Post-methionine Load Research Articles

Hyperhomocysteinemia and hypofibrinolysis in young adults with ischemic stroke.

Data from epidemiological and case-control studies suggest that increased total homocysteine (tHcy) levels are associated with increased risk for thromboembolic disease. The mechanisms by which hyperhomocysteinemia contributes to thrombogenesis are incompletely understood. The main objectives of this study of young ischemic stroke patients were (1) to examine fasting and post-methionine load levels of tHcy, (2) to ascertain the genotype frequency of the C677CT mutation in the methylenetetrahydrofolate reductase gene (TT genotype), and (3) to study the possible interaction between plasma tHcy levels and fibrinolytic factors. This case-control study was based on 80 consecutive patients aged 18 to 44 years admitted between January 1992 and May 1996 as a result of a first-ever ischemic stroke. Forty-one healthy control subjects were recruited. Measurement of fasting tHcy and post-methionine load levels and evaluation of the fibrinolytic system were undertaken at least 3 months (mean, 5.1+/-1. 9 months) after admission. Genotyping of the methylenetetrahydrofolate reductase gene was performed. Although the increase after methionine loading (ie, postload tHcy minus fasting-level tHcy) was significantly higher among patients, there was no difference in fasting and postload tHcy levels. After adjustment for conventional risk factors, elevated postload increase tHcy levels were associated with a 4.8-fold increased risk of ischemic stroke. There was no difference between patients and control subjects in either TT genotype frequency or T allele frequency. Abnormal response to methionine loading was associated with higher tissue plasminogen activator (tPA) mass concentration, higher plasminogen activator inhibitor-1 levels, and lower tPA activity. After adjustment for age, sex, body mass index, serum cholesterol, and triglycerides, an abnormal increase in postload tHcy levels remained significantly associated with tPA mass concentration levels (P=0.03). A moderately elevated increase in tHcy levels after methionine loading was associated with an increased risk for ischemic stroke in young adults. In contrast, fasting tHcy levels did not differ between patients and controls. A moderately elevated increase in tHcy after methionine loading may provide a additional thrombogenic risk mediated in part by interactions with the fibrinolytic system. In young stroke patients, a methionine loading test to detect hyperhomocysteinemia should always be considered in the convalescent phase of the disease.

Genetic causes of mild hyperhomocysteinemia in patients with premature occlusive coronary artery diseases

Elevated plasma homocysteine is increasingly being recognized as a risk factor for coronary artery disease (CAD). Although there is general agreement on the importance of micronutrients and genetic predisposition to elevated plasma homocysteine, the exact influence of the known prevalent mutations in genes which regulate homocysteine metabolism is not clear. We studied 376 cases of individuals with premature CAD with respect to their fasting and post-methionine load (PML) total homocysteine (tHcy) concentrations. We also determined the presence or absence of the T 833C and G 919A mutations of the cystathionine- β-synthase (CBS) gene, the C 677T mutation of the methylene tetrahydrofolate reductase (MTHFR) gene, and the A 2756G transition of the B 12 dependent methionine synthase (MS) gene. Our objectives were therefore both to confirm the relationship of plasma homocysteine with premature CAD and to examine the importance of genetic influence on both fasting and PML homocysteine. Approximately 32% of the CAD patients had fasting hyperhomocysteinemia and 16% had PML hyperhomocysteinemia. Of these, 8.5% had both forms of hyperhomocysteinemia (combined hyperhomocysteinemia). The T 833C mutation in the CBS gene and the thermolabile C 677T mutation in the MTHFR gene seem to play an important role in the subset of individuals with combined hyperhomocysteinemia. The A 2756G transition in the MS gene is not associated with elevated plasma tHcy. Many cases (47%) of hyperhomocysteinemia are not associated with micronutrient deficiencies, impaired renal function, and/or currently known genetic mutations. Further work is needed to study whether unknown mutations, particularly those residing in the intronic sequences of the genes involved in homocysteine metabolism, other environmental factors, or interaction of gene, nutrient, and environmental factors may be the cause of currently unexplained cases of mild hyperhomocysteinemia.

