Post-methionine Load Homocysteine Research Articles

Abstract 3012: Significant Genome Wide Association Identified Between the Glycine N-Methyltransferase Gene (GNMT) and Post-Methionine Load Test Homocysteine Levels in the Vitamin Intervention for Stroke Prevention (VISP) Cohort

The Vitamin Intervention for Stroke Prevention (VISP) trial was a multi-center, controlled, double blinded clinical trial, designed to determine whether the daily intake of high dose folic acid, vitamins B6 and B12 reduced recurrent cerebral infarction. Baseline post-methionine load homocysteine levels were predictive of recurrent stroke risk in VISP. We have conducted a genome-wide association study (GWAS), investigating 2100 VISP stroke cases required to have homocysteine levels greater than the 25th percentile at enrolment. Using imputation with 1000 genomes and principal component analysis, we were able to detect an association of p≤6.70x10-17 for SNPs within, or flanking, the glycine N-methyltransferase (GNMT) gene and post-methionine load test homocysteine level. Change in homocysteine levels pre and post-methionine load test also resulted in significant GWAS scores in the chromosome 6 region (p = 2.54x10-23, rs7760250). GNMT catalyzes the conversion of S-adenosyl-L-methionine to S-adenosyl-L-homocysteine and sarcosine via the folate one-carbon metabolism pathway. In addition to being an essential component in the conversion of methionine to homocysteine, GNMT plays a significant role in the global epigenetic state as homocysteine is an important methyl donor. This region displays significant linkage disequilibrium, warranting close analysis of the entire GNMT locus in search of both rare and common variants. Cases who carry the minor allele haplotype at associated loci had a higher level of post-methionine load homocysteine (37.69µM/L) than those who carry the major allele haplotype (27.33µM/L), inferring functional differences due to GNMT variants. Taken together these data suggest a clear and important role for GNMT in post-methionine load test homocysteine level, epigenetic state and stroke risk.

Dietary and supplementary betaine: Effects on betaine and homocysteine concentrations in males

Background and aims Betaine is an osmolyte that when catabolised decreases plasma total homocysteine. A betaine-rich meal has acute effects similar to a supplement, but the effects of a longer-term increase in dietary betaine intake need clarification. We compared the effects of two weeks of dietary and supplementary betaine on plasma betaine and homocysteine concentrations both fasting and after a methionine load. Methods and results In a randomized crossover study, 8 healthy males (22–36 y) consumed either a betaine-rich diet (∼800 mg/day) or a betaine supplement (0.5 g twice daily) for 14 days. Fasting blood samples were collected on day −5, −1 (pre-treatment) 0, 2, 6, 9, 13 (treatment), 14 and 18 (post-treatment). Post-methionine load blood samples were collected on day −5, 0, 6 and 13, while 24 h urine samples were collected on day −5, 0, 6, 13 and 14. Plasma betaine, dimethylglycine, homocysteine and urine betaine, dimethylglycine and creatinine concentrations were measured. Plasma betaine concentrations significantly increased for both treatments compared to pre-treatment values ( P < 0.001). Fasting homocysteine levels were minimally affected. Both treatments reduced post-methionine load homocysteine and this effect tended to be greater following a betaine-rich diet ( P = 0.108). Small increases in urinary betaine excretion were observed following both treatments (≈1.5% of supplement; ≈1.3% of dietary betaine). Most was attributable to increased excretion of betaine as dimethylglycine. Conclusions Supplemental or dietary betaine similarly increase circulating betaine concentrations and attenuate the post-methionine load rise in homocysteine concentrations.

B-vitamins, homocysteine and gene polymorphism in adults with fasting or post-methionine loading hyperhomocysteinemia

