A common mutation in the methylenetetrahydrofolate reductase gene (C677T) increases the risk for deep-vein thrombosis in patients with mutant factor V (factor V:Q506)

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.

Standing genetic variation affects phenotypic heterogeneity in an SCN5A-mutation founder population with excess sudden cardiac death

BACKGROUND

The Worm Study, ascertained from a multigeneration pedigree segregating a single amino acid deletion in SCN5A (c.4850_4852delTCT, p.(Phe1617del), rs749697698), is characterized by substantial phenotypic heterogeneity and overlap of sudden cardiac death, long-QT syndrome, cardiac conduction disease, Brugada syndrome, and isorhythmic atrioventricular dissociation. Linkage analysis for a synthetic trait derived from these phenotypes identified a single peak (logarithm of the odds [LOD] = 4.52) at the SCN5A/SCN10A/SCN11A locus on chromosome 3.

OBJECTIVE

This study explored the role of additional genetic variation in the chromosome 3 locus as a source of phenotypic heterogeneity in the Worm Study population.

METHODS

Genotypes underlying the linkage peak (n = 70) were characterized using microarrays. Haplotypes were determined using family-aware phasing and a population-specific reference panel. Variants with minor allele frequencies >0.10 were tested for association with cardiac conduction disease and isorhythmic dissociation using LAMP and logistic regression.

RESULTS

Only 1 haplotype carried the p.Phe1617del/rs749697698 deletion, suggesting relatively recent development (∼18 generations); this haplotype contained 5 other missense variants spanning SCN5A/SCN10A/SCN11A. Noncarrier haplotypes (n = 74) ranged in frequency from 0.5% to 5%. Although no variants were associated with cardiac conduction disease, a homozygous missense variant in SCN10A was associated with isorhythmic dissociation after correction for multiple comparisons (odds ratio 11.23; 95% confidence interval 2.76-23.39; P = 1.2 × 10^-4). This variant (rs12632942) was previously associated with PR interval.

CONCLUSION

Our data suggest that other variants, alongside a pathogenic mutation, are associated with phenotypic heterogeneity. Single-mutation screening may be insufficient to predict electrical heart disease in patients and family members. In the Worm Study population, segregating a pathogenic SCN5A mutation, compound variation in the SCN5A/SCN10A/SCN11A locus determines arrhythmic outcome.

Integrative analyses of genes about venous thromboembolism: An umbrella review of systematic reviews and meta-analyses

BACKGROUND

In recent years, many studies have found possible links between gene polymorphisms and venous thromboembolism (VTE). By identifying genetic risk factors before facing environmental risk factors such as surgical interventions and COVID-19 vaccination, we could rapidly respond to the risk of VTE. The aim of this study was to perform an umbrella review of genetic variants related to VTE. Integrative gene analysis of VTE was performed to identify critical genetic variations.

METHODS

This study conducted an umbrella review of systematic reviews and meta-analyses. All included studies were selected from the PubMed/MEDLINE database. To select eligible studies, the following variables were extracted: first author name; effect size of each study genetic variant; year of publication; the number of studies included in each article; ethnicity, sample size, P values, and heterogeneity estimates. To assess cumulative evidence in genetic epidemiology about effects of gene polymorphisms on VTE, Human Genome Epidemiology Network's Venice criteria were used. Methodological quality assessment was conducted with JBI Critical Appraisal Checklist for Systematic Reviews and Research Syntheses.

RESULTS

Genes provided in the present study with genetic variants associated with VTE were FVL (G1691A), Prothrombin (G20210A), MTHFR (C677T, A1298C), PAI-1 (4G/5G), factor VII activating protease (1601G > A), and endothelial protein C receptor (g.6936A_G, c.4600A_G). Among them, variants in FVL, Prothrombin, MTHFR, and PAI-1 showed high significance. Particularly, variants in Prothrombin (G20210A), MTHFR (C677T), and PAI-1 (4G/5G) had more than 2 types of model significance.

CONCLUSION

The present study performed a systematic review of genetic variants associated with VTE. Our results could lead to a more comprehensive understanding of VTE etiology. These results could give a strategy of prediagnosis about evaluating individual risks of VTE who might be exposed to environmental risk factors.

Identifying genetic markers associated with susceptibility to cardiovascular diseases

The development of cardiovascular diseases (CVDs) is due to a complex interaction between the genome and the environment. Understanding how genetic differences in individuals contribute to their susceptibility to CVDs can help guide practitioners to give the best advice to achieve a favorable outcome for the patient. As genome technologies evolve, genotyping of individuals could be available to all patients using a simple saliva test. Large-scale genome-wide association studies and meta analyses have provided powerful insights into polymorphisms that may be predictive of disease and an individual's response to certain nutrients, but moving forward it is imperative that these insights can be applied in the medical setting to reduce the incidence and mortality of CVDs.

Cardiovascular diseases (CVDs) are the leading cause of death worldwide, and while most CVDs can be prevented by adopting a healthy lifestyle, this is only half the story. Evidence suggests changes in an individual's genes or DNA can cause some form of CVDs, highlighting a complex relationship between genes and the environment. Genotyping, a process used to determine genetic differences within an individual's DNA, can provide doctors with relevant information to identify individuals who are at high risk of developing CVDs. This would allow treatment to begin early and encourage individuals to adopt a healthy lifestyle to reduce their risk.

High prevalence of factor V Leiden and prothrombin G20101A mutations in Kashmiri patients with venous thromboembolism

AIM

The genetic variants of the factor V (G1691A), prothrombin (G20210A) and MTHFR (C677T) genes have been widely implicated as inherited risk factors for developing venous thrombosis. This study was undertaken to reveal the frequency of these mutations in Kashmiri patients with venous thromboembolism.

METHODOLOGY

A case-control study was designed with 250 VTE patients and 250 healthy controls. The mutations were analysed using ARMS-PCR and PCR-RFLP approach.