Combination of low-dose folic acid and pyridoxine for treatment of hyperhomocysteinaemia in patients with premature arterial disease and their relatives

Hyperhomocysteinaemia is an independent risk factor for atherosclerotic disease and venous thrombosis. The optimal homocysteine-lowering vitamin dose and target total homocysteine (tHcy) concentration are currently unknown. We prospectively studied the homocysteine-lowering effect after 8 weeks low-dose combination of folic acid (0.5 mg) and pyridoxine (100 mg) in 49 hyperhomocysteinaemic persons (33 patients with documented premature arterial disease and 16 of their first-degree relatives). Hyperhomocysteinaemia was in both sexes defined as fasting tHcy concentration > 12 micromol/l and/or post-methionine load tHcy concentration > 38 micromol/l. Low-dose vitamin therapy significantly reduced fasting tHcy concentration (median 13.9 to 9.3 micromol/l, reduction 32% (95% CI: 27-37%)) and post-load tHcy concentration (median 55.2 to 36.5 micromol/l, reduction 30% (95% CI: 25-35%)). Fasting tHcy reduction was similar in women and men, as well as in patients and relatives. Post-load tHcy reduction was significantly less in men compared to women (P = 0.04) and in relatives compared to patients (P = 0.03). Although low-dose combination of folic acid and pyridoxine results in a substantial reduction of tHcy concentrations (30-32%) in subjects with hyperhomocysteinaemia, the normalisation percentage to predefined criteria was less impressive (49%).

Folate status, homocysteine metabolism, and methylene tetrahydrofolate reductase genotype in rural south african blacks with a history of pregnancy complicated by neural tube defects

The birth incidence of neural tube defects (NTDs) in South Africa is threefold to sixfold higher in rural compared with urban blacks. We investigated whether folate deficiency and aberrant homocysteine metabolism could explain the high NTD incidence in rural black populations. Plasma folate and total homocyst(e)ine (tHcy) concentrations were determined in apparently healthy rural black women (n = 107), rural black women with a history of pregnancy complicated by NTDs (n = 54), and urban blacks (n = 101). Methionine load tests were performed on the 54 women with a history of NTD-affected pregnancy and 54 controls matched for age and body mass. The presence of the 677C --> T mutation in the methylene tetrahydrofolate reductase (MTHFR) gene was investigated in both groups by a polymerase chain reaction (PCR) of genomic DNA and HinfI digestion of the PCR product. Apparently healthy urban black women (n = 101) had a lower (P < .001) plasma folate concentration compared with rural black women (n = 107). Women with a history of NTD-affected pregnancy did not differ significantly from controls with respect to plasma folate, fasting homocyst(e)ine, methionine, and the post-methionine load increase in plasma homocyst(e)ine. More than 50% of both of the latter groups had a post-methionine load increase in plasma tHcy less than the fifth percentile as observed in a healthy white control group. No homozygotes for the 677C --> T mutation in the MTHFR gene were found in black mothers with NTD-affected offspring or controls. It is concluded that black urbanization is characterized by a diminished folate status that is paradoxically associated with a lower NTD birth incidence. Homozygosity for the 677C --> T mutation in the gene coding for MTHFR does not constitute a genetic risk factor for NTDs in blacks. No aberrant homocysteine metabolism could be demonstrated in black women with NTD-affected pregnancies.

