The C677T methylenetetrahydrofolate reductase gene mutation in hemodialysis patients

Relationship Between Gene Polymorphism of Methylenetetrahydrofolate Reductase C677T and Left Ventricular Hypertrophy in Chinese Patients with Chronic Kidney Disease

OBJECTIVE

This study aimed to investigate the relationship between the gene polymorphism of methylenetetrahydrofolate reductase (MTHFR) C677T and left ventricular hypertrophy (LVH) in patients with chronic kidney disease (CKD).

METHODS

A total of 763 Chinese patients with CKD undergoing genetic testing were included in the study. The association between the gene polymorphism of MTHFR C677T and echocardiographic parameters was analyzed through univariate and multivariate analyses.

RESULTS

We found a remarkably positive association between MTHFR C677T gene polymorphism and LVH indexes, including interventricular septal thickness (F = 3.8; P = .022), left ventricular posterior wall thickness (F = 3.0; P = .052), left ventricular mass (F = 3.9; P = .022), and left ventricular mass index (F = 2.6; P = .075). After adjusting for the potential confounders linking the polymorphism,we found that the positive association between the polymorphism and LVH indexes still existed in patients with CKD in some multiple linear regression models (P <.05).

CONCLUSION

MTHFR C677T gene polymorphism may be a genetic susceptibility marker for the development of LVH in patients with CKD.

Correlations of MTHFR 677C>T polymorphism with cardiovascular disease in patients with end-stage renal disease: a meta-analysis

OBJECTIVE

This meta-analysis was conducted to evaluate the correlations of a common polymorphism (677C>T) in the methylenetetrahydrofolate reductase (MTHFR) gene with risk of cardiovascular disease (CVD) in patients with end-stage renal disease (ESRD).

METHOD

The following electronic databases were searched without language restrictions: Web of Science (1945∼2013), the Cochrane Library Database (Issue 12, 2013), MEDLINE (1966∼2013), EMBASE (1980∼2013), CINAHL (1982∼2013) and the Chinese Biomedical Database (CBM) (1982∼2013). Meta-analysis was performed using STATA statistical software. Odds ratios (ORs) with their 95% confidence intervals (95%CIs) were calculated.

RESULTS

Eight cohort studies met all inclusion criteria and were included in this meta-analysis. A total of 2,292 ESRD patients with CVD were involved in this meta-analysis. Our meta-analysis results revealed that the MTHFR 677C>T polymorphism might increase the risk of CVD in ESRD patients (TT vs. CC: OR = 2.75, 95%CI = 1.35∼5.59, P = 0.005; CT+TT vs. CC: OR = 1.39, 95%CI = 1.09∼1.78, P = 0.008; TT vs. CC+CT: OR = 2.52, 95%CI = 1.25∼5.09, P = 0.010; respectively). Further subgroup analysis by ethnicity suggested that the MTHFR 677C>T polymorphism was associated with an elevated risk for CVD in ESRD patients among Asians (TT vs. CC: OR = 3.38, 95%CI = 1.11∼10.28, P = 0.032; CT+TT vs. CC: OR = 1.44, 95%CI = 1.05∼1.97, P = 0.022; TT vs. CC+CT: OR = 3.15, 95%CI = 1.02∼9.72, P = 0.046; respectively), but not among Africans or Caucasians (all P>0.05).

CONCLUSION

Our findings indicate that the MTHFR 677C>T polymorphism may be associated with an elevated risk for CVD in ESRD patients, especially among Asians.

Contribution of GSTM1, GSTT1, and MTHFR polymorphisms to end-stage renal disease of unknown etiology in Mexicans

Oxidative stress is increased in chronic kidney disease, owing to an imbalance between the oxidative and antioxidant pathways as well as a state of persistent hyperhomocysteinemia. The enzymes glutathione S-transferases (GSTs) and methylenetetrahydrofolate reductase (MTHFR) are implicated in the regulation of these pathways. This study investigates the association between polymorphisms in the Glutathione S-transferase Mu 1 (GSTM1), glutathione S-transferase theta 1 (GSTT1), and MTHFR genes and end-stage renal disease (ESRD) of unknown etiology in patients in Mexico. A Case-control study included 110 ESRD patients and 125 healthy individuals. GSTM1 and GSTT1 genotypes were determined using the multiplex polymerase chain reaction (PCR). The MTHFR C677T polymorphism was studied using a PCR/restriction fragment length polymorphism method. In ESRD patients, GSTM1 and GSTT1 null genotype frequencies were 61% and 7% respectively. GSTM1 genotype frequencies differed significantly between groups, showing that homozygous deletion of the GSTM1 gene was associated with susceptibility to ESRD of unknown etiology (P = 0.007, odds ratios = 2.05, 95% confidence interval 1.21-3.45). The MTHFR C677T polymorphism genotype and allele distributions were similar in both groups (P > 0.05), and the CT genotype was the most common genotype in both groups (45.5% and 46.6%). Our findings suggest that the GSTM1 null polymorphism appears to be associated with the ESRD of unknown etiology in patients in Mexico.

