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

Carriers of autosomal recessive conditions: are they really 'unaffected?'

Mendel's Law of Dominance suggests that recessive disease expression requires the inheritance of two mutated alleles as the dominant, wildtype allele suppresses disease presentation leading to the expression of physiological normal phenotypes. However, there is existing evidence that challenges this school of thought. Here, we summarise existing literature evaluating metabolic and health impacts among carriers of autosomal recessive conditions, focusing on phenylketonuria (PKU), classical homocystinuria, galactosemia and Usher syndrome as examples. Our findings suggest that carriers, often described as 'unaffected', may actually display attenuated symptoms for the recessive disease they are carrying. For instance, PKU is an inborn error of metabolism characterised by the build-up of plasma phenylalanine attributed to the deficiency of the phenylalanine hydroxylase (PAH) enzyme. While less severe, PKU carriers also exhibit this impaired enzymatic activity, leading to elevated plasma phenylalanine levels, especially after phenylalanine consumption. Related to these metabolic alterations in the PAH pathway, there is early evidence to suggest that PKU carriers may have compromised cognitive and mental health outcomes. Overall, research on the health and metabolic impacts of PKU carriers is sparse, with most studies conducted several decades ago. However, early evidence suggests that intermediate phenotypes among carriers of autosomal recessive conditions are plausible. The illustrated possible intermediate phenotypes observed among carriers necessitates future research to determine possible clinical implications among this population.

Correlation between plasma homocysteine and first myocardial infarction in young patients: Case-control study in Constanta County, Romania

An elevated level of total plasma homocysteine has been associated with a higher risk of atherosclerosis and coronary heart disease. The aim of our research was to study the relation between homocysteine and myocardial infarction (MI) in young patients. We conducted a case-control study in Constanţa County, Romania including 61 patients, divided in two groups. The first group, the MI group, consisted of 28 patients, male (67.9%) and female (32.1%) aged less than 45 years who were consecutively admitted to the Intensive Coronary Care Unit of the Emergency County Hospital of Constanţa from September 1, 2017 to August 31, 2018 (12 months), with an established diagnosis of first acute MI. The second group, the control group, included 33 patients, male (75.8%) and female (24.2%) aged less than 45 years, with cardiovascular risk factors and/or stable angina pectoris that were consecutively addressed for ambulatory cardiac evaluation at the Outpatient Clinic of Emergency County Hospital of Constanţa during the same period. Fasting plasma homocysteine was determined in both groups, within 24 h after MI onset, respectively after first cardiac exam in the controls. High homocysteine was statistically confirmed to be a risk factor in the study group, especially in association with smoking, chronic kidney disease (CKD), and to a lesser extent with diabetes mellitus (DM) and hypertension. Data analysis was performed using IBM SPSS Statistics 23. The procedures used included descriptive statistics, parametric statistical tests (Independent sample t-test), non-parametric statistical tests [Chi-square test of the association, with the evaluation of odds ratio (OR)]; the significance level used in the analysis (P-value) was 0.05. After adjusting for variables, our study results pointed out a strong association between plasma homocysteine and first acute MI among young patients, emphasising plasma homocysteine as a possible risk factor for myocardial infarction.

Hyperhomocysteinemia in patients with acute porphyrias: A potentially dangerous metabolic crossroad?

BACKGROUND

Acute porphyrias (AP) are characterized by heme deficiency and induction of hepatic 5-aminolevulinate synthase (ALAS1). Hyperhomocysteinemia (HHcy) is associated with endothelial damage, neurotoxicity and increased risk for vascular diseases. Interestingly, both heme biosynthesis and sulphur amino acid metabolism require vitamin B6, (Pyridoxal-phosphate, PLP) an important cofactor of ALAS1 and of cystathionine β-synthase (CBS) and cystathionine γ-lyase (CGL) enzymes that catabolize homocysteine (Hcy). Moreover, heme itself is an important cofactor for CBS.

AIM

to assess plasma Hcy status and HHcy main determinants in patients with AP.

MATERIALS AND METHODS

A total of 46 patients with AP (31 with Acute Intermittent Porphyria,15 with Variegate Porphyria) were assessed for clinical status (symptomatic vs. asymptomatic), serum Hcy, Cysteine (Cys), Vit.B6, Vit.B12, red blood cell folates and urinary delta-aminolevulinic acid (ALA) and porphobilinogen(PBG) levels (mean of six measurements).

RESULTS

Symptomatic AP patients had significantly higher urinary ALA and PBG levels, plasma Hcy, HHcy prevalence and Hcy/Cys ratio when compared to asymptomatic carriers of AP. Even though no significant correlation was observed between ALA/PBG urinary levels and serum Hcy levels, patients with higher levels of ALA and PBG had significantly higher levels of Hcy, a higher prevalence of moderate-to severe HHcy and serum PLP levels below the 25^th percentile of a reference assessment with 300 healthy Italian subjects(<45nmol/L).

CONCLUSIONS

Most patients with symptomatic AP present HHcy resulting from alterations in sulphur amino acid metabolism. HHcy may represent an indirect marker of ALAS1 induction and its prevalence may be suggestive of a role of HHcy in the pathogenesis and/or comorbidities of AP.

The association between homocysteine and ischemic stroke subtypes in Chinese: A meta-analysis

BACKGROUND

The findings on the association between elevated plasma homocysteine levels and the risk of the trial of org 10172 in acute stroke treatment (TOAST) of ischemic stroke have been inconsistent in Chinese. So far, there is no meta-analysis about the association between Hcy and the TOAST subtypes of ischemic stroke in Chinese. This study; therefore, aimed to evaluate whether elevated homocysteine levels are associated with the TOAST subtypes of ischemic stroke using a meta-analysis.

MATERIALS AND METHODS

A systematic search of electronic databases were conducted for studies reporting homocysteine levels in ischemic stroke and the TOAST of ischemic stroke to April 18, 2018. The data were extracted after the application of inclusion and exclusion criteria. All the data were analyzed using Stata software version 9.0 (Stata Corp LP, College Station, TX). The standardized mean difference (SMD) and 95% confidence interval (CI) were used to compare continuous variables.

RESULTS

Thirteen studies comprising 3114 participants (2243 patients and 871controls) met the eligibility criteria and were included in the meta-analysis. The meta-analysis revealed that the ischemic stroke group had significantly higher levels of homocysteine than controls (SMD = 1.15, 95% CI = 0.85-1.45, P < .05). The subgroup analyses suggested that the groups of patients with large-artery atherosclerosis, small-vessel occlusion, cardioembolism, stroke of other determined etiology and stroke of undetermined etiology had significantly higher levels of homocysteine compared to those in the control group (large-artery atherosclerosis: SMD = 2.12, 95% CI = 1.40-2.84, P < .05; small-vessel occlusion: SMD = 1.10, 95% CI = 0.72-1.48, P < .05; CE: SMD = 1.17, 95% CI = 0.64-1.71, P < .05; stroke of other determined etiology: SMD = 0.88, 95% CI = 0.53-1.24, P < .05; stroke of undetermined etiology: SMD = 1.50, 95% CI = 0.66-2.33, P < .05, respectively).

CONCLUSION

This meta-analysis found that ischemic stroke patients and the TOAST of ischemic stroke patients in Chinese had significantly higher homocysteine levels than the controls, suggesting that serum homocysteine levels may be a risk factor for ischemic stroke and the TOAST subtypes of ischemic stroke in Chinese.

Nitric Oxide and Hydrogen Sulfide Regulation of Ischemic Vascular Growth and Remodeling

Ischemic vascular remodeling occurs in response to stenosis or arterial occlusion leading to a change in blood flow and tissue perfusion. Altered blood flow elicits a cascade of molecular and cellular physiological responses leading to vascular remodeling of the macro- and micro-circulation. Although cellular mechanisms of vascular remodeling such as arteriogenesis and angiogenesis have been studied, therapeutic approaches in these areas have had limited success due to the complexity and heterogeneous constellation of molecular signaling events regulating these processes. Understanding central molecular players of vascular remodeling should lead to a deeper understanding of this response and aid in the development of novel therapeutic strategies. Hydrogen sulfide (H₂ S) and nitric oxide (NO) are gaseous signaling molecules that are critically involved in regulating fundamental biochemical and molecular responses necessary for vascular growth and remodeling. This review examines how NO and H₂ S regulate pathophysiological mechanisms of angiogenesis and arteriogenesis, along with important chemical and experimental considerations revealed thus far. The importance of NO and H₂ S bioavailability, their synthesis enzymes and cofactors, and genetic variations associated with cardiovascular risk factors suggest that they serve as pivotal regulators of vascular remodeling responses. © 2019 American Physiological Society. Compr Physiol 9:1213-1247, 2019.

Association of Cystathionine β-Synthase Gene Polymorphisms With Preeclampsia

Preeclampsia (PE) is a pregnancy disorder that increases maternal and fetal morbidity and mortality worldwide. High plasma levels of homocysteine (Hcy) are a risk factor for several cardiovascular diseases. Cystathionine β-synthase (CBS) plays an important role in Hcy homeostasis catalyzing the irreversible degradation of Hcy to cystathionine, protecting the endothelium from injury caused by hypoxia. Several mutations and polymorphisms may alter the expression of the CBS gene, resulting in variable levels of Hcy. The purpose of this study was to investigate the association of CBS gene polymorphisms with PE in Mexican women. A case–control study consisting of 129 pregnant women with PE (37 severe and 92 mild) and 173 women with uncomplicated pregnancies was performed. Polymorphisms, such as G797A, C785T, T833C, G919A, T959C, C1105T, and 844ins68 base pair, in the CBS gene were genotyped. The polymorphism G797A was monomorphic in cases with the presence of only G797A-G allele. Allele C785T-T and genotype C785T-C/T were associated with susceptibility in severe and mild PE. Alleles G797A-G and T959C-T were associated with susceptibility only in severe PE. Haplotype TGTWGTC was of susceptibility for severe PE and of protection for mild PE. Haplotypes CGTWGCC and CATWGTC seem to be protective for severe PE, but the latter is related to susceptibility in mild PE. The results suggest that C785T, G797A, and T959C mutations are contributing in different ways in severe and mild PE in our population and could be count as another related factor for this disease.

Effect of homocysteine on pregnancy: A systematic review

Research purpose was to put together the available pieces of present scientific data and to close the gap in the knowledge of Hcy levels in pregnancy and its association with some pregnancy complications. Scientific data were taken from research papers published between January 1990 and December 2017, and found on the Internet (PubMed, ClinicalKey and Embase databases) by the following tags entered in English, Russian, French and German languages: pregnancy, homocysteine, pregnancy complications, pregnancy loss, preeclampsia, intrauterine growth restriction, and placental abruption. The review showed that Hcy levels range in uncomplicated pregnancy. Upon that, Hcy level tends to decrease during the second and third trimesters. Some studies have revealed a link between polymorphism and abortion. Sufficient data were obtained indicating the relationship between HHcy and PE. Placental abruption was also associated with high Hcy levels increasing the risk 5.3-fold, but still there are data not supporting the hypothesis that Hcy levels correlate with placental abruption.

The communal relation ofMTHFR,MTR,ACEgene polymorphisms and hyperhomocysteinemia as conceivable risk of coronary artery disease

Homocysteine and its modulating genes have strongly emerged as novel biomarkers for coronary artery disease (CAD). In the present study, we investigated whether polymorphisms in homocysteine pathway genes and the plasma levels of homocysteine, folate, and vitamin B12, independently or in combination, are associated with CAD risk. A total of 504 participants were recruited (cases, n = 254; controls, n = 250, respectively). Tetra primer allele refractory mutation system polymerase chain reaction (PCR) was used for resolving the genotypes of 5′10′ methylenetetrahydrofolate reductase ‘MTHFR’ polymorphisms (rs1801133, rs1801131), 5′ methyl tetrahydrofolate homocysteine methyltransferase ‘MTR’ polymorphism (rs1805087), paroxanse1 ‘PON1’ polymorphism (rs662), and cystathionine beta synthase ‘CBS’ polymorphism (rs5742905). Conventional PCR amplification was carried out for resolving angiotensin converting enzyme ‘ACE’ insertion/deletion (I/D) polymorphism (rs4646994). ANOVA analysis, adjusted for the covariates, revealed that rs1801133, rs1805087 polymorphisms and homocysteine levels were associated with CAD. Logistic regression analysis (adjusted) revealed similar findings. Logistic regression analysis after applying factorial design to the studied single nucleotide polymorphisms (SNPs) revealed that homocysteine levels and heterozygous and mutant alleles at rs1801133, rs1805087, along with mutant alleles at rs1801131, rs4646994, conferred higher risk for CAD. Our results provide insight into the multifactorial nature of coronary artery disease. We highlight that SNPs in folate pathway genes and homocysteine have role in disease causation and can be used in disease prediction strategies.

Potential Links between Impaired One-Carbon Metabolism Due to Polymorphisms, Inadequate B-Vitamin Status, and the Development of Alzheimer's Disease

Alzheimer's disease (AD) is the major cause of dementia and no preventive or effective treatment has been established to date. The etiology of AD is poorly understood, but genetic and environmental factors seem to play a role in its onset and progression. In particular, factors affecting the one-carbon metabolism (OCM) are thought to be important and elevated homocysteine (Hcy) levels, indicating impaired OCM, have been associated with AD. We aimed at evaluating the role of polymorphisms of key OCM enzymes in the etiology of AD, particularly when intakes of relevant B-vitamins are inadequate. Our review indicates that a range of compensatory mechanisms exist to maintain a metabolic balance. However, these become overwhelmed if the activity of more than one enzyme is reduced due to genetic factors or insufficient folate, riboflavin, vitamin B6 and/or vitamin B12 levels. Consequences include increased Hcy levels and reduced capacity to synthetize, methylate and repair DNA, and/or modulated neurotransmission. This seems to favor the development of hallmarks of AD particularly when combined with increased oxidative stress e.g., in apolipoprotein E (ApoE) ε4 carriers. However, as these effects can be compensated at least partially by adequate intakes of B-vitamins, achieving optimal B-vitamin status for the general population should be a public health priority.

Endothelial dysfunction: the link between homocysteine and hydrogen sulfide

High level of homocysteine (hyperhomocysteinemia, HHcy) is associated with increased risk for vascular disease. Evidence for this emerges from epidemiological studies which show that HHcy is associated with premature peripheral, coronary artery and cerebrovascular disease independent of other risk factors. Possible mechanisms by which homocysteine causes vascular injury include endothelial injury, DNA dysfunction, proliferation of smooth muscle cells, increased oxidative stress, reduced activity of glutathione peroxidase and promoting inflammation. HHcy has been shown to cause direct damage to endothelial cells both in vitro and in vivo. Clinically, this manifests as impaired flow-mediated vasodilation and is mainly due to a reduction in nitric oxide synthesis and bioavailability. The effect of impaired nitric oxide release can in turn trigger and potentiate atherothrombogenesis and oxidative stress. Endothelial damage is a crucial aspect of atherosclerosis and precedes overt manifestation of disease. In addition, endothelial dysfunction is also associated with hypertension, diabetes, ischemia reperfusion injury and neurodegenerative diseases. Homocysteine is a precursor of hydrogen sulfide (H2S) which is formed by transulfuration process catalyzed by the enzymes, cystathionine β-synthase and cystathionine γ-lyase. H2S is a gasotransmitter that has emerged recently as a novel mediator in cardiovascular homeostasis. As a potent vasodilator, it plays several roles which include regulation of vessel diameter, protection of endothelium from redox stress, ischemia reperfusion injury and chronic inflammation. However, the precise mechanism by which it mediates these beneficial effects is complex and still remains unclear. Current evidence indicates H2S modulates cellular functions by a variety of intracellular signaling processes. In this review, we summarize the mechanisms of HHcy-induced endothelial dysfunction and the metabolism and physiological functions of H2S as a protective agent.

Genetic polymorphism of MTHFR C677T and premature coronary artery disease susceptibility: A meta-analysis

The association between 5, 10-methylenetetrahydrofolate reductase (MTHFR) C677T gene polymorphism and premature coronary artery disease (PCAD) is controversial. To explore a more precise estimation of the association, a meta-analysis was conducted in the present study. The relevant studies were identified by searching PubMed, EMBASE, the Web of Science, Cochrane Collaboration Database, Chinese National Knowledge Infrastructure, Wanfang Database and China Biological Medicine up to November, 2014. The meta-analysis was performed by STATA 11. 21 studies with a total of 6912 subjects, including 2972 PCAD patients and 3940 controls. The pooled analysis showed that MTHFR C677T gene polymorphism was probably associated with PCAD (CT vs. CC: OR=1.13, 95% CI=1.01-1.27; dominant model: OR=1.16, 95% CI=1.04-1.29; recessive model: OR=1.19, 95% CI=1.00-1.40; allele analysis: OR=1.17, 95% CI=1.01-1.34). Subgroup analysis by plasma homocysteine concentration showed a significant association in the homocysteine >15μmol/L subgroup (CT vs. CC: OR=1.44, 95% CI=1.10-1.88; TT vs. CC: OR=2.51, 95% CI=1.12-5.63; dominant model: OR=1.51, 95% CI=1.16-1.96; recessive model: OR=2.33, 95% CI=1.05-5.20; allele analysis: OR=1.48, 95% CI=1.18-1.87). Subgroup analysis by continent displayed a significant association among the Asian population (CT vs. CC: OR=1.51, 95% CI=1.23-1.86; TT vs. CC: OR=2.81, 95% CI=1.87-4.23; dominant model: OR=1.65, 95% CI=1.35-2.01; recessive model: OR=2.22, 95% CI=1.53-3.21; allele analysis: OR=1.61, 95% CI=1.37-1.89). The statistical stability and reliability was demonstrated by sensitivity analysis and publication bias outcomes. In conclusion, the meta-analysis suggests that MTHFR C677T gene polymorphism may be associated with PCAD.

Heterozygous carriers of classical homocystinuria tend to have higher fasting serum homocysteine concentrations than non-carriers in the presence of folate deficiency

BACKGROUND & AIMS

Many studies have reported that serum total homocysteine (tHcy) levels in cystathionine-beta-synthase (CBS) carriers are usually normal and only elevated after a methionine load. However, the amount of methionine required for a loading test is non-physiological and is never reached with regular feeding. Therefore, CBS carriers do not seem to be at an increased risk of cardiovascular diseases. However, the risk of cardiovascular diseases of CBS carriers with folate deficiency has not been studied. We recently found an extraordinarily high carrier rate (1/7.78) of a novel CBS mutation (p.D47E, c.T141A) in an Austronesian Taiwanese Tao tribe who live in a geographic area with folate deficiency. We evaluated if the CBS carriers tend to have higher fasting serum tHcy concentrations than non-carriers in presence of folate deficiency.

METHODS

The serum tHcy and folate levels before and after folate replacement were measured in 48 adult Tao carriers, 40 age-matched Tao non-carriers and 40 age-matched Han Taiwanese controls.

RESULTS

The serum tHcy level of the Tao CBS carriers (17.9 ± 3.8 μmol/l) was significantly higher than in Tao non-carriers (15.7 ± 3.5 μmol/l; p < 0.008) and Taiwanese controls (11.8 ± 2.9 μmol/l; p < 0.001). Furthermore, a high prevalence of folate deficiency in the Tao compared with the Taiwanese controls (4.9 ± 1.8 ng/ml vs. 10.6 ± 5.5 ng/ml; p < 0.001) was also noted. Of note, the difference in tHcy levels between the carriers and non-carriers was eliminated by folate supplementation. (carriers:13.65 ± 2.13 μmol/l; non-carriers:12.39 ± 3.25 μmol/l, p = 0.321).

CONCLUSIONS

CBS carriers tend to have a higher tHcy level in the presence of folate deficiency than non-carriers. Although many reports have indicated that CBS carriers are not associated with cardiovascular disease, the risk for CBS carriers with folate deficiency has not been well studied. Owing to a significantly elevated level of fasting tHcy without methionine loading, it is important to evaluate the risk of cardiovascular disease in CBS carriers with folate deficiency.

Haemostaseome-associated SNPs: has the thrombotic phenotype a greater influence than ethnicity? GMT study from Aquitaine including Basque individuals

The Genetic Markers for Thrombosis (GMT) study compared the relative influence of ethnicity and thrombotic phenotype regarding the distribution of SNPs implicated in haemostasis pathophysiology ("haemostaseome"). We assessed 384 SNPs in three groups, each of 480 subjects: 1) general population of Aquitaine region (Southwestern France) used as control; 2) patients with venous thromboembolism from the same area; and 3) autochthonous Basques, a genetic isolate, who demonstrate unusual characteristics regarding the coagulation system. This study sought to evaluate i) the value of looking for a large number of genes in order to identify new genetic markers of thrombosis, ii) the value of investigating low risk factors and potential preferential associations, iii) the impact of ethnicity on the characterisation of markers for thrombosis. We did not detect any previously unrecognised SNP significantly associated with thrombosis risk or any preferential associations of low-risk factors in patients with thrombosis. The sum of ϰ² values for our 110 significant SNPs demonstrated a smaller genetic distance between patients and controls (321 cumulated ϰ² value) than between Basques and controls (1,570 cumulated ϰ² value). Hence, our study confirms the genetic particularity of Basques especially regarding a significantly lower expression of the non-O blood group (p< 0.0004). This is mitigated by a higher prevalence of factor II Leiden (p< 0.02) while factor V Leiden prevalence does not differ. Numerous other differences covering a wide range of proteins of the haemostaseome may result in an overall different genetic risk for venous thromboembolism.

Prevalence of MTHFR C677T and MS A2756G polymorphisms in major depressive disorder, and their impact on response to fluoxetine treatment

OBJECTIVE

To examine the prevalence of the C677T polymorphism of the methylene tetrahydrofolate reductase (MTHFR) gene and the A2756G polymorphism of methionine synthase (MS), and their impact on antidepressant response.

METHODS

We screened 224 subjects (52% female, mean age 39 ± 11 years) with SCID-diagnosed major depressive disorder (MDD), and obtained 194 genetic samples. 49 subjects (49% female, mean age 36 ± 11 years) participated in a 12-week open clinical trial of fluoxetine 20-60 mg/day. Association between clinical response and C677T and A2756G polymorphisms, folate, B12, and homocysteine was examined.

RESULTS

Prevalence of the C677T and A2756G polymorphisms was consistent with previous reports (C/C = 41%, C/T = 47%, T/T = 11%, A/A = 66%, A/G = 29%, G/G = 4%). In the fluoxetine-treated subsample (n = 49), intent-to-treat (ITT) response rates were 47% for C/C subjects and 46% for pooled C/T and T/T subjects (nonsignificant). ITT response rates were 38% for A/A subjects and 60% for A/G subjects (nonsignificant), with no subjects exhibiting the G/G homozygote. Mean baseline plasma B12 was significantly lower in A/G subjects compared to A/A, but folate and homocysteine levels were not affected by genetic status. Plasma folate was negatively associated with treatment response.

CONCLUSION

The C677T and A2756G polymorphisms did not significantly affect antidepressant response. These preliminary findings require replication in larger samples.

Genetic aspects of folate metabolism

The vitamin folate functions within the cell as a carrier of one-carbon units. The requirement for one-carbon transfers is ubiquitous and all mammalian cells carry out folate dependent reactions. In recent years, low folate status has been linked to risk of numerous adverse health conditions throughout life from birth defects and complications of pregnancy to cardiovascular disease, cancer and cognitive dysfunction in the elderly. In many instances inadequate intake of folate seems to be the primary contributor but there is also evidence that an underlying genetic susceptibility can play a modest role by causing subtle alterations in the availability, metabolism or distribution of intermediates in folate related pathways. Folate linked one-carbon units are essential for DNA synthesis and repair and as a source of methyl groups for biological methylation reactions. The notion of common genetic variants being linked to risk of disease was relatively novel in 1995 when the first functional folate-related polymorphism was discovered. Numerous polymorphisms have now been identified in folate related genes and have been tested for functionality either as a modifier of folate status or as being associated with risk of disease. Moreover, there is increasing research into the importance of folate-derived one-carbon units for DNA and histone methylation reactions, which exert crucial epigenetic control over cellular protein synthesis. It is thus becoming clear that genetic aspects of folate metabolism are wide-ranging and may touch on events as disparate as prenatal imprinting to cancer susceptibility. This chapter will review the current knowledge in this area.

Three genetic polymorphisms of homocysteine-metabolizing enzymes and risk of coronary heart disease: a meta-analysis based on 23 case-control studies

Many epidemiological studies have explored the relationships between three genetic polymorphisms of genes encoding homocysteine-metabolizing enzymes (methionine synthase [MTR] A2756G, methionine synthase reductase [MTRR] A66G, and N(5),N(10)-methylenetetrahydrofolate reductase [MTHFR] A1298C) and risk of coronary heart disease (CHD), but no conclusive results were obtained. Therefore, we performed a meta-analysis of 23 case-control studies. Odds ratio (OR) and 95% confidence interval (95% CI) were used to examine the strength of the associations. Among those primary studies, 22 studies were for Europeans, and one study focused on the MTR A2756G polymorphism in Asians. The results of combined analyses of the MTR A2756G polymorphism suggested that the G allele was associated with increased risk of CHD and myocardial infarction (MI) especially for Europeans (GG vs. AA for CHD: OR [95% CI]=1.63 [1.18-2.25], p(z)(-test)=0.001, p(heterogeneity)=0.274; GG+AG vs. AA for MI: OR [95% CI]=1.44 [1.08-1.93], p(z)(-test)=0.014, p(heterogeneity)=0.611). In addition, the G allele was also associated with higher risk CHD based on population-based case-control studies (PCC) (GG vs. AA: OR [95% CI]=1.75 [1.24-2.49], p(z)(-test)=0.002, p(heterogeneity)=0.316). The results suggested that the MTRR A66G polymorphism was not associated with risk of CHD for Europeans (AA vs. GG: OR [95% CI]=1.07 [0.59-1.94], p(z)(-test)=0.831, p(heterogeneity)<0.01). The results suggested that the C allele of the MTHFR A1298C polymorphism might be associated with the increased risk of MI for Europeans (CC vs. CA+AA: OR [95% CI]=1.37 [1.03-1.84], p(z)(-test)=0.033, p(heterogeneity)=0.668). However, when subgroup analyses for sources of controls were performed, conflicting results were obtained. The results suggested that the C allele was associated with decreased risk of CHD based on hospital-based case-control studies, but associated with increased risk of CHD based on PCC. This meta-analysis suggests that MTR A2756G polymorphism, but not MTRR A66G and MTHFR A1298C, is associated with risk of CHD for Europeans. Because of limitations and potential bias, more well-designed studies with larger sample size, especially focused on Asians and Africans, should be performed in the future.

Tetra primer ARMS-PCR relates folate/homocysteine pathway genes and ACE gene polymorphism with coronary artery disease

Cardiovascular disorders and coronary artery disease (CAD) are significant contributors to morbidity and mortality in heart patients. As genes of the folate/homocysteine pathway have been linked with the vascular disease, we investigated association of these gene polymorphisms with CAD/myocardial infarction (MI) using the novel approach of tetraprimer ARMS-PCR. A total of 230 participants (129 MI cases, 101 normal subjects) were recruited. We genotyped rs1801133 and rs1801131 SNPs in 5'10' methylenetetrahydrofolate reductase (MTHFR), rs1805087 SNP in 5' methyltetrahydrofolate homocysteine methyltransferase (MTR), rs662 SNP in paroxanse1 (PON1), and rs5742905 polymorphism in cystathionine beta synthase (CBS). Angiotensin converting enzyme (ACE) insertion/deletion polymorphism was detected through conventional PCR. Covariates included blood pressure, fasting blood sugar, serum cholesterol, and creatinine concentrations. Our results showed allele frequencies at rs1801133, rs1801131, rs1805087 and the ACE insertion/deletion (I/D) polymorphism varied between cases and controls. Logistic regression, after adjusting for covariates, demonstrated significant associations of rs1801133 and rs1805087 with CAD in the additive, dominant, and genotype model. In contrast, ACE I/D polymorphism was significantly related with CAD where recessive model was applied. Gene-gene interaction against the disease status revealed two polymorphism groups: rs1801133, rs662, and rs1805087; and rs1801131, rs662, and ACE I/D. Only the latter interaction maintained significance after adjusted for covariates. Our study concludes that folate pathway variants exert contributory influence on susceptibility to CAD. We further suggest that tetraprimer ARMS-PCR successfully resolves the genotypes in selected samples and might prove to be a superior technique compared to the conventional approach.

[Hyperhomocysteinemia and cardiometabolic risk]

Hyperhomocysteinemia, when considered as a causal factor of vascular diseases, has been subject of much discussion. Case-control, retrospective and prospective studies have identified a relationship between high plasma concentrations of homocysteine and vascular disease. The aim of the present review was to better understand the interrelation between plasma concentrations of homocysteine and vascular diseases, as well as the involvement of classical risk factors for the disease: genetic factors, such as mutations in the genes that codify the enzymes involved in the metabolism of homocysteine, and nutritional factors, such as complex B vitamin deficiency. The publications of the main databases in health were consulted for the period 1962 to 2009. The mechanism by which hyperhomocysteinemia acts as a risk factor for vascular diseases still has not been fully clarified, but involvement of endothelial dysfunction and lipid peroxidation is suggested. The treatment of hyperhomocysteinemia is based on food supplements and medication, with folic acid and vitamins B6 and B12.

Association between the 2756A> G variant in the gene encoding methionine synthase and myocardial infarction in Tunisian patients

BACKGROUND

Elevated plasma total homocysteine (tHcy), a risk factor for coronary artery disease (CAD), is due to defects in genes encoding for enzymes involved in tHcy metabolism or from inadequate status of vitamins involved in tHcy disposal. Methionine synthase (MS), a vitamin B(12)-dependent enzyme, catalyses the remethylation of homocysteine to methionine using a methyl group donated by 5-methyltetra-hydrofolate, which is the major circulating form of folate in the body. Functional genetic variants of the MS may alter tHcy as well as folate levels which are independent risk factors for CAD. The influence of a common genetic polymorphism 2756A>G of the MS gene (MTR) on plasma tHcy, folate and vitamin B(12) levels and its relation to the risk of myocardial infarction (MI) in a Tunisian case-control study was investigated.

METHODS

A total of 321 Tunisian patients with MI and 343 healthy controls were included in the study. The 2756A>G variant of the MTR was determined by polymerase chain reaction-restriction fragment length polymorphism analysis. Plasma tHcy was assessed with a fluorescent polarising immunoassay method. Plasma vitamin B(12) and folate were determined by microparticular enzyme immunoassay and ion-capture, respectively.

RESULTS

A significant difference in genotype distribution and allele frequency was observed between patients and controls. Patients with MI had a frequency of 1.9% for the GG genotype, 26.2% for the AG genotype and 72% for the AA genotype. Controls had a frequency of only 0.9% for the GG genotype, 18.7% for the AG genotype and 80.5% for the AA genotype (chi(2)=6.97, p=0.03). The MI patient group showed a significant higher frequency of the G allele compared to controls (0.149 vs. 0.101; OR 1.55; 95% CI 1.10-2.18; p=0.008). The association between the 2756A>G variant in the gene encoding MS and MI was no longer significant after adjustment for other well-established risk factors. When clinical and laboratory values were compared amongst genotypes in the study groups, no significant differences were noted.

CONCLUSIONS

The present study showed a significant but not independent association between the 2756A>G polymorphism of the MTR (presence of G allele) and MI in the Tunisian population.

Hyperhomocysteinemia: association with renal transsulfuration and redox signaling in rats

Despite substantial evidence indicating the association of hyperhomocysteinemia (hHcys) and end-stage renal disease (ESRD), the pathogenic role of increased plasma homocysteine (Hcys) levels in the progression of ESRD remains unclear. This review will briefly summarize recent findings regarding the role of hHcys in the development of glomerulosclerosis, the association of hHcys with reduced renal transsulfuration and Hcys-induced changes of redox signaling in the development of glomerulosclerosis in rat kidneys. Based on these results, it is concluded that hHcys is implicated in glomerular sclerosis in hypertension, elevated plasma Hcys in Dahl salt-sensitive (SS) hypertensive rats is due to downregulation of cystathionine beta-synthase (CBS) expression and consequent abnormality of transsulfuration in the kidney compared with normotensive rats. Hcys-induced superoxide (O(2)(*-)) production by activation of NADPH oxidase as a triggering mechanism contributes to the effects of Hcys on the homeostasis of extracellular matrix and consequent sclerosis in the glomeruli, and NADPH oxidase activation by Hcys is associated with enhanced Rac GTPase activity.

[Evaluation of MTHFR C677T gene polymorphism and homocysteine level in coronary atherosclerotic disease]

OBJECTIVE

The aim of this study is to determine the prevalence of C677T methylenetetrahydrofolate reductase (MTHFR) polymorphism and correlate it with plasma homocysteine levels in coronary artery disease (CAD).

METHODS

Ninety-three patients with documented CAD from Hospital Universitário Oswaldo Cruz (Recife, PE, Brazil) and 108 healthy controls were evaluated. Homocysteine and folate levels were determined by HPLC and chemoluminescence, respectively, and lipid profile was considered. Genotyping was done by RFLP/PCR.

RESULTS

The groups were homogeneous for the C677T polymorphisms. The homocysteine level in cases (11.7 micromol/L) was statistically different from that observed in controls (8.84 micromol/L, p< 0.05). It was also observed that 72% of the patients had homocysteine values above 12 micromol/L while the control group presented only 32% in this range. There was no relationship between homozygosity for the C677T polymorphism and the homocysteine level (p= 0.634). We noticed statistical differences between folate levels from patients and controls (6.22 and 7.69 ng/dL, p< 0.05, respectively). However, there was no correlation between homocysteine and folate concentrations in the entire group (r= -0.202). Comparing cases and controls, the odds ratio (OR) when homocysteine is high and folate is low was OR= 11.9; CI 95%= 4.16-34.42, p< 0.01.

CONCLUSION

A lack of correlation between C677T mutation and homocysteine level suggests that environmental factors and others genetic factors seem to exert more influence on homocysteine level in this population.

Relation between plasma homocysteine, gene polymorphisms of homocysteine metabolism-related enzymes, and angiographically proven coronary artery disease

BACKGROUND

Hyperhomocyteinemia (HHcy) is a risk factor for coronary artery disease (CAD), and methylenetetrahydrofolate reductase (MTHFR), methionine synthase (MTR), and methionine synthase reductase (MTRR) polymorphisms may contribute to plasma total homocysteine (tHcy) variation. We investigated the association of polymorphisms 1298A-->C in the MTHFR gene, 2756A-->G in the MTR gene, and 66A-->G in the MTRR gene with tHcy levels and with CAD in patients undergoing coronary angiography.

METHODS

CAD patients (n=151) and control subjects (n=79) were compared regarding the prevalence of the polymorphisms, risk factors, and biochemical parameters.

RESULTS

The mean tHcy concentration was significantly higher in CAD patients than in control subjects (P<0.001). HHcy (tHcy>/=15 mumol/l) conferred an OR of CAD of 4.1 (95% CI 2.2-7.5, P<0.001). In both cases and controls, smokers had a higher tHcy level than non-smokers and demonstrated a markedly increased risk for CAD (OR=2.5, 95% CI 1.7-3.3, P<0.001). The allele frequencies of the MTHFR 1298A-->C, MTR 2756A-->G, and MTRR 66A-->G mutations were 36.7%, 15.7%, and 36.6%, respectively. The 1298C allele frequency was significantly higher in the CAD group than in controls (P<0.05) and showed a significant association with CAD in heterozygote carriers. There was no statistically significant difference between cases and controls in the frequencies of the A2756G alleles/genotypes in the MTR gene and of the A66G alleles/genotypes in the MTRR gene. The contributions to tHcy levels of the three common mutations were statistically significant. The heterozygosity of the MTHFR 1298AC genotype, MTR 2756G allele, and MTRR 66G allele yielded an OR of 3.4, 2.0, and 2.1, respectively, for having HHcy.

CONCLUSION

We suggest that HHcy confers a risk for CAD, and smokers with tHcy are at a greatly increased risk. Our finding supports an important role of the MTHFR gene in CAD and provides evidence of polygenic regulation of tHcy.

Hyperhomocysteinemia and thrombosis: an overview

CONTEXT

Homocysteine, a sulfur-containing amino acid, absent in natural diets, is a metabolic intermediary in transmethylation and transsulfuration reactions. Such reactions are essential to normal cellular growth, differentiation, and function. Excess homocysteine is associated with vascular disease and related disorders.

OBJECTIVE

To review homocysteine metabolism, the pathogenesis and classification of hyperhomocysteinemia, and the published literature investigating the association of homocysteine and methylenetetrahydrofolate reductase defects with arterial and venous thromboembolism and related disorders. The role of vitamin supplementation in patients with hyperhomocysteinemia is addressed.

DATA SOURCES

Published medical and scientific literature. Articles addressing the objectives were selected and reviewed. Pertinent studies and conclusions were summarized, grouped, and contrasted.

CONCLUSIONS

The association of hyperhomocysteinemia and arterial and venous thrombosis is controversial. Severe hyperhomocysteinemia is associated with atherosclerosis. The effect of mild hyperhomocysteinemia is less certain. Coinheritance of methylenetetrahydrofolate reductase defects and factor V Leiden is likely to increase the risk of venous thromboembolism. The association of methylenetetrahydrofolate reductase defects combined with no additional thrombophilic risk factors with venous thrombosis is less clear. High doses of folic acid to lower homocysteine levels might not be necessary.

Hydrogen sulfide: neurochemistry and neurobiology

Current evidence suggests that hydrogen sulfide (H2S) plays an important role in brain functions, probably acting as a neuromodulator as well as an intracellular messenger. In the mammalian CNS, H2S is formed from the amino acid cysteine by the action of cystathionine beta-synthase (CBS) with serine (Ser) as the by-product. As CBS is a calcium and calmodulin dependent enzyme, the biosynthesis of H2S should be acutely controlled by the intracellular concentration of calcium. In addition, it is also regulated by S-adenosylmethionine which acts as an allosteric activator of CBS. H2S, as a sulfhydryl compound, has similar reducing properties as glutathione. In neurons, H2S stimulates the production of cAMP probably by direct activation of adenylyl cyclase and thus activate cAMP-dependent processes. In astrocytes, H2S increases intracellular calcium to an extent capable of inducing and propagating a "calcium wave", which is a form of calcium signaling among these cells. Possible physiological functions of H2S include potentiating long-term potentials through activation of the NMDA receptors, regulating the redox status, maintaining the excitatory/inhibitory balance in neurotransmission, and inhibiting oxidative damage through scavenging free radicals and reactive species. H2S is also involved in CNS pathologies such as stroke and Alzheimer's disease. In stroke, H2S appears to act as a mediator of ischemic injuries and thus inhibition of its production has been suggested to be a potential treatment approach in stroke therapy.

Influence of combined methionine synthase (MTR 2756A > G) and methylenetetrahydrofolate reductase (MTHFR 677C > T) polymorphisms to plasma homocysteine levels in Korean patients with ischemic stroke

PURPOSE

Methionine synthase (MTR) and 5,10-methylenetetrahydrofolate reductase (MTHFR) are the main regulatory enzymes for homocysteine metabolism. The present case- control study was conducted to determine whether there is an association between the MTR 2756A > G or MTHFR 677C > T polymorphism and plasma homocysteine concentration in Korean subjects with ischemic stroke.

MATERIALS AND METHODS

DNA samples of 237 patients who had an ischemic stroke and 223 age and sex-matched controls were studied. MTR 2756A > G and MTHFR 677C > T genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

Frequencies of mutant alleles for MTR and MTHFR polymorphisms were not significantly different between the controls and cases. The patient group, however, had significantly higher homocysteine concentrations of the MTR 2756AA and MTHFR 677TT genotypes than the control group (p=0.04 for MTR, p=0.01 for MTHFR). The combined MTR 2756AA and MTHFR 677TT genotype (p= 0.04) and the homocysteine concentrations of the patient group were also higher than those of the controls. In addition, the genotype distribution was significant in the MTHFR 677TT genotype (p=0.008) and combined MTR 2756AA and MTHFR 677TT genotype (p=0.03), which divided the groups into the top 20% and bottom 20% based on their homocysteine levels.

CONCLUSION

The results of the present study demonstrate that the MTR 2756A > G and MTHFR 677C > T polymorphisms interact with elevated total homocysteine (tHcy) levels, leading to an increased risk of ischemic stroke.

Homocysteine

Elevated homocysteine levels are associated with a variety of vascular diseases. Specifically, hyperhomocysteinemia is a risk factor for coronary artery disease, cerebrovascular disease, and peripheral arterial disease. Laboratory-based strategies for its detection and quantification have evolved to meet the increasing need for accuracy in risk prediction. Although new technologies have been developed over the past 2 decades that have enhanced the precision of measurement, universal guidelines for circulating homocysteine determination remain lacking.

Impact of methionine synthase gene and methylenetetrahydrofolate reductase gene polymorphisms on the risk of sudden sensorineural hearing loss

Idiopathic sudden sensorineural hearing loss (SSNHL) represents a frequently encountered otological disease of unknown etiology. In recent years, several inherited risk factors have been found in the pathogenesis of vascular diseases. In the present study, we determined whether specific polymorphism or the combination of polymorphisms in folate-dependent homocysteine metabolism genes can act as predisposing inherited vascular risk factors in the development of SSNHL. We conducted a prospective case-control study using DNA samples extracted from 81 patients diagnosed as suffering from SSNHL and 264 healthy control subjects. Three functional polymorphisms were analyzed by polymerase chain reaction amplification, restriction enzyme digestion, and DNA fragment separation by electrophoresis: methylenetetrahydrofolate reductase (MTHFR) C677T, MTHFR A1298C, and methionine synthase (MTR) A2756G polymorphisms. The prevalence of the homozygous genotype of MTR 2756GG in the SSNHL patients (9%) was significantly higher than in the control group (4%) (p = 0.011). The allelic frequency of the G allele of the MTR A2756G polymorphism among SSNHL patients (12.5%) was also significantly higher than in the control group (5%) (p = 0.033). The prevalence of patients possessing two polymorphisms (31%) and three polymorphisms (17%) in the SSNHL group was significantly higher than in the control group (23 and 9%, respectively; p = 0.019). The frequency of patients with a very high rank risk (double homozygous) was significantly higher in the SSNHL group, MTHFR 677TT/MTR 2675GG--7%, than the frequency of patients in the control group, MTHFR 677TT/MTR 2675GG--3% (p = 0.030). Certain polymorphisms in genes encoding enzymes in the folate-dependent homocysteine metabolism are associated with SSNHL. In our case-control study, a significant association between MTR 2756GG genotype and SSNHL was found which may represent an inherited vascular risk factor in the pathogenesis of SSNHL.

Gene-gene and gene-environment interactions in mild hyperhomocysteinemia

Mild/moderate hyperhomocysteinemia (HHcy), a highly prevalent condition, is independently associated with an increased risk of arterial and venous thromboembolic diseases. Early reports of the association of mild/moderate HHcy with juvenile venous thromboembolism have shown familiarity for HHcy in relatives of index cases with thrombosis. Similar to inherited thrombophilia defects, inheritance of the HHcy phenotype was accordingly retained important for the definition of HHcy as an independent risk factor for thrombosis. A number of common polymorphisms in genes coding for methylenetetrahydrofolate reductase(MTHFR), methionine-synthase, methionine-synthase reductase and cysthationine beta-synthase (CBS) have been explored for their association with homocysteine levels, fasting and post-methionine load, and with thrombotic diseases. MTHFR thermolability accounts for a 10-fold increase in the risk of mild/moderate HHcy. With the possible exception of the CBS844ins68 insertion, there is no evidence for an increased risk of HHcy for any of these polymorphisms, isolated or in association with MTHFR thermolability. Environmental factors and MTHFR thermolability are main determinants of the HHcy phenotype.If mild/moderate HHcy is a pathogenetic risk factor for thrombosis, intervention aimed to improve the vitamin status appears of major importance, irrespective of common gene polymorphisms of the homocysteine metabolism.

Hyperhomocysteinaemia in chronic liver diseases: role of disease stage, vitamin status and methylenetetrahydrofolate reductase genetics

BACKGROUND/AIMS

The liver plays a key role in sulphur aminoacid metabolism hence, homocysteine metabolism may be impaired in chronic liver diseases. The aim of this study was to investigate, in patients affected by chronic liver diseases, (1) the prevalence of hyperhomocysteinaemia and (2) the role of its determinants such as the stage and the aetiology of disease, vitamin status, genetic documented alterations (methylenetetrahydrofolate reductase deficiency) and presence/absence of documented malignant evolution (hepatocellular carcinoma).

MATERIAL AND METHODS

One hundred and thirty patients with chronic liver disease (34 with chronic active hepatitis, 12 with fatty liver and 88 with liver cirrhosis) and 50 healthy age-matched control subjects were included into the study.

RESULTS

Hyperhomocysteinaemia was defined as homocysteine plasma levels greater than 12.6 micromol/l. Hyperhomocysteinaemia prevalence in liver cirrhosis group was 40.9%, significantly higher (all P<0.01) with respect to controls (12%), chronic active hepatitis (14.7%) and fatty liver (25%) groups and increased with Child-Pugh stage [Child A: 22.2%, Child B (50%); Child C (58.3%)]. In chronic-active hepatitis and liver cirrhosis, the prevalence of subjects with methylenetetrahydrofolate reductase C677-->T mutation (both as CT and as TT) and hyperhomocysteinaemia results in significantly higher levels with respect to controls. Methylenetetrahydrofolate reductase C677-->T mutation and disease stage showed to be the most important predictive factors of hyperhomocysteinaemia in liver cirrhosis whereas the influence of homocysteine-related vitamin status seems to have a secondary role.

CONCLUSIONS

In conclusion hyperhomocysteinaemia is highly prevalent in liver cirrhosis but not in other chronic liver diseases; it may contribute to fibrogenesis and vascular complication of liver cirrhosis.

Relevance of post-methionine homocysteine and lipoprotein (a) in evaluating the cardiovascular risk in young CAD patients

BACKGROUND

Aims of our study were to evaluate the prevalence of high lipoprotein (a) [Lp(a)] and homocysteine levels - both in the fasting state (FHcy) and post-methionine (PMHcy) - in young coronary artery disease (CAD) patients, and to investigate the role of genetic and environmental factors for hyperhomocysteinaemia.

MATERIALS AND METHODS

We studied 140 patients with angiographically documented CAD (24 women </= 55 years and 116 men </= 50 years) and 140 healthy subjects as controls.

RESULTS

Both FHcy [13.2 (5.4-45.8) vs. 9.0 (5.1-24) micromol L(-1)); P < 0.0001] and PMHcy [(39.4 (9.0-66.4) vs. 25.2 (16.4-33.9); P < 0.0001] were significantly higher in patients than in controls. Lp(a) levels were significantly higher in patients than in controls (200 (3-1486) mg L(-1) vs. 97 (10-412) mg L(-1); P < 0.0001). At the multivariate analysis, adjusted for the classical cardiovascular risk factors and creatinine levels, the OR (95% CI) for CAD at young age significantly increased in the fourth quartile of the distribution of FHcy, PMHcy and Lp(a) levels [FHcy: 14.9 (4.1-58), P < 0.0001; PMHcy: 19.2 (4.0-86.3); P < 0.0001; Lp(a): 19.6 (4.7-78.6): < 0.0001]. Vitamin deficiencies were detected in 28/140 (20%) patients. The prevalence of the homozygous C677T (+/+) methylenetetrahydrofolatereductase genotype was higher, but not significantly different, in patients (22.8%) than in controls (18.6%). The allele frequency of the 844ins68 insertion variant in the cystathionine beta-synthase gene was 0.08 in the control group and 0.06 in the patient group.

CONCLUSIONS

Results of the present study indicate the usefulness of including fasting and post-methionine Hcy, and Lp(a) determination in the diagnostic panels of young CAD patients, in order to obtain a better assessment of their cardiovascular risk profile.

Cystathionine beta-synthase c.844ins68 gene variant and non-syndromic cleft lip and palate

Non-syndromic cleft lip with or without cleft palate (CL/P) is a common birth defect with substantial clinical and social impact and whose causes include both genetic and environmental factors. Folate and homocysteine (Hcy) metabolism have been indicated to play a role in the etiology of CL/P, and polymorphisms in folate and Hcy genes may act as susceptibility factors. We investigated a common polymorphism in the cystathionine beta-synthase (CBS) gene (c.844ins68) in 134 Italian CL/P cases and their parents using the transmission disequilibrium test (TDT). Although no overall linkage disequilibrium was observed, considering the parent-of-origin transmission of the CBS 68 bp insertion a significant (P = 0.002) transmission distortion was detected. When children receive the c.844ins68 allele from the mother compared to the father, they show a 18.7-fold increase in risk for CL/P. This evidence suggests CBS as a candidate gene for CL/P and supports a role of maternal-embryo interactions in the etiology of CL/P.

Homocysteine, glycine betaine, and N,N-dimethylglycine in patients attending a lipid clinic

We recruited nondiabetic subjects (n = 158) attending a lipid disorders clinic, a subset of whom (n = 46) had established cardiovascular disease. Glycine betaine, N,N-dimethylglycine, and carnitine were measured in fasting plasma and urine samples. The concentrations and excretions were related to known cardiovascular risk factors in multivariate regression models. The relationships between homocysteine and plasma and urinary glycine betaine were highly significant (P < .002), comparable with the known relationships with folate and plasma creatinine. The regression coefficient for plasma glycine betaine was consistently approximately -0.1 in 5 different regression models (3 best-subsets and forward and backward stepwise regression models) for predicting homocysteine using 23 variables. Plasma glycine betaine was higher in males than in females, and the difference was associated with a difference in percentage of body fat. Its concentration included a constant factor of approximately 20 micromol/L that was independent of any of the variables investigated here. In the total group, body fat, homocysteine, and carnitine were significant predictors of plasma glycine betaine. Carnitine, an important betaine that is involved in lipid metabolism positively correlated with both homocysteine and glycine betaine. In our sample, the urinary excretion of glycine betaine was outside the reference range in 14 of the 158 subjects and the betaine fractional clearances were above the reference range in 23 subjects. Fractional clearance correlated strongly with plasma homocysteine (r = 0.50), and this relationship may be stronger in patients with known vascular disease. Urinary loss of glycine betaine may contribute to hyperhomocysteinemia and the development of cardiovascular disease.

A role for homocysteine increase in haemolysis of megaloblastic anaemias due to vitamin B12 and folate deficiency: results from an in vitro experience

Megaloblastic anaemias (MA) are frequently associated with haemolysis. The pathogenesis of these finding is not clear, but it is thought to depend on the greater destruction of abnormal and fragile megaloblastic erythrocytes. Vitamin B(12) and folate deficiencies are the commonest cause of MA; these deficiencies may simultaneously induce a significant alteration in homocysteine metabolism leading to hyperhomocysteinemia. Blood cells have enzymes involved in homocysteine metabolism. Considering the possible effects of hyperhomocysteinemia in erythrocyte toxicity (due to oxidative damage and/or to interaction with sulfhydryl residues of structural and enzymatic proteins), the aim of our study was to evaluate (1) the homocysteine blood cells production in patients with MA due to vitamin B(12) and folate deficiency and (2) the possible role and mechanism of hyperhomocysteinemia in MA haemolysis. After incubation at 37 degrees C, blood samples from MA patients showed higher and significant levels of Hcy, LDH, lipid peroxidation parameters (MDA), and ghost protein-bound Hcy than controls. Haemolysis (%) was higher in MA patients than controls and was significantly correlated with Hcy accumulation in the medium, lipid peroxidation indices and ghost protein-bound Hcy. No significant (or significantly lower) alterations through time in considered parameters were observed in the corresponding samples incubated at 4 degrees C or in samples incubated with methionine-free medium (lower Hcy production). Our data, deriving from an in vitro experience, suggest a possible role of Hcy accumulation due to vitamin B(12) and folate deficiencies in haemolysis associated to MA due to vitamin deficiency.

Polymorphisms and haplotypes in folate-metabolizing genes and risk of non-Hodgkin lymphoma

Folate metabolism plays an essential role in DNA synthesis and methylation processes. Deviations in the flux of folate due to genetic variation could result in selective growth and genomic instability and affect susceptibility to various cancers including lymphoma. To test this hypothesis, genetic polymorphisms in the folate metabolic pathway were investigated using DNA from a population-based case-control study of non-Hodgkin lymphoma (NHL) conducted in the San Francisco Bay Area between 1988 and 1995. The polymorphisms examined and haplotypes generated included thymidylate synthase (TYMS 28-bp triple repeat [3R] → double repeat [2R], 1494del6, IVS6 -68C&gt;T, 1122A&gt;G, and 1053C&gt;T); 5,10-methylenetetrahydrofolate reductase (MTHFR 677C&gt;T and 1298A&gt;C); serine hydroxymethyltransferase (SHMT1 C1420T); reduced folate carrier (RFC G80A); and methionine synthase (MTR A2756G), making the present study the largest and most comprehensive to date to evaluate associations between genetic polymorphisms in folatemetabolizing genes and NHL risk. The TYMS 6 base pair (bp)-6bp- (homozygous for 6bp deletion), IVS6 -68C&gt;T, and 1053C&gt;T genotypes (all in complete linkage disequilibrium) were all inversely associated with NHL (TYMS; odds ratio [OR] = 0.57; 0.34-0.94), particularly with diffuse large cell lymphoma (DLCL; OR = 0.29; 0.10-0.82). Further, the MTR 2756AG/GG and the MTHFR 677TT genotypes were associated with increased risk for NHL (OR = 1.3; 0.99-1.7) and follicular lymphoma (FL; OR = 1.8; 0.98-3.1), respectively. We did not observe any significant differences in genotype frequencies of the SHMT1 and RFC polymorphisms between the cases and controls. The associations of DLCL and FL with TYMS 1494del6 and MTHFR 677TT genotypes, respectively, suggest that folate metabolism may play an important role in the pathogenesis of specific subtypes of NHL. (Blood. 2004;104: 2155-2162)

Correlation between C677T MTHFR gene polymorphism, plasma homocysteine levels and the incidence of CAD

The lesions of coronary atherosclerosis represent the result of a complex, multicellular, inflammatory-healing response in the coronary arterial wall. In vivo and in vitro cellular and molecular studies have suggested a role for tissue homocysteine in endothelial cell injury and adverse extra-cellular matrix remodeling. Gene polymorphisms in relation with numerous risk factors might increase the incidence of coronary artery disease (CAD). In this review we have focused on the correlations between plasma homocysteine levels, the incidence of cardiovascular disease and the cytosine-to-thymidine substitution at nucleotide 677 (C677T) of the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene, coding for a key enzyme in methionine-homocysteine metabolism. The role of the C677T MTHFR gene polymorphism in the causation of CAD is controversial. We reviewed 12 recent case-control studies comprising 5370 genotyped patients with CAD and 4961 genotyped participants without CAD. There was no significant difference between those with and without CAD in the frequency of the C677T polymorphism (34.9 vs 33.6%). The frequency of homozygous C677T polymorphism in these groups was 10.9 versus 12.8%, respectively, although there were some ethnic differences in the C677T MTHFR polymorphism. In the analysis of the 12 studies, the odds ratio of CAD associated with the TT genotype (homozygous C677T polymorphism) was 1.18. Only slightly higher plasma homocysteine levels were observed in participants with the val/val (TT) genotype (14.4+/-2.9 micro mol/L in TT genotype vs 11.1+/-1.9 and 11.9+/-2 micro mol/L in CC and CT genotype, respectively). In addition, the relation between homocysteine increase after methionine loading and MTHFR genotypes is also controversial. However, hyperhomocysteinemia because of the C677T MTHFR allele may be corrected with oral folic acid therapy. Further investigations on the relationships between MTHFR genotypes and the incidence of CAD should be based on larger samples, paying attention to the differences between various ethnic populations. Individual therapeutic strategies based on single nucleotide polymorphism may become increasingly important for preventive treatment against polygenic CAD.

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

INTRODUCTION

Elevated plasma homocysteine levels have been associated with increased risk of cardiovascular disease. A 2756A>G polymorphism has been found in the gene (MTR) coding for methionine synthase, an enzyme catalyzing remethylation of homocysteine to methionine.

MATERIALS AND METHODS

In a Dutch case-control study comprising 123 cases with coronary heart disease (CHD) and 540 controls, we evaluated whether the MTR 2756A>G polymorphism was associated with plasma homocysteine, vitamin B12, folate concentrations, and CHD risk.

RESULTS AND CONCLUSIONS

The polymorphism was not associated with fasting or post-methionine load homocysteine concentrations. Individuals with the GG genotype had 30% lower vitamin B12 concentrations than individuals with AA or AG genotype (P < 0.05). After adjustment for CHD risk factors, the odds ratio (OR) of CHD was 4.0 (95% CI 1.4-11.6) for the GG genotype and 0.7 (95% CI 0.4-1.2) for the AG genotype, when compared to the AA genotype. In conclusion, despite the absence of an association with plasma homocysteine, the GG genotype represented a four-fold increased risk of CHD when compared to the AA genotype. Before putting effort in additional epidemiological studies, it needs to be established first whether this polymorphism has functional consequences for enzyme activity.

Variability of post-methionine load plasma homocysteine assays

BACKGROUND

Numerous variations of the methionine load test are frequently used as dynamic function tests to assess homocysteine metabolism. Lack of standardization impedes inter-laboratory comparisons. Criteria based on biological variation are suggested to standardize the methionine load test.

METHODS

Weekly methionine load tests (n=5) with blood sampling at 0, 4, 6 and 8 h were performed on 15 young men. For both basal and post-methionine load homocysteine measurements, total variance (sigma(S)(2)), within-subject variance (sigma(I)(2)), between-subject variance (sigma(G)(2)) and analytical variance (sigma(A)(2)) were calculated from an appropriate analysis of variance (ANOVA).

RESULTS

Plasma homocysteine concentrations measured 6 h after methionine loading had analytical, within-subject and between-subject coefficients of variation of 5.2%, 17.5% and 9.7%, respectively. Measurements at 4 h had a higher within-subject coefficient of variation. Adjustment of post-methionine load homocysteine concentrations for basal levels resulted in considerable increases of all the measures of variation.

CONCLUSIONS

Adjustment of post-methionine load plasma homocysteine concentrations for basal levels does not improve the interpretation of changes in serial results due to the higher analytical and biological variance of adjusted concentrations. It is suggested that the methionine load test is standardized to a single, unadjusted homocysteine measurement at 6 h.

Epidemiologic considerations to assess altered DNA methylation from environmental exposures in cancer

Epidemiologic studies in human populations have identified a broad spectrum of risk factors for cancer. Gene-damaging agents have been a primary focus of cancer epidemiology; however, all xenobiotics do not interact with DNA directly. Some exogenous agents induce epigenetic changes. In view of this, markers that measure changes to the epigenome must also be incorporated into molecular epidemiologic studies. We review the current understanding of the impact of exogenous agents including: micronutrients, chemotherapeutic agents, metals, and others, on DNA methylation. Two categories of genes are described: (1) genes that can alter susceptibility to aberrant DNA methylation and (2) genes that increase susceptibility to cancer when they are silenced through DNA methylation. Methods for incorporating markers of DNA methylation status into etiologic investigations of the impact of environmental exposures on disease (e.g., cancer) are discussed.