Plasma tHcy Levels Research Articles

Evidence of Major Genes Effects on Serum Homocysteine and Fibrinogen Levels, and Premature Ischemic Heart Disease in Italian Extended Families

Objectives: The purpose of the present study was to investigate the effect of novel genetic factors on plasma levels of total homocysteine (tHcy) and fibrinogen (FIB). As tHcy and FIB have been consistently associated to increased risk of ischemic heart disease (IHD) and acute myocardial infarction (MI) also genes-trait-MI mediational effects were tested. Methods: A complex segregation analysis, and a mediation analysis of a highly selected group of 44 extended families (302 subjects), each including at least one member with fatal premature (<50 years) IHD were carried out. Results: tHcy and FIB levels turned out to be influenced by at least two major genes. A significant tHcy latent class-MI association (OR = 3.24; 95% CI, 1.37 to 7.68), and a non-significant tHcy plasma level-MI association (OR = 1.65 per 1 = log 10 µmol/l, 95% CI, 0.56 to 4.81) were estimated, suggesting a direct influence of the homocysteine major gene as suppressor of plasma tHcy levels effect. In contrast, FIB latent class-MI association (OR = 0.97; 95% CI, 0.31 to 3.05) and FIB level-MI association (OR = 1.32 per 1 = 70 g/l; 95% CI, 0.88 to 2.00) were not statistically significant. Conclusion: These data provide evidence for a major latent gene effect influencing variation in tHcy plasma levels, which is independent on C677T MTHFR polymorphism, and significantly affecting the risk of MI.

Intravenous N-acetylcysteine with Saline Hydration Improves Renal Function and Ameliorates Plasma Total Homocysteine in Patients Undergoing Cardiac Angiography

Proinflammatory cytokines and hyperhomocysteinemia are associated with clinically relevant restenosis in coronary artery disease. N-acetylcysteine (NAC) can decrease proinflammatory cytokines and plasma homocystine as well as reduce contrast-induced nephropathy. The aim of this study, therefore, was to compare normal saline hydration with and without intravenous NAC in terms of changes in renal function, proinflammatory cytokines, inflammatory markers, and plasma total homocysteine during coronary angiography. Forty-six patients who underwent coronary angiography and/or stent implantation for unstable angina were enrolled and assigned to NAC or NS treatment groups based on normal saline hydration with or without intravenous NAC, respectively. The NS group had lower serum creatinine (Cre: p = 0.02) and plasma total homocysteine (tHcy; p < 0.001) and increased glomerular filtration rate (GFR; p = 0.003) after angiography. In the NAC group, the serum blood urea nitrogen (BUN; p = 0.001), Cre (p < 0.001), and plasma tHcy (p < 0.001) were lower, and the GFR (P = 0.013) was increased after angiography. There were no statistically significant differences in serum high-sensitivity C reactive protein (hs-CRP), tumor necrosis factor-α (TNF-α), or interleukin-10 (IL-10) before and after angiography in the NS and NAC groups. Intergroup comparison revealed that plasma tHcy level was lower for the NAC-treated patients (p = 0.002), with lower plasma tHcy level before and after treatment in this group (p < 0.001). Normal saline hydration can improve renal function and decrease plasma tHcy after coronary angiography with or without NAC; however, the combination of the two decreases plasma tHcy more than normal saline hydration alone.

Homocysteine, Cystatin C and N-Terminal-Pro Brain Natriuretic Peptide

Background: There is increasing evidence that vascular disease contributes to cognitive impairment and dementia. Clarification of the role of vascular risk factors in dementia is important because most are modifiable, in contrast to other risk factors such as age and genetics. Methods: In 451 patients with mental illness we have investigated three biochemical markers related to vascular disease, total plasma homocysteine (tHcy), cystatin C, and N-terminal-pro brain natriuretic peptide (NT-proBNP), and their association with vascular disease, diagnoses, and brain imaging findings (CT). Results: Plasma tHcy, serum cystatin C, and serum NT-proBNP showed significantly increased frequencies of elevated levels in patients with vascular disease, in patients with a pathological CT finding indicating cerebrovascular disease, and in patients above 75 years of age. Conclusion: It is possible that the control of conventional vascular risk factors and therapy could be guided by the level of plasma tHcy, serum cystatin C, and serum NT-proBNP. Patients with an elevation of any of these three parameters could be selected for a lower target level of risk factors such as blood pressure, hyperlipidemia etc. than conventional target levels.

