Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:1.5.7.1 (methylenetetrahydrofolate reductase)
2,116 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Genetic polymorphisms for apolipoprotein E (apo E) and methylenetetrahydrofolate reductase (MTHFR) are believed to modulate risk of coronary heart disease (CHD) acting through regulation of lipid and homocysteine metabolism, respectively. The distributions of apo E and MTHFR alleles in Black South Africans, a population with a low CHD incidence, and UK Caucasians from the Cambridge area, with a higher CHD incidence, were therefore compared. Clinically healthy volunteers (207), including 107 UK Caucasians from the Cambridge area and 100 Black South Africans, participated in the study. Apo E and MTHFR genotypes were determined in all of them. Analyses for serum total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides and plasma fibrinogen were carried out in 65 UK Caucasians and 60 Black South Africans. The apo E epsilon4 allele, which is associated with elevated CHD risk, was present in 48% of Black South Africans compared to 20.8% of Caucasians (P < 0.0001); however, both total and LDL cholesterol levels in Black South Africans were 18-32% lower than in Caucasians with similar apo E genotypes. Hyperhomocysteinemia-causing MTHFR 677T variant was detected in only 20% of Black South Africans (no homozygotes) versus 56% of Caucasians with 12% homozygotes (P<0.0001). Our findings suggest that the potentially unfavourable pattern of apo E allele distribution in Black South Africans does not result in increased CHD incidence due to protection by dietary and/or other life style related factors. The exceptionally low frequency of MTHFR mutant homozygotes in this population suggests that this polymorphism should not be regarded as an important CHD risk factor among Black South Africans.
...
PMID:Apolipoprotein E and methylenetetrahydrofolate reductase genetic polymorphisms in relation to other risk factors for cardiovascular disease in UK Caucasians and Black South Africans. 1042 3

The purpose of this study is to observe the influence of the methylenetetrahydrofolate reductase (MTHFR) gene (677C-->T substitution) on plasma homocysteine levels in end-stage renal disease (ESRD) patients who received a relatively large amount of folate (2 mg/d) and are undergoing hemodialysis. A cross-sectional study of plasma homocysteine, vitamin B(12), and folate was performed in patients with ESRD. The study population for the MTHFR gene study included 312 healthy subjects and 106 patients with ESRD undergoing hemodialysis. The C677T transition in the MTHFR gene was detected by HinF 1 restriction enzyme analysis and subsequent electrophoresis in a 3% agarose gel. The genotype of the MTHFR gene in 106 patients with ESRD was homozygous C677T mutation (VV) in 17 patients (16.1%) and heterozygous (AV) in 63 patients (58.4%); 26 patients (24.5%) did not carry this mutation (AA). The mean levels of homocysteine, vitamin B(12), and folate in the patients with ESRD were 23.3 +/- 14.0 mmol/L, 620.2 +/- 98.5 pmol/L, and 138.6 +/- 55.6 nmol/L, respectively. There was no significant difference in homocysteine levels among the three genotypes: 28.2 +/- 19.4 mmol/L for VV, 22.7 +/- 14.9 mmol/L for AV, and 23.4 +/- 11.1 mmol/L for AA genotype (P > 0.05). There was no difference in genotype distribution between the patient groups of less than 25th and greater than 75th percentiles, classified according to plasma homocysteine levels (P = 0.47). In conclusion, with high-dose folate supplementation, the hyperhomocysteinemia in patients with ESRD does not seem to be caused by the 677C-->T mutation in the MTHFR gene.
...
PMID:Influence of 5,10-methylenetetrahydrofolate reductase gene polymorphism on plasma homocysteine concentration in patients with end-stage renal disease. 1043 Sep 72

Homocysteine is a sulfur amino acid whose metabolism stands at the intersection of two pathways: remethylation to methionine, which requires folate and vitamin B12 (or betaine in an alternative reaction); and transsulfuration to cystathionine, which requires pyridoxal-5'-phosphate. The two pathways are coordinated by S-adenosylmethionine, which acts as an allosteric inhibitor of the methylenetetrahydrofolate reductase reaction and as an activator of cystathionine beta-synthase. Hyperhomocysteinemia, a condition that recent epidemiological studies have shown to be associated with increased risk of vascular disease, arises from disrupted homocysteine metabolism. Severe hyperhomocysteinemia is due to rare genetic defects resulting in deficiencies in cystathionine beta synthase, methylenetetrahydrofolate reductase, or in enzymes involved in methyl-B12 synthesis and homocysteine methylation. Mild hyperhomocysteinemia seen in fasting conditions is due to mild impairment in the methylation pathway (i.e. folate or B12 deficiencies or methylenetetrahydrofolate reductase thermolability). Post-methionine-load hyperhomocysteinemia may be due to heterozygous cystathionine beta-synthase defect or B6 deficiency. Early studies with nonphysiological high homocysteine levels showed a variety of deleterious effects on endothelial or smooth muscle cells in culture. More recent studies with human beings and animals with mild hyperhomocysteinemia provided encouraging results in the attempt to understand the mechanism that underlies this relationship between mild elevations of plasma homocysteine and vascular disease. The studies with animal models indicated the possibility that the effect of elevated homocysteine is multifactorial, affecting both the vascular wall structure and the blood coagulation system.
...
PMID:Homocysteine metabolism. 1044 23

