Low folate levels may be an atherogenic factor regardless of homocysteine levels in young healthy nonsmokers

Low folate and high homocysteine levels are emerging as important risk factors for atherosclerosis and predictors of early coronary heart disease. We evaluated folate and homocysteine levels, compared them with endothelial function, and analyzed their association with the methylenetetrahydrofolate reductase (MTHFR) and endothelial nitric oxide synthase genotypes. We recruited 71 young healthy male nonsmokers without overt cardiovascular or renal disease. Plasma homocysteine levels were enhanced 2-fold in the subjects with the MTHFR 677T/T compared with the others (P = .0001) and also enhanced in the subjects with the endothelial nitric oxide synthase -786C allele (P = .031). Homocysteine levels were independently predicted only by the MTHFR genotype. A relationship between folate and homocysteine levels was not significant. Plasma folate levels were associated independently either with high-density lipoprotein cholesterol levels or with endothelial function in the brachial artery. These results suggest that low folate levels may be a risk factor for cardiovascular diseases regardless of homocysteine levels and that the subjects with lower folate levels should be recommended for dietary folic acid supplementation to elevate endothelial function and probably increase high-density lipoprotein cholesterol levels.

Transcobalamin-II variants, decreased vitamin B12 availability and increased risk of frailty

OBJECTIVE

This project was designed to follow-up prior evidence that demonstrated a significant association between vitamin B12 transport and metabolism and the frailty syndrome in community-dwelling older women. The cross-sectional relationship between genetic variants within six candidate genes along this pathway with serum methylmalonic acid (MMA) levels and frailty was evaluated in this same population of older women.

METHODS

Baseline measures were collected prior to folate fortification from 326 women in the Women's Health and Aging Studies I and II. Odds ratios and statistical tests were estimated for single SNP and haplotype via linear regression models for serum MMA, a marker for available vitamin B12, and in logistic regression models for frailty.

RESULTS

Fifty-six SNPs from CBS, MTHFR, MTR, MTRR, TCN1 and TCN2 genes were genotyped. Several SNPs in MTHFR, MTR and MTRR demonstrated a modest association to elevated MMA, while SNPs in TCN2 showed significant association to the frailty syndrome. TCN2 polymorphisms, particularly one SNP reported to be in perfect LD with functional variant Pro259Arg, were significantly associated with increased odds of frailty, after adjustment for age, presence of cardiovascular disease and elevated MMA (OR = 2.25, p-value = 0.009).

CONCLUSIONS

Using MMA as a marker for vitamin B12, these results suggest that TCN2 gene variants may lead to decreased vitamin B12 availability, leading to reduced energy metabolism, ultimately contributing to frailty pathology. Further studies to determine the biological role of functional TCN2 polymorphisms in frailty are needed.

[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.

Meta- and pooled analyses of the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and colorectal cancer: a HuGE-GSEC review

Worldwide, over 1 million cases of colorectal cancer (CRC) were reported in 2002, with a 50% mortality rate, making CRC the second most common cancer in adults. Certain racial/ethnic populations continue to experience a disproportionate burden of CRC. A common polymorphism in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene has been associated with a lower risk of CRC. The authors performed both a meta-analysis (29 studies; 11,936 cases, 18,714 controls) and a pooled analysis (14 studies; 5,068 cases, 7,876 controls) of the C677T MTHFR polymorphism and CRC, with stratification by racial/ethnic population and behavioral risk factors. There were few studies on different racial/ethnic populations. The overall meta-analysis odds ratio for CRC for persons with the TT genotype was 0.83 (95% confidence interval (CI): 0.77, 0.90). An inverse association was observed in whites (odds ratio = 0.83, 95% CI: 0.74, 0.94) and Asians (odds ratio = 0.80, 95% CI: 0.67, 0.96) but not in Latinos or blacks. Similar results were observed for Asians, Latinos, and blacks in the pooled analysis. The inverse association between the MTHFR 677TT polymorphism and CRC was not significantly modified by smoking status or body mass index; however, it was present in regular alcohol users only. The MTHFR 677TT polymorphism seems to be associated with a reduced risk of CRC, but this may not hold true for all populations.

Hyperhomocysteinemia is associated with hypertriglyceridemia in mice with methylenetetrahydrofolate reductase deficiency

Hyperhomocysteinemia (HHcy) can result from genetic or nutritional disturbances in folate metabolism. The most common genetic cause of mild HHcy is methylenetetrahydrofolate reductase (MTHFR) deficiency. To explore interactions between HHcy and lipid metabolism in atherogenesis, we measured plasma homocysteine (Hcy), triglycerides and cholesterol in Mthfr(+/+) and Mthfr(+/-) mice on C57BL/6 and BALB/c backgrounds, fed control or folate-deficient diets. We also crossed ApoE(C57)(-/-) mice with Mthfr(C57)(+/-) and Mthfr(BALB/c)(+/-) mice, and examined the same plasma variables as well as lipid accumulation in aortic sinus and whole aorta. Mthfr(+/-) mice had significantly higher plasma Hcy and plasma triglycerides relative to Mthfr(+/+) mice. A significant positive correlation was observed between plasma Hcy and plasma triglycerides in all mice. Mthfr(+/-) mice had lower plasma ApoA-IV protein levels which could reduce clearance of triglyceride-rich lipoproteins from the circulation. In the double mutant experiments, plasma Hcy was higher in Mthfr(+/-) compared with Mthfr(+/+) in ApoE(C57)(-/-)/Mthfr(C57) and ApoE(C57)(-/-)/Mthfr(BALB/c) mice. Triglycerides in female ApoE(C57)(-/-)/Mthfr(BALB/c)(+/-) mice were higher than those in ApoE(C57)(-/-)/Mthfr(BALB/c)(+/-) mice and correlated positively with Hcy. ApoE(C57)(-/-)/Mthfr(C57)(+/-) male mice had more lipid deposition in aortic sinus and whole aorta compared with ApoE(C57)(-/-)/Mthfr(c57)(+/+) mice. Our results suggest that HHcy is associated with hypertriglyceridemia and that MTHFR deficiency may exacerbate lipid accumulation in ApoE deficiency.

[Study of the genetic markers of thrombosis in hypertensive patients of the native population in the Republic of Mordovia]

The genetic markers (encoding factor of blood coagulation, the PAI-1 gene, the prothrombin gene, the GP IIb/IIIa gene, and the MTHFR gene) of thrombosis were studied in the Mordovians and Russians with essential hypertension (EH), who were residents of the Republic of Mordovia. One hundred and forty patients with TH and 90 healthy individuals of three nationalities, such as Russian, Moksha-Mordovian, and Erzya-Mordovian, were examined. Along with the routine clinical and instrumental studies, alleles of polymorphic markers were identified by the polymerase chain reaction (PCR). The polymorphic markers of the Arg 506 Gln gene, encoding factor V of blood coagulation, 4G5G of the PAI-1 gene, the G 20210 A prothrombin gene, the GP IIb/IIIa gene, and the A 1298 C MTHFR gene were also studied. The data were statistically analyzed using a package of the programs: Statistica for Windows 6.0 (Stat Soft), SPSS (version 14.0), and MS Excel XP (Microsoft). The authors used a chi-2 (chi-square) test was used to compare the incidence of genotypes and alleles in the patient groups. Hypertensive and normotensive persons were found to have no significant differences in the distribution of genotypes (encoding factor of blood coagulation, the PAI-1 gene, the prothrombin gene, and the GP IIb/IIIa gene) with regard to ethnicity in the Russian, and Moksha-Mordovian, and Erzya-Mordovian groups). Meanwhile, there was a significant preponderance of MTHFR gene mutation with the unfavorable genotype for Moksha-Mordovian patients with EH. The findings suggest that drug therapy for preventing venous thrombosis in patients with EH should be adjusted in relation to ethnicity.

Genetic and environmental factors for hyperhomocysteinaemia and its clinical implications in Parkinson's disease

Elevated homocysteine (Hcy) plasma levels are caused by genetic and environmental factors. Polymorphisms of Hcy metabolizing enzyme genes may result in its plasma increase. Experimental and clinical studies have shown the possible role of hyperhomocysteinaemia in pathogenesis of Parkinson's disease (PD), Alzheimer's disease and vascular disorders. The results of clinical studies in PD generally do not support the theoretical hypotheses, and animal studies remain controversial. A major environmental factor responsible for Hcy increase in PD seems to be levodopa therapy. Its metabolism results in Hcy increase and may be reduced with folate and vitamins B6, B12 supplementation or inhibition of catechol-O-methyltransferase (COMT) activity. Therefore, the potential harmful role of Hcy may be diminished in PD patients with vascular comorbidities. Further studies are needed to establish the real role of Hcy for PD and other neurological disorders. The paper summarizes the current knowledge on the genetic and environmental factors responsible for Hcy increase in PD.

Choline intake, plasma riboflavin, and the phosphatidylethanolamine N-methyltransferase G5465A genotype predict plasma homocysteine in folate-deplete Mexican-American men with the methylenetetrahydrofolate reductase 677TT genotype

We previously showed that provision of the folate recommended dietary allowance and either 300, 550, 1100, or 2200 mg/d choline for 12 wk resulted in diminished folate status and a tripling of plasma total homocysteine (tHcy) in men with the methylenetetrahydrofolate reductase (MTHFR) 677TT genotype. However, the substantial variation in tHcy within the 677TT genotype at wk 12 implied that several factors were interacting with this genotype to affect homocysteine. As an extension of this work, the present study sought to identify the main predictors of wk-12 plasma tHcy, alone and together with the MTHFR C677T genotype (29 TT, 31 CC), using linear regression analysis. A basic model explaining 82.5% of the variation (i.e. adjusted R(2) = 0.825) was constructed. However, the effects of the variables within this model were dependent upon the MTHFR C677T genotype (P for interaction < or = 0.021). Within the 677TT genotype, serum folate (P = 0.005) and plasma riboflavin (P = 0.002) were strong negative predictors (inversely related) explaining 12 and 15%, respectively, of the variation in tHcy, whereas choline intake (P = 0.003) and serum creatinine (P < 0.001) were strong positive predictors, explaining 19 and 25% of the variation. None of these variables, except creatinine (P = 0.021), correlated with tHcy within the 677CC genotype. Of the 8 additional polymorphisms tested, none appeared to influence tHcy. However, when creatinine was not in the model, the phosphatidylethanolamine N-methyltransferase 5465G-->A variant predicted lower tHcy (P < 0.001); an effect confined to the MTHFR 677TT genotype. Thus, in folate-deplete men, several factors with roles in 1-carbon metabolism interact with the MTHFR C677T genotype to affect plasma tHcy.

Pathomechanism of leukoaraiosis: a molecular bridge between the genetic, biochemical, and clinical processes (a mitochondrial hypothesis)

Ischemic demyelination in the white matter of the brain is a frequent clinical entity. In neuroimaging terms, it is referred to as leukoaraiosis (LA). LA can reflect a broad public health problem, which is caused by a cognitive impairment ranging from mild slowness of thinking to full-blown subcortical dementia. One-quarter of subjects aged 65 yr or over are affected by some degree of white matter changes. There are a number of genetic factors that can be associated with circulatory disturbances of the white matter of the brain. A slight chronic hypoperfusion or an endothelial dysfunction associated with unfavorable genetic variations such as methylenetetrahydrofolate reductase C677T variation and angiotensin-converting enzyme I/D polymorphism then may lead indirectly to a malfunction of the molecular cross-talk between the nucleus and the mitochondria. This results in a decrease in the production of energy in the glia cells and thereby the beginning of demyelination. From another aspect, the presence of either the apolipoprotein E 2 or 4 alleles may cause an increased vulnerability to a slight chronic hypoperfusion of the white matter by reducing the range of mechanical and chemical flexibility of the glial cytoskeleton. In consequence of the chronic hypoperfusion, the functionally damaged kinesin protein gives rise also to the disturbances of the trafficking of the myelin basic protein mRNAs in the oligodendrocytes. On the basis of the current knowledge on LA, this article suggests a hypothetical molecular bridge between the genetic, biochemical, and clinical processes.

Genetic variation in homocysteine metabolism, cognition, and white matter lesions

Several studies have shown an association between homocysteine concentration and cognitive performance or cerebral white matter lesions. However, variations in genes encoding for enzymes and other proteins that play a role in homocysteine metabolism have hardly been evaluated in relation to these outcome measures. In the population-based Rotterdam Scan Study, we examined the association of seven polymorphisms of genes involved in homocysteine metabolism (MTHFR 677C>T, MTHFR 1298A>C, RFC 80G>A, TC 776C>G, MTR 2756A>G, MTRR 66A>G, and CBS 844ins68) with plasma total homocysteine, cognitive performance, and cerebral white matter lesions among 1011 non-demented elderly participants. Of all the studied polymorphisms, only MTHFR 677C>T was associated with homocysteine concentration. No significant relationship was observed for any of the polymorphisms with cognitive performance or severity of cerebral white matter lesions.

[Genetic diversity and the structure of linkage disequilibrium in the methylenetetrahydrofolate reductase locus]

Investigation of linkage disequilibrium block architecture in human genome is modern, intensely investigated field of molecular genetics. In the present study, genetic differentiation and linkage disequilibrium pattern in the methylenetetrahydrofolate reductase (MTHFR) locus was examined in the populations of Russians, Tuvinians, and Northern and Southern Kyrgyzes. Methylenetetrahydrofolate reductase is the key enzyme of folate cycle, responsible for reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate. Decreased enzymatic activity of this protein often caused by certain associations of MTHFR alleles results in the increased plasma homocysteine levels. In the population groups examined, genotype and allele frequencies at five polymorphic MTHFR loci: rs17037397, rs4846052, rs1801133, rs1801131, and rs1537516 were evaluated. Statistically significant genetic differences between the population group of Southern Kyrgyzes and the other groups, as well as between Russians and Tuvinians, were demonstrated. In the MTHFR gene from the population of Southern Kyrgyzes one block was revealed; in the populations of Russians, Tuvinians, and Northern Kyrgyzes two blocks were detected. Thus, the structure of linkage disequilibrium in the MTHFR locus demonstrated population-specific pattern.

Association between the 1793G> A MTHFR polymorphism and sporadic colorectal cancer in Iran

BACKGROUND

It has been proposed that folate and polymorphisms of the enzyme methylenetetrahydrofolate reductase (MTHFR), which regulates influx of folate for methylation reactions for DNA synthesis and repair, are involved in colorectal cancer. This study was designed to determine the influence of a genetic variant (MTHFR G1793A) and folate on colon cancer in Iran.

MATERIALS AND METHODS

We analyzed 227 cases and 239 normal unmatched controls using pyrosequencing. Odds ratios and 95% confidence intervals (95% CI) were calculated to evaluate associations of the MTHFR gene polymorphism with colorectal cancer risk.

RESULTS

A significantly reduced risk of recurrence was observed in patients heterozygous for the MTHFR G1793A polymorphism (OR: 0.17; 95% CI, 0.05-0.52). The frequency of GG, GA and AA genotypes of MTHFR among the colorectal cancer patients were 98%, 2% and 0% respectively, while the frequencies among controls were 90%, 10% and 0%, respectively. Furthermore, a significant reduction in recurrence risk was seen in MTHFR G1793A heterozygotes limited to those who received folate supplements.

CONCLUSION

Our study is compatible with previous findings concerning a reverse association between the MTHFR 1793G> A genotype with cancers in different populations.

Toxic encephalopathy and delayed MTX clearance after high-dose methotrexate therapy in a child homozygous for the MTHFR C677T polymorphism

BACKGROUND

High-dose methotrexate (HD-MTX) is one of the most important agents in the therapy of osteosarcoma (OSC). Acute and delayed toxicities still constitute clinical problems. Methylenetetrahydrofolate reductase (MTHFR) has a key role in the folate cycle. In case of homozygosity of the 677C-->T polymorphism, treatment with antimetabolites, such as MTX, can cause additional toxicity.

CASE REPORT

In the present work, we describe the case of a 10-year-old boy with OSC. After the first HD-MTX infusion (12 g/m2/6 h) acute neurological disturbances were detected followed by severe hepatotoxicity. Plasma concentrations of MTX and 7-OH-MTX showed delayed clearance. Calcium folinate was administered to the patient until +186 hours. Tha patient was homozygous for the 677 polymorphism and wild-type for the 1298 polymorphism of the MTHFR gene.

CONCLUSION

We hypothesize that MTX toxicity can be explained by the association between homozygosity of the MTHFR C677T polymorphism causing disturbances in the folate status and thus an enhanced vulnerability of the central nervous system to antimetabolites and to the prolonged MTX exposure due to delayed MTX clearance.

[Genetic polymorphisms related to fluoropyrimidine sensitivity and toxicity]

Fluoropyrimidine such as 5-fluorouracil(5-FU)exerts its antitumor activities via anabolism by several enzymes. Genetic polymorphisms of these enzymes related to sensitivity and toxicity of fluoropyrimidines are reviewed. Expression of thymidylate synthase(TS), a target enzyme of 5-FU, is regulated by variable number of a 28 bp tandem repeat in the enhancer region. The double tandem repeat is associated with low TS expression, and consequently, patients with double tandem repeat demonstrated higher sensitivity to 5-FU than those with triple tandem repeat. Single nucleotide polymorphism within the second tandem repeat and loss of heterozygosity are also reported to be related to fluoropyrimidine sensitivity. In addition, patients having a 6 bp deletion in 3'-UTR region showed remarkably high antitumor activity by 5-FU based chemotherapy. Genetic variations in 5-FU catabolic enzymes can also have a profound effect on 5-FU toxicity. So far 39 mutations/ polymorphisms have been identified in dihydropyrimidine dehydrogenase(DPD)gene, a major catabolic enzyme of 5- FU. Among them, IVS14+1G>A is reported to be highly associated with severe toxicity caused by chemotherapy with fluoropyrimidine. A polymorphism that may influence the efficacy of 5-FU by influencing folate pools is that of the methylenetetrahydrofolate reductase(MTHFR)gene. C677T mutation was associated with a higher response rate on 5-FU/folinic acid chemotherapy. Prospective clinical trials to confirm the predictability of genetic polymorphism for sensitivity and toxicity of 5-FU should be performed.

Thrombophilia in young patients with acute myocardial infarction

OBJECTIVE

To investigate the association of thrombophilia and coronary artery disease (CAD) in patients with myocardial infarction (MI).

METHODS

Under the age of 45 years, 129 patients with MI and 107 control subjects were included into the study. Traditional risk factors of CAD and protein C, S, antithrombin III deficiencies, factor V Leiden (FV Leiden), prothrombin G20210A and methylenetetrahydrofolate reductase (MTHFR) C677T mutations were investigated.

RESULTS

There were statistically significant differences in terms of obesity, smoking, triglyceride, total cholesterol, high-density lipoprotein, high-density lipoprotein, and very-low-density lipoprotein cholesterol, family history, hypertension, diabetes, and left ventricular hypertrophy between patients and controls. None of the patients and controls had protein C, protein S, and antithrombin III deficiencies. Ten patients (7.8%) and 4 controls (3.7%) had heterozygote FV Leiden mutation. Homozygous prothrombine G20210A gene mutation was detected in one patient (1.1%). Homozygous MTHFR C677T mutation was observed in 7.8% (patients) and in 6.5% (controls). Heterozygous MTHFR C677T mutation was detected 36.4% in patients and 31.7% in controls. The difference was not statistically significant in terms of carriage of thrombophilic mutations.

CONCLUSION

We found that traditional risk factors increased the risk of CAD. Prothrombin G20210A, FV Leiden and MTHFR C677T mutations, protein C, S and AT-III deficiencies did not increase the risk of CAD in our young population.

Methylenetetrahydrofolate reductase C677T gene polymorphism in osteosarcoma and chondrosarcoma patients

This study was designed to investigate the association of MTHFR C677T polymorphism and the risk of two common musculoskeletal sarcomas, osteosarcoma and chondrosarcoma. MTHFR genotypes were determined in 56 patients (44 osteosarcoma, 12 chondrosarcoma) and 44 controls using the PCR-RFLP technique. In the gender subgroup analysis, wild-type A allele frequency was higher in male osteosarcoma patients than in male control subjects (P = 0.064). Mutant V allele and mutant VV genotype were similar in the control group compared to the sarcoma groups (P > 0.05). No correlation could be proved between patient tumour site, presence of metastasis, and local tumour relapse and MTHFR polymorphism. The MTHFR C677T polymorphism may not be important in an individual's susceptibility to osteosarcoma and chondrosarcoma in Turkey and may not be a useful marker for identifying patients at high risk of developing sarcomas.

Methylenetetrahydrofolate reductase C677T genotypes and clinical outcome following hematopoietic cell transplant

OBJECTIVE

Methotrexate may be used as a prophylactic agent against graft-versus-host disease in hematopoietic cell transplant. The drug exerts its effect on folate metabolism; 5,10-methylenetetrahydrofolate reductase is a critical enzyme involved in this cycle and is related to the toxicity of methotrexate.

METHODS

We examined the association of a single nucleotide polymorphism at position 677 in the 5,10-methylenetetrahydrofolate reductase gene and the clinical outcomes of patients treated with allogeneic hematopoietic cell transplant. Genotyping of 5,10-methylenetetrahydrofolate reductase was performed by polymerase chain reaction-restriction fragment length polymorphism on 30 patients receiving hematopoietic cell transplant and their HLA-matched related donors. Patients were given a short course of methotrexate as prophylaxis to prevent graft-versus-host disease.

RESULTS

Donors and recipients who carried a 677T allele showed mildly higher total bilirubin, aspartic transaminase, and alanine transaminase levels, but these increases above the normal values were not statistically significant (P > .05). The platelet recovery to 20 000/muL and granulocyte recovery to 500/muL were slower for patients who carried a 677T allele, but these correlations also were not statistically significant. The 5,10-methylenetetrahydrofolate reductase genotypes of neither the donors nor the recipients had any effect on the incidence of acute graft-versus-host disease.

CONCLUSIONS

No association was observed between the C677T polymorphism and the outcome parameters for any of the different genotypes studied here. Additional studies with larger samples are necessary to further elucidate the influence of 5,10- methylenetetrahydrofolate reductase genotyping on clinical outcomes of patients treated with hematopoietic cell transplant who receive methotrexate.

The many flavors of hyperhomocyst(e)inemia: insights from transgenic and inhibitor-based mouse models of disrupted one-carbon metabolism

Mouse models that perturb homocysteine metabolism, including genetic mouse models that result in deficiencies of methylenetetrahydrofolate reductase, methionine synthase, methionine synthase reductase, and cystathionine beta-synthase, and a pharmaceutically induced mouse model with a transient deficiency in betainehomocysteine methyl transferase, have now been characterized and can be compared. Although each of these enzyme deficiencies is associated with moderate to severe hyperhomocyst(e)inemia, the broader metabolic profiles are profoundly different. In particular, the various models differ in the degree to which tissue ratios of S-adenosylmethionine to S-adenosylhomocysteine are reduced in the face of elevated plasma homocyst(e)ine, and in the distribution of the tissue folate pools. These different metabolic profiles illustrate the potential complexities of hyperhomocyst(e)inemia in humans and suggest that comparison of the disease phenotypes of the various mouse models may be extremely useful in dissecting the underlying risk factors associated with human hyperhomocyst(e)inemia.

Methotrexate-induced mucositis in acute leukemia patients is not associated with the MTHFR 677T allele in Mexico

Methylenetetrahydrofolate reductase (MTHFR) has two common variants with reduced activity due to polymorphisms at nucleotides 677 and 1298. Both affect folate metabolism and thus remethylation of homocysteine, but are also thought to affect nucleotide synthesis and DNA methylation. Methotrexate (MTX), which interrupts folate metabolism, is used in the treatment of a variety of diseases including acute lymphoblastic leukemia (ALL), but exerts in some patients toxic effects on fast dividing tissues such as mucosal epithelia. The enhanced toxicity may be due to cooperative effects between MTX and MTHFR variants. Accordingly, it has been reported that carrying the 677T allele of the MTHFR is a risk factor for MTX-associated mucositis. As in the Mexican population, which is characterized by a high prevalence of the 677T MTHFR variant, several of its commonly associated defects have not been observed, we investigated the relationship between MTX toxicity and the 677T allele. Out of 28 patients with ALL (CC: 2, CT: 10, TT: 16), 16 had episodes of MTX-associated mucositis (CC: 0, CT: 6, TT: 10). Neither at the gene level nor at the genotype level was a significant association with mucositis found. It may be postulated that the risk of higher MTX toxicity in patients with decreased MTHFR activity could be neutralized by the normally folate rich diet in Mexico.

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

BACKGROUND

Methylenetetrahydrofolate reductase (MTHFR) of the folate metabolism pathway is a candidate gene for neural tube defects (NTDs). Frequency of the second common polymorphism, A1298C, in the MTHFR gene is not well known in Mexico. Conflicting results exist regarding the association of A1298C-MTHFR with NTDs. One explanation for this controversy might be that alleles are differently distributed among various populations. The aim of the study was to determine the frequency of the A1298C-MTHFR polymorphism and its association with NTDs in a population of Yucatan, Mexico.

METHODS

Genotyping was performed by use of polymerase chain reaction with restriction fragment length polymorphisms using MbOII endonuclease (PCR-RFLPs MbOII). Allele and genotype frequencies were compared between cases with NTDs, their mothers and fathers with matched controls based on an association analysis using EpiInfo software.

RESULTS

A1298C genotypes were distributed according to Hardy-Weinberg expectations for all studied groups. Frequencies of allele C and heterozygous AC genotype were significantly higher in males (p = .006 and p = .011, respectively) in control group. Significant differences were not observed between cases and controls, except in mothers of NTD cases compared with mothers of healthy offspring for both allele C and heterozygous AC genotype (p = .009 and p = .01, respectively).

CONCLUSIONS

The polymorphism A1298C-MTHFR is not associated with NTDs, except for mothers, suggesting only a maternal association with having NTD-affected offspring in the Yucatan population. The frequency of allele C in the control population was 10%, which is significantly lower than in other reported control populations worldwide (p < .01).

The combination of homozygous MTHFR 677T and angiotensin II type-1 receptor 1166C variants confers the risk of small-vessel-associated ischemic stroke

Previous studies have suggested that both angiotensin II type-1 receptor (AT1R) 1166C and methylenetetrahydrofolate reductase (MTHFR) 677T variants can have disadvantageous effects on the small-vessel circulation under certain conditions. The purpose of this study was to analyze the possible consequences of the simultaneous distribution of these two genetic variants in different types of ischemic stroke. The genetic and clinical data on 357 ischemic stroke patients and 263 control subjects were analyzed by using univariate and logistic statistical approaches. Neither the MTHFR 677T nor the AT1R 1166C genetic variant alone conferred the risk of any subtype of ischemic stroke. The combination of the homozygous MTHFR 677TT genotype and at least one AT1R 1166C allele occurred more frequently in the ischemic stroke patients (8.68%) than in the controls (4.56%, p < 0.05). Specific subclassification of the patients revealed an accumulation of this combination in small-vessel-associated ischemic stroke (12.2%, p < 0.01); multivariate logistic regression analysis of the data confirmed this association, with an odds ratio of 2.66 (95% confidence interval, 1.28-7.89; p < 0.05). These findings suggest that the combination of these two genetic factors can contribute to the development of small-vessel cerebral infarcts. Although the exact mechanism of action is not known, addition of the unfavourable effects on the endothelial function can be presumed.

Homocysteine and abdominal aortic aneurysms

There is evidence to suggest that increased levels of homocysteine play a significant role in vascular disease. It has been suggested that lowering homocysteine levels by dietary folate supplementation may reduce the risk of stroke and coronary heart disease. It is plausible that homocysteine may also play a role in the pathogenesis of abdominal aortic aneurysms (AAA) and that patients with this disease may benefit from folate supplementation. Our objective was to review the published work with regard to the role of homocysteine in the pathogenesis of AAA. Searches were carried out in published work in English with the keywords 'abdominal aortic aneurysm' and 'homocysteine'. There is evidence from in vitro and animal model studies that activation of metalloproteinases by homocysteine can influence aortic wall structure. Several case-control studies report an association between increased levels of homocysteine and the presence of an AAA. There are conflicting genotypic data concerning the association between methylenetetrahydrofolate reductase gene variants and AAA. Although there is evidence for an association between homocysteine and AAA, it is not strong enough to conclude that it plays a causal role in the pathogenesis of AAA. Further research is needed, given the potential benefit that simple vitamin supplementation may have for patients with AAA.

The role of one-carbon metabolism in schizophrenia and depression

OBJECTIVE

Physicians often check folate and cobalamin levels in patients with schizophrenia and depression. The reasons for this practice are reviewed, as well as implications for treatment.

METHOD

The physiology of the one-carbon cycle, involving folate, cobalamin, homocysteine, S-adenosyl-methionine, and methylene tetrahydrofolate reductase (MTHFR) is first reviewed, and then the particular contributions of folate and B12 are reviewed. PubMed was searched for studies of the association between folate, cobalamin, homocysteine, and MTHFR polymorphisms and schizophrenia and depression.

RESULTS

The recent key studies from the large literature addressing these topics are summarized. Treatment implications are discussed.

CONCLUSION

It is important to check folate and B12 levels in certain situations, such as alcoholism, malnutrition, malabsorption, and the concurrent use of some medications. Checking homocysteine and methylmalonic levels might be useful. With respect to treatment, folate and cobalamin deficiencies should be corrected. Cobalamin supplementation is probably not helpful. Folate supplementation is indicated in pregnancy but may exacerbate the effects of cobalamin deficiency. SAMe may prove to be a useful antidepressant. In the future, screening for MTHFR polymorphisms might be useful.

Plasma vitamin B-6 forms and their relation to transsulfuration metabolites in a large, population-based study

BACKGROUND

Vitamin B-6 exists in different forms; one of those forms, pyridoxal 5'-phosphate (PLP), serves a cofactor in many enzyme reactions, including the transsulfuration pathway, in which homocysteine is converted to cystathionine and then to cysteine. Data on the relations between indexes of vitamin B-6 status and transsulfuration metabolites in plasma are sparse and conflicting.

OBJECTIVE

We investigated the distribution and associations of various vitamin B-6 species in plasma and their relation to plasma concentrations of transsulfuration metabolites.

DESIGN

Nonfasting blood samples from 10 601 healthy subjects with a mean age of 56.4 y were analyzed for all known vitamin B-6 vitamers, folate, cobalamin, riboflavin, total homocysteine, cystathionine, total cysteine, methionine, and creatinine. All subjects were genotyped for the methylenetetrahydrofolate reductase (MTHFR) 677C-->T polymorphism.

RESULTS

Plasma concentrations of the main vitamin B-6 vitamers--PLP, pyridoxal, and 4-pyridoxic acid--were strongly correlated. Among the vitamin B-6 vitamers, PLP showed the strongest and most consistent inverse relation to total homocysteine and cystathionine, but the dose response was different for the 2 metabolites. The PLP-total homocysteine relation was significant only in the lowest quartile of the vitamin B-6 distribution and was strongest in subjects with the MTHFR 677TT genotype, whereas cystathionine showed a graded response throughout the range of vitamin B-6 vitamer concentrations, and the effect was not modified by the MTHFR 677C-->T genotype.

CONCLUSION

This large population-based study provided precise estimates of the relation between plasma concentrations of vitamin B-6 forms and transsulfuration metabolites as modified by the MTHFR 677C-->T genotype.