Identification of six methylenetetrahydrofolate reductase (MTHFR) genotypes resulting from common polymorphisms: impact on plasma homocysteine levels and development of coronary artery disease

Potential Links between Impaired One-Carbon Metabolism Due to Polymorphisms, Inadequate B-Vitamin Status, and the Development of Alzheimer's Disease

Alzheimer's disease (AD) is the major cause of dementia and no preventive or effective treatment has been established to date. The etiology of AD is poorly understood, but genetic and environmental factors seem to play a role in its onset and progression. In particular, factors affecting the one-carbon metabolism (OCM) are thought to be important and elevated homocysteine (Hcy) levels, indicating impaired OCM, have been associated with AD. We aimed at evaluating the role of polymorphisms of key OCM enzymes in the etiology of AD, particularly when intakes of relevant B-vitamins are inadequate. Our review indicates that a range of compensatory mechanisms exist to maintain a metabolic balance. However, these become overwhelmed if the activity of more than one enzyme is reduced due to genetic factors or insufficient folate, riboflavin, vitamin B6 and/or vitamin B12 levels. Consequences include increased Hcy levels and reduced capacity to synthetize, methylate and repair DNA, and/or modulated neurotransmission. This seems to favor the development of hallmarks of AD particularly when combined with increased oxidative stress e.g., in apolipoprotein E (ApoE) ε4 carriers. However, as these effects can be compensated at least partially by adequate intakes of B-vitamins, achieving optimal B-vitamin status for the general population should be a public health priority.

Association between methylenetetrahydrofolate reductase C677T polymorphism and epilepsy susceptibility: a meta-analysis

PURPOSE

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism has been implicated as a potential risk factor for epilepsy. To date, many case-control studies have investigated the association between MTHFR C677T polymorphism and epilepsy susceptibility. However, those findings were inconsistent. The objective of this study is to evaluate the precise association between MTHFR C677T polymorphism and epilepsy.

METHODS

An electronic search of PubMed, EMBASE for papers on the MTHFR C677T polymorphism and epilepsy susceptibility was performed. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to assess the association.

RESULTS

Ten case-control studies containing 1713 cases and 1867 controls regarding MTHFR C677T polymorphism were selected. A significant association between the MTHFR C677T polymorphism and epilepsy susceptibility was revealed in this meta-analysis (for T vs. C: OR=1.19, 95% CI=1.08-1.32; for TT+CT vs. CC: OR=1.20, 95% CI=1.05-1.38; for TT vs. CC: OR=1.48, 95% CI=1.20-1.83; for TT vs. CT+CC: OR=1.35, 95% CI=1.12-1.64). In subgroup analysis by ethnicity, the results also indicated the association between the MTHFR C677T polymorphism and epilepsy susceptibility within the Asian populations (for T vs. C: OR=1.55, 95% CI=1.15-2.07; for TT+CT vs. CC: OR=1.67, 95% CI=1.08-2.59; for TT vs. CC: OR=2.33, 95% CI=1.30-4.20; for TT vs. CT+CC: OR=1.89, 95% CI=1.12-3.18).

CONCLUSION

The results indicated that MTHFR C677T polymorphism was associated with an increased risk of epilepsy. However, further studies in various regions are needed to confirm the findings from this meta-analysis.

Role of methylenetetrahydrofolate reductase gene polymorphisms (C677T, A1298C, and G1793A) in the development of early onset vasculogenic erectile dysfunction

BACKGROUND AND AIMS

The methylenetetrahydrofolate reductase (MTHFR) gene plays a key role in the metabolism of folate and homocysteine (Hcy) and its mutations have been associated with high serum Hcy level. Elevated serum Hcy has been linked to impaired endothelial function and occlusive vascular disease. We studied the association among the different genotypes of all three MTHFR polymorphisms (C677T, A1298C, and G1793A) and the risk of early-onset vasculogenic erectile dysfunction (VED).

METHODS

We performed a case-control study of 114 men with early-onset VED and 228 age-matched controls. Genotyping of MTHFR gene polymorphisms was performed using polymerase chain reaction restriction fragment length polymorphism (PCR-RLFP) technique. We also measured plasma lipids, Hcy, folate, and vitamin B12 levels.

RESULTS

Patients with early-onset VED had higher serum Hcy levels (12.29 ± 2.32 vs. 9.82 ± 2.35 μmol/L, p = 0.001) and higher prevalence of 677TT homozygocity compared to controls (15.8% vs. 11.4%, p = 0.01). Serum Hcy concentration was significantly higher in individuals with 677TT, 1298CC, and 1793GG genotypes. Subgroup analysis according to severity of ED (mild, moderate, and severe) showed that patients with severe VED had higher serum Hcy levels compared to patients with mild VED (13.48 ± 2.51 vs. 11.21 ± 2.32 μmol/L, p = 0.001).

CONCLUSIONS

Odds ratio seems to demonstrate that individuals with the MTHFR 677TT genotype and the 677TT + 1298AC combined genotype had a 3.16- and 3.89-fold increased risk for developing VED, suggesting a possible association of MTHFR polymorphisms with the risk of early-onset VED.

