A common polymorphism in methionine synthase reductase increases risk of premature coronary artery disease

BACKGROUND: Methionine synthase reductase (MTRR) catalyzes the regeneration of methylcobalamin, a cofactor of methionine synthase, an enzyme essential for maintaining adequate intracellular pools of methionine and tetrahydrofolate, as well as for maintaining homocysteine concentrations at nontoxic levels. We recently identified a common A-->G polymorphism at position 66 of the cDNA sequence of MTRR; this variant was associated with a greater than normal risk for spina bifida in the presence of low levels of cobalamin. OBJECTIVE: To investigate whether the polymorphism was associated with alterations in levels of homocysteine, folate, and vitamin B12, and with risk of developing premature coronary artery disease (CAD), in a population of individuals presenting for cardiac catheterization procedures. METHODS: We screened 180 individuals aged < 58 years with angiographically documented coronary-artery occlusions or occlusion-free major arteries for the presence of the 66A-->G MTRR polymorphism using a polymerase-chain-reaction-based assay. RESULTS: We identified a trend in risk of premature CAD across the genotype groups (P = 0.03) with a sex-adjusted relative risk of premature CAD equal to 1.49 (95% confidence interval 1.10-2.03) for the GG versus AA genotype groups. There was no difference in fasting levels of plasma total homocysteine, serum folate, and vitamin B12 among the three MTRR genotypes. CONCLUSIONS: Our findings suggest that the GG genotype of MTRR is a significant risk factor for the development of premature CAD, by a mechanism independent of the detrimental vascular effects of hyperhomocysteinemia. This association needs to be confirmed in other studies.     

Influence of methionine synthase (A2756G) and methionine synthase reductase (A66G) polymorphisms on plasma homocysteine levels and relation to risk of coronary artery disease

BACKGROUND: Elevated plasma total homocysteine (tHcy) is increasingly being recognized as a risk factor for coronary artery disease (CAD) and other defects. Recent genetic studies have characterized molecular determinants contributing to altered homocysteine metabolism. Our objectives were therefore to confirm the relationship of tHcy with CAD and to examine the importance of genetic influence on tHcy in the coronary angiograms and conventional cardiovascular risk factors recorded in 230 subjects. We also determined the genotype frequencies distribution of the A2756G transition of the B12-dependent methionine synthase (MTR) gene and the A66G mutation of the methionine synthase reductase (MTRR) gene. RESULTS: Patients with CAD (n=151) had significantly higher tHcy concentrations than control subjects (15.49 +/- 2.75 micromol/l vs. 11.21 +/- 3.54 micromol/l, P < 0.001). Hyperhomocysteinaemia (tHcy > or =15 micromol/l) was a risk factor for CAD [RR = 4.07, 95% CI: 2.21 - 7.47, P < 0.001]. The homocysteine concentrations were significantly different between smokers and non-smokers, at 15.63 +/- 3.10 vs. 12.45 +/- 3.84 micromol/l, P < 0.05. In addition, smokers with hyperhomocysteinaemia demonstrated a markedly increased risk of CAD (OR = 2.50, 95% CI: 1.67 - 3.32, P < 0.05) compared with non-smokers with normal homocysteine.The 2756G and the 66G allele contribute to a moderate increase in homocysteine levels (P = 0.008 and P = 0.007, respectively), but not to CAD (P > 0.05). Combined MTR and MTRR polymorphisms, the 2756AG + 66AG and the 2756AG + 66GG were the combined genotypes that were a significant risk factor for having hyperhomocysteinaemia (14.4 +/- 2.8 micromol/l, OR = 2.75, IC 95% = 1.21 - 6.24, P=0.016 and 17.9 +/- 4.1 micromol/l, OR = 6.28, IC 95% = 1.46 - 12.1, P = 0.021, respectively). Statistic analysis using the UniANOVA test shows that these two polymorphisms have an interactive effect circulating homocysteine levels (P < 0.05). CONCLUSION: Our data suggest that moderately elevated tHcy levels are prevalent in our population and are associated with an increased risk for CAD. This study provides evidence that the MTR A2756G and MTRR A66G polymorphisms significantly influence the circulating homocysteine concentration. In addition, the MTR and MTRR genes may interact to increase the risk for having hyperhomocysteinaemia.     

