Plasma homocysteine, methylenetetrahydrofolate reductase mutation and carotid damage in elderly healthy women

MTHFR C677T polymorphism affects normotensive diastolic blood pressure independently of blood lipids

BACKGROUND

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism was found to be associated with hypertension. High blood pressure (BP) is a major risk factor for cardiovascular disease, gestational hypertension, and high-risk pregnancy. BP is a complex trait strongly associated with blood lipid parameters. However, studies of the effect of MTHFR C677T polymorphism on BP levels independently of blood lipids are scarce. Our objective was to analyze and quantify the effect of MTHFR C677T polymorphism on normotensive BP independently of blood lipids.

METHODS

MTHFR C677T genotyping was done for 151 Israeli women attending the genetics clinic at Soroka Medical Center. Biochemical (blood lipids) and BP data were extracted from Soroka Medical Center records. BP was regarded as a continuous parameter using analysis of covariance and post hoc Tukey's HSD (honestly significant difference) analysis.

RESULTS

The frequencies of genotypes CC, TT, and CT were 41%, 12%, and 47%, respectively. A significant (P < 0.0001) association was found between genotype and diastolic BP (DBP) when adjusted to body mass index and age. Mean DBP was significantly lower for CC than for TT genotypes (71.2 vs. 78.7 mm Hg); however the difference between the heterozygotes (73.9 mm Hg) and the other 2 genotypes was not significant. Cholesterol, LDLcalc (LDLcalculaed), and homocysteine blood levels significantly contributed to the effect of MTHFR C677T polymorphism on the DBP trait. There was also significant association between genotype and folic acid levels.

CONCLUSIONS

MTHFR C677T polymorphism significantly affects DBP in Israeli women, independently of blood lipids. Each C to T substitution is associated with a mean 3.4-mm Hg increase in DBP.

Association of MTHFR C667T polymorphism with bone mineral density and fracture risk: an updated meta-analysis

This meta-analysis investigated the association of C677T polymorphism in MTHFR gene with bone mineral density (BMD) and fracture risk. The results suggested that C677T polymorphism was marginally associated with fracture risk. In addition, this polymorphism was modestly associated with BMD of lumbar spine, femoral neck, total hip, and total body, respectively.

INTRODUCTION

The methylenetetrahydrofolate reductase (MTHFR) gene has been implicated in the regulation of BMD and, thus, may serve as a potential risk factor for the development of fracture. However, results have been inconsistent. In this study, a meta-analysis was performed to clarify the association of C677T polymorphism in MTHFR gene with BMD and fracture risk.

METHODS

Published literature from PubMed and EMBASE were searched for eligible publications. Pooled odds ratio (OR) or weighted mean difference (WMD) and 95% confidence interval (CI) were calculated using a fixed- or random-effects model.

RESULTS

Twenty studies (3,525 cases and 17,909 controls) were included in this meta-analysis. The TT genotype of C677T polymorphism was marginally associated with an increased risk of fracture under recessive model (TT vs. TC + CC: OR = 1.23, 95% CI 1.04-1.47). Using this model, similar results were found among East Asians (OR = 1.40, 95% CI 1.07-1.83), female subpopulation (1.27, 95% CI 1.04-1.55), cohort studies (OR = 1.24, 95% CI 1.08-1.44), and subjects younger than aged 60 years (OR = 1.51, 95% CI 1.10-2.07). In addition, under homogeneous co-dominant model, there was a modest association of C677T polymorphism with BMD of lumbar spine (WMD = -0.017 g/cm(2); 95%CI, -0.030-(-0.005) g/cm(2)), femoral neck (WMD = -0.010 g/cm(2); 95% CI -0.017-(-0.003) g/cm(2)), total hip (WMD = -0.013 g/cm(2), 95% CI -0.022-(-0.004) g/cm(2)), and total body (WMD = -0.020 g/cm(2); 95% CI -0.027-(-0.013) g/cm(2)), respectively.

CONCLUSIONS

This meta-analysis suggested that C677T polymorphism was marginally associated with fracture risk. In addition, this polymorphism was modestly associated with BMD of lumbar spine, femoral neck, total hip, and total body, respectively.

A bootstrap-based regression method for comprehensive discovery of differential gene expressions: an application to the osteoporosis study

A common purpose of microarray experiments is to study the variation in gene expression across the categories of an experimental factor such as tissue types and drug treatments. However, it is not uncommon that the studied experimental factor is a quantitative variable rather than categorical variable. Loss of information would occur by comparing gene-expression levels between groups that are factitiously defined according to the quantitative threshold values of an experimental factor. Additionally, lack of control for some sensitive clinical factors may bring serious false positive or negative findings. In the present study, we described a bootstrap-based regression method for analyzing gene-expression data from the non-categorical microarray experiments. To illustrate the utility of this method, we applied it to our recent gene-expression study of circulating monocytes in subjects with a wide range of variations in bone mineral density (BMD). This method allows a comprehensive discovery of gene expressions associated with osteoporosis-related traits while controlling other common confounding factors such as height, weight and age. Several genes identified in our study are involved in osteoblast and osteoclast functions and bone remodeling and/or menopause-associated estrogen-dependent pathways, which provide important clues to understand the etiology of osteoporosis.

AVAILABILITY

SAS code is available from the authors upon request.

