in global DNA methylation. During repletion, the raw change and the percent change in the methylcytosine/total cytosine ratio increased (P = 0.03 and P = 0.04, respectively) only in the subjects with the TT genotype. Moderate folate depletion in young women may cause a decrease in overall DNA methylation. The response to folate repletion suggests that following folate depletion women with the MTHFR 677 TT genotype have a greater increase in DNA methylation with folate repletion than women with the CC genotype.     

Folate intake and MTHFR polymorphism C677T is not associated with ovarian cancer risk: evidence from the meta-analysis

Folate is essential for DNA synthesis and methylation and implicated in the process of carcinogenesis. Several studies inconclusively suggested increased folate intake may reduce ovarian cancer risk. Studies concerning the association between C677T polymorphism in methylenetetrahydrofolate reductase (MTHFR), an important enzyme in folate metabolism, and ovarian cancer risk also resulted in no agreement. The meta-analysis was conducted based on current studies to assess the association between folate intake, the MTHFR C667T polymorphism and ovarian cancer risk. 1,158 cases out of 217,309 participants from four cohort studies, 4,519 cases and 6,031 controls from four case–control studies about folate intake along with 5,617 cases and 9,808 controls from 10 publications concerning the polymorphism were pooled, respectively. We detected no significant association between total folate (RR = 1.04, 95 % confidence interval (CI) = 0.87–1.23) or dietary folate (RR = 0.88, 95 % CI = 0.75–1.05) intake and ovarian cancer risk, and also no significant relationship was found between MTHFR C677T polymorphism and ovarian cancer risk (TT vs. CC: odds ratio (OR) = 1.15, 95 % CI = 0.90–1.46; CT vs. CC: OR = 1.04, 95 % CI = 0.94–1.16). Our analysis indicated neither folate intake nor MTHFR C677T polymorphism is related to altered susceptibility of ovarian cancer.     

The association between MTHFR C677T polymorphism and ovarian cancer risk: a meta-analysis of 18, 628 individuals

Methylenetetrahydrofolate reductase (MTHFR) enzyme plays an important role in folate metabolism and MTHFR polymorphisms have been suggested to be associated with risk of various cancers. MTHFR C677T polymorphism is a common genetic alteration and may affect the host susceptibility to ovarian cancer. The aim of this study was to investigate the association between MTHFR C677T polymorphism and ovarian cancer risk by performing a meta-analysis. Pubmed, Embase, Web of Science and Chinese Biomedical Database (CBM) databases were searched for case–control studies investigating the association between MTHFR C677T polymorphism and ovarian cancer. Odds ratio (OR) and its 95 % confidence interval (95 % CI) was used to assess this possible association. 13 individual case–control studies from 10 publications with a total of 18, 628 subjects (5, 932 cases and 12, 696 controls) were included into this meta-analysis. Meta-analyses showed there was no association between MTHFR C677T polymorphism and ovarian cancer risk in Caucasians under all five genetic models (All P values for the pooled ORs were more than 0.05), whereas there was an obvious association between MTHFR C677T polymorphism and ovarian cancer risk in Asians under four genetic models (for T vs C, OR (95 % CI) = 1.38(1.19–1.61); for TT vs CC, OR (95 % CI) = 2.32(1.63–3.29); for TT vs TC+CC, OR (95 % CI) = 2.04(1.47–2.85); for TT+TC vs CC, OR (95 % CI) = 1.36(1.12–1.65)). Subgroup analyses suggested ethnicity was the major source of heterogeneity. This meta-analysis supports an association between MTHFR C677T polymorphism and ovarian cancer risk, and there might be a race-specific effect in this association. Further studies with large sample size and careful design are needed to identify this association more comprehensively.     