Although fasting and post-methionine loading (PML) homocysteine concentrations are not necessarily related, a high percentage of hyperhomocysteinemia cases would be missed if methionine loading was not performed. The influences of B-vitamins and genetic polymorphism (methylenetetrahydrofolate reductase 677C --> T, MTHFR 677C --> T) on fasting and PML homocysteine concentrations and the relationship between fasting and PML homocysteine were studied. This study was a cross-sectional study. Healthy subjects were divided into either fasting hyper-homocysteinemia (>or=12.2 micromol/l) (fasting hyper-hcy, n = 51), PML hyper-homocysteinemia (fasting homocysteine <12.2 micromol/l but PML homocysteine >or=25.6 micromol/l) (PML hyper-hcy, n = 29), or normo-homocysteinemia (fasting homocysteine <12.2 micromol/l and PML homocysteine <25.6 micromol/l) (normo-hcy, n = 118) group based on elevated fasting and PML homocysteine levels of the 75th percentile of the population. The concentrations of plasma fasting and PML homocysteine, serum folate, vitamin B-12, plasma pyridoxal 5'- phosphate (PLP) were measured. The genetic polymorphisms were determined. Fasting homocysteine, but not PML homocysteine and MTHFR 677C --> T genotype, was significantly and inversely affected by serum folate concentration after adjusting for potential confounders (beta = -0.062, P < 0.01). Fasting and PML homocysteine were highly associated in the fasting hyper-hcy and pooled groups (P < 0.01) but not in the PML hyper-hcy and normo-hcy groups. PML homocysteine did not interact with either serum folate (P = 0.302), vitamin B-12 (P = 0.465), plasma PLP (P = 0.996) or MTHFR 677C --> T genotype (P = 0.136) to affect fasting homocysteine concentration. Approximately one-third (36.3%) of hyperhomocysteinemia cases would be missed if methionine loading were not performed. Even though subjects may have a normal fasting homocysteine concentration, they need further screening for their PML homocysteine.

Post-methionine load test: A more sensitive tool to reveal hyperhomocysteinemia in Alzheimer patients?

Objective To identify the real number of hyperhomocysteinemic Alzheimer's patients who may benefit from homocysteine-lowering therapy. Methods Basal and post-methionine load homocysteine levels were assessed by rp-HPLC system. Results PML test revealed twice as many hyperhomocysteinemic AD subjects with respect to the fasting analysis. Conclusion PML test resulted useful in detecting higher number of hyperhomocysteinemic AD patients who may have the chance of an early folate treatment.

Assessment of pre- and post-methionine load homocysteine for prediction of recurrent stroke and coronary artery disease in the Vitamin Intervention for Stroke Prevention Trial

Assessment of pre- and post-methionine load homocysteine for prediction of recurrent stroke and coronary artery disease in the Vitamin Intervention for Stroke Prevention Trial

Assessment of pre- and post-methionine load homocysteine for prediction of recurrent stroke and coronary artery disease in the Vitamin Intervention for Stroke Prevention Trial

Methionine (Met) loading increases total plasma homocysteine (tHcy) and assesses homocysteine metabolism. We tested the hypothesis that pre- or post-Met tHcy will predict recurrent stroke or coronary artery disease (CAD) in a subgroup analysis of the Vitamin Intervention for Stroke Prevention (VISP) trial. VISP subjects with non-disabling stroke underwent measurement of tHcy at baseline (fasting pre- and post-Met load) and were randomized to high/low-dose B-vitamin therapy for prevention of recurrent stroke or CAD. In the sample cohort of 2124 subjects, mean ± S.D. tHcy levels in μmol/l were pre-Met 13.2 ± 4.3, post-Met 30.4 ± 9.76, and pre/post-Met Δ 17.1 ± 8.3. The hazard ratio (HR) for recurrent stroke was 1.16 ( p = 0.026) for 1 S.D. higher pre-Met tHcy and 1.15 ( p = 0.054) for 1 S.D. higher post-Met tHcy. For CAD, the HR for 1 S.D. higher pre-Met tHcy was 1.27 ( p = 0.001) and was 1.00 ( p = 0.99) for post-Met tHcy. In survival analyses using pre- or post-Met as covariates, the coefficient of pre/post-Met Δ was not significant for stroke and was only marginally significant for CAD ( p < 0.08), but was negative. We conclude that fasting, pre-Met tHcy is as effective as post-Met tHcy or pre/post-Met Δ in predicting the risk for stroke and CAD.