Role of methylenetetrahydrofolate reductase gene polymorphisms (C677T, A1298C, and G1793A) in the development of early onset vasculogenic erectile dysfunction

BACKGROUND AND AIMS

The methylenetetrahydrofolate reductase (MTHFR) gene plays a key role in the metabolism of folate and homocysteine (Hcy) and its mutations have been associated with high serum Hcy level. Elevated serum Hcy has been linked to impaired endothelial function and occlusive vascular disease. We studied the association among the different genotypes of all three MTHFR polymorphisms (C677T, A1298C, and G1793A) and the risk of early-onset vasculogenic erectile dysfunction (VED).

METHODS

We performed a case-control study of 114 men with early-onset VED and 228 age-matched controls. Genotyping of MTHFR gene polymorphisms was performed using polymerase chain reaction restriction fragment length polymorphism (PCR-RLFP) technique. We also measured plasma lipids, Hcy, folate, and vitamin B12 levels.

RESULTS

Patients with early-onset VED had higher serum Hcy levels (12.29 ± 2.32 vs. 9.82 ± 2.35 μmol/L, p = 0.001) and higher prevalence of 677TT homozygocity compared to controls (15.8% vs. 11.4%, p = 0.01). Serum Hcy concentration was significantly higher in individuals with 677TT, 1298CC, and 1793GG genotypes. Subgroup analysis according to severity of ED (mild, moderate, and severe) showed that patients with severe VED had higher serum Hcy levels compared to patients with mild VED (13.48 ± 2.51 vs. 11.21 ± 2.32 μmol/L, p = 0.001).

CONCLUSIONS

Odds ratio seems to demonstrate that individuals with the MTHFR 677TT genotype and the 677TT + 1298AC combined genotype had a 3.16- and 3.89-fold increased risk for developing VED, suggesting a possible association of MTHFR polymorphisms with the risk of early-onset VED.

Analysis of three functional polymorphisms in relation to osteoporosis phenotypes: replication in a Spanish cohort

Osteoporosis is a complex disease involving many putative genetic factors. Association analysis of functional SNPs in candidate genes is an important tool for their identification. However, this approach is affected by limited power, population stratification, and other drawbacks that lead to discordant results. Replication in independent cohorts is essential. We performed association analyses of three functional polymorphisms previously associated with bone phenotypes--namely, Ala222Val in MTHFR, Ile1062Val in LRP6, and -13910C>T in LCT--in a cohort of 944 postmenopausal Spanish women, all of them with lumbar spine (LS) bone mineral density (BMD) data and most with femoral neck (FN) BMD and fracture data. We found significant differences between genotypes only for the MTHFR polymorphism and vertebral factures, with an OR of 2.27 (95% CI 1.17-4.38) for the TT vs. CC/CT genotypes, P = 0.018. We present genotype and allele frequency data for LCT -13910C>T for a Spanish population, where the T allele (conferring lactase persistence) has a frequency of 38.6%. Genotype frequencies were consistent with observed clines in Europe and with the prevalence of lactase nonpersistence. The LCT -13910C>T polymorphism was significantly associated with height and weight, such that T allele carriers were 0.88 cm taller (95% CI 0.08-1.59 cm, P = 0.032, adjusted by age) than CC individuals and TT homozygotes were 1.91 kg heavier than CC/CT individuals (95% CI 0.11-3.71 kg, P = 0.038, adjusted by age). In conclusion, no significant association was observed between the studied polymorphisms and LS BMD or FN BMD in postmenopausal Spanish women, and only MTHFR Ala222Val was associated with vertebral fractures.

MTHFR 677 C>T Polymorphism reveals functional importance for 5-methyltetrahydrofolate, not homocysteine, in regulation of vascular redox state and endothelial function in human atherosclerosis

BACKGROUND

The role of circulating homocysteine as an atherosclerosis risk factor has recently been questioned. However, 5-methyl-tetrahydrofolate (5-MTHF), the circulating metabolite of folic acid participating in homocysteine metabolism, has direct effects on vascular function. We sought to distinguish the effects of plasma versus vascular tissue 5-MTHF and homocysteine on vascular redox and endothelial nitric oxide bioavailability in human vessels.

METHODS AND RESULTS

We used the methyl tetrahydrofolate reductase (MTHFR) gene polymorphism 677C>T as a model of chronic exposure of the vascular wall to varying 5-MTHF levels in 218 patients undergoing coronary artery bypass graft surgery. Vascular superoxide, vascular 5-MTHF, and total homocysteine were determined in saphenous veins and internal mammary arteries obtained during surgery. Nitric oxide bioavailability was evaluated by organ bath studies on saphenous vein rings. MTHFR genotype was a determinant of vascular 5-MTHF (not vascular homocysteine). Both MTHFR genotype and vascular 5-MTHF were associated with vascular nitric oxide bioavailability and superoxide generated by uncoupled endothelial nitric oxide synthase. In contrast, vascular homocysteine was associated only with NADPH-stimulated superoxide.

CONCLUSIONS

Genetic polymorphism 677 C>T on MTHFR affects vascular 5-MTHF (but not homocysteine) and can be used as a model to distinguish the chronic effects of vascular 5-MTHF from homocysteine on vascular wall. Vascular 5-MTHF, rather than plasma or vascular homocysteine, is a key regulator of endothelial nitric oxide synthase coupling and nitric oxide bioavailability in human vessels, suggesting that plasma homocysteine is an indirect marker of 5-MTHF rather than a primary regulator of endothelial function.