Prevalence of methylenetetrahydrofolate gene (MTHFR) C677T polymorphism among chronic hemodialysis patients and its association with cardiovascular disease: a cross-sectional analysis

INTRODUCTION

Cardiovascular disease (CVD) remains the main cause of morbidity and mortality in end stage renal disease (ESDR) patients. A common C-T mutation at nucleotide position 677 (C677T) has been identified in the gene coding for methylenetetrahydrofolate reductase (MTHFR), which is involved in the remethylation of homocysteine (Hcy). The C677T mutation decreases MTHFR activity, tends to increase Hcy concentrations in individuals who are homozygous for the T/T genotype, and may predispose to CVD. Recent reports suggested that the T/T genotype may predispose type 2 diabetic and hypertensive patients to the development of progressive renal insufficiency. The aim of this cross-sectional study is to analyze the prevalence of the MTHFR C677T gene polymorphism among a group of chronic dialysis patients in comparison to age- and gender-matched controls. We also examined the possible association between CVD and MTHFR gene mutation in this group of patients.

PATIENTS AND METHODS

Fifty chronic hemodialysis patients were included in the study. They were 29 males and 21 females with a mean age of 41.57 +/- 11.76 years. Three patients (6%) were diabetic (type 2). Mean duration of dialysis was 6.4 +/- 3.2 years (range 1-15 years). CVD was defined as being present if there was a medical history of coronary artery disease, cerebrovascular stroke or transient ischemic attacks. MTHFR C677T gene polymorphism was analyzed by PCR in order to discriminate between homozygous (C/C and T/T) and heterozygous (C/T) genotypes. We also measured serum vitamin B(12), folate, total plasma Hcy (tHcy), lipid profile and serum albumin concentrations in the study group. Thirty healthy subjects (16 males and 14 females with mean age of 37.42 +/- 7.63 years) served as healthy controls.

RESULTS

Thirteen patients (26%) experienced at least one cardiovascular event: two (4%) had a history of ischemic cerebrovascular disease, 13 (26%) had coronary artery disease, and one patient (2%) had myocardial infarction. The C677T mutation of MTHFR was not found to be different in hemodialysis patients and healthy controls. Thirty dialysis patients (60%) and 19 healthy subjects (63.33%) had only the wild-type allele (C/C), 16 dialysis patients (32%) and nine healthy controls (30%) had one T allele (C/T), and four dialysis patients (8%) and two healthy controls (6.67%) had two copies (T/T) of the T allele. There were no differences between patients with the three different MTHFR genotypes (C/C, C/T, T/T) regarding cardiovascular events or cardiovascular risk factors. Age, gender, percentages of diabetic and hypertensive patients, serum folate, vitamin B(12), lipid profile, and tHcy levels were not significantly different between the three groups (P > 0.05). Hemodialysis patients with CVD were significantly older compared to those without CVD (P = 0.02). Diabetes status was significantly associated with cardiovascular events (P = 0.01).

CONCLUSIONS

In the dialysis population that we studied, MTHFR C677T gene polymorphism occurred in a pattern similar to that seen for age- and gender-matched healthy controls. No significant association was detected between the T/T genotype and CVD in dialysis patients. Plasma total homocysteine levels were not affected by mutation of the gene coding for MTHFR, and this may be explained by the normal serum folate and vitamin B(12) levels found in the study group.

Effect of the MTHFR C677T and A1298C polymorphisms on survival in patients with advanced CKD and ESRD: a prospective study

BACKGROUND

Abnormalities in the gene regulating methylenetetrahydrofolate reductase (MTHFR) are associated with increased homocysteine levels and increased mortality in normal and chronic kidney disease (CKD) populations.

STUDY DESIGN

Gene association study.

