Thermolabile Variant Of Methylenetetrahydrofolate Reductase Research Articles

Congenital MTHFR deficiency causing early-onset cerebral stroke in a case homozygous for MTHFR thermolabile variant

Hyperhomocysteinemia is a risk factor for early-onset venous thrombosis. It can be caused by genetic defects in methionine-homocysteine metabolism. The thermolabile variant of methylene-tetrahydrofolate reductase (MTHFR), c.677C>T, is one of the most common genetic condition, which has been associated with mild to moderate hyperhomocysteinemia, and carriers of this variant are at increased risk of an early-onset stroke-like episode. However, congenital MTHFR deficiency is a rare inborn error of folate metabolism, causing marked hyperhomocysteinemia, and its combination with the thermolabile variant is rarely reported. In this report, we describe a young adult with cerebral infarction. The patient was homozygous for the MTHFR thermolabile variant, but markedly elevated hyperhomocysteinemia led us to investigate the whole MTHFR gene, which revealed two novel MTHFR mutations. This is the first report of MTHFR deficiency in a Korean patient, and one of only a few cases reported in East Asian countries. Despite its rarity, our report underlines the importance of its identification in hyperhomocysteinemia for patient prognosis with appropriate management.

Stroke in children: inherited and acquired factors and age‐related variations in the presentation of 48 paediatric patients

Stroke is relatively rare in children and the clinical presentation of paediatric stroke is often subtle. Numerous predisposing risk factors are known, and these can be both inherited and acquired. They include cardiac disease, vascular abnormalities, endothelial damage, infectious diseases, collagen tissue diseases, certain inborn errors of metabolism and anticardiolipin antibody, lupus anticoagulant and deficiencies of protein C, protein S, antithrombin or plasminogen. In addition, abnormal activated protein C resistance (or Factor V Leiden), Factor II G20219A variant, and the thermolabile variant of methylenetetrahydrofolate reductase (MTHFR C677T) need to be considered. To explore the prevalence of different predisposing conditions in paediatric stroke patients, we evaluated 48 patients, including subjects with ischaemic and haemorrhagic stroke subtypes. Only 7 out of 48 (14.5%) had no recognizable risk factors: the majority of paediatric stroke patients had pre-existing risk factors that predisposed to the condition. The major genetic risk factor in our series of patients was homozygosity for the MTHFR C677T mutation (7 out of 48 patients); three more patients were found to be heterozygous for the Factor V Leiden mutation. Acquired predisposing conditions were present in 23 out of 48 patients and included pulmunar stenosis, head trauma, hyperlipidaemia and varicella infection. A total of 17 patients had both genetic and acquired predisposing factors. Our results emphasize that multiple predisposing risk factors commonly predispose to paediatric stroke. In addition, the primary clinical presentation appeared to differ between the older and younger children: hemiparesis was the typical presentation in children <1 year of age while seizure predominated in older children.

Protective effect against alcohol dependence of the thermolabile variant of MTHFR

Background Hyperhomocysteinemia is frequently observed in alcohol-dependent subjects, in particularly in those with marked withdrawal symptoms. The common C677T transition on the methylenetetrahydrofolate reductase ( MTHFR) gene influences homocysteinemia. Our objective was to study the prevalence of the MTHFR C677T polymorphism in alcohol-dependent subjects and the influence of this polymorphism on symptoms associated with alcoholism. Methods MTHFR C677T polymorphism was determined in 93 control subjects and 242 alcohol-dependent subjects. Serum homocysteine, folate and vitamin B 12 levels together with hepatic biological parameters were determined in the control and alcohol-dependent subjects. Results Hyperhomocysteinemia is frequently observed in alcohol-dependent subjects, particularly in those with marked withdrawal symptoms. Alcohol-dependent subjects showed a significant decrease in MTHFR 677TT prevalence (9%, 21/242) compared to controls (18%, 17/93) ( p < 0.02). The relative risk estimated as an odds ratio for alcoholism in subjects with the TT genotype is 0.42 (odd ratio 95% confidence interval, 0.21–0.83). Moreover, drinkers with TT genotype presented lower values for markers of alcohol misuse ( p < 0.05), better liver function tests, a lower frequency of relapses and no marked withdrawal symptoms as assessed by the Lesch typology. Conclusion MTHFR 677TT genotype could play a protective role against alcohol dependence. Moreover, when subjects with MTHFR 677TT genotype become dependent to alcohol, they seem to constitute a subgroup of alcoholic patients with a decreased risk for developing neurotoxic withdrawal symptoms and hepatic toxicity.