A family history of myocardial infarction is a major determinant of ischemic disease. A C->T677 polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene has been identified as a cause of mild hyperhomocysteinemia, a risk factor for arterial thrombosis. We have investigated the relationship between the MTHFR TT genotype and a family history of myocardial infarction in a cohort of 982 apparently healthy individuals. Subjects whose first-degree relatives suffered from a myocardial infarction, showed raised median age (p <0.001), total cholesterol (p <0.001) and plasma fibrinogen (p = 0.023) and a higher than normal frequency of C-reactive protein levels >0.33 mg/dl (p = 0.012). Moreover, when compared to subjects without such family history, a higher number of homozygotes for the T allele of the MTHFR gene (p = 0.027), and of the 4G allele of the plasminogen activator inhibitor-1 gene (p = 0.002) was found in the subsetting of the offspring of patients with myocardial infarction. In a multiple logistic regression analysis, age (OR 1.02 [95%-CI: 1.00-1.05]), total cholesterol (OR 1.40 [95%-CI: 1.14-1.71]), C-reactive protein levels >0.33 mg/l (OR: 1.87 [95%-CI: 1.10-3.20]), plasminogen activator inhibitor-1 4G/4G (OR: 1.84 [95%-CI: 1.27-2.66]), and MTHFR TT genotype (OR 1.62 [95%-CI: 1.08-2.42]), were all associated with a family history of myocardial infarction. Thus, the MTHFR TT genotype independently accounts for the risk of a family history for myocardial infarction in the present setting.
...
PMID:Genetic polymorphism of 5,10-MTHFR reductase gene in offspring of patients with myocardial infarction. 1045 48

The present study describes 403 patients with thrombosis, from a uniform ethnic and geographical background. Two-hundred-and-seven individuals had suffered mild or moderate stroke and 196 individuals suffered venous thromboembolism. We recorded levels of antithrombin, protein C and protein S, plasminogen and plasma homocysteine, and the presence of the factor V Leiden mutation, the prothrombin 20210G-->A variant, and the methylenetetrahydrofolate reductase (MTHFR) 677C-->T polymorphism. Controls for the mutation frequencies consisted of Guthrie card blood spots from a cohort of new-born babies. The cumulative prevalence of deficiencies in antithrombin, protein C, protein S or plasminogen was 2.4% in patients with stroke and 11.2% in patients with venous thrombosis. The factor V Leiden mutation was present in 11.1% of patients with stroke and 26.5% of patients with venous thrombosis, compared with 6.6% of controls (n = 4188; P < 0.05 and P < 0.0001, respectively). The prevalence of the prothrombin 20210A variant was 3.1% in patients with venous thrombosis, 1.9% in patients with stroke and 2.0% in controls (n = 500; P > 0.05). Hyperhomocysteinemia was present in 16.0% of patients with stroke and 17.6% of patients with venous thrombosis. The prevalence of the MTHFR 677T/T genotype was no different in patients with stroke (10.6%) and venous thrombosis (8.7%) than in controls (8.3%; n = 1084; P > 0.05); thus, it apparently contributed to thrombosis only via its influence on total plasma homocysteine, which was significantly increased in patients with the T/T genotype (P < 0.001). The MTHFR T/T genotype did not further increase the risk for thrombosis in carriers of the factor V Leiden mutation. Overall, thrombotic events were associated with a known risk factor in 27% of patients with stroke and 55% of patients with venous thrombosis.
...
PMID:Thrombophilic predisposition in stroke and venous thromboembolism in Danish patients. 1045 16