Low vitamin B6, and not plasma homocysteine concentration, as risk factor for abdominal aortic aneurysm: A retrospective case–control study

Hyperhomocysteinemia has been associated with vascular disease in many epidemiologic studies, but only a few have reported on the relation between hyperhomocysteinemia and aneurysms of the abdominal aorta (AAAs). Although these studies showed higher homocysteine concentrations in patients with AAA than in controls, little attention had been given to possible confounding factors. Most patients with AAA are of older age, have an impaired renal function, and have other risk factors for cardiovascular disease. This matched case-control study investigated the relation between homocysteine concentration (before and after methionine loading) and AAA, taking into account possible confounders such as age, sex, and concentrations of creatinine and B vitamins. Patients with a history of AAA were recruited from the outpatient clinic; 60% had already undergone surgery for their AAA. They were asked to invite a friend or neighbor to participate as a control subject (age-matched and sex-matched). Concentrations of homocysteine, vitamin B6, vitamin B12, folate, and creatinine were determined in the fasting state, and blood was taken for methylenetetrahydrofolate reductase (MTHFR) mutation analysis. Six hours after oral methionine loading, the postmethionine load homocysteine concentration was determined. Univariate analysis showed an odds ratio (OR) of 2.2 (95% confidence interval (CI), 0.9 to 5.5) for the risk of AAA for the highest quartile of homocysteine concentration. After adjustment for creatinine, the OR was markedly reduced to 1.24 (95% CI, 0.42 to 3.66), and this risk further attenuated in the multivariate analysis. Univariate analysis of the B vitamins showed an increased risk of AAA for the bottom quartile of vitamin B6 (OR, 3.75; 95% CI, 1.22 to 11.54), which even increased after adjustments. The relative risk associated with the MTHFR 677TT polymorphism was 2.1 (95% CI, 0.9 to 5.3). Vitamin B6, but not homocysteine, is an independent risk factor for AAA. The role of vitamin B6 in the pathogenesis of AAA needs to be further elucidated.

Metabolic and Genetic Risk Factors for Migraine in Children

Migraine can induce ischaemic stroke, and is considered an independent risk factor for stroke in the young. To date, the nature of the link between migraine and stroke is essentially unknown. Forty-five children were studied. Homocysteine levels (fasting and post methionine load), vitamin B12 and plasma folate levels, factor V Leiden, factor II G20210A, methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C mutations were examined. Compared with controls, patients with migraine had higher levels of post-methionine load homocysteine values (19.5 +/- 4.9 vs. 16.9 +/- 1.9; P = 0.025) and significantly lower folate levels (5.8 +/- 2.6 vs. 7.5 +/- 2.1; P = 0.002). We found a trend toward an increased risk of migraine in subjects carrying a homozygous mutant genotype for MTHFR C677T and MTHFR A1298C polymorphisms. Genetic prothrombotic conditions do not seem to be related to migraine in the young, whereas the biochemical differences between migrainous patients and controls are an appealing topic for further investigation.

Homocysteine levels – before and after methionine loading – in 51 Dutch families

Elevated levels of homocysteine are a risk factor for vascular disease, thrombosis, neural tube defects and dementia. The 677C>T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene appears to be the most important single determinant of plasma homocysteine concentration. In the current study, we estimated heritability and fit a series of models of inheritance for both fasting and postmethionine-load homocysteine levels in the HOFAM-study (HOmocysteine in FAMilies study), which included 306 participants from 51 pedigrees, ascertained through a hyperhomocysteinemic proband. The crude heritability was 21.6% for fasting and 67.5% for postloading homocysteine. After adjustment for MTHFR 677C>T genotype, heritability dropped to 5.2 and 63.9%, respectively. Segregation analysis revealed that a nongenetic model with equal transmission was the best fitting and most parsimonious model for fasting homocysteine levels, while a two-distribution, Mendelian model with residual familial correlation was best for postmethionine-load homocysteine levels. This study shows that postload homocysteine levels have a stronger genetic determination than do fasting homocysteine levels. The heritability of postload homocysteine levels were not strongly affected by adjustment for MTHFR 677C>T genotype, in contrast to fasting homocysteine levels. Further studies are needed to identify the genes responsible for the inheritance of postload homocysteine levels.

The 2756A>G variant in the gene encoding methionine synthase: its relation with plasma homocysteine levels and risk of coronary heart disease in a Dutch case-control study