No association between hip geometry and four common polymorphisms associated with fracture: the Danish osteoporosis prevention study

Both osteoporosis and hip geometry are independently associated with fracture risk. There is a significant genetic contribution to the risk of osteoporosis, and evidence provided by twin studies has suggested that hip geometry may also in part be genetically programmed. Polymorphisms in a number of genes, including those coding for methylene-tetrahydrofolate reductase (MTHFR c.677C > T), the purinergic P2X(7) receptor (Glu496Ala and Ile568Asn), and the low-density lipoprotein receptor-related protein 5 (LRP5 exon 9 [c.266A > G]), have been associated with an increased fracture incidence and/or reduced bone mineral density (BMD). The aim of the present study was to test whether these polymorphisms influence hip structural geometry in perimenopausal women. The four polymorphisms were genotyped in 800 healthy recently perimenopausal women never using hormone replacement therapy. BMD of the femoral neck was measured using a Hologic QDR-2000 densitometer and femoral neck axis length, neck width, neck shaft angle, and femoral head diameter were measured from the screen images. Genotype frequencies were compatible with Hardy-Weinberg equilibrium. No significant differences between homozygotes for the minor allele and carriers of the common allele regarding parameters of hip geometry were demonstrated. According to the anthropometric characteristics of the subjects, only body height in the MTHFR TT genotype group was significantly different from the combined CT/CC genotype group (P < 0.05). The geometric dimensions of the proximal femur in perimenopausal women are not associated with the MTHFR c.677C > T, P2X(7) (Glu496Ala), P2X(7) (Ile568Asn), and LRP5 exon 9 (c.266A > G) polymorphisms.

Methylentetrahydrofolate reductase and nitric oxide synthase polymorphism in patients with atherosclerosis and diabetes

The development of the atherosclerosis is based on multifactorial causes. In addition to the traditional risk factors, gene polymorphisms can play a role in the disease. Therefore in this study we investigated whether the eNOS and MTHFR gene polymorphisms is associated with myocardial infarction and stroke in patients with or without diabetes. We have identified polymorphisms in the NOS 3 gene and one of these polymorphisms, Glu(298-->)Asp, was found to be a major risk factor for carotid artery disease and myocardial infarction. Our results indicate that the MTHFR G677T allele is significantly associated with MI. MTHFR 677 G/T genotyping may be of clinical importance as a prognostic and therapeutic marker, although further studies are needed to substantiate this hypothesis.

Hyperhomocysteinemia, intima-media thickness and C677T MTHFR gene polymorphism: a correlation study in patients with cognitive impairment

OBJECTIVE

Intima-media thickness (IMT) seems associated with risk of Alzheimer disease (AD). Homocysteine (hcy) is a risk factor for vascular diseases and dementia. This study aimed at investigating the possible relationship among IMT, plasma hcy and C677T methylentetrahydrofolate reductase (MTHFR) polymorphism in relation to cognitive status.

METHODS

Sixty-three patients with cognitive impairment and 64 controls underwent biochemical, neuropsychological and carotid ultrasound assessment.

RESULTS

After age and folate adjustment, plasma hcy correlated with both Mini Mental State Examination (MMSE) score (r=-0.7, p<0.01) and IMT (r=0.7, p<0.01). Among patients with cognitive impairment, carriers of TT677 MTHFR genotype had plasma hcy (p<0.001) and IMT (p<0.01) values higher than non carriers. Furthermore, multiple regression analysis showed that MMSE scores were associated with plasma hcy (beta=-0.3, p=0.01), IMT (beta=-0.3, p=0.01) and TT677 MTHFR genotype (beta=-0.3, p=0.02). Structural equation modelling showed that the relation between hcy levels and MMSE score was partly direct (parameter estimate=-0.6; p=0.01) and partly mediated by IMT values (parameter estimate=-0.4; p=0.03). Finally, IMT resulted associated with hypertension (parameter estimate=0.8; p<0.0001).

CONCLUSION

Our findings suggest that TT677 MTHFR genotype promotes plasma homocysteine increase which in turn may favour intima-media thickening in patients with cognitive impairment. Hcy may promote neuronal damage through multiple mechanisms, including a micro-vascular damage, mediated by IMT increase, and a direct neuro-toxic effect.

Measuring subclinical atherosclerosis: is homocysteine relevant?

OBJECTIVES

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.

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Associations of methylenetetrahydrofolate reductase C677T polymorphism with markers of subclinical atherosclerosis: the Cardiovascular Risk in Young Finns Study

OBJECTIVE

To study whether the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism or serum homocysteine concentration is associated with carotid artery intima media thickness (IMT), carotid artery compliance (CAC) or brachial artery flow mediated dilatation (FMD) in a healthy Finnish adult population.

METHODS

Cross-sectional data obtained in 2001 for the Cardiovascular Risk in Young Finns Study were used. Carotid artery IMT, CAC and brachial FMD were measured by ultrasound and serum homocysteine concentrations using a commercial immunoassay kit. We studied 1,440 subjects (aged 24-39 years). Genotyping was performed using the 5' nuclease TaqMan assay.

RESULTS

Homocysteine values differed between genotypes in women and men (ANOVA, p<0.001 for both sex groups): the genotype raised values in the order of CC, CT, TT. There was a significant difference in CAC values between the MTHFR genotypes in men (ANOVA, p = 0.008), and the CC genotype had the lowest values. In multivariate linear regression analysis adjusted for other major coronary risk factors (e.g. age, smoking, body mass index, systolic blood pressure, C-reactive protein), the association remained significant (R (2) = 25.8 %, beta = 0.091; p = 0.02). Homocysteine level was directly associated with CAC in the whole population (R (2) = 18.0 %, beta = 0.012; p = 0.014) and in women (R (2) = 9.3%, beta = 0.02; p = 0.013), but not in men (R (2) = 15.2 %, beta = 0.004; p = 0.444). We found no association between homocysteine level or the MTHFR polymorphism and carotid IMT or brachial artery FMD.