Methylenetetrahydrofolate reductase (MTHFR) 677C>T and methionine synthase reductase (MTRR) 66A>G polymorphisms: association with serum homocysteine and angiographic coronary artery disease in the era of flour products fortified with folic acid

We analyzed the association between the methylenetetrahydrofolate reductase (MTHFR) 677C>T and methionine synthase reductase (MTRR) 66A>G polymorphisms with serum homocysteine and with coronary artery disease (CAD) in 504 patients undergoing clinically-indicated angiography between July 1998 and January 1999. Significant CAD (>/=50% stenosis in >/=one artery, blinded to risk factors) was present in 271 patients (54%). Median homocysteine (micromol/l) was 8.8 (interquartile range: 7.5-10.7). The prevalence of the MTHFR TT, CT, and CC genotypes was 11, 44 and 45%, respectively. Median tHcy (with interquartile ranges) for the entire population was 8.8 (7.5-10.7), and for the TT, CT, and CC genotypes was 9.7 (8.2-11.4), 8.8 (7.5-10.7), and 8.6 (7.3-10.6) micromol/l, respectively (P=0.04). On multiple logistic regression analysis, the MTHFR TT genotype was associated with hyperhomocysteinemia (adjusted OR=3.57; 95% CI, 1.47-8.70), but not with significant CAD. The prevalence of the MTRR AA, AG, GG genotypes was 19, 50 and 31%, respectively. There were no differences in mean homocysteine, prevalence of hyperhomocysteinemia and significant CAD between the three genotypes. On multivariate analysis, the MTRR genotypes were not associated with serum homocysteine or with significant CAD.     

2756GG genotype of methionine synthase reductase gene is more prevalent in rheumatoid arthritis patients treated with methotrexate and is associated with methotrexate-induced nodulosis

OBJECTIVE: To investigate the distribution of the A2756G polymorphism of the methionine synthase reductase (MTR) gene in patients with rheumatoid arthritis (RA) treated with methotrexate (MTX) compared with a healthy control group; and to examine the relationships among the A2756G polymorphism, plasma total homocysteine (tHcy), serum folate and vitamin B12 levels, disease activity, and MTX toxicity in patients with RA. METHODS: A cross-sectional study was performed on 86 MTX-treated RA patients, consisting of a clinical interview and physical examination to determine disease activity and MTX-related adverse reactions. Genotype analysis of the MTR gene was performed. Fasting plasma tHcy, serum folate, and vitamin B12 levels were measured. Allele and genotype distributions were compared to a healthy control group. RESULTS: The frequency of the 2756GG genotype (16.3%) in the RA study group was higher than that expected in the general population (3.6%; p < 0.000001). This genotype was associated with MTX-induced accelerated rheumatoid nodulosis (MIARN). No association of disease activity variables or plasma homocysteine with MTR A2756G polymorphisms was observed. The MTR 2756GG genotype, low plasma vitamin B12 levels, and the presence of rheumatoid nodules predicted MIARN. No association of nodulosis with any other indicator of disease activity or medical treatment was found. CONCLUSION: In our population of MTX-treated RA patients the 2756GG genotype of the MTR gene was more common than expected and was associated with MIARN.     

Methionine synthase reductase MTRR 66A > G has no effect on total homocysteine, folate, and Vitamin B12 concentrations in renal transplant patients

The association of variants of the gene encoding methionine synthase reductase (MTRR) with hyperhomocysteinemia, folate and Vitamin B(12) status in kidney graft recipients is unknown. We examined two mutations in MTRR in a cross-sectional study of 733 kidney graft recipients. The allele frequency of MTRR 66G was 0.55. 369 patients (50.3%) were heterozygous and 219 patients (29.9%) were homozygous for the mutation. None of the patients showed the 997C > G mutation. The allelic variants of MTRR 66A > G showed no significant association with total homocysteine (tHcy) levels, both in univariate analyses, and in a multivariate model controlling for age, gender, body mass index, renal function, time since transplantation, underlying kidney disease, as well as the MTHFR 677C > T/1298A > C genotypes. Similarly, no significant associations between the MTRR 66A > Ggenotypes and plasma folate or Vitamin B(12) levels were found. In conclusion, MTRR 66A > G has no major effect on tHcy, folate, or Vitamin B(12) plasma concentrations in kidney graft recipients.     

血浆同型半胱氨酸及其代谢酶基因多态性与溃疡性结肠炎的相关性研究

目的 探讨血浆同型半胱氨酸(Hcy)、叶酸和维生素B12水平及Hcy代谢酶基因多态性与溃疡性结肠炎(UC)的关系.方法 收集310例UC患者和936名正常对照者,采用聚合酶链反应-限制性片断长度多态性(PCR-RELP)法检测亚甲基四氢叶酸还原酶(MTHFR)C677T、A1298C、甲硫氨酸合成酶(MTR) A2756G和甲硫氨酸合成还原酶(MTRR) A66G基因多态性;并从中随机选取88例UC患者和100名正常对照者,采用循环酶法检测血浆Hcy水平,微粒子免疫化学发光法检测叶酸和维生素B12浓度.结果 UC患者MTHFR A1298C、MTR A2756G和MTRRA66G突变的等位基因及基因型频率均明显增高(P值均<0.01).UC患者Hcy平均水平为(21.73±6.59)mmol/L,较正常对照组显著增高[(12.47±5.01)mmol/L,P<0.01],而叶酸和维生素B12平均水平分别为(11.25±6.19)nmol/L和(322.81±128.47)pmol/L,明显较正常对照组降低[(15.28±7.72)nmol/L和(422.59±129.36)pmol/L,P值均<0.01].Logistic回归分析提示血浆Hcy、叶酸和维生素B12浓度是UC的独立危险因素(P值均<0.01).结论 Hcy代谢酶基因多态性及血浆Hcy、叶酸和维生素B12水平异常与UC明显相关,为临床采用叶酸、维生素B12补充疗法治疗UC提供了理论依据.     

Effect of heterozygosity for the methionine synthase 2756 A-->G mutation on the risk for recurrent cardiovascular events

Increased dietary intake of folate has been shown to significantly reduce the risk for fatal myocardial infarction, possibly by lowering homocysteine levels. We therefore investigated the association between recurrent cardiovascular events and a mutation in methionine synthase (2756 A-->G)--an enzyme directly involved in folate and homocysteine metabolism. This mutation significantly reduced the risk for recurrent cardiovascular events and elevated red blood cell folate levels.     

Genetic modulation of homocysteinemia

With the identification of hyperhomocysteinemia as a risk factor for cardiovascular disease, an understanding of the genetic determinants of plasma homocysteine is important for prevention and treatment. It has been known for some time that homocystinuria, a rare inborn error of metabolism, can be due to genetic mutations that severely disrupt homocysteine metabolism. A more recent development is the finding that milder, but more common, genetic mutations in the same enzymes might also contribute to an elevation in plasma homocysteine. The best example of this concept is a missense mutation (alanine to valine) at base pair (bp) 677 of methylenetetrahydrofolate reductase (MTHFR), the enzyme that provides the folate derivative for conversion of homocysteine to methionine. This mutation results in mild hyperhomocysteinemia, primarily when folate levels are low, providing a rationale (folate supplementation) for overcoming the genetic deficiency. Additional genetic variants in MTHFR and in other enzymes of homocysteine metabolism are being identified as the cDNAs/genes become isolated. These variants include a glutamate to alanine mutation (bp 1298) in MTHFR, an aspartate to glycine mutation (bp 2756) in methionine synthase, and an isoleucine to methionine mutation (bp 66) in methionine synthase reductase. These variants have been identified relatively recently; therefore additional investigations are required to determine their clinical significance with respect to mild hyperhomocysteinemia and vascular disease.     

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

Elevated plasma homocysteine is increasingly being recognized as a risk factor for coronary artery disease (CAD). Although there is general agreement on the importance of micronutrients and genetic predisposition to elevated plasma homocysteine, the exact influence of the known prevalent mutations in genes which regulate homocysteine metabolism is not clear. We studied 376 cases of individuals with premature CAD with respect to their fasting and post-methionine load (PML) total homocysteine (tHcy) concentrations. We also determined the presence or absence of the T833C and G919A mutations of the cystathionine-beta-synthase (CBS) gene, the C677T mutation of the methylene tetrahydrofolate reductase (MTHFR) gene, and the A2756G transition of the B12 dependent methionine synthase (MS) gene. Our objectives were therefore both to confirm the relationship of plasma homocysteine with premature CAD and to examine the importance of genetic influence on both fasting and PML homocysteine. Approximately 32% of the CAD patients had fasting hyperhomocysteinemia and 16% had PML hyperhomocysteinemia. Of these, 8.5% had both forms of hyperhomocysteinemia (combined hyperhomocysteinemia). The T133C mutation in the CBS gene and the thermolabile C677T mutation in the MTHFR gene seem to play an important role in the subset of individuals with combined hyperhomocysteinemia. The A2756G transition in the MS gene is not associated with elevated plasma tHcy. Many cases (47%) of hyperhomocysteinemia are not associated with micronutrient deficiencies, impaired renal function, and/or currently known genetic mutations. Further work is needed to study whether unknown mutations, particularly those residing in the intronic sequences of the genes involved in homocysteine metabolism, other environmental factors, or interaction of gene, nutrient, and environmental factors may be the cause of currently unexplained cases of mild hyperhomocysteinemia.     

Are genetic variants of the methyl group metabolism enzymes risk factors predisposing to obesity?

Obesity, due to the combination of inherited genes and environmental factors, is continually increasing. We evaluated the relationship between polymorphisms of methylene-tetrahydrofolate reductase (MTHFR C677T and A1298C), methionine synthase (MTR A2756G), methionine synthase reductase (MTRR A66G), betaine:homocysteine methyltransferase (BHMT G742A) and cystathionine beta-synthase (CBS 68-bp ins) genes and the risk of obesity. We studied these polymorphic variants in 54 normal and 82 obese subjects [body mass index (BMI)=22.4+/-1.8, 34.1+/-7.1; ages 35.2+/-10.7, 43.3+/-10.6 respectively]. Levels of total plasma homocysteine (t-Hcy), folates, and vitamins B6 and B12 were not significantly different, while leptin concentration was significantly higher (p=0.005) in the obese patients compared to the lean controls. The frequency of only (a) MTHFR (AC), (b) MTR (AG), and (c) MTRR (AG) heterozygous genotypes was statistically different in the obese compared to the control group (p=0.03, p=0.007, and p=0.01). Single (a), (b), and (c) heterozygous genotypes had a significant risk of developing obesity [p=0.02, 0.01, and 0.03; odds ratio (OR)=2.5, 3.0, and 2.4; 95% confidence interval (CI)=1.2-5.3, 1.3-7.1, and 1.2-5.1 respectively] and the risk remarkably increased for combined genotypes a+b, a+c, b+c, and a+b+c (p=0.002, 0.002, 0.016, 0.006; OR=7.7, 5.4, 5.8, 15.4; 95% CI=1.9-30.4, 1.7-16.8, 1.4-23.2, 1.6- 152.3). These findings suggest that in obese subjects, Hcy cycle efficiency is impaired by MTHFR, MTR, and MTRR inability to supply methyl-group donors, providing evidence that MTHFR, MTR, and MTRR gene polymorphisms are genetic risk factors for obesity.     

CblE type of homocystinuria due to methionine synthase reductase deficiency: clinical and molecular studies and prenatal diagnosis in two families

The cblE type of homocystinuria is a rare autosomal recessive disorder, which manifests with megaloblastic anaemia and developmental delay in early childhood. This disease is caused by a defect in reductive activation of methionine synthase (MTR). Our study was directed at clinical, biochemical, enzymatic and molecular characterization of two Czech patients with the cblE type of homocystinuria. Case 1 involves a 20-year-old mentally retarded patient who presented with megaloblastic anaemia at 10 weeks of age. She was treated with folates and vitamin B₁₂, and subsequent attempts to cease administration of folates led to recurrence of megaloblastic anaemia. Biochemical features included severe hyperhomocysteinaemia and hypomethioninaemia and in fibroblasts defective formation of methionine from formate, and no complementation with cblE cells. Subsequent molecular analysis of the methionine synthase reductase (MTRR) gene revealed compound heterozygosity for a transition c.1459G>A (G487R) and a 2bp insertion (c.1623–1624insTA). Case 2 involves an 8-year-old girl with nystagmus and developmental delay in whom megaloblastic anaemia was detected at 11 weeks of age. Severe hyperhomocysteinaemia with normal methionine levels was found and enzymatic and complementation studies confirmed the cblE defect. This patient is homozygous for a 140bp insertion (c.903–904ins140). The insertion is caused by a T>C transition within intron 6 of the MTRR gene, which presumably leads to activation of an exon splicing enhancer. In the families of both patients, enzymatic and mutation analyses were successfully used for prenatal diagnosis. Our study expands the knowledge of the phenotypic and genotypic variability of the cblE type of homocystinuria and supports the concept that this disorder is caused by mutations in the MTRR gene.     

Methylenetetrahydrofolate reductase 677C>T and methionine synthase 2756A>G mutations: no impact on survival, cognitive functioning, or cognitive decline in nonagenarians

BACKGROUND: Several reports have shown an association between homocysteine, cognitive functioning, and survival among the oldest-old. Two common polymorphisms in the genes coding for methylenetetrahydrofolate reductase (MTHFR 677C>T) and methionine synthase (MTR 2756A>G) have an impact on plasma homocysteine level. METHODS: We examined the effect of the MTHFR 677C>T and MTR 2756A>G genotypes on baseline cognitive functioning, cognitive decline over 5 years measured in three assessments, and survival in a population-based cohort of 1581 nonagenarians. Cognitive functioning was assessed by using the Mini-Mental State Examination (MMSE) and five brief cognitive tests (cognitive composite). RESULTS: There are no differences in MMSE score (p =.83) or in cognitive composite (p =.56) at intake as a function of genotype tested by analysis of variance, whereas sex and social group have a impact on MMSE (p < or =.03), and social group on the cognitive composite (p <.01). The mean MMSE was lower for women than for men. However, considering the group participating in all three assessments, there were no sex-related differences in MMSE (p =.34). The cognitive decline in the group participating in all three assessments was investigated using regression models for the relationship between cognitive performance and genotype, age, sex, and social group and revealed no significant difference. Furthermore, the MTHFR 677T and MTR 2756A heterozygous and homozygous genotype had no significant impact on survival, with hazard ratios of 1.05 (95% confidence interval [CI], 0.93-1.17), 0.93 (95% CI, 0.77-1.14), 1.05 (95% CI, 0.94-1.18), and 0.97 (95% CI, 0.74-1.28). CONCLUSIONS: MTHFR and MTR genotypes are not associated with cognitive functioning, cognitive decline, or survival among nonagenarians.     

Genetic and nutritional factors contributing to hyperhomocysteinemia in young adults

A modestly elevated total plasma homocysteine concentration (tHcy) is generally accepted as an independent and graded risk factor for various pathologies, including vascular diseases, neural tube defects, Alzheimer disease, and pregnancy complications. We analyzed 5 common functional polymorphisms in enzymes involved in homocysteine metabolism (ie, methylenetetrahydrofolate reductase [MTHFR] 677C>T and 1298A>C, methionine synthase [MTR] 2756A>G, cystathionine beta-synthase [CBS] 844ins68, and methionine synthase reductase [MTRR] 66A>G) in 452 young adults, and quantified their independent and interactive effects on tHcy concentrations. Serum folate, red cell folate, vitamin B(12), and tHcy concentrations were significantly influenced by MTHFR 677C>T genotypes. A particularly strong interaction was observed between the MTHFR 677TT genotype and serum folate, which led to a high tHcy phenotype that was more pronounced in males. The genetic contribution to the variance in tHcy was estimated to be approximately 9%, compared with approximately 35% that could be attributed to low folate and vitamin B(12). Our study indicates that dietary factors are centrally important in the control of tHcy levels in young adults with additional, but somewhat weaker, genetic effects. These data underscore the potential benefits that may be gained by improving the dietary status of young adults, and provide support for the implementation of folate/B-vitamin food fortification programs.     

The 1298A-->C polymorphism in methylenetetrahydrofolate reductase (MTHFR): in vitro expression and association with homocysteine

A common mutation in methylenetetrahydrofolate reductase (MTHFR), 677C-->T, is associated with reduced enzyme activity, a thermolabile enzyme and mild hyperhomocysteinemia, a risk factor for vascular disease. Recently, a second common mutation (1298A-->C; glutamate to alanine) was reported, but this mutation was suggested to increase homocysteine only in individuals who carried the bp677 variant. To evaluate the functional consequences of this mutation, we performed site-directed mutagenesis and in vitro expression. For in vivo assessment of clinical impact, we examined the 1298A-->C genotypes and plasma homocysteine in 198 individuals from the NHLBI Family Heart Study that had previously been assessed for the 677 substitution. Site-directed mutagenesis of the human cDNA was performed to generate enzymes containing each of the two mutations, as well as an enzyme containing both substitutions. Enzyme activity and thermolability were assessed in bacterial extracts. The activity of the wild-type cDNA was designated as 100%; mutant enzymes containing the 1298 and 677 mutations separately had 68% (+/-5.0) and 45% (+/-10.8), respectively, of control activity while the enzyme containing both mutations had 41% (+/-12.8) of control activity. The 1298 mutation was not associated with a thermolabile enzyme. In the Family Heart Study, fasting homocysteine was significantly higher (P<0.05) in individuals heterozygous for both substitutions, compared to individuals who carried only the 677C-->T variant. This study suggests that two variants in MTHFR should be assessed as genetic risk factors for hyperhomocysteinemia.     

Methylenetetrahydrofolate reductase C677T and methionine synthase A2756G gene polymorphisms and associated risk of cardiovascular diseases: A study from Jammu region

AimPotent risk factors at both genetic and non-genetic levels are accountable for susceptibility and instigation of different cardiovascular phenotypes. Recently, homocysteine is being identified as an important predictor for cardiovascular diseases. Homocysteine remethylation plays a key role in the synthesis of methionine and S-adenosine methionine. Methylenetetrahydrofolate reductase (MTHFR) and methionine synthase (MTR) genes are known to regulate the homocysteine remethylation reaction and higher homocysteine level is significantly associated with diverse cardiovascular phenotypes. In this context, we aimed to carry out a study on the association of MTHFR (C677T) and MTR (A2756G) gene polymorphism with CVD in population of Jammu region of J&K state.Materials and methodsA total of 435 individuals were enrolled (195 CVD patients and 240 controls) for the case–control study. Genotyping of MTHFR C677T and MTR A2756G gene polymorphism was done by PCR-RFLP technique. Biochemical parameters were estimated by biochemical analyser.ResultsMetabolic variables such as serum LDL-C, TC and TG were significantly higher in patients (p < 0.0001), whereas serum HDL-C was higher in controls. Majority of the patients were having history of hypertension (57.44%; p < 0.0001) as a concomitant condition. The evaluation of genetic association showed that, MTHFR C6877T (OR: 8.89, 95% CI: 2.01–39.40) and MTR A2756G (OR: 1.48, 95% CI: 1.09–2.00) polymorphisms associated with higher risk of CVD.ConclusionThe present study reveals significant differences in nongenetic variables among patients and control as well as association of gene polymorphisms with CVD risk.     

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

BackgroundHyperhomocyteinemia (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.MethodsCAD patients (n = 151) and control subjects (n = 79) were compared regarding the prevalence of the polymorphisms, risk factors, and biochemical parameters.ResultsThe mean tHcy concentration was significantly higher in CAD patients than in control subjects (P < 0.001). HHcy (tHcy ≥ 15 μmol/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.ConclusionWe 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.     

The atherogenic effect of excess methionine intake

Methionine is the precursor of homocysteine, a sulfur amino acid intermediate in the methylation and transsulfuration pathways. Elevated plasma homocysteine (hyperhomocysteinemia) is associated with occlusive vascular disease. Whether homocysteine per se or a coincident metabolic abnormality causes vascular disease is still an open question. Animals with genetic hyperhomocysteinemia have so far not displayed atheromatous lesions. However, when methionine-rich diets are used to induce hyperhomocysteinemia, vascular pathology is often observed. Such studies have not distinguished the effects of excess dietary methionine from those of hyperhomocysteinemia. We fed apolipoprotein E-deficient mice with experimental diets designed to achieve three conditions: (i) high methionine intake with normal blood homocysteine; (ii) high methionine intake with B vitamin deficiency and hyperhomocysteinemia; and (iii) normal methionine intake with B vitamin deficiency and hyperhomocysteinemia. Mice fed methionine-rich diets had significant atheromatous pathology in the aortic arch even with normal plasma homocysteine levels, whereas mice fed B vitamin-deficient diets developed severe hyperhomocysteinemia without any increase in vascular pathology. Our findings suggest that moderate increases in methionine intake are atherogenic in susceptible mice. Although homocysteine may contribute to the effect of methionine, high plasma homocysteine was not independently atherogenic in this model. Some product of excess methionine metabolism rather than high plasma homocysteine per se may underlie the association of homocysteine with vascular disease.     

Effect of polymorphisms in folate-related genes on in vitro methotrexate sensitivity in pediatric acute lymphoblastic leukemia

We studied whether common polymorphisms in genes involved in folate metabolism affect methotrexate (MTX) sensitivity. Ex vivo MTX sensitivity of lymphoblasts obtained from pediatric patients with acute lymphoblastic leukemia (ALL; n = 157) was determined by the in situ thymidylate synthase inhibition assay after either continuous (21 hours; TSI(50, cont)) or short-term (3 hours; TSI(50, short)) MTX exposure. DNA was isolated from lymphoblasts obtained from cytospin slides. Polymorphisms in methylenetetrahydrofolate reductase (MTHFR 677C>T, MTHFR 1298A>C), methionine synthase (MTR 2756A>G), methionine synthase reductase (MTRR 66A>G), methylenetetrahydrofolate dehydrogenase (MTHFD1 1958G>A), serine hydroxymethyl transferase (SHMT1 1420C>T), thymidylate synthase (TS 2R3R), and the reduced folate carrier (RFC 80G>A) were detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) or real-time PCR. Patients with the MTHFR 1298AC variant or the MTRR 66 G-allele showed decreased in vitro MTX sensitivity measured under both test conditions. SHMT1 1420TT homozygotes only showed decreased MTX sensitivity in the TSI(50, cont). In conclusion, polymorphisms in the folate-related genes MTHFR, MTRR, and SHMT1 are related to MTX resistance in pediatric patients with ALL.     

Association of MTRR 66A>G polymorphism with superoxide dismutase and disease activity in patients with Crohn's disease

OBJECTIVES: The aim of this study was to evaluate the association of nutritional (folate, vitamin B12) and genetic (MTHFR, MTR, MTRR, TCN) determinants of homocysteine metabolism and of superoxide dismutase with Crohn's disease (CD). METHODS: One hundred forty patients with CD were compared with 248 matched healthy controls. RESULTS: Plasma homocysteine levels were higher in CD patients than controls (11.8 vs 10.4 micromol/L, P= 0.0004). Vitamin B12 and folate levels were lower in CD subjects compared to controls (207 vs 255 pmol/L, P= 0.0082, and 8.6 vs 11 nmol/L, P= 0036, respectively). Patients with a personal history of ileal resection, ileitis, or colectomy had significantly lower vitamin B12 levels. In multivariate analysis, vitamin B12 and MTHFR 677 TT carriers were the two significant independent factors of plasma homocysteine >15 micromol/L in CD patients (P= 0.0187 and 0.0048, respectively). The significant association between homocysteine and vitamin B12 levels remained significant only in patients with the highest superoxide dismutase values (P < 0.0001). The MTRR AA genotype was a significant independent predictor of CD risk (odds ratio 3.7, 95% CI 1.218-11.649, P= 0.0213). The level of superoxide dismutase was significantly higher (P= 0.0143) and was correlated with Crohn's Disease Activity Index (CDAI) scores (P for trend = 0.0276) in patients carrying MTRR AA genotype. CONCLUSIONS: Vitamin B12 and MTHFR 677 TT genotype are the main determinants of hyperhomocysteinemia in CD patients. The association of MTRR 66A>G polymorphism with oxidant stress and disease activity provides rationale for screening vitamin deficiencies in these patients.     

Update and new concepts in vitamin responsive disorders of folate transport and metabolism

Derivatives of folic acid are involved in transfer of one-carbon units in cellular metabolism, playing a role in synthesis of purines and thymidylate and in the remethylation of homocysteine to form methionine. Five inborn errors affecting folate transport and metabolism have been well studied: hereditary folate malabsorption, caused by mutations in the gene encoding the proton-coupled folate transporter (SLC46A1); glutamate formiminotransferase deficiency, caused by mutations in the FTCD gene; methylenetetrahydrofolate reductase deficiency, caused by mutations in the MTHFR gene; and functional methionine synthase deficiency, either as the result of mutations affecting methionine synthase itself (cblG, caused by mutations in the MTR gene) or affecting the accessory protein methionine synthase reductase (cblE, caused by mutations in the MTRR gene). Recently additional inborn errors have been identified. Cerebral folate deficiency is a clinically heterogeneous disorder, which in a few families is caused by mutations in the FOLR1 gene. Dihydrofolate reductase deficiency is characterized by megaloblastic anemia and cerebral folate deficiency, with variable neurological findings. It is caused by mutations in the DHFR gene. Deficiency in the trifunctional enzyme containing methylenetetrahydrofolate dehydrogenase, methenyltetrahydrofolate cyclohydrolase and formyltetrahydrofolate synthetase activities, has been identified in a single patient with megaloblastic anemia, atypical hemolytic uremic syndrome and severe combined immune deficiency. It is caused by mutations in the MTHFD1 gene.