Hyperhomocysteinemia is a condition caused by both genetic and nongenetic factors. To determine whether a common methylenetetrahydrofolate reductase (MTHFR) variant is related to elevated homocysteine concentrations in epileptic patients receiving anticonvulsants, we investigated the plasma total homocysteine (tHcy) level, folate level, and MTHFR 677 C --> T mutation using a polymerase chain reaction (PCR) and restriction fragment length polymorphism analysis with HinfI digestion in 103 patients with epilepsy and 103 normal controls. The prevalence of hyperhomocysteinemia (> or = 11.4 micromol/L, 90th percentile of control group) was higher in patients than in controls (25% v 10.0%, P = .007). The homozygosity for the 677 C --> T mutation of MTHFR was associated with elevated tHcy and low folate levels. The magnitude of hyperhomocysteinemia in MTHFR TT homozygotes was more pronounced in epileptic patients than in controls (18.2 +/- 1.6 v 9.1 +/- 1.2 micromol/L, P = .04). In epileptic patients, hyperhomocysteinemia was more frequent in MTHFR TT genotypes versus CT or CC genotypes (58% v 17% and 16%, P < .001). Multiple logistic regression analysis showed that MTHFR TT genotype was an independent predictor of hyperhomocysteinemia in epileptic patients receiving anticonvulsants (phenytoin and carbamazepine but not valproic acid), suggesting that gene-drug interactions induce hyperhomocysteinemia. These findings indicate that epileptic patients receiving anticonvulsants may have a higher folate requirement to maintain a normal tHcy level, especially homozygotes for MTHFR 677 C --> T mutation.
...
PMID:A common mutation in the methylenetetrahydrofolate reductase gene is a determinant of hyperhomocysteinemia in epileptic patients receiving anticonvulsants. 1045 72

Background: Elevated levels of homocysteine are an independent risk factor for venous thrombosis. A common mutation in methylenetetrahydrofolate reductase (MTHFR), an enzyme required for efficient homocysteine metabolism, creates a thermolabile (tl-) enzyme with reduced activity that may predispose to hyperhomocysteinemia. Methods and Results: To assess whether this common mutation is a risk factor venous thromboembolism, a polymerase chain reaction-based genotyping assay was used to compare the prevalence of this mutation in a group with thrombosis versus several control groups. Of the 331 thrombosis subjects, 47% were heterozygous and 11% homozygous for tl-MTHFR. In comparison, heterozygotes constituted 42-47% and homozygous 15-16% of each of three control groups (totaling 593 subjects). There was no significant difference in the tl-MTHFR homozygote frequency or allele frequency between the thrombosis and control study groups. Although the prevalence of the factor V R506Q (Leiden) mutation causing activated protein C resistance was significantly higher in the thrombosis (19%) than in the control groups (4-9%), the concomitant presence of tl-MTHFR with factor V R506Q did not contribute to any excess thrombotic risk. Conclusions: Although the tl-MTHFR mutation may predispose to hyperhomocysteinemia, a known risk factor for venous thrombosis, this common genotype is not a direct genetic risk factor for venous thrombosis, either alone or in combination with the factor V R506Q mutation.
...
PMID:Risk of Venous Thrombosis in Carriers of a Common Mutation in the Homocysteine Regulatory Enzyme Methylenetetrahydrofolate Reductase. 1046 93

Recently, a mild to moderate elevation in the plasma homocysteine (Hcy) level has been found to be an important risk factor for stroke. Homozygosity for a common mutation (C677T) in the gene encoding for the enzyme methylenetetrahydrofolate reductase (MTHFR) involved in Hcy metabolism has been associated with increased levels of Hcy. To determine the role of hyperhomocysteinemia in the pathogenesis of stroke in children with sickle cell disease (SCD), Hcy levels and C677T MTHFR genotype were determined in 40 patients homozygous for hemoglobin SS and compared with 197 healthy children. Eleven of 40 patients with SCD had a history of stroke. The prevalence of homozygosity for the C677T MTHFR variant was 5% in the patients with SCD. The median Hcy level was 5.8 micromol/L in the patients versus 5.4 micromol/L in the controls (Fisher's, P > 0.05). There was no correlation of Hcy levels with the MTHFR genotype in patients with SCD. In patients with SCD and stroke, the median Hcy level was 4.8 micromol/L versus 6.0 micromol/L in those without stroke (P = 0.44, Mann-Whitney rank sum test). There was no difference in the proportion of patients with SCD with or without stroke who were homozygous for the C677T MTHFR mutation (0/11 versus 2/29; Fisher's, P = 1.000). In conclusion, this study failed to demonstrate an elevation in plasma Hcy levels in children with SCD compared with normal controls. Furthermore, hyperhomocysteinemia did not seem to be a significant factor in the pathogenesis of stroke in children with SCD.
...
PMID:Correlation of the C677T MTHFR genotype with homocysteine levels in children with sickle cell disease. 1052 53