[6S]-5-methyltetrahydrofolate increases plasma folate more effectively than folic acid in women with the homozygous or wild-type 677C-->T polymorphism of methylenetetrahydrofolate reductase

BACKGROUND AND PURPOSE

5,10-Methylenetetrahydrofolate reductase (MTHFR) is responsible for the synthesis of 5-methyltetrahydrofolate (5-MTHF). The 677C-->T mutation of MTHFR reduces the activity of this enzyme. The aim of this study was, first, to compare pharmacokinetic parameters of [6S]-5-MTHF and folic acid (FA) in women with the homozygous (TT) and wild-type (CC) 677C-->T mutation, and second, to explore genotype differences. The metabolism of [6S]-5-MTHF and FA was evaluated by measuring plasma folate derivatives.

EXPERIMENTAL APPROACH

Healthy females (TT, n= 16; CC, n= 8) received a single oral dose of FA (400 microg) and [6S]-5-MTHF (416 microg) in a randomized crossover design. Plasma folate was measured up to 8 h after supplementation. Concentration-time-profile [area under the curve of the plasma folate concentration vs. time (AUC)], maximum concentration (C(max)) and time-to-reach-maximum (t(max)) were calculated.

KEY RESULTS

AUC and C(max) were significantly higher, and t(max) significantly shorter for [6S]-5-MTHF compared with FA in both genotypes. A significant difference between the genotypes was observed for t(max) after FA only (P < 0.05). Plasma folate consisted essentially of 5-MTHF irrespective of the folate form given. Unmetabolized FA in plasma occurs regularly following FA supplementation, but rarely with [6S]-5-MTHF.

CONCLUSIONS AND IMPLICATIONS

These data suggest that [6S]-5-MTHF increases plasma folate more effectively than FA irrespective of the 677C-->T mutation of the MTHFR. This natural form of folate could be an alternative to FA supplementation or fortification.

Polycystic ovary syndrome and the single nucleotide polymorphisms of methylenetetrahydrofolate reductase: a pilot observational study

Polycystic ovary syndrome (PCOS), insulin resistance and overall mortality due to diabetes and coronary artery disease are higher in South Asians than in Caucasians.

AIMS

We compared the prevalence of the C677T and A1298C single nucleotide polymorphisms in the methylenetetrahydrofolate reductase gene in South Asian and Caucasian women, its association with folate and homocysteine (Hcy) metabolism, and its relevance to future atherogenic events.

METHODS AND RESULTS

71 women were recruited for the study: South Asian PCOS (21) plus controls (9) and Caucasian PCOS (25) plus controls (16). Anthropometric and laboratory parameters were compared. South Asian PCOS women were significantly hyperandrogenic and exhibited a greater degree of insulin resistance. Caucasian PCOS women had higher plasma Hcy concentrations with a 1.9 times higher frequency of the T allele than the South Asian PCOS group. In the presence of this variant allele, plasma Hcy levels appear to be higher in both PCOS groups. The South Asians had a 1.8 times higher frequency of the C allele than the Caucasians; however, the overall frequency was comparable in the two PCOS groups. The frequency of homozygosity, i.e. TT677 and CC1298, was 7.2% and 4.9% in the Caucasians and 0% and 16.6% in the South Asian recruits, respectively. Dietary inadequacies in the South Asian women can influence their plasma folate and B12 concentrations resulting in hyperhomocysteinemia which, in combination with dyslipidaemia and insulin resistance, can lead to long-term atherogenic consequences.

CONCLUSIONS

Current data suggests that the mechanisms of atherothrombosis have separate pathways in the two ethnic groups. Larger studies exploring the current theme need to be carried out in the PCOS groups to obtain adequate insight.

Genetic polymorphisms involved in folate metabolism and concentrations of methylmalonic acid and folate on plasma homocysteine and risk of coronary artery disease

OBJECTIVES

Alterations in the enzymes involved in homocysteine (Hcy) metabolism or vitamin deficiency could play a role in coronary artery disease (CAD) development. This study investigated the influence of MTHFR and MTR gene polymorphisms, plasma folate and MMA on Hcy concentrations and CAD development. MMA and folate concentrations were also investigated according to the polymorphisms.

METHODS

Two hundred and eighty-three unrelated Caucasian individuals undergoing coronary angiography (175 with CAD and 108 non-CAD) were assessed in a case-control study. Plasma Hcy and MMA were measured by liquid chromatography/tandem mass spectrometry. Plasma folate was measured by competitive immunoassay. Dietary intake was evaluated using a nutritional questionnaire. Polymorphisms MTHFR and MTR were investigated by polymerase chain reaction (PCR) followed by enzyme digestion or allele-specific PCR.