RESULT

The factor V Leiden G1691A mutation was found in 17/250 (6.8%) VTE patients and prothrombin G20210A mutation was found in 7/250 (2.8%) VTE patients while no mutation was found in any of the healthy controls. Both the mutations were found to be significantly associated with the increased risk of VTE (p = 0.0001 and 0.0150 respectively) while no association of VTE risk with MTHFR C677T polymorphism was found (p = 0.53).

CONCLUSION

The increased frequency of factor V Leiden G1691A and prothrombin G20210A mutation in VTE patients indicates a significant role of these mutations in the development of VTE in our population. We therefore suggest the routine screening of these two mutations as thrombophilic markers in Kashmiri patients with venous thromboembolism.

Impact of the MTHFR C677T polymorphism on colorectal cancer in a population with low genetic variability

PURPOSES

Methylenetetrahydrofolate reductase (MTHFR) plays a key role in folate metabolism, and folate is implicated in carcinogenesis by its role in DNA methylation, repair, and synthesis. We analyzed the impact of MTHFR C677T polymorphism in colorectal cancer in a region of the Tenerife Island whose population has a history of genetic isolation and a low genetic variability. This allows analyzing the effects of the polymorphism that are not due to interactions with different genetic variants.

METHODS

Genomic DNA of 50 Spanish sporadic colorectal cancer (CRC) patients and 103 controls was analyzed by PCR/RFLP and sequencing.

RESULTS

The T allele is more frequent in controls than in patients (P < 0.01). The variant (T) carriers displayed significant odds ratio values for the CT heterozygotes (P = 0.026) and even when grouping heterozygote (CT) and homozygotes (TT) (P = 0.015). Patients carriers of the variant T (CT y TT) show a higher survival rate after chemotherapy than the CC homozygotes (log rank; P = 0.001).

CONCLUSIONS

The MTHRF C677T variant has a protective effect on CRC development in a population with low allelic variability and an optimal intake of folic acid. Moreover, patients carrying the variant (T) show a better prognosis after 5-fluorouracil/folinic acid-based chemotherapy.

Risk of venous thromboembolism associated with single and combined effects of Factor V Leiden, Prothrombin 20210A and Methylenetethraydrofolate reductase C677T: a meta-analysis involving over 11,000 cases and 21,000 controls

Genetic and environmental factors interact in determining the risk of venous thromboembolism (VTE). The risk associated with the polymorphic variants G1691A of factor V (Factor V Leiden, FVL), G20210A of prothrombin (PT20210A) and C677T of methylentetrahydrofolate reductase (C677T MTHFR) genes has been investigated in many studies. We performed a pooled analysis of case-control and cohort studies investigating in adults the association between each variant and VTE, published on Pubmed, Embase or Google through January 2010. Authors of eligible papers, were invited to provide all available individual data for the pooling. The Odds Ratio (OR) for first VTE associated with each variant, individually and combined with the others, were calculated with a random effect model, in heterozygotes and homozygotes (dominant model for FVL and PT20210A; recessive for C677T MTHFR). We analysed 31 databases, including 11,239 cases and 21,521 controls. No significant association with VTE was found for homozygous C677T MTHFR (OR: 1.38; 95 % confidence intervals [CI]: 0.98-1.93), whereas the risk was increased in carriers of either heterozygous FVL or PT20210 (OR = 4.22; 95 % CI: 3.35-5.32; and OR = 2.79;95 % CI: 2.25-3.46, respectively), in double heterozygotes (OR = 3.42; 95 %CI 1.64-7.13), and in homozygous FVL or PT20210A (OR = 11.45; 95 %CI: 6.79-19.29; and OR: 6.74 (CI 95 % 2.19-20.72), respectively). The stratified analyses showed a stronger effect of FVL on individuals ≤ 45 years (p value for interaction = 0.036) and of PT20210A in women using oral contraceptives (p-value for interaction = 0.045). In this large pooled analysis, inclusive of large studies like MEGA, no effect was found for C677T MTHFR on VTE; FVL and PT20210A were confirmed to be moderate risk factors. Notably, double carriers of the two genetic variants produced an impact on VTE risk significantly increased but weaker than previously thought.

Factors associated with the development of superficial vein thrombosis in patients with varicose veins

INTRODUCTION

Superficial vein thrombosis (SVT) is a common and controversial clinical entity. Recent studies have demonstrated that SVT should be seen as a venous thromboembolism (VTE). The objective of this study was to investigate the prevalence of thrombophilia defects and to estimate the role of age, sex and body mass index (BMI) in patients with varicose veins (VVs) and SVT.

MATERIALS AND METHODS

A total of 230 patients with VVs, 128 with, and 102 without SVT underwent thrombophilia testing included factor V Leiden, prothrombin G20210A, methylenetetrahydrofolate reductase and plasminogen activator inhibitor- 1 mutations, protein C, protein S (PS), anti-thrombin III and plasminogen deficiencies and levels of A2 antiplasmin, activate protein C resistance and lupus anticoagulant. According to Clinical-Etiology-Anatomy-Pathophysiology (CEAP) classification patients were categorized in two subgroups: moderate disease (C2,3) and severe disease (C4,5,6). Age and body mass index were also assessed.

RESULTS

The prevalence of thrombophilia defects was significantly higher in patients with moderate disease and SVT (p=0.002). In the C2,3 group, SVT was associated with PS deficiency (p=0.018), obesity (p<0.001), male gender (p=0.047) and age (p<0.001). There were no significant differences in patients with severe disease.

CONCLUSIONS

Age, male sex, obesity and PS deficiency are factors associated with SVT development among patients with VVs having moderate disease (C2,3).

