High prevalence of hyperhomocyst(e)inemia in patients with juvenile venous thrombosis

Hyperhomocysteinemia and retinal vascular occlusive disease

PURPOSE

Elevated plasma homocysteine is an independent risk factor for thrombosis and vascular disease. This prospective study compared plasma total homocysteine levels in patients with retinal vascular occlusive disease and in matched healthy controls.

METHODS

We measured plasma total homocysteine in 56 consecutive patients with recently diagnosed retinal vascular occlusive disease: 36 had central retinal vein occlusion, 12 branch retinal vein occlusion, and 8 retinal artery occlusion, and compared them with 59 age- and sex-matched healthy controls. Homocysteine levels were determined by high-performance liquid chromatography with electrochemical detection. Hyperhomocysteinemia was defined as a plasma homocysteine level above the 95th percentile in the control group (13.6 micromol/L).

RESULTS

Mean plasma total homocysteine levels were significantly higher in patients than controls (16.1 +/- 8.3 vs. 8.96 +/- 5.6 micromol/L p < 0.001). Mean homocysteine levels were significantly higher in the retinal vein occlusion and retinal artery occlusion groups than the control group (15.3 +/- 8.2 and 20.95 +/- 6.9 vs 8.96 +/- 5.6 micromol/L, p < 0.001). Estimates of the relative risk indicated that the risk of hyperhomocysteinemia was significantly higher in patients with retinal vascular occlusive disease than controls. Hyperhomocysteinemia was present in 37 (66.1%) of the 56 patients with retinal vascular occlusive disease but only 2 (3.4%) controls (odds ratio [OR] 47.5, 95% confidence interval [CI] 9.8-149.9). Hyperhomocysteinemia was present in 29 (60.4%) of the patients with retinal vein occlusion (OR 43.5, 95% CI 8.77-141.93) and in 6 (75%) patients with retinal artery occlusion (OR 85.5, 95% CI 7.49-1,173.1).

CONCLUSIONS

High plasma homocysteine is a risk factor for retinal vascular occlusive disease so it may be useful to measure homocysteine in the management of these patients. A randomized, controlled trial is required to study the effect of lowering with homocysteine folic acid and other B vitamins on the risk of recurrent vascular occlusion in the same eye or its development in the fellow eye.

Laboratory evaluation of hypercoagulability with venous or arterial thrombosis

OBJECTIVE

To provide recommendations for hypercoagulation testing for patients with venous, arterial, or neurovascular thrombosis, as reflected in the medical literature and the consensus opinion of recognized experts in the field.

DATA SOURCES, EXTRACTION, AND SYNTHESIS

The authors extensively examined the literature and current practices, and prepared a draft manuscript with preliminary recommendations. The draft manuscript was circulated to each of the expert participants (n = 30) in the consensus conference prior to the convening of the conference. The manuscript and recommendations were then presented at the conference for discussion. Recommendations were accepted if a consensus of the 28 experts attending the conference was reached. The discussions were also used to revise the manuscript into its final form.

CONCLUSIONS

The resulting article provides 17 recommendations for hypercoagulation testing in the setting of venous, arterial, or neurovascular thrombosis. The supporting evidence for test selection is analyzed and cited, and consensus recommendations for test selection are presented. Issues for which a consensus was not reached at the conference are also discussed.

Hyperhomocysteinemia and the MTHFR C677T mutation in Budd-Chiari syndrome

Hyperhomocysteinemia (HH) is a factor that predisposes individuals to thrombosis, and the C677T mutation in the 5,10-methylenetetrahydrofolate reductase (MTHFR) is known to give increased plasma homocysteine. However, little is known about their roles in Budd-Chiari syndrome (BCS). This study evaluated the roles of HH and the MTHFR C677T mutation in patients with BCS. We compared 41 BCS patients with 80 sex- and age-matched healthy controls. The mean plasma homocysteine level was significantly higher in patients with BCS (20.15 +/- 5.78 micromol/L) compared with normal controls (15.80 +/- 6.58 micromol/L), P < 0.01. HH (>19.5 micromol/L in men and >15.0 micromol/L in women) was detected in 15 (36.59%) patients and in 14 (17.5%) controls (odds ratio [OR], 2.72; 95% confidence internal [CI], 1.17-6.32). The prevalence of the mutated MTHFR 677TT genotype and the 677T allele in normal controls was 10.0% and 31.3%, respectively. The mutant 677T homozygotes and alleles were more frequent in patients with BCS than in controls (22.0% vs. 10.0%, 0.025 < P < 0.05; 45.1% vs. 31.3%, 0.025 < P < 0.05). The relative risk of BCS among the carriers of 677TT was significantly increased (OR, 3.3; 95% CI, 1.1-10.0). The mutant MTHFR heterozygous 677C/T carriers were not significantly increased in patients with BCS compared with controls (46.3% vs. < 2.5%, P > 0.05). The relative risk OR of BCS among carriers of 677C/T was 1.6 (95% CI, 0.7-3.6). This study suggests that both HH and the homozygous C677T mutation in the MTHFR gene are important risk factors of BCS.

Hyperhomocysteinemia and thrombosis

Homocysteine (Hcy) is a sulfhydryl amino acid derived from the metabolic conversion of methionine, which is dependent on vitamins (folic acid, B12, and B6) as cofactors or cosubstrates. In 1969, McCully first reported the presence of severe atherosclerotic lesions in patients with severe hyperhomocysteinemia and hypothesized the existence of a pathogenic link between hyperhomocysteinemia and atherogenesis. Several case-control and cross-sectional studies were consistent with the initial hypothesis of McCully, showing that moderate hyperhomocysteinemia is also associated with heightened risk of occlusive arterial disease. Less consistent results have been reported by prospective cohort studies of subjects who were healthy at the time of their enrollment, whereas prospective cohort studies of patients with overt coronary artery disease or other conditions at risk consistently confirmed the association between moderate hyperhomocysteinemia and cardiovascular morbidity and mortality. More recently, an association between moderate hyperhomocysteinemia and heightened risk of venous thromboembolism has been documented, suggesting that hyperhomocysteinemia might be involved not only in atherogenesis, but also in thrombogenesis. The mechanisms by which hyperhomocysteinemia might contribute to atherogenesis and thrombogenesis are incompletely understood. The mainstay of treatment of hyperhomocysteinemia is folic acid, alone or in combination with vitamin B12 and vitamin B6. Although it is quite clear that vitamins effectively reduce the plasma levels of total homocysteine (tHcy), we do not yet know whether they will decrease the risk of vascular disease. The results of ongoing randomized, placebo-controlled, double-blind trials of the effects of vitamins on the thrombotic risk will help in defining whether the relationship between hyperhomocysteinemia and thrombosis is causal, and will potentially have a dramatic effect in the prevention of thromboembolic events.

Homocysteine and occlusive arterial disease

BACKGROUND

An increased plasma level of homocysteine has been proposed as an independent risk factor for atherosclerosis; this review examines the evidence.

METHODS

A Medline search was undertaken for English language articles on homocysteine and vascular disease. Further papers were identified by cross-referencing from the reference lists of relevant major articles.

RESULTS

Although much interest has been generated about homocysteine and atherosclerotic disease, contradictory data exist regarding its role in disease progression. There is insufficient current evidence to regard increased homocysteine level as a causative factor in atherosclerotic disease.

CONCLUSION

It is not known whether lowering plasma homocysteine concentration will reduce cardiovascular risk in the long term. Until such data become available, there is no evidence for the widespread use of folic acid therapy to reduce cardiovascular disease risk.

Mutations C677T and A1298C of the 5,10-methylenetetrahydrofolate reductase gene and fasting plasma homocysteine levels are not associated with the increased risk of venous thromboembolic disease

Mild hyperhomocysteinemia is associated with homozygosity for the thermolabile variant of 5,10-methylenetetrahydrofolate reductase (MTHFR) and could increase the risk of venous thromboembolic disease (VTD). Recently, the second A1298C mutation of the MTHFR gene was described. The present study aimed to analyze both mutations of the MTHFR gene and plasma homocysteine levels in subjects with VTD. The study groups comprised 146 patients with VTD and 100 healthy subjects. There were no statistical differences in carrier frequency and allelic frequency for both A1298C and C677T mutations, nor were there any differences encountered between subjects with VTD and controls in either plasma homocysteine levels or according to C677T or A1298C genotypes of MTHFR. In our VTD patients and controls, neither MTHFR 677CT/1298CC nor MTHFR 677TT/1298CC combined genotypes were observed; double heterozygotes (A1298C/C677T) were represented only in 11% of VTD patients, and in 15% of the controls. In conclusion, the polymorphisms C677T and A1298C of MTHFR and fasting plasma homocysteine levels do not seem to be significant risk factors for venous thromboembolic disease.

Low risk of thrombosis in family members of patients with hyperhomocysteinaemia

Mild to moderate hyperhomocysteinaemia, a metabolic disorder due to genetic and/or acquired factors, is associated with an increased risk of venous and arterial thrombosis. To establish whether measuring homocysteine in members of families of hyperhomocysteinaemic patients is warranted, we investigated 169 relatives of patients diagnosed with hyperhomocysteinaemia after they developed arterial or venous thrombosis. The prevalence of hyperhomocysteinaemia was 16.6%; the relative risk of thrombosis in relatives with hyperhomocysteinaemia compared to those without was 1.2 (odds ratio; 95% CI 0.24-4.2), with similarly low absolute annual incidences of thrombosis (0.28% and 0.24%). The low prevalence of hyperhomocysteinaemia among relatives of patients with this metabolic disorder, and their low risk of thrombosis, do not justify family screening.

Homocysteine and arterial disease. Experimental mechanisms

Hyperhomocysteinemia (hH(e)) in the general population is associated with incidence and progression of arterial occlusive disease, although the underlying mechanisms are not well defined. Current research supports a role for homocysteine (H(e))-mediated endothelial damage and endothelial dysfunction. This mechanism appears to be a key factor in subsequent impaired endothelial-dependent vasoreactivity and decreased endothelium thromboresistance. These consequences may predispose hyperhomocysteinemic vessels to the development of increased atherogenesis. Additional mechanisms of H(e)-mediated vascular pathology, including protein homocysteinylation and vascular smooth muscle cell proliferation may also play a role. Continued investigation into the mechanisms contributing to H(e) toxicity will provide further insight into the processes by which hH(e) may increase atherosclerosis.

Hyperhomocysteinemia and venous thromboembolism: a risk factor more prevalent in the elderly and in idiopathic cases

Fasting plasma homocysteine level and the related clinical findings were analysed in 240 consecutive patients with venous thromboembolism. Hyperhomocysteinemia, defined as a plasma level above 20 micromol/l (corresponding to the percentile 95th in the controls), was present in 11.2% of the patients. Plasma homocysteine level was similar in patients presenting with either deep venous thrombosis, pulmonary embolism or both conditions. It was significantly higher in patients with primary (unprovoked) VTE than in patients with secondary disease (associated with at least one risk factor): 12.3 vs. 9.55 micromol/l (p < 0.005). Mean homocysteine was higher in male than in female patients (14.51 vs. 12.9 micromol/l, p < 0.05) and increased significantly with age. Hyperhomocysteinemia was more frequent in patients with relapsing disease (14 of 76, 18.4%) than in those presenting with a single episode (13 of 164, 7.9%) (p = 0.034). Furthermore, hyperhomocysteinemia was correlated with reduced protein C level (p = 0.013). In a multivariate analysis, two factors were significantly associated with hyperhomocysteinemia: older age (p < 0.0001) and idiopathic occurrence (p < 0.02). Since the frequency of homozygous MTHFR thermolabile variant was rather similar in patients and controls, testing for C677T mutation was not helpful in screening VTE patients. However, the homozygous mutation was significantly more prevalent among hyperhomocysteinemia patients, confirming its role in the genesis of hyperhomocysteinemia. According to its prevalence, to the putative role in venous and arterial disease and the availability of an effective and low-cost corrective therapy, hyperhomocysteinemia deserves interest, especially in the elderly and in the patients with idiopathic VTE disease.

Hyperhomocysteinemia increases the risk of venous thrombosis independent of the C677T mutation of the methylenetetrahydrofolate reductase gene in selected Brazilian patients

Fasting total homocysteine (tHcy) and the methylenetetrahydrofolate reductase (MTHFR) C677T mutation were evaluated in 91 patients with venous thromboembolism and without acquired thrombophilia, and in 91 age-matched and sex-matched controls. Hyperhomocysteinemia was detected in 11 patients (12.1%) and in two controls (2.2%), yielding an odds ratio (OR) for venous thrombosis of 6.1 [95% confidence interval (CI), 1.3-28.4]. After excluding 21 patients and four controls with other known genetic risk factors for venous thrombosis, the OR was not substantially changed (7.0; 95% CI, 1.5-33.1). The prevalence of the MTHFR 677TT genotype was not significantly different in patients (9.9%) and in controls (5.5%), with an OR for venous thrombosis of 1.8 (95% CI, 0.6-5.8). Subjects with the MTHFR 677TT genotype showed higher levels of tHcy compared with the 677CC genotype in patients (P = 0.010) and in controls (P = 0.030). In conclusion, we found that fasting hyperhomocysteinemia is a risk factor for venous thrombosis in patients without known acquired thrombophilia and other genetic risk factors for venous thrombosis. Although tHcy levels are significantly higher in those homozygous for the MTHFR C677T mutation, this genotype does not increase the thrombotic risk in our study population.

Homocysteine and vascular access thrombosis in hemodialysis patients

BACKGROUND

Vascular access remains the Achilles' heel of successful hemodialysis, and thrombosis is the leading cause of vascular access failure. Hyperhomocystinemia is common in hemodialysis patients and is associated with venous and arterial thrombosis in patients without end-stage renal disease.

SUBJECTS AND METHODS

In the study, 65 hemodialysis patients with native arteriovenous fistula were included. Two groups of patients were defined: group A including 45 patients with their vascular access either never or only once thrombosed, and group B including 20 patients with two or more thromboses of their vascular access. We determined serum concentrations of total homocysteine (immunoassay, Abbott) in our patients.

RESULTS

In 63 (96.9%) patients, hyperhomocystinemia was presented. There was no statistically significant difference between group A and B regarding age, gender and duration of hemodialysis treatment. Total homocysteine concentrations were higher in group A (42.1 +/- 18.6 micromol/l) than in group B (36.1 +/- 18.1 micromol/l) patients but the difference was small and not statistically significant.

CONCLUSION

We found no significant differences in total homocysteine concentrations between group A (thrombosis non-prone) and group B (thrombosis prone) patients. Our results suggest that thrombosis of native arteriovenous fistulas may not be caused by hyperhomocystinemia in these patients.

[Evolution of homocysteine during ovarian stimulation for IVF or ICSI]

OBJECTIVE

To determine the homocysteine evolution during ovarian stimulation in IVF or ICSI protocols and in, a second time, to evaluate the role of hyperhomocysteine as thrombotic risk factor for the treated patients.

MATERIAL AND METHODS

Plasma homocysteine was determined three times for each of 31 women included in an IVF/ICSI program. Dosages were realised before stimulation, after gonadotrophin-releasing hormone agonist treatment (GnRH) and on the day of hCG injection. Vitamin B12 and folates were determined before stimulation. In case of hyperhomocysteinemia, a research of APCR (Activated Protein C Resistance) was realised.

RESULTS

Five hyperhomocysteinemia cases were discovered (16.12% of studied population). APCR was found in a patient with hyperhomocysteinemia (14 mumol/L, before stimulation). Molecular biology has confirmed an heterozygous mutation of factor V Leiden. During the ovarian stimulation the evolution of homocysteine was independent of the 17 beta oestradiol evolution.

CONCLUSION

The prevalence of hyperhomocysteinemia was not significative according to the limited size of the studied population. The increase of oestradiol during induction protocols is unrelated to the homocysteine level. This work must be continued with largest population to have better knowledge of the prevalence of hyperhomocysteinemia among women included in ovarian stimulation protocols.

Inherited thrombophilia and stillbirth

Thrombophilias are inherited or acquired conditions that predispose individuals to thromboembolism. New inherited thrombophilias are recognized each year. Some, but not all, studies have found an association between inherited thrombophilias and adverse pregnancy outcomes, including fetal loss. The controversy regarding the clinical implications of thrombophilias in pregnancy is clouded by differences in study populations, the number of thrombophilias tested, interactions between thrombophilias, and the retrospective nature of most studies, just to name a few factors. The lack of adequately designed studies also extends to clinical management. Clear evidence to determine when to test, whom to test, which thrombophilias to test for, when to treat, and what to treat with is not available. Further studies to investigate these questions are urgently needed.

Update on selected inherited venous thrombotic disorders

The inherited thrombophilias are a group of inherited conditions that predispose to thrombotic events. Most of the inherited thrombotic disorders are associated with venous thromboembolism rather than arterial thrombosis. Frequently, one or more predisposing genetic factors and/or environmental risk factor are identified in thrombosis patients. Significant advances in the identification of etiologies of inherited thrombosis have recently been reported. The most common inherited thrombotic disorders include activated protein C (APC) resistance (factor V Leiden), hyperhomocysteinemia, the prothrombin gene variant G20210A, elevated factor VIII levels, and deficiencies of thrombomodulin, protein C, protein S, and antithrombin. Less well characterized disorders include elevated factor IX, X, and XI levels. Recognition of these disorders now permits a laboratory diagnosis in approximately 70% of patients being evaluated for inherited thrombosis. This review focuses on the clinical and laboratory aspects of some of the most common inherited venous thrombotic disorders, including APC resistance, hyperhomocysteinemia, the prothrombin G20210A mutation, and elevated coagulation factor levels.

Epidemiology of venous thromboembolic disease

From the information presented in this article, it can be concluded that clinical suspicion of VTE should be increased in patients with a history of VTE, recent surgery, spinal cord injury, trauma, or malignancy. A variety of medical illnesses also increase the risk of venous thrombosis, including congestive heart failure, myocardial infarction, stroke with paresis, nephrotic syndrome, cigarette smoking, and obesity. Hypercoagulable states, such as antithrombin III deficiency, protein C deficiency, protein S deficiency, or factor V Leiden mutation should be considered in those patients who develop VTE in the absence of known risk factors. Additionally, the presence of vena caval filters does not exclude the possibility of PE or recurrent DVT. With a careful assessment of risk, physicians can hope to increase the diagnostic yield of VTE and decrease the significant morbidity and mortality of caused by this disease.

Hyperhomocysteinemia as a risk factor for venous thrombosis

Classical homocystinuria is associated with arterial vascular diseases and venous thrombosis. In the last decade, several studies have been published indicating that even mild hyperhomocysteinemia is a risk factor for venous thrombosis. The 677C-->T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene is an important cause of mild hyperhomocysteinemia, but this polymorphism does not seem to be a risk factor for venous thrombosis. Studies on the interaction between hyperhomocysteinemia and other thrombotic risk factors are conflicting. Little is known about the pathophysiology of venous thrombosis in hyperhomocysteinemia. Several mechanisms proposed for vascular disease may be applied to venous thrombosis as well. However, up to now there is no satisfying model which might explain a thrombophilic state at plasma homocysteine concentrations in the range of mild hyperhomocysteinemia. The results of a first clinical intervention study are expected in 2002. As the results are pending, clinicians could perform homocysteine measurements in patients with venous thrombosis if screening for thrombophilia is indicated. Vitamin supplementation could be prescribed if homocysteine levels are elevated. However, the patient should be informed about the uncertainty of the benefits of vitamin supplementation.

Importance of hyperhomocysteinemia as a risk factor for venous thromboembolism in a Taiwanese population. A case-control study

OBJECTIVE

To determine the current status of hyperhomocysteinemia, which is a known risk for venous thrombosis (DVT), in Taiwan.

SUBJECTS

101 unselected patients with a minimum of one episode of deep leg DVT, either initial inpatients or current compliant outpatients in a teaching hospital.

METHODS

Various thrombophilic risks, gene polymorphism and clinical predisposition were evaluated.

RESULTS AND CONCLUSIONS

Patients presented higher fast total plasma homocysteine (hcy) levels than age- and sex-matched controls did (14.1 vs. 9.94 microM). Based on the 95th percentile of control values, hyperhomocysteinemia had a four- to nine-fold risk for DVT, irrespective of clinical predisposition, as well as other thrombophilic risks surveyed. Polymorphism of a metabolizing enzyme, methylenetetrahydrofolate reductase (MTHFR), was not associated with DVT, although homozygous thermolabile mutation tended to have higher plasma hcy levels. Factor V Leiden was absent in analysis of 80 patients. In complete evaluation (hcy, antithrombin (AT), protein S (PS), protein C (PC), lupus anticoagulant (LA), anticardiolipin antibody) of a subset of 83 patients hyperhomocysteinemia was the most prevalent risk (33.7%), with PC or PS deficiencies following (22.9%). Thus, hyperhomocysteinemia is a prominent risk for DVT in Taiwan.

Coexistence of the methylenetetrahydrofolate reductase single-nucleotide polymorphism (C677T) in patients with the factor V Leiden or prothrombin G20210A polymorphisms

Venous thromboembolism is a complex disease resulting from the interaction of a multitude of both genetic and environmental factors that can affect the cascade of biochemical reactions involved. Single-nucleotide polymorphisms in the genes that code for coagulation factors V (factor V Leiden) and II (prothrombin G20210A), as well as the methylenetetrahydrofolate reductase (MTHFR C677T) gene, have been implicated in the majority of cases of hereditary thrombophilia. In this study the authors evaluated the coexistence of the MTHFR polymorphism in 96 patients with a clinical suspicion for thrombosis who also have either the factor V Leiden polymorphism or the prothrombin G20210A polymorphism. Results indicate that the frequency of the MTHFR polymorphism was similar between the study and control groups with respect to heterozygosity (36.5% vs. 55.3%) and homozygosity (20.8% vs. 14.9%). These data suggest that the MTHFR polymorphism is not associated preferentially with patients who have had or who are at risk of developing a thrombotic event. In this study, patients with the factor V Leiden polymorphism or the prothrombin G20210A polymorphism were considered to be at risk.

Impaired homocysteine metabolism and atherothrombotic disease

Based on recent retrospective, prospective, and experimental studies, mild to moderate elevation of fasting or postmethionine-load plasma homocysteine is accepted as an independent risk factor for cardiovascular disease and thrombosis in both men and women. Hyperhomocysteinemia results from an inhibition of the remethylation pathway or from an inhibition or a saturation of the transsulfuration pathway of homocysteine metabolism. The involvement of a high dietary intake of methionine-rich animal proteins has not yet been investigated and cannot be ruled out. However, folate deficiency, either associated or not associated with the thermolabile mutation of the N(5,10)-methylenetetrahydrofolate reductase, and vitamin B(6) deficiency, perhaps associated with cystathionine beta-synthase defects or with methionine excess, are believed to be major determinants of the increased risk of cardiovascular disease related to hyperhomocysteinemia. Recent experimental studies have suggested that moderately elevated homocysteine levels are a causal risk factor for atherothrombotic disease because they affect both the vascular wall structure and the blood coagulation system. The oxidant stress that results from impaired homocysteine metabolism, which modifies the intracellular redox status, might play a central role in the molecular mechanisms underlying moderate hyperhomocysteinemia-mediated vascular disorders. Because folate supplementation can efficiently reduce plasma homocysteine levels, both in the fasting state and after methionine loading, results from further prospective cohort studies and from on-going interventional trials will determine whether homocysteine-lowering therapies can contribute to the prevention and reduction of cardiovascular risk. Additionally, these studies will provide unequivocal arguments for the independent and causal relationship between hyperhomocysteinemia and atherothrombotic disease.

Homocysteine inhibits inactivation of factor Va by activated protein C

We report the effect of homocysteine on the inactivation of factor Va by activated protein C (APC) using clotting assays, immunoblotting, and radiolabeling experiments. Homocysteine, cysteine, or homocysteine thiolactone have no effect on factor V activation by alpha-thrombin. Factor Va derived from homocysteine-treated factor V was inactivated by APC at a reduced rate. The inactivation impairment increased with increasing homocysteine concentration (pseudo first order rate k = 1.2, 0.9, 0.7, 0.4 min(-1) at 0, 0.03, 0.1, 1 mm homocysteine, respectively). Neither cysteine nor homocysteine thiolactone treatment of factor V affected APC inactivation of derived factor Va. Western blot analyses of APC inactivation of homocysteine-modified factor Va are consistent with the results of clotting assays. Factor Va, derived from factor V treated with 1 mm beta-mercaptoethanol was inactivated more rapidly than the untreated protein sample. Factor V incubated with [(35)S]homocysteine (10-450 micrometer) incorporated label within 5 min, which was found only in those fragments that contained free sulfhydryl groups: the light chain (Cys-1960, Cys-2113), the B region (Cys-1085), and the 26/28-kDa (residues 507-709) APC cleavage products of the heavy chain (Cys-539, Cys-585). Treatment with beta-mercaptoethanol removed all radiolabel. Plasma of patients assessed to be hyperhomocysteinemic showed APC resistance in a clot-based assay. Our results indicate that homocysteine rapidly incorporates into factor V and that the prothrombotic tendency in hyperhomocysteinemia may be related to impaired inactivation of factor Va by APC due to homocysteinylation of the cofactor by modification of free cysteine(s).

Maternal plasma homocysteine levels in women with preterm premature rupture of membranes

Homocysteine is a sulfur-containing amino acid produced by the breakdown of methionine. Plasma homocysteine levels can be elevated due to a variety of genetic and nutritional factors. Poor nutrition from diets low in folate and vitamin B12 can lead to hyperhomocysteinemia. Mildly elevated levels of homocysteine have been implicated in a number of disease processes such as atherosclerotic vascular disease and adverse obstetrical outcomes. High levels of plasma homocysteine are also associated with abnormal collagen cross-linking. Due to homocysteine's effects on connective tissue integrity, it is hypothesized that hyperhomocysteinemia in pregnancy is associated with preterm premature rupture of membranes (PPROM). Hyperhomocysteinemia, therefore, could be a treatable cause of this important public health concern.

Hyperhomocysteinemia and pregnancy--review of our present understanding and therapeutic implications

Homocysteine results from the transmethylation of methionine. Its metabolism depends primarily on three enzymes and several vitamin cofactors. Genetic abnormality in these enzymes or deficiency of these vitamins lead to hyperhomocysteinemia (HHCh). HHCh is usually biologically defined by a fasting value >15 micromol/l. HHCh belongs among the congenital hypercoagulable states and is a long-known vascular disease risk factor. The discovery that HHCh may also be responsible for several pregnancy complications has only recently been made. Studies in this area are still scarce and report on limited numbers of patients. It nevertheless appears clear that HHCh is associated with the syndromes of repeated miscarriage, pre-eclampsia, placenta abruptio, thromboembolic events, neural tube defects, and perhaps with fetal death-in-utero and intra-uterine growth retardation. Supplementation with vitamin B9 can reduce plasma HC levels, and is thus recommended in patients with HHCh. The prevention of thromboembolic events during pregnancy by anticoagulant treatment is also desirable in these patients.

Mild hyperhomocysteinemia and fibrinolytic factors in patients with history of venous thromboembolism

Mild hyperhomocysteinemia is recognized as a risk factor for venous thromboembolism (VTE), though its role in the thrombogenic processes is not understood. Its possible association with impaired fibrinolysis was investigated in 157 patients (61 women, 96 men) below the age of 60 years (43+/-11, mean+/-SD) with a history of objectively confirmed VTE. Patients had significantly higher fasting total plasma homocysteine (tHcy) levels than 138 apparently healthy subjects (8.0, 6.6-9.9 micromol/L vs. 7.2, 5.9-8.6 micromol/L, P=0. 001; median, range between first and third quartile). In 17 of 157 patients (12%) hyperhomocysteinemia (tHcy>11.4 micromol/L for women and tHcy>12.6 micromol/L for men) was established. The adjusted odds ratio as an estimate of relative risk for VTE was 2.3 (0.8-7.0; 95% confidence interval). When patients with hyperhomocysteinemia were compared to patients without hyperhomocysteinemia, no significant differences in t-PA (antigen 9.2+/-5.5 microg/L and 9.7+/-4.7 microg/L, respectively; activity 1.3+/-0.5 IU/mL and 1.3+/-0.7 IU/mL, respectively) and PAI-1 (antigen 19.3+/-17.5 microg/L and 22.6+/-20. 4 microg/L, respectively; activity 15.0+/-12.6 and 15.8+/-13.3 IU/mL, respectively) were observed. In conclusion, this study showed an association between mild hyperhomocysteinemia and VTE, but provided no evidence for an independent association between hyperhomocysteinemia and alterations in fibrinolytic proteins.

High levels of factor IX increase the risk of venous thrombosis

Elevated plasma levels of factor VIII (&gt; 150 IU/dL) are an important risk factor for deep vein thrombosis (DVT). Factor VIII is the cofactor of factor IXa in the activation of factor X. The risk of thrombosis in individuals with an elevated factor IX level is unknown. This study investigated the role of elevated factor IX levels in the development of DVT. We compared 426 patients with a first objectively diagnosed episode of DVT with 473 population controls. This study was part of a large population-based case-control study on risk factors for venous thrombosis, the Leiden Thrombophilia Study (LETS). Using the 90th percentile measured in control subjects (P90 = 129 U/dL) as a cutoff point for factor IX levels, we found a 2- to 3-fold increased risk for individuals who have factor IX levels above 129 U/dL compared with individuals having factor IX levels below this cutoff point. This risk was not affected by adjustment for possible confounders (age, sex, oral contraceptive use, and high levels of factor VIII, XI, and vitamin K-dependent proteins). After exclusion of individuals with known genetic disorders, we still found an odds ratio (OR) of 2.5 (95% confidence interval [CI]: 1.6-3.9). The risk was higher in women (OR: 2.6, CI: 1.6-4.3) than in men (OR: 1.9, CI: 1.0-3.6) and appeared highest in the group of premenopausal women not using oral contraceptives (OR: 12.4, CI: 3.3-47.2). These results show that an elevated level of factor IX is a common risk factor for DVT.

High levels of factor IX increase the risk of venous thrombosis

Elevated plasma levels of factor VIII (> 150 IU/dL) are an important risk factor for deep vein thrombosis (DVT). Factor VIII is the cofactor of factor IXa in the activation of factor X. The risk of thrombosis in individuals with an elevated factor IX level is unknown. This study investigated the role of elevated factor IX levels in the development of DVT. We compared 426 patients with a first objectively diagnosed episode of DVT with 473 population controls. This study was part of a large population-based case-control study on risk factors for venous thrombosis, the Leiden Thrombophilia Study (LETS). Using the 90th percentile measured in control subjects (P90 = 129 U/dL) as a cutoff point for factor IX levels, we found a 2- to 3-fold increased risk for individuals who have factor IX levels above 129 U/dL compared with individuals having factor IX levels below this cutoff point. This risk was not affected by adjustment for possible confounders (age, sex, oral contraceptive use, and high levels of factor VIII, XI, and vitamin K-dependent proteins). After exclusion of individuals with known genetic disorders, we still found an odds ratio (OR) of 2.5 (95% confidence interval [CI]: 1.6-3.9). The risk was higher in women (OR: 2.6, CI: 1.6-4.3) than in men (OR: 1.9, CI: 1.0-3.6) and appeared highest in the group of premenopausal women not using oral contraceptives (OR: 12.4, CI: 3.3-47.2). These results show that an elevated level of factor IX is a common risk factor for DVT.

Pulmonary thrombosis, homocysteinemia, and reperfusion edema in an adolescent

Deep vein thrombosis, pulmonary embolism, and pulmonary thrombosis in situ are rare in childhood and adolescence [1,2]. Unfortunately, these diagnoses may be unsuspected in a pediatric patient with dyspnea and chest pain. This article illustrates the diagnostic and therapeutic challenges that arose from unrecognized chronic thrombotic disease in an adolescent.

Common C677T polymorphism in the methylenetetrahydrofolate reductase gene increases the risk for deep vein thrombosis in patients with predisposition of thrombophilia

The alanine/valine (A/V) gene polymorphism of 5, 10-methylenetetrahydrofolate reductase (MTHFR), one of the key enzymes catalyzing remethylation of homocysteine, has been reported and the VV genotype is associated with increased plasma homocysteine levels as a result of the reduced activity and increased thermolability of this enzyme. Although previous studies have suggested that the VV genotype is a risk factor for arterial occlusive disease, whether the VV genotype is a risk factor for venous thrombosis is still controversial. Here we screened 72 Japanese patients with deep venous thrombosis (DVT) and 85 controls for this mutation, and we measured plasma levels of homocysteine to determine whether the thermolabile variant with the VV genotype is a risk factor for DVT in a Japanese population. Of the 72 patients with DVT, 10 (13.9%) were found to be homozygous for the VV genotype, and in 6 (7.0%) of 85, control individuals and the difference was not significant (odds ratio=2.12, 95% CI=0.73-6.16, p=0.19). When we divided the DVT patients into subgroups, with and without predisposition of thrombophilia, including deficiencies of proteins C and S, plasminogen, and lupus anticoagulant, the prevalence of the VV genotype in DVT patients with predisposition was significantly higher than that of the normal controls (odds ratio=5.99, 95% CI=1. 56-22.96, p=0.01). However, the prevalence of the VV genotype in DVT patients without predisposition was not significantly different from that of the normal controls (odds ratio=1.20, 95% CI=0.32-4.47, p=0. 75). The plasma homocysteine levels in patients with DVT (11.6+/-5.2 nmol/ml) was not significantly different from that of the control subjects (11.6+/-3.7 nmol/ml). Individuals with the VV genotype showed higher plasma homocysteine levels (15.4+/-6.9 nmol/ml) than did individuals with the AV genotype (11.2+/-3.7 nmol/ml, p=0.009) or in individuals with the AA genotype (11.1+/-4.2 nmol/ml, p=0.004). Serum folate and vitamin B12 levels were not correlated with the plasma homocysteine levels. In conclusion, even though homozygosity for the VV genotype of the MTHFR gene was associated with higher plasma homocysteine levels, we found no association between plasma levels of homocysteine and DVT or between the genotype of the MTHFR gene and the DVT incidence. However, we found that the VV genotype of the MTHFR gene is a risk factor for DVT only when combined with the predisposition of thrombophilia.

[Lowering high levels of fasting total homocysteine with folic acid and vitamins B in patients with venous thromboembolism: relationship between response and the C677T methylenetetrahydrofolate reductase (MTHRF) genotype]

BACKGROUND

High levels of plasma total homocysteine (tHcy) are involved in arterial or venous occlusive diseases. It essentially depends on the nutritional status of folic acid (FA) and vitamins B12 or B6, but also on the methylenetetrahydrofolate reductase (MTHFR) enzymatic activity. We aim to evaluate the response of the hyperhomocysteinemia (HHcy) to a standard schedule of vitamin supplementation, according with the MTHFR genotype.

PATIENTS AND METHODS

227 patients, diagnosed with venous thromboembolism (VTE) were analysed for tHcy (in fasting conditions), and for the MTHFR-C677T gene polymorphism. When the tHcy exceeded the cut-off point (men = 16, women = 15 mumol/l), the patients were supplemented with a dose equivalent to 1 mg FA, 0.2 mg B12 and 100 mg of B6, daily by 6 weeks. Afterwards they were reanalysed and the reduction was stratified by MTHFR genotype, looking for any difference in the response.

RESULTS

The mean fasting tHcy was 12.3 mumol/l (SD = 8). The 51 hyperhomocysteinemic patients (22%) were older (65.1 y) than the normal ones (55.0 y) (p = 0.0001). The treatment was carried out properly in 46 patients (90%). The pre-treatment mean Hcy was 23.2 (SD = 10.5) mumol/l, and it was reduced to 13.0 (SD = 5.9) (p = 0.0001) (mean reduction = 42.1%). By genotype, the C/C reduced from 21.0 to 13.2 mumol/l (37%) (n = 18), the C/T from 25.0 to 12.6 mumol/l (46%) (n = 24), and the abnormal homozygotes T/T from 22.7 to 14.5 mumol/l (39%) (n = 4), although no statistical significant differences were found. In 80% of cases (37/46), tHcy values normalised. A negative correlation (r = -0.471) (p = 0.005) was observed between age and response.

CONCLUSIONS

The FA/B6/B12 based therapy reduces in a simple, quick and effective way (> 40% in 6 weeks) the pathologic tHcy levels on a VTE population and this is not influenced by the MTHFR genotype. As HHcy seems related with recurrences of venous thrombosis, we could speculate if it would be useful to analyse routinely the tHcy, attempting reduction in selected cases.

Total homocysteine and cardiovascular disease

Recent data have shown that an elevated plasma level of the amino acid homocysteine (Hcy) is a common, independent, easily modifiable and possibly causal risk factor for cardiovascular disease (CVD) which may be of equal importance to hypercholesterolemia, hypertension and smoking. This paper reviews the biochemical, clinical, epidemiological and experimental data underlying this conclusion and is critically questioning whether elevated tHcy is a causal factor.

Hyperhomocysteinaemia

Homocysteine is a sulphur-containing amino acid that is derived primarily from protein of animal origin. Classical homocystinuria is an inherited metabolic disorder that arises from defects in either the re-methylation or trans-sulphuration pathways of homocysteine metabolism and leads to skeletal abnormalities, mental retardation and a high risk of vascular disease. In contrast, moderate hyperhomocysteinaemia is associated with an increased risk of both arterial and venous thrombotic disease but no other abnormalities. This increased risk appears to be independent of other conventional risk factors. Many cases of hyperhomocysteineaemia have been attributed to defects in the enzyme cystathionine-beta-synthase (CBS) but this accounts for less than 1.5% of cases. A thermolabile variant of the enzyme methylenetetrahydrofolate reductase (MTHFR) arises from a C --> T transition at nucleotide 677 in the MTHFR gene resulting in an alanine-to-valine substitution. While the mutation does not appear to be associated with an increased risk of vascular disease, it results in excessively high homocysteine levels in response to a low or low-normal serum folate. Supplementation of the diet with folate, B6 and B12 can reduce homocysteine levels and this is the mainstay of treatment. Supplementation of grain with folate is undertaken in the USA to reduce the risk of neural tube defects in pregnant women. However, by reducing plasma homocysteine levels, it is estimated that this will save up to 50,000 lives per annum.

Influence of three potential genetic risk factors for thrombosis in 43 families carrying the factor V Arg 506 to Gln mutation

The factor V (FV) Arg 506 to Gln mutation is the most common abnormality observed in familial thrombophilia. Many studies have shown that its clinical expression differs among families and among carriers. Some thrombotic patients carry an additional genetic risk factor such as protein C, protein S or antithrombin deficiency. We sought to identify other genetic risk factors potentially favouring expression of the thrombotic phenotype in 370 members of 43 families with the FV Arg 506 to Gln mutation. We analysed three candidate polymorphisms in genes involved in the PC anticoagulant pathway, consisting of two polymorphic sites in the 5' non-transcribed region of the PC gene, -1654 C/T and -1641 A/G, with three known combinations (TA, CA and CG) that influence the protein C plasma level; one polymorphic site (4070 A/G) in exon 13 of the FV gene, which influences the plasma factor V concentration, and one polymorphic site (677 C/T) in the methylenetetrahydrofolate reductase gene, which is often associated with moderate hyperhomocysteinaemia. The distribution of these different polymorphisms was similar in patients with a history of thrombosis and those who remained asymptomatic, ruling out the possibility that each of these polymorphisms alone can play a role in the onset of thrombosis in carriers of the FV Arg 506 to Gln mutation.

Homocysteine: cholesterol of the 90s?

Homocysteine is a sulfur-containing amino acid generated through the demethylation of methionine. It is largely catabolized by trans-sulfuration to cysteine but it may also be remethylated to methionine. Dubbed 'the cholesterol of the 90s' by the lay press, homocysteine is thought to be thrombophilic and to damage the vascular endothelium. Total plasma homocysteine (tHcy) is now established as a clinical risk factor for coronary artery disease, as well as other arterial and venous occlusive disease in adult populations. Regulation of homocysteine is dependent on nutrient intake, especially folate, vitamins B6 and B12. It is also controlled by common genetic variations (polymorphisms) in how vitamins are utilized as cofactors in the reactions controlling homocysteine metabolism. Moreover, concentrations are age- and sex-dependent and are altered by renal function, hormonal status, drug intake and a variety of other common clinical factors. Considerable care must be taken in assaying tHcy. Plasma should be separated shortly after collection, to avoid artifactual increases due to synthesis by blood cells in vitro. Reference methods have not been validated and criteria for establishing reference ranges should take into account the variable prevalence of physiological hyperhomocysteinemia. Determination of tHcy should probably be limited to centres with relevant expertise and ability to maintain the high degree of precision required for reliable interpretation. Molecular testing for the genetic polymorphisms is still in the research phase but the ease and reliability of molecular diagnosis will speed its introduction into clinical laboratory practice--particularly in relation to diagnosis of thrombophilic disorders. Clinical research initiatives are being driven by the benefit that should be achieved by correction with vitamin supplements, particularly folate and B vitamins, but it must be recognized that prospective controlled studies to validate clinical benefit are only now being initiated. At the moment, it is safe to say that hyperhomocysteinemia is one of the few prevalent biochemical risk factors for thromboembolic disease that might be corrected by vitamin supplements. Such a possibility lies behind the growing momentum to recommend increased supplements of folate and B vitamins to at-risk population and patient groups today.

Prevalence of mild hyperhomocysteinaemia and association with thrombophilic genotypes (factor V Leiden and prothrombin G20210A) in Italian patients with venous thromboembolic disease

Mild hyperhomocysteinaemia is an established risk factor for deep vein thrombosis (DVT); few data concerning its potential interaction with thrombophilic genotypes are available at the present time. We investigated 121 thrombosis-free individuals and 111 patients with at least one objectively confirmed episode of DVT. A thrombophilic condition (deficiency in antithrombin, protein C and S, factor V Leiden, prothrombin G20210A) was detected in 25.2% of the patients; mutant factor V or prothrombin genotypes were present in 6.6% of the controls. Hyperhomocysteinaemia was found in 14.4% of patients and 3. 3% of the controls, with a 3.7-fold increase in risk for DVT (95% CI 1.1-12.3). Adoption of different cut-off levels for definition of hyperhomocysteinaemia did not substantially change the magnitude of the risk. Carriership of both hyperhomocysteinaemia and factor V Leiden or prothrombin G20210A was detected in 2.7% of patients for each combination and in none of the controls. An approximate estimate of 30-fold increased risk in carriers of both hyperhomocysteinaemia and factor V Leiden and 50-fold increased risk in carriers of both hyperhomocysteinaemia and prothrombin G20210A was calculated, suggesting a synergistic interaction between hyperhomocysteinaemia and such thrombophilic genotypes. Yet statistical analysis is highly unstable due to the small number of individuals with combined defects. Further investigations on large series of patients are needed.

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.

Homocysteine

Homocysteine is a sulfur-containing amino acid generated through the demethylation of methionine. It is largely catabolized by trans-sulfuration to cysteine, but it may also be remethylated to methionine. Regulation of homocysteine is dependent on nutrient intake, especially folate, vitamins B6 and B12. It is also controlled by individual genetic differences in how vitamins are utilized as cofactors in the reactions controlling homocysteine metabolism. In excess quantities, homocysteine is thought to be thrombophilic and to damage the vascular endothelium. Total plasma homocysteine (tHcy) is now established as a clinical risk factor for coronary artery disease, as well as other arterial and venous occlusive disease in adult populations. These effects are probably related to its role as a teratogen in the pathogenesis of neural tube defects--genetic variants causing hyperhomocysteinemia are associated with both neural tube defects in susceptible pregnancies and with risks for vaso-occlusive disease in later years. Considerable care must be taken in assaying tHcy. Plasma should be separated shortly after collection to avoid artifactual increases due to synthesis by blood cells in vitro. tHcy concentrations must be interpreted in light of the fact that serum albumin, urate, creatinine, and vitamin concentrations may be important analytical covariates. Moreover, concentrations are age- and sex-dependent and are altered by renal function, hormonal status, drug intake, and a variety of other common clinical factors. Why then is homocysteine now of such great clinical and scientific interest? If the homocysteine moiety itself is important in the pathogenesis of vaso-occlusive disease, then simple treatment of hyperhomocysteinemia with vitamins should lead to a significant reduction in disease risk. Such a possibility lies behind the growing momentum to recommend increased supplements of folate and B vitamins to at-risk populations and patient groups today.

Low folate levels and thermolabile methylenetetrahydrofolate reductase as primary determinant of mild hyperhomocystinemia in normal and thromboembolic subjects

Several studies have indicated that mild to moderate hyperhomocystinemia is a common cause of arterial occlusive disease. Whether hyperhomocystinemia per se is an independent risk factor for vein thromboembolism (VTE) is still somewhat controversial. Both genetic and nutritional factors influence plasma homocysteine levels. Therefore, we evaluated plasma total homocysteine (tHcy), folate, and vitamin B12 levels and established, by polymerase chain reaction, the presence of the C677T mutation (A223V) in the methylenetetrahydrofolate reductase (MTHFR) gene in 220 cases with VTE without well-established prothrombotic defects. As a control group, 220 healthy subjects from the same geographic area as the cases were investigated. Hyperhomocystinemia was defined as a plasma tHcy level above the 95th percentile in the controls (18.05 micromol/L). Hyperhomocystinemia was found in 16% of cases (odds ratio=3.59; P<0.001); deficiencies of folate (<2.47 ng/mL) or vitamin B12 (<165 pg/mL), defined as values below the 5th percentile in controls, were found in 17.7% (P<0.001) and 12.3% (P=0.015) of cases, respectively. The homozygous condition for the MTHFR mutation (VV) was present in 28.2% of cases and 17.7% of controls (odds ratio=1.82; P=0.013). Comparing only the idiopathic forms of VTE (n=80/220; 36.3%) with normal controls, individuals with hyperhomocystinemia, or individuals homozygous for MTHFR mutation increased the odds ratios to 4.03 (P=0.005) and 2.11 (P=0.018), respectively. No statistically significant difference was observed in the MTHFR genotype distribution of cases and controls with hyperhomocystinemia (P=0.386); however, the normal MTHFR genotype (AA) appeared in control subjects only when tHcy levels were below the 80th percentile (10.57 micromol/L) of the distribution, whereas in case patients, it was present at the highest tHcy levels. A strong association between mutated homozygosity (VV), low folate levels, and hyperhomocystinemia was found in both groups. We conclude that in patients with VTE who do not have coexisting prothrombotic defects, hyperhomocystinemia increases the risk of developing idiopathic and venous thrombosis; the homozygous condition for the MTHFR mutation confers a moderate risk but, together with low folate levels, it is the main determinant of mild hyperhomocystinemia in normal and thromboembolic populations.

Venous thrombosis: a multicausal disease

The risk factors for venous thrombosis differ from those for arterial vascular disease. During the past 5 years, knowledge about the aetiology of venous thrombosis has advanced with the discovery of several factors that contribute to the incidence of thrombosis, particularly the role of coagulation abnormalities. These abnormalities are common in the general population and therefore will be present simultaneously in some individuals. The resultant gene-gene and gene-environment interactions between risk factors are the key to the understanding of why a certain person develops thrombosis at a specific point in time.

Combination of low-dose folic acid and pyridoxine for treatment of hyperhomocysteinaemia in patients with premature arterial disease and their relatives

Hyperhomocysteinaemia is an independent risk factor for atherosclerotic disease and venous thrombosis. The optimal homocysteine-lowering vitamin dose and target total homocysteine (tHcy) concentration are currently unknown. We prospectively studied the homocysteine-lowering effect after 8 weeks low-dose combination of folic acid (0.5 mg) and pyridoxine (100 mg) in 49 hyperhomocysteinaemic persons (33 patients with documented premature arterial disease and 16 of their first-degree relatives). Hyperhomocysteinaemia was in both sexes defined as fasting tHcy concentration > 12 micromol/l and/or post-methionine load tHcy concentration > 38 micromol/l. Low-dose vitamin therapy significantly reduced fasting tHcy concentration (median 13.9 to 9.3 micromol/l, reduction 32% (95% CI: 27-37%)) and post-load tHcy concentration (median 55.2 to 36.5 micromol/l, reduction 30% (95% CI: 25-35%)). Fasting tHcy reduction was similar in women and men, as well as in patients and relatives. Post-load tHcy reduction was significantly less in men compared to women (P = 0.04) and in relatives compared to patients (P = 0.03). Although low-dose combination of folic acid and pyridoxine results in a substantial reduction of tHcy concentrations (30-32%) in subjects with hyperhomocysteinaemia, the normalisation percentage to predefined criteria was less impressive (49%).

Biological variability and reference intervals for total plasma homocysteine

We determined the intra-individual biological variability of plasma homocysteine in 20 healthy subjects. The intra-individual coefficient of variation was relatively low (8.3%), indicating that a single measurement can be used to characterize the average homocysteine concentration. A population study measuring plasma homocysteine and serum folate levels was conducted on serum samples collected from 1109 randomly selected, fasting adults with a wide age range. We determined age- and gender-specific central 0.95 intervals and found that subjects in the highest quartile of serum folate had significantly lower (P = 0.0001) mean plasma homocysteine concentrations than did those in the lowest quartile of folate values. An 'ideal' homocysteine reference range, based on targeting those subjects who are likely to be folate replete, is preferable to the population-based range using the central 0.95 interval.

Low-dose folic acid supplementation decreases plasma homocysteine concentrations: a randomized trial

BACKGROUND

An elevated plasma total homocysteine concentration is a risk factor for cardiovascular disease and neural tube defects. A high daily intake of supplemental folic acid is known to decrease total homocysteine concentrations.

OBJECTIVE

We studied the effect of low-dose folic acid administration (250 or 500 (microgram/d) for 4 wk on plasma total homocysteine concentrations and folate status. We also investigated whether total homocysteine concentrations and blood folate concentrations returned to baseline after an 8-wk washout period.

DESIGN

In this placebo-controlled study, 144 healthy women aged 18-40 y received 500 microgram folic acid/d, 500 microgram folic acid every second day (250 microgram/d), or a placebo tablet with their habitual diet (mean dietary folate intake: 280 microgram/d).

RESULTS

Administration of 250 and 500 microgram folic acid/d for 4 wk significantly increased folate concentrations in plasma (P < 0.001) and red blood cells (P < 0.01). Total homocysteine concentrations decreased significantly (P < 0.001) in women (n = 50) who took 250 microgram folic acid/d [mean (+/-SEM) deviation from baseline: - 11.4 +/- 198%] and in women (n = 45) who took 500 microgram folic acid/d (-21.8 + 1.49%). Eight weeks after the end of the intervention period (week 12), plasma total homocysteine concentrations in the folic acid-supplemented groups had not returned to baseline (week 0).

CONCLUSIONS

Doses of folic acid as low as 250 microgram/d, on average, in addition to usual dietary intakes of folate significantly decreased plasma total homocysteine concentrations in healthy, young women. An 8-wk washout period was not sufficient for blood folate and plasma total homocysteine concentrations to return to baseline concentrations.

Evaluation of hyperhomocysteinaemia in children with stroke

Hyperhomocysteinaemia is associated with an increased risk of arterial vascular disease and thrombosis in adults. Our aim was to study the association of hyperhomocysteinaemia and stroke in children. Since some patients who had suffered a stroke developed seizures and received treatment with anti-epileptic (antifolate) drugs, we also examined the possible interaction between anti-epileptic drugs and hyperhomocysteinaemia. Plasma total homocysteine was measured in 68 children with stroke (23 of the 68 were taking anti-epileptic drugs) and 100 children undergoing anti-epileptic treatment but without history of stroke, and we compared the values with our reference values for similar ages (n = 195). Total homocysteine was determined by high profile liquid chromatography with fluorescence detection. Hyperhomocysteinaemia was defined as a homocysteine concentration above the 95th percentile for the reference values. Significant differences were found in total homocysteine values of children with stroke and those taking anti-epileptic drugs compared with our reference values for similar ages, except for the adolescent group. Total homocysteine values above the 95th percentile for the reference values were found in 36% of patients with stroke and 28% of children on anti-epileptic treatment. Total homocysteine concentrations in the 23 patients with both stroke and anti-epileptic drug treatment were similar to those of untreated patients with stroke in all age groups. In summary, systematic screening for hyperhomocysteinaemia should be included in the protocol to investigate the aetiology of stroke, even in paediatrics. Anti-epileptic treatment in children with stroke may be responsible for the mild hyperhomocysteinaemia observed in some of them. A dietary supplement of folate may be of benefit in children with stroke and in patients taking anti-epileptic drugs.

Inherited DNA mutations contributing to thrombotic complications in patients with sickle cell disease

Thrombosis may play an important role in the pathophysiology of certain complications of sickle cell disease (SCD), including stroke and avascular necrosis (AVN). Currently there is no laboratory or clinical parameter that can identify patients who are at highest risk of developing these thrombotic complications. We hypothesized that some patients with SCD have an inherited hypercoagulable state that results in an increased risk of developing stroke or AVN. We examined the role of two common inherited thrombophilic mutations that, in other populations, have been associated with arterial and venous thrombosis and are amenable to screening with DNA restriction enzyme analysis. The C677T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene and the C1565T mutation in the platelet glycoprotein IIIa (GPIIIa) gene were evaluated. We analyzed genomic DNA from 86 children and adults with SCD, including 16 patients with a history of a clinical stroke and 14 patients with AVN, for the presence of these mutations. The C677T MTHFR mutation was found in 19% of patients with stroke, 14% of patients with AVN, and 14% of patients with neither complication (P = NS). The C1565T GPIIIa mutation was found in 25% of patients with stroke, 14% of patients with AVN, and 18% of patients with neither complication (P = NS). Although each of these mutations is relatively common in patients with SCD, neither is independently associated with an increased risk of developing stroke or AVN.

Additional genetic risk factors for venous thromboembolism in carriers of the factor V Leiden mutation

Only a minority of subjects with factor V (FV) Leiden mutation develop venous thromboembolism (VTE), suggesting that additional genetic risk factors may be present in symptomatic carriers. We screened 157 unrelated carriers of the FV Leiden mutation with a first episode of VTE and 291 unrelated asymptomatic FV carriers for the presence of two frequent mutations, i.e. G20210A of the prothrombin gene and C677T of the methylenetetrahydrofolate reductase gene. Carriers with other inherited or acquired thrombophilia-associated abnormalities were excluded from analysis. Heterozygotes for the G20210A mutation were more prevalent among symptomatic carriers than in asymptomatic carriers (10.8% v 2.7%, P<0.0001); homozygotes for the C677T mutation were also more prevalent in symptomatic carriers (21.6% v 14.4%, P = 0.05). Factor V Leiden carriers who had had a VTE episode during oral contraceptive intake were more frequently carriers of the G20210A mutation (14.3%, P = 0.03). These results further support the idea that VTE in carriers of FV Leiden results from interaction with additional genetic or circumstantial risk factors, and that an accurate search for such factors is required to identify carriers at risk.