RESULTS

Hcy mean concentrations were higher in CAD patients compared to controls, but below statistical significance (P = 0.246). Increased MMA mean concentrations were frequently observed in the CAD group (P = 0.048). Individuals with MMA concentrations >0.5 micromol/l (vitamin B(12) deficiency) were found only in the CAD group (P = 0.004). A positive correlation between MMA and Hcy mean concentrations was observed in both groups, CAD (P = 0.001) and non-CAD (P = 0.020). MMA mean concentrations were significantly higher in patients with hyperhomocysteinemia in both groups, CAD and non-CAD (P = 0.0063 and P = 0.013, respectively). Folate mean concentration was significantly lower in carriers of the wild-type MTHFR 1298AA genotype (P = 0.010).

CONCLUSION

Our results suggest a correlation between the MTHFR A1298C polymorphism and plasma folate concentration. Vitamin B(12) deficiency, reflected by increased MMA concentration, is an important risk factor for the development both of hyperhomocysteinemia and CAD.

Thymidylate synthase and methylenetetrahydrofolate reductase gene polymorphisms and toxicity to capecitabine in advanced colorectal cancer patients

PURPOSE

To evaluate the effect of thymidylate synthase (TYMS) and methylenetetrahydrofolate reductase (MTHFR) genotypes on toxicity in patients treated with capecitabine for advanced colorectal cancer and to determine the effect of these polymorphisms on the pretreatment levels of serum folate and plasma homocysteine.

EXPERIMENTAL DESIGN

Fifty-four patients with a diagnosis of metastatic colorectal cancer were treated with fixed-dose capecitabine. Germ line DNA from patients was genotyped for TYMS TSER, TSER*3G>C, and 3'-untranslated 6 bp insertion/deletion (3' untranslated region insertion/deletion), and MTHFR c.677C>T and c.1298A>C using PCRs and RFLP. Toxicity was graded by National Cancer Institute Common Toxicity Criteria version 2.0. Response was assessed by Response Evaluation Criteria in Solid Tumors.

RESULTS

MTHFR c.677C>T and c.1298A>C genotypes and diplotypes predicted for grade 2/3 toxicities, whereas the TYMS genotypes had no influence. MTHFR c.677 genotype tended to predict overall survival (P = 0.08). MTHFR c.677 influenced pretreatment homocysteine (P < 0.05) and serum folate levels (P < 0.05). Multivariate analysis suggests that MTHFR c.1298 is an independent predictor of toxicity.

CONCLUSIONS

This study suggests that common genetic variation in MTHFR but not TYMS may be useful for predicting toxicity from capecitabine in patients with advanced colorectal cancer. In addition, MTHFR single nucleotide polymorphisms predicted serum folate and plasma homocysteine levels, and, combined, these factors may be important predictors of capecitabine-induced toxicity.

Relationship between small-for-gestational age births and maternal thrombophilic mutations

Small gestational age (SGA) is one of the major causes of fetal mortality and morbidity. Altered maternal homeostasis as a result of point mutations in the coagulation cascade has been reported as an important risk factor for this adverse pregnancy outcome. This study aims to investigate the relationship between mother's thrombophilic mutations and SGA deliveries in our population. The study group was consisted of sixty-six women who gave birth to one or more SGA babies. 104 women who gave birth to appropriate-for-gestational age (AGA) babies were sampled for the control group. Restriction fragment size analysis were performed by visualizing digested PCR products for Factor V Leiden (G1691A), Factor V Cambridge (A1090G), Factor V A1299G, prothrombin G20210A, methylene tetrahydropholate reductase C677T, A1298C and T1317C mutations. The results of this study indicate that maternal C677T (p=0.01) and A1298C (p<0.01) mutations in MTHFR gene may be suggested as risk factors for SGA outcome in our population. Therefore, maternal screening of these two mutations in the first trimester of pregnancy could help in the assessment of patients.

Improved real-time multiplex polymerase chain reaction detection of methylenetetrahydrofolate reductase (MTHFR) 677C>T and 1298A>C polymorphisms using nearest neighbor model-based probe design

The disorders of folate metabolism caused by methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms may lead to several disease states including coronary heart disease, venous thrombosis, and several types of cancer. We have developed a real-time multiplex single-tube polymerase chain reaction procedure on the LightCycler for the detection of the two most commonly occurring variants, 677C>T and 1298A>C, in the MTHFR gene. An improved probe design, based on the nearest neighbor model for nucleic acid-probe duplex stability, resulted in a better separation (DeltaTm approximately 10 degrees C) of melting peaks of the wild-type and mutant alleles than that by the existing method (DeltaTm approximately 3 degrees C) for specimens heterozygous for the 1298A>C polymorphism. Of the 333 blood specimens analyzed by this procedure, we did not find any samples that gave ambiguous results. The specimens with homozygous mutation for one polymorphism were of the wild type for the other variant. The assay was validated by the comparison of the genotyping results of 50 blood specimens from the LightCycler polymerase chain reaction with the conventional restriction fragment length polymorphism procedures. There was 100% concordance of the test results obtained by the two techniques. This assay is reliable, economical, and can be performed by less trained technologists compared with the procedure performed by the conventional restriction fragment length polymorphism technique.