Factor V Leiden, prothrombin 20210G>A, MTHFR 677C>T and 1298A>C, and homocysteinemia in Tunisian blood donors

Specific genetic conditions are known to be associated with high risk of venous thromboembolism. This genetic basis varies widely between ethnic groups. We investigated the distribution of four inherited polymorphisms in 113 unselected Tunisian blood donors by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. The allele frequencies of Factor V Leiden (FVL), prothrombin 20210G>A, methylenetetrahydrofolate reductase (MTHFR) 677C>T, and MTHFR 1298A>C mutations were 3, 0.9, 30, and 31%, respectively. The MTHFR 677C>T polymorphism was influenced by age. Twenty-nine of the 113 blood donors demonstrated more than one genetic markers. Hyperhomocysteinemia was found in 12 subjects, and it was statistically associated to the MTHFR 677TT genotype. Principal component analysis allowed disclosing the resemblance between Mediterranean populations. Our findings may be helpful for population genetics study, and provide epidemiologic database for further studies in thrombosis field among Tunisians.

Thrombophilia among Chinese women with venous thromboembolism during pregnancy

AIMS

To assess the prevalence of thrombophilia among Chinese women with venous thromboembolism (VTE) developed during pregnancy.

METHODS

Based on information from a tertiary teaching unit, all recorded cases of deep vein thrombosis (DVT) and pulmonary embolism (PE) during pregnancy diagnosed between 1997 and 2005, were assessed for prevalence of thrombophilia. Fifty-five healthy women, who had at least one normal pregnancy but without any previous history of VTE, were recruited as controls.

RESULTS

A total of 44 subjects completed thrombophilia screening, of whom 5 (11%) were confirmed to have thrombophilia [protein C (PC) deficiency (2), protein S (PS) deficiency (1), combined PC & PS deficiency (1) and antithrombin III deficiency (1)]. Homozygous 5,10-methylenetetrahydrofolate reductase (C677T) gene mutation was found in 6 (14%) subjects but not in the controls. There was no antiphospholipid syndrome, activated PC resistance, factor V Leiden or prothrombin gene mutations.

CONCLUSION

In the Chinese population, PS and PC deficiencies are common thrombophilia for VTE during pregnancy and thrombophilia screening should be recommended in all pregnant women who suffer from VTE.

The 677C>T Mutation of the MTHFR Gene Increases the Risk of Venous Thromboembolism in Koreans and a Meta-Analysis From Asian Population

The frequency of methylenetetrahydrofolate reductase (MTHFR) mutations varies between racial and ethnic groups, and there are also conflicting data regarding MTHFR gene mutations in Asian patients with venous thromboembolism (VTE). The aim of this study was to examine the association between common MTHFR gene mutations (677C>T and 1298A>C) and risk of VTE in Koreans. This study was a retrospective case–control study. We enrolled 203 patients with VTE and 403 controls. For the 677C>T polymorphism, there was no difference in the frequency of the CT genotype and TT genotype between the patients with VTE and the controls. However, in the recessive analysis (CC + CT vs TT), the frequency of the TT genotype was significantly higher in VTE than in controls (odds ratio = 1.700; 95% confidence interval = 1.108-2.607, P = .015). In conclusion, the TT genotype of MTHFR 677C>T increases the risk of VTE in Koreans. This finding was supported by meta-analysis of previous Asian studies.

Pulmonary Thromboembolism Following Radio-Frequency Ablation of the Atrioventricular Node in a Patient Heterozygous for the Factor V Leiden and the Mthfr C677T Mutations

Patients who undergo radiofrequency ablation of the atrioventricular (AV) node rarely develop acute major complications. A 41-year-old Caucasian male smoker, was admitted to the Pulmology Teaching Hospital at Belgrade, Serbia, for sharp persistent chest pain, fever and fatigue following AV node radiofrequency ablation for arrhythmia. Chest X-ray showed obtuse right costo-phrenic angle and laminar atelectasis in the right lower lung lobe. The plasma D-dimer level was elevated. A perfusion lung scan showed multiple bilateral perfusion defects and multislice computed tomography showed thrombotic mass in the right pulmonary artery. Genetic analysis revealed that he was heterozygous for the prothrombin Factor V (FV) Leiden and MTHFR C677T mutations. Therapy started with intravenous heparin, followed by warfarin. He had no other episodes over a 2-year follow-up. Lifelong oral anticoagulant therapy was recommended.

Hereditary thrombophilic risk factors for recurrent pregnancy loss

This review summarizes current knowledge about the role of hereditary hypercoagulation factors predisposing to thrombophilia-associated recurrent fetal loss. Thrombophilias are a major cause of adverse pregnancy outcome, playing a role in the etiology of up to 40% of cases worldwide. Hereditary thrombophilic predispositions to recurrent pregnancy wastage include genetic lesions in blood coagulation factors II and V as well as natural anticoagulants antithrombin, protein C, and protein S. Furthermore, methylenetetrahydrofolate reductase gene variants conferring higher thrombophilia risk in combination with these mutations and the newly described annexin A5 gene M2 promoter allele are associated with repeated fetal loss. The review gives a concise description of the molecular defects arising from the genetic changes, of the role these factors play in the timing and definition of fetal loss, and risk estimates from available studies and meta-analysis. This knowledge is instrumental for a more precise assessment of individual risks for repeated fetal loss and should guide therapeutic strategies, where relevant. Since the average childbearing age increases in Western societies, the importance of a timely diagnosis of fetal loss predisposition is increasing.

ABO blood groups and genetic risk factors for thrombosis in Croatian population

AIM

To assess the association between ABO blood group genotypes and genetic risk factors for thrombosis (FV Leiden, prothrombin G20210A, and methylenetetrahydrofolate reductase C677T mutations) in the Croatian population and to determine whether genetic predisposition to thrombotic risk is higher in non-OO blood group genotypes than in OO blood group genotypes.

METHODS

The study included 154 patients with thrombosis and 200 asymptomatic blood donors as a control group. Genotyping to 5 common alleles of ABO blood groups was performed by polymerase chain reaction with sequence specific primers (PCR-SSP). FV Leiden was determined by PCR-SSP, while prothrombin and methylenetetrahydrofolate reductase were determined by PCR and restriction fragment length polymorphism (PCR-RFLP).