Henoch–Schonlein purpura: polymorphisms in thrombophilia genes

Henoch-Schonlein purpura (HSP) is a small-sized vasculitis affecting mainly children. Based on the hypothesis that an inherited predilection to hypercoagulability may predispose to HSP or may mark those who develop acute clinical manifestations, we evaluated the possible roles of methylenetetrahydrofolate reductase (MTHFR) gene C677T, factor V (FV) gene G1691A (Leiden), and prothrombin gene G20210A polymorphisms in patients with HSP. Fifty-two HSP patients (32 boys and 20 girls) from different ethnic groups (22 Jews and 30 Arabs) and 104 ethnically matched controls were studied for these three polymorphisms. The frequencies of these mutations for each group, separately and in combinations, are described. The mutation frequencies in the MTHFR, prothrombin and FV genes in HSP patients did not differ from those in controls. In a small number of individuals (n=5) homozygosity for the 677T thermolabile variant of MTHFR was associated with hematuria. To summarise, hypercoagulability does not seem to play a role in HSP. Studies in larger cohorts and possibly inclusion of additional factors may be needed to ascertain whether homozygoty for MTHFR 677T polymorphism can influence disease severity.

Folate‐related genes and omphalocele

Women who take folic acid in the periconceptional period greatly reduce their chances of having a child with a neural tube defect (NTD). Using multivitamins may also reduce the risk of having a child with an omphalocele. In this study, we tested single nucleotide polymorphisms in folate-related enzyme genes for association with omphalocele. Polymorphisms in methylenetetrahydrofolate reductase (MTHFR), methylenetetrahydrofolate dehydrogenase (MTHFD1), the reduced folate carrier (SLC19A1), and transcobalamin II (TCN2) were examined in 25 children with euploid omphalocele and 59 matched controls. Omphalocele cases were significantly more likely to carry the T allele of MTHFR 677C-->T, a known risk factor for NTDs (odds ratio 3.50, 95% confidence interval 1.07-11.47, P=0.035). The MTHFD1 R653Q, SLC19A1 R27H, and TCN2 P259R polymorphisms showed no significant association with omphalocele. In this small study, the thermolabile variant of MTHFR, 677C-->T, was associated with an increased risk for omphalocele. This variant causes reduced enzyme activity, thus suggesting a mechanism by which multivitamins with folic acid might prevent omphalocele. Additional investigation is required.

Might erectile dysfunction be due to the thermolabile variant of methylenetetrahydrofolate reductase?

Hyperhomocysteinemia is considered one of the most important cardiovascular risk factors increasing considerably the risk of stroke and myocardial infarction. With respect to endothelial function, direct effects of hyperhomocysteinemia on vascular endothelial cells have been demonstrated through the reduction of endothelial nitric oxide production. In this paper, we report the case of a young man with homozygote genotype mutated with 5-methylenetetrahydrofolate reductase (MTHFR) thermolabile variant who, in the absence of relational stress, developed an erectile dysfunction (ED) refractory to the vasoactive type-V phosphodiesterase (PDE5) inhibitor therapy. After one month of treatment with 5 mg/day folic acid and 1000 microg/day cyanocobalamin, the patient restarted the assumption of 50 mg sildenafil, obtaining satisfying erections during sexual intercourse. We suggest that hyperhomocysteinemia may interfere with penile blood supply and, thus, be responsible for ED. If this relationship is confirmed, plasma levels and urinary homocysteine (HCy) should be evaluated in selected young patients with vascular ED. Furthermore, careful attention should be given to the risk of ED when dealing with this metabolic disturbance.

Polymorphism of the MTHFR Gene is Associated with Altered Gene Expression in Colorectal Cancer

Aims: Folate supplementation appears to reduce colorectal cancer (CRC) risk. CRC risk is also modulated by the C to T polymorphism at position 677 of the methylenetetrahydrofolate reductase (MTHFR) gene which results in a thermolabile variant of MTHFR and is associated with reduced cellular folate levels. We looked for a relationship between MTHFR expression in colorectal tumour tissue and the C677T polymorphism.