Adecuación de las dosis de ácido fólico en la prevención de defectos congénitos

BACKGROUND AND OBJECTIVE

Synthetic folic acid (FA) is in the form of pteroylmonoglutamate (PGA), a form that does not occur in nature, where it is in form of pteroylpolyglutamate, mainly as 5-methyltetrahydrofolate. The organism transforms PGA into 5-methyltetrahydrofolate, and it has been detected that this process is saturated at doses of 0.4 mg of PGA. Recently, some concern has been expressed on the use of higher than recommended doses of FA, because of the possibility of saturating the biotransformation process and the consequent plasmatic accumulation of unmetabolized synthetic FA. The objective of this study is to analyze the doses of synthetic FA that are being currently used in Spain, as well as its secular and geographic distribution.

PATIENTS AND METHODS

The study was based on 16,761 mothers of non-malformed infants from the data base of the Spanish Collaborative Study of Congenital Malformations. All forms of folates (folic or folinic) have been considered under the general term of FA.

RESULTS

Although an increasing trend in the proportion of mothers using FA in the last study period (2003-2004), only 17.37% of the mothers had FA supplements since before pregnancy. Among the rest, 71.13% started using FA once they knew they were pregnant, and 11.50% never took this vitamin. In addition, more than 70% of mothers who took FA ingested doses of 4 mg or more. The results by Spanish Autonomic Regions are quite similar, with more that 50% of the mothers (of the period 2003-2004), in the great majority of the Regions, taking mean daily doses of FA that are between 12.5 and 20-fold higher than the recommended 0.4 mg/day.

CONCLUSIONS

Most of women are having FA after conception, or do not ingest FA at all. Most of those women who take FA use doses much higher than recommended. The results of this study show that it is necessary to spread these aspects among the health professionals implicated.

Localized depletion: the key to colorectal cancer risk mediated by MTHFR genotype and folate?

Dietary folate has been consistently associated with reduced risk of colorectal cancer (CRC). One of the known biochemical roles of folate is donation of methyl moieties. DNA hypomethylation is an early and almost ubiquitous occurrence in tumor tissue. Therefore, it was originally suggested that adequate folate intake contributed to reduced risk of CRC by facilitating methyl-mediated silencing of oncogenes. Methylene tetrahydrofolate reductase (MTHFR) metabolizes 5,10-MTHF (important in DNA synthesis) to 5-MTHF (contributes to downstream methylation reactions by regeneration of methionine from homocysteine). A common polymorphism in the MTHFR gene (C677T) results in a thermolabile phenotype associated with increased homocysteine levels and DNA hypomethylation. Consistent with the folate/methylation hypothesis, it was originally proposed that C677T may increase risk of CRC due to hypomethylation of oncogenes. However, most subsequent studies have reported a reduced risk associated with this polymorphism. This is inconsistent with methylation as the mechanism by which folate and MTHFR genotype mediate CRC risk. The hypothesis presented here proposes that localized folate depletion combined with the effect of the C677T polymorphism on enzyme stability, impacts on the DNA synthesis pathway and accounts for the observed variation in risk associated with genotype and folate status.

Haemophilia A: molecular insights

Haemophilia A is the most common inherited bleeding disorder caused by defects in the

Clin Chem Lab Med 2007;45:450–61.

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.

Screening for C677T and A1298C MTHFR polymorphisms in patients with epilepsy and risk of hyperhomocysteinemia

Hyperhomocysteinemia can result from decreased methylenetetrahydrofolate reductase (MTHFR) enzyme activity, owing to genetic polymorphisms andor inadequate folate intake. This study was aimed at investigating the prevalence of C677T and A1298C MTHFR polymorphisms, and their impact on hyperhomocysteinemia in 95 epileptic patients and 98 controls. Double gradient-denaturing gradient gel electrophoresis screening revealed that the frequency of T677 polymorphic allele was similar between cases and controls (46.3% vs 42.3%), whereas that of C1298 allele was significantly higher in patients (30.5% vs 19.4%, p < 0.05). Significant differences between the two groups were also found for the frequencies of genotypes AA1298 (46.3% in cases vs 67.3% in controls, p < 0.01) and AC1298 (46.3% in cases vs 26.6% in controls, p < 0.01). Other genotype frequencies did not show any statistically significant differences. Haplotype frequencies significantly differed between the two groups. The CT677/AC1298 diplotype was significantly more frequent in epileptic patients than in controls (32.6% vs 18.4%, p < 0.05). Patients treated with enzyme-inducing antiepileptic drugs, having this diplotype and concomitant low folate concentration (i.e., < 3.4 nmol/L), exhibited plasma homocysteine levels significantly higher than normal values (27.1 +/- 2.44 micromol/L, p < 0.001). This increase, however, was lower than that observed in folate-deficient patients with diplotype TT677/AA1298 (41.3 +/- 3.41 micromol/L, p < 0.001). Indeed, these two diplotypes could be regarded as risk factors for hyperhomocysteinemia. Conversely, we found that the CC677/AA1298 diplotype was significantly more frequent in controls (p < 0.01), suggesting a protective role. Our study suggests that both C677T and A1298C MTHFR polymorphisms should be examined when assessing genetic risk factors of hyperhomocysteinemia in epilepsy.