Introduction: Elevated plasma homocysteine levels have been associated with increased risk of cardiovascular disease. A 2756A>G polymorphism has been found in the gene ( MTR) coding for methionine synthase, an enzyme catalyzing remethylation of homocysteine to methionine. Materials and methods: In a Dutch case-control study comprising 123 cases with coronary heart disease (CHD) and 540 controls, we evaluated whether the MTR 2756A>G polymorphism was associated with plasma homocysteine, vitamin B 12, folate concentrations, and CHD risk. Results and conclusions: The polymorphism was not associated with fasting or post-methionine load homocysteine concentrations. Individuals with the GG genotype had 30% lower vitamin B 12 concentrations than individuals with AA or AG genotype ( P<0.05). After adjustment for CHD risk factors, the odds ratio (OR) of CHD was 4.0 (95% CI 1.4–11.6) for the GG genotype and 0.7 (95% CI 0.4–1.2) for the AG genotype, when compared to the AA genotype. In conclusion, despite the absence of an association with plasma homocysteine, the GG genotype represented a four-fold increased risk of CHD when compared to the AA genotype. Before putting effort in additional epidemiological studies, it needs to be established first whether this polymorphism has functional consequences for enzyme activity.

A Pilot Study of Vitamins to Lower Plasma Homocysteine Levels in Alzheimer Disease

OBJECTIVE Authors determined the impact of high-dose vitamin supplements on plasma homocysteine levels in patients with Alzheimer disease (AD). METHODS Authors used an open-label trial of folic acid, vitamin B12, and vitamin B6, in combination for 8 weeks, with measurement of plasma homocysteine levels in the fasting state and after methionine-loading. A total of 69 subjects with AD were enrolled, including 33 who were taking standard multivitamin supplements; 66 were available at 8-week follow-up. RESULTS The high-dose vitamin regimen was associated with a significant reduction in fasting and post–methionine-loading homocysteine. Reductions were greater in the subgroup not using multivitamins, but were also significant in the multivitamin users. CONCLUSION High-dose vitamin supplementation reduces homocysteine levels in patients with AD. The effect of supplementation on rate of cognitive decline will be assessed later in a randomized, double-blind study. Authors determined the impact of high-dose vitamin supplements on plasma homocysteine levels in patients with Alzheimer disease (AD). Authors used an open-label trial of folic acid, vitamin B12, and vitamin B6, in combination for 8 weeks, with measurement of plasma homocysteine levels in the fasting state and after methionine-loading. A total of 69 subjects with AD were enrolled, including 33 who were taking standard multivitamin supplements; 66 were available at 8-week follow-up. The high-dose vitamin regimen was associated with a significant reduction in fasting and post–methionine-loading homocysteine. Reductions were greater in the subgroup not using multivitamins, but were also significant in the multivitamin users. High-dose vitamin supplementation reduces homocysteine levels in patients with AD. The effect of supplementation on rate of cognitive decline will be assessed later in a randomized, double-blind study.

Low diagnostic value of fasting and post-methionine load homocysteine tests. A study in Dutch subjects with homocysteine test indications

Background: Homocysteine is a cardiovascular disease risk factor. We investigated, both in subjects with past plasma total homocysteine (tHcy) test indications and healthy adults, the diagnostic value of a fasting (tHcy) (f-tHcy) and the added value of a post-methionine-load tHcy (postload-tHcy). Methods: Plasma homocysteine cut-off values were retrospectively used for hyperhomocysteinemia assessment in 3477 subjects with past tHcy test indications and 177 apparently healthy subjects. Cut-off values were based on reference limits (f-tHcy≤15.0; postload-tHcy≤50.0 μmol/l), relative risk (f-tHcy≤12.0, postload-tHcy≤38.0; or f-tHcy≤10.0 μmol/l) and vitamin-optimized reference limits (f-tHcy≤9.3; postload-tHcy≤35.1 μmol/l). Results: Use of the American Heart Association 10 μmol/l f-tHcy cut-off value gave hyperhomocysteinemia prevalences of 65% in subjects with past tHcy test indications and 50% in healthy subjects. The combination of the vitamin-optimized reference limits for f-tHcy and postload-tHcy gave a hyperhomocysteinemia prevalence of 79% in subjects with tHcy test indications, of which only 5% was on account of increased postload-tHcy. Corresponding values for healthy subjects were 68% and 3%, respectively. Conclusions: Employment of a 10 μmol/l (American Heart Association) or 9.3 μmol/l (vitamin-optimized reference) cut-off value leaves no indications for tHcy testing from an evidence-based point-of-view.