CONCLUSIONS

The findings suggest that the MTHFR polymorphism does not influence IMT or FMD, but that the T allele may have an effect on CAC in men.

Polymorphisms and the expression of genes encoding enzymes involved in cardiovascular diseases

BACKGROUND

Atherosclerosis, a multi-factorial disease, is the main determinant of cardiovascular disease (CVD) leading to high mortality and morbidity in westernized countries. Gene polymorphisms and gene expression related to the atherosclerosis process can be identified using a genome-wide approach or looking for candidate disease-causing genes.

METHODS

Using genome wide strategy or candidate gene approach various genes, including paraoxonase genes, which are involved in lipid metabolism, oxidation, inflammation and coagulation, have been associated to atherosclerosis.

CONCLUSION

Evaluation of gene polymorphisms, together with traditional and novel biochemical parameters, may help identify individuals at a high risk for CVD. Genetic characterization of susceptibility genes may also lead to new drugs for atherosclerosis prevention and treatment. In addition, gene expression studies can provide novel insights into the molecular mechanism of lesion development and progression.

B-group vitamins, MTHFR C677T polymorphism and carotid intima-media thickness in clinically healthy subjects

OBJECTIVE

Plasma B-group vitamins and age may affect the carotid intima-media thickness (IMT) in subjects with different 677TT genotype of the methylenetetrahydrofolate reductase (MTHFR) gene.

DESIGN

A hospital-based cross-study.

SETTING

Genomic and Vascular Center, Changhua Christian Hospital, Changhua, Taiwan.

SUBJECTS

Five hundred and forty-one clinically healthy subjects.

INTERVENTION

Fasting plasma, homocysteine (Hcy), vitamin B(6), vitamin B(12), folate and B-mode carotid ultrasound.

RESULTS

MTHFR genotype, plasma concentrations of folate, vitamin B(6) and vitamin B(12) and age were significantly correlated to the plasma Hcy concentration. MTHFR 677TT carriers had higher concentrations of Hcy than did subjects with the CC and CT genotypes. Age, sex, body mass index and plasma Hcy were independent contributors to increase carotid IMT. However, with stratification by mean value of age and B-group vitamins concentrations, we found that at advanced age, lower plasma folate and vitamin B(12) were three risk factors involved in the enhancing effect of the MTHFR 677TT genotype on the increase of plasma Hcy and carotid IMT.

CONCLUSION

MTHFR 677TT-related carotid atherosclerosis was only identified in healthy elderly subjects with lower level of plasma folate and vitamin B(12).

SPONSORSHIP

Changhua Christian Hospital.

Molecular genetic studies of gene identification for osteoporosis: a 2004 update

This review summarizes comprehensively the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of December 2004. It is intended to constitute a sequential update of our previously published review covering the available data up to the end of 2002. Evidence from candidate gene association studies and genome-wide linkage studies in humans, as well as quantitative trait locus mapping animal models are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. An important extension of this update is incorporation of functional genomic studies (including DNA microarrays and proteomics) on osteogenesis and osteoporosis, in light of the rapid advances and the promising prospects of the field. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

Homocysteine is not associated with arterial thickness and stiffness in healthy middle-aged French volunteers

BACKGROUND

To study the association between the total plasma homocysteine (tHcy) concentration and the carotid artery intima-medial wall thickness (IMT), pulse wave velocity (PWV) and the presence of arterial plaques in a French population.

METHODS

Cross-sectional analysis of data from 556 male and 559 female middle-aged participants (mean (+/-SD) age 59.6+/-4.7 years) provided by an ongoing intervention trial.

RESULTS

Mean geometric tHcy concentration was higher for men than for women (10.6 vs. 8.5 micromol/L, p<0.001) and was associated in the expected direction with known determinants. The mean IMT was 0.71+/-0.1 mm for men and 0.69+/-0.1 mm for women (p<0.001), the mean PWV was, respectively, 12.0+/-2.8 and 10.9+/-2.2 m/sec (p<0.001), and the percentages of subjects with plaques were, respectively, 40.8% and 22.7% (p<0.001). In men only, the age-adjusted mean IMT and PWV increased with an increasing tHcy concentration: the IMT was 0.71 mm in the first tHcy-quartile and 0.73 mm in the fourth tHcy-quartile (p for linear trend=0.03), the PWV values were, respectively, 11.6 and 12.4 m/sec (p for linear trend=0.01). These associations disappeared after adjustment for conventional cardiovascular disease risk factors.

CONCLUSION

In this population, the tHcy concentration was not associated with measures of arterial thickness and stiffness.