Quantitative assessment of the associations between MTHFR C677T and A1298C polymorphisms and risk of fractures: a meta-analysis

Many studies have investigated the associations between methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C polymorphisms and risk of fractures, but the impact of MTHFR polymorphisms on fractures risk is unclear owing to the obvious inconsistence among those studies. This study aims to quantify the strength of association between MTHFR C677T and A1298C polymorphisms and risk of fractures. We searched the PubMed, Embase and Wanfang databases for articles relating the association between MTHFR C677T and A1298C polymorphisms and risk of fractures in humans. We estimated summary odds ratios (ORs) with their confidence intervals (CIs) to assess the associations. Meta-analyses suggested MTHFR C677T polymorphism was associated with increased risk of any site fractures (for T vs. C, OR = 1.17, 95 % CI 1.03–1.32; for TT vs. CC, OR = 1. 31, 95 % CI 1.11–1.54; for TT vs. CT, OR = 1.22, 95 % CI 1.04–1.43; for TT vs. CT/CC, OR = 1.31, 95 % CI 1.13–1.51). Besides, MTHFR A1298C polymorphism was also associated with increased risk of any site fractures. Subgroup meta-analyses suggested MTHFR C677T polymorphism was associated with increased risk of vertebral fractures under three genetic contrast modes (for TT vs. CC, OR = 1.43, 95 % CI 1.05–1.95; for TT vs. CT, OR = 1.36, 95 % CI 1.01–1.85; for TT vs. CT/CC, OR = 1.50, 95 % CI 1.17–1.91), but there was no association between MTHFR C677T polymorphism and risk of hip fractures and non-vertebral fractures (all P values were more than 0.05). Thus, individuals with homozygote genotype TT of MTHFR C677T have obviously increased risk of vertebral fractures compared those with heterozygote genotype CT or homozygote genotype CC. There is no association between MTHFR C677T polymorphism and risk of hip fractures and non-vertebral fractures.     

Prevalence of methylenetetrahydrofolate reductase 677 C-T polymorphism among mothers of Down syndrome children

INTRODUCTION:

The relationship between chromosomal non-disjunction leading to aneuploidy and folate metabolism has drawn attention in the recent years. In this study, we examined the polymorphism in the gene encoding the folate metabolizing enzyme methylenetetrahydrofolate reductase (MTHFR), namely, 677 C-T in women having Down syndrome (DS) children.

MATERIALS AND METHODS:

The prevalence of these variant genotypes (MTHFR 677 C-T polymorphism) in women having DS children (case mothers) (n = 110) was compared with controls (n = 111) from Punjab. Genotyping was done using the polymerase chain reaction method followed by restriction fragment length polymorphism.

RESULTS:

In the present study, 1.8% of case mothers had TT genotype while none of the control mothers showed this genotype. T allele frequency among cases was 0.13 and 0.11 in controls. The Chi-square value showed a non-significant difference between cases and controls.

CONCLUSION:

No association has been observed between 677 C-T polymorphism and risk of non-disjunction in case mothers. Detection of polymorphisms in more genes of folate pathway is required to find out the exact cause of non-disjunction.     

Polymorphisms of 5,10-methylenetetralydrofolate reductase (MTHFR), fruit and vegetable intake, and the risk of stomach cancer

Stomach cancer is a serious public health problem in China. 5,10-Methylenetetralydrofolate reductase (MTHFR) may be involved in both DNA methylation and DNA synthesis. Folate deficiency is associated with cancer risk that may be modulated by a genetic variation in the MTHFR gene in folate metabolism. The main goal of this study was to evaluate the association between polymorphisms of the MTHFR gene and the risk of stomach cancer. This study also explored the modification effects of fruit and vegetable intake (one of the main constituents is folate) on the risk of this disease. A population-based case-control study was conducted in Taixing, China, consisting of 206 newly diagnosed cases with primary stomach cancer and 415 healthy population controls. Polymorphisms of MTHFR C677T and A1298C were assayed by polymerase chain reaction-restricted fragment length polymorphism (PCR-RFLP) techniques. The data were analysed using the logistic regression model. No obvious association between the MTHFR A1298C polymorphism and the risk of stomach cancer was observed in this study. The frequencies of 677 C/C, C/T, and T/T were 34.5, 50.9, and 14.6%, respectively, in controls. The frequency of the MTHFR 677 wild homozygotic genotype was 25.8% in cases, which was lower than that in controls (34.5%). The adjusted odds ratio (OR) for the MTHFR 677 any T genotype was 2.05 (95% confidence interval (CI), 1.26-3.34) when compared with the C/C genotype. In the low fruit and vegetable intake group an increasing trend was observed with the T allele exposure, p=0.0056. The adjusted ORs were 1.68 (95% CI = 0.86-3.29) for the C/T genotype and 3.58 (95% CI = 1.46-8.75) for the T/T genotype, respectively. The MTHFR 677 any T genotype was associated with an increased risk of primary stomach cancer among the Chinese population. Folate deficiency might modify the MTHFR gene polymorphism and influence the risk of stomach cancer.     