Gene--nutrition interactions in coronary artery disease: correlation between the MTHFR C677T polymorphism and folate and homocysteine status in a Korean population

INTRODUCTION

Elevated plasma total homocysteine is a major risk for coronary artery disease (CAD). Methyltetrahydrofolate reductase (MTHFR) is a main regulatory enzyme in homocysteine metabolism; a common C677T mutation in the MTHFR gene results in decreased enzyme activity, and contributes to increased homocysteine levels and decreased folate levels. We investigated the frequency of MTHFR C677T alleles in a Korean population, determined the genotype-specific threshold levels of folate or vitamin B12, and investigated the relationship between the TT genotype and the risk of CAD.

MATERIALS AND METHODS

We enrolled a study population of 163 CAD patients and 50 control subjects, and screened the MTHFR C677T polymorphism using real-time PCR with melting point analysis. Levels of plasma homocysteine, folate and vitamin B12 were also determined. We then defined the genotype-specific threshold values of folate and vitamin B12 required to keep homocysteine levels in a normal range for individuals of each MTHFR C677T genotype.

RESULTS

The frequency of the TT genotype was 18% in control subjects and 26% in patients group (P>0.05). Individuals homozygous for the TT genotype had significantly elevated homocysteine levels (P<0.05). The genotype-specific folate threshold level was significantly higher in TT individuals than in the CC or CT genotypes. The OR of individuals with low folate status and the TT genotype to estimate the relative risk of CAD was 2.2 and the OR of those with high folate status and the TT genotype was 1.5 (95% CI, 0.5-9.6 and 0.7-3.2, respectively).

CONCLUSION

We were able to define a gene-nutrient interaction that shows a higher risk for CAD based on specific threshold folate levels required by different MTHFR C677T genotypes in a Korean population.

The methylenetetrahydrofolate reductase gene polymorphism (C677T) is associated with increased cardiovascular mortality in Hungary

The gene for methylenetetrahydrofolate reductase (MTHFR) has two different alleles (C and T), where the T is associated with decreased enzyme activity, hyperhomocysteinaemia, and increased risk for thromboembolism in coronary heart disease (CHD). The study was conducted using a sample of 378 Hungarian newborn infants: 96 control subjects (age: 59.9+/-8.6 years) with chest pain and 315 CHD patients (61.4+/-7.5 years). All adult subjects had undergone coronary angiography. It can be concluded that the carriers of T allele with CHD died earlier due to myocardial infarction and the C allele with lower homocysteine level may provide protection against fatal coronary artery occlusion.

C677T mutation of methylenetetrahydrofolate reductase gene and serum homocysteine levels in Turkish patients with coronary artery disease

Elevated levels of homocysteine is a risk factor for coronary artery disease. The C677T transition in methylenetetrahydrofolate reductase (MTHFR) is associated with increased homocysteine levels in the general population. We analysed the association between the MTHFR C677T polymorphism and serum homocysteine concentrations in patients with coronary artery disease (CAD). Allele frequencies for the 'C' (wild-type) and 'T' alleles were 0.71 and 0.29 in CAD patients and 0.70 and 0.30 in controls, respectively. There was no difference in the distribution of MTHFR genotypes between patients with CAD and control subjects (p > 0.05). In the patient group, homocysteine levels were higher than controls but not significantly (13.99 +/- 7.44 vs. 11.77 +/- 5.18 micromol l(-1); p > 0.05). Serum homocysteine concentration was significantly higher in the TT genotype with respect to CC and CT genotypes in both the control group (p < 0.01) and patient group (p < 0.01). Systolic and diastolic blood pressures in subjects with different MTHFR genotypes did not differ significantly. In conclusion, MTHFR C677T mutation was significantly related to hyperhomocysteinemia. In spite of the clear effect of the MTHFR polymorphism on elevated homocysteine levels, we did not observe any associations among the MTHFR genotypes with a the risk of CAD in the Turkish population.

A haplotype of the methylenetetrahydrofolate reductase gene is protective against late-onset Alzheimer's disease

Epidemiological studies have shown that elevated plasma homocysteine (Hcy) levels play an important role in the pathogenesis of Alzheimer's disease (AD). In spite of the evidence that a C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene elevates plasma Hcy levels, the impact of the C677T polymorphism on the development of AD is controversial. Here, we performed a genetic case-control study in a Japanese population to investigate whether three polymorphisms of the MTHFR gene, C677T (Ala222Val), A1298C (Glu429Ala), and A1793G (Arg594Gln), are associated with the development of late-onset AD (LOAD). In our study, the MTHFR gene had four major regional haplotypes: Haplotype A (677C-1298A-1793G), Haplotype B (677T-1298A-1793G), Haplotype C (677C-1298C-1793G), and Haplotype D (677C-1298C-1793A). The frequency of Haplotype C in LOAD was significantly lower than that in control group. Furthermore, the benefit conferred by the presence of at least one Haplotype C was stronger in LOAD patients who lacked the ApoE 4 allele (OR=0.293; 95% CI=0.115-0.744; P=0.010). The results indicate that Haplotype C of the MTHFR gene is protective against the development of LOAD.