High-performance liquid chromatographic method for measuring total plasma homocysteine levels

We have modified a high-performance liquid chromatographic (HPLC) procedure based on SBD-F (ammonium-7-fluorobenzo-2-oxa-1,3-diazole-4-sulphonate) pre-column derivatization to obtain an assay that is useful for routine clinical total plasma homocysteine (tHcy) analysis. The introduction of easily handled sodium borohydride instead of the traditional tri- n-butylphosphine in dimethylformamide as a reductant and a 14-min run-time using basic isocratic HPLC equipment are the more notable advantages. The addition of mercaptopropionylglycine as an internal standard contributed to improvements in the reproducibility of the assay, yielding within- and between-run precisions of 1.9 and 4% (C.V.), respectively. Reference values for fasting tHcy were 7.65±2.3 and 8.9±2.4 μmol/l, while post-methionine load gave tHcy levels of 19.9±5.5 and 26.8±5.5 μmol/l, for women and men, respectively ( n=40).

Plasma homocysteine and folate are related to arterial blood pressure in type 2 diabetes mellitus

The aim of this study was to assess the relationship between homocysteine (tHcy), folate and vitamin B 12 levels, urinary albumin excretion, and arterial blood pressure in patients with non–insulin-dependent diabetes mellitus (NIDDM). Our study was carried out in 33 NIDDM patients (16 men, 17 women) and 16 healthy volunteers as controls (seven men, nine women). Fasting and postmethionine load plasma tHcy levels were assessed, together with folate, vitamin B 12, and urinary albumin excretion levels. In NIDDM patients, there were correlations between folate and mean arterial pressure (r = −0.352, P = .046), folate and systolic blood pressure (r = −0.437, P = .013), folate and vitamin B 12 (r = 0.499, P = .004), tHcy and vitamin B 12 (r = −0.348, P = .04), ln tHcy and ln folate (r = −0.404, P = .01), and, lastly, between tHcy, either fasting or postload, and urinary albumin excretion. Patients with elevated tHcy levels had significantly higher diastolic blood pressure ( P = .04) and mean arterial pressure ( P = .03). Otherwise, higher folate values were associated with lower systolic blood pressure ( P = .004) and mean arterial pressure ( P = .02). In addition, NIDDM patients with complications presented higher tHcy basal values than the group without complications ( P = .003). A particular propensity of such patients towards endothelial dysfunction could explain the presence of correlations between these metabolic parameters and arterial blood pressure.

Fasting and post—methionine load homocyst(e)ine values are correlated with microalbuminuria and could contribute to worsening vascular damage in non—insulin-dependent diabetes mellitus patients

The study aim was to assess the relationship between homocyst(e)inemia and microalbuminuria in non—insulin-dependent diabetes mellitus (NIDDM) patients. The study was performed on 33 NIDDM patients (16 males and 17 females), and 16 healthy control subjects (seven males and nine females). Plasma fasting and post—methionine load homocyst(e)ine (tHcy), together with other parameters that could modify tHcy levels, were assessed. There were no significant differences between NIDDM patients with controls for fasting tHcy (8.12 ± 3.17 v 7.19 ± 2.40 μmol/L) and post—methionine load tHcy (26.51 ± 11.50 v 25.06 ± 10.76 μmol/L). Moreover, there was a significant correlation between urinary albumin excretion (IUAE) and fasting tHcy ( r = .340, P = .05) and post—methionine load tHCy ( r = .502, P = .004) in NIDDM patients. Fasting tHCy was correlated both with post—methionine load tHcy ( r = .429, P = .01) and with vitamin B 12 ( r = .349, P = .04) in NIDDM patients. Microalbuminuric NIDDM patients had higher fasting tHCy (9.05 ± 3.83 μmol/L) than normoalbuminurics (7.12 ± 1.95 μmol/L). In addition, NIDDM patients with complications presented higher fasting tHcy values than the group without complications (9.61 ± 3.34 v 6.53 ± 2.09 μmol/L, Kolmogorov-Smirnov two-sample test for nonparametric data [KS] = 1.794, P = .003), without any other significant differences in the parameters considered. tHcy could be an important risk factor worsening the prognosis in NIDDM patients, especially microalbuminuric patients. Microalbuminuric NIDDM patients could be particularly prone to hyperhomocyst(e)inemia, probably due to endothelial or renal dysfunction with a reduction in the scavenging of tHcy.