RESULTS

There was an association between non-OO blood group genotypes and the risk of thrombosis (odds ratio [OR] 2.08, 95% confidence interval [CI], 1.32-3.27). The strongest association with thrombotic risk was recorded for A1B/A2B blood group genotypes (OR, 2.73; 95% CI, 1.10-6.74), followed by BB/O1B/O2B (OR, 2.29; 95% CI, 1.25-4.21) and O1A1/O2A1 (OR, 1.95; 95% CI, 1.15-3.31). FV Leiden increased the risk of thrombosis 31-fold in the group of OO carriers and fourfold in the group of non-OO carriers. There was no significant difference in the risk of thrombosis between OO and non-OO blood groups associated with prothrombin mutation. Non-OO carriers positive for methylenetetrahydrofolate reductase had a 5.7 times greater risk of thrombosis than that recorded in OO carriers negative for methylenetetrahydrofolate reductase.

CONCLUSION

Study results confirmed the association of non-OO blood group genotypes with an increased risk of thrombosis in Croatia.

Hyperhomocysteinaemia, low folate concentrations and methylene tetrahydrofolate reductase C677T mutation in acute mesenteric venous thrombosis

OBJECTIVES

Acute mesenteric venous thrombosis (AMVT) was first reported by Fagge and was recognised as a distinct clinical entity by Warreen in 1935. However, its pathogenesis is still unclear. Elevated plasma levels of homocysteine (Hcy) are associated with an increased risk of deep vein thrombosis. This case-control study examines the potential association among hyperhomocysteinaemia (hyper-Hcy), low serum folate and vitamin B(12) levels and the common C677T mutation of the MTHFR gene in patients with AMVT.

MATERIALS AND METHODS

Sixty-three patients with AMVT and 75 sex- and age-matched healthy controls were recruited, and their plasma Hcy, folate and vitamin B(12) levels were measured by high performance liquid chromatography (HPLC) and immunological assays. The polymorphism of MTHFR C677T was detected by PCR-RFLP.

RESULTS

The mean plasma Hcy levels were significantly higher in patients with AVMT compared with controls (23.5 standard deviation (S.D.) 8.8 vs. 12.6+/-6.6micromoll(-1), P<0.01). The fasting Hcy correlated negatively with folate (AMVT: r=-0.42, P<0.01;

CONTROL

r=-0.40, P<0.01). The frequency of homozygous (TT) genotype in MTHFR C677T mutation was significantly higher in patients with AMVT than that in control subjects (33% vs. 17%; chi square (chi(2))=6.31, P<0.05; odds ratio (OR)=2.80; 95% confidence interval (CI): 1.25-6.25). Compared with the control subjects, the mean serum vitamin B(12) levels were lower in patients, but it was not statistically significant (365+/-88pmoll(-1) vs. 408+/-108pmoll(-1), P>0.05).

CONCLUSIONS

Hyper-Hcy and low serum folate levels were associated with an increased risk of AMVT. The homozygous (TT) genotype of MTHFR gene mutation may be a crucial hereditary risk factor in the development of AMVT for a Chinese population.

Na VPA-induced acute ischemic stroke in an epileptic patient with methylenetetrahydrofolate reductase gene polymorphism

A 23-year-old man using Na-Valproic acid (VPA) was admitted to our clinic due to convulsion. The neurological examination revealed right hemiparesis. From the exitus notes, we learned that his two siblings had died from status epilepticus. Magnetic resonance imaging (MRI), MRI spectroscopy, and diffusion-weighted investigations (DWI) showed acute-subacute ischemic stroke in the left temporo-parieto-occipital region. The patient had an ischemic stroke. Heterozygote methylenetetrahydrofolate reductase (MTHFR) 677C/T polymorphism was determined on genetic examination. The homocysteine (Hcy) level was 18.2 mmol/l (5-15 mmol/l). So VPA treatment was stopped and oxcarbazepine treatment was started. MTHFR 677C/T polymorphism is associated with the risk of vascular diseases due to hyperhomocysteinemia. Heterozygote (MTHFR) 677C/T polymorphism has not been reported to be associated with epilepsy. In patients with heterozygote (MTHFR) 677C/T polymorphism and under long-term use of certain drugs the determination of Hcy plasma levels may be useful to prevent the development of atherothrombotic disease.

Superficial venous thrombosis: prevalence of common genetic risk factors and their role on spreading to deep veins

INTRODUCTION

Superficial venous thrombosis (SVT) has been considered for a long time a limited clinical condition with a low importance, but this approach has changed in recent years, when several studies demonstrated spreading to deep veins occurring from 7.3 to 44%, with high prevalence of pulmonary embolism.

MATERIALS AND METHODS

To evaluate the prevalence of genetic risk factors for VTE in patients suffering from SVT on both normal and varicose vein, and to understand their role on spreading to deep veins, we studied 107 patients with SVT, without other risk factors. Ultrasound examination was performed, and the presence of FV Leiden, Prothrombin G20210A mutation, and MTHFR C677T mutation was researched.

RESULTS

In the patients where SVT occurred in normal veins, the presence of FV Leiden was 26.3% of the non-spreading and 60% of the spreading to deep veins SVT; Prothrombin mutation was found in 7.9% of the former case and in 20% of the latter; MTHFR C677T mutation was found respectively in 23.7% and 40%. In the patients with SVT on varicose veins, the presence of these factors was less evident (6.7%, 4.4% and 6.7% respectively), but their prevalence was considerably higher (35.7%, 7.4% and 21.4% respectively) in SVT spreading to deep veins than in non-spreading.

CONCLUSIONS

Our data demonstrate the high prevalence of these mutations, especially FV Leiden and associations, in patients with SVT on normal veins and their role in the progression to deep vein system.