Prevalence and Role of Methylenetetrahydrofolate Reductase 677 C→T and 1298 A→C Polymorphisms in Coronary Artery Disease in Arabs

Context.—Previous studies reported an association of 677 C→T and 1298 A→C methylenetetrahydrofolate reductase (MTHFR) variants with coronary artery disease (CAD). No previous studies concerning the prevalence of these 2 MTHFR variants or their possible association with CAD in Arabs are currently available in the literature.

Objective.—To determine the prevalence of MTHFR variants and their potential relevance to CAD among Arabs.

Design.—We used polymerase chain reaction and restriction enzyme digestion to determine the prevalence of these 2 MTHFR polymorphisms in 625 healthy blood donors (BDs) and 545 angiographically confirmed CAD patients of Arab origin.

Results.—For the 677 C→T variant within the CAD group, 64.2% were homozygous wild-type C/C, 32.1% were heterozygous C/T, and 3.7% were homozygous T/T genotype. Within the BD group tested for the 677 C→T variant, 72.2% were homozygous wild-type C/C, 25.8% were heterozygous C/T, and 2% were homozygous T/T genotype. Within the CAD group tested for the 1298 A→C variant (n = 540), 45.7% were homozygous wild-type A/A, 46.9% were heterozygous A/C, and 7.4% were homozygous C/C genotype. Within the BD group tested for the 1298 A→C variant (n = 625), 39.4% were homozygous wild-type A/A, 51.5% were heterozygous A/C, and 9.1% were homozygous C/C genotype. The distribution and allele frequency of these 2 MTHFR variants followed the Hardy-Weinberg equilibrium and were similar in the CAD and BD study groups. The prevalence of the 677 C→T and 1298 A→C compound heterozygosity was 9.6% for the BD group and 12.3% for the CAD group.

Conclusion.—The 2 MTHFR variants tested in this study, individually or compound, are not associated with CAD. Therefore, neither of these 2 variants can be considered an independent risk factor or a predictor for CAD in this population.

Methionine synthase (MTR) 2756 (A --> G) polymorphism, double heterozygosity methionine synthase 2756 AG/methionine synthase reductase (MTRR) 66 AG, and elevated homocysteinemia are three risk factors for having a child with Down syndrome

Contradictory findings have been recently published on the evaluation of genetic polymorphisms of methylenetetrahydrofolate reductase (MTHFR 677 C-->T) and methionine synthase reductase (MTRR 66 A-->G) as risk factors for having a child with Down syndrome (DS); however, the influence of polymorphisms of methionine synthase (MTR 2756 A-->G) and of MTHFR 1298 A-->C has never been evaluated. In this study, the risk of being a DS case or having a DS child (case mother) was studied by multiple logistic regression analysis of the independent and combined genotypes and of plasma homocysteine, folates, and vitamin B12 in 92 DS cases and 140 control subjects as well as in 63 case mothers and 72 age-matched control mothers from Sicily. (The MTHFR 677 T allele frequency was not different in DS cases and case mothers, compared to the respective control groups). After adjustment for age, total homocysteine (t-Hcys) and MTR 2756 AG/GG genotype were significant risk factors for having a DS child, with odds ratio (OR) of 6.7 (95% CI: 1.4-32.0, P = 0.016) and of 3.5 (95% CI: 1.2-10.9, P = 0.028), respectively. By comparison, MTR 2756 AG/GG genotype increased significantly the risk of being a DS case, with an OR of 3.8 (95% CI: 1.4-10.5, P = 0.009). The double heterozygosity MTR 2756 AG/MTRR 66 AG was the single combined genotype that was a significant risk factor for having a DS child, with an OR estimated at 5.0 (95% CI: 1.1-24.1), after adjustment for t-Hcys. In conclusion, our results provide evidences that homocysteine and MTR genetic polymorphism are two potent risk factors for mothers to have a DS child in Sicily.

Common gene polymorphisms and nutrition: emerging links with pathogenesis of multifactorial chronic diseases (review)