Polymorphism in the methylenetetrahydrofolate reductase (C677T) gene and homocysteine levels: a comparison in Brazilian patients with coronary arterial disease, ischemic stroke and peripheral arterial obstructive disease

This study aimed to compare plasma levels of total homocysteine (tHcy) in different arterial events as well as to investigate an association between homocysteine levels and C677T polymorphism in Brazilian patients. A total of 145 subjects were enrolled in this study including 43 patients with coronary arterial disease (CAD), 21 with ischemic stroke (IS), 44 with peripheral arterial obstructive disease (PAOD) and 37 control subjects. A preliminary analysis showed significant difference for tHcy plasma levels between patients with CAD (P = 0.003) or PAOD (P = 0.03) compared to controls. However, after adjustment for sex, age, total cholesterol, LDL, diabetes, tabagism or C677T polymorphism, no significant differences were detected in tHcy levels among patients groups and controls. No significant correlation was demonstrated for C677T polymorphism and homocysteine levels. These results indicate that increased Hcy levels may not be considered an independent risk factor for atherothrombotic diseases in Brazilian patients.

Mutations in exons 2 and 3 of the FOLR1 gene in demented and non-demented elderly subjects

We have previously reported six novel mutations in the 5'-UTR of the gene for folate receptor-alpha (FOLR1). In our search for additional mutations we screened patients, referred for investigation of suspected dementia (DGM subgroup) by SSCP and DNA sequencing from the end of exon 1 to the first bases of intron 3. We found 4 sequence variations, FOLR1 g.1314G>A, g.1816delC, g.1841G>A, and g.1928C>T. Pyrosequencing genotyping assays were developed for all of them, and 389 active seniors (AS subgroup) and the 202 DGM patients were genotyped for these mutations. The frequency q of the mutated allele was, among the AS subjects, 0.068, 0.0026, 0.0026, and 0.024 respectively, and among the DGM subjects, 0.067, 0.0076, 0.0078, and 0.023. The g.1816delC and g.1841G>A mutations thus were more frequent in the DGM than in the AS subgroup, but the difference did not reach statistical significance. The mutated alleles, FOLR1 1816(-) and 1841A, always occurred together in the same subjects, suggestive of a rare double-mutant haplotype. The two common polymorphisms, FOLR1 g. 1314G>A and g.1928C>T seemed not to raise tHcy plasma levels, whereas the double-mutated g.1816(-)-g.1841A haplotype may possibly have a slight tHcy-raising effect. Thus, so far 8 novel rare FOLR1 mutations with a combined prevalence of approximately 1.3% in Whites as well as two common polymorphisms with 5% and 13%, respectively, have been demonstrated. Only a few of the rare mutations may potentially be associated with raised plasma tHcy concentrations. No association with dementia was found.

Testosterone regulation of renal cystathionine β-synthase: implications for sex-dependent differences in plasma homocysteine levels