Efficacy of family history in determining thrombophilia risk

STUDY OBJECTIVE

This retrospective study sought to examine the importance of family history of cardiovascular disease (CVD) or venous thromboembolism (VTE) in predicting risk for an inherited thrombophilia.

DESIGN/METHODS

A cohort of 88 adolescent females who had a thrombophilia panel in the last three years was identified for this retrospective chart review. Family history data of CVD or VTE were collected in addition to laboratory results from the thrombophilia screen.

SETTING

Adolescent patients who had a thrombophilia screen within the last three years at University OB-GYN Associates, Louisville, KY.

RESULTS

Within the cohort (n=88), 21% of patients were found to have a documented thrombophilia. At least 47% of individuals diagnosed with thrombophilia had more than one screening abnormality. A family history of VTE was noted to have a positive predictive value (PPV) of 40% and a negative predictive value (NPV) of 88% for detection of thrombophilia. Patients with a family history of CVD alone carried a PPV of 24% and NPV of 100%. Finally, among individuals with both family history risk factors, PPV was strengthened at 52% while NPV remained unchanged.

CONCLUSIONS

Within the last decade, inherited thrombophilias have gained more clinical interest. While thrombophilia disease prevalence data is available for the adult population, there remains a paucity of data in adolescents. Our results reinforce the importance for screening adolescent females, prior to contraceptive administration, if family history risk factors exist.

Hyperhomocysteinemia and thrombosis: an overview

CONTEXT

Homocysteine, a sulfur-containing amino acid, absent in natural diets, is a metabolic intermediary in transmethylation and transsulfuration reactions. Such reactions are essential to normal cellular growth, differentiation, and function. Excess homocysteine is associated with vascular disease and related disorders.

OBJECTIVE

To review homocysteine metabolism, the pathogenesis and classification of hyperhomocysteinemia, and the published literature investigating the association of homocysteine and methylenetetrahydrofolate reductase defects with arterial and venous thromboembolism and related disorders. The role of vitamin supplementation in patients with hyperhomocysteinemia is addressed.

DATA SOURCES

Published medical and scientific literature. Articles addressing the objectives were selected and reviewed. Pertinent studies and conclusions were summarized, grouped, and contrasted.

CONCLUSIONS

The association of hyperhomocysteinemia and arterial and venous thrombosis is controversial. Severe hyperhomocysteinemia is associated with atherosclerosis. The effect of mild hyperhomocysteinemia is less certain. Coinheritance of methylenetetrahydrofolate reductase defects and factor V Leiden is likely to increase the risk of venous thromboembolism. The association of methylenetetrahydrofolate reductase defects combined with no additional thrombophilic risk factors with venous thrombosis is less clear. High doses of folic acid to lower homocysteine levels might not be necessary.

Vascular and cellular stress in inflammatory bowel disease: revisiting the role of homocysteine

Moderate hyperhomocysteinemia is a complex trait commonly associated with inflammatory bowel disease (IBD). Nutritional deficiencies and genetic determinants have been identified as risk factors for moderate hyperhomocysteinemia, such as folate and vitamin B(12) deprivation and polymorphisms in the 5,10 methylenetetrahydrofolate reductase (MTHFR) encoding gene, respectively. Homocysteine has a crucial role in cellular stress, epigenetic events, inflammatory processes, and host-microbial interactions. Hyperhomocysteinemia might therefore influence the clinical history of IBD, including disease severity, susceptibility to particular enteric infections, and the risk for the development of colorectal cancer. In contrast, homocysteine metabolism does not seem to contribute to the greater risk of thrombosis in IBD subjects. Herein, we review the evidence linking homocysteine metabolism to the pathophysiology of IBD. Furthermore, we discuss the relevance of screening and treating folate and vitamin B(12) deficiencies in IBD subjects. Given the peculiar frequency of such deficiencies in IBD, normalizing vitamin levels should be an integral part of the management of these patients, especially those with active disease, history of intestinal resection, and/or treated with methotrexate.

Hyperhomocysteinemia and the compound heterozygous state for methylene tetrahydrofolate reductase are independent risk factors for deep vein thrombosis among South Indians

To investigate the role of methylene tetrahydrofolate reductase (MTHFR) (677 C-->T and 1298 A-->C), factor V (1691 G-->A), factor II (20210 G-->A) genetic polymorphisms and hyperhomocysteinemia in the aetiology of deep vein thrombosis (DVT) in 163 cases and 163 controls. Polymerase chain reaction-restriction fragment length polymorphism was used for genotyping, reverse-phase high-performance liquid chromatography for plasma homocysteine, and Student's t-test and Fisher exact tests were used for statistical analysis. Elevated mean plasma homocysteine levels were observed in DVT cases irrespective of gender differences. Homocysteine elevation above the 95th percentile of the control group associated with 9.4-fold and 7.6-fold increased risk for DVT in men and women, respectively. Genotyping showed the MTHFR 677CT/1298AC genotype (i.e. compound heterozygosity) is associated with 3.5-fold risk for thrombosis. The factor V Leiden mutation frequency was higher in DVT cases, but not statistically significant; however, genetic predisposition to this mutation was associated with early age of DVT onset. Factor II mutation was absent in cases and controls. Co-segregation of two or more risk factors was associated with 11.7-fold increased risk for thrombosis. This study projects that hyperhomocysteinemia and compound heterozygous state for MTHFR are independent risk factors for DVT among South Indians.

