UMLS:C0020538 - FACTA Search

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Query: UMLS:C0020538 (hypertension)
170,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Over the past few years, a substantial body of evidence has accumulated that indicates hyperhomocysteinemia as a significant risk factor for cardiovascular disease. Hyperhomocysteinemia arises from a lack of key enzymes or vitamins such as methylenetetrahydrofolate reductase, vitamin B6, and folate which are involved in homocysteine metabolism. Heavy coffee consumption is also known to elevate homocysteine levels. The adverse effects associated with hyperhomocysteinemia are extensive. It increases risk of myocardial infarction, cardiovascular-related morbidity and mortality, peripheral vascular disease, atherosclerosis, coronary heart disease, and cerebrovascular disease. Its seriousness as a risk factor has been equated to hypercholesterolemia and smoking, two leading causes for cardiovascular disease. It also has been shown to produce a multiplicative effect with these and other risk factors such as hypertension. Two major hypotheses have been proposed to explain how homocysteine induces its harmful effects. It can damage endothelial cells lining the vasculature, allowing plaque formation. Simultaneously, it interferes with the vasodilatory effect of endothelial derived nitric oxide. Also, homocysteine has been found to promote vascular smooth muscle cells hypertrophy. Both of these processes induce vessel occlusion. Maintaining a normal plasma level of homocysteine as a means to prevent cardiovascular disease appears promising. This is achieved through increased intake of folate and vitamin B6 through diet or supplementation. Despite the overwhelming evidence suggesting homocysteine as a significant risk factor, no long-term prospective studies have been completed to demonstrate that folate and vitamin B6 can prevent cardiovascular disease related morbidity and mortality in patients with hyperhomocysteinemia. Homocysteine is a key metabolite in amino acid synthesis. During the process of methylation, S-adenosylmethionine (Ado Met), derived from methionine, is converted to S-Adenosylhomocysteine (Figure 1). This product is quickly hydrolyzed to form homocysteine and adenosine. Homocysteine can undergo 1 of 3 reactions depending on the status of the organism. If cysteine levels are inadequate, homocysteine utilizes the coenzyme pyridoxal phosphate (vitamin B6) to condense with serine, forming the intermediate cystathionine. Subsequent reactions with cystathionine lead to the formation of cysteine. When methionine levels are low, homocysteine is remethylated in a reaction involving the coenzyme N5-methyltetrahydrofolate or betaine. Finally, when both amino acids are in adequate supply, homocysteine is cleaved by the enzyme homocysteine desulthydrase (cystathionase) to form a-ketobutyrate, ammonia, and H2S. Thus, homocysteine's physiological role is to assist in maintaining sulfur-amino acid homeostasis. Beyond these metabolic processes, homocysteine is beginning to be recognized as a significant risk factor for cardiovascular disease including atherosclerosis, coronary artery disease, cerebrovascular disease, and myocardial infarction.
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PMID:Hyperhomocysteinemia: an additional cardiovascular risk factor. 1063 97

Few and contrasting data are available on the prevalence of hemostatic risk factors in patients with central retinal vein occlusion (CRVO). Aim of this study was to investigate the metabolic and inherited risk factors for venous thrombosis in 100 CRVO patients (age: 59 yrs; range 18-77) and in 100 controls (age: 56 yrs; range 18-84). In patients homocysteine (Hcy) levels were significantly higher than in controls and were affected by the C677T methylenetetrahydrofolate reductase (MTHFR) polymorphism (p < 0.001). The prevalences of activated protein C resistance (APCR), factor V Leiden positivity, elevated PAI-1 and Lp(a) levels were significantly higher in patients with respect to controls. At multivariate analysis, only hyperhomocysteinemia (OR 11, 95% CI 3.6-36.2; p < 0.0001) and elevated PAI-1 levels (OR 8.9, 95% CI 3.5-41.3; p < 0.01), in addition to hypertension (OR 40.5, 95% CI 8.6-188.8; p < 0.00001) and hypercholesterolemia (OR 3.1, 95% CI 1.6-20.5; p < 0.05), were independent risk factors for CRVO. These data demonstrate a potential role of hemostatic risk factors in the pathophysiology of CRVO.
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PMID:Thrombophilic risk factors in patients with central retinal vein occlusion. 1208 91