Rapid progress in human genome decoding has accelerated search for the role of gene polymorphisms in the pathogenesis of complex multifactorial diseases. This review summarizes the results of recent studies on the associations of common gene variants with multifactorial chronic conditions strongly affected by nutritional factors. Three main individual sections discuss genes related to energy homeostasis regulation and obesity, cardiovascular disease (CVD), and cancer. It is evident that several major chronic diseases are closely related (often through obesity) to deregulation of energy homeostasis. Multiple polymorphic genes encoding central and peripheral determinants of energy intake and expenditure have been revealed over the past decade. Food intake control may be affected by polymorphisms in the genes encoding taste receptors and a number of peripheral signaling peptides such as insulin, leptin, ghrelin, cholecystokinin, and corresponding receptors. Polymorphic central regulators of energy intake include hypothalamic neuropeptide Y, agouti-related protein, melanocortin pathway factors, CART (cocaine- and amphetamine-regulated transcript), some other neuropeptides, and receptors for these molecules. Potentially important polymorphisms in the genes encoding energy expenditure modulators (alpha- and beta- adrenoceptors, uncoupling proteins, and regulators of adipocyte growth and differentiation) are also discussed. CVD-related gene polymorphisms comprising those involved in the pathogenesis of atherosclerosis, blood pressure regulation, hemostasis control, and homocysteine metabolism are considered in a separate section with emphasis on multiple polymorphisms affecting lipid transport and metabolism and their interactions with diet. Cancer-associated polymorphisms are discussed for groups of genes encoding enzymes of xenobiotic metabolism, DNA repair enzymes, factors involved in the cell cycle control, hormonal regulation-associated proteins, enzymes related to DNA methylation through folate metabolism, and angiogenesis-related factors. There is an apparent progress in the field with hundreds of new gene polymorphisms discovered and characterized, however firm evidence consistently linking them with pathogenesis of complex chronic diseases is still limited. Ways of improving the efficiency of candidate gene approach-based studies are discussed in a short separate section. Successful unraveling of interaction between dietary factors, polymorphisms, and pathogenesis of several multifactorial diseases is exemplified by studies of folate metabolism in relation to CVD and cancer. It appears that several new directions emerge as targets of research on the role of genetic variation in relation to diet and complex chronic diseases. Regulation of energy homeostasis is a fundamental problem insufficiently investigated in this context so far. Impacts of genetic variation on systems controlling angiogenesis, inflammatory reactions, and cell growth and differentiation (comprising regulation of the cell cycle, DNA repair, and DNA methylation) are also largely unknown and need thorough analysis. These goals can be achieved by complex simultaneous analysis of multiple polymorphic genes controlling carefully defined and selected elements of relevant metabolic and regulatory pathways in meticulously designed large-scale studies.

5,10-Methylenetetrahydrofolate reductase 677C-->T and 1298A-->C mutations are genetic determinants of elevated homocysteine

BACKGROUND

Methylenetetrahydrofolate reductase (MTHFR) is one of the main regulatory enzymes of homocysteine metabolism. Elevated plasma total homocysteine (tHcy) is a major risk for cardiovascular disease. A common 677C-->T mutation in the MTHFR gene results in decreased enzymic activity, and contributes to increased plasma tHcy, in association with low plasma folate. A recently described 1298A-->C mutation in the MTHFR gene clearly reduces MTHFR activity (although to a lesser extent than the 677C-->T) but its effect on plasma tHcy levels is not yet clear.

AIM

To investigate the frequency of these two MTHFR polymorphisms in a Portuguese population, and to correlate the MTHFR genotype with the biochemical phenotype at the level of homocysteine and folate concentrations.

DESIGN

Prospective population survey.

METHODS

We studied 117 healthy volunteers (71 females, 46 males). The 677C-->T and 1298A-->C mutations were screened by PCR-RFLP. Levels of plasma tHcy and folate, and red blood cell folate, were determined.

RESULTS

The allele frequencies of the 677C-->T and 1298A-->C mutations were 0.33 and 0.28, respectively. Homozygotes for the 677C-->T mutation had significantly elevated plasma tHcy and RBC folate levels and significantly lowered plasma folate concentrations than subjects without the mutation. The 1298A-->C mutation showed a significant effect on plasma tHcy, but not on plasma folate or RBC folate levels.

DISCUSSION

The observed 677T allele frequency is not consistent with the idea of a north-south gradient as previously suggested. The 1298A-->C mutation is common in Portugal. Both MTHFR mutations showed effects on plasma tHcy levels.

Heterogeneity in the prevalence of methylenetetrahydrofolate reductase gene polymorphisms in women of different ethnic groups

OBJECTIVE

To determine the prevalence of methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms in women of different ethnic groups and to relate these common mutations to plasma homocysteine, red cell folate, and serum folate.

DESIGN

A one-time fasting blood sample was obtained for MTHFR genotype (C677T and A1298C) determinations (n=433). Serum folate, red cell folate, and homocysteine analyses were performed in nonfolic acid supplement users (n=215).

SUBJECTS/SETTING

This study involved 433 women from four ethnic groups, including 193 Hispanic women of Mexican descent, 139 white women, 53 Asian women of mixed descent, and 48 African American women. STATISTICAL ANALYSIS PREFORMED: Chi;(2), t Test, and analysis of variance were used.

RESULTS

Mexican women (18.1%) had a higher frequency of the 677 TT genotype compared with white (7.2%), Asian (3.8%), and African American (0%) women. White women (7.9%) had a higher frequency of the 1298 CC genotype than the other ethnic groups (range=1.9% to 2.6%). The frequency of compound heterozygosity (677 CT + 1298 AC) was higher in Mexican (17.6%) and white (15.1%) women than Asian and African American ( approximately 4% to 6%) women. In the era of folic acid fortification, neither genotype, independently or together, was associated with homocysteine or blood folate concentrations when ethnic groups were combined. In Mexican women, however, a linear trend (P

APPLICATIONS/CONCLUSIONS

These data demonstrate ethnic differences in genetic polymorphisms that are diet responsive and may be useful when investigating ethnic variations in chronic disease, developmental anomalies, and folate requirements.