Association of homocysteine, vitamin B12, folic acid, and MTHFR C677T in patients with a thrombotic event or recurrent fetal loss

Hyperhomocysteinemia (HHC) is a known risk factor for venous and arterial thrombosis. Thrombophilia workup includes the level of homocysteine and other related parameters such as: vitamin B(12), folic acid, and methylenetetrahydrofolate reductase (MTHFR) C677T genotype. As the levels of homocysteine, vitamin B(12), folic acid, and MTHFR C677T genotype are linked biochemically, we hypothesized that a statistical association will be found between them. The purpose of the present study was to assess the association between the four parameters in patients with a thrombotic event or recurrent fetal loss. The potential study population included 326 patients who were referred to the Thrombosis and Hemostasis Unit; 125 of these patients had at least one pathological test result of the four parameters. The correlations between homocysteine and vitamin B(12) as well as between homocysteine and folic acid were found to be weak (r = -0.236 and r = -0.209, respectively). No significant difference was revealed between the mean homocysteine level and the CC, CT, and TT MTHFR genotypes (p = 0.246). In conclusion, in the population studied, the association between homocysteine, vitamin B(12), folic acid, and MTHFR C677T is weak. The results raise doubt as to whether the current routine evaluation of HHC, as part of thrombophilia workup, truly reflects the increased risk of thrombosis.

Venous thrombosis associated with pernicious anaemia. A report of two cases and review

Since homocystinuria, an inborn metabolism error is complicated by venous thrombosis in about half of the patients, hyperhomocysteinemia has been suspected of favouring thrombosis. Several case-control studies and even meta-analysis have confirmed a link between venous thrombosis and mild hyperhomocysteinemia. Nevertheless, the proper role of homocysteine remains debated. Hyperhomocysteinemia is induced by vitamin B9 or B12 deficiencies in a vast majority of cases. The authors report on two patients with venous thrombosis revealing pernicious anemia and review nine similar cases found in the world literature. The literature concerning the relationships between homocysteine and venous thrombosis is briefly reviewed.

Celiac sprue, hyperhomocysteinemia, and MTHFR gene variants

GOALS

To describe the association of untreated celiac disease with hyperhomocysteinemia and variants of the methylenetetrahydrofolicacid reductase (MTHFR) gene found in clinical practice.

STUDY

Case studies with description of associated clinical, biochemical, and genetic findings and review of literature.

RESULTS

Five new cases and 7 additional cases found from literature search of hyperhomocysteinemia with celiac sprue are reported. Treatment with gluten-free diet and folic acid led to the variable improvement in homocysteine levels. MTHFR gene variants were present in the each of the new patients described.

CONCLUSIONS

Untreated celiac disease may be associated with hyperhomocysteinemia caused by a combination of vitamin deficiencies and variants in the MTHFR gene. Abnormalities do not consistently improve with gluten-free diet. The abnormal findings could result from vitamin deficiencies or variant MTHFR status. Possible clinical implications for patients with celiac disease and hyperhomocysteinemia are reviewed.

The influence of risk factors in promoting thrombosis during childhood: the role of acquired factors

Thrombo-embolism in childhood is a multifactorial disorder. The present study is a case-control study that investigated the role of genetic and acquired risk factors in 60 children with thrombosis and compared the results with the controls. Acquired and inherited risk factors precipitating thrombosis were present in 75 and 40% of the thrombotic children, respectively. The most frequent acquired risk factor was infection (58%). Of the genetic factors, factor V G20210A was the most common (38%). The comparison of the genetic and acquired risk factors in thrombotic versus nonthrombotic settings identified that acquired factors played a more significant role in causing thrombosis (OR:14.44; 95% CI: 7.05-29.94, p < .001). This study has clearly suggested that the prevention of acquired risk factors, particularly infection, could decrease the risk of thrombosis in pediatric cases.

Prevalence of factor V Leiden, prothrombin G20210A, and MTHFR G677A among 594 thrombotic Jordanian patients

Venous thromboembolism develops as the result of multiple interactions between non-genetic and genetic risk factors. In order to estimate the frequency of factor V Leiden, prothrombin G20210A, and MTHFR C677T mutations in Jordanian thrombotic patients, we studied 594 patients admitted to the King Hussein Medical Center for thrombophilia assessment. Polymerase chain reaction detected 25.7% (20.7% heterozygous, 5% homozygous), 6% (5.8% heterozygous, 0.2% homozygous) and 31.7% (25% heterozygous, 6.7% homozygous) for factor V Leiden, prothrombin G20210A and MTHFR C677T mutations, respectively. A one-stage clotting assay was used to measure prothrombin activity. None of the prothrombin G20210A mutant patients had high prothrombin activity. The high prevalence found among our study group of factor V Leiden and prothrombin G20210A confirms the importance of thrombophilia screening for patients with venous thrombosis with family history and those with additional risk factors. On the contrary, the high prevalence of the MTHFR C677T mutation among arterial thrombosis patients shows its importance in screening in arterial thrombosis patients. These results, which are close to the prevalence found by other studies in the region, suggests that the Eastern Mediterranean region is probably the area of origin of these mutations, especially factor V Leiden. The knowledge of these frequencies in the Middle East region through population-based studies will contribute to a better understanding of the interaction between genetic and environmental risk factors underlying the mentioned mutations.

Risk factors for venous thrombosis in Swedish children and adolescents

AIM

To identify prothrombotic risk profiles in children and adolescents referred to a regional coagulation centre in southern Sweden for a first thrombotic event.

METHODS

One hundred and twenty-eight consecutive children and adolescents (newborn to 20 y) referred for evaluations of a first episode of venous thrombosis were investigated. Clinical data were collected retrospectively, and the following variables were investigated: protein C, protein S, antithrombin; resistance to activated protein C; the genotypes FV-G1691A, F II-G20210A, MTHFR-C677T, MTHFR- A1298C; coagulation factors VIII and XI.

RESULTS

104/128 subjects (81%) had identifiable acquired risk factors, most often indwelling catheters and hormone therapy. Predisposing genetic factors related to thromboembolic events were revealed in 53/83 (64%) of subjects who agreed to follow-up blood sampling, and 17/83 (20%) had two or more inherited risk factors. Combinations of genetic and acquired risk factors were identified in 45/83 (54%) of the subjects, and 77/83 (93%) had at least one such risk factor. Both sexes had one peak in frequency at less than 1 y of age and then an increase during adolescence, more in females than in males. Plasma values for coagulation factors VIII and XI were age appropriate and showed a normal Gaussian distribution.