Variability of post-methionine load plasma homocysteine assays

Background: Numerous variations of the methionine load test are frequently used as dynamic function tests to assess homocysteine metabolism. Lack of standardization impedes inter-laboratory comparisons. Criteria based on biological variation are suggested to standardize the methionine load test. Methods: Weekly methionine load tests ( n=5) with blood sampling at 0, 4, 6 and 8 h were performed on 15 young men. For both basal and post-methionine load homocysteine measurements, total variance ( σ S 2), within-subject variance ( σ I 2), between-subject variance ( σ G 2) and analytical variance ( σ A 2) were calculated from an appropriate analysis of variance (ANOVA). Results: Plasma homocysteine concentrations measured 6 h after methionine loading had analytical, within-subject and between-subject coefficients of variation of 5.2%, 17.5% and 9.7%, respectively. Measurements at 4 h had a higher within-subject coefficient of variation. Adjustment of post-methionine load homocysteine concentrations for basal levels resulted in considerable increases of all the measures of variation. Conclusions: Adjustment of post-methionine load plasma homocysteine concentrations for basal levels does not improve the interpretation of changes in serial results due to the higher analytical and biological variance of adjusted concentrations. It is suggested that the methionine load test is standardized to a single, unadjusted homocysteine measurement at 6 h.

Cystathionine beta-synthase polymorphisms and hyperhomocysteinaemia: an association study.

Hyperhomocysteinaemia is generally accepted as an independent and graded risk factor for both arterial occlusive disease and venous thrombosis. The only way of homocysteine degradation is conversion to cysteine in the transsulfuration pathway in which the regulating step is catalysed by cystathionine beta-synthase (CBS). Mild impairment of CBS function could therefore affect homocysteine concentration, in particular after methionine loading, and consequently cardiovascular disease (CVD) risk. We analysed two silent polymorphisms and one short tandem repeat in the CBS gene (ie 699C-->T, 1080C-->T and -5697 (GT) STR) as genetic markers potentially in linkage disequilibrium with a functional polymorphism. We assessed their association with fasting and post-methionine load homocysteine in 190 patients with arterial occlusive disease, and in 381 controls. No differences in CBS genotype frequencies between cases and controls were found, nor was a particular CBS genotype associated with an elevated risk of arterial occlusive disease. Although we did find a high rate of linkage disequilibrium between the two single nucleotide polymorphisms and the GT STR, none of the genotypes defined by the three CBS variants studied showed an association with elevated fasting, post-load or increase upon methionine loading homocysteine concentrations. In conclusion, we did not find any indication that genetic variation in the CBS gene is associated with increased homocysteine concentrations.

Hyperhomocysteinemia is associated with low plasma pyridoxine levels in children with sickle cell disease.

Elevated plasma homocysteine levels have been shown to be a risk factor for endothelial cell damage and thrombosis, which are implicated in sickle cell disease (SCD)-related vaso-occlusion. The aim of this study was to determine the prevalence of hyperhomocysteinemia in SCD. Fasting and postmethionine load (PML) homocysteine, red cell folate, and the MTHFR C677T mutation were determined in 77 patients with SCD and 110 African-American controls. Plasma methylmalonic acid and pyridoxine levels were determined in 54 patients and all controls. For analysis, the subjects were divided into two age groups (2-10 years and 10.1-21 years). In both age groups, median PML homocysteine levels were significantly elevated in patients with SCD compared with controls. Fasting homocysteine levels were elevated in patients with SCD versus controls only in those older than 10 years. Hyperhomocysteinemia was noted in 38% of patients versus 7% in controls. Folate levels were higher among patients than controls and showed a significant negative correlation with PML homocysteine levels in patients with SCD. Pyridoxine levels in patients with SCD were significantly lower than in controls and showed a negative correlation with PML homocysteine levels. Among patients with SCD, pyridoxine deficiency was more common (62%) among those with hyperhomocysteinemia compared with those with normal homocysteine levels (30%). Homozygosity for the MTHFR C677T mutation was rare. These data suggest that children with SCD have significant hyperhomocysteinemia, associated with pyridoxine and relative folate deficiencies.

Postmethionine-load homocysteine determination for the diagnosis hyperhomocysteinaemia and efficacy of homocysteine lowering treatment regimens.