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Key Words Collapse

MESH Headings

• Adolescent
• Adult
• Aged
• Aged, 80 and over
• Asian/genetics
• Asian People/genetics
• Black People/genetics
• Ethnicity/genetics
• Ethnicity/statistics & numerical data
• Female
• Folic Acid/administration & dosage
• Folic Acid/blood
• Gene Frequency
• Genetic Heterogeneity
• Genotype
• Homocysteine/blood
• Humans
• Methylenetetrahydrofolate Reductase (NADPH2)
• Mexican Americans/genetics
• Middle Aged
• Mutation
• Nutritional Requirements
• Oxidoreductases Acting on CH-NH Group Donors/genetics
• Polymorphism, Genetic
• Prevalence
• Racial Groups/genetics
• White People/genetics
• Black or African American

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Grants

• S06GM53933 NIGMS NIH HHS

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Affiliation(s)

Setareh Torabian Esfahani Agricultural Sciences in the Human Nutrition and Food Science Department, Cal Poly Pomona University, Pomona, CA 91768, USA
Edward A Cogger
Marie A Caudill

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Polymorphisms in the methylenetetrahydrofolate reductase gene: clinical consequences

5,10-Methylenetetrahydrofolate reductase (MTHFR) plays a key role in folate metabolism by channeling one-carbon units between nucleotide synthesis and methylation reactions. Severe enzyme deficiency leads to hyperhomocysteinemia and homocystinuria, with altered folate distribution and a phenotype that is characterized by damage to the nervous and vascular systems. Two frequent polymorphisms in the human MTHFR gene confer moderate functional impairment of MTHFR activity for homozygous mutant individuals. The C to T change at nucleotide position 677, whose functional consequences are dependent on folate status, has been extensively studied for its clinical consequences. A second polymorphism, an A to C change at nucleotide position 1298, is not as well characterized. Still equivocal are associations between MTHFR polymorphisms and vascular arteriosclerotic or thrombotic disease. Neural tube defects and pregnancy complications appear to be linked to impaired MTHFR function. Colonic cancer and acute leukemia, however, appear to be less frequent in individuals homozygous for the 677T polymorphism.MTHFR polymorphisms influence the homocysteine-lowering effect of folates and could modify the pharmacodynamics of antifolates and many other drugs whose metabolism, biochemical effects, or target structures require methylation reactions. However, only preliminary evidence exists for gene-drug interactions. This review summarizes the biochemical basis and clinical evidence for interactions between MTHFR polymorphisms and several disease entities, as well as potential interactions with drug therapies. Future investigations of MTHFR in disease should consider the influence of other variants of functionally-related genes as well as the medication regimen of the patients. Animal models for genetic deficiencies in folate metabolism will likely play a greater role in our understanding of folate-dependent disorders.

Homocysteine and methylenetetrahydrofolate reductase genotype: association with risk of coronary heart disease and relation to inflammatory, hemostatic, and lipid parameters

AIM

It has been suggested that homocysteine (tHcy) levels and methylenetetrahydrofolate reductase (MTHFR) genotype are primary risk factors for coronary heart disease (CHD). We performed a case-control study to investigate whether tHcy levels and MTHFR genotype (677 C-->T mutation and 1298 A-->C mutation) are associated with CHD under special consideration of the possibility for confounding.

METHODS

German speaking patients aged 40-68 years who underwent coronary angiography at the University of Ulm between April 1996 and November 1997 and who had at least one coronary stenosis greater than 50% were included in the study. Controls were sampled from voluntary blood donors and were matched for sex and age. tHcy levels were measured by high performance liquid chromatography and MTHFR genotype by means of polymerase chain reaction. In addition, C-reactive protein, fibrinogen, plasma viscosity, leukocytes, HDL-cholesterol and Lp(a) were determined.

RESULTS

Overall, 312 patients and 479 controls were enrolled in the study (response in patients 78%, in controls 84%). Mean tHcy value was 9.43 micromol/l in CHD patients and 8.91 micromol/l in controls (P=0.145). Prevalence of 677TT-polymorphism was 9.9% in patients and 10.4% in controls (P=0.295). Prevalence of 1298CC-polymorphism was 9.7% in patients and 13.8% in controls (P=0.346). There was a clear association of tHcy-values, but not of 677TT- or 1298CC-genotype with conventional CHD risk factors. After adjustment for these risk factors no increased risk for CHD could be associated with increased tHcy-values, with 677TT or 1298CC-genotype, or with their combination. Also no statistically significant relationships of these parameters to inflammatory, rheologic or hemostatic parameters or lipids were detectable.

CONCLUSION

These results do not confirm an independent relationship of tHcy values and MTHFR genotype with risk of CHD in the population studied.