CONCLUSION

This study identified prothrombotic risk profiles in almost all children and adolescents with venous thrombosis, which underlines the importance of careful evaluation of genetic and acquired risk factors.

A Case Control Study on the Contribution of Factor V-Leiden, Prothrombin G20210A, and MTHFR C677T Mutations to the Genetic Susceptibility of Deep Venous Thrombosis

BACKGROUND

Insofar as the inherited prothrombotic single nucleotide polymorphisms (SNPs) factor V G1691A (FV-Leiden), prothrombin (PRT) G20210A, and methylenetetrahydrofolate reductase (MTHFR), C677T are inherited risk factors of venous thromboembolism (VTE), the aim of this study was to determine the prevalence of single and combined SNPs in 198 patients with documented deep venous thrombosis (DVT), and 697 control subjects, and to estimate the associated risks.

METHODS

Factor V-Leiden, PRT G20210A, and MTHFR C677T were analyzed by PCR and restriction fragment length polymorphism (RFLP).

RESULTS

The prevalence of the heterozygote and homozygous variants for FV-Leiden (52.02 vs. 14.78%, RR 6.28), PRT G20210A (19.2 vs. 3.6%; RR 6.38), and to a lesser extent the T/T genotype of MTHFR C677T (20.71 vs. 11.0%; RR 1.49) were higher among DVT patients vs. controls, respectively. Two or more SNPs were detected in 90 of 198 patients (45.5%) and in 60 of 697 controls (8.6%), with odds ratios of 16.754 for joint occurrence of FV-Leiden and PRT G20210A, 10.471 for FV-Leiden and MTHFR C677T, and 6.283 for PRT G20210A SNPs and MTHFR 677T/T. Logistic regression analysis showed a further increased odds for FV-Leiden in combination with PRT G20210A (85.198) or homozygous MTHFR C677T (81.133), and to a lesser extent for PRT G20210A in combination with homozygous MTHFR C677T (20.812).

CONCLUSIONS

This indicates that FV-Leiden and PRT G20210A, more than MTHFR C677T, are important risk factors for DVT, and that the presence of more than one prothrombotic SNPs was associated with a significant risk of DVT.

Homocysteine, MTHFR and risk of venous thrombosis: a meta-analysis of published epidemiological studies

CONTEXT

It has been suggested that elevated total plasma homocysteine levels are associated with the risk of venous thrombosis.

OBJECTIVE

To assess the relationship of homocysteine and the MTHFR 677TT genotype and the risk of venous thrombosis by conducting a meta-analysis of all relevant studies.

DATA SOURCES AND SELECTION

Studies (case-control or nested case-control) were identified by searches of electronic literature for relevant reports published before July 2003 on homocysteine and the MTHFR 677TT genotype and venous thrombosis as an end-point, by hand-searching reference lists of original articles (including meta-analyses) on this topic and by contact with investigators in the field.

DATA EXTRACTION

A meta-analysis of 24 retrospective (n = 3289 cases) and three prospective studies (n = 476 cases) was carried out to examine the association of homocysteine with venous thrombosis. A meta-analysis of 53 studies (n = 8364 cases) of the MTHFR 677TT genotype (that increases homocysteine) was carried out to assess if this association is causal.

DATA SYNTHESIS

A 5 micromol L(-1) higher measured homocysteine level was associated with a 27% (95% CI: 1-59) higher risk of venous thrombosis in prospective studies and a 60% (95% CI: 10-134) higher risk in retrospective studies. The 677TT genotype was associated with a 20% (95% CI: 8-32) higher risk of venous thrombosis compared with the 677CC genotype. In contrast with non-American studies, the 677TT genotype had no effect on venous thrombosis in North America, due probably to the higher intake of folate and riboflavin in North America.

CONCLUSION

This meta-analysis of prospective and retrospective studies demonstrates a modest association of homocysteine with venous thrombosis. The elevated risk associated with the MTHFR 677TT genotype provides some support for causality.

Impact of environmental and hereditary risk factors on the clinical manifestation of thrombophilia in homozygous carriers of factor V:G1691A

BACKGROUND

Limited data exist on the clinical manifestations of homozygous factor (F)V:G1691A mutation (FV Leiden) and the impact of environmental and genetic risk factors.

OBJECTIVES

To assess the contribution of these factors on the thrombophilic phenotype.

PATIENTS AND METHODS

In a retrospective multicenter cohort study 165 individuals with homozygous FV:G1691A mutation, of whom 129 had previous venous thromboembolism (VTE), were included. To study the role of environmental risk factors, patients were compared by the use of a standardized questionnaire to 165 sex- and age-matched individuals (reference group A); of these, two had previous VTE. To assess the role of genetic risk factors, factor (F)II:G20210A and MTHFR:C677T were determined in individuals homozygous for FV:G1691A and in 177 healthy individuals without previous VTE (reference group B).

RESULTS

The first VTE occurred significantly earlier in women (median age 25 years) than men (35.5 years). In 81% of women and 29% of men an environmental risk factor was present before first VTE. Oral contraceptives increased the risk of thrombosis 4-fold [odds ratio (OR) 4.0, 95% confidence interval (CI) 1.7, 10.4] in women with homozygous FV:G1691A. Postoperative and post-traumatic VTE as first manifestation occurred in 13% and 15% of surgical/traumatic events in patients and in 0.7% and 1.8% in reference group A, respectively (OR 19.7, 95% CI 2.5, 154 and OR 9.2, 95% CI 1.1, 79.4). Heterozygous FII:G20210A was more prevalent in symptomatic patients (11.7%) compared with reference group B (2.8%, OR 4.6, 95% CI 1.6, 13.2). The prevalence of homozygous MTHFR:C677T genotype was similar in patients and reference group B.