Substantial epidemiological evidence supports the vision that moderate hyperhomocysteinaemia is a graded and independent cardiovascular risk factor. The additional value of the methionine loading test for the assessment of hyperhomocysteinaemia continues to be disputed. This overview presents the historical background for the rationale of the methionine loading test and describes determinants and variability of the postmethionine-load homocysteine concentration. The association of postmethionine-load homocysteine concentrations and the risk of cardiovascular events is discussed. Furthermore, the results of homocysteine lowering treatment on postmethionine-load homocysteine are given. Up to 50% of subjects with hyperhomocysteinaemia can only be detected after performing a methionine loading test; these subjects have a normal fasting homocysteine. Both fasting and postmethionine-load homocysteine concentrations are influenced by serum folate and creatinine concentrations and by the methylenetetrahydrofolate reductase genotype, and may be subject to a wide intra-individual variability (approximately 20%). Cross-sectional studies suggest that cardiovascular risk may increase gradually from postmethionine-load homocysteine concentrations above 38 micromol/l. Supplementation with folic acid 0.5 mg daily adequately reduces postmethionine-load homocysteine; addition of pyridoxine appears to have no further homocysteine lowering effect. Prospective studies supporting the clinical significance of the methionine loading test for individual patient counselling are lacking; it seems, therefore, prudent to restrict this test for research purposes.

Continuous combined hormone replacement therapy with oral 17??-estradiol and norethisterone acetate improves homocysteine metabolism in postmenopausal women

To evaluate the effect of a continuous combined oral hormone replacement therapy (HRT) on basal and post-methionine load homocysteine levels in postmenopausal women. Twenty-two postmenopausal women (PMW) were randomly allocated to receive either continuous combined oral HRT (2 mg of estradiol plus 1 mg of norethisterone acetate; n = 11) or no treatment (controls, n = 11) for 6 months. A methionine oral load (0.1 g/kg body weight) was performed in each subject at time 0 and after 6 months. Serum homocysteine levels were measured by high-performance liquid chromatography in samples collected at time 0 and at 4, 8, and 24 h after the methionine load, while levels of vitamin B6 (by high-performance liquid chromatography) and B12 and folate (both by ELISA) were assayed in samples collected at time 0. Serum levels of glucose and body mass index increased in treated PMW, whereas folate decreased in controls. In treated PMW, basal homocysteine tended to decrease (10.6 +/- 3.3 micromol/L vs. 9.62 +/- 2.8 micromol/L, p = 0.062), whereas in controls it significantly increased (10.7 +/- 2.65 micromol/L vs. 12.17 +/- 3.89 micromol/L, p < 0.05). This increase was not significant after correction for vitamin status (p = 0.072). Homocysteine values 4 h (31.9 +/- 13.53 micromol/L vs. 39.83 +/- 22.53 micromol/L, p < 0.05) and 8 h (35.1 +/- 13.13 vs. 43.34 +/- 22.15 micromol/L) after methionine, and integrated homocysteine response to methionine (392.5 +/- 133.8 micromol/24 h vs. 458.8 +/- 104.8 micromol/24 h; p < 0.05), were significantly reduced in HRT-treated, but not in untreated, PMW. Continuous combined oral HRT with17beta-estradiol plus norethisterone acetate reduces homocysteine levels, mainly after a methionine load. This effect seems to be independent of vitamin status and may have positive implications for the prevention of cardiovascular diseases in PMW.

C677T and A1298C Polymorphisms of the Methylenetetrahydrofolate Reductase Gene: Incidence and Effect of Combined Genotypes on Plasma Fasting and Post-Methionine Load Homocysteine in Vascular Disease

Moderately increased plasma concentrations of total homocysteine (tHcy) have been shown to be an important risk factor for vascular diseases. Two common polymorphisms of the methylenetetrahydrofolate reductase (MTHFR) gene, the thermolabile C677T and a more recently reported A1298C polymorphism, may contribute to hyperhomocysteinemia. Using PCR and restriction fragment length polymorphism analysis, we studied the prevalence of the C677T and A1298C MTHFR genotypes and the combined effect of these polymorphisms on plasma tHcy concentrations, as measured by HPLC with fluorometric detection, both fasting and post-methionine load (PML), in 1238 individuals. The prevalences of the C677T and A1298C genotypes did not differ significantly in 772 individuals with documented coronary artery disease (CAD), 137 individuals with deep-vein thrombosis (DVT), and 329 individuals without documented vascular disease. Individuals homozygous for the 677T allele had significantly increased fasting tHcy, particularly in the presence of low folate, compared with individuals homozygous for the wild-type allele. Neither the 1298AC nor the 1298CC genotype was associated with significantly increased fasting or PML tHcy concentrations irrespective of serum folate. Of the nine combined MTHFR genotypes, six were present in >10% of the population. Of these, the difference in mean fasting tHcy reached statistical significance (P<0.005) only in individuals with the 677TT/1298AA genotype compared with individuals with the wild-type 677CC/1298AA genotype. Differences in mean fasting tHcy did not reach statistical significance in individuals heterozygous for both MTHFR variants. We detected two 677CT/1298CC and three 677TT/1298AC individuals; only one, an 677TT/1298AC individual, had increased tHcy (both fasting and PML). No individuals had the 677TT/1298CC genotype. The prevalences of the C677T and A1298C polymorphisms did not differ among individuals with CAD, DVT, or those without documented vascular disease. In contrast to the C677T polymorphism, the A1298C polymorphism is not associated with increased fasting tHcy. Although the two polymorphisms usually exist in trans configuration, crossover may occur rarely to form recombinant chromosomes.

