Methylenetetrahydrofolate reductase 677 C/T genotype and cardiovascular disease mortality in postmenopausal women

Homozygosity of the TT methylenetetrahydrofolate reductase C677T genotype is an independent long-term predictor of cardiac death in patients with premature myocardial infarction

BACKGROUND

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism is the main genetic modulator of homocysteine. Data suggest a potential association of homozygosity for the TT MTHFR genotype with premature myocardial infarction (MI). We explored whether TT homozygosity is associated with long-term prognosis in patients with premature ST-segment elevation MI (STEMI).

METHODS

A total of 265 consecutive patients who had survived their first STEMI ≤35 years of age were followed for a median of 8 years (5-12). Primary endpoints were cardiac death and secondary endpoints were hospitalizations for acute coronary syndrome, myocardial revascularization, arrhythmic event or ischemic stroke. Serum lipids, homocysteine, folate levels were measured at baseline and all patients were also tested for the MTHFR C677T polymorphism.

RESULTS

During follow-up 14 patients died (cardiac death) [5.3%] while 84 (31.7%) met the secondary endpoints. In univariate Cox regression analysis TT homozygosity predicted the occurrence of cardiac death (Hazard ratio (HR): 4.071; 95% confidence interval (CI): 1.404-11.809, p = .010) but not the occurrence of secondary endpoints (HR: 0.877; 95% CI: 0.479-1.605, p = .669). TT homozygosity remained an independent predictor of cardiac death after adjustment for conventional risk factors (i.e., sex, diabetes mellitus, hypertension, family history of premature coronary artery disease [CAD]) [HR: 4.350; 95% CI: 1.472-12.856, p = .008]. The association also remained after adjustment for left ventricular ejection fraction or the presence of significant CAD.

CONCLUSIONS

Homozygosity for the TT MTHFR is an independent long-term predictor of cardiac death in patients with premature STEMI.

Interaction of serum vitamin B12 and folate with MTHFR genotypes on risk of ischemic stroke

OBJECTIVE

We evaluated the interaction of serum folate and vitamin B₁₂ with methylenetetrahydrofolate reductase (MTHFR) C677T genotypes on the risk of first ischemic stroke and on the efficacy of folic acid treatment in prevention of first ischemic stroke.

METHODS

A total of 20,702 hypertensive adults were randomized to a double-blind treatment of daily enalapril 10 mg and folic acid 0.8 mg or enalapril 10 mg alone. Participants were followed up every 3 months.

RESULTS

Median values of folate and B₁₂ concentrations at baseline were 8.1 ng/mL and 280.2 pmol/L, respectively. Over a median of 4.5 years, among those not receiving folic acid, participants with baseline serum B₁₂ or serum folate above the median had a significantly lower risk of first ischemic stroke (hazard ratio [HR], 0.74; 95% confidence interval [CI], 0.57-0.96), especially in those with MTHFR 677 CC genotype (wild-type) (HR, 0.49; 95% CI, 0.31-0.78). Folic acid treatment significantly reduced the risk of first ischemic stroke in participants with both folate and B₁₂ below the median (2.3% in enalapril-folic acid group vs 3.6% in enalapril-only group; HR, 0.62; 95% CI, 0.46-0.86), particularly in MTHFR 677 CC carriers (1.6% vs 4.9%; HR, 0.24; 95% CI, 0.11-0.55). However, TT homozygotes responded better with both folate and B₁₂ levels above the median (HR, 0.28; 95% CI, 0.10-0.75).

CONCLUSIONS

The risk of first ischemic stroke was significantly higher in hypertensive patients with low levels of both folate and B₁₂. Effect of folic acid treatment was greatest in patients with low folate and B₁₂ with the CC genotype, and with high folate and B₁₂ with the TT genotype.

Interaction between arsenic exposure from drinking water and genetic polymorphisms on cardiovascular disease in Bangladesh: a prospective case-cohort study

BACKGROUND

Epidemiologic data on genetic susceptibility to cardiovascular effects of arsenic exposure from drinking water are limited.