Elevated plasma total homocysteine (tHcy) is an independent risk factor for ischemic heart disease and stroke. Epidemiological studies reveal that men have higher tHcy levels than women, but the mechanism underlying this sex-dependent difference is unknown. One route for intracellular disposal of homocysteine is catalyzed by cystathionine beta-synthase (CBS). Renal function is known to be an important determinant of tHcy, and, in this study, we demonstrate that renal CBS expression and activity in mice diminished approximately twofold after castration, whereas ovariectomization was without effect. The higher renal CBS activity in males (22.7 +/- 3.1 mmol cystathionine.h(-1).kg kidney(-1)) vs. females (8.4 +/- 3.4 mmol cystathionine.h(-1).kg kidney(-1), P < or = 10(-6)) in C57Bl/6J mice was associated with lower plasma tHcy levels in males vs. females, and this difference was exacerbated in Cbs+/- mice (7.7 +/- 1.9 micromol/l in males vs. 13.8 +/- 6.4 micromol/l in females, P = 0.005). Surprisingly, mammals exhibit a diversity of regulatory patterns for kidney CBS, with females exhibiting lower CBS activity in mice, higher in rats and humans, and being indistinguishable from males in rabbit, hamster, and guinea pig. Our data suggest that testosterone-dependent regulation of human CBS in kidney may contribute to sex-dependent differences in homocysteine transsulfuration.

Plasma Homocysteine, Folate, and Vitamin B12 and the Risk of Hip Fracture: The Hordaland Homocysteine Study

Homocysteine and related factors were evaluated as risk factors for subsequent hip fractures among 4766 elderly men and women. High levels of homocysteine and low levels of folate predicted fracture, whereas vitamin B12 and genotypes were not related to fracture risk. High homocysteine may be a modifiable risk factor for hip fracture. Elevated plasma total homocysteine (tHcy) and deficiencies of folate and vitamin B12 are associated with risk of osteoporosis and fracture. We examined whether plasma levels of tHcy, folate, and vitamin B12 and the methylenetetrahydrofolate reductase (MTHFR) 677C-->T and 1298C-->T polymorphisms predicted hip fracture. This was a population-based prospective study of 2639 women and 2127 men who were 65-67 yr at enrollment in 1992-1993. Information on hip fracture was obtained from computerized records of discharge diagnoses from all hospitalizations in the region in the period between enrollment and November 30, 2005. Cox proportional hazard regression was used to estimate fracture risk according to levels of plasma tHcy, folate, and vitamin B12 and for different genotypes. Over a median follow-up period of 12.6 yr, hip fracture was recorded in 184 (7.0%) women and 90 (4.2%) men. The adjusted hazard ratio (95% CI) for fracture in subjects with high (>or=15 microM) compared with low levels (<9.0 microM) of tHcy was 2.42 (1.43-4.09) among women and 1.37 (0.63-2.98) among men. Dose-response analyses indicated a positive association between plasma tHcy and risk of fracture in both sexes and a negative association between plasma folate and risk of fracture among women only. Plasma vitamin B12 level or MTHFR genotype was not significantly related to risk of fracture after adjustments for confounding factors. The association between tHcy and risk of hip fracture was only slightly weakened by adjustments for plasma levels of vitamin B12 and folate. tHcy seems to be a predictor for hip fracture among elderly men and women. Folate was a predictor among women only, whereas vitamin B12 and MTHFR genotype did not predict hip fracture. Our data corroborate the hypothesis that homocysteine may play a role in the pathogenesis of osteoporotic fractures.

Polymorphisms of MTHFD, Plasma Homocysteine Levels, and Risk of Gastric Cancer in a High-Risk Chinese Population

Accumulative evidence suggests that folate has a protective effect on gastric cancer. The methylenetetrahydrofolate dehydrogenase (MTHFD) plays an important role in folate and homocysteine metabolisms, and polymorphisms of MTHFD may result in disturbance of the folate-mediated homocysteine pathway. The aim of this study is to test the hypothesis that genetic variants of MTHFD and plasma homocysteine levels are associated with risk of gastric cancer and modulated by genotypes of methylenetetrahydrofolate reductase (MTHFR). We genotyped G1958A and T401C in MTHFD and C677T in MTHFR and detected total plasma homocysteine (tHcy) levels in a case-control study of 589 gastric cancer cases and 635 cancer-free controls in a high-risk Chinese population. The variant genotypes of MTHFD 1958AA and 401CC were associated with a significantly increased risk of gastric cancer [adjusted odds ratio (OR), 2.05; 95% confidence interval (95% CI), 1.34-3.13 for 1958AA; adjusted OR, 1.43; 95% CI, 1.14-1.80 for 401CC] compared with 1958GG/GA and 401TT/TC genotypes, respectively. Both of the effects were more evident in the subjects carrying MTHFR 677CT/TT genotypes. The average tHcy level was significantly higher in gastric cancer cases than in controls (P < 0.01), and the upper quartile of tHcy (>13.6 micromol/L) was associated with an 82% significantly increased risk of gastric cancer, compared with the lowest quartile of tHcy (<or=8.0 micromol/L; adjusted OR, 1.82; 95% CI, 1.20-2.75). The strong associations between MTHFD variants and the plasma tHcy levels and gastric cancer risk suggest, for the first time, a possible gene-environment interaction between genetic variants of folate-metabolizing genes and high tHcy levels in gastric carcinogenesis.

Association of total plasma homocysteine with methylenetetrahydrofolate reductase genotypes 677C&gt;T, 1298A&gt;C, and 1793G&gt;A and the corresponding haplotypes in Swedish children and adolescents

We studied 692 Swedish children and adolescents (aged 9-10 or 15-16 years, respectively), in order to evaluate the effect of the methylenetetrahydrofolate reductase (MTHFR) 677C>T, 1298A>C, and 1793G>A polymorphisms on total plasma homocysteine concentrations (tHcy). Genotyping was performed with Pyrosequencing technology. The MTHFR 677C>T polymorphism was associated with increased tHcy concentrations in both the children and the adolescents (P<0.001 for both age groups) in both genders. The effect of MTHFR 1298A>C was studied separately in subjects with the 677CC and 677CT genotypes, and the 1298C allele was found to be associated with higher tHcy levels both when children were stratified according to 677C>T genotypes, and when using haplotype analyses and diplotype reconstructions. The 1793A allele was in complete linkage disequilibrium with the 1298C allele. It was still possible to show that the 1793A allele was associated with lower tHcy levels, statistically significant in the adolescents. In conclusion, a haplotype-based approach was slightly superior in explaining the genetic interaction on tHcy plasma levels in children and adolescents than a simple genotype based approach (R2 adj 0.44 vs. 0.40). The major genetic impact on tHcy concentrations is attributable to the MTHFR 677C>T polymorphism. The common 1298A>C polymorphism had a minor elevating effect on tHcy, whereas the 1793G>A polymorphism had a lowering effect on tHcy.

The Effect of Mesna on Plasma Total Homocysteine Concentration in Hemodialysis Patients

Plasma total homocysteine (tHcy) level is an independent risk factor for the development of atherosclerosis. The degree of risk in most of the population is decreased by using dietary vitamin supplementation; however, more than 90% of patients with end-stage renal disease have increased tHcy levels despite supplementation. Only a small fraction of tHcy is removed by hemodialysis because of extensive disulfide bonding to albumin. The objective of this study is to determine whether a single intravenous dose of mesna, a thiol-containing drug analogue of taurine, facilitates tHcy clearance during hemodialysis. Initial in vitro thiol exchange tests were performed with mesna in plasma from dialysis patients. Mesna, 300 micromol/L (49.2 mg/L), was incubated with plasma at 37 degrees C, and free homocysteine was measured at various times. In vivo, mesna activity was tested in 10 hemodialysis patients by administering 2.5 or 5.0 mg/kg of mesna intravenously at the beginning of a treatment cycle. Blood samples were drawn throughout dialysis, and plasma tHcy levels were compared with those obtained from a previous dialysis session in which mesna was not administered. In vitro, mesna liberated 36.5% +/- 2.5% of protein-bound homocysteine in 30 minutes. In vivo, a single 2.5-mg/kg dose of mesna was ineffective; however, at 5.0 mg/kg, it caused a 55.2% +/- 3.9% decrease in plasma tHcy levels postdialysis compared with a 34.2% +/- 5.3% decrease with dialysis alone (P < 0.001). Intravenous mesna causes a rapid decrease in plasma tHcy levels during hemodialysis.

Thermolabile Methylenetetrahydrofolate Reductase C677T Polymorphism and Homocysteine Are Risk Factors for Coronary Artery Disease in Moroccan Population

Increased plasma total homocysteine (tHcy) levels have been shown to be a risk factor for coronary artery disease (CAD). The common methylenetetrahydrofolate reductase C677T (MTHFR C677T) polymorphism has been reported to be a strong predictor of mild hyperhomocysteinaemia (HHcy). We assessed whether this mutation was associated with increased risk of CAD and plasma levels of tHcy. We also evaluated interactions between this polymorphism, mild elevated tHcy levels and conventional risk factors of CAD. Method. Using PCR-RFLP analysis, we studied the frequency of the C677T genotypes and its effect on CAD and on tHcy concentrations in 400 subjects without and with CAD angiographically confirmed. There were 210 subjects with CAD and 190 subjects without CAD. Results. The frequencies of the C677T genotypes were 53% (59.5% in controls versus 48.1% in cases), 34.8% (32.1 in controls versus 37.1 in cases), and 11.8% (8.4% in controls versus 14.8% in cases), respectively, for 677CC, 677CT, and 677TT. The genotype frequencies were significantly different between case and control groups (P < .05). The 677T allele enhances the risk of CAD associated to HHcy (P < .01). In multivariate analysis models, MTHFR C677T polymorphism effect on CAD was masked by other risk factors. HHcy was only and independently influenced by MTHFR polymorphism and smoking habits, and it is a strong predictor of CAD independently of conventional risk factors. Conclusion. Our data suggest that HHcy is strongly and independently associated to CAD risk increase; and MTHFR C677T polymorphism and smoking habits were the main predictors of tHcy levels. The CAD risk increase is mainly associated with mild HHcy in 677TT, whereas in 677CT and 677CC it is mainly associated with the conventional risk factors.

Relationship between Metabolic Syndrome Categorized by Newly Recommended by International Diabetes Federation Criteria with Plasma Homocysteine Concentration

Plasma total homocysteine (tHcy) is an independent risk factor for cardiovascular disease and increased tHcy levels have been reported to be a novel risk factor of atherosclerotic disease. The aim of this study was to assess the association of the metabolic syndrome components with plasma (tHcy) level. Total 722 participants (284 men, 438 women) from the medical checkup program were enrolled in this study. The clinical characteristics and biochemical parameters of the subjects were assessed and the tHcy levels were compared according to the components of metabolic syndrome diagnosed by Adult Treatment Panel (ATP) III guideline and International Diabetes Federation (IDF) criteria. Among the components, groups with larger waist circumference and higher fasting blood glucose levels showed significantly higher tHcy level than the counterparts. Although statistically insignificant, mean concentrations of tHcy was higher in subjects with metabolic syndrome defined by both criteria. In multiple regression analysis, age, sex and systolic blood pressure were the independent determinants of tHcy level. In conclusion, tHcy level was not associated with metabolic syndrome defined by either criteria in Korean subjects.

Measuring subclinical atherosclerosis: is homocysteine relevant?

We systematically reviewed published studies looking at the relationship between total serum homocysteine (tHcy) and subclinical markers of atherosclerosis, such as carotid intimal-medial thickness (C-IMT), coronary artery calcium (CAC) and ankle-brachial index (ABI) in asymptomatic individuals. We analyzed these studies to examine this relationship as well as to guide future avenues of investigation by identifying studies that will help in the inclusion of tHcy levels in current guidelines on atherosclerotic disease management. tHcy has been known to be associated with clinically evident atherosclerotic disease. However, tHcy is not incorporated in current guidelines for diagnosis of subclinical disease in high-risk asymptomatic individuals. We searched online databases (e.g., PUBMED, MEDLINE) for published articles assessing the relationship between tHcy and C-IMT, CAC and ABI. We limited the studies to asymptomatic populations, and excluded any study including symptomatic patients or individuals with a history of coronary, peripheral or cerebrovascular disease. A systemic review of 19 articles revealed a significant association between elevated levels of tHcy and subclinical markers of atherosclerosis in asymptomatic individuals in most studies. Mean tHcy levels were consistently found to be higher in men compared to women. A total of 12 studies showed a significant association between tHcy and other risk markers of atherosclerosis, even after adjusting for age, sex and conventional risk factors. There were seven studies in unique populations that showed no significant relationship. We also observed that studies lowering baseline tHcy levels did not lead to an improvement in C-IMT, CAC or ABI scores. This might indicate that tHcy has a stronger role as a marker of atherosclerotic disease than as a risk factor for the same. Based on our review, we conclude that there is a significant association between the subclinical atherosclerotic process and tHcy, and it shows potential as a cheap marker for risk stratification of asymptomatic patients. However, future studies further elucidating this association and elaborating the exact role of tHcy in the atherosclerotic disease process are required. The results of these studies suggest the incorporation of plasma tHcy levels in future risk reduction protocols for identification of individuals at higher risk of atherosclerotic events, and thus to categorize them for more aggressive treatment with established preventive and therapeutic measures.

Homocysteine, MTHFR C677 T, Vitamin B12, and Folate Levels in Thai Children With Ischemic Stroke: A Case-control Study

Hyperhomocysteinemia has been identified as a risk factor for venous and arterial thrombosis especially in adult populations. Twenty-eight patients with an initial diagnosis of ischemic stroke and 100 controls, aged <or=18 years, were enrolled in this study. The mean plasma total homocysteine (tHcy) levels in patients and controls were significantly different with values of 8.7+/-3.6 and 7.5+/-2.4 micromol/L, respectively (P=0.01). The plasma tHcy at the 95th percentile was 11.5 micromol/L and patients whose plasma tHcy was above the 95th percentile had an odds ratio of 8.2 (95% confidence interval 1.4-47.2, P=0.02) for developing ischemic stroke. The genetic and acquired factors that could have affected plasma tHcy levels were studied and no differences were found between patients and controls. Factors that were investigated were vitamin B12, red blood cell folate, and serum folate levels as well as methylenetetrahydrofolate reductase C677T polymorphism. It is of note, however, that subjects whose plasma tHcy was above the 95th percentile had significantly lower serum folate levels (P=0.02).

Association of Homocysteine and Asymmetric Dimethylarginine With Atherosclerosis and Cardiovascular Events in Maintenance Hemodialysis Patients

Homocysteine (Hcy) and asymmetric dimethylarginine (ADMA) recently were recognized as potential risk factors for atherosclerosis in the general population, and the metabolism of each of these substances seems to be closely related. This study investigates the association between these substances and whether elevated serum Hcy and ADMA levels are related to high risk for atherosclerosis and cardiovascular events in maintenance hemodialysis (HD) patients. A study was made of 197 HD patients (132 men, 65 women; mean age, 56.9 +/- 8.6 years) for the correlation between plasma total Hcy (tHcy) and ADMA concentrations and the association of these substances with atherosclerotic indices of cervical intima-media thickness, plaque diameter, aortic calcification index, and aortic elongation. Cardiovascular events were followed up for 5 years in these patients. Mean plasma tHcy (37.3 +/- 25.8 micromol/L) and ADMA (0.77 +/- 0.16 micromol/L) levels were significantly greater in HD patients than in healthy subjects. Plasma tHcy level did not correlate with plasma ADMA level (r = -0.1; P = not significant). Although ADMA level was associated significantly with atherosclerotic indices from a simple regression analysis, this association was less from multiple regression analysis. When patients were classified into 3 groups according to ADMA level, cardiovascular events during 5 years were significantly greater in the group with the highest ADMA levels than in the other groups, confirmed by using a Cox proportional hazard model. However, no association was found between tHcy levels and atherosclerotic indices or cardiovascular events. ADMA level emerged as a potential risk factor for cardiovascular events that might be mediated in part by atherosclerosis in HD patients. Conversely, neither high nor low plasma tHcy levels were associated with atherosclerotic indices and cardiovascular events. This result for our HD patients does not fulfill the terms of traditional epidemiology and paradoxical reverse epidemiology of Hcy.

Plasma Homocysteine, Cobalamin/Folate Status, and Vascular Disease in a Large Population of Psychogeriatric Patients

Background: Cobalamin/folate deficiency and vascular disease are prevalent in elderly subjects and may lead to mental symptoms, but may even more often influence the severity of other organic and non-organic mental diseases. In the present study, we have evaluated cobalamin–folate status and the presence of vascular disease in 1,982 psychogeriatric patients investigated and diagnosed in a psychogeriatric clinic. The objective of the present study is to obtain information on the role of cobalamin/folate status and vascular disease in different diagnoses of psychogeriatric patients and their association with plasma homocysteine (tHcy). Methods: We have measured serum cobalamin, blood/serum folate, serum creatinine, plasma tHcy and evaluated the presence of vascular disease in 1,982 well-defined psychogeriatric patients. Results and Conclusions: The present study indicates that cobalamin/folate deficiencies do not play an important role in cognitive dysfunction in psychogeriatric patients, since only about 7% of the study population had metabolic cobalamin/folate deficiencies. Furthermore, cobalamin/folate deficiencies were rare in younger patients (below 70 years of age). We were also able to confirm our previous finding that there was no association between dementia of Alzheimer type (AD) and plasma tHcy level or metabolic cobalamin/folate deficiencies. Furthermore, we observed a low proportion of vascular disease in patients with AD, which does not give support for an association between well-defined AD and the presence of vascular disease. The presence of vascular disease was higher and of similar degree in patients with mild cognitive impairment and depression, which indicates an association between these diagnoses and the presence of vascular disease. The present study also shows that at plasma tHcy levels below 14 µmol/l, the likelihood of cobalamin/folate deficiency is small and further investigation of cobalamin/folate status could be omitted.

Molecular genetic analysis of the human dihydrofolate reductase gene: relation with plasma total homocysteine, serum and red blood cell folate levels

Disturbances in folate metabolism may increase the risk of certain malignancies, congenital defects and cardiovascular diseases. The gene dihydrofolate reductase (DHFR) is primarily involved in the reduction of dihydrofolate, generated during thymidylate synthesis, to tetrahydrofolate in order to maintain adequate amounts of folate for DNA synthesis and homocysteine remethylation. In order to reveal possible variation that may affect plasma total homocysteine (tHcy), serum folate and red blood cell (RBC) folate levels, we sequenced the DHFR coding region as well as the intron-exon boundaries and DHFR flanking regions from 20 Caucasian individuals. We identified a 9-bp repeat in the 5'-upstream region that partially overlapped with the 5'-untranslated region, and several single-nucleotide polymorphisms, all in non-coding regions. We screened subjects for the 9-bp repeat (n=417), as well as the recently reported 19-bp deletion in intron 1 (n=330), and assessed their associations with plasma tHcy, serum and RBC folate levels. The 19-bp del/del genotype was associated with a lower plasma tHcy (-14.4% [95% confidence interval: -23.5 to -4.5], P=0.006) compared with the wild-type genotype. This may suggest that intracellular folate levels are affected.

Direct, reverse or reciprocal causation in the relation between homocysteine and ischemic heart disease

Background Whether mild hyperhomocysteinemia is a risk factor for ischemic heart disease (IHD) or it is a secondary epiphenomenon remains unknown. We tested the alternative hypotheses that the Hcy–IHD relation is due to direct, reversal or reciprocal causality. Methods Ninety-four families from 32 pedigrees (296 members) including subjects who died for a premature (< 50 years) IHD and with at least one family member with also a premature IHD were selected. Three Structural Equation Models were created, in which causal ( Model 1), reversal ( Model 2), and reciprocal ( Model 3) tHcy–IHD relation were tested. Results were confirmed by testing “Pearl's instrumental inequalities”. Results A significant tHcy–IHD association was found in Model 1 (OR = 1.38, 95% CI: 1.01 to 1.88, for any increase of + 10 μmol/l in tHcy), as opposed to a non-significant association in the other models ( Model 2: MD = + 1.63 μmol/l, 95% CI: − 1.72 to + 4.99 μmol/l; Model 3: OR = 0.69, 95% CI: 0.17 to 2.78 for tHcy predictor of IHD; MD = − 0.46 μmol/l, 95% CI: − 2.41 to 1.48 μmol/l, for IHD predictor of tHcy). “Pearl's instrumental inequalities” qualify MTHFR as an instrument relative to the tHcy–IHD relation. A suppression effect may explain the non-significant total MTHFR–IHD relation (OR = 1.275, 95% CI: 1.02 to 1.71 for the indirect MTHFR–tHcy–IHD path; OR = 0.52, 95% CI: 0.17 to 1.64 for the direct MTHFR–IHD path). Conclusion Our findings support the assumption of a triangular genotype–phenotype–disease mediation process in the Hcy–IHD relation, and indirectly, of a causal relationship between moderately elevated plasma tHcy levels and IHD.

Total plasma homocysteine values among elderly subjects: Findings from the Maracaibo Aging Study

Objectives: The present study generated baseline data for total homocysteine (tHcy) in elderly Caribbeans of Hispanic ancestry, residing in Venezuela, their country of origin. Design and methods: 2106 participants in the Maracaibo Aging Study (MAS), older than 55 years, underwent standardized clinical and laboratory assessments, including measurement of plasma tHcy levels, folate, and vitamin B12 in fasting samples. Results: tHcy concentration in the healthy, normative group ranged from 4.1 to 31.8 μmol/L, with a median of 11.5 ± 4.7 μmol/L. tHcy level increased with age, was significantly higher in men than in women, and exhibited inverse correlations with folate and vitamin B12. Conclusions: tHcy levels of the MAS participants were generally higher than levels previously reported for community-dwelling elderly populations from other countries. The normative centile curves for tHcy can be used in disease risk analysis for this population, and possibly for other Hispanic populations residing in the Caribbean.

Elevated plasma homocysteine levels: Risk factor or risk marker for the development of dementia and Alzheimer's disease?

Elevated plasma homocysteine (tHcy) concentrations have been associated with an increased risk of developing dementia and Alzheimer's disease (AD). It is not clear, however, if an elevation in tHcy concentration is a "risk factor" with a direct pathophysiological role in the development of the disease or merely a "risk marker" reflecting an underlying process such as oxidative stress responsible for both the high tHcy concentrations and the development of AD. Epidemiological studies have confirmed that elevations in plasma tHcy temporally precede the development of dementia and that there is a continuous, inverse linear relation between plasma tHcy concentrations and cognitive performance in older persons. Several potential biological pathways that could mediate the observed association are briefly reviewed. In light of these data and the growing parallel interest in plasma tHcy as an emerging vascular risk factor there was considerable hope that vitamin therapy with folate, B12 and B6, shown to lower plasma tHcy levels, could significantly reduce the risk of stroke and dementia permitting healthy brain aging. The results from recent trials addressing the secondary prevention of stroke and myocardial infarction trials have been disappointing. However, the role of vitamins and other homocysteine lowering treatments in the primary prevention of stroke and dementia, as well as their role in preserving cognition among persons with mild cognitive impairment and early dementia deserves to be fully pursued.