SETTING & PARTICIPANTS

This was a substudy of 677 patients from 21 Veterans Affairs medical centers participating in a randomized clinical trial (Homocysteinemia in Kidney and End-Stage Renal Disease [HOST]) of the effect on all-cause mortality of vitamin-induced lowering of plasma homocysteine levels. Of 677 patients, 213 (31%) were treated by using dialysis (end-stage renal disease [ESRD]) and 464 (69%) had a Cockcroft-Gault estimated creatinine clearance less than 30 mL/min (advanced CKD).

PREDICTOR

Polymorphisms C677T (rs1801133) and A1298C (rs1801131) of the MTHFR gene.

OUTCOMES

Unadjusted and adjusted all-cause mortality.

MEASUREMENTS

DNA was extracted from blood samples and amplified by means of polymerase chain reaction.

RESULTS

The adjusted hazard ratio in a recessive model of the relationship between the C677T polymorphism and all-cause mortality in all patients was 1.47 (95% confidence interval, 1.00 to 2.16; P = 0.05). In patients with ESRD with the mutant TT genotype, the adjusted hazard ratio for mortality in all patients was 2.27 (95% confidence interval, 1.07 to 4.84; P = 0.03); patients with advanced CKD showed a similar, although not significant, trend. The risk of myocardial infarction (P = 0.05) and composite risk of myocardial infarction, stroke, lower-extremity amputation, and mortality (P = 0.02) were greater in patients with ESRD with the mutant T allele at nucleotide 677. The overall relationship between the A1298C polymorphism and mortality was not significant (P = 0.6).

LIMITATIONS

Participants were 98% men; DNA samples were not obtained at enrollment in HOST; linkage disequilibrium with another causal polymorphism is a potential confounding factor; and power was reduced by the limited number of participants.

CONCLUSIONS

These findings provide additional support for the hypothesis that the mutant TT genotype at nucleotide 677 of the gene regulating MTHFR activity may increase the mortality risk in patients with ESRD.

5-methyltetrahydrofolate administration is associated with prolonged survival and reduced inflammation in ESRD patients

BACKGROUND

Hemodialysis (HD) patients have a greatly increased risk of cardiovascular morbidity and mortality. For this reason, attempts are often made to normalize hyperhomocysteinemia. This randomized prospective study sought to determine which risk factors are predictors of mortality and whether high doses of folates or 5-methyltetrahydrofolate (5-MTHF) could improve hyperhomocysteinemia and survival in HD patients.

METHODS

341 patients were divided into two groups: group A was treated with 50 mg i.v. 5-MTHF, and group B was treated with 5 mg/day oral folic acid. Both groups received i.v. vitamin B(6) and B(12). By dividing patients into C-reactive protein (CRP) quartiles, group A had the highest survival for CRP <12 mg/l, whereas no survival difference was found for group B. CRP was the only predictive risk factor for death (RR 1.17, range 1.04-1.30, p = 0.02). Dialysis age, hyperhomocysteinemia, methylenetetrahydrofolate reductase polymorphism, albumin, lipoprotein (a) and folate did not influence mortality risk. Survival in group A was higher than that in group B, namely 36.2 +/- 20.9 vs. 26.1 +/- 22.2 months (p = 0.003).

RESULTS

Our results suggest that CRP, but not hyperhomocysteinemia, is the main risk factor for mortality in HD patients receiving vitamin supplements. Intravenous 5-MTHF seems to improve survival in HD patients independent from homocysteine lowering.

Pharmacogenetic study of methylenetetrahydrofolate reductase and thymidylate synthase in Japanese and assessment of ethnic and gender differences

OBJECTIVES

We investigated the four polymorphisms of the 5,10-methylenetetrahydrofolate reductase (MTHFR) and thymidylate synthase (TYMS) genes that are related to the pharmacologically active sites of methotrexate for the treatment of rheumatoid arthritis in 102 healthy Japanese adults and assessed the possibility of ethnic and gender differences.

METHODS

Polymorphisms of MTHFR C677T, A1298C, the two or three 28-bp tandem repeats in the TYMS 5'-untranslated regions (UTR), and the 6-bp deletion/insertion in the TYMS 3'-UTR were measured using polymerase chain reaction with restriction fragment length polymorphism method. Published data on allelic frequencies by ethnic group and gender were collected from Medline.

