Thermolabile methylenetetrahydrofolate reductase in patients with coronary artery disease

Infant blood concentrations of folate markers and catabolites are modified by 5,10-methylenetetrahydrofolate reductase C677T genotype and dietary folate source

BACKGROUND

Folate intake and polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene may affect folate metabolism in infants.

OBJECTIVES

We investigated the association between infant's MTHFR C677T genotype, the dietary folate source, and concentrations of folate markers in the blood.

METHODS

We studied 110 breastfed infants (reference) and 182 infants who were randomly assigned to receive infant formulas enriched with either 78 μg folic acid or 81 μg (6S)-5-methyltetrahydrofolate (5-MTHF) per 100 g milk powder for 12 wk. The blood samples were available at the ages of <1 mo (baseline) and 16 wk. MTHFR genotype and concentrations of folate markers and catabolites [i.e., para-aminobenzoylglutamate (pABG)] were analyzed.

RESULTS

At baseline, carriers of the TT genotype (vs. CC) had lower mean (SD) concentrations (all in nmol/L) of red blood cell (RBC) folate [1194 (507) vs. 1440 (521), P = 0.033) and plasma pABG [5.7 (4.9) vs. 12.5 (8.1), P < 0.001] but higher plasma 5-MTHF [33.9 (16.8) vs. 24.0 (12.6), P < 0.001]. Irrespective of the genotype, infant formula with 5-MTHF (vs. folic acid) caused a significant increase in RBC folate concentration [1278 (466) vs. 947 (552), P < 0.001]. In breastfed infants, plasma concentrations of 5-MTHF and pABG increased significantly by 7.7 (20.5) and 6.4 (10.5), respectively, from baseline to 16 wk. Infant formula that complies with the present EU legislation for folate intake increased RBC folate and plasma pABG concentrations at 16 wk (P < 0.001) than formula-fed infants. At 16 wk, plasma pABG concentrations remained ∼50% lower in carriers of the TT (vs. the CC) genotype among all feeding groups.

CONCLUSIONS

Folate intake from infant formula according to the present EU legislation increased RBC folate and plasma pABG concentrations in infants to a greater extent than breastfeeding, particularly in carriers of the TT genotype. However, this intake did not completely abolish the between-genotype differences in pABG. Whether these differences have any clinical relevance, however, remains unclear. This trial was registered at clinicaltrials.gov as NCT02437721.

A call to action: MTHFR polymorphisms should not be a part of inherited thrombophilia testing

Testing for polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene is still a standard part of thrombophilia testing in many laboratories. However, it is clear that these polymorphisms are not risk factors for arterial or venous thrombosis and therefore should not be part of thrombophilia testing. Eliminating MTHFR from thrombophilia testing will reduce patient concerns and health care costs.

Methylation map genes can be critical in determining the methylome of intracranial aneurysm patients

Aim: Intracranial aneurysm is often asymptomatic until the time of rupture. Elevated homocysteine is reported in vascular diseases. Identifying early events in homocysteine metabolism through methylation map genes may prevent fatality. Materials & methods: In the present study, we investigated the role of variants in methylation map genes in ethnically matched 480 individuals that can influence the homocysteine levels and promote development of aneurysm. Results: The study demonstrates that the genetic variants in folate cycle and methionine cycle genes such as MTHFR, MTRR, MTR, BHMT and DNMT1 are associated with the risk of aneurysm. Conclusion: The associated allelic variants in these genes have functional relevance and are predictive of decreased expression indicative of altered methylation levels that may result in elevated homocysteine.

Analytic Approaches for the Treatment of Hyperhomocysteinemia and Its Impact on Vascular Disease

Homocysteine is an intermediary metabolite in the methionine cycle. Accumulation of homocysteine is caused either by mutation of relevant genes or by nutritional depletion of related vitamin(s). This review covers the historical background of hyperhomocysteinemia in which indispensable subjects in relation to underlying pathophysiological processes are discussed with the view of metabolism and genetics of folate and methionine cycles. This review emphasizes the unique role of homocysteine that is clearly distinct from other risk factors, particularly cholesterol in the development of vascular disease. The critical issue in understanding the role of homocysteine is the relation with plasma folic acid. The majority of subjects with homocysteine > 15 μmol/L exhibit plasma folate < 9 nmol/ L, indicating that depletion of folate is the main cause of hyperhomocysteinemia irrespective of the presence or absence of vascular disease. Furthermore, only the group of subjects with homocysteine levels > 15 μmol/L demonstrated a higher prevalence of vascular disease. Analytic approaches to treat hyperhomocysteinemia are discussed in which stepwise administration with nutritional doses of folic acid, 5-methyitetrahydrofolate (5-MTHF), and betaine is provided singly or by combined manner based on clinical and laboratory evaluations. Whether correction of hyperhomocysteinemia is able to prevent the development of homocysteine-associated vascular disease remains an unresolved issue. The review discussed a biochemical and mechanistic approach to resolve questions involved in the relation between homocysteine and the development of atherosclerotic vascular disease.

Methylenetetrahydrofolate reductase C677T variant and hyperhomocysteinemia in subarachnoid hemorrhage patients from India

Methylenetetrahydrofolate reductase (MTHFR) polymorphism (C677T, A1298C) has been implicated in increased plasma homocysteine (Hcy) levels. The present study was designed to investigate the association between MTHFR polymorphism and increased Hcy levels in subarachnoid haemorrhage (SAH) patients. A total of 150 subjects from North India were included in the study, comprising of 100 SAH patients and 50 healthy controls. Plasma Hcy levels was determined and MTHFR polymorphism (C677T, A1298C) was screened by High resolution melting (HRM) analysis. Plasma Hcy levels were found to be significantly higher (p < 0.001) in SAH patients than in healthy controls. No significant difference in the genotype and allele frequency of MTHFR A1298C was observed. However, frequency of MTHFR C677T genotype, CT (53% vs. 20%; p < 0.001) and TT (15% vs. 2%; p < 0.05) was significantly higher in SAH group as compared to healthy controls. The frequency of T allele (41.5% vs. 12%; p < 0.001) was also found to be higher in SAH patients in comparison to healthy controls. Furthermore, Hcy levels were higher in SAH patients with TT genotype than in patients having CT genotype, whereas CC genotype had lower Hcy levels. The study suggests that higher frequency of MTHFR C677T allele may contribute to etiopathology of SAH through increase in Hcy levels.