Thrombotic Events of Arteriovenous Fistulae in Hemodialysis Patients Related to the C677T Thermolabile Variant of Methylenetetrahydrofolate Reductase

Hyperhomocysteinemia is a risk factor for thrombosis, a frequent complication of vascular access (VA) in hemodialysis (HD). The enzyme methylenetetrahydrofolate reductase (MTHFR) is necessary for the remethylation of homocysteine (Hcy) to methionine. It has been postulated that patients homozygous and, to a lesser extent, heterozygous for the C677T thermolabile variant of this enzyme present a reduced catalytic activity, with secondary increases in plasmatic Hcy levels (normal: 10 +/- 5 micromol/L) and an elevated risk of vascular thromboses. Sixty-two patients on chronic HD were divided into two groups: group A (n = 23, 37.1%) was normal for the enzyme (CC); group B (n = 39, 62.9%) was heterozygous (CT). Both groups were not different according to age, sex, time on HD, hematocrits (Hct), baseline levels of Hcy, folic acid and vitamin B12. After the 1st HD session patients were started on folic acid 10 mg/day and 500 microg/week of intravenous (i.v.) methylcobalamin. Two years later, thrombotic events were not different between the two groups. Group A = 5 (21.7%) vs. group B = 12 (30.7%), Hcy levels were significantly different between final and baseline measurements (group A 21.5 +/- 5.2 vs. 16.6 +/- 3.9 micromol/L, p = 0.02; group B 22.1 +/- 8.9 vs. 16.1 +/- 3.9 micromol/L, p = 0.008), folic acid (group A 22.1 vs. 346.9 ng/ml, range (r) =166-527, p < 0.001; group B 19.2 vs. 218.5 ng/ml, r = 138-298, p < 0.001) and vitamin B12 (group A 1489 vs. 3192.3 pg/ml, r = 1494-4890, p = 0.01; group B 1086 vs. 1513.8 pg/ml, r = 1092-1934, p = 0.02). HD patients heterozygous for the C677T variant of the enzyme MTHFR can present a similar risk of thrombotic events in arteriovenous fistulae (AVF) compared to patients normal for the enzyme at a 1-yr follow-up. These results could be explained by an adequate control of Hcy levels after folic acid and methylcobalamin replacement therapy.

Contribution of thermolabile methylenetetrahydrofolate reductase variant to total plasma homocysteine levels in healthy men and women. Inter99 (2).

Elevation in plasma total homocysteine (tHcy) is believed to be causally related to cardiovascular disease. Like age and sex, the thermolabile variant of methylenetetrahydrofolate reductase (MTHFR(C677T)) is an important nonmodifiable determinant of tHcy, which may be considered when describing normal ranges of tHcy in the general population. We investigated the simultaneous effect of sex, age, and MTHFR(C677T) genotype on the distribution of tHcy in a cross-sectional study design. THcy concentrations and MTHFR(C677T) genotype were determined in a population-based sample of 2,788 Danish men and women aged 30-60 years participating in the Inter99 Study. The prevalences of MTHFR(C677T) genotypes were 48.8% (CC), 42.4% (CT), and 8.8% (TT). The overall median tHcy was 8.1 micromol/l, and the 2.5-97.5 percentiles were 4.8-17.8 micro mol/l. The estimated proportionally higher level of tHcy in men compared to women was 14.3% (P<0.001). A significant interaction term was found between age and MTHFR(C677T) genotype (P<0.001). The estimated changes in tHcy per 5 years of age were 1.5% in CC individuals (P<0.01), 2.1% in CT individuals (P<0.001), and -4.1% in TT individuals (P<0.01). The T allele was associated with elevated tHcy. However, the proportionally higher level of tHcy in TT individuals compared to CT and CC individuals decreased with increasing age. The MTHFR(C677T) polymorphism explained 6% of the phenotypic variation in tHcy. In conclusion, we found that tHcy is associated with sex, age, and MTHFR genotype. Our results indicate that the effect of age is modified by MTHFR genotype.