RESULTS

Allelic frequencies in healthy Japanese adults were: MTHFR 677T allele 41%, MTHFR 1298C allele 22%, TYMS 5'-UTR 3R allele 84%, and TYMS 3'-UTR-6-bp allele 59%. Significant differences were found in the distribution of MTHFR C677T between black and Japanese populations, of TYMS 5'-UTR alleles between Caucasian or black and Japanese populations, and of TYMS 3'-UTR alleles between Caucasian and Japanese populations (p < 0.001). Moreover, a gender difference was found in TYMS 3'-UTR allelic frequency in Japanese (p = 0.015).

CONCLUSION

Ethnic and gender variations in the distribution of these allelic frequencies may associate with the difference in the effects of methotrexate in rheumatoid arthritis patients.

MTHFR A1298C polymorphism is associated with cardiovascular risk in end stage renal disease in North Indians

The methylenetetrahydrofolate reductase (MTHFR) C677T gene polymorphism has been shown to be associated with cardiovascular disease and in patients with end-stage renal disease (ESRD). However, the relationship between MTHFR polymorphisms and cardiovascular disease (CVD) in patients on hemodialysis has not been examined. The aim of this study was to assess the association of polymorphisms of MTHFR gene with homocysteine (Hcy) and intimal medial thickness (IMT) in patients on hemodialysis. We performed case-control study involving107 patients with ESRD and 103 healthy controls. Plasma Hcy was measured in all the subjects and these subjects were genotyped for three MTHFR polymorphisms (C677T, A1298C, and G1793A). We observed significantly higher Hcy levels in patients as compared to controls. The frequency of MTHFR 1298CC genotype was significantly higher in ESRD patients than in controls (21.4% vs. 2.9%); the frequency of the MTHFR C677T genotypes did not differ between groups (26.1% vs. 17.4%). Compound heterozygous MTHFR 677CT/1298AC genotypes showed maximum association with the risk of ESRD (OR: 12.8; 5%CI: 1.64-10.01, P < 0.05). Concurrent occurrence of MTHFR 677CC wild genotype with either 1298CC or 1793GA significantly increased the risk of disease (OR: 7.20; 95%CI: 2.06-2.51, P < 0.001 and OR: 7.60; 95%CI: 1.68-34.35; P < 0.05, respectively). MTHFR 1298CC genotype was associated with higher Hcy levels. IMT was also significantly higher in patients with the 1298CC genotype (P < 0.05). Thus, A1298C polymorphism of MTHFR gene appears to be associated with the severity of carotid atherosclerosis and co-occurrence of MTHFR polymorphisms may be a risk factor for CVD in patients on hemodialysis.

The C677T methylenetetrahydrofolate reductase gene mutation does not influence cardiovascular risk in the dialysis population: results of a multicentre prospective study

BACKGROUND

Although the methylenetetrahydrofolate reductase (MTHFR) C677T gene polymorphism has been identified as an independent cardiovascular risk factor (CRF) in the general population and among uraemic subjects, the validity of this association remains controversial.

METHODS

To verify this hypothesis, we enrolled all subjects on maintenance dialysis treatment from a specific Italian district. We also enrolled, from the same area, 1307 subject to serve as controls. Genomic DNA was obtained and MTHFR C677T gene polymorphisms were determined. After a baseline evaluation, patients were followed-up for 37+/-13 months, and all cardiovascular events and causes of mortality were recorded.

RESULTS

A total of 461 patients (417 on haemodialysis and 44 on peritoneal dialysis) were investigated, and these included patients with and without cardiovascular diseases at baseline. At enrollment, mean age was 58.8+/-15.6 years and dialytic age was 82+/-69 months. Genotype frequencies were not different between controls and uraemics. During the follow-up, the mean mortality rate was 8.81%/year, with cardiovascular events as the most frequent cause of death (n = 68, 56.6%). There was no relationship between the MTHFR genotype and cardiovascular morbidity, overall mortality or cardiovascular mortality.

CONCLUSIONS

In end-stage renal disease, MTHFR C677T polymorphisms were not associated with cardiovascular disease or mortality.