OBJECTIVE

We investigated whether the association between well-water arsenic and cardiovascular disease (CVD) differed by 170 single nucleotide polymorphisms (SNPs) in 17 genes related to arsenic metabolism, oxidative stress, inflammation, and endothelial dysfunction.

METHOD

We conducted a prospective case-cohort study nested in the Health Effects of Arsenic Longitudinal Study, with a random subcohort of 1,375 subjects and 447 incident fatal and nonfatal cases of CVD. Well-water arsenic was measured in 2000 at baseline. The CVD cases, 56 of which occurred in the subcohort, included 238 coronary heart disease cases, 165 stroke cases, and 44 deaths due to other CVD identified during follow-up from 2000 to 2012.

RESULTS

Of the 170 SNPs tested, multiplicative interactions between well-water arsenic and two SNPs, rs281432 in ICAM1 (padj = 0.0002) and rs3176867 in VCAM1 (padj = 0.035), were significant for CVD after adjustment for multiple testing. Compared with those with GC or CC genotype in rs281432 and lower well-water arsenic, the adjusted hazard ratio (aHR) for CVD was 1.82 (95% CI: 1.31, 2.54) for a 1-SD increase in well-water arsenic combined with the GG genotype, which was greater than expected given aHRs of 1.08 and 0.96 for separate effects of arsenic and the genotype alone, respectively. Similarly, the joint aHR for arsenic and the rs3176867 CC genotype was 1.34 (95% CI: 0.95, 1.87), greater than expected given aHRs for their separate effects of 1.02 and 0.84, respectively.

CONCLUSIONS

Associations between CVD and arsenic exposure may be modified by genetic variants related to endothelial dysfunction.

Interaction between arsenic exposure from drinking water and genetic susceptibility in carotid intima-media thickness in Bangladesh

Epidemiologic studies that evaluated genetic susceptibility for the effects of arsenic exposure from drinking water on subclinical atherosclerosis are limited. We conducted a cross-sectional study of 1078 participants randomly selected from the Health Effects of Arsenic Longitudinal Study in Bangladesh to evaluate whether the association between arsenic exposure and carotid artery intima-media thickness (cIMT) differs by 207 single-nucleotide polymorphisms (SNPs) in 18 genes related to arsenic metabolism, oxidative stress, inflammation, and endothelial dysfunction. Although not statistically significant after correcting for multiple testing, nine SNPs in APOE, AS3MT, PNP, and TNF genes had a nominally statistically significant interaction with well-water arsenic in cIMT. For instance, the joint presence of a higher level of well-water arsenic (≥ 40.4 μg/L) and the GG genotype of AS3MT rs3740392 was associated with a difference of 40.9 μm (95% CI = 14.4, 67.5) in cIMT, much greater than the difference of cIMT associated with the genotype alone (β = -5.1 μm, 95% CI = -31.6, 21.3) or arsenic exposure alone (β = 7.2 μm, 95% CI = -3.1, 17.5). The pattern and magnitude of the interactions were similar when urinary arsenic was used as the exposure variable. Additionally, the at-risk genotypes of the AS3MT SNPs were positively related to the proportion of monomethylarsonic acid (MMA) in urine, which is indicative of arsenic methylation capacity. The findings provide novel evidence that genetic variants related to arsenic metabolism may play an important role in arsenic-induced subclinical atherosclerosis. Future replication studies in diverse populations are needed to confirm the findings.

ACMG Practice Guideline: lack of evidence for MTHFR polymorphism testing

MTHFR polymorphism testing is frequently ordered by physicians as part of the clinical evaluation for thrombophilia. It was previously hypothesized that reduced enzyme activity of MTHFR led to mild hyperhomocysteinemia which led to an increased risk for venous thromboembolism, coronary heart disease, and recurrent pregnancy loss. Recent meta-analyses have disproven an association between hyperhomocysteinemia and risk for coronary heart disease and between MTHFR polymorphism status and risk for venous t-hromboembolism. There is growing evidence that MTHFR polymorphism testing has minimal clinical utility and, therefore should not be ordered as a part of a routine evaluation for thrombophilia.

