Lars Brattström

Common Methylenetetrahydrofolate Reductase Gene Mutation Leads to Hyperhomocysteinemia but Not to Vascular Disease The Result of a Meta-Analysis

BACKGROUND The results of retrospective and prospective case-control studies have clearly established that mild elevations of the plasma homocysteine level are associated with increased risk of coronary, cerebral, and peripheral vascular disease. Recently, a mutation (677C-->T) was identified in the methylenetetrahydrofolate reductase (MTHFR) gene that results in reduced folate-dependent enzyme activity and reduced remethylation of homocysteine to methionine. Mutant homozygotes (TT genotype) constitute approximately 12% of the white population and frequently have mildly elevated circulating homocysteine. Therefore, it seems likely that they would also be at increased risk of vascular disease. A number of studies have investigated this during the past 3 years, and the present article evaluates the results in a meta-analysis. METHODS AND RESULTS We identified 13 studies in which there were measurements of plasma homocysteine in relation to the 3 genotypes (TT, CT, and CC) and 23 case-control studies comprising 5869 genotyped cardiovascular disease patients (mostly coronary artery disease) and 6644 genotyped control subjects. Those bearing the TT genotype had plasma homocysteine concentrations 2.6 micromol/L (25%) higher than those with the CC genotype. However, there was no difference between patients and control subjects either in the frequency of mutant alleles (T) (34.3% versus 33.8%) or the TT genotype (11.9% versus 11.7%). In the analysis of the 23 studies, the relative risk (OR) of vascular disease associated with the TT genotype was 1.12 (95% CI, 0.92 to 1.37). CONCLUSIONS We conclude that although the C677T/MTHFR mutation is a major cause of mild hyperhomocysteinemia, the mutation does not increase cardiovascular risk. Our findings suggest that the mild hyperhomocysteinemia found frequently in vascular disease patients is not causally related to the pathogenesis of the vascular disease.

Low Circulating Folate and Vitamin B6 Concentrations Risk Factors for Stroke, Peripheral Vascular Disease, and Coronary Artery Disease

BACKGROUND A high plasma homocysteine concentration is a risk factor for atherosclerosis, and circulating concentrations of homocysteine are related to levels of folate and vitamin B6. This study was performed to explore the interrelationships between homocysteine, B vitamins, and vascular diseases and to evaluate the role of these vitamins as risk factors for atherosclerosis. METHODS In a multicenter case-control study in Europe, 750 patients with documented vascular disease and 800 control subjects frequency-matched for age and sex were compared. Plasma levels of total homocysteine (before and after methionine loading) were determined, as were those of red cell folate, vitamin B12, and vitamin B6. RESULTS In a conditional logistic regression model, homocysteine concentrations greater than the 80th percentile for control subjects either fasting (12.1 micromol/L) or after a methionine load (38.0 micromol/L) were associated with an elevated risk of vascular disease independent of all traditional risk factors. In addition, concentrations of red cell folate below the lowest 10th percentile (<513 nmol/L) and concentrations of vitamin B6 below the lowest 20th percentile (<23.3 nmol/L) for control subjects were also associated with increased risk. This risk was independent of conventional risk factors and for folate was explained in part by increased homocysteine levels. In contrast, the relationship between vitamin B6 and atherosclerosis was independent of homocysteine levels both before and after methionine loading. CONCLUSIONS Lower levels of folate and vitamin B6 confer an increased risk of atherosclerosis. Clinical trials are now required to evaluate the effect of treatment with these vitamins in the primary and secondary prevention of vascular diseases.

Moderate homocysteinemia--a possible risk factor for arteriosclerotic cerebrovascular disease.