Methylenetetrahydrofolate reductase gene A222V polymorphism and risk of ischemic stroke

The 5,10-methylenetetrahydrofolate reductase ( MTHFR ) gene 677C --> T polymorphism causes an A222V amino acid change which affects MTHFR enzyme activity and can increase homocysteine, a vascular disease risk factor. This polymorphism was examined for association with stroke. In a case-control study of 241 ischemic stroke patients and 304 controls in Hong Kong, the V allele increased in stroke [28% vs. 20%, odds ratio (OR) 1.5, p=0.003]. A lack of significance for the increase in the VV genotype (7.5% vs. 4.6%, OR 1.7, p = 0.16) may be due to its rarity in this region. V -allele carriers had more severe strokes (according to the NIH stroke scale). The association of the V allele with stroke occurred mostly in women or older subjects and was due to decreasing V allele frequency with age, as seen in other studies. This V frequency decline with age might be due to a loss of V -carrying controls from a higher risk of cancer, vascular disease, bone fracture, and kidney failure when folate is sparse. Examination of previous studies revealed that the association of VV genotype with stroke appeared stronger in Japan than elsewhere, possibly due to dietary differences. Perhaps folate supplementation for stroke prevention would particularly benefit VV individuals in such high-risk regions.

Low concentrations of folate, not hyperhomocysteinemia, are associated with carotid intima-media thickness

AIM

We examined whether total homocysteine, B vitamins and the 5,10-methylenetetrahydrofolate reductase (MTHFR) 677C-->T polymorphism are related to common carotid intima-media thickness, a marker of atherosclerosis, and carotid distension, a marker of arterial stiffness.

METHODS

We used cross-sectional data from 819 individuals aged 50-70 years. B-mode ultrasound of the distal common carotid arteries was performed to determine maximum carotid intima-media thickness, mean carotid intima-media thickness and distension.

RESULTS

Carotid intima-media thickness and distension did not differ across homocysteine, serum folate, vitamin B(6) and vitamin B(12) quartiles or between MTHFR C677T genotype. Erythrocyte folate was independently associated with maximum carotid intima-media thickness (mean difference first versus third quartile, 0.03 mm, 95% CI 0.004-0.06 mm; first versus fourth quartile, 0.03 mm, 95% CI -0.002 to 0.06 mm). Further adjustment for homocysteine did not affect this association. Folate deficient subjects had greater maximum carotid intima-media thickness than those with high-normal folate concentrations (serum folate: mean difference 0.05 mm, 95% CI 0.01-0.08 mm; erythrocyte folate: mean difference 0.04 mm, 95% CI -0.03 to 0.11 mm).

CONCLUSION

Low folate concentrations, independent of hyperhomocysteinemia, may promote atherogenesis. Our findings confirm the null association of homocysteine with carotid intima-media thickness observed in other population-based studies, suggesting that hyperhomocysteinemia does not perpetuate atherosclerosis or arterial stiffness.

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism is associated with osteoporotic vertebral fractures, but is a weak predictor of BMD

Osteoporosis is a common disease with a strong genetic component. Linkage studies have suggested linkage between BMD and loci on chromosome 1. The MTHFR gene is located on chromosome 1. MTHFR catalyzes the conversion of 5,10-methylenetetrahydrofolate to 5-methylenetetrahydrofolate, which is used for homocysteine methylation to methionine. The rare genotype (TT) of the C677T polymorphism has previously been demonstrated to be associated with increased plasma homocysteine levels in individuals with inadequate plasma folate levels. Recently, the TT genotype has been found to be associated with reduced bone mass. We therefore examined if the C677T polymorphism in the MTHFR gene is associated with changes in bone mass and risk of osteoporotic fractures in 388 osteoporotic patients and 336 normal individuals. The distributions of the genotypes CC, CT and TT in women with osteoporotic vertebral fractures and normal controls were 43.5%, 42.2% and 14.3% and 52.0%, 42.0% and 8.0%, respectively, chi2 = 5.62, P = 0.06. Since studies of the functionality of this polymorphism have revealed that only the TT genotype is associated with biochemical changes, we also compared the prevalence of the TT genotype versus the CT- and CC genotypes in patients and controls and found that the TT genotype is significantly more common in women with vertebral fractures (14.3%) compared with normal controls (8.0%), chi2 = 4.31, P < 0.05. Logistic regression analysis demonstrated that vertebral fractures were significantly associated with BMD (lumbar spine) and height but only marginally with the MTHFR genotype (P = 0.06). Multiple linear regression analysis revealed that weight, age and the MTHFR polymorphism were predictors of lumbar spine BMD in women. However, age- and gender-corrected BMD of the lumbar spine and the hip was not significantly different between MTHFR genotypes. Furthermore, individuals with the TT genotype did not have BMD significantly lower than the combined group of individuals with the CT- or CC genotypes. In conclusion, we have demonstrated that the rare TT genotype of the C677T polymorphism in the MTHFR gene is associated with increased risk of osteoporotic fractures in women and a weak predictor of lumbar spine BMD.

The genetics of stroke

PURPOSE OF REVIEW

Ischaemic stroke is a heterogeneous disease caused by different pathogenic mechanisms, of which small artery and large artery stroke are the most common. The identification of the genes involved is unclear. The likely candidate genes associated with stroke are those that are associated with matrix deposition (stromelysin-1, MMP3), inflammation (IL-6), and lipid metabolism (hepatic lipase, APOE, PON1) and clotting (factor V Leiden, fibrinogen).

RECENT FINDINGS

In this review we will only discuss those genes in which there has been a significant contribution to the understanding of stroke since October 2003.

SUMMARY

The published data were reviewed to determine the robustness of these associations and to examine whether there is any evidence of risk modification by factors such as smoking habit, known to be associated with stroke.