Riboflavin Deficiency in Rats Decreases de novo Formate Production but Does Not Affect Plasma Formate Concentration

Background: The one-carbon metabolism pathway is highly dependent on a number of B vitamins in order to provide one-carbon units for purine and thymidylate biosynthesis as well as homocysteine remethylation. Previous studies have examined folate and vitamin B-12 deficiency and their effects on formate metabolism; as of yet, to our knowledge, no studies on the effects of riboflavin deficiency on formate metabolism have been published.Objective: Our objective was to determine the effects of riboflavin deficiency on formate metabolism.Methods: Weanling male rats were randomly assigned either to control, riboflavin-replete (RR) or to experimental, riboflavin-deficient (RD) versions of the AIN-93G diet for 13 d, at which time a constant infusion of [¹³C]-formate was carried out to ascertain the effects of deficiency on formate production. Gas chromatography-mass spectrometry was used to measure plasma formate concentration and [¹³C]-formate enrichment. HPLC, LC-mass spectrometry (MS)/MS, and enzymatic assays were used for the measurement of one-carbon precursors and other metabolites.Results: RD rats had significantly lower rates of formate production (15%) as well as significantly reduced hepatic methylenetetrahydrofolate reductase activity (69%) and protein concentration (54%) compared with RR rats. There was no difference in plasma formate concentrations between the groups. Plasma serine, a potential one-carbon precursor, was significantly higher in RD rats (467 ± 73 μM) than in RR rats (368 ± 52 μM).Conclusions: Although deficiencies in folate and vitamin B-12 lead to major changes in plasma formate concentrations, riboflavin deficiency results in no significant difference; this disagrees with the prediction of a published mathematical model. Our observation of a lower rate of formate production is consistent with a role for flavoproteins in this process.

Homocysteine and the C677T Gene Polymorphism of Its Key Metabolic Enzyme MTHFR Are Risk Factors of Early Renal Damage in Hypertension in a Chinese Han Population

The combined hyperhomocysteinemia condition is a feature of the Chinese hypertensive population. This study used the case-control method to investigate the association between plasma homocysteine and the C677T gene polymorphism of its key metabolic enzyme, 5, 10-methylenetetrahydrofolate reductase (MTHFR), and early renal damage in a hypertensive Chinese Han population.A total of 379 adult essential hypertensive patients were selected as the study subjects. The personal information, clinical indicators, and the C677T gene polymorphism of MTHFR were texted. This study used the urine microalbumin/urine creatinine ratio (UACR) as a grouping basis: the hypertension without renal damage group (NRD group) and the hypertension combined with early renal damage group (ERD group).Early renal damage in the Chinese hypertensive population was associated with body weight, systolic pressure, diastolic pressure, urea nitrogen, serum creatinine, cystatin C, uric acid, aldosterone, and glomerular filtration rate. The homocysteine level and the UACR in the TT genotype group were higher than those in the CC genotype group. The binary logistic regression analysis results showed that after sex and age were adjusted, the MTHFR C677T gene polymorphism was correlated with early renal damage in hypertension in both the recessive model and in the additive model.Plasma homocysteine and the C677T gene polymorphism of its key metabolic enzyme MTHFR might be independent risk factors of early renal damage in the hypertensive Chinese Han population.

Association between the methylenetetrahydrofolate reductase c.677C>T polymorphism and bone mineral density: an updated meta-analysis

Many studies have reported an association between the methylenetetrahydrofolate reductase (MTHFR) c.677C>T polymorphism and reduced bone mineral density (BMD), but results have been inconsistent. We, therefore, performed a meta-analysis to further explore this association. Twenty-one studies, comprising 33,045 subjects, analyzed the association of MTHFR c.677C>T with femoral neck BMD. Significant association with reduced BMD was observed in Caucasians (recessive model: WMD = -0.004 g/cm(2), 95 % CI -0.008 to -0.006), post-menopausal women (recessive model: WMD = -0.005 g/cm(2), 95 % CI -0.007 to -0.003), men (dominant model: WMD = -0.004 g/cm(2), 95 % CI -0.005 to -0.004; recessive model: WMD = -0.004 g/cm(2), 95 % CI -0.005 to -0.004; TT vs. CC: WMD = -0.006 g/cm(2), 95 % CI -0.006 to -0.006; CT vs. CC: WMD = -0.003 g/cm(2), 95 % CI -0.003 to -0.003), and cohort studies (recessive model: WMD = -0.003 g/cm(2), 95 % CI -0.006 to -0.001). Twenty-two studies, which included 32,271 subjects, analyzed the MTHFR c.677C>T association with lumbar spine BMD. Significant association with reduced BMD was observed in Caucasians, women, post-menopausal women, men, and cohort studies. Seven studies, comprising 6806 subjects, analyzed the MTHFR c.677C>T association with total hip BMD, but no significant association was observed in any population. Nine studies involving 5591 subjects analyzed the association with total body BMD. Significant association with reduced BMD was observed in overall and women subgroup analyses. In summary, this meta-analysis indicates that the MTHFR c.677C>T polymorphism is associated with reduced BMD in lumbar spine and femoral neck in Caucasians, post-menopausal women, and men, and with total body BMD in women. In addition, our results suggest that new studies examining the association between MTHFR c.677C>T polymorphism and BMD of lumbar spine and femoral neck in Asians is warranted, because I (2) > 75.0 % was observed.

Vitamins B6 and cancer

Epidemiologic and laboratory animal studies have suggested that the availability of vitamin B6 modulates cancer risk. The means by which B6 mediates this effect is not known with any surety but it has been reported that high dietary vitamin B6 attenuates and low dietary vitamin B6 increases the risk of cancer. In fact vitamin B6 is widely distributed in foods and overt deficiency of this vitamin is not common. Nevertheless, marginal or secondary vitamin B6 deficiency, which might have an adverse effect on carcinogenesis, is rather common especially among old adults and alcoholics. This chapter addressed currently available information regarding the relationship between vitamin B6 and cancer.

MTHFR promotes heterochromatin maintenance

Methylenetetrahydrofolate reductase (MTHFR), a key enzyme in the folate cycle, catalyzes the reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a co-substrate for homocysteine remethylation to methionine. Methionine serves as the precursor of the active methyl donor S-adenosylmethionine, which provides methyl groups for many biological methylations. It has been reported that MTHFR is highly phosphorylated under unperturbed conditions and T34 is the priming phosphorylation site. In this report, we generated a phospho-specific antibody that recognized T34-phosphorylated form of MTHFR and revealed that MTHFR was phosphorylated at T34 in vivo and this phosphorylation peaked during mitosis. We further demonstrated that the cyclin-dependent kinase 1 (CDK1)/Cyclin B1 complex is the kinase that mediates MTHFR phosphorylation at T34 and the MTHFR immunocomplex purified from mitotic cells exhibited lower enzymatic activity. Inhibition of MTHFR expression resulted in a decrease of H3K9me3 levels, and an increase of transcription of the centromeric heterochromatin markers. Taken together, our results demonstrated that CDK1/Cyclin B1 phosphorylates MTHFR on T34 and MTHFR plays a role in the heterochromatin maintenance at the centromeric region.

Pharmacogenetics and pharmacogenomics in rheumatology

Pharmacogenetics and pharmacogenomics deal with possible associations of a single genetic polymorphism or those of multiple gene profiles with responses to drugs. In rheumatology, genes and gene signatures may be associated with altered efficacy and/or safety of anti-inflammatory drugs, disease-modifying antirheumatic drugs (DMARDs) and biologics. In brief, genes of cytochrome P450, other enzymes involved in drug metabolism, transporters and some cytokines have been associated with responses to and toxicity of non-steroidal anti-inflammatory drugs, corticosteroids and DMARDs. The efficacy of biologics may be related to alterations in cytokine, chemokine and FcγR genes. Numerous studies reported multiple genetic signatures in association with responses to biologics; however, data are inconclusive. More, focused studies carried out in larger patient cohorts, using pre-selected genes, may be needed in order to determine the future of pharmacogenetics and pharmacogenomics as tools for personalized medicine in rheumatology.