MTHFR C677T polymorphism contributes to colorectal cancer susceptibility: evidence from 61 case–control studies

Methylenetetrahydrofolate reductase (MTHFR) is believed to be involved in folate metabolism which plays a critical role in carcinogenesis. To date, many case-control studies have investigated the association between MTHFR C677T polymorphism and colorectal cancer risk. However, the results were inconsistent. In order to derive a more precise estimation of the association, we conducted this meta-analysis. This meta-analysis recruited 61 published studies which were selected by a search of PubMed up to 31st September 2011, including 16,111 colorectal cancer cases and 23,192 controls. We used crude odds ratios (ORs) with 95?% confidence intervals (CIs) to assess the association between MTHFR C677T polymorphism and colorectal cancer susceptibility. Our results showed that MTHFR C667T polymorphism contributed to the decreased colorectal cancer risk in overall population (for TT vs. CC: OR?=?0.89, 95?% CI?=?0.82-0.97; for TT vs. CT/CC: OR?=?0.88, 95?% CI?=?0.83-0.92). In subgroup analysis by ethnicity, the results also indicated a correlation between the T allele of MTHFR C667T and the colorectal cancer risk in Asian population (for TT vs. CC: OR?=?0.82, 95?% CI?=?0.69-0.97; for TT vs. CT/CC: OR?=?0.81, 95?% CI?=?0.74-0.90). Additionally, the correlation was also observed in male subgroup in sub-analysis by gender (for TT vs. CC: OR?=?0.82, 95?% CI?=?0.71-0.93; for TT vs. CT/CC: OR?=?0.81, 95?% CI?=?0.71-0.92). In summary, our meta-analysis strongly indicated the MTHFR C667T polymorphism was associated with a reduced risk of CRC.     

Methylenetetrahydrofolate reductase genotypes and haplotypes associated with susceptibility to colorectal cancer in an eastern Chinese Han population

Methylenetetrahydrofolate reductase (MTHFR) plays an important role in folate metabolism and is involved in DNA synthesis, DNA repair and DNA methylation. The two common functional polymorphisms of MTHFR, C677T and A1298C have been associated with several diseases, including cancer. We made a case-control study to analyze a possible association of MTHFR gene polymorphisms C677T and A1298C with risk for colorectal cancer in an eastern Chinese Han population of 137 patients with a confirmed histopathological diagnosis of CRC and 145 age- and gender-matched controls with no history of cancer. DNA was isolated from peripheral blood samples and the genotypes were determined by PCR-RFLP. The concentrations of folate in plasma were measured by chemiluminescence immunoassay. The MTHFR 677TT genotype had a protective effect against colorectal cancer, with an odds ratio (OR) = 0.467 (95% confidence interval (CI) = 0.225-0.966). The 1298CC genotype was significantly correlated with a reduced risk of colorectal cancer (OR = 0.192; 95%CI = 0.040-0.916). Compared with the MTHFR 677CC and MTHFR 1298 AA genotypes, for individuals who carried both MTHFR 677CC and 1298CC genotypes, the OR of colorectal cancer was 0.103 (95%CI = 0.012-0.900); among individuals who carried both MTHFR 677TT and 1298AC genotypes, the OR for risk of colorectal cancer was 0.169 (95%CI = 0.044-0.654). MTHFR 677TT+CT genotypes had a significantly lower plasma folate concentration than those with the MTHFR 677CC genotype. MTHFR 1298AC+CC genotypes had a lower plasma folate concentration than those with the MTHFR 1298AA genotype (P < 0.05). In conclusion, subjects with the MTHFR 677TT and MTHFR 1298CC genotypes appeared to have a significantly lower risk for colorectal cancer. MTHFR haplotypes 677CC/1298CC and 677TT/1298AC were less common in cases than in controls. These haplotypes, when compared to the most common haplotype 677CC/1298AA, were associated with a decreased risk for colorectal cancer. We conclude that plasma folate level is influenced by MTHFR genotypes.     