C677T mutation of methylenetetrahydrofolate reductase gene and serum homocysteine levels in Turkish patients with coronary artery disease

Elevated levels of homocysteine is a risk factor for coronary artery disease. The C677T transition in methylenetetrahydrofolate reductase (MTHFR) is associated with increased homocysteine levels in the general population. We analysed the association between the MTHFR C677T polymorphism and serum homocysteine concentrations in patients with coronary artery disease (CAD). Allele frequencies for the 'C' (wild-type) and 'T' alleles were 0.71 and 0.29 in CAD patients and 0.70 and 0.30 in controls, respectively. There was no difference in the distribution of MTHFR genotypes between patients with CAD and control subjects (p > 0.05). In the patient group, homocysteine levels were higher than controls but not significantly (13.99 +/- 7.44 vs. 11.77 +/- 5.18 micromol l(-1); p > 0.05). Serum homocysteine concentration was significantly higher in the TT genotype with respect to CC and CT genotypes in both the control group (p < 0.01) and patient group (p < 0.01). Systolic and diastolic blood pressures in subjects with different MTHFR genotypes did not differ significantly. In conclusion, MTHFR C677T mutation was significantly related to hyperhomocysteinemia. In spite of the clear effect of the MTHFR polymorphism on elevated homocysteine levels, we did not observe any associations among the MTHFR genotypes with a the risk of CAD in the Turkish population.

Homocysteine and carotid intima-media thickness: a critical appraisal of the evidence

This review examines the relationship between hyperhomocysteinemia, a risk factor for vascular disease, and carotid intima-media thickness (CIMT), a valid marker of generalized atherosclerosis and future vascular disease risk. The relationship between two important determinants of hyperhomocysteinemia in the general population-folate status and the 677C --> T methylenetetrahydrofolate reductase (MTHFR) polymorphism-and CIMT is also covered.

METHODS

We searched literature databases for articles examining homocysteine and CIMT published before September 2003.

RESULTS

We identified 54 studies. Observational studies generally failed to demonstrate a relationship between homocysteine and CIMT in homocystinuric, uremic, hypercholesterolemic or non-insulin-dependent diabetes mellitus patients or in subjects with insulin insensitivity. Weak associations, but usually only in certain sub-populations were found in vascular disease patients and in population-based studies. B vitamins reduce the progression of CIMT in renal transplant recipients and vascular disease patients as demonstrated by two trials. The majority of studies demonstrated increased CIMT in individuals with the MTHFR 677TT genotype. Folate status showed no relation to CIMT.

DISCUSSION

In non-patient populations, hyperhomocysteinemia is weakly associated with CIMT. The association of the 677 C--> T MTHFR polymorphism with CIMT further supports this finding. Lastly, folate levels may need to reach a critically low status before an association can be found between folate and CIMT. Larger trials in various population types are needed to determine whether folate alone or in combination with Vitamins B6 and B12 will slow down or even reverse atherosclerotic progression.

Methylene tetrahydrofolate reductase C677T mutation and left ventricular hypertrophy in Turkish patients with type II diabetes mellitus

This study was designed to investigate, in the Turkish population, the association of methylene tetrahydrofolate reductase (MTHFR) C677T polymorphism and left ventricular hypertrophy (LVH) in patients with type II diabetes mellitus. Our study included 249 patients with type II diabetes mellitus (102 men, 147 women) and 214 healthy volunteers as controls (91 men, 123 women). MTHFR C677T genotypes were determined by polymerase chain reaction, restriction fragment length polymorphism techniques. No differences were observed in the distribution of MTHFR genotypes or allele frequencies in the cases versus the controls. The frequency of the MTHFR-mutated allele (T) was 31.7% in the type II diabetes mellitus versus 31.1% of the controls. The homozygous mutation (T/T) in the MTHFR gene was identified in 12% of the type II diabetes mellitus versus 9.3% of the controls. Patients with the TT genotype showed a higher prevalence of LVH when compared to patients with the CC and CT genotypes (p = 0.01). The MTHFR gene C677T mutation may be a possible risk factor for the development of LVH in the type II diabetic patients.

Genetics of Ultrasonographic Carotid Atherosclerosis

The search for genes related to the cause of common complex disorders such as cardiovascular disease has been frustrating, partly because of the many factors known to contribute to cardiovascular disease and the potential "distance" of cardiovascular disease as a phenotype from genes and gene products. Linkage and association studies for phenotypes more proximal in the pathway from DNA sequence variation to overt clinical disease, such as ultrasound-defined carotid atherosclerosis, may potentially be more enlightening. Only one genetic variant previously reported to be associated with atherosclerosis or clinically evident cardiovascular disease, matrix metalloproteinase (MMP) 3, has shown consistently positive associations with carotid disease, although it has not been studied widely. Another, PON1 L55M, is weakly associated in subgroups only, and 2, ApoE and MTHFR, are equivocal. Genetic variants reported to be associated with clinical cardiovascular disease show weak or no relationship to carotid atherosclerosis. This may reflect the known inconsistency in associations of genetic variants with clinical cardiovascular disease itself. Alternatively, genetic determinants of ultrasound-defined carotid atherosclerosis may differ from those of clinically manifest cardiovascular disease and may require pursuit through large-scale genomic studies of carotid atherosclerosis as a distinct phenotype. Only 1 genetic variant, MMP 3, has shown consistently positive associations with ultrasonographic carotid disease, although it has not been studied widely. Another, PON1 L55 mol/L, is weakly associated in subgroups only. Genetic variants reported to be associated with clinical cardiovascular disease show weak or no relationship to carotid atherosclerosis.