Cardiovascular disease has a multifactorial aetiology that is influenced by both genetic and environmental factors. Endothelial dysfunction is a key event in the pathogenesis of vascular disease that occurs before structural vascular changes or clinical symptoms are evident. Conventional risk factors, for example hypertension and diabetes mellitus, are associated with endothelial dysfunction, but the influence of other putative risk factors is not clear. The methylenetetrahydrofolate reductase (MTHFR) C677T genotype, a common polymorphism that induces hyperhomocysteinaemia, has been proposed as being a genetic risk factor for cardiovascular disease. A total of 126 healthy adults recruited by MTHFR C677T genotype (42 of each genotype, i.e. CC, CT and TT) underwent assessment of endothelial function. Brachial artery endothelium-dependent flow-mediated dilatation (FMD) was measured using high-resolution ultrasonic vessel "wall-tracking". Using multiple regression analysis, MTHFR genotype and 21 other subject and subject-lifestyle variables were investigated as potential predictors of endothelial function. FMD was influenced positively by frequency of aerobic exercise and by hormone replacement therapy, and negatively by increases in systolic blood pressure. MTHFR C677T genotype and the associated variation in plasma homocysteine levels did not influence FMD. Additionally, other factors, including plasma cholesterol and self-supplementation with either antioxidant vitamins or cod liver oil, showed no significant relationship with FMD, although these findings are compromised by the narrow range studied for cholesterol and the small number of subjects taking supplements. These observations have implications for risk factor management in the primary prevention of cardiovascular disease in healthy individuals.
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PMID:Influence of methylenetetrahydrofolate reductase genotype, exercise and other risk factors on endothelial function in healthy individuals. 1174 60

Moderately elevated plasma homocysteine levels have been established as independent risk factors in vascular disease, including ischemic stroke. Recently, a common mutation (C677T) in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene reducing the activity of MTHFR and increasing homocysteine levels in plasma was reported. The C677T MTHFR mutation may be a risk factor for ischemic stroke, but the results of previous studies have been conflicting. One possible explanation is that the association with the MTHFR genotype may be different according to gender. To investigate the association for ischemic stroke, we conducted a case-control study of 77 hospital cases (49 men and 28 women) with ischemic stroke and 229 (120 men and 109 women) control subjects in Japanese. The prevalence of conventional vascular risk factors and MTHFR genotypes were determined in case and controls. After adjustment by multiple analysis in all there was no statistical significance in MTHFR genotypes. The conventional vascular risk factors such as diabetes mellitus (adjusted odds ratio [OR], 17.21), hypertension (adjusted OR, 4.67), smoking habit (adjusted OR, 4.70), and hyperlipidemia (adjusted OR, 2.73) were identified independently associated with ischemic stroke. With a separate sex analysis it was identified that the relationship of the MTHFR T/T gneotype was statisticaly significant in women (adjusted OR, 9.49; 95% CI, 1.75-51.47, P=0.0091). The relevance of the MTHFR T/T mutation appears to be restricted to women, suggesting a role of female hormones in the resistance to elevated homocysteine levels due to the MTHFR T/T mutation.
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PMID:Methylenetetrahydrofolate reductase gene polymorphism and ischemic stroke: sex difference in Japanese. 1187 Mar 35