Low Concentrations of Folate in Serum and Erythrocytes of Smokers: Methionine Loading Decreases Folate Concentrations in Serum of Smokers and Nonsmokers

Recent data suggest that hyperhomocysteinemia is associated with an increased risk for premature vascular disease. Total plasma homocysteine (tHcy) may be increased by impaired activity of enzymes or suboptimal availability of B vitamins (1). Homocysteine transsulfuration reactions are catalyzed by the enzymes cystathionine β-synthase and cystathionine lyase in the presence of coenzyme vitamin B6, and remethylation of homocysteine is performed by the enzymes methionine synthase and betaine-homocysteine methyltransferase with vitamin B12 as a coenzyme for the former enzyme. 5-Methyltetrahydrofolate (5-methylTHF) or betaine are methyl donors during remethylation. The enzyme 5,10-methylenetetrahydrofolate reductase (MTHFR) with coenzyme FADH2 synthesizes 5-methyl-THF from 5,10-methylenetetrahydrofolate (5,10-MTHF) (2). The postmethionine load (PML) abnormal tHcy increments may reflect suboptimal plasma vitamin B6 or deficiency of cystathionine β-synthase (3). The present report describes the effects of methionine loading on serum and erythrocyte folate, tHcy, and related thiols in smokers and nonsmokers. We recruited 63 apparently healthy smokers [ages 37.8 ± 0.8 years; body mass index (BMI), 25.4 ± 0.5; male/female, 39/24; cigarettes/day, 16.2 ± 0.8; smoking period (years), 19.7 ± 0.7], 44 nonsmokers (ages 37.8 ± 1.0 years; BMI, 24.5 ± 0.5; male/female, 26/18), and 23 former smokers who refrained from smoking for ≥3 months …

Excess prevalence of fasting and postmethionine-loading hyperhomocysteinemia in stable renal transplant recipients.

Hyperhomocysteinemia, either fasting or after methionine loading, may contribute to the increased incidence of cardiovascular disease events experienced by renal transplant recipients. Limited data are available on fasting homocysteine (Hcy) levels, and none on postmethionine-loading Hcy levels, in these patients. We assessed the prevalence and potential determinants of fasting and postmethionine-loading hyperhomocysteinemia in 29 stable renal transplant recipients and 58 age- and sex-matched, population-based controls free of renal disease with serum creatinine levels of 1.5 mg/dL or less. Total (t) plasma Hcy was determined fasting and 2 hours after methionine loading, along with fasting determinations of the B-vitamin cofactors/substrates for Hcy metabolism, ie, pyridoxal 5'-phosphate, B-12, and folate and serum creatinine. Geometric mean fasting (18.1 versus 9.8 microM, P < .001) and postmethionine-loading increase (22.0 versus 15.2, P = .001) in tHcy levels were significantly greater in the renal transplant recipients, as were the prevalence odds (with 95% confidence intervals) for fasting [14.8 (3.4-64.7)], postmethionine loading [6.9 (1.5-32.8)], combined fasting and postmethionine-loading [18.0 (2.3-142.1)] hyperhomocysteinemia, and inadequate circulating folate [4.2 (1.1-16.5)] or pyridoxal 5'-phosphate [3.2 (0.9-11.0) status. Correlation analyses suggested important potential relationships between creatinine and both fasting (+0.64, P < .001) and postmethionine-load increase (+0.38, P = .045) in tHcy, folate and fasting (-0.41, P = .025) tHcy, and pyridoxal 5'-phosphate and postmethionine-loading increase (-0.33, P = .091) in tHcy. We conclude that there is an excess prevalence of fasting and postmethionine-loading hyperhomocysteinemia in stable renal transplant recipients. Renal function is related to both fasting and postmethionine loading-hyperhomocysteinemia, inadequate folate status is associated with fasting hyperhomocysteinemia, and inadequate vitamin B-6 status may be related to postmethionine-loading hyperhomocysteinemia in this patient population.