Homocysteine, folate, vitamin B12 levels, and C677T MTHFR mutation in children with renal failure

Hyperhomocysteinemia is well documented in chronic renal failure (CRF) and premature and progressive occlusive vascular disease is common in CRF. The combined effects of renal failure, folate and vitamin B(12) levels, and a common mutation (C677T) in the methylenetetrahydrofolate reductase (MTHFR) gene that leads to total plasma homocysteine (tHcy) elevation in CRF children were investigated. Forty-two children (15 females) with CRF, mean age 10.3+/-4.7 years, were included. The mean glomerular filtration rate (GFR) was 37.3+/-16.9 ml/min per 1.73 m(2). The control group comprised 33 children (18 females) with a mean age of 8.6+/-3.4 years. There were 40% of CRF patients with hyperhomocysteinemia. Folate and vitamin B(12) deficiencies were identified in 14% (n=6) and 5% (n=2), respectively, of all patients. On univariate analysis, the tHcy serum concentration was negatively correlated with the plasma folate concentration (P<0.05) in controls, and with GFR (P<0.05) in patients. On multiple regression analysis for the predictors of tHcy serum concentrations, folic and vitamin B(12 )were significant in controls, whereas only GFR was significant in CRF children. In our patients no effect of the MTHFR polymorphism on tHcy levels was seen This result, in addition to the limited number of patients, may partially be explained by the low prevalence of folate deficiency in our patients.

The methylentetrahydrofolate reductase C677T point mutation is a risk factor for vascular access thrombosis in hemodialysis patients

BACKGROUND

Many reports indicate that a high homocysteine (Hcy) level is a potential risk factor for such thrombotic diseases as arteriosclerosis, myocardial infarction, and cerebral infarction in healthy individuals or hemodialysis (HD) patients. The methylentetrahydrofolate reductase (MTHFR) C677T polymorphism has been reported to be closely related to plasma Hcy level.

METHODS

Using a cross-sectional design in this study, the relationship between arteriovenous fistula (AVF) obstruction and the MTHFR C677T point mutation was examined in 337 HD patients.

RESULTS

Results of multivariate analysis showed no significant influence of age, HD therapy duration, sex, or the presence of diabetes mellitus, cerebral infarction, or myocardial infarction. Only the presence of the MTHFR C677T polymorphism yielded a significant difference. Percentages of patients who experienced AVF obstruction were as follows: CC (12.6%), CT (20.3%), and TT (31.8%). The number of those who experienced obstruction was significantly larger with the TT than CC (P < 0.01). Moreover, total obstruction episode ratios were as follows: CC, 1 in 107.21 episodes/patient-month; CT, 1 in 74.08 episodes/patient-month; and TT, 1 in 50.33 episodes/patient-month. Episode percentages tended to be greater when the degree of mutation was greater, and a significant difference was observed between the CC and TT alleles (P < 0.01).

CONCLUSION

Although AVF obstruction is affected by numerous factors, there was a strong relationship between MTHFR C677T mutation and AVF obstruction. These findings suggest that the MTHFR C677T point mutation could serve as an important indicator in identifying susceptibility to AVF obstruction.

Polymorphisms in the methylenetetrahydrofolate reductase gene: clinical consequences

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

Methylenetetrahydrofolate reductase genotype, vitamin B12, and folate influence plasma homocysteine in hemodialysis patients

Hyperhomocysteinemia, a well-recognized cardiovascular risk factor, is frequent in hemodialysis (HD) patients. A common polymorphism in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene, C-->T substitution at nucleotide 677, is associated with homocysteine (Hcy) level elevation. We examined whether three factors involved in the methionine cycle could influence plasma Hcy concentrations in HD patients: MTHFR polymorphism; vitamin B12, an essential cofactor; and folate, the substrate. In a cross-sectional study, serum vitamin B12, folate, and plasma Hcy were measured and MTHFR genotyping was performed in 534 HD patients. Effects of MTHFR genotypes, vitamin B12, and folate on plasma Hcy levels were examined in 450 HD patients not administered vitamin B12 or folate. To examine the effect of vitamin B12 on plasma Hcy concentrations, we compared plasma Hcy concentrations in HD patients with and without vitamin B12 supplementation. To examine whether functional vitamin B12 deficiency exists even in HD patients with normal vitamin B12 concentrations, 15 HD patients (serum vitamin B12 concentrations, 250 to 2,100 pg/mL) were treated with vitamin B12 (mecobalamin, 1.5 mg/d) for 8 weeks. Serum concentrations of methylmalonic acid (MMA) and vitamin B12 were measured. Hcy levels were higher and folate levels were lower in patients with the TT and CT genotypes compared with patients with the CC genotype. Analysis of covariance to determine independent predictors of high Hcy levels identified low serum vitamin B12 and folate levels and high albumin (Alb) levels in CC-genotype patients, low folate levels and high Alb levels in CT-genotype patients, and low folate levels in TT-genotype patients. Plasma Hcy levels were lower in CC- and CT-genotype patients with vitamin B12 supplementation than in those without supplementation. Vitamin B12 supplementation for 8 weeks significantly reduced MMA concentrations in HD patients with normal serum vitamin B12 concentrations. These results indicate that MTHFR genotype influences the correlation of Hcy level with vitamin B12 and folate levels in HD patients. Functional vitamin B12 deficiency may exist, even in HD patients with normal vitamin B12 concentrations. The efficacy of vitamin B12 and folate supplementation on plasma Hcy levels may depend on MTHFR genotype.