Genetic risk factors for stroke and carotid atherosclerosis: insights into pathophysiology from candidate gene approaches

Ischaemic stroke is the most common form of stroke and is caused by atherosclerosis in most patients. Several genetic determinants contribute to stroke risk. Of these, carotid intimal-medial wall thickness (IMT) is particularly relevant, because it is a surrogate measure of subclinical atherosclerosis and a strong predictor of future ischaemic stroke. Studies of twins, siblings, and families have provided significant evidence for heritability, but the genes involved have not been identified. Some researchers have reported that IMT is high in people with functional variants of genes related to matrix deposition (MMP3), inflammation (interleukin 6), and lipid metabolism (hepatic lipase, APOE, CETP, and PON1). In this review, we assess the robustness of these associations and examine whether there is any evidence of risk modification by factors, such as smoking.

The C677T polymorphism of the methylenetetrahydrofolate reductase gene is associated with the level of decrease on diastolic blood pressure in essential hypertension patients treated by angiotensin-converting enzyme inhibitor

OBJECTIVES

Elevated plasma homocysteine has been implicated as a risk factor for hypertension. C677T polymorphism in methylenetetrahydrofolate reductase gene (MTHFR) is a major determinant of hyperhomocysteinemia, which results in endothelial dysfunction. Angiotensin-converting enzyme (ACE) inhibitors appear to remedy the endothelial dysfunction and restore endothelium-dependent vasodilatation. The co-existence of genetic polymorphisms in drug metabolizing enzymes, targets, receptors, and transporters may influence the drug efficacy. The purpose of this study was to investigate whether short-term blood pressure control by benazepril, an ACE inhibitor, was modulated by C677T MTHFR gene polymorphism.

METHODS AND RESULTS

A total of 444 hypertensive patients, aged 27 to 65 years, without any anti hypertensive therapy within 2 weeks were included. All of them were treated orally with benazepril at a single daily fixed dosage of 10 mg for 15 consecutive days. Blood pressures were measured at baseline and on the 16th day of treatment. Among them, the frequency of MTHFR C677T genotype CC, CT and TT was 24.3%, 51.8%, and 23.9%, respectively. In a recessive model (CC+CT versus TT genotype), both baseline diastolic blood pressure (DBP) and diastolic blood pressure response (DeltaDBP) were significantly higher in patients with the TT genotype than in those with the CT or CC genotype (P value=0.0076 for DBP, and P value=0.0005 for DeltaDBP). We further divided all patients into three groups based on the tertiles of the DeltaBP distribution. Compared to subjects in the lowest tertile of DeltaDBP, the adjusted relative odds of having the TT genotype among subjects in the highest tertile was 2.6 (95% CI, 1.4 to 4.9). However, baseline systolic blood pressure (SBP) and SBP response did not significantly associate with MTHFR C677T polymorphism.

CONCLUSIONS

Our finding suggests that MTHFR C667T polymorphism modulated baseline DBP and DBP responsiveness by short-term treatment of ACE inhibitor in Chinese essential hypertensive patients.

Elevated plasma homocysteine is positively associated with age independent of C677T mutation of the methylenetetrahydrofolate reductase gene in selected Egyptian subjects

This study aimed to evaluate the plasma homocysteine (tHcy) and folate levels as well as the methylenetetrahydrofolate reductase (MTHFR) C677T mutation in Egyptian subjects. Fasting total homocysteine (tHcy) and the (MTHFR) C677T mutation were evaluated in 50 healthy young control males (age 35-50 years, Gp1), 50 elderly males age ranged between 50-75 years without any cardiovascular diseases (Gp2) and 50 age matched elderly male patients (Gp3) with myocardial infarction. There was a significant elevation of plasma tHcy in the patients group and Gp2 compared to the young control group (Gp1). The total plasma homocysteine (tHcy) in the control group, Gp2 and the patients group were 17.99 +/- 9.76, 39.9 +/- 20.06 and 43.8 +/- 13.13 mumol/L respectively. The frequency of the TT genotype was 12% in the patient group compared with 8 % in the young healthy controls and elderly subjects (Gp2). The CT genotype constituted 36%, 48% and 44% in the control group, Gp2 and the patients group respectively. There was no significant difference in the occurrence of the TT genotype between the studied groups. Plasma tHcy correlated positively with age, total cholesterol, urea, creatinine, glucose levels and carotid intimal thickness (CIT). Conclusion: The MTHFR mutation does not seem to be associated with either high tHcy or the occurrence of cardiovascular diseases in the studied patients. However, elevated plasma tHcy level positively correlates with age in the studied subjects.

Age and Gender Affect the Relation between Methylenetetrahydrofolate Reductase C677T Genotype and Fasting Plasma Homocysteine Concentrations in the Framingham Offspring Study Cohort

The C677T variant of methylenetetrahydrofolate reductase (MTHFR), a key enzyme in the remethylation of homocysteine to methionine, is a frequent genetic cause of mild hyperhomocysteinemia among individuals with low folate status. However, little is known about the influence of subject characteristics, such as age and sex, on the relation between the C677T MTHFR polymorphism and fasting plasma total homocysteine (tHcy) concentrations. The aim of the present study was to explore the influence of age and gender, together with folate status, on the association between the C677T polymorphism and tHcy concentrations. The C677T genotype was determined for 1820 participants from the fifth examination of the Framingham Offspring Study. Mean age of the participants was 56 y (range 28-82 y). The allelic distribution was not different from the Hardy-Weinberg equilibrium, with a TT frequency comparable in men and women (14%). Geometric mean tHcy was 15% higher in men than in women (P < 0.001), and women had significantly higher plasma folate levels (P < 0.001). Geometric mean tHcy was significantly higher in TT participants (P = 0.001) than in participants with the CC and CT genotypes among those with plasma folate <12.5 nmol/L, but not among those with higher folate status. Because of a significant age and sex interaction (P = 0.02), we further stratified the low folate group by age and sex, and observed that the association between genotype and tHcy was confined to men <55 y old (P < 0.001). Our results suggest that age and sex modify the contribution of the MTHFR C677T mutation to fasting tHcy concentrations.