4.P.59 Fasting and post-methionine load homocyst(e)ine values are correlated to microalbuminuria and could contribute to worsen vascular damage in NIDDM patients

4.P.59 Fasting and post-methionine load homocyst(e)ine values are correlated to microalbuminuria and could contribute to worsen vascular damage in NIDDM patients

The role of vitamins in the pathogenesis and treatment of hyperhomocyst(e)inaemia.

The relation between vitamin nutritional status and circulating plasma homocyst(e)ine concentrations is reviewed. Several studies have shown that plasma concentrations of folate, vitamin B12 and pyridoxal 5'-phosphate are inversely associated with plasma total homocyst(e)ine concentrations. Of the three vitamins mentioned above, folate is the most powerful homocyst(e)ine lowering agent and a daily supplement of 0.65 mg/day is sufficient to normalize moderate hyperhomocyst(e)inaemia in most individuals with normal renal function. In patients with severe renal failure, high doses of folate are required to treat hyperhomocyst(e)inaemia. Folic acid is ineffective in reducing plasma total homocyst(e)ine concentrations in patients with a vitamin B12 deficiency. Vitamin B6 supplementation has no effect on fasting plasma total homocyst(e)ine concentrations, but attenuates the post-methionine load plasma homocyst(e)ine peak. At least one report has shown that some individuals appear to be unable to maintain plasma total homocyst(e)ine concentrations in the normal reference range by a dietary intake of folic acid only. Long-term vitamin supplementation may be indicated in these individuals. However, the clinical benefit of vitamin supplementation has not yet been demonstrated and controlled trials are urgently required.

Elevations of serum cystathionine and total homocysteine in pyridoxine-, folate-, and cobalamin-deficient rats

Because both basal and postmethionine load hyperhomocysteinemia are correlated with vascular disease, there is a need to determine the underlying causes. Although deficiencies of folate, cobalamin, and pyridoxine have all been implicated there are difficulties in distinguishing among them. The objective was to determine the changes in total homocysteine, cystathionine, and other methionine, one carbon- and tryptophan-related metabolites in rats with dietary induced folate or pyridoxine deficiency and cobalamin analogue induced deficiency. Pyridoxine-deficient diet (0 mg/kg) increased basal serum cystathionine levels (14 fold) after 51 days with a smaller increase in basal total homocysteine. Diets with 0 to 1.5 mg/kg pyridoxine also caused graded increases in serum cystathionine. Total homocysteine and cystathionine were markedly increased postmethionine load in the pyridoxine deficient rats as compared to the control, folate-, or cobalamin-deficient rats. Folate- and cobalamin-deficient rats had marked increases in basal total homocysteine and moderate increases in basal cystathionine, but the increments in postmethionine load values were not different than control. Pyridoxine deficiency decreased liver serine transhydroxymethylase activity to 6%. Post-tryptophan load serum xanthurenic acid was equal in cobalamin- and pyridoxine-deficient rats. Serum quinolinic acid was increased only in the cobalamin-deficient rats. Plasma pyridoxal-5′-phosphate levels were not as sensitive as serum cystathionine in pyridoxine deficiency. Basal and postmethionine load serum cystathionine levels are very sensitive in detecting pyridoxine deficiency and will be useful when determining the cause of clinical hyperhomocysteinemia.

Total plasma homocysteine determination by liquid chromatography before and after methionine loading: Results in cerebrovascular disease