Hyperhomocysteinaemia, folate and vitamin B12 in unsupplemented haemodialysis patients: effect of oral therapy with folic acid and vitamin B12

BACKGROUND

Hyperhomocysteinaemia, a risk factor for atherosclerosis, is common in dialysis patients and particularly in those homozygous for a common polymorphism in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene (C677T transition). B-complex vitamin supplements have been shown to lower plasma total homocysteine (tHcy) concentrations, but the respective effectiveness of folate and oral vitamin B12 is not yet known. Our objectives were: (i) to determine the status of folate and vitamin B12 in a cohort of unsupplemented dialysis patients (ii) to assess the homocysteine-lowering effect of a folate supplement and then of a folate supplement with added vitamin B12. The responses were analysed for the C677T genotypes of MTHFR.

METHODS

Plasma tHcy, folate and vitamin B12 were measured in 51 haemodialysis patients genotyped for the C677T MTHFR mutation (homozygotes, TT; heterozygotes, CT; without mutation, CC). All patients were then given daily supplements of 15 mg of folic acid for 2 months. They were given daily supplements of 1 mg of vitamin B12 in addition to the folate supplements for a further 2 months. Plasma tHcy, folate and vitamin B12 were monitored after each intervention.

RESULTS

At baseline folate and vitamin B12 deficiencies were found in 10% and 6% of the patients. Initial plasma tHcy concentrations were high in all patients (mean 38.1+/-15 micromol/l). CC patients tended to have a lower tHcy concentration than pooled CT and TT patients. After 2 months of folate therapy, tHcy concentration decreased significantly to 20.2+/-7 micromol/l (P<0.001) and no significant differences were observed between the different genotype subgroups (19.4+/-6 for CC, 21.3+/-8 for CT, 18.5+/-4 for TT). A significant positive relationship was found between the reduction of tHcy and its initial value (rho=0.615, P<0.0001). The impact of the added vitamin B12 was negligible since tHcy concentrations did not change for the patients as a whole (19.8+/-7 micromol/l, NS) or in any subgroup (19.1+/-5 for CC, 20.3+/-9 for CT and 20+/-7 micromol/l for TT).

CONCLUSIONS

(i) Folate and vitamin B12 deficiencies were observed in 10% and 6% respectively of our unsupplemented dialysis patients. (ii) After folate therapy, tHcy levels decreased significantly in all patients and were identical between the three C677T MTHFR genotype subgroups. (iii) Vitamin B12 supplements are useful in folate treated patients to prevent cobalamin deficiency and its neurological consequences but they did not lower tHcy plasma levels for the patients as a group or for any of the MTHFR subgroups.

Increased prevalence of combined MTR and MTHFR genotypes among individuals with severely elevated total homocysteine plasma levels

The prevalence of the methionine synthase (MTR) 2756A-->G polymorphism among individuals with severely elevated total homocysteine (tHcy) plasma levels is unknown. Therefore, 1,716 subjects, including 415 hemodialysis patients, 179 peritoneal dialysis patients, 733 kidney graft recipients, and 389 healthy subjects, were investigated. The distribution of MTR 2756A-->G, as well as 5,10-methylenetetrahydrofolate reductase (MTHFR) 677C-->T/1298A-->C, genotypes among study participants with extremely high tHcy plasma levels (>90th percentile) was compared with the genotype distribution of subjects with very low tHcy plasma levels (<10th percentile). The prevalence of MTR 2756AG and GG genotypes alone did not differ between individuals with extremely high or extremely low tHcy levels (P = 0.7402; odds ratio [OR], 1.076; 95% confidence interval [CI], 0.697 to 1.662). Conversely, combined MTR and MTHFR genotypes (MTR 2756AG and 2756GG and MTHFR 677TT/1298AA and 677CT/1298AC) were found more often in the highest (n = 34) compared with the lowest plasma tHcy decile (n = 19; P = 0.0252; OR, 1.983; 95% CI, 1.079 to 3.643). The number of patients with the wild-type MTR and MTHFR genotype was three times greater in the lowest compared with the highest decile (17 versus 6 patients, respectively; P = 0.0155; OR, 0.330; 95% CI, 0.126 to 0.861). In summary, our study shows that the 2756A-->G transition of MTR in combination with MTHFR 677TT/1298AA and 677CT/1298AC can be associated with extremely high tHcy plasma levels.