CONCLUSIONS

Our study supports the concept of thrombophilia as a multifactorial disorder. The knowledge of coexisting factors predisposing to VTE is useful for medical advice for primary and secondary prophylaxis in these patients.

Risk-factor profile in severe, generalized, obliterating vascular disease

A 74-year-old woman had a history over 25 years of endarterectomy of both renal arteries, iliac venous thrombosis, pulmonary embolism, left internal carotid artery endarterectomy, coronary angioplasty, aortocoronary bypass grafting, occlusion of the right axillary artery, lower-limb claudication due to common iliac artery aneurysm, external iliac artery stenosis, multiple femoral artery stenoses, bifurcational stent grafting, occlusion of the left brachial artery and the right external iliac artery, and stroke. Assessment of the risk-factor profile revealed an absence of classic risk factors but the presence of the factor V Leiden mutation, the methylenetetrahydrofolate reductase AI298C mutation, the HFE C282Y mutation, plasminogen activator inhibitor-1 gene mutation, the -455 G/A fibrinogen gene polymorphism, the epsilon3/epsilon4 apolipoprotein E -675 4G gene polymorphism, and hyperhomocysteinemia. This case shows that severe, generalized, occlusive vascular disease may be due to the combination of various genetic risk factors for atherosclerosis and venous thromboembolism.

Croatian population data for the C677T polymorphism in methylenetetrahydrofolate reductase: frequencies in healthy and atherosclerotic study groups

BACKGROUND

The aim of this study was to investigate the frequency of C677T methylenetetrahydrofolate reductase (MTHFR) mutation in healthy Croatian volunteers and in patients with atherosclerosis.

METHODS

The C677T MTHFR gene mutation was determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 640 subjects, residents of the Zagreb city or Zagreb surroundings. Control group (n=298) was healthy blood donors. Patients (n=342) were divided into two groups of those with coronary heart disease, CAD (n=247) and those with >60% carotid stenosis, CS (n=95).

RESULTS

CC genotype was recorded in 45% of healthy volunteers and 46% of patients (46.3% with CS and 46.2% with CAD). TC genotype was found in 49% of healthy volunteers and 45% of patients (46.3% with CS and 44.9% with CAD). There was no significant difference (p>0.05) from the control group in the genotype or allele frequency either for the overall group of patients with atherosclerosis or for the patient subgroups.

CONCLUSION

The preliminary study of MTHFR polymorphism in control subjects and cardiovascular disease/carotid stenosis patients revealed that in Croats there was a low frequency of TT genotype (6% in controls vs. 9% in patients) and T allele (31% for cases and controls). Additionally, our results did not show significantly higher frequency of MTHFR mutation in CAD and CS studied groups.

[A common mutation C677T in the 5,10-methyltetrahydrofolate reductase gene is associated to idiopathic deep venous thrombosis]

PURPOSE

Moderate hyperhomocysteinemia is a risk factor for deep venous thrombosis. The homozygous C677T methylenetetrahydrofolate reductase (MTHFR) mutation is associated with increased level of total plasma homocysteine. The association between homozygous C677T mutation and deep venous thrombosis is still controversial.

METHOD

In order to evaluate this association, we studied the prevalence of C677T mutation in 168 patients with confirmed deep venous thrombosis; 31 with an idiopathic deep venous thrombosis (group A) and 137 with thromboembolic event explained by one or more clinical and/or biological risk factors (group B).

RESULTS

The distribution of genotypes was different between group A and B [++/+ -/- -(n(%))] : 9(29)/10(32)/12(39) vs 16(12)/57(42)/64(46) (chi(2) : 6.03; P: 0.049). The comparison between homozygotes and the two other genotypes showed significant statistical relationship between homozygous genotype and idiopathic character of deep venous thrombosis (chi(2) : 6.01; P : 0.014; OR : 3.09 [IC 95% : 1.06-8.53]).

CONCLUSION

These results suggest that homozygous C677T methylenetetrahydrofolate reductase mutation could be considered as a genetic risk factor for venous thrombosis.

Overestimation of genetic risks owing to small sample sizes in cardiovascular studies

We sought evidence of publication bias to explain conflicting findings in studies of angiotensin-converting enzyme deletion polymorphism (ACE D) and glycoprotein IIIa PlA2 (PLA2) polymorphism and the risk of myocardial infarction. Factor 5 Leiden (F5L), a well-established thrombotic risk factor, served as an internal comparison. We conducted systematic reviews of published studies involving ACE D, PLA2, F5L and relevant outcomes, searching medline (January 1990 through February, 2001), bibliographies, and meta-analyses. Random effects pooled odds ratios (95% confidence interval) for cardiovascular outcomes were as follows: PLA2 (n = 13,167 subjects): 1.13 (1.02, 1.26); ACE D (n = 42,140 subjects): 1.22 (1.11, 1.35); and F5L (n = 27,277 subjects): 4.43 (3.65, 5.38). However, funnel plots of ACE D and PLA2, but not F5L, showed an inverse relationship between sample size and odds ratios for ACE D (p = 0.02) and PLA2 (p = 0.04) but not F5L (p = 0.65) by Egger's test for potential publication bias. Despite research-based genotyping of over 50,000 subjects, the overall risk for myocardial infarction as a result of PLA2 and ACE D remains doubtful. Our study provides a clear example of how publication of underpowered studies can spuriously implicate polymorphisms as genetic risk factors.

Is miscarriage a coagulopathy?

PURPOSE OF REVIEW

Pregnancy is a hypercoaguable state. The hypothesis has been developed that many cases of recurrent miscarriage and of later pregnancy complications are caused by a defective maternal haemostatic response leading to thrombosis of the uteroplacental vasculature and subsequent fetal loss. The evidence upon which this hypothesis is based is reviewed.

RECENT FