MTHFR 677C-->T mutation, folate intake, neural-tube defect, and risk of cardiovascular disease

Consistent Correlation between MTHFR and Vascular Thrombosis in Neonates-Case Series and Clinical Considerations

BACKGROUND

MTHFR polymorphism has been inconsistently linked to thrombotic events-some studies have shown its contribution to venous thrombosis, arterial thrombosis, and ischemic stroke, whereas others have found no statistically significant correlation between them.

METHODS

A descriptive case series study was performed in the Neonatal Intensive Care Unit of "Marie Sklodowska Curie" Emergency Clinical Hospital for Children in Bucharest, Romania.

RESULTS

All patients had positive results for MTHFR variants; 14 patients were positive for compound heterozygosity, 13 patients for MTHFR C677T (seven of which were homozygous), and 13 patients for MTHFR A1298C (three of which were homozygous). Eighteen patients received anticoagulants (heparin, enoxaparin, or bivalirudin), and thrombolytics (alteplase) were administered in six cases. In one case, a thrombectomy was performed; in another, vascular plasty was undertaken. Only in six cases was complete revascularization possible. Incomplete revascularization occurred for one patient with a negative outcome.

CONCLUSION

The particularity of this case series is that every patient in our unit who developed thrombi had a positive genetic result for MTHFR mutations. MTHFR mutations should be regarded as a thrombotic risk factor for critically ill patients, and screening for MTHFR mutations should be performed in every admitted patient to intensive care units, thus achieving the prevention of thrombi.

Variants in maternal COMT and MTHFR genes and risk of neural tube defects in offspring

Methylenetetrahydrofolate reductase (MTHFR) C677T and catechol-O-Methyltransferase (COMT) G158A are associated with a risk of neural tube defects (NTDs) in offspring. This study examined the effect of a MTHFR × COMT interaction on the risk of NTDs in a Chinese population with a high prevalence of NTDs. A total of 576 fetuses or newborns with NTDs and 594 controls were genotyped for MTHFRrs1801133, MTHFRrs1801131, and COMTrs4680 and COMTrs737865. Information on maternal sociodemographic characteristics, reproductive history, and related behavior was collected through face-to-face interviews. Possible interactions between genetic variants of MTHFR and COMT were examined. MTHFR C677T homozygous TT was associated with an elevated risk of total NTDs (odds ratio [OR] = 1.37, 95 % confidence interval [CI] = 0.93-2.03) and of anencephaly (OR = 1.67, 95 % CI = 0.98-2.84) compared with the CC genotype. There was a COMT rs737865 CC × MTHFR rs1801133 TT interaction for total NTDs (OR = 3.02, 95 % CI = 1.00-9.14) and for anencephaly (OR = 3.39, 95 % CI = 0.94-12.18). No interaction was found between COMT rs4680 AA/AG and MTHFR CT/TT genotypes for total NTDs or any subtype of NTD. The interaction of COMT rs737865 and MTHFR C677T was associated with an increased risk of NTDs, especially anencephaly, in a Chinese population with a high prevalence of NTDs.

Metabolic correction in the management of diabetic peripheral neuropathy: improving clinical results beyond symptom control

Current Clinical Management Guidelines of Diabetic Peripheral Neuropathy (DPN) are based on adequate glucose control and symptomatic pain relief. However, meticulous glycemic control could delay the onset or slow the progression of diabetic neuropathy in patients with DM type 2, but it does not completely prevent the progression of the disease. Complications of DPN as it continues its natural course, produce increasing pain and discomfort, loss of sensation, ulcers, infections, amputations and even death. In addition to the increased suffering, disability and loss of productivity, there is a very significant economic impact related to the treatment of DPN and its complications. In USA alone, it has been estimated that there are more than 5,000,000 patients suffering from DPN and the total annual cost of treating the disease and its complications is over $10,000 million dollars. In order to be able to reduce complications of DPN, it is crucial to improve or correct the metabolic conditions that lead to the pathology present in this condition. Pathophysiologic mechanisms implicated in diabetic neuropathy include: increased polyol pathway with accumulation of sorbitol and reduced Na+/K+-ATPase activity, microvascular damage and hypoxia due to nitric oxide deficit and increased oxygen free radical activity. Moreover, there is a decrease in glutathione and increase in homocysteine. Clinical trials in the last two decades have demonstrated that the use of specific nutrients can correct some of these metabolic derangements, improving symptom control and providing further benefits such as improved sensorium, blood flow and nerve regeneration. We will discuss the evidence on lipoic acid, acetyl-L-carnitine, benfotiamine and the combination of active B vitamins L-methylfolate, methylcobalamin and piridoxal-6-phosphate. In addition, we discuss the role of metformin, an important drug in the management of diabetes, and the presence of specific polymorphic genes, in the risk of developing DPN and how metabolic correction can reduce these risks.

A mouse model for glucocorticoid-induced osteonecrosis: effect of a steroid holiday

Glucocorticoid-induced osteonecrosis is a common and dose-limiting adverse event. The goal of this study was to establish a mouse model of glucocorticoid-induced osteonecrosis suitable for testing the effects of different treatment strategies on its frequency. Fourteen murine strains were screened using various glucocorticoids, routes of administration, and diets. Four-week-old male BALB/cJ mice were treated with oral dexamethasone for up to 12 weeks either by continuous dosing or by discontinuous dosing, with or without asparaginase. Histopathological features of the distal femurs were examined by light microscopy. Osteonecrotic lesions were characterized by empty lacunae and osteocyte ghosts in trabecular bone surrounded by necrotic marrow and edema. The incidence of dexamethasone induced osteonecrosis in BALB/cJ mice was 40-45% (4/10 or 5/11) at 12 weeks. The frequency of osteonecrosis trended lower after discontinuous compared to continuous dosing for 12 weeks (8 vs. 45%) (p = 0.06) despite comparable cumulative plasma exposure. Asparaginase hastened the occurrence of osteonecrosis, which was observed as early as 4 weeks and the incidence was 50% after 6 weeks. A mouse model of glucocorticoid-induced osteonecrosis was established. Discontinuous was less osteonecrotic than continuous dexamethasone treatment, consistent with the possible benefits of a "steroid holiday" seen in clinical settings. Moreover, asparaginase hastened osteonecrosis, indicating that drugs may interact with glucocorticoids to affect osteonecrosis risk.

Homocysteine as a risk factor for cardiovascular and related disease: nutritional implications

The objectives were firstly to assess the evidence that homocysteine is a significant and independent risk factor for vascular disease with special reference to cardiovascular disease, and secondly to evaluate the evidence that a food staple fortified with folic acid will reduce this problem on a population basis.

The structure of plasma homocysteine (tHcy) is described. Homocysteine, a highly reactive compound, is synthesized from the amino acid, methionine, and is metabolized by two pathways, the catabolic transsulphuration routeviacystathionine β-synthase (EC 4.2.1.22) and the remethylation path using 5-methyltetrahy-drofolate polyglutamate, the product of 5,10-methylenetetrahydrofolate reductase (MTHFR; EC 1.1.1.171),viathe cobalamin dependent enzyme, methionine synthase (MS; EC 2.1.1.13).

The mechanisms whereby hyper-tHcy is produced include both increased rates of synthesis and decreased metabolism. The latter may occur owing to nutritional deficiency of the vitamin cofactors which are necessary for the normal function of the metabolic enzymes. In particular, folate is required for methylene reductase, pyridoxal phosphate for cystathionine synthase and cobalamin for methionine synthase. When these vitamins are deficient hyper-tHcy is induced and this occurs especially in the elderly. Alternatively, a variant form of methylene reductase has recently been described which occurs in nearly 10% of the normal population. This variant is associated with hyper-tHcy, especially in situations associated with a low folate nutritional status.

Meta-analysis of both retrospective case-control studies, nested prospective case-control surveys and a secondary trial of mortality in postmyocardial infarct patients have shown that the association of hyper-tHcy with vascular disease is beyond doubt. This has been further supported by direct assessments of the degree of vascular disease in the carotid brachial and aortic arteries in relation to tHcy levels. Furthermore, treatment with a cocktail of the vitamin cofactors has produced lowering of tHcy levels and regression of the vascular disease in the carotid arteries of affected individuals.

Suggested pathogenic mechanisms in vascular disease induced by hyper-tHcy include vascular endothelial cell dysfunction, smooth muscle proliferation and derangements of normal intravascular regulation mechanisms. A variety of clinical conditions are known to be associated with a high incidence of thromboembolic complications. Some of these are associated with hyper-tHcy.

Low physiological doses of folic acid, as well as pharmocological doses, lower tHcy. However, because of the poor bioavailability of food folate (50%) and the considerable chemical instability of the naturally occurring reduced forms of folate, in most people it would require unacceptably high consumption of green vegetables to accomplish the necessary increase in intracellular folate and reduction in tHcy. Accordingly, folic acid, the nonreduced synthetic form of the vitamin, which is 100% bioavailable and chemically extremely stable, should be added to a food staple such as flour to ensure maximum protection for most of the population.

Association of methylenetetrahydrofolate reductase genetic polymorphisms with atlantoaxial dislocation

Object

Genetic mechanisms of atlantoaxial dislocation (AAD) have not previously been elucidated. The authors studied association of polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene, which encodes enzymes of the folate pathway (implicated in causation of neural tube defects [NTDs]), in patients with AAD.

Methods

Molecular analysis of MTHFR polymorphisms (677C→T, cytosine to thymine and, 1298A→C, adenine to cytosine, substitutions) was carried out using polymerase chain reaction and restriction enzyme digestion in 75 consecutive patients with AAD and in their reducible (nine patients, 12%) and irreducible (66 patients, 88%) subgroups. Controls were 60 age- and sex-matched patients of the same ethnicity. Comparisons of genotype and allele frequencies were performed using a chi-square test (with significance at p < 0.05).

Results

The CT genotype frequency of MTHFR 677C→T polymorphism was significantly increased in the full group of patients with AAD (odds ratio [OR] 3.00, 95% confidence interval [CI] 1.28–7.14, p = 0.005) as well as in the irreducible subgroup (OR 2.81, 95% CI 1.17–6.86, p = 0.01). The frequency of T alleles was also higher in the AAD group (25.3%) than in controls (15%). The comparison of the combined frequency of CT and TT genotypes with the frequency of the CC genotype again showed significant association in AAD (OR 2.63, 95% CI 1.98–5.90, p = 0.009) and the irreducible (OR 2.5, 95% CI 1.1–5.74, p = 0.016) subgroup. There was, however, no significant association of MTHFR 1298A→C polymorphism with AAD.

Conclusions

Both MTHFR 677C→T polymorphism and higher T allele frequency have significant associations with AAD, especially the irreducible variety. Perhaps adequate supplementation of periconceptional folic acid to circumvent effects of this missense mutation (as is done for prevention of NTDs) would reduce the incidence of AAD.

MTHFR 677C-->T and 1298A-->C polymorphisms: evaluation of maternal genotypic risk and association with level of neural tube defect

BACKGROUND

Neural tube defects (NTDs) are common birth defects (1 in 1,000) leading to significant morbidity and mortality. Periconceptional folic acid supplementation helps in prevention of 70% of NTDs. Recently, polymorphisms in genes encoding enzymes of the folate pathway have been implicated in causation of NTDs. Since the closure of neural tube occurs at multiple sites, the etiology of defect at different sites may be different - which explains the failure of folic acid supplementation to prevent all NTDs.

METHODS

Molecular analysis of methylenetetrahydrofolate reductase polymorphisms was carried out using polymerase chain reaction and restriction enzyme digestion. We studied the association of these polymorphisms in mothers with a previous child with NTD and further refined the risk by stratification based on level of defect.

RESULTS

The frequency of 677C-->T homozygotes was higher in mothers with a previous child with NTD than the controls (OR = 1.6 (0.38-6.7), 95% CI, p = 0.72) but the difference was statistically insignificant. There was a significant difference in frequency of T alleles among mothers with a previous child with a 'lower' type of defect compared to controls (OR = 2.15 (1.13-4.1), 95% CI, p = 0.02). We did not find any significant association of 1298A-->C polymorphism with the level of NTDs.

CONCLUSIONS

We conclude that in the North Indian population, the 677C-->T allele of the MTHFR gene may be associated with the occurrence of a lower type of NTD. This points towards the differential role of thermolabile MTHFR at different sites of neural tube closure.

Pharmacogenetic Risk Factors for Osteonecrosis of the Hip Among Children With Leukemia

Purpose

One of the adverse effects of therapy for acute lymphoblastic leukemia (ALL) is osteonecrosis of the hip. Putative risk factors for osteonecrosis have included being female, white race, and older age. Our goal was to define possible genetic risk factors for osteonecrosis among children treated for newly diagnosed ALL.

Methods

Using a candidate gene approach, we determined the genotypes for 16 common polymorphisms in genes likely to affect the pharmacokinetics or pharmacodynamics of antileukemic medications in 64 children with ALL. Therapy included glucocorticoids and antifolates. Magnetic resonance imaging of both hips was used to diagnose osteonecrosis, and was performed at similar times from the start of ALL therapy (P = .61) in the 25 patients with and the 39 patients without osteonecrosis (median, 447 days and 443 days, respectively).

Results

In addition to age older than 10 years (odds ratio [OR], 24.2; P = .0001) and white race (OR, 11.1; P = .037), host factors for osteonecrosis included the vitamin D receptor FokI start site CC genotype (OR, 4.5; P = .045), and the thymidylate synthase low activity 2/2 enhancer repeat genotype (OR, 7.4; P = .049).

Conclusion

Because folate-related and vitamin D–receptor genetic variants have been associated with bone and vasculature morbidity, these pharmacogenetic associations likely reflect the interaction of antileukemic medications with germline sensitivity to drug actions, and might identify ALL patients at highest risk to develop osteonecrosis.

Peripheral circulation in patients with myelodysplasia

Patients with myelodysplasia have increased wound dehiscence and ulcer formation compared with the normal population. While neurologic deficits and resultant muscle imbalance are the presumed etiologies for these complications, no study has investigated the role of peripheral circulation in myelodysplasia. Eighty-two patients (ages 2-20) were prospectively recruited for this study, consisting of 41 patients with myelodysplasia and 41 age-matched controls. Peripheral circulation was quantified using systolic blood pressures in arms and legs (ankle-brachial index [ABI]) and transcutaneous pO2 measurements (TcO2) in a standardized location in the forefoot. Both groups had similar mean age. Patients with myelodysplasia had a lower ABI but similar TcO2 compared with the control group. Among the patients with myelodysplasia, the ABI and TcO2 did not vary according to the level of neurologic deficit or the patient's age. However, those with prior surgical procedures had significantly higher ABI and TcO2 compared with those without prior surgery (P < 0.05). This study suggests that patients with myelodysplasia may have decreased peripheral circulation compared with normal controls. Vascular insufficiency may therefore contribute to increased wound healing complications and ulcer formation in these patients.

Evaluation of infant methylenetetrahydrofolate reductase genotype, maternal vitamin use, and risk of high versus low level spina bifida defects

BACKGROUND

Several studies have suggested that homozygosity for the C677T 5,10-methylenetetrahydrofolate reductase (MTHFR) variant is a potential risk factor for neural tube defects (NTDs), as individuals homozygous for the C677T allele have slightly elevated homocysteine concentrations under conditions of low folic acid intake. It has been hypothesized that maternal folic acid supplementation prevents NTDs by partially correcting reduced MTHFR activity associated with the variant form of the enzyme.

METHODS

Genomic DNA was extracted from newborn screening blood spots obtained from 145 infants with spina bifida (SB) and 260 nonmalformed control infants. The MTHFR C677T genotype was determined by restriction enzyme digestion of PCR amplification products with Hinf1. We investigated whether infant MTHFR genotype influenced the risk for the anatomic level of the SB lesion (high vs. low); we also explored whether maternal vitamin use influenced this risk.

RESULTS

Compared to controls, the frequency of SB infants with the homozygous 677 TT genotype was greatest in those infants with high level SB defects (26%; odds ratio [OR] = 2.9; 95% confidence interval [CI] = 0.9-10.1) than for those with low level SB defects (22%; OR = 1.8; 95% CI = 0.9-3.2). Furthermore, homozygous 677TT infants whose mothers did not use vitamins containing folic acid had a modestly increased risk of SB (OR = 1.8; 95% CI = 0.8-3.9), with this risk increasing more than three-fold (OR = 5.5; 95% CI = 0.8-28.1) for those infants with high level SB defects whose mothers did not use vitamins.

CONCLUSIONS

Based upon our observations, it is suggested that the association between the infant MTHFR homozygous variant genotype and spina bifida risk may be conditional upon both lesion level and maternal vitamin use.

The epidemiology of developmental disabilities in low-income countries

Although most of the world's children live in developing countries and may be at high risk for disability, very little is known about the prevalence and causes of developmental disabilities in these countries. This paper discusses methodological difficulties contributing to this lack of knowledge, and provides an overview of what is known about the epidemiology of developmental disabilities in low-income countries. At least some forms of developmental disability appear to be more common in low-income countries than in wealthier countries, despite the probability of higher mortality among children with disabilities in low-income countries. For example, most studies of severe mental retardation in low-income countries report prevalences greater than 5 per 1,000 children, while prevalence estimates from industrialized countries are consistently below this. Major risk factors for developmental disabilities in some low-income countries include specific genetic diseases, a higher frequency of births to older mothers, consanguinity, and specific micronutrient deficiencies and infections. Trauma and toxic exposures are also important risk factors, but their contributions to the etiology of developmental disabilities in low-income countries are not well documented. Though many of the causes of developmental disabilities are understood and preventable, proven methods of prevention are not being fully implemented in developing countries. Epidemiologic studies are needed to raise awareness of the public health impacts of developmental disabilities in low-income countries and to provide a basis for setting priorities and designing efficient interventions.

Folate, homocysteine and neural tube defects: an overview

Folate administration substantially reduces the risk on neural tube detects (NTD). The interest for studying a disturbed homocysteine (Hcy) metabolism in relation to NTD was raised by the observation of elevated blood Hcy levels in mothers of a NTD child. This observation resulted in the examination of enzymes involved in the folate-dependent Hcy metabolism. Thus far, this has led to the identification of the first and likely a second genetic risk factor for NTD. The C677T and A1298C mutations in the methylenetetrahydrofolate reductase (MTHFR) gene are associated with an increased risk of NTD and cause elevated Hcy concentrations. These levels can be normalized by additional folate intake. Thus, a dysfunctional MTHFR partly explains the observed elevated Hcy levels in women with NTD pregnancies and also, in part, the protective effect of folate on NTD. Although the MTHFR polymorphisms are only moderate risk factors, population-wide they may account for an important part of the observed NTD prevalence.

Thrombophilia, polymorphisms, and vascular disease

Thrombophilia traditionally refers to rare inherited defects leading to enhanced coagulation, especially of the venous system. In recent years, a broader search for genetic polymorphisms of prothrombotic genes has been carried out to determine the relative impact on venous and arterial thrombosis. The bulk of evidence is drawn from numerous, often small, heterogeneous, case control association studies, with a variety of end points (deep venous thrombosis, myocardial infarction, or stroke). The data are often conflicting and inconclusive with only factor V Leiden and prothrombin polymorphisms having clear associations with venous thrombosis. Many of the polymorphisms interact with established cardiovascular risk factors, in particular smoking, to increase greatly the risk of a thrombotic episode. Future studies will need to consider the confounding factors of sample size, race, and clinical end points as well gene-environment interactions.

Spina bifida and other neural tube defects

NTDs, resulting from failure of the neural tube to close during the fourth week of embryogenesis, are the most common severely disabling birth defects in the United States, with a frequency of approximately 1 of every 2000 births. Neural tube malformations involving the spinal cord and vertebral arches are referred to as spina bifida, with severe types of spina bifida involving protrusion of the spinal cord and/or meninges through a defect in the vertebral arch. Depending on the level of the lesion, interruption of the spinal cord at the site of the spina bifida defect causes paralysis of the legs, incontinence of urine and feces, anesthesia of the skin, and abnormalities of the hips, knees, and feet. Two additional abnormalities often seen in children with spina bifida include hydrocephalus and the Arnold-Chiari type II malformation. Despite the physical and particular learning disabilities children with spina bifida must cope with, participation in individualized educational programs can allow these children to develop skills necessary for autonomy in adulthood. Advances in research to uncover the molecular basis of NTDs is enhanced by knowledge of the link between both the environmental and genetic factors involved in the etiology of NTDs. The most recent development in NTD research for disease-causing genes is the discovery of a genetic link to the most well-known environmental cause of neural tube malformation, folate deficiency in pregnant women. Nearly a decade ago, periconceptional folic acid supplementation was proven to decrease both the recurrence and occurrence of NTDs. The study of folate and its association with NTDs is an ongoing endeavor that has led to numerous studies of different genes involved in the folate metabolism pathway, including the most commonly studied thermolabile mutation (C677T) in the MTHFR gene. An additional focus for NTD research involves mouse models that exhibit both naturally occurring NTDs, as well as those created by experimental design. We hope the search for genes involved in the risk and/or development of NTDs will lead to the development of strategies for prevention and treatment. The most recent achievement in treatment of NTDs involves the repair of meningomyelocele through advancements in fetal surgery. Convincing experimental evidence exists that in utero repair preserves neurologic function, as well as resolving the hydrocephalus and Arnold-Chiari malformation that often accompany meningomyelocele defects. However, follow-up is needed to completely evaluate long-term neurologic function and overall improved quality of life. And in the words of Olutoye and Adzick, "until the benefits of fetal [meningomyelocele] repair are carefully elucidated, weighed against maternal and fetal risks, and compared to conventional postnatal therapy, this procedure should be restricted to a few centers that are committed (clinically and experimentally) to investigating these issues."

Neural tube defects and a disturbed folate dependent homocysteine metabolism

Folate administration substantially reduces the risk on neural tube defects (NTD). The interest for a disturbed homocysteine (Hcy) metabolism in relation to NTD was raised by the observation of elevated blood Hcy levels in mothers of a NTD child. This observation resulted in the examination of enzymes involved in the folate dependent Hcy metabolism. This leads to the identification of the first and likely a second genetic risk factor for NTD. The C677T and A1298C mutations in the methylenetetrahydrofolate reductase (MTHFR) gene are associated with an increased risk of NTD and cause elevated Hcy concentrations. These levels can be normalized by an additional folate intake. Thus, a dysfunctional MTHFR partly explains the observed elevated Hcy levels in women with NTD pregnancies, and also in part the protective effect of folate on NTD. Although, the MTHFR polymorphisms are only moderate risk factors, population wide they may account for an important part of the observed NTD prevalence.

Dietary folate and the prevalence of neural tube defects in the British Isles: the past two decades

OBJECTIVES

To measure the changes in folate consumption and the prevalence of neural tube defects in the British and Irish populations during the past two decades.

DESIGN

Ecological study.

MAIN OUTCOME MEASURES

Average daily dietary folate consumption for Britain for the period 1980-1996 was estimated from the National Food Survey. Annual neural tube defect prevalences for the same period were obtained from the Oxford Record Linkage Study Neural Tube Defect register, the Glasgow EUROCAT register, and the three Irish EUROCAT registers (Belfast, Dublin and Galway).

RESULTS

Dietary folate consumption increased on average by 1.6% per annum in Scotland and 1.4% in England during the study period. The annual rate of decline of neural tube defect prevalence averaged 10.4% in the Irish population, 8.2% in Glasgow, and 5.2% in Oxfordshire and West Berkshire.

CONCLUSIONS

The decline in neural tube defect prevalence observed in all British and Irish populations since the early 1970s continued with the introduction of folate fortification of cereals, which produced measurable increases in average daily folate consumption. Further declines in neural tube defect prevalence may be achieved by targeted folate supplementation during the periconceptual period.

Methylene tetrahydrofolate reductase (MTHFR) and nitric oxide synthase (ecNOS) genes and risks of peripheral arterial disease and coronary heart disease: Edinburgh Artery Study

Hyperhomocysteinaemia and reduced nitric oxide synthesis may each result in endothelial dysfunction predisposing to atherogenesis. Genetic variants of methylene tetrahydrofolate reductase (MTHFR) and endothelial nitric oxide synthase (ecNOS) influence homocysteine metabolism and nitric oxide synthesis, respectively and might thus be determinants of the risk of atherosclerotic disease. The aim of our study was to identify, in a general population sample, the risks of peripheral arterial disease and of coronary heart disease related to MTHFR (175;198) and ecNOS (4;5) polymorphisms. In the Edinburgh Artery Study, which is a population based cohort study, 940 men and women aged 60-79 years, who had previously been selected at random from the general population, had DNA extracted from a venous blood sample. Based on a clinical examination at baseline and follow up investigations, three groups of subjects were identified: those with peripheral arterial disease (n=80), those with coronary heart disease (n=137), and healthy controls who had no evidence of cardiovascular disease (n=300). The distributions of the ecNOS and MTHFR genotypes did not differ significantly between the groups with and without cardiovascular disease. However, the ecNOS-4 allele (frequency 0.13) was related to the occurrence of coronary heart disease in non smokers, OR=2.47 (95% CI [1.42, 4.34], P=0.02). No association was found with peripheral arterial disease. The MTHFR-175 allele (frequency 0.31) was not related to coronary heart disease, but was associated with a reduced risk of peripheral arterial disease, OR=0.54 (95% CI [0.32, 0.90], P=0.02). Neither the ecNOS-4 allele or MTHFR-175 allele was related to the ankle brachial pressure index in the whole study population. In conclusion, the ecNOS-4 allele was associated with a slightly increased risk of coronary heart disease in non-smokers, but otherwise the MTHFR and ecNOS genotypes appeared to have little influence on the risks of peripheral arterial disease and coronary heart disease in this older population.

High prevalence of hyperhomocysteinemia in critically ill patients

OBJECTIVE

To test the hypothesis that the prevalence of hyperhomocysteinemia is increased in critically ill patients and correlates with disease severity and mortality in these patients.

DESIGN

A prospective study.

SETTING

Three medical intensive care units at the University of vienna Medical School serving both medical and surgical patients.

PATIENTS

All consecutive admissions (n = 56) during a period of 4 wks. A total of 112 age- and gender-matched healthy individuals constituted the control group.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Blood samples were drawn within 24 hrs after admission for analysis of total homocysteine (tHcy), folate, vitamin B6 levels, and vitamin B12 levels as well as to identify the 677C-->T polymorphism in the gene coding for the enzyme 5,10-methylenetetrahydrofolate reductase. Acute Physiology and Chronic Health Evaluation III scores at admission and 24 hrs after admission as well as 30-day survival were documented in all patients. Hyperhomocysteinemia was more prevalent in critically ill patients (16.1%; 95% confidence interval, 7.6% to 28.3%) compared with age- and gender-matched healthy individuals (5.4%; 95% confidence interval, 2.0% to 11.3%; chi-square test; p = .022). There was no difference in tHcy plasma concentrations in the first 24 hrs after admission to an intensive care unit between survivors and nonsurvivors. The 5,10-methylenetetrahydrofolate reductase 677C-->T polymorphism had no influence on tHcy levels and survival of intensive care unit patients.

CONCLUSIONS

The prevalence of hyperhomocysteinemia is increased in critically ill patients compared to age- and gender-matched healthy individuals. The clinical significance of this finding remains to be determined.

Community-living nonagenarians in northern ireland have lower plasma homocysteine but similar methylenetetrahydrofolate reductase thermolabile genotype prevalence compared to 70-89-year-old subjects

This cross-sectional study assessed relationships between plasma homocysteine, 'thermolabile' methylenetetrahydrofolatereductase (MTHFR) genotype, B vitamin status and measures of renal function in elderly (70-89 years) and nonagenarian (90+ years) subjects, with the hypothesis that octo/nonagenarian subjects who remain healthy into old age as defined by 'Senieur' status might show reduced genetic or environmental risk factors usually associated with hyperhomocysteinaemia. Plasma homocysteine was 9.1 micromol/l (geometric mean [GM]) for all elderly subjects. Intriguingly, homocysteine was significantly lower in 90+ (GM; 8.2 micromol/l) compared to 70-89-year-old subjects (GM; 9.8 micromol/l) despite significantly lower glomerular filtration rate (GFR) and serum B12 in nonagenarian subjects and comparable MTHFR thermolabile (TT) genotype frequency, folate and B6 status to 70-89-year-olds. For all elderly subjects, the odds ratio and 95% confidence intervals for plasma homocysteine being in the highest versus lowest quartile was 4.27 (2.04-8.92) for age <90 compared >90 years, 3.4 (1.5-7.8) for serum folate <10.7 compared >10.7nmol/l, 3.0 (0.9-10.2) for creatinine >140 compared <140 umol/l and 2.1 (1.0-4.4) for male sex. This study shows that plasma homocysteine does not invariably increase with age. Compared to similarly enlisted 70-89-year-olds, apparently well, mentally alert, community-living 90+ year olds approximating 'Senieur' status, show lower homocysteine, which is unexplained by renal function, TT genotype and B vitamin status, suggesting that lower homocysteine may be associated with survival.

Cause of portal or hepatic venous thrombosis in adults: the role of multiple concurrent factors

According to a recent hypothesis, venous thrombosis results from the concurrence of several factors. This hypothesis was assessed in patients with portal or hepatic venous thrombosis by simultaneously investigating most of the currently identified prothrombotic disorders, local precipitating factors, and other risk factors such as oral contraceptive use. Patients with a tumorous obstruction and patients with cirrhosis with portal vein thrombosis were excluded. The prothrombotic disorders that were investigated included classical and occult myeloproliferative disorders; antiphospholipid syndrome; protein C; protein S and antithrombin deficiency; factor V Leiden; factor II; and methylene-tetrahydrofolate-reductase gene mutations. We found 1 or several prothrombotic disorders and a local precipitating factor in 26 and 10 of the 36 patients with portal vein thrombosis, respectively; and in 28 and none of the 32 patients with hepatic vein thrombosis, respectively. We found a combination of prothrombotic disorders in 5 and 9 patients with portal and hepatic vein thrombosis, respectively, whereas such a combination is expected in less than 1% of asymptomatic subjects. Of the 10 patients with a local precipitating factor, 8 had a prothrombotic disorder. Of the 13 patients who use oral contraceptives, 10 had a prothrombotic disorder. We conclude that portal or hepatic venous thrombosis should be regarded as an index for 1 or several prothrombotic disorders, whether or not local precipitating factors or oral contraceptive use are found. Concurrence of prothrombotic disorders is more common than expected. Extensive investigation of prothrombotic disorders and anticoagulation should be considered in patients with portal or hepatic venous thrombosis.

Saccharomyces cerevisiae expresses two genes encoding isozymes of methylenetetrahydrofolate reductase

The identification, expression, and assay of two Saccharomyces cerevisiae genes encoding methylenetetrahydrofolate reductases (MTHFR) is described. MTHFR catalyzes the reduction of 5, 10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, used to methylate homocysteine in methionine synthesis. The MET12 gene is located on chromosome XVI and encodes a protein of 657 amino acids. The MET13 gene is located on chromosome VII and encodes a protein of 599 amino acids. The deduced amino acid sequences of these two genes are 34% identical to each other and 32-37% identical to the human MTHFR. A phenotype for the single disruption of MET12 was not observed, however, single disruption of MET13 resulted in methionine auxotrophy. Double disruption of both MET12 and MET13 also resulted in methionine auxotrophy. Growth of the methionine auxotrophs was supported by both methionine and S-adenosylmethionine. Transcripts of both MET12 and MET13 were detected in total RNA from wild type cells grown in the presence or absence of methionine. The methionine requirement of the met12 met13 double disruptant was complemented by plasmid-borne MET13, but not MET12 even when a multicopy plasmid was used. Furthermore, overexpression of the human MTHFR in the met12 met13 double disruptant complemented the methionine auxotrophy of this strain. In contrast, overexpression of the Escherichia coli metF gene did not complement the methionine requirement of met12 met13 cells. Assays for MTHFR in crude extracts and expression of the yeast proteins in Escherichia coli verified that both MET12 and MET13 encode functional MTHFR isozymes.

Similarities in the epidemiology of neural tube defects and coronary heart disease: is homocysteine the missing link?

It is hypothesised that a single aetiological pathway could explain both the strong ecological association between the birth prevalence of neural tube defects (NTD) and coronary heart disease (CHD) mortality and the potential efficacy of dietary measures, especially increased folic acid intake, in their prevention. The epidemiological similarities between NTD and CHD are strong and consistent suggesting that the relation is real rather than artefactual. It is suggested that this epidemiological association reflects a shared aetiology arising from the role of disturbed homocysteine metabolism in the pathogenesis of both conditions. Current public health measures designed to increase the intake of periconceptional folic acid in women, reinforced by a broadening of this policy to target both sexes throughout life, will (if successful) result in a reduction in both the birth prevalence of NTD and the incidence of CHD, although not necessarily contemporaneously. If disordered homocysteine metabolism is the cause of both NTD and CHD, this has implications for future research and preventive strategies for these serious and often lethal diseases.

The influence of 5,10 methylenetetrahydrofolate reductase genotypes on enzyme activity in placental tissue

OBJECTIVE

To study the effects of heterozygosity and homozygosity for the C677T mutation of the 5,10 methylenetetrahydrofolate reductase (MTHFR) gene on the activity of this enzyme in placental tissue from pregnancies not affected by neural tube defect.

DESIGN

Placental tissue was genotyped for the C677T variants of MTHFR. Total enzyme activity and residual activity after heating to 46 degrees C for 5 minutes was then measured.

SETTING

A teaching hospital.

SAMPLE

Placental samples (n = 200), one from each of 200 uncomplicated term deliveries.

MAIN OUTCOME MEASURES

Total and residual enzyme activity for MTHFR.

RESULTS

Placentae heterozygous for the C677T mutation of the MTHFR gene had significantly lower total enzyme activity than those without the mutation; the lowest activity occurred in homozygotes for the mutation. The same pattern was seen in relation to enzyme activity after heating.

CONCLUSION

This study demonstrates that reduced enzyme activity is associated with the C677T variant of MTHFR in placental tissue. This is an important metabolic step in folic acid metabolism and pro-

Homocysteine metabolism

Homocysteine is a sulfur amino acid whose metabolism stands at the intersection of two pathways: remethylation to methionine, which requires folate and vitamin B12 (or betaine in an alternative reaction); and transsulfuration to cystathionine, which requires pyridoxal-5'-phosphate. The two pathways are coordinated by S-adenosylmethionine, which acts as an allosteric inhibitor of the methylenetetrahydrofolate reductase reaction and as an activator of cystathionine beta-synthase. Hyperhomocysteinemia, a condition that recent epidemiological studies have shown to be associated with increased risk of vascular disease, arises from disrupted homocysteine metabolism. Severe hyperhomocysteinemia is due to rare genetic defects resulting in deficiencies in cystathionine beta synthase, methylenetetrahydrofolate reductase, or in enzymes involved in methyl-B12 synthesis and homocysteine methylation. Mild hyperhomocysteinemia seen in fasting conditions is due to mild impairment in the methylation pathway (i.e. folate or B12 deficiencies or methylenetetrahydrofolate reductase thermolability). Post-methionine-load hyperhomocysteinemia may be due to heterozygous cystathionine beta-synthase defect or B6 deficiency. Early studies with nonphysiological high homocysteine levels showed a variety of deleterious effects on endothelial or smooth muscle cells in culture. More recent studies with human beings and animals with mild hyperhomocysteinemia provided encouraging results in the attempt to understand the mechanism that underlies this relationship between mild elevations of plasma homocysteine and vascular disease. The studies with animal models indicated the possibility that the effect of elevated homocysteine is multifactorial, affecting both the vascular wall structure and the blood coagulation system.

The role of inherited thrombophilia in venous thromboembolism associated with pregnancy

Venous thromboembolism is an important cause of maternal morbidity and mortality. The puerperium should be regarded as the period of greatest risk. However, fatalities in early pregnancy emphasise the need to assess thrombotic risk at all stages of pregnancy. In many cases those at increased risk are potentially identifiable on clinical grounds alone such as those with a personal or family history of venous thromboembolism, obesity, or surgery. Identification of women with multiple clinical risks for thrombosis during pregnancy remains the key to reducing the incidence of this condition. In women who present with a personal or family history of proven venous thromboembolism, thrombophilia screening should be performed in early pregnancy, since the results may influence subsequent management during pregnancy. The investigation and management of patients considered at increased risk of venous thrombosis during pregnancy requires close liaison between obstetricians and haematologists familiar with this rapidly expanding and complex field of thrombophilia.

Hyperhomocysteinemia and hypofibrinolysis in young adults with ischemic stroke

BACKGROUND AND PURPOSE

Data from epidemiological and case-control studies suggest that increased total homocysteine (tHcy) levels are associated with increased risk for thromboembolic disease. The mechanisms by which hyperhomocysteinemia contributes to thrombogenesis are incompletely understood. The main objectives of this study of young ischemic stroke patients were (1) to examine fasting and post-methionine load levels of tHcy, (2) to ascertain the genotype frequency of the C677CT mutation in the methylenetetrahydrofolate reductase gene (TT genotype), and (3) to study the possible interaction between plasma tHcy levels and fibrinolytic factors.

METHODS

This case-control study was based on 80 consecutive patients aged 18 to 44 years admitted between January 1992 and May 1996 as a result of a first-ever ischemic stroke. Forty-one healthy control subjects were recruited. Measurement of fasting tHcy and post-methionine load levels and evaluation of the fibrinolytic system were undertaken at least 3 months (mean, 5.1+/-1. 9 months) after admission. Genotyping of the methylenetetrahydrofolate reductase gene was performed.

RESULTS

Although the increase after methionine loading (ie, postload tHcy minus fasting-level tHcy) was significantly higher among patients, there was no difference in fasting and postload tHcy levels. After adjustment for conventional risk factors, elevated postload increase tHcy levels were associated with a 4.8-fold increased risk of ischemic stroke. There was no difference between patients and control subjects in either TT genotype frequency or T allele frequency. Abnormal response to methionine loading was associated with higher tissue plasminogen activator (tPA) mass concentration, higher plasminogen activator inhibitor-1 levels, and lower tPA activity. After adjustment for age, sex, body mass index, serum cholesterol, and triglycerides, an abnormal increase in postload tHcy levels remained significantly associated with tPA mass concentration levels (P=0.03).

CONCLUSIONS

A moderately elevated increase in tHcy levels after methionine loading was associated with an increased risk for ischemic stroke in young adults. In contrast, fasting tHcy levels did not differ between patients and controls. A moderately elevated increase in tHcy after methionine loading may provide a additional thrombogenic risk mediated in part by interactions with the fibrinolytic system. In young stroke patients, a methionine loading test to detect hyperhomocysteinemia should always be considered in the convalescent phase of the disease.

Thermolabile methyltetrahydrofolate reductase associated with unusual venous and arterial thromboses

We report a patient with unusual venous and arterial thromboses in association with the common thermolabile methyltetrahydrofolate (MTHFR) variant. The patient responded directly to folate supplementation. To our knowledge, this is the first report describing hyperhomocysteinemia in association with this type of thrombosis.

Plasma homocysteine levels in indigenous Australians

OBJECTIVES

To determine plasma homocysteine levels in indigenous Australians living in urban areas, and the relationship of these levels with other risk factors in this population.

DESIGN

Cross-sectional study.

SUBJECTS AND SETTING

365 urban indigenous Australian subjects, 153 men and 212 women, mean (SE) age 42 (1) years, ascertained without regard to history of atherosclerotic disease, in collaboration with community-based health centres in five indigenous communities in south-east Queensland, 1997-1998.

MAIN OUTCOME MEASURES

Plasma homocysteine levels, age, sex, smoking history, metformin therapy, history of atherosclerotic vascular disease, serum creatinine level, red cell folate and serum vitamin B12 levels.

RESULTS

89 subjects (24%) had plasma homocysteine levels 15 mumol/L or above. Homocysteine levels were higher in men than in women (men: 14.4 mumol/L; 95% confidence interval [CI], 13.6-15.2; women: 11.9 mumol/L; 95% CI, 11.4-12.5) (P < 0.001); correlated with age (P < 0.001); higher in current smokers (P = 0.02); higher in subjects taking metformin therapy (P = 0.007); and higher in subjects with a history of atherosclerotic vascular disease (P < 0.001). Homocysteine levels were also correlated with serum levels of creatinine (P < 0.001), red cell folate (P < 0.001), and vitamin B12 (P < 0.001).

CONCLUSIONS

These data indicate that the high plasma levels of homocysteine of Australian indigenous subjects are associated with a history of vascular disease, and correlated with, among other things, smoking, and folate and vitamin B12 nutritional deficiency. These are potentially reversible risk factors, and our data suggest that focusing public health initiatives on these issues may reduce the high prevalence of cardiovascular disease in the Australian indigenous population.

The C677T mutation of the 5,10-methylenetetrahydrofolate reductase gene is a moderate risk factor for spina bifida in Italy

OBJECTIVE

To estimate the risk for spina bifida associated with the common mutation C677T of the MTHFR gene in a country with a relatively low prevalence of NTDs.

DESIGN

Case-control study.

SUBJECTS

CASES

203 living patients affected with spina bifida (173 myelomeningocele and 30 lipomeningocele); controls: 583 subjects (306 young adults and 277 unselected newborns) from northern and central-southern Italy.

SETTING

CASES

three spina bifida centres; young adult controls: DNA banks; newborn controls: regional neonatal screening centres.

MAIN OUTCOME MEASURES

Prevalence of the C677T genotypes in cases and controls by place of birth; odds ratios for spina bifida and estimated attributable fraction.

RESULTS

The prevalence of T/T, T/C, and C/C genotype was 16.6%, 53.7%, and 29.7% in controls and 25.6%, 43.8%, and 30.6% in cases, respectively. We found no differences between type of defect or place of birth. The odds ratio for spina bifida associated with the T/T genotype v C/C plus T/C was 1.73 (95% CI 1.15, 2.59) and the corresponding attributable fraction was 10.8%. No increased risk was found for heterozygous patients (OR=0.79, 95% CI 0.53-1.18).

CONCLUSION

This study, as well as the meta-analysis we updated, shows that homozygosity for the MTHFR C677T mutation is a moderate risk factor in Europe, and even in Italy where there is a relatively low prevalence of spina bifida. The estimated attributable fraction associated with this risk factor explains only a small proportion of cases preventable by periconceptional folic acid supplementation. Thus, other genes involved in folate-homocysteine metabolism, their interaction, and the interaction between genetic and environmental factors should be investigated further.

B vitamins and homocysteine in cardiovascular disease and aging

The sulfur-containing amino acid, homocysteine, is formed from the essential amino acid methionine, and a number of B vitamins are involved in methionine metabolism. Pyridoxine, vitamin B6, is a cofactor for cystathionine beta synthase, which mediates the transformation of homocysteine to cystathionine, the initial step in the transsulfuration pathway and the urinary excretion of sulfur. In a normal diet there is conservation of the carbon skeleton, and about 50% of the homocysteine formed is remethylated to methionine via steps that require folic acid and vitamin B12. A deficiency of any of these three vitamins leads to modest homocyst(e)ine elevation, as does diminished renal function, both of which are common in the elderly. It is also established that homocyst(e)ine elevation of this order is associated with increased cardiovascular risk but is also associated with most established risk factors, although it is thought to be an independent contributor. In the inborn error of metabolism homocystinuria due to cystathionine beta synthase deficiency there is greatly increased circulating homocyst(e)ine and a clear association with precocious vascular disease. In about 50% of these patients there is a vascular event before the age of 30 years. The homocysteine-induced adverse vascular changes appear to result from endothelial and smooth muscle cell effects and increased thrombogenesis. We have documented a highly significant reduction in the occurrence of vascular events during 539 patient years of treatment in 32 patients with cystathionine beta synthase deficiency (mean age 30 years, range 9-66 years) by aggressive homocyst(e)ine lowering with pyridoxine, folic acid, and B12 (p = 0.0001). The 15 pyridoxine nonresponsive patients also received oral betaine. Although a cause and effect relationship is postulated for the increased cardiovascular risk associated with mild homocysteine elevation, a common cause of this elevation is the methylenetetrahydrofolate reductase C677T mutation. Homozygotes occur in about 11% of Caucasian populations. However, the mutation is not associated with increased coronary risk. Since mild homocysteine elevation is easily normalized by B vitamin supplementation, usually with folic acid, it remains for controlled clinical trials of this inexpensive therapy to determine whether normalizing mild homocyst(e)ine elevation reduces cardiovascular risk.

Relationship between homocysteine and thrombotic disease

Hyperhomocysteinemia is a condition which, in the absence of kidney disease, indicates a disrupted sulfur amino acid metabolism, either because of vitamin deficiency (folate, B12 and B6) or a genetic defect. Epidemiologic evidence suggests that mild hyperhomocysteinemia is associated with increased risk of arteriosclerotic disease and stroke. The relationship between hyperhomocysteinemia and thrombosis has been investigated in 10 studies involving a total of 1200 patients and 1200 controls. Eight of these studies demonstrated positive association with odds ratios that ranged from two to 13. This association was enhanced by including a methionine loading test. There is some evidence which suggests that hyperhomocysteinemia and activated protein C resistance have synergistic effect on the onset of thrombotic disease. Recent studies with animal models for mild hyperhomocysteinemia provided encouraging results in the understanding of the mechanism that underlies this relationship between mild elevations of plasma homocysteine and vascular disease. These animal models pointed to the possibility that the effect of elevated homocysteine is multifactorial, affecting both the vascular wall structure and the blood coagulation system.

Inherited thrombophilia and pregnancy

Inherited thrombophilia is associated with an increased risk of thrombosis. Classically it consists of protein C and protein S deficiency, activated protein C resistance and antithrombin III deficiency. In pregnancy, in addition to thrombosis, inherited thrombophilia is associated with poor obstetric outcome, including recurrent miscarriage, late fetal loss, abruption and pre-eclampsia. Hyperhomocysteinaemia is a newly recognized cause of familial thrombophilia. It is likely that further causes such as prothrombin gene mutations will be added to the rapidly expanding list. The diagnosis of some forms of genetic thrombophilia must, however, be approached with caution during pregnancy, particularly protein S deficiency and activated protein C resistance.

ACP Broadsheet No 152: March 1998. Clinical implications of plasma homocysteine measurement in cardiovascular disease

Plasma homocysteine is emerging as an important risk factor for cardiovascular disease. Measurement in clinical laboratories is feasible by several techniques, including HPLC. Of particular importance is the potential for treatment by dietary modification and vitamin supplements, particularly folic acid. The outcome of vitamin intervention on cardiovascular events is awaited with interest. If the role of homocysteine is confirmed then it may rival cholesterol in importance as a cardiovascular risk factor.