DNA samples collected as part of a large population-based case-control study were genotyped to examine the associations of five prothrombotic gene polymorphisms with pre-eclampsia (PE) and gestational hypertension (GH). The polymorphisms studied were: G1691A in Factor V (Factor V Leiden; FVL), prothrombin G20210A, methylenetetrahydrofolate reductase (MTHFR) C677T, plasminogen activator inhibitor-1 4G/5G and the platelet collagen receptor alpha2beta1 C807T. A group of 404 women who developed PE were retrospectively compared with 303 women with GH and 164 control women. The frequency of genotypes did not differ significantly between cases of PE or GH and controls for any of the five polymorphisms studied. We conclude that these prothrombotic genotypes are not associated with the development of PE or GH in our population. The systematic review supports our conclusion, for all but cases of severe disease. which appear to be associated with FVL and, to a lesser extent, MTHFR C677T. There is little value in antenatal screening for prothrombotic polymorphisms to predict the development of pre-eclampsia or gestational hypertension.
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PMID:Prothrombotic genotypes are not associated with pre-eclampsia and gestational hypertension: results from a large population-based study and systematic review. 1203 75

The effect of the C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene, traditionally associated with ischaemic heart disease (IHD), was assessed in a Spanish population. The transmission disequilibrium test (TDT) was used to determine a possible association in a sample of 101 trios of IHD patients. The distribution of MTHFR genotypes was similar in the IHD subjects and the parental group; the TT genotype was present in 14.9% of IHD patients, as compared to 15.2% in the parents. The frequency of the T allele was also similar in IHD cases and parents (39.6% vs. 42.4%; p = 0.649). The TDT confirmed that the observed transmission of the T allele did not deviate significantly from the expected one (chi2 = 0.743; p > 0.4). Our TDT analysis clearly demonstrates a lack of association between the T allele of the C677T mutation in MTHFR and cardiovascular artery disease, both for the general group and for different risk subgroups (smokers, hypertension, male sex, overweight and type A behaviour pattern) in the Spanish population.
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PMID:Lack of association between methylenetetrahydrofolate reductase (MTHFR) C677T and ischaemic heart disease (IHD): family-based association study in a Spanish population. 1222 Apr 40

Mutations such as factor V Leiden G1691A (FVL), prothrombin G20210A (FIIM), methylenetetrahydrofolate reductase (MTHFR) C677T, cystathionine beta-synthase (CBS) 844ins68 and endothelial cell protein C receptor (EPCR) 4031ins23 are risk factors for thromboembolism. To assess the role of these mutations in young adults with cerebral ischemia of otherwise undetermined etiology, 93 patients younger than 50 years old with thromboembolic strokes or transient ischemic attacks were studied. One hundred and eighty-six healthy age-matched and sex-matched blood donors served as controls. The FVL mutation was detected in 15/93 patients and 13/186 controls. After adjustment for smoking, arterial hypertension, and hyperlipidemia, the association of the FVL mutation with cerebral ischemia [odds ratio (OR), 3.19; 95% confidence interval (CI), 1.38-7.39] remained significant. One of 93 patients and 6/186 controls were carriers of FIIM (OR, 0.33; 95% CI, 0.04-2.75). We detected the MTHFR TT677 genotype in 9/93 patients and 26/186 controls (OR, 0.66; 95% CI, 0.30-1.47), a CBS 844ins68 mutation in 12/93 patients and 19/186 controls (OR, 1.30; 95% CI, 0.60-2.81), and an EPCR 4031ins23 mutation in 1/93 patients and in no control individual (P = 0.33). In conclusion, in younger adults the FVL mutation is a risk factor for cerebrovascular disease. FIIM, the MTHFR TT677 genotype and the CBS 844ins68 mutation did not contribute to the risk in this group of patients. The EPCR 4031ins23 mutation is very rare, its possible role needs further investigation.
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PMID:Genetic risk factors in young adults with 'cryptogenic' ischemic cerebrovascular disease. 1243 43

Asian Indians who have settled overseas and those in urban India have increased risk of coronary events. Reasons for this increased risk are thought to be genetic but are yet unclear. Advances in molecular cardiology have revealed a number of single nucleotide polymorphisms associated with atherosclerosis. In this review, gene polymorphisms that have been associated with coronary diseases among Indians are discussed. Topics include the genes involved in hyperlipidemia, hypertension, and homocysteine. Mutations in the low-density lipoprotein receptor (LDLR) gene resulting in familial hypercholesterolemia have strong association with premature atherosclerosis. Common polymorphism of the apolipoproteins (apo) B-100 and E genes have been associated with variation in lipid and lipoprotein levels. Recently identified polymorphisms in the apoC3 (T-455C, C-482T), and cholesteryl ester transfer protein (CETP) (B1/B2 allele) genes are associated with increased triglycerides and reduced high-density lipoprotein (HDL)-levels, a feature now also common among Asian Indians. Angiotensin-converting enzyme-deletion (DD) polymorphism has been shown to influence beta-blocker therapy in heart failure. Mutations in methylenetetrahydrofolate reductase (C667T), cystathionine beta-synthase (T833C), and methionine synthase (A2756G) genes cause hyperhomocysteinemia, an independent risk factor for atherothrombosis. As the genetics of atherosclerosis continues to evolve, these factors along with the newer emerging factors may become a part of the routine assessment, aiding prediction of future coronary events.
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PMID:Gene polymorphism and coronary risk factors in Indian population. 1247 35

The C677T transition of methylenetetrahydrofolate reductase (MTHFR) gene causes a moderate increase in total plasma homocysteine (tHcy). We studied the effect of MTHFR TT homozygosity and mild hyperhomocysteinemia on arterial hypertension. Normotensive controls (n = 223) and hypertensive subjects (n = 235) were matched for age, gender, and history of cardiovascular disease. Homocysteine levels were measured by a polarization immunoassay method. Methylenetetrahydrofolate reductase we determined by polymerase chain reaction and restriction fragment analysis. Hypertensives showed elevated tHcy compared to normotensive group in men (P = 0.039). Homocysteine values higher than 15 micromol/L were associated with increased hypertensive risk in the male population [odds ratios (OR) = 1.63; 95% confidence interval (CI) = 1.06-2.52; P = 0.027]. In multivariate analysis, TT genotype was associated with an increased risk of hypertension in males (OR = 2.27; 95% CI = 1.12-4.60; P = 0.022) An increased hypertensive risk was observed in those TT males with tHcy levels higher than 15 micromol/L (OR = 2.78; 95% CI = 1.05-7.3; P = 0.032) but not in those non-TT males with tHcy levels higher than 15 micromol/L (P = 0.33). Our findings do not support the possibility that mild hyperhomocysteinemia my solely account for the hypertensive risk associated to the TT genotype.
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PMID:The effect of methylenetetrahydrofolate reductase C677T common variant on hypertensive risk is not solely explained by increased plasma homocysteine values. 1279 95

Although coronary heart disease (CHD) is extremely common in South African Indians, there is little published data on the possible causes leading to myocardial infarction (MI) in young Indians. The aim of this study was to identify common environmental risk factors and to examine the relationship between two polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene, the 677 C right arrow-hooked T and 1298 A right arrow-hooked C in young South African Indians with MI. Demographic and risk factor data were obtained from245 patients </= 45 years with MI who were admitted to the RK Khan Hospital, Durban. Venous blood from 195 of the 245 patients with MI, as well as from the sublings of the MI patients (n = 107), and 300 healthy age-matched Indian control subjects, were collectd from genetic analysis. Cigarette smoking was the most important risk factor, occurring in three-quarters of patients, followed by dyslipidaemia in half of the subjects. Diabetes (19%) and hypertension (22%) were found not to be major risk factors for MI. A strong familial link was observed not only for a history of CHD (54%), but also for diabetes (42%) and hypertension (41%). No difference was found in the thermolabile variant of the MTFHR gene (677 C right arrow-hooked T) or the second variant 1298 A right arrow-hooked C between controls and patients with MI or their siblings. The two polymorphisms did not appear to work in synergy, neither was there any relationship to common risk factors for CHD. In conclusion, smoking, dyslipidaemia and obesity were the most common phenotypic risk factors for MI. Neither the 667 C right arrow-hooked T nor the 1298 A right arrow-hooked C MTFHR variants appeared to be risk factors for premature CHD in this group.
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PMID:Risk factors and methylenetetrahydrofolate reductase gene polymorphisms in a young South African Indian-based population with acute myocardial infarction. 1284 96

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