Association of methylenetetrahydrofolate reductase gene polymorphism with carotid atherosclerosis depending on smoking status in a Japanese general population

BACKGROUND AND PURPOSE

The association of the methylenetetrahydrofolate reductase gene (MTHFR) with carotid atherosclerosis remains inconsistent. This may be due to small sample size and inappropriate analysis. We investigated the association of C677T/MTHFR with blood pressure and carotid atherosclerosis in a Japanese general population.

METHODS

Subjects (30 to 89 years of age; 1693 women, 1554 men) who gave informed consent were randomly selected from a general population in Suita, Japan. MTHFR genotypes were determined by TaqMan polymerase chain reaction. Carotid atherosclerosis was evaluated by high-resolution ultrasonography with atherosclerotic indexes of intimal-medial thickness (IMT), maximum IMT in the common carotid artery (CCA), plaque score, and stenosis (>50%).

RESULTS

Age-adjusted diastolic blood pressure was significantly higher in women with the TT genotype than in those with the CC genotype. In a recessive model (CC+CT versus TT), all adjusted odds ratios for hypertension and >50% stenosis in women were 1.42 and 3.42 (95% confidence intervals, 1.01 to 1.99 and 1.23 to 9.53), respectively. In women, maximum IMT in CCA for smokers with the TT genotype was significantly higher than for smokers with the CC genotype and nonsmokers with the TT genotype (P<0.05).

CONCLUSIONS

Our study suggests that the MTHFR TT genotype is a risk factor for hypertension and carotid stenosis in women. Significant interactions between C677T/MTHFR and smoking on maximum IMT in CCA were observed in women but not in men. Smoking cessation for subjects with the TT genotype is important in the prevention of cerebrovascular disease.

Genetics of intima-media thickness

PURPOSE OF REVIEW

Increased carotid artery intima-media thickness is associated with an increased risk of coronary heart disease or cerebrovascular disease and is a powerful predictor of cardiovascular and cerebrovascular outcomes. Consequently, the measurement is now used in a number of case control, cohort and familial and linkage studies as an intermediate phenotype for the investigation of the genetic and environmental determinants of atherosclerosis. The aim of this paper is to review the most recent available data on the genetic determinants of carotid intima-media thickness.

RECENT FINDINGS

Genes could account for a significant amount of variation in carotid intima-media thickness: up to 30-66%. Carotid intima-media thickness progressed more rapidly with age in familial hypercholesterolemia patients than in patients without his condition. Familial hypercholesterolemia patients with a null LDL receptor allele tended to have higher carotid intima-media thickness than patients carrying the LDL receptor defective allele. Small association studies showing positive or negative results with the angiotensinogen gene variants as well as with the angiotensin converting enzyme I/D polymorphism add to the confusion in this largely controversial area. Differing results may depend on the vascular territory and genetic background. New associations have been described in small studies.

SUMMARY

Studies on the association of polymorphisms and intima-media thickness are frequently disappointing and lead occasionally to conflicting results. Among study limitations is the fact that mostly single gene effects are considered; longitudinal cohort studies may be more appropriate than case control studies. Ongoing large prospective population studies and clinical trials have integrated the measurements of intima-media thickness and genotype determination with a genomic approach. As a result, in the near future we may see more important and robust results with significant consequences on our understanding of genetic determinants of atherosclerotic cardiovascular disease.

Homocysteine levels and C677T polymorphism of methylenetetrahydrofolate reductase in women with polycystic ovary syndrome

The aim of this study was to investigate the homocysteine (Hcy) levels and the C677T polymorphism of 5,10-methylenetetrahydrofolate reductase (MTHFR), a crucial factor of the Hcy metabolism in young women with polycystic ovary syndrome (PCOS). Seventy young women with PCOS and another 70 healthy women with low folate intake were enrolled. Cases and controls were matched for age, body mass index, and allele frequency. Hcy, vitamin B(12), and folate levels were measured, and a genetic analysis of 5,10-MTHFR at nucleotide 677 was performed in all subjects. No difference in mean Hcy levels was observed between PCOS women in comparison to the control group. Considering the different MTHFR polymorphism, no significant difference was found in serum Hcy levels between subjects with PCOS and controls showing CC (10.4 +/- 3.1 vs. 9.7 +/- 2.9 micromol/liter +/- SD) and CT genotypes (10.9 +/- 3.8 vs. 11.0 +/- 3.2 micromol/liter +/- SD). In subjects with a TT homozygous state, a significant (P < 0.05) difference was observed between PCOS and control women (11.5 +/- 3.9 vs. 22.0 +/- 7.8 micromol/liter +/- SD). In conclusion, our data show that in PCOS women, the serum Hcy levels are normal, and the C677T polymorphism of MTHFR does not influence the Hcy levels like in controls.