Impact of the MTHFR C677T polymorphism on colorectal cancer in a population with low genetic variability

PURPOSES

Methylenetetrahydrofolate reductase (MTHFR) plays a key role in folate metabolism, and folate is implicated in carcinogenesis by its role in DNA methylation, repair, and synthesis. We analyzed the impact of MTHFR C677T polymorphism in colorectal cancer in a region of the Tenerife Island whose population has a history of genetic isolation and a low genetic variability. This allows analyzing the effects of the polymorphism that are not due to interactions with different genetic variants.

METHODS

Genomic DNA of 50 Spanish sporadic colorectal cancer (CRC) patients and 103 controls was analyzed by PCR/RFLP and sequencing.

RESULTS

The T allele is more frequent in controls than in patients (P < 0.01). The variant (T) carriers displayed significant odds ratio values for the CT heterozygotes (P = 0.026) and even when grouping heterozygote (CT) and homozygotes (TT) (P = 0.015). Patients carriers of the variant T (CT y TT) show a higher survival rate after chemotherapy than the CC homozygotes (log rank; P = 0.001).

CONCLUSIONS

The MTHRF C677T variant has a protective effect on CRC development in a population with low allelic variability and an optimal intake of folic acid. Moreover, patients carrying the variant (T) show a better prognosis after 5-fluorouracil/folinic acid-based chemotherapy.

Unilateral adrenal infarction in pregnancy

A 25-year-old pregnant woman at 28 weeks gestational age presented with increasing abdominal pain and was found to have a unilateral adrenal infarction on a CT scan of the abdomen. Her medical history was unremarkable. There was no evidence of adrenal insufficiency with normal cortisol and adenocorticotropic hormone levels for pregnancy. Evaluation of thrombophilia disorders established the patient to be heterozygous for methylenetetrahydrofolatereductase C677T gene mutation as the only finding. The patient was anticoagulated to prevent contralateral thrombosis. At 32 weeks she experienced spontaneous rupture of membranes. One week later she delivered vaginally and remained anticoagulated for the puerperium.

Response of serum and red blood cell folate concentrations to folic acid supplementation depends on methylenetetrahydrofolate reductase C677T genotype: results from a crossover trial

SCOPE

By increasing blood folate concentrations, folic acid supplementation reduces risk for neural tube defect-affected pregnancies, and lowers homocysteine concentrations. We assessed response of red blood cell (RBC) and serum folate to folic acid supplementation, and examined association of response with the genetic polymorphism C677T of the methylenetetrahydrofolate NAD(P)H (MTHFR) gene.

METHODS AND RESULTS

Randomized, controlled, crossover trial with two folic acid supplement treatment periods and a 30-week washout period. The primary outcome is blood folate (serum and RBC) concentrations. Volunteers (n = 142) aged 18-69 were randomized to two of three doses (0, 200, and 400 μg) of folic acid for 12 weeks. Serum folate response depended on treatment period with significant responses to 200 μg seen only in the second treatment periods (4.4 ng/mL or 3.4 ng/mL). Additionally, serum folate increased as folic acid dose increased to 400 μg (p < 0.01) and response was greater after the washout period (8.7 ng/mL), than after a 6-week run-in (2.3 ng/mL). The differential change attributable to a daily supplement of 400 μg compared to 200 μg was 96.8 ng/mL; while the change attributable to 400 μg compared to 0 μg was 121.4. Increases in RBC folate concentrations with 400 μg occurred within MTHFR gene mutation (C677T); and in the African American group.

CONCLUSION

Serum folate concentration is responsive to modest increases in folic acid intake. RBC folate increases only with higher additional doses of folic acid supplementation, and this is true for each MTHFR C677T genotype.

Polymorphisms in 1-carbon metabolism, epigenetics and folate-related pathologies

Folate-mediated 1-carbon metabolism is a network of interconnected metabolic pathways necessary for the synthesis of purine nucleotides, thymidylate and the remethylation of homocysteine to methionine. Disruptions in this pathway influence both DNA synthesis and stability and chromatin methylation, and result from nutritional deficiencies and common gene variants. The mechanisms underlying folate-associated pathologies and developmental anomalies have yet to be established. This review focuses on the relationships among folate-mediated 1-carbon metabolism, chromatin methylation and human disease, and the role of gene-nutrient interactions in modifying epigenetic processes.

Genetic aspects of folate metabolism

The vitamin folate functions within the cell as a carrier of one-carbon units. The requirement for one-carbon transfers is ubiquitous and all mammalian cells carry out folate dependent reactions. In recent years, low folate status has been linked to risk of numerous adverse health conditions throughout life from birth defects and complications of pregnancy to cardiovascular disease, cancer and cognitive dysfunction in the elderly. In many instances inadequate intake of folate seems to be the primary contributor but there is also evidence that an underlying genetic susceptibility can play a modest role by causing subtle alterations in the availability, metabolism or distribution of intermediates in folate related pathways. Folate linked one-carbon units are essential for DNA synthesis and repair and as a source of methyl groups for biological methylation reactions. The notion of common genetic variants being linked to risk of disease was relatively novel in 1995 when the first functional folate-related polymorphism was discovered. Numerous polymorphisms have now been identified in folate related genes and have been tested for functionality either as a modifier of folate status or as being associated with risk of disease. Moreover, there is increasing research into the importance of folate-derived one-carbon units for DNA and histone methylation reactions, which exert crucial epigenetic control over cellular protein synthesis. It is thus becoming clear that genetic aspects of folate metabolism are wide-ranging and may touch on events as disparate as prenatal imprinting to cancer susceptibility. This chapter will review the current knowledge in this area.

Hyperhomocysteinaemia, low folate concentrations and methylene tetrahydrofolate reductase C677T mutation in acute mesenteric venous thrombosis

OBJECTIVES

Acute mesenteric venous thrombosis (AMVT) was first reported by Fagge and was recognised as a distinct clinical entity by Warreen in 1935. However, its pathogenesis is still unclear. Elevated plasma levels of homocysteine (Hcy) are associated with an increased risk of deep vein thrombosis. This case-control study examines the potential association among hyperhomocysteinaemia (hyper-Hcy), low serum folate and vitamin B(12) levels and the common C677T mutation of the MTHFR gene in patients with AMVT.

MATERIALS AND METHODS

Sixty-three patients with AMVT and 75 sex- and age-matched healthy controls were recruited, and their plasma Hcy, folate and vitamin B(12) levels were measured by high performance liquid chromatography (HPLC) and immunological assays. The polymorphism of MTHFR C677T was detected by PCR-RFLP.

RESULTS

The mean plasma Hcy levels were significantly higher in patients with AVMT compared with controls (23.5 standard deviation (S.D.) 8.8 vs. 12.6+/-6.6micromoll(-1), P<0.01). The fasting Hcy correlated negatively with folate (AMVT: r=-0.42, P<0.01;

CONTROL

r=-0.40, P<0.01). The frequency of homozygous (TT) genotype in MTHFR C677T mutation was significantly higher in patients with AMVT than that in control subjects (33% vs. 17%; chi square (chi(2))=6.31, P<0.05; odds ratio (OR)=2.80; 95% confidence interval (CI): 1.25-6.25). Compared with the control subjects, the mean serum vitamin B(12) levels were lower in patients, but it was not statistically significant (365+/-88pmoll(-1) vs. 408+/-108pmoll(-1), P>0.05).

CONCLUSIONS

Hyper-Hcy and low serum folate levels were associated with an increased risk of AMVT. The homozygous (TT) genotype of MTHFR gene mutation may be a crucial hereditary risk factor in the development of AMVT for a Chinese population.

Insights into metabolic mechanisms underlying folate-responsive neural tube defects: a minireview

Neural tube defects (NTDs), including anencephaly and spina bifida, arise from the failure of neurulation during early embryonic development. Neural tube defects are common birth defects with a heterogenous and multifactorial etiology with interacting genetic and environmental risk factors. Although the mechanisms resulting in failure of neural tube closure are unknown, up to 70% of NTDs can be prevented by maternal folic acid supplementation. However, the metabolic mechanisms underlying the association between folic acid and NTD pathogenesis have not been identified. This review summarizes our current understanding of the mechanisms by which impairments in folate metabolism might ultimately lead to failure of neural tube closure, with an emphasis on untangling the relative contributions of nutritional deficiency and genetic risk factors to NTD pathogenesis.

Peripheral arterial disease and methylenetetrahydrofolate reductase (MTHFR) C677T mutations: A case-control study and meta-analysis

OBJECTIVE

Hyperhomocysteinaemia is associated with peripheral arterial disease (PAD). There are inter-individual variations in the metabolism of homocysteine because of genetic polymorphisms. This study analyzed the role of one polymorphism that is associated with raised homocysteine, as a risk factor for PAD.

METHODS

This study considered the association of methylenetetrahydrofolate reductase (MTHFR) C677T polymorphisms with the incidence of PAD by performing a case-control study and a cross sectional study of homocysteine levels. We recruited 133 patients with PAD in Norfolk and compared the MTHFR allele distribution with 457 healthy individuals. We also carried out a meta-analysis to place our data within the context of other published studies. We searched Medline, Embase, and Cochrane databases up to March 2008 for any studies on the association between MTHFR C677T polymorphism and PAD.

RESULTS

The MTHFR C677T allele frequencies in the cases and controls were 0.37 and 0.33, and the odds ratios for the association of the 677 T allele or TT genotype with PAD were 1.18 (95% Confidence Interval [CI] 0.89, 1.58) and 1.99 (95% CI 1.09, 3.63). Homozygotes for the MTHFR C677T mutation had higher concentrations of plasma total homocysteine, odds ratio 2.82 (95% CI 1.03, 7.77) compared to homozygotes for the MTHFR 677 CC genotype. Twelve of 72 articles retrieved from the database search reported the prevalence of mutations in PAD patients. A meta-analysis of 9 appropriate studies, including our own, showed that being homozygous for the C677T allele was associated with an increased risk of PAD, pooled odds ratio 1.36 (95% CI 1.09, 1.68).

CONCLUSION

We have found a strong association between raised homocysteine, the TT genotype, and PAD.

Clinical utility of genotyping the 677C>T variant of methylenetetrahydrofolate reductase in humans is decreased in the post-folic acid fortification era

Moderate hyperhomocysteinemia is associated with many diseases. Major factors affecting plasma total homocysteine (tHcy) concentrations include folate concentrations and polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene. Because U.S.-mandated fortification of grain products with folic acid has improved folate and tHcy status in Americans, we investigated the effect of the MTHFR 677C>T variant before and after fortification. We determined tHcy and folate concentrations in sera from 844 Caucasian and 587 African American participants in the Coronary Artery Risk Development in Young Adults study before and after fortification and we genotyped the MTHFR 677C>T variant. MTHFR 677TT homozygotes had higher (P < 0.01) tHcy concentrations both before and after fortification compared with MTHFR 677CC homozygotes. However, the difference between these 2 genotypes decreased from 2.5 micromol/L before fortification to <0.7 micromol/L postfortification (P < 0.01). In addition, the prevalence of moderate hyperhomocysteinemia (tHcy > 13 micromol/L) in 677TT homozygotes decreased from 33% before fortification to 12% postfortification (P < 0.01). Using a cutoff value of 13 micromol/L to define moderate hyperhomocysteinemia, the sensitivity of the MTHFR 677TT genotype to predict elevations in homocysteine was low (approximately 30%) both before and after folic acid fortification. Increasing the cutoff from 13 to 19 micromol/L increased the sensitivity of the assay before fortification to 62% but decreased the sensitivity to 17% postfortification. We conclude that after folic acid fortification in the US, measurement of tHcy rather than genotyping of MTHFR 677TT should be used as the primary assay for the diagnosis and monitoring of moderate hyperhomocysteinemia.

Folate-mediated one-carbon metabolism

Tetrahydrofolate (THF) polyglutamates are a family of cofactors that carry and chemically activate one-carbon units for biosynthesis. THF-mediated one-carbon metabolism is a metabolic network of interdependent biosynthetic pathways that is compartmentalized in the cytoplasm, mitochondria, and nucleus. One-carbon metabolism in the cytoplasm is required for the synthesis of purines and thymidylate and the remethylation of homocysteine to methionine. One-carbon metabolism in the mitochondria is required for the synthesis of formylated methionyl-tRNA; the catabolism of choline, purines, and histidine; and the interconversion of serine and glycine. Mitochondria are also the primary source of one-carbon units for cytoplasmic metabolism. Increasing evidence indicates that folate-dependent de novo thymidylate biosynthesis occurs in the nucleus of certain cell types. Disruption of folate-mediated one-carbon metabolism is associated with many pathologies and developmental anomalies, yet the biochemical mechanisms and causal metabolic pathways responsible for the initiation and/or progression of folate-associated pathologies have yet to be established. This chapter focuses on our current understanding of mammalian folate-mediated one-carbon metabolism, its cellular compartmentation, and knowledge gaps that limit our understanding of one-carbon metabolism and its regulation.

Homocysteine as a risk factor for cardiovascular and related disease: nutritional implications

The objectives were firstly to assess the evidence that homocysteine is a significant and independent risk factor for vascular disease with special reference to cardiovascular disease, and secondly to evaluate the evidence that a food staple fortified with folic acid will reduce this problem on a population basis.

The structure of plasma homocysteine (tHcy) is described. Homocysteine, a highly reactive compound, is synthesized from the amino acid, methionine, and is metabolized by two pathways, the catabolic transsulphuration routeviacystathionine β-synthase (EC 4.2.1.22) and the remethylation path using 5-methyltetrahy-drofolate polyglutamate, the product of 5,10-methylenetetrahydrofolate reductase (MTHFR; EC 1.1.1.171),viathe cobalamin dependent enzyme, methionine synthase (MS; EC 2.1.1.13).

The mechanisms whereby hyper-tHcy is produced include both increased rates of synthesis and decreased metabolism. The latter may occur owing to nutritional deficiency of the vitamin cofactors which are necessary for the normal function of the metabolic enzymes. In particular, folate is required for methylene reductase, pyridoxal phosphate for cystathionine synthase and cobalamin for methionine synthase. When these vitamins are deficient hyper-tHcy is induced and this occurs especially in the elderly. Alternatively, a variant form of methylene reductase has recently been described which occurs in nearly 10% of the normal population. This variant is associated with hyper-tHcy, especially in situations associated with a low folate nutritional status.

Meta-analysis of both retrospective case-control studies, nested prospective case-control surveys and a secondary trial of mortality in postmyocardial infarct patients have shown that the association of hyper-tHcy with vascular disease is beyond doubt. This has been further supported by direct assessments of the degree of vascular disease in the carotid brachial and aortic arteries in relation to tHcy levels. Furthermore, treatment with a cocktail of the vitamin cofactors has produced lowering of tHcy levels and regression of the vascular disease in the carotid arteries of affected individuals.

Suggested pathogenic mechanisms in vascular disease induced by hyper-tHcy include vascular endothelial cell dysfunction, smooth muscle proliferation and derangements of normal intravascular regulation mechanisms. A variety of clinical conditions are known to be associated with a high incidence of thromboembolic complications. Some of these are associated with hyper-tHcy.

Low physiological doses of folic acid, as well as pharmocological doses, lower tHcy. However, because of the poor bioavailability of food folate (50%) and the considerable chemical instability of the naturally occurring reduced forms of folate, in most people it would require unacceptably high consumption of green vegetables to accomplish the necessary increase in intracellular folate and reduction in tHcy. Accordingly, folic acid, the nonreduced synthetic form of the vitamin, which is 100% bioavailable and chemically extremely stable, should be added to a food staple such as flour to ensure maximum protection for most of the population.

Folate-mediated one-carbon metabolism and neural tube defects: balancing genome synthesis and gene expression

Neural tube defects (NTDs) refer to a cluster of neurodevelopmental conditions associated with failure of neural tube closure during embryonic development. Worldwide prevalence of NTDs ranges from approximately 0.5 to 60 per 10,000 births, with regional and population-specific variation in prevalence. Numerous environmental and genetic influences contribute to NTD etiology; accumulating evidence from population-based studies has demonstrated that folate status is a significant determinant of NTD risk. Folate-mediated one-carbon metabolism (OCM) is essential for de novo nucleotide biosynthesis, methionine biosynthesis, and cellular methylation reactions. Periconceptional maternal supplementation with folic acid can prevent occurrence of NTDs in the general population by up to 70%; currently several countries fortify their food supply with folic acid for the prevention of NTDs. Despite the unambiguous impact of folate status on NTD risk, the mechanism by which folic acid protects against NTDs remains unknown. Identification of the mechanism by which folate status affects neural tube closure will assist in developing more efficacious and better targeted preventative measures. In this review, we summarize current research on the relationship between folate status and NTDs, with an emphasis on linking genetic variation, folate nutriture, and specific metabolic and/or genomic pathways that intersect to determine NTD outcomes.

Associations of methylenetetrahydrofolate reductase C677T polymorphism with markers of subclinical atherosclerosis: the Cardiovascular Risk in Young Finns Study

OBJECTIVE

To study whether the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism or serum homocysteine concentration is associated with carotid artery intima media thickness (IMT), carotid artery compliance (CAC) or brachial artery flow mediated dilatation (FMD) in a healthy Finnish adult population.

METHODS

Cross-sectional data obtained in 2001 for the Cardiovascular Risk in Young Finns Study were used. Carotid artery IMT, CAC and brachial FMD were measured by ultrasound and serum homocysteine concentrations using a commercial immunoassay kit. We studied 1,440 subjects (aged 24-39 years). Genotyping was performed using the 5' nuclease TaqMan assay.

RESULTS

Homocysteine values differed between genotypes in women and men (ANOVA, p<0.001 for both sex groups): the genotype raised values in the order of CC, CT, TT. There was a significant difference in CAC values between the MTHFR genotypes in men (ANOVA, p = 0.008), and the CC genotype had the lowest values. In multivariate linear regression analysis adjusted for other major coronary risk factors (e.g. age, smoking, body mass index, systolic blood pressure, C-reactive protein), the association remained significant (R (2) = 25.8 %, beta = 0.091; p = 0.02). Homocysteine level was directly associated with CAC in the whole population (R (2) = 18.0 %, beta = 0.012; p = 0.014) and in women (R (2) = 9.3%, beta = 0.02; p = 0.013), but not in men (R (2) = 15.2 %, beta = 0.004; p = 0.444). We found no association between homocysteine level or the MTHFR polymorphism and carotid IMT or brachial artery FMD.

CONCLUSIONS

The findings suggest that the MTHFR polymorphism does not influence IMT or FMD, but that the T allele may have an effect on CAC in men.

The 5, 10 methylenetetrahydrofolate reductase C677T mutation and risk of fetal loss: a case series and review of the literature

BACKGROUND

The true relationship between methylenetetrahydrofolate reductase C677T homozygosity and risk of recurrent spontaneous abortion is unknown, and it is unclear if women with these mutations should be anticoagulated during pregnancy.

OBJECTIVES

We report a series of 8 patients with this issue and review the current literature.

METHODS

8 patients (3 of whom were actively pregnant) were referred with histories of spontaneous fetal loss; hypercoaguability work-ups revealed each were homozygous for the MTHFR C677T mutation without other thrombophilias.

RESULTS

In the 3 women who have conceived, treatment with LMW heparin during pregnancy led to two full-term births and one additional pregnancy without complication. For the 5 who have not, we recommended treatment with LMW heparin upon conception.

CONCLUSION

We provide evidence to support the relationship between MTHFR C677T mutations and recurrent fetal loss, and to suggest that anticoagulation of these patients during pregnancy can lead to a successful pregnancy outcome.

Polymorphisms of MTHFD, plasma homocysteine levels, and risk of gastric cancer in a high-risk Chinese population

PURPOSE

Accumulative evidence suggests that folate has a protective effect on gastric cancer. The methylenetetrahydrofolate dehydrogenase (MTHFD) plays an important role in folate and homocysteine metabolisms, and polymorphisms of MTHFD may result in disturbance of the folate-mediated homocysteine pathway. The aim of this study is to test the hypothesis that genetic variants of MTHFD and plasma homocysteine levels are associated with risk of gastric cancer and modulated by genotypes of methylenetetrahydrofolate reductase (MTHFR).

EXPERIMENTAL DESIGN

We genotyped G1958A and T401C in MTHFD and C677T in MTHFR and detected total plasma homocysteine (tHcy) levels in a case-control study of 589 gastric cancer cases and 635 cancer-free controls in a high-risk Chinese population.

RESULTS

The variant genotypes of MTHFD 1958AA and 401CC were associated with a significantly increased risk of gastric cancer [adjusted odds ratio (OR), 2.05; 95% confidence interval (95% CI), 1.34-3.13 for 1958AA; adjusted OR, 1.43; 95% CI, 1.14-1.80 for 401CC] compared with 1958GG/GA and 401TT/TC genotypes, respectively. Both of the effects were more evident in the subjects carrying MTHFR 677CT/TT genotypes. The average tHcy level was significantly higher in gastric cancer cases than in controls (P < 0.01), and the upper quartile of tHcy (>13.6 micromol/L) was associated with an 82% significantly increased risk of gastric cancer, compared with the lowest quartile of tHcy (<or=8.0 micromol/L; adjusted OR, 1.82; 95% CI, 1.20-2.75).