Elevated homocysteine (HCY) levels in tissues and blood are associated with premature occlusive diseases. A number of techniques have been developed to assay HCY, including high-performance liquid chromatography (HPLC) with fluorimetric or electrochemical detection, and radioenzymatic methods. The present study evaluated the adaptation of a liquid chromatographic, ion-exchange technique with postcolumn derivatization using ninhydrin. Fasting and moreover post-methionine load total plasma HCY were assayed in 50 patients three months after a stroke and in 20 age-matched controls. Ion-exchange liquid chromatography was performed on an amino acid analyzer using a modified procedure to improve methionine and HCY separation. HCY values in the fasting state were moderately but significantly increased ( P<0.05) in the patients compared to the controls: 10.5±3.4 versus 9.3±2.3 μmol/l. The difference between the two groups was amplified in post-load HCY results, which were significantly increased ( P<0.05) in the patients: 41.6±17.8 versus 29.2±5.5 μmol/l in controls. The relationship between cerebrovascular disease and impaired HCY metabolism has previously been emphasized by other investigators. Our findings suggest that certain inherited and/or acquired HCY disorders observed in the fasting state (14%) and especially in post-methionine load conditions (32%) may occur during acute disease, and that total plasma HCY can be determined by ion-exchange chromatography even after oral methionine loading.

Elevated high-density lipoprotein cholesterol, not protective in the presence of homocysteinemia

Homocysteinemia may increase atherosclerosis risk by a variety of mechanisms.6–9 The disorder can be diagnosed by fasting, or postmethionine load homocyst(e)ine values. An abnormal postload range (>95th percentile) has been suggested to be 20 to 40 nmol/ml.10,11 Twenty-eight percent of patients with peripheral vascular and cardiovascular disease have an abnormal response to the methionine load tests compared with 1% of the healthy population. Therapy is relatively low risk and involves folate or pyridoxine supplementation. Despite the protective effects of very high HDL cholesterol, atherosclerosis can still occur in the setting of hyperhomocysteinemia.

Mild Hyperhomocysteinemia and Hemostatic Factors in Patients with Arterial Vascular Diseases

Mild hyperhomocysteinemia, due to genetic or to environmental factors, is now recognized as a risk factor for premature arterial disease, including peripheral arterial occlusion, thrombotic stroke and myocardial infarction. It is defined by either an increased level of fasting homocysteine or by an increased level after loading with methionine, which is more frequently altered than the former. We studied the hemostatic parameters in 88 patients with premature arterial disease (mean age 43 +/- 11 years). We confirmed previously known hemostatic alterations described in vascular patients when compared to controls, but found that, among patients, some of these parameters were more altered in hyperhomocysteinemic patients. When fasting homocysteine was increased, higher alterations were found in factors VIIIc, von Willebrand and thombin-antithrombin complexes were more elevated. When post-methionine load homocysteine was increased, alterations in fibrinolytic parameters were more pronounced.

The effect of a subnormal vitamin B-6 status on homocysteine metabolism.

Homocysteine, an atherogenic amino acid, is either remethylated to methionine or metabolized to cysteine by the transsulfuration pathway. The biochemical conversion of homocysteine to cysteine is dependent upon two consecutive, vitamin B-6-dependent reactions. To study the effect of a selective vitamin B-6 deficiency on transsulfuration, we performed oral methionine load tests on 22 vitamin B-6-deficient asthma patients treated with theophylline (a vitamin B-6 antagonist) and 24 age- and sex-matched controls with a normal vitamin B-6 status. Both groups had normal circulating vitamin B-12 and folate concentrations. Methionine loading resulted in significantly higher increases in circulating total homocyst(e)ine (P < 0.01) and cystathionine (P < 0.05) concentrations in vitamin B-6-deficient patients compared with controls. 6 wk of vitamin B-6 supplementation (20 mg/d) significantly (P < 0.05) reduced post-methionine load increases in circulating total homocyst(e)ine concentrations in deficient subjects, but had no significant effect on the increase in total homocyst(e)ine concentrations in controls. The increases in post-methionine load circulating cystathionine concentrations were significantly (P < 0.01) reduced in both groups after vitamin supplementation. It is concluded that a vitamin B-6 deficiency may contribute to impaired transsulfuration and an abnormal methionine load test, which is associated with premature vascular disease.

Molecular and biochemical approaches in the identification of heterozygotes for homocystinuria

We compared biochemical and molecular methods for the identification of heterozygous carriers of mutations in the cystathionine β-synthase (CBS) gene. Eleven relatives of seven unrelated patients with homocystinuria due to homozygous CBS deficiency and controls were studied with respect to total homocysteine concentrations before and after methionine loading. In addition, we determined CBS activity in cultured skin fibroblasts and tested for the presence of five known mutations by a PCR-based method in these seven patients, their relatives and controls. The results demonstrate that measurement of homocysteine after methionine loading and assay of CBS enzyme activity in cultured fibroblasts identify most but not all heterozygotes. There was significant correlation between homocysteine concentrations and CBS activities only after methionine loading ( r = 0.12, 0.48, 0.48 and 0.50 at 0, 4, 6 and 8 h, respectively). Among the homozygous patients, molecular approaches identified five T 833C and two G 919A mutations out of 14 independent alleles, confirming the studies of others that these represent the two most prevalent mutations. In addition, we found that three of six heterozygotes with the T 833C allele had post-methionine loading homocysteine levels which overlapped with controls and of the other three, one (as well as an obligate heterozygote who did not carry any of the five mutant alleles tested) had CBS activity comparable to that of controls. These findings demonstrate that genotyping is useful as an adjunctive method for the diagnosis of the heterozygous carrier state of CBS deficiency.

Plasma homocysteine and severity of atherosclerosis in young patients with lower-limb atherosclerotic disease.

Elevated plasma homocysteine levels are recognized as an independent risk factor for atherosclerotic disease. It is not known (1) whether the severity of atherosclerotic disease is related to hyperhomocyst(e)inemia or (2) whether any such relation differs between fasting and post-methionine loading plasma homocysteine levels. Therefore, in 171 consecutive patients under 55 years of age with first symptoms of lower-limb disease, we examined the relation between severity of atherosclerosis and plasma homocysteine concentration. Severity of atherosclerotic disease was estimated from the prevalence of coronary artery disease and cerebrovascular disease and from the angiographic extent of lower-limb disease. Plasma homocysteine was measured after a period of fasting and in response to methionine loading (0.1 g/kg). In multivariate analysis, the prevalence of coronary artery disease plus cerebrovascular disease was related to both fasting and postmethionine homocysteine levels (odds ratio [OR] for the upper quartile versus the lower three quartiles, 2.8, 95% confidence interval [CI], 1.1 to 7.5; and OR 3.0, 95% CI, 1.1 to 7.8, respectively). The extent of lower-limb disease was weakly related to the fasting homocysteine level (partial correlation coefficient, .12; P = .17) and more strongly related to the postmethionine homocysteine level (partial correlation coefficient, .25; P = .003). These relations tended to be more pronounced in women than in men. They were independent of age, total serum cholesterol, blood pressure, and smoking habit. We concluded that the severity of atherosclerotic disease in young patients with lower-limb atherosclerotic disease is associated with high postmethionine and fasting homocysteine concentrations.

Post-methionine load hyperhomocysteinemia in persons with normal fasting total plasma homocysteine: initial results from The NHLBI Family Heart Study

Hyperhomocysteinemia, either fasting or after oral methionine loading, appears to be an independent risk factor for coronary heart disease (CHD). It remains unclear whether fasting total homocysteine determination alone adequately detects the full spectrum of hyperhomocysteinemic individuals. We measured fasting and 4-h post methionine loading (0.1 g L-methionine/kg body weight) total plasma homocysteine in 274 participants in The NHLBI Family Heart Study, a population-based investigation of genetic and non-genetic determinants of CHD. Of the total number ( n = 47) of hyperhomocysteinemic persons, 43% ( 20 47 ) were identified only by methionine loading, while 32% ( 15 47 ) of the total number, and 75% of those with post-methionine loading hyperhomocysteinemia only ( 15 20 ), had fasting total homocysteine concentrations below the 75th percentile (10.7 μmol/l). We conclude that fasting total plasma homocysteine determination alone fails to identify a sizable percentage (> 40%) of persons who may have clinically relevant hyperhomocysteinemia post methionine loading.

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.