Inherited and acquired risk factors and their combined effects in pediatric stroke

The aim of this study was to identify hereditary and acquired risk-factors as they are related to the occurrence of stroke in children. We identified 21 children with stroke. A search of the Factor V Leiden mutation, the Factor II G20210A variant, and the thermolabile variant of methylenetetrahydrofolate reductase was performed in patients and in a control group (n = 115). We identified risk factors of acquired and/or hereditary nature for stroke in 19 of 21 children. Eleven children had three or more risk factors, seven had two risk factors, and one child had only one risk factor. We found three carriers (14.3%) of the Factor V Leiden mutation, two carriers (9.5%) of the Factor II G20210A variant, eleven (52.4%) thermolabile variant of methylenetetrahydrofolate reductase heterozygote carriers, and one (4.8%) homozygotes for this variant. Frequencies of the Factor V Leiden mutation and the Factor II variant were higher in patients than in controls, suggesting that these variants are associated with an increased risk of stroke in childhood. Homozygosity for the thermolabile variant of methylenetetrahydrofolate reductase was equally frequent amongst patients and controls. Our study confirms that stroke in children is commonly associated with a combination of multiple risk factors, both genetic and acquired, and that the Factor V Leiden mutation and the Factor II G20210A variant are predisposing factors for this situation.

Serum C-Reactive Protein in Canadian Inuit and Its Association with Genetic Variation on Chromosome 1q21

Mortality from cardiovascular disease among Inuit living in the far north of Canada is ∼40% lower than in the rest of the country (1). This might be attributable to the protection resulting from environmental factors such as dietary ω-3 fatty acids in Arctic fish (1). Genetic factors may also be important. For example, the thermolabile variant of methylenetetrahydrofolate reductase is much less prevalent among Inuit than among subjects of European origin (2). However, there are also paradoxical genetic findings in these people. For example, some common genetic variants associated with a higher risk of cardiovascular disease, such as the APOE E4 and AGT T235 alleles, are more prevalent among Inuit than among subjects of European origin (3). These apparent inconsistencies may be related to the fact that there are numerous determinants of susceptibility to cardiovascular disease and that these determinants may differ among ethnic groups (4). As newer determinants of cardiovascular disease risk are identified, these can be evaluated in the Inuit. C-Reactive protein (CRP), an acute-phase reactant originally detected through its interaction with pneumococcal C polysaccharide (5), has been proposed to be a risk factor for cardiovascular disease (6). When detected with a high-sensitivity assay (6), increased serum CRP could be related to increased vascular disease risk either directly through its association with inflammation (7) or indirectly through its association with obesity and insulin resistance (8). The serum CRP concentration in the Inuit has not been reported. Furthermore, the role of possible genetic …

Reduction of the Homocysteine Plasma Concentration by Intravenously Administered Folinic Acid and Vitamin B12 in Uraemic Patients on Maintenance Haemodialysis

Background: Hyperhomocysteinaemia is an independent cardiovascular risk factor which can induce vascular lesions, thus contributing to the early development of atherosclerosis. Low-dose folic acid supplementation reduces the pretreatment homocysteine plasma levels by 25–35%. Recent studies report that higher intravenous or oral administration of the active form of folic acid reduces the homocysteine plasma concentration by nearly 70%. The reduction could also be influenced by the thermolabile variant of methylenetetrahydrofolate reductase (tMTHFR) and by the dialysis modality. Methods: A cross-sectional clinical study was performed to evaluate the effect of a drug containing folinic acid and vitamin B₁₂ on the plasma homocysteine concentration and whether this variable could also be influenced by the presence of a genetic variant of the methionine pathway and the use of different dialysis modalities. The plasma homocysteine concentration was measured in 55 patients undergoing haemodialysis, 27 of whom have been treated intravenously for megaloblastic anaemia using a drug containing low concentrations of folinic acid and vitamin B₁₂ at the end of each dialysis session for 6 months. The presence of tMTHFR was sought by molecular analysis, and the role of the dialysis modality was also investigated. Results: The patients given the folic acid treatment had lower homocysteine plasma levels than those not so treated. The plasma homocysteine concentration was significantly higher in the tMRHFR homozygotes than in the patients with a normal genotype, significantly lower in the treated than in the untreated homozygotes, and significantly higher in the untreated homozygotes than in the untreated subgroup with a normal genotype. The homocysteine level was also significantly lower in the patients who underwent convective haemodialysis than in those who received standard bicarbonate dialysis. Conclusions: A drug containing low concentrations of folinic acid combined with vitamin B₁₂ using an intermittent intravenous regimen is effective in reducing the homocysteine plasma concentration in uraemic patients. The homocysteine levels seem also to depend on genotype and dialysis modality.

THE METHYLENE TETRAHYDROFOLATE REDUCTASE (C677T) MUTATION AS A POTENTIAL RISK FACTOR FOR AVASCULAR NECROSIS IN SICKLE CELL DISEASE

Avascular necrosis (AVN) of the humeral and femoral heads is a frequent and debilitating complication of sickle cell disease. Some of the risk factors for AVN are a-thalassemia and age. Recently, newly discovered thrombophilia mutations have been associated with AVN in patients without sickle cell disease. We studied the frequency of the thermolabile methylene tetrahydrofolate reductase (MTHFR) variant (C677T) in adult sickle cell patients with and without AVN. The frequency of the MTHFR mutation was 35.6% in patients with AVN and 12.9% in those without AVN (p=0.006). These data suggest that the thermolabile MTHFR variant may be a contributing risk factor for AVN in some populations with sickle cell disease.

Incidence of thrombophilia in patients with Gaucher disease.

An inherited risk for thrombosis, including mutant thermolabile variant of methylenetetrahydrofolate reductase (MTHFR), factor V Leiden, or prothrombin may be the co-factor(s) for avascular necrosis (AVN) in patients with sickle cell disease. Similarly, heterozygosity for factor V Leiden is sufficient to explain the increased blood viscosity observed in children with Legg-Calve-Perthes disease who develop AVN. Because there are no laboratory tests or clinical markers that are helpful in predicting which patients with Gaucher disease may develop AVN, the current study was undertaken to ascertain if there exists an inherited predilection to hypercoagulability in patients with Gaucher disease and AVN. Analysis was performed on genomic DNA extracted from 56 adult patients with type I Gaucher disease. In this cohort of Ashkenazi Jewish patients, the frequency of mutations in the MTHFR, prothrombin, and factor V Leiden genes was found to be low, as was the presence of anticardiolipin antibodies; and none was correlated with increased incidence of AVN. Splenectomy, that may be a predisposing factor to AVN in patients with Gaucher disease, was factored out. Hence the presence of any of the above thrombophilic factors, and which by extension may be risk factors for AVN in other diseases, are not more common in patients with Gaucher disease who develop AVN. Studies in larger cohorts and possibly inclusion of additional factors may be needed to ascertain whether a correlation exists.

Homocysteine and other thiol compounds in ageing

Homocysteine, the demethylated derivative of methionine, is an important branch-point metabolite in methionine metabolism, occurring at the intersection of two metabolic pathways. In the remethylation pathway, intracellular homocysteine may be salvaged by acquiring a methyl-group from betaine or S-methyltetrahydrofolate, thus forming methionine. In the transulfuration pathway, when cysteine has to be synthesized or when methionine is in excess, homocysteine condenses with serine to form cystathionine, which is hydrolyzed to a-ketobutyrate and cysteine. Recent studies show that hyperhomocysteinemia can be an independent risk factor of cardiovascular diseases, arteriosclerosis and arterial and venous thromboembolism. Thus, increased blood levels of homocysteine could produce harmful effects on endothelium and an impairment of coagulation process [1‐ 3]. Also, it has been suggested that homocysteine alters the intact lipoprotein(a) particle, increasing the reactivity of the plasminogen-like apolipoprotein(a) portion of the molecule and the affinity of lipoprotein(a) for fibrin [4]. Homocysteine can also enhance autooxidation of LDL cholesterol, cause changes in redox thiol status [11] and increase adhesiveness of the platelets. Other physiological thiol compounds such as cysteine, cysteinglycine and glutathione could differentially mediate Cu 2+ -a nd Fe 3+ -dependent low-density lipoprotein (LDL) oxidation, an early event in atherogenesis [6]. Hyperhomocysteinemia may have multiple causes. It may be due to enzyme polymorphisms and variants, i.e., cystathionine -synthase deficiency or possession of a thermolabile variant of methylenetetrahydrofolate reductase, the enzyme required in the remethylation of homocysteine to methionine. It is also possible that nutritional deficiencies could contribute to hyperhomocysteinemia since the effective metabolism of homocysteine requires an adequate supply of vitamin B6, vitamin B12 and folate. Elevated levels may result from low levels of folate, vitamin B6, or vitamin B12 [10]. Since there is increasing evidence of augmented blood homocysteine levels in elderly healthy subjects [8] and other thiol compounds could also be increased, the risk of suffering cardiovascular diseases could be high because of the several impaired redox processes related with these thiol compounds that increase the production of oxygen-free radicals during ageing, and to a higher extent in ageing diseases such as non-insulin-dependent diabetes mellitus (type II diabetes) [5].

Folic Acid and Homocyst(e)ine Metabolic Defects and the Risk of Placental Abruption, Pre-eclampsia and Spontaneous Pregnancy Loss: A Systematic Review

Placental infarction or abruption, recurrent pregnancy loss and pre-eclampsia are thought to arise due to defects within the placental vascular bed. Deficiencies of vitamin B12 and folate, or other abnormalities within the methionine-homocyst(e)ine pathway have been implicated in the development of such placental diseases. We conducted a systematic literature review to quantify the risk of placental disease in the presence of these metabolic defects.Studies were identified through OVID Medline between 1966 and February 1999. Terms relating to the measurement of vitamin B12, folic acid, methylenetetrahydrofolate reductase or homocyst(e)ine were combined with those of pre-eclampsia, placental abruption/infarction or spontaneous and habitual abortion. Human studies comprising both cases and controls and published in the English language were accepted. Their references were explored for other publications.Data were abstracted on the matching of cases with controls, the mean levels of folate, B12 or homocyst(e)ine in each group or the frequency of the homozygous state for the thermolabile variant of methylenetetrahydrofolate reductase. The definition of ‘abnormal’ for each exposure was noted and the presence or absence of the exposure of interest for each outcome was calculated as an absolute rate with a 95 per cent confidence interval. The crude odds ratios were calculated for each study and then pooled using a random effects model.Eighteen studies were finally included. Eight studies examined the risk of placental abruption/infarction in the presence of vitamin B12 or folate deficiency, or hyperhomocyst(e)inaemia. Folate deficiency was a prominent risk factor for placental abruption/infarction among four studies, though not statistically significant (pooled odds ratio 25.9, 95 per cent CI 0.9–736.3). Hyperhomocyst(e)inaemia was also associated with placental abruption/infarction both without (pooled odds ratio 5.3, 95 per cent CI 1.8–15.9) and with methionine loading (pooled odds ratio 4.2, 95 per cent CI 1.2–15.0), as was the homozygous state for methylenetetrahydrofolate reductase (pooled odds ratio 2.3, 95 per cent CI 1.1–4.9). Vitamin B12 deficiency was not a demonstrable risk factor.Eight studies examined blood levels among women with spontaneous abortion or recurrent pregnancy loss. The pooled odds ratios were 3.4 (95 per cent CI 1.2–9.9) for folate deficiency, 3.7 (95 per cent CI 0.96–16.5) for hyperhomocyst(e)inaemia following methionine challenge, and 3.3 (95 per cent CI 1.2–9.2) for the methylenetetrahydrofolate reductase mutation.Five case-control studies examined the relationship between pre-eclampsia and abnormal levels of vitamin B12, folate, homocyst(e)ine or methylenetetrahydrofolate reductase. Folate deficiency was not an associated risk factor (odds ratio 1.2, 95 per cent CI 0.5–2.7), but hyper-homocyst(e)inaemia was (pooled odds ratio 20.9, 95 per cent CI 3.6–121.6). Similarly, homozygosity for the methylenetetrahydrofolate reductase thermolabile variant was associated with a moderate risk of preeclampsia (odds ratio 2.6, 95 per cent CI 1.4–5.1). Some pooled data were associated with significant statistical heterogeneity, however.There is a general agreement among several observational studies that folate deficiency, hyperhomocyst(e)inaemia and homozygosity for the methylenetetrahydrofolate reductase thermolabile variant are probable risk factors for placenta-mediated diseases, such as pre-eclampsia, spontaneous abortion and placental abruption. Vitamin B12 deficiency is less well defined as an important risk factor. Due to the limited quality of these data, including insufficient matching of cases with controls, and possible laboratory measurement bias relating to pregnancy, prospective studies are needed to confirm these findings and guide future preventative and therapeutic research.

Homocysteine and risk of stroke.

The balance of evidence from observational studies suggests that elevated levels of homocysteine are associated with increased risk of carotid artery disease and stroke. There is, however, a paucity of prospective studies. There are also concerns regarding confounding caused by factors associated with hyperhomocysteinaemia, including renal impairment, an atherogenic diet and cigarette smoking. Homozygosity for a defective thermolabile variant of methylene-tetrahydrofolate reductase, a common genetic polymorphism which results in hyperhomocysteinaemia, has not been consistently linked with stroke or other vascular diseases. Additional prospective studies are required, with sufficient power to characterise the form of the association between homocysteine concentrations and stroke risk, whether linear or threshold, and to study interactions between homocysteine, other dietary markers and established stroke risk factors such as smoking and hypertension. Ultimately, the case for a causal role for elevated levels of homocysteine in vascular disease, including stroke, will depend on data from randomised controlled trials of homocysteine-lowering interventions. Given the high prevalence of hyperhomocysteinaemia in apparently well-nourished populations and the tendency for homocysteine concentrations to increase with age, modest effects of homocysteine on stroke risk will have profound implications for public health.

Factor V Leiden and thermolabile methylenetetrahydrofolate reductase gene variants in an East Anglian preeclampsia cohort.

Preeclampsia is a heritable condition that develops as a result of widespread vascular endothelial dysfunction. The thrombotic tendency in this condition has suggested a number of candidate genes, and there have been recent reports of positive association with the Leiden variant of factor V and the thermolabile variant of methylenetetrahydrofolate reductase. We attempted to reproduce these results in a large cohort of well-characterized women with preeclampsia, recruited prospectively within the East Anglian region of the United Kingdom. Women in the preeclampsia cohort (n=283) were genotyped for both the Leiden variant (G1691A) of factor V and the thermolabile variant (C677T) of methylenetetrahydrofolate reductase. Genotype and allele frequencies were compared with those of 2 control groups, one consisting of women recruited prospectively (n=100) from the same maternity hospital as the subjects and another consisting of normotensive women (n=100) from East Anglia. No significant differences were detected. Specifically, the carrier rate for the Leiden variant was 5.3% in the preeclampsia group and 5. 5% in the combined control group. T677 homozygotes for methylenetetrahydrofolate reductase were 11% and 11.5% in the 2 groups, respectively. We conclude that there is no evidence of association of preeclampsia with either of these 2 polymorphisms in our study population.

A common mutation in the methylenetetrahydrofolate reductase gene is associated with an accumulation of formylated tetrahydrofolates in red blood cells.

A common mutation (C677T) in the gene encoding for methylenetetrahydrofolate reductase (MTHFR) (5-methyltetrahydrofolate:(acceptor) oxidoreductase, EC 1.7.99.5), a key regulatory enzyme in one-carbon metabolism, results in a thermolabile variant of the MTHFR enzyme with reduced activity in vitro. In the present study we used a chromatographic method for folate analysis to test the hypothesis that this mutation would be associated with altered distribution of red blood cell (RBC) folates. An alteration was found as manifested by the presence of formylated tetrahydrofolate polyglutamates in addition to methylated derivatives in the RBCs from homozygous mutant individuals. 5-Methyltetrahydrofolate polyglutamates were the only folate form found in RBCs from individuals with the wild-type genotype. Existence of formylated folates in RBCs only from individuals with the thermolabile MTHFR is consistent with the hypothesis that there is in vivo impairment in the activity of the thermolabile variant of MTHFR and that this impairment results in an altered distribution of RBC folates.

Prevalence of the mutation C677 --> T in the methylene tetrahydrofolate reductase gene among distinct ethnic groups in Brazil.

Vascular disease is a serious public health problem in the industrialized world, and is a frequent cause of death among the adult population of Brazil. Mild hyperhomocysteinemia has been identified as a risk factor for arterial disease, venous thrombosis, and neural tube defects. Individuals homozygous for the thermolabile variant of methylenetetrahydrofolate reductase (MTHFR-T) are found in 5-15% of the general population and have significantly elevated plasma homocysteine levels which represent one of the genetic risk factors for vascular diseases. We have analyzed the prevalence of individuals homozygous for the MTHFR-T in 327 subjects representing the three distinct ethnic groups in Brazil. The prevalence of homozygotes for the mutated allele MTHFR-T was high among persons of Caucasian descent (10%) and considerably lower among Black (1.45%) and Indians persons populations (1.2%). These data suggest that screening for the MTHFR-T allele should help in identifying individuals with a high risk of vascular disease among populations with a heterogeneous background.