CONCLUSIONS

The strong associations between MTHFD variants and the plasma tHcy levels and gastric cancer risk suggest, for the first time, a possible gene-environment interaction between genetic variants of folate-metabolizing genes and high tHcy levels in gastric carcinogenesis.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

[Steatosis, chronic hepatitis virus C infection and homocysteine]

Homocysteine, a sulfuric amino acid involved in methionine metabolism, belongs to the group of intracellular thiols. Hyperhomocysteinemia is frequent in the Caucasian population (more than 15%) and its role in vascular pathology has been clearly established. In hepatology, experimental data in transgenic mice deficient in homocysteine metabolism enzymes have shown the presence of severe liver steatosis with occasional steatohepatitis. In human beings, many studies have found a correlation between homocysteine and steatosis or even NASH. Some authors have suggested a discriminating threshold to differentiate simple steatosis from NASH. In chronic hepatitis C, preliminary data have shown that hyperhomocysteinemia is an independent risk factor for steatosis or even fibrosis. The physiopathological mechanism has now begun to be better understood. On one hand, there is a strong correlation between homocysteine and insulin resistance whatever its etiology. On the other hand, homocysteine has a direct effect on the liver, resulting in over expression of SREBP-1 and favouring steatosis. It stimulates proinflammatory cytokine secretion such as NF kappa B increasing the risk of NASH. Finally, homocysteine could increase the risk of fibrosis by stimulating TIMP 1. Moreover hepatitis C virus induces hypomethylation of STAT 1 and could decrease the antiviral activity of interferon. Results from in vitro studies have shown that the normalisation of STAT 1 methylation by bringing betaine and S Adenosyl Methionine (which belongs to homocysteine cycle) restores the antiviral activity of interferon. These data should be confirmed to evaluate the importance of homocysteine dosage in the diagnosis of NASH. Finally, treatment of hyperhomocysteinemia could have favourable consequences in steatopathies and HCV infection.

High frequency of vitamin B12 deficiency in asymptomatic individuals homozygous to MTHFR C677T mutation is associated with endothelial dysfunction and homocysteinemia

The aim of this study was to examine the association of homozygosity for the methylenetetrahydrofolate reductase (MTHFR) C677T mutation and vitamin B12 deficiency in 360 asymptomatic individuals and to investigate forearm endothelial function in C677T homozygotes. MTHFR C677T mutation and levels of vitamin B12, folic acid, and homocysteine were measured in study participants. Frequency of homozygosity for the C677T mutation was 67/360 (18.6%). Homocysteine levels were elevated in homozygous compared with heterozygous subjects or those without the mutation (20.6 +/- 18.8 vs. 9.4 +/- 3.2 mumol/l; P < 0.0001). The number of subjects with vitamin B12 deficiency (<150 pmol/l) was significantly higher among the homozygote than the heterozygote subjects or subjects without mutation [20/67 (29.8%) vs. 27/293 (9.2%); P < 0.0001]. Homozygote subjects had 4.2 times higher probability of having B12 deficiency (95% confidence interval = 2.1-8.3). Forearm endothelial function was assessed in 33 homozygote and 12 control subjects. Abnormal endothelial function was observed in homozygous subjects and was worse in homozygote subjects with vitamin B12 deficiency. Endothelial function was normalized after B12 and folic acid treatment. We found that homozygosity for the C677T mutation is strongly associated with B12 deficiency. Coexistence of homozygosity for the C677T mutation and B12 deficiency is associated with endothelial dysfunction and can be corrected with vitamin B12 and folic acid treatment.

Effects of SNPs in the Col1a1 and Methylenetetrahydrofolate Reductase Genes on BMD in Postmenopausal Women in Malta

Two common single nucleotide polymorphisms (SNPs) within the COL1A1 gene and the C677T variant within the methylenetetrahydrofolate reductase (MTHFR) gene have been studied for correlation with bone mineral density (BMD) in 126 postmenopausal Maltese women (55.6 ± 7.1 years). All polymorphisms were analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), while BMD at the lumbar spine (LS), femoral neck (FN), Ward's triangle and trochanter was measured by dual energy X-ray absorptiometry (DEXA).

The observed genotype frequencies were similar to those in other populations and were in Hardy-Weinberg equilibrium. No association was observed between polymorphisms in the COL1A1 gene and BMD, even after adjustment for age, body mass index (BMI) and years since menopause. The C allele of the C677T variant of the MTHFR gene had a negative effect on trochanter BMD when testing for genetic models of dominant and recessive alleles (independent sample t-test: p = 0.03). Genotype frequencies of both genes did not differ significantly between normal women and those with a low BMD at either the LS or FN.

DIFFERENT ALLELE-DISTRIBUTION OF MTHFR 677 C → T AND MTHFR −393 C → A IN PATIENTS CLASSIFIED ACCORDING TO SUBTYPES OF LESCH'S TYPOLOGY

AIMS

The typology by Lesch distinguishes between four subtypes: type 1 (model of allergy), type 2 (model of anxiety or conflict), type 3 (alcohol as an antidepressant), and type 4 (alcohol as adaptation). Taking into account that alcohol dependence is associated with elevated homocysteine levels, this study was undertaken to investigate different MTHFR (methylenetetrahydrofolate reductase) genotypes related to homocysteine metabolism in patients with alcohol dependence who were classified according to Lesch's typology (LT).

SUBJECTS AND METHODS

134 non-abstinent chronic alcoholics (112 males, 22 females; mean age 44.2 (SD 8.9) years) were classified according to LT and divided into four groups: LT 1 (n = 26), LT 2 (n = 65), LT 3 (n = 58), and LT 4 (n = 18). Total plasma homocysteine levels and MTHFR genotypes -393, 677, and 1,793 were determined.

RESULTS

We observed a significantly higher frequency of the thermolabile MTHFR 677 C-->T variant (TT) in patients classified as subtype LT4 when compared with subtypes LT2 and LT3 (P = 0.005). Furthermore, for the MTHFR -393 C --> A-polymorphism, significantly more AC/AA variants were found in subtype LT4 (P = 0.034). No differences in allele-distribution were detected for MTHFR 1793.

CONCLUSION

To our knowledge, this is the first study evaluating MTHFR genotypes in patients who were classified according to LT. Significantly different distributions of MTHFR 677 and -393 variants within Lesch Type 4 as compared with Types 2 and 3 hint at genetic determination of Lesch subtypes.

Structural perturbations in the Ala --> Val polymorphism of methylenetetrahydrofolate reductase: how binding of folates may protect against inactivation

In human methylenetetrahydrofolate reductase (MTHFR) the Ala222Val (677C-->T) polymorphism encodes a heat-labile gene product that is associated with elevated levels of homocysteine and possibly with risk for cardiovascular disease. Generation of the equivalent Ala to Val mutation in Escherichia coli MTHFR, which is 30% identical to the catalytic domain of the human enzyme, creates a protein with enhanced thermolability. In both human and E. coli MTHFR, the A --> V mutation increases the rate of dissociation of FAD, and in both enzymes, loss of FAD is linked to changes in quaternary structure [Yamada, K., Chen, Z., Rozen, R., and Matthews, R. G. (2001) Proc. Natl. Acad. Sci. U.S.A. 98, 14853-14858; Guenther, B. D., Sheppard, C. A., Tran, P., Rozen, R., Matthews, R. G., and Ludwig, M. L. (1999) Nat. Struct. Biol. 6, 359-365]. Folates have been shown to protect both human and bacterial enzymes from loss of FAD. Despite its effect on affinity for FAD, the A --> V mutation is located at the bottom of the (betaalpha)(8) barrel of the catalytic domain in a position that does not contact the bound FAD prosthetic group. Here we report the structures of the Ala177Val mutant of E. coli MTHFR and of its complex with the 5,10-dideazafolate analogue, LY309887, and suggest mechanisms by which the mutation may perturb FAD binding. Helix alpha5, which immediately precedes the loop bearing the mutation, carries several residues that interact with FAD, including Asn168, Arg171, and Lys172. In the structures of the mutant enzyme this helix is displaced, perturbing protein-FAD interactions. In the complex with LY309887, the pterin-like ring of the analogue stacks against the si face of the flavin and is secured by hydrogen bonds to residues Gln183 and Asp120 that adjoin this face. The direct interactions of bound folate with the cofactor provide one mechanism for linkage between binding of FAD and folate binding that could account in part for the protective action of folates. Conformation changes induced by folate binding may also suppress dissociation of FAD.

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.

Nutritional genomics

Nutritional genomics has tremendous potential to change the future of dietary guidelines and personal recommendations. Nutrigenetics will provide the basis for personalized dietary recommendations based on the individual's genetic make up. This approach has been used for decades for certain monogenic diseases; however, the challenge is to implement a similar concept for common multifactorial disorders and to develop tools to detect genetic predisposition and to prevent common disorders decades before their manifestation. The preliminary results involving gene-diet interactions for cardiovascular diseases and cancer are promising, but mostly inconclusive. Success in this area will require the integration of different disciplines and investigators working on large population studies designed to adequately investigate gene-environment interactions. Despite the current difficulties, preliminary evidence strongly suggests that the concept should work and that we will be able to harness the information contained in our genomes to achieve successful aging using behavioral changes; nutrition will be the cornerstone of this endeavor.

Association of a common polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene with bone phenotypes depends on plasma folate status

A study of a polymorphism in the MTHFR gene, plasma folate, and bone phenotypes in 1632 individuals revealed that the genotype effect on BMD and quantitative ultrasound was dependent on the level of folate. Our findings support the hypothesis that the association between an MTHFR polymorphism and bone phenotypes depends on folate status.

INTRODUCTION

Genome-wide screens using quantitative ultrasound (QUS) and BMD phenotypes have shown suggestive linkage on chromosome 1pter-1p36.3, a region containing the methylenetetrahydrofolate reductase (MTHFR) gene. Individuals homozygous (TT) for the MTHFR C677T polymorphism who have low plasma folate concentrations exhibit elevated plasma homocysteine (tHcy) concentrations that may compromise bone quality. We hypothesized that folate status might modify an association between the C677T polymorphism and bone, possibly by influencing homocysteine concentrations.

MATERIALS AND METHODS

QUS (broadband ultrasound attenuation [BUA], speed of sound, and quantitative ultrasound index) of the heel and BMD of the hip and spine were measured in 1632 male and female members of the Framingham Offspring Study (1996-2001). Participants were assessed for plasma folate concentration and genotyped for the MTHFR C677T polymorphism. TT participants were compared with individuals in the CC + CT group using analysis of covariance.

RESULTS

Adjusted mean QUS and BMD measures did not differ between C677T groups. Although all participants with plasma folate concentrations > or =4 ng/ml had approximately 2% higher QUS and BMD than those with folate <4 ng/ml, the association disappeared after controlling for tHcy. Suggestive interactions between folate status and the C677T group (CC + CT versus TT) were found for hip BMD (p < or = 0.05) and BUA (p = 0.11). Compared with CC + CT participants, TT individuals had lower mean BUA (p = 0.06) and Ward's area BMD (p = 0.08) within the folate <4 ng/ml group and significantly higher hip BMD (p < or = 0.05) within the folate > or =4 ng/ml group. For both folate groups, TT participants had higher age-adjusted mean plasma tHcy versus CC + CT participants. Controlling for tHcy in these models did not affect the statistical significance of the interaction effects.

CONCLUSIONS

Our findings support the hypothesis that the association between the C677T MTHFR polymorphism and bone phenotypes depends on folate status. The mechanism mediating the association, however, remains unclear, but may be partially caused by homocysteine effects on bone.

Homocysteine levels are associated with the severity of peripheral arterial disease in Type 2 diabetic patients

BACKGROUND

Homocysteine levels are positively associated with the risk of cardiovascular disease. They might be determined by both MTHFR677C-->T polymorphisms and folate or B-vitamin status.

OBJECTIVES

To investigate the possible association between plasma homocysteine levels and its genetic or environmental determinants and either the presence or the severity of peripheral arterial disease (PAD), in Type 2 diabetic patients.

METHODS

From a cohort of 944 patients with Type 2 diabetes, 135 patients with PAD were selected, and frequency-matched for age and sex with 219 Type 2 diabetic control patients without macrovascular complications. According to the increasing severity of the disease, patients were divided into PAD1 (only diffuse calcifications of the arteries without any stenosis or occlusion), PAD2 (one or two stenosis or occlusions) and PAD3 (three or more).

RESULTS

Homocysteine levels were similar in control and case patients (10.3 micromol L-1 vs. 10.7 micromol L-1, P = 0.53); however, a significant increase was found in PAD3 patients: odds ratio = 2.77 (95% confidence interval 1.14, 6.72) for patients with homocysteine levels above the median vs. those under the median in multivariate analysis. Although all significantly associated with homocysteine levels, neither MTHFR genotype nor folic acid or vitamin B12 levels were associated with severity of PAD. A significant interaction (P < 0.05) was found between folic acid and MTHFR polymorphism in determining the levels of homocysteine.

CONCLUSIONS

In Type 2 diabetes, homocysteine was associated with the angiographic severity of PAD, but neither the genotypes nor vitamin levels contributed to this association.

Hypercoagulable states and central retinal vein occlusion

Central retinal vein occlusion is a common cause of permanent visual loss. Work up and laboratory evaluation of patients requires the clinician to rule out hypertension, diabetes, hyperlipidemia, and glaucoma. Patients without an identifiable risk factor are often subject to extensive testing for primary and secondary thrombophilias. The purpose this paper is to review the literature to determine which of these tests is associated with central retinal vein occlusion. Antiphospholipid antibodies and elevated plasma homocysteine levels appear to be the tests associated most commonly in patients with central retinal vein occlusion in most controlled studies. Primary thrombophilias are found rarely when screening patients with central retinal vein occlusion. Extensive testing for thrombophilias is not warranted in the vast majority of patients with central retinal vein occlusion. Older patients with any of the common vascular risk factors do not require thrombophilic screening. By carefully selecting the patients who are evaluated for thrombophilias, the likelihood of finding true-positive tests is increased.

Homocysteine levels and C677T polymorphism of methylenetetrahydrofolate reductase in women with polycystic ovary syndrome

The aim of this study was to investigate the homocysteine (Hcy) levels and the C677T polymorphism of 5,10-methylenetetrahydrofolate reductase (MTHFR), a crucial factor of the Hcy metabolism in young women with polycystic ovary syndrome (PCOS). Seventy young women with PCOS and another 70 healthy women with low folate intake were enrolled. Cases and controls were matched for age, body mass index, and allele frequency. Hcy, vitamin B(12), and folate levels were measured, and a genetic analysis of 5,10-MTHFR at nucleotide 677 was performed in all subjects. No difference in mean Hcy levels was observed between PCOS women in comparison to the control group. Considering the different MTHFR polymorphism, no significant difference was found in serum Hcy levels between subjects with PCOS and controls showing CC (10.4 +/- 3.1 vs. 9.7 +/- 2.9 micromol/liter +/- SD) and CT genotypes (10.9 +/- 3.8 vs. 11.0 +/- 3.2 micromol/liter +/- SD). In subjects with a TT homozygous state, a significant (P < 0.05) difference was observed between PCOS and control women (11.5 +/- 3.9 vs. 22.0 +/- 7.8 micromol/liter +/- SD). In conclusion, our data show that in PCOS women, the serum Hcy levels are normal, and the C677T polymorphism of MTHFR does not influence the Hcy levels like in controls.

Thermolabile methylenetetrahydrofolate reductase, homocysteine, and cardiovascular disease risk: the European Concerted Action Project

BACKGROUND

Homozygotes for the thermolabile mutation (TT genotype) of the methylenetetrahydrofolate reductase (MTHFR; EC 1.5.1.20) enzyme have elevated plasma concentrations of the cardiovascular disease risk factor homocysteine, particularly if folate depleted.

OBJECTIVE

We examined the relations between thermolabile MTHFR, plasma homocysteine, plasma folate, and vascular disease risk.

DESIGN

This was a case-control comparison in 711 vascular disease cases and 747 controls from 9 European countries.

RESULTS

The TT genotype was associated with higher homocysteine and lower plasma folate than the CC and CT genotypes in both cases and controls and a nonsignificant increase in vascular disease risk (1.26; 95% CI: 0.88, 1.81; P = 0.20). The frequency of the TT genotype in cases was not significantly different from that in controls (12.8% compared with 10.8%). After adjustment for traditional risk factors, the TT genotype was associated with an odds ratio of 1.48 (1.0, 2.20) for risk of vascular disease. This risk was attenuated after further adjustment for homocysteine. In subgroups with homocysteine concentrations >or= 9 micro mol/L, risk tended to be higher in CC than in TT subjects. However, CC subjects were characterized by a higher prevalence of the conventional risk factors associated with both elevated plasma homocysteine and serum creatinine. After adjustment, the risk of vascular disease associated with each genotype was not significantly different.

CONCLUSIONS

There was a strong graded association between homocysteine and vascular risk in all genotypes. MTHFR genotype is a key determinant of plasma total homocysteine concentrations. The initially nonsignificant risk estimate associated with the TT genotype was strengthened after adjustment for conventional cardiovascular disease risk factors but was attenuated after adjustment for plasma folate and total homocysteine. The modest risk increase conferred by the TT genotype is mediated mainly by increased total homocysteine and low plasma folate concentrations.

Homocysteine: Chemistry, metabolism and roles in pathophysiology processes

In 1962, 30 years after chemical structure discovery of homocysteine, Carson and Neil reported work in which they described cases of two young people with severe mental retardation and high homocysteinuria. In 1975 McCully emphasized the association between homocysteinuria and thrombus-occlusive vascular changes. Period 1991-98, is the time of very extensive comparative studies, with aim of establishing links between premature coronary artery disease and high homocysteine level in plasma. These results in a whole show that biochemical findings of a mild increase of homocysteine plasma levels in span of 15-45 mmol/L, are independent risk factor for premature coronary artery disease appearance. So far mechanism of direct homociysteine uninfluenced on endothelial vascular vessels cells, or influence of any other factor, which play role in methionine-homocysteine-cysteine path (vitamins B6, B12, folic acid) are not strictly elucidated.

A polymorphism, R653Q, in the trifunctional enzyme methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase/formyltetrahydrofolate synthetase is a maternal genetic risk factor for neural tube defects: report of the Birth Defects Research Group

Women who take folic acid periconceptionally reduce their risk of having a child with a neural tube defect (NTD) by >50%. A variant form of methylenetetrahydrofolate reductase (MTHFR) (677C-->T) is a known risk factor for NTDs, but the prevalence of the risk genotype explains only a small portion of the protective effect of folic acid. This has prompted the search for additional NTD-associated variants in folate-metabolism enzymes. We have analyzed five potential single-nucleotide polymorphisms (SNPs) in the cytoplasmic, nicotinamide adenine dinucleotide phosphate-dependent, trifunctional enzyme methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase/formyltetrahydrofolate synthetase (MTHFD1) for an association with NTDs in the Irish population. One SNP, R653Q, in this gene appears to be associated with NTD risk. We observed an excess of the MTHFD1 "Q" allele in the mothers of children with NTD, compared with control individuals. This excess was driven by the overrepresentation of QQ homozygotes in the mothers of children with NTD compared with control individuals (odds ratio 1.52 [95% confidence interval 1.16-1.99], P=.003). We conclude that genetic variation in the MTHFD1 gene is associated with an increase in the genetically determined risk that a woman will bear a child with NTD and that the gene may be associated with decreased embryo survival.

Hyperhomocysteinemia and the MTHFR C677T mutation in Budd-Chiari syndrome

Hyperhomocysteinemia (HH) is a factor that predisposes individuals to thrombosis, and the C677T mutation in the 5,10-methylenetetrahydrofolate reductase (MTHFR) is known to give increased plasma homocysteine. However, little is known about their roles in Budd-Chiari syndrome (BCS). This study evaluated the roles of HH and the MTHFR C677T mutation in patients with BCS. We compared 41 BCS patients with 80 sex- and age-matched healthy controls. The mean plasma homocysteine level was significantly higher in patients with BCS (20.15 +/- 5.78 micromol/L) compared with normal controls (15.80 +/- 6.58 micromol/L), P < 0.01. HH (>19.5 micromol/L in men and >15.0 micromol/L in women) was detected in 15 (36.59%) patients and in 14 (17.5%) controls (odds ratio [OR], 2.72; 95% confidence internal [CI], 1.17-6.32). The prevalence of the mutated MTHFR 677TT genotype and the 677T allele in normal controls was 10.0% and 31.3%, respectively. The mutant 677T homozygotes and alleles were more frequent in patients with BCS than in controls (22.0% vs. 10.0%, 0.025 < P < 0.05; 45.1% vs. 31.3%, 0.025 < P < 0.05). The relative risk of BCS among the carriers of 677TT was significantly increased (OR, 3.3; 95% CI, 1.1-10.0). The mutant MTHFR heterozygous 677C/T carriers were not significantly increased in patients with BCS compared with controls (46.3% vs. < 2.5%, P > 0.05). The relative risk OR of BCS among carriers of 677C/T was 1.6 (95% CI, 0.7-3.6). This study suggests that both HH and the homozygous C677T mutation in the MTHFR gene are important risk factors of BCS.