It is not clear to what extent methylenetetrahydrofolate reductase (MTHFR) gene and hyperhomocysteinemia effect the severity and extent of coronary atherosclerosis in Asian populations. We examined the MTHFR genotypes and plasma homocysteine (HCY) concentrations in 192 Taiwanese and investigated their relationship with coronary artery disease (CAD), and the severity and extent of coronary atherosclerosis. The distribution of MTHFR genotypes was similar in 116 CAD patients and 76 non-CAD subjects. Homozygosity was noted in 8% of CAD patients and 13% of non-CAD subjects (P=0.33; 95% CI, 0. 2-1.6). The geometric mean of HCY values was higher in CAD patients (11.10+/-1.51 micromol/l) than in non-CAD subjects (9.21+/-1.55 micromol/l) (P=0.003). HCY levels were higher in patients with multi-vessel disease (P<0.05) or in patients with > or = 90% stenotic lesions (P=0.005), compared with non-CAD subjects. The CAD risks in the top two HCY quartiles (> or = 14.0 and 10.1-13.9 micromol/l) were 4.0 (95% CI, 1.7-9.2) and 3.2 (95% CI, 1.4-7.4) times higher than in the lowest quartile (< or = 7.9 micromol/l) (P=0.001 and 0.007, respectively). Linear regression analysis showed significant correlations between HCY concentrations and the severity and extent of atherosclerosis (P=0.0001 for both). In conclusion, hyperhomocysteinemia appears to have a graded effect on the risk of CAD as well as the severity and extent of coronary atherosclerosis. Our findings do not support the homozygous genotype of MTHFR as a genetic risk factor for CAD in this Taiwanese population. Perhaps a further study including assessment of vitamin status is needed to better clarify the relationship between MTHFR genotypes and CAD.
...
PMID:The graded effect of hyperhomocysteinemia on the severity and extent of coronary atherosclerosis. 1055 24

Over the past few years, a substantial body of evidence has accumulated that indicates hyperhomocysteinemia as a significant risk factor for cardiovascular disease. Hyperhomocysteinemia arises from a lack of key enzymes or vitamins such as methylenetetrahydrofolate reductase, vitamin B6, and folate which are involved in homocysteine metabolism. Heavy coffee consumption is also known to elevate homocysteine levels. The adverse effects associated with hyperhomocysteinemia are extensive. It increases risk of myocardial infarction, cardiovascular-related morbidity and mortality, peripheral vascular disease, atherosclerosis, coronary heart disease, and cerebrovascular disease. Its seriousness as a risk factor has been equated to hypercholesterolemia and smoking, two leading causes for cardiovascular disease. It also has been shown to produce a multiplicative effect with these and other risk factors such as hypertension. Two major hypotheses have been proposed to explain how homocysteine induces its harmful effects. It can damage endothelial cells lining the vasculature, allowing plaque formation. Simultaneously, it interferes with the vasodilatory effect of endothelial derived nitric oxide. Also, homocysteine has been found to promote vascular smooth muscle cells hypertrophy. Both of these processes induce vessel occlusion. Maintaining a normal plasma level of homocysteine as a means to prevent cardiovascular disease appears promising. This is achieved through increased intake of folate and vitamin B6 through diet or supplementation. Despite the overwhelming evidence suggesting homocysteine as a significant risk factor, no long-term prospective studies have been completed to demonstrate that folate and vitamin B6 can prevent cardiovascular disease related morbidity and mortality in patients with hyperhomocysteinemia. Homocysteine is a key metabolite in amino acid synthesis. During the process of methylation, S-adenosylmethionine (Ado Met), derived from methionine, is converted to S-Adenosylhomocysteine (Figure 1). This product is quickly hydrolyzed to form homocysteine and adenosine. Homocysteine can undergo 1 of 3 reactions depending on the status of the organism. If cysteine levels are inadequate, homocysteine utilizes the coenzyme pyridoxal phosphate (vitamin B6) to condense with serine, forming the intermediate cystathionine. Subsequent reactions with cystathionine lead to the formation of cysteine. When methionine levels are low, homocysteine is remethylated in a reaction involving the coenzyme N5-methyltetrahydrofolate or betaine. Finally, when both amino acids are in adequate supply, homocysteine is cleaved by the enzyme homocysteine desulthydrase (cystathionase) to form a-ketobutyrate, ammonia, and H2S. Thus, homocysteine's physiological role is to assist in maintaining sulfur-amino acid homeostasis. Beyond these metabolic processes, homocysteine is beginning to be recognized as a significant risk factor for cardiovascular disease including atherosclerosis, coronary artery disease, cerebrovascular disease, and myocardial infarction.
...
PMID:Hyperhomocysteinemia: an additional cardiovascular risk factor. 1063 97


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---