Highly elevated concentrations of homocysteine measured as homocysteine or cysteine- homocysteine mixed disulfide (MDS) are found in plasma and urine in subjects with inherited abnormalities of the methionine metabolism. These subjects have a high incidence of arteriosclerotic vascular complica- tions during childhood. Homocysteine causes endothelial cell injury and cell detachment that initiates the development of arteriosclerosis. The present study demonstrates a significantly elevated mean plasma MDS concentration in 19 patients with arteriosclerotic cerebrovascular disease compared to 17 controls. Our findings suggest that moderate homocysteinemia might be a risk factor for arteriosclerotic cerebrovascular disease. Stroke Vol 15, No 6, 1984

Plasma homocysteine in the acute and convalescent phases after stroke

BACKGROUND AND PURPOSE Stroke patients frequently manifest moderate hyperhomocysteinemia. In most published studies, plasma homocysteine was measured at least 1 month after stroke (or the interval was not reported). To determine whether plasma homocysteine concentrations change in the acute phase, we compared acute-phase values with both convalescent-phase and control values. METHODS Plasma homocysteine concentrations were measured in the acute phase (mean, 2 days after stroke onset) in 162 first-ever stroke patients aged 50 years or more (median, 75 years) and again at a median interval of 583 days (range, 460 to 645 days) after stroke onset in a subgroup of 17 patients, with values for 60 age-matched subjects serving as controls. Twenty of the control subjects were reexamined 2 to 3 years after their initial examination. RESULTS The median plasma homocysteine concentration was 13.4 mumol/L in the patient group compared with 13.8 mumol/L for control subjects (NS, Mann-Whitney U test) and increased from 11.4 mumol/L in the acute phase to 14.5 mumol/L in the convalescent phase in the subgroup of patients examined twice (P < .01, Wilcoxon signed rank test). In the 20 reexamined control subjects, no significant change over time in plasma homocysteine concentration was found. CONCLUSIONS The post-acute-phase increase in plasma homocysteine may explain why higher values were obtained for stroke patients than for control subjects in previous studies. Possible reasons for the variation in plasma homocysteine concentrations over time are (1) an acute-phase reduction secondary to a decrease in plasma albumin and (2) an increase in plasma homocysteine during the convalescent phase due to modified vitamin intake and/or lifestyle. The timing of plasma homocysteine measurements relative to stroke onset is a factor to be considered in the interpretation of results.

Folic acid responsive postmenopausal homocysteinemia

Homocysteinemia is associated with juvenile arteriosclerosis, recurrent thromboembolic complications and osteoporosis. Plasma homocysteine, measured as homocysteine-cysteine mixed disulfide (MDS), has in other than homocysteinemics been reported to be higher in patients with coronary heart or cerebrovascular disease than in controls, and higher in men than in premenopausal women. Here, in groups of normal men and normal premenopausal and postmenopausal women, we measured plasma MDS in the fasting state and four hours after a methionine load (100 mg/kg body weight), before and after four weeks of folic acid therapy at 5 mg daily. In their fasting plasma, postmenopausal women (n = 5) had significantly (P less than 0.05) higher MDS concentrations than premenopausal women (n = 5) and younger men (n = 5). After the methionine load MDS concentrations in postmenopausal women rose markedly, reaching levels significantly higher than those in younger men (P less than 0.05), and with no overlap with values in premenopausal women (P less than 0.01), or in older men (n = 5, P less than 0.01). Folic acid therapy resulted in substantial reductions (n = 15, P less than 0.01) of MDS concentrations both before the methionine load (-31%) and after (-28%), though subjects had initially had normal concentrations of serum and erythrocyte folates. We speculate that moderate homocysteinemia might contribute to postmenopausal arteriosclerosis and osteoporosis. Should this prove to be the case, folic acid might be a useful prophylactic.

Plasma homocysteine in venous thromboembolism.

Severe hyperhomocysteinemia due to inborn errors of methionine metabolism results in precocious development of arteriosclerosis and predisposition to venous and arterial thromboembolism. Although the findings of several studies have indicated that mild hyperhomocysteinemia is common in occlusive arterial disease, no similar studies have been made on venous thromboembolism. In this study of subjects under 50 years of age, we found no significant differences in the plasma homocysteine concentrations, either in the fasting state or after methionine loading, between 42 patients with venous thromboembolism and 42 healthy controls. Nonetheless, male patients manifested a tendency toward higher homocysteine concentrations than male controls; 6 patients (14%) versus 2 controls (5%) responded abnormally to methionine loading which might indicate heterozygosity for cystathionine synthase deficiency. Thus, further studies on plasma homocysteine in venous thromboembolism are warranted.