An MTHFR variant, homocysteine, and cardiovascular comorbidity in renal disease

BACKGROUND

It is unclear whether total serum homocysteine (tHcy) and the C677T mutation of methylenetetrahydrofolate reductase (MTHFR) are associated with cardiovascular disease (CVD) in patients with end-stage renal disease (ESRD).

METHODS

A cross-sectional sample of 459 patients with ESRD on chronic dialysis was assessed to determine whether tHcy and the C677T mutation are associated with CVD prevalence in multiple logistic regression. As CVD mortality is high, we examined the relationship between homozygosity and duration of dialysis.

RESULTS

Mean tHcy was higher in patients without a history of CVD (35.2 micromol/L vs. 30.4 micromol/L, P = 0.02). In multivariate models, CVD was negatively associated with tHcy and positively associated with TT genotype, male gender, and body mass index. Mean tHcy levels were higher among those with the TT genotype compared with those with the CC genotype when adjusted for age, folate, creatinine, and albumin (37.9 micromol/L vs. 31.9 micromol/L, P = 0.005). Among whites, the prevalence of the TT genotype was higher in those having undergone less than one year of dialysis (P = 0.002).

CONCLUSIONS

The C677T genotype of MTHFR is associated with CVD in ESRD and may be a more meaningful marker than tHcy for abnormal homocysteine metabolism in ESRD. Prospective data from ongoing clinical trials are needed to improve our understanding of these findings. Screening for this polymorphism may help guide prevention measures.

Hyperhomocysteinemia is related to residual glomerular filtration and folate, but not to methylenetetrahydrofolate-reductase and methionine synthase polymorphisms, in supplemented end-stage renal disease patients undergoing hemodialysis

Glomerular filtration is one of the major determinants of plasma total homocysteine (tHcy). To evaluate the respective roles of residual glomerular filtration (by measuring a specific protein marker, cystatin C), genetic polymorphisms and nutritional status in tHcy blood levels in end-stage renal disease patients (ESRD) under hemodialysis and supplemented with folate, we measured tHcy, folate, vitamin B12 (B12), creatinine, cystatin C, albumin and C-reactive protein and determined the polymorphism of methylenetetrahydrofolate reductase (MTHFR) (C677T and A1289C) and of methionine synthase (MS) (A2756G) in 114 ESRD patients before hemodialysis and 76 control subjects. All patients received a folate supplementation of 700 microg/day. Hyperhomocysteinemia was observed in all patients and exceeded the upper normal limit by 2-fold in 52.4% of the patients. Serum folate was significantly increased and the B12 level was not different from controls. Folate, Cystatin C and creatinine were significantly correlated to tHcy, while no correlation was found between tHcy, albumin and C-reactive protein. No difference in genotype frequency between ESRD patients and controls was found for MTHFR A1289C and MS A2756G. The MTHFR 677TT genotype was less frequent and was associated with a significantly higher tHcy level in patients. Folate and residual glomerular filtration estimated by cystatin C and creatinine levels were two independent determinants of tHcy in ESRD patients. These data suggest that hyperhomocysteinemia is a consequence as well as a complicating factor of renal failure.

Association of two MTHFR polymorphisms with total homocysteine plasma levels in dialysis patients

The effect of the combined 5,10-methylenetetrahydrofolate reductase (MTHFR) 677C-->T and 1298A-->C genotype on total homocysteine (tHcy), folate, and vitamin B(12) plasma levels was investigated in 983 subjects, including 415 hemodialysis patients, 179 peritoneal dialysis patients, and 389 healthy individuals. Mean tHcy plasma concentrations were 27.2 +/- 15.8 micromol/L in hemodialysis patients, 25.4 +/- 19.1 micromol/L in peritoneal dialysis patients, and 8.9 +/- 3.5 micromol/L in healthy individuals. Hyperhomocysteinemia (tHcy > 15 micromol/L) was detected in 81.6% of patients and 2.6% of controls. Multiple stepwise regression analysis showed that the MTHFR 677C-->T/1298A-->C genotype (CC/AA, CC/AC, CC/CC, CT/AA, CT/AC, TT/AA), vitamin use, age, folate and vitamin B(12) plasma level were significant predictors of tHcy plasma levels. Analysis of variance showed that this effect of MTHFR genotypes on tHcy level was caused by significantly greater tHcy levels in 677TT/1298AA hemodialysis and peritoneal dialysis patients versus other genotypes. Compound heterozygous controls (677CT/1298AC genotype) had significantly greater tHcy levels compared with 677CC/1298AA controls. There was no major effect of MTHFR polymorphisms on folate and vitamin B(12) plasma concentrations. This study shows that the MTHFR 677TT/1298AA genotype, but not the 677CT/1298AC genotype, is a significant predictor of tHcy plasma levels in dialysis patients.