The effect of different treatment regimens in reducing fasting and postmethionine-load homocysteine concentrations.

To determine the homocysteine-lowering effect of different treatment regimens on both fasting and postmethionine-load plasma total homocysteine (tHcy) concentrations. Descriptive study of consecutive hyperhomocysteinaemic subjects per treatment regimen. Homocysteine was measured in the fasting state and 6 h after methionine loading, both before and after 8 weeks of vitamin therapy. Hyperhomocysteinaemia was defined as a fasting tHcy and/or increase in tHcy (postmethionine-load minus fasting tHcy concentration) exceeding the 95th percentile of local controls. Outpatient clinic of internal medicine of a large non-academic teaching hospital. One hundred and seventeen hyperhomocysteinaemic subjects (vascular patients and first-degree relatives). There were four regimens: pyridoxine, 200 mg; folic acid, 5 mg; combination of folic acid 0.5 mg and pyridoxine 100 mg; and folic acid, 0.5 mg daily. All regimens, except pyridoxine 200 mg, significantly reduced fasting tHcy without differences in the percentage reduction (32-38%). All regimens produced a significant reduction in the increase in tHcy and postmethionine-load tHcy. The reduction in postmethionine-load tHcy was smaller for pyridoxine 200 mg than for combination therapy. No differences were found in the percentage reduction (for both increase in tHcy and postmethionine-load tHcy) between folic acid 5 mg and folic acid 0.5 mg. Monotherapy folic acid (0.5 mg daily) is the lowest effective therapy for reducing both fasting and postmethionine-load tHcy concentrations, with the same results as high-dose folic acid (5 mg daily). Pyridoxine has no additional value.

Plasma homocysteine concentrations and risk of coronary heart disease in UK Indian Asian and European men

Reasons for the increase in mortality due to coronary heart disease (CHD) in UK Indian Asians are not well understood. In this study, we tested the hypotheses that elevated plasma homocysteine concentrations are a risk factor for CHD in Indian Asians, and explain part of their increased CHD risk, compared with Europeans. We undertook two parallel case-control studies, one in Europeans and one in Indian Asians. We recruited 551 male cases (294 European, 257 Indian Asian) and 1025 healthy male controls (507 European, 518 Indian Asian). Fasting and post-methionine load homocysteine, vitamin B12 and folate concentrations, and conventional CHD risk factors were measured. Fasting homocysteine concentrations were 8% higher (95% CI 3-14) in cases compared with controls, in both ethnic groups. The odds ratio of CHD for a 5 micromol/L increment in fasting plasma homocysteine was 1.3 (1.1-1.6) in Europeans and 1.2 (1.0-1.4) in Indian Asians. The association between fasting plasma homocysteine and CHD was independent of conventional CHD risk factors in both ethnic groups. Post-load homocysteine concentrations were not significantly different in cases compared with controls. Among the controls, fasting homocysteine concentrations were 6% (2-10) higher in Indian Asians than in Europeans. From the results we estimate that elevated homocysteine may contribute to twice as many CHD deaths in Indian Asians, compared with Europeans. The differences in homocysteine concentrations between the two ethnic groups were explained by lower vitamin B12 and folate levels in Asians. Plasma homocysteine is a novel and independent risk factor for CHD in Indian Asians, and may contribute to their increased CHD risk. Raised homocysteine concentrations in Indian Asians may be related to their reduced vitamin B12 and folate levels, implying that the increased CHD risk in this group may be reduced by dietary vitamin supplementation.