Methylenetetrahydrofolate Reductase C677T Polymorphism and Type 2 Diabetes Mellitus in Chinese Population: A Meta-Analysis of 29 Case-Control Studies

Background

Methylenetetrahydrofolate reductase (MTHFR), a key enzyme in folate metabolism, had significant effects on the homocysteine levels. The common functional MTHFR C677T polymorphism had been extensively researched. Several studies had evaluated the relationship between MTHFR C677T polymorphism and type 2 diabetes mellitus (T2DM), but the results were still controversial in the Chinese Han population. This meta-analysis was conducted to evaluate the relationship between MTHFR C677T polymorphism and T2DM in the Chinese Han population.

Methods

We searched the relevant studies in multiple electronic databases, which published up to December 2013. We reviewed and extracted data from all the included studies on the relationship between MTHFR C677T polymorphism and T2DM in the Chinese Han population. The odds ratios (ORs) and their 95% confidence intervals (95%CIs) were used to evaluate the relationship. Fixed-effects and random-effects meta-analysis were used to pool ORs by the heterogeneity. Publication bias and sensitivity analysis were also examined.

Results

29 studies were finally included in our meta-analysis, which contained 4656 individuals with T2DM and 2127 healthy controls. There was a significant relationship between MTHFR C677T polymorphism and T2DM under dominant (OR: 1.70, 95% CI: 1.42–2.02), recessive (OR: 1.48, 95% CI: 1.21–1.80), homozygous (OR: 1.89, 95% CI: 1.47–2.42), heterozygous (OR: 1.58, 95% CI: 1.33–1.87), and additive (OR: 1.46, 95% CI: 1.28–1.68) genetic model in a random-effects model. Subgroup analysis also reached similar results. Sensitivity analysis indicated that the overall result were dependable.

Conclusions

There was a significant relationship between MTHFR C677T polymorphism and T2DM in the Chinese Han population. The results of our meta-analysis suggested that MTHFR 677T allele might be a risk genetic factor of T2DM in the Chinese Han population.     

Molecular genetics of MTHFR: polymorphisms are not all benign

Methylenetetrahydrofolate reductase (MTHFR) is a key regulatory enzyme in folate and homocysteine metabolism. Research performed during the past decade has clarified our understanding of MTHFR deficiencies that cause homocystinuria or mild hyperhomocysteinemia. Our cloning of the MTHFR coding sequence was initially followed by the identification of the first deleterious mutations in MTHFR, in patients with homocystinuria and marked hyperhomocysteinemia. Shortly thereafter, we identified the 677C-->T variant and showed that it encoded a thermolabile enzyme with reduced activity. Currently, a total of 41 rare but deleterious mutations in MTHFR, as well as about 60 polymorphisms have been reported. The 677C-->T (Ala222Val) variant has been particularly noteworthy since it has become recognized as the most common genetic cause of hyperhomocysteinemia. The disruption of homocysteine metabolism by this polymorphism influences risk for several complex disorders, including cardiovascular disease, neural tube defects and some cancers. We describe here the complex structure of the MTHFR gene, summarize the current state of knowledge on rare and common mutations in MTHFR and discuss some relevant findings in a mouse model for MTHFR deficiency.     

Methylenetetrahydrofolate reductase polymorphism is not risk factor for Down syndrome in North India

BACKGROUND:

Down syndrome (DS) is the most common cause of mental retardation of genetic etiology with the prevalence rate of 1/700 to 1/1000 live births worldwide. Several polymorphisms in folate/homocysteine metabolism pathways genes have been reported as a risk factor in women for bearing DS child, but very few studies investigated these polymorphisms in DS cases whether there are a risk factor for being DS or not.

OBJECTIVE:

We have investigated the association of methylenetetrahydrofolate reductase (MTHFR) with the occurrence of DS in Indian population. MTHFR is one of the key regulatory enzymes involved in the metabolic pathway of homocysteine responsible for the reduction of methyltetrahydrofolate. A total of 32 DS cases and 64 age, sex matched controls were genotyped for MTHFR C677T polymorphism by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS:

The observed genotype frequencies were CC = 0.81; CT = 0.17 and TT = 0.02 in controls and CC = 0.81 and CT = 0.19 in DS cases. Frequency of T allele in DS and controls were 0.09 and 0.1, respectively. Significant difference in the distribution of mutant 677T allele was not observed between DS cases and controls (odds ratio = 0.915; 95% confidence intervals: 0.331-2.53; P = 0.864).

CONCLUSION:

Results of this study indicate that MTHFR C677T polymorphism is not risk factor for DS.     

Epistatic interactions between loci of one-carbon metabolism modulate susceptibility to breast cancer

In view of growing body of evidence substantiating the role of aberrations in one-carbon metabolism in the pathophysiology of breast cancer and lack of studies on gene–gene interactions, we investigated the role of dietary micronutrients and eight functional polymorphisms of one-carbon metabolism in modulating the breast cancer risk in 244 case–control pairs of Indian women and explored possible gene–gene interactions using Multifactor dimensionality reduction analysis (MDR). Dietary micronutrient status was assessed using the validated Food Frequency Questionnaire. Genotyping was done for glutamate carboxypeptidase II (GCPII) C1561T, reduced folate carrier (RFC)1 G80A, cytosolic serine hydroxymethyltransferase (cSHMT) C1420T, thymidylate synthase (TYMS) 5′-UTR tandem repeat, TYMS 3′-UTR ins6/del6, methylenetetrahydrofolate reductase (MTHFR) C677T, methyltetrahydrofolate-homocysteine methyltransferase (MTR) A2756G, methyltetrahydrofolate-homocysteine methyltransferase reductase (MTRR) A66G polymorphisms by using the PCR-RFLP/AFLP methods. Low dietary folate intake (P < 0.001), RFC1 G80A (OR: 1.38, 95% CI 1.06–1.81) and MTHFR C677T (OR: 1.74 (1.11–2.73) were independently associated with the breast cancer risk whereas cSHMT C1420T conferred protection (OR: 0.72, 95% CI 0.55–0.94). MDR analysis demonstrated a significant tri-variate interaction among RFC1 80, MTHFR 677 and TYMS 5′-UTR loci (P _trend < 0.02) with high-risk genotype combination showing inflated risk for breast cancer (OR 4.65, 95% CI 1.77–12.24). To conclude, dietary as well as genetic factors were found to influence susceptibility to breast cancer. Further, the current study highlighted the importance of multi-loci analyses over the single-locus analysis towards establishing the epistatic interactions between loci of one-carbon metabolism modulate susceptibility to the breast cancer.     

Two MTHFR polymorphisms, maternal B-vitamin intake, and CHDs

BACKGROUND: The methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C polymorphisms are associated with complex congenital malformations. Whether these polymorphisms are associated with CHDs is not clear. We studied both MTHFR polymorphisms, folate and vitamin B2 by maternal food intake and supplements, and CHD risk. METHODS: A case‐control family study was conducted in a European population in the Netherlands including 230 case and 251 control children with both parents. Approximately 17 months after the index pregnancy, mothers filled out standardized questionnaires on periconception use of folic acid supplements and a validated food frequency questionnaire on current dietary folate and vitamin B2 intake. All subjects were genotyped for the MTHFR C677T and A1298C polymorphisms. Data were analyzed by logistic regression analysis and ORs and 95% CIs were calculated. For the interaction analysis the dominant model was used. RESULTS: The risk estimates for the MTHFR 677 CT genotypes were 1.4 (0.9–2.0) in mothers, 1.1 (0.8–1.6) in fathers, and 1.2 (0.8–1.7) in children, and for the MTHFR 677 TT genotypes 0.9 (0.6–1.2), 1.4 (1.0–1.9), and 1.0 (0.7–1.3), respectively. The MTHFR 1298 CC genotype in fathers and the MTHFR 1298 AC genotype in children significantly reduced CHD risk, 0.6 (0.5–0.9) and 0.6 (0.4–0.9), respectively. Of interest is the significant interaction (p = .008) towards a nearly twofold increased risk in mothers carrying the MTHFR 1298C allele and using a periconception folic acid supplement. CONCLUSIONS: The MTHFR C677T and A1298C polymorphisms are not strong risk factors for CHDs. Birth Defects Research (Part A), 2008. © 2008 Wiley‐Liss, Inc.