A common methylenetetrahydrofolate reductase gene mutation and longevity

Homozygotes (TT genotype) for the C677T mutation in the gene of methylenetetrahydrofolate reductase (C677T/MTHFR mutation) constitute about 12% of the Caucasian population. They have mild hyperhomocysteinemia which is an established risk factor for cardiovascular disease. If the mutation is associated with premature death its prevalence is expected to be lower in the elderly than in the young. To test this we determined the C677T/MTHFR genotypes in 220 newborn and 222 elderly 80-108-year-old Swedes. In the newborn and elderly, the allele frequency, of the C677T/MTHFR mutation was 29.1 and 27.0% and the mutant homozygote frequency was 10.0 and 9.5%, respectively. In a meta analysis of the present and three previous studies including a total of 1388 elderly and 1415 younger subjects, the odds ratio (OR) representing the likelihood of the TT genotype to attain old age relative to the CC genotype was 0.87 (95% confidence interval (CI), 0.69-1.11) and relative to both the CC and CT genotypes was 0.83 (95% CI, 0.66-1.04). This finding does not suggest that the C677T/MTHFR mutation is a strong risk factor for diseases frequently leading to premature death.

The effect of excess daily methionine intake on plasma homocysteine after a methionine loading test in humans

Impaired homocysteine metabolism might be a risk factor for vascular disease. Peroral methionine loading and post-load determination of methionine and homocysteine in plasma has frequently been used for identifying subjects with genetically impaired homocysteine metabolism. However, a methionine-rich diet induces a more efficient homocysteine catabolism in the rat, which suggests that humans on diets with differing methionine content might respond differently to the methionine loading test. To study this we performed methionine loading in six healthy subjects before and after 2 wk of excessive daily methionine intake (300% of normal). On each occasion plasma homocysteine and methionine were measured at several intervals post-load. However, neither the methionine clearance nor the post-load homocysteine concentrations were affected by excess methionine. We conclude that variations in the daily methionine intake will not influence the methionine loading test.

Plasma Homocysteine and Methionine Tolerance in Early-Onset Vascular Disease

In three different studies we tested the hypothesis that early-onset vascular disease is associated with impaired homocysteine metabolism which could contribute to the development of arteriosclerosis and thrombosis. In patients with occlusive vascular disease before the age of 60, a post-methionine load increase of plasma homocysteine exceeding the highest value for comparable healthy control subjects was found in 1 of 21 with myocardial infarction (5%), 14 of 37 with aorto-iliac disease (38%), and 17 of 53 with cerebrovascular disease (32%). This might indicate heterozygosity for homocystinuria due to cystathionine beta-synthase deficiency. Concentrations of serum vitamin B12 and red cell folate had an important modulating effect on plasma homocysteine concentrations in the fasting state.

Plasma total homocysteine levels in postmenopausal women with unstable coronary artery disease.

An elevated plasma total homocysteine (tHcy) level is considered a risk factor for coronary artery disease (CAD), but the relationship between plasma tHcy and well-defined CAD in women is still unclear. Plasma tHcy concentrations and the covariates serum folate, vitamin B12, and creatinine were analysed in 157 angiographically examined postmenopausal women with unstable CAD and in 101 healthy controls. At coronary angiography, 16% had normal vessels and 84% had coronary atherosclerosis. Mean plasma tHcy concentration (micromol/l, 95% confidence interval) did not differ in patients compared to controls (13.1 (12.3-13.8) vs. 12.5 (11.6-13.5)) or in patients with or without coronary atherosclerosis (13.3 (12.4-14.1) vs. 12.0 (10.8-13.2)). A trend to an increasing plasma tHcy with increasing degree of coronary atherosclerosis was attenuated after adjustment for age and the previous mentioned covariates. Odds ratio for the risk of coronary artery disease and coronary atherosclerosis in hyperhomocysteinemic patients (> or =90th percentile in controls) was approximately 3. However, the confidence interval included unity in half of the groups and the significance was therefore difficult to judge. Receiver operating characteristics showed age to be the only variable with a significant discriminatory ability regarding the presence of coronary atherosclerosis (area 0.77). Mild hyperhomocysteinemia seems not to be related to the risk of unstable CAD in postmenopausal women. The trend towards higher plasma tHcy with increasing degree of coronary atherosclerosis may be a marker of the disease. In future studies adjustment for age and the other three covariates should be considered.