Biological and clinical implications of the MTHFR C677T polymorphism

The enzyme methylenetetrahydrofolate reductase (MTHFR) directs folate species either to DNA synthesis or to homocysteine (Hcy) remethylation. The common MTHFR C677T polymorphism affects the activity of the enzyme and hence folate distribution. Under conditions of impaired folate status, the homozygous TT genotype has been regarded as harmful because it is associated with a high concentration of plasma total Hcy, increased risk of neural tube defects and colorectal neoplasias, and can also predispose individuals to adverse effects from drugs with antifolate effects. The MTHFR C677T polymorphism shows no consistent correlation with cardiovascular risk and longevity but, in combination with positive folate balance, the TT genotype is associated with decreased risk of colorectal neoplasias. Because of the high prevalence of this polymorphism in most populations, the TT variant might represent an ancestral genetic adaptation to living constraints (tissue injury or unbalanced vitamin intake) that has become a determinant of disease profiles in modern times.

Recent insights into the molecular genetics of the homocysteine metabolism

The homocysteine plasma level is determined by non-genetic and genetic factors. In recent years evidence has accumulated that the total homocysteine plasma level of patients under different forms of renal replacement therapy is influenced by a common mutation at nucleotide position 677 of the gene coding for 5,10-methylenetetrahydrofolate reductase (MTHFR 677C-->T). Furthermore, compound heterozygosity for the 677T allele and a novel A-->C polymorphism at nucleotide position 1298 of MTHFR is suggested to correlate with a decrease of folate plasma concentrations. Because polymorphisms of genes coding for proteins involved in the metabolism of homocysteine may contribute to elevated total homocysteine plasma concentrations, molecular genetic analyses of the homocysteine pathways experienced a drift towards screening for candidate genes with a putative relationship to total homocysteine plasma levels. One example is the cloning of the FOLR1 gene coding for the folate-binding protein (Folbp1), which has recently been inactivated in mice, thus representing an elegant model to investigate the consequence on the homocysteine metabolism. Furthermore, the recent characterization of the CUBN gene encoding the intrinsic factor-vitamin B12 receptor (cubilin) provides a basis to identify the causative mutations in patients suffering from a hereditary syndrome of hyperhomocysteinemia that presents with megaloblastic anemia and proteinuria. This review focuses on recent insights into the molecular genetics of MTHFR, FOLR1, and CUBN, and their relationships to the metabolism of the amino acid homocysteine.

Therapeutic potential of total homocysteine-lowering drugs on cardiovascular disease

An elevated total homocysteine (tHcy) plasma concentration is associated with increased morbidity and mortality due to cardiovascular disease in the general population and in patients with impaired renal function. The prevalence of hyperhomocysteinaemia (plasma levels above 15 micromol/l) in the general population is less than 5% and can be as high as 50% in patients with vascular disease. In patients with renal insufficiency, elevated tHcy plasma levels are detected in 50 - 100% of the patients. Total homocysteine plasma levels can be lowered or normalised by folic acid and/or vitamin B(6) and vitamin B(12) supplementation. In patients with advanced chronic renal insufficiency or end-stage renal disease, hyperhomocysteinaemia is partially resistant to folic acid or vitamin therapy. However, higher tHcy plasma levels may also reflect tissue damage and the increase in Hcy after an acute incident such as stroke or myocardial infarction may be necessary for tissue repair mechanisms. This implies, that lowering tHcy may even be harmful to some patients. Currently, prospective studies are underway to clarify whether folate supplementation, with or without additional other vitamins, improves cardiovascular disease morbidity and mortality in the general population, as well as in renal failure patients. While population-wide screening for and treatment of hyperhomocysteinaemia is generally not recommended, treatment of high risk patients may be considered.