Prospective study of methylenetetrahydrofolate reductase (MTHFR) variant C677T and risk of all-cause and cardiovascular disease mortality among 6000 US adults

BACKGROUND

The association between blood homocysteine concentration and the risk of cardiovascular disease (CVD) remains controversial, but few studies have examined the association between MTHFR C677T (a proxy for high homocysteine concentration) and death from CVD.

OBJECTIVE

The objective was to examine associations of MTHFR C677T, a proxy for high homocysteine concentrations, with CVD mortality and with all-cause mortality in a national representative prospective cohort of the US adult population before the introduction of mandatory folic acid fortification of flour.

DESIGN

We used Mendelian randomization to examine the association of MTHFR C677T with cause-specific mortality in 5925 participants by accessing the NHANES III (1991-1994) Linked Mortality File (through 2006).

RESULTS

A comparison of homozygotes at baseline showed that individuals with a TT genotype had a 2.2-μmol/L higher homocysteine and a 1.4-ng/mL lower folate concentration, respectively, than did those with a CC genotype. The TT genotype frequency varied from 1.2% (95% CI: 0.7, 2.0) in non-Hispanic blacks and 11.6% (95% CI: 9.6, 14.0) in non-Hispanic whites to 19.4% (95% CI: 16.7, 22.3) in Mexican Americans. After adjustment for ethnic group and other CVD risk factors, the MTHFR C677T TT genotype was associated with significantly lower CVD mortality (HR: 0.69; 95% CI: 0.50, 0. 95) but had no significant effect on all-cause mortality (HR: 0.79; 95% CI: 0.59, 1.05). After stratification by period of follow-up, the inverse association of MTHFR with CVD mortality was significant only in the period after introduction of mandatory folic acid fortification.

CONCLUSION

The inverse association of MTHFR with CVD mortality was unexpected and highlights the need for caution in interpretation of Mendelian randomization studies, which, like other observational studies, can be influenced by chance, bias, or confounding.

Homocysteine, 5,10-Methylenetetrahydrofolate Reductase 677C>T Polymorphism, Nutrient Intake, and Incident Cardiovascular Disease in 24 968 Initially Healthy Women

Background: Hyperhomocysteinemia has been associated with a higher risk of cardiovascular disease (CVD) in epidemiological studies, but recent trials have failed to show a benefit of lowering homocysteine. To address this apparent paradox, we explored whether interaction between genetic and dietary factors related to homocysteine metabolism contributes to CVD risk.

Methods: We evaluated the associations of homocysteine, methylenetetrahydrofolate reductase (MTHFR) 677C>T genotype, and dietary intake of folate/B-vitamins with subsequent CVD events in 24 968 apparently healthy white American women followed for 10 years. Plasma homocysteine was measured using an enzymatic assay. MTHFR genotype was determined with a multiplex PCR using biotinylated primers.

Results: In unadjusted analyses, homocysteine showed moderately strong linear associations with CVD, with hazard ratios (95% CI) comparing top with bottom quintiles for total CVD of 1.92 (1.55–2.37), myocardial infarction 2.32 (1.52–3.54), and ischemic stroke 2.25 (1.45–3.50), all Ptrend <0.001. These ratios were markedly attenuated after adjusting for traditional risk factors and socioeconomic status to 1.08 (0.86–1.36), Ptrend = 0.12; 1.20 (0.76–1.87), Ptrend = 0.14; and 1.21 (0.75–1.94), Ptrend = 0.50, respectively. Homocysteine was associated with MTHFR genotype (1.4 μmol/L higher homocysteine for TT vs CC, P <0.001) and inversely with intake of folate, vitamin B2, B6, and B12, all Ptrend <0.001. However, there was no association of MTHFR genotype or dietary folate/B-vitamins with CVD. In addition, there were no gene–diet or gene–homocysteine interactions in relation to CVD.

Conclusions: In this large-scale prospective study, the association of homocysteine with CVD was markedly attenuated after adjusting for risk factors and was not modified by MTHFR 677C>T or intake of folate or B-vitamins.

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.

Methylenetetrahydrofolate reductase gene A222V polymorphism and risk of ischemic stroke

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

Folate, homocysteine levels, methylenetetrahydrofolate reductase (MTHFR) 677C --> T variant, and the risk of myocardial infarction in young women: effect of female hormones on homocysteine levels

In young women data are limited about the association between myocardial infarction (MI) and hyperhomocysteinemia, low folate or methylenetetrahydrofolate reductase (MTHFR) genotypes. The effect of oral contraceptive (OC) use on plasma homocysteine levels is not clear. We assessed the association between hyperhomocysteinemia, low folate, MTHFR 677TT mutation and risk of MI, and we investigated the effect of OC use on homocysteine levels in controls. In 181 patients with a first MI and 601 controls 18-49 years of age from a population-based case-control study, non-fasting blood samples were available. The homozygote mutant allele (TT) was detected in 12% of the patients and in 10% of controls. The odds ratio (OR) for MI in TT patients compared with the wild-type (CC) controls was 1.3 [95% confidence interval (CI) 0.8, 2.3]. For all MTHFR genotypes combined, the OR for MI in the lowest quartile of folate (<5.4 nmol L-1) compared with the highest quartile (>10.4 nmol L-1) was 3.0 (95% CI 1.7, 5.1). A 2-fold increased risk of MI was found in women with the TT genotype who had folate levels below the median of 7.4 nmol L-1 compared with CC genotype and folate levels above the median (OR = 2.0; 95% CI 1.0, 3.7). Mean homocysteine levels were 12.2 micromol L-1 in OC users and 12.3 micromol L-1 in non-users. Only at the 97.5 percentile (cut-off 21.0 micromol L-1) was the adjusted OR for higher vs. lower homocysteine levels increased by 2.8-fold (95% CI 1.2, 6.8). Low folate is a risk factor for MI, particularly in women with the MTHFR 677TT genotype. Homocysteine levels were not influenced by OC use.

Homocysteine and the stage of atherosclerotic disease: a study in patients suffering from clinically silent and clinically manifest atherosclerotic disease

BACKGROUND

Elevated serum levels of homocysteine are considered a risk factor for cardiovascular disease. It has been suggested that homocysteine is a late stage predictor of adverse cardiovascular events, which might explain reported controversies in literature. The objective of the present study was to study the relationship between homocysteine levels and the stage of atherosclerotic disease.

METHODS

In a cross-sectional study we compared the prevalence of hyperhomocysteinemia in high risk patients without silent or clinically overt atherosclerosis (group I, n = 196) with two patient groups: patients with clinically manifest atherosclerosis in the past or asymptomatic atherosclerosis (group II, n = 364) and patients who currently suffer from a clinically relevant manifestation of ischemic cardiovascular disease (group III, n = 967). In addition, we related homocysteine levels with a cumulative index of atherosclerotic disease (SMART-score).

RESULTS

Homocysteine levels (micromol L(-1)) for the different groups were 13.5 +/- 8.9 (group I), 13.7 +/- 8.2 (group II) and 14.7 +/- 7.7 (group III). After adjustment for age, body mass index, creatinine levels and current use of vitamins, no significant differences in the prevalence of hyperhomocysteinemia were observed, compared with the reference category. Linear regression analysis revealed a significant relationship between Smart score and homocysteine levels that remained after adjustment for potential confounders (Beta = 0.36 (0.14-0.59), P = 0.001).

CONCLUSION

If homocysteine levels are associated with the presence and indicators of atherosclerotic plaque burden, then this relationship is apparently not affected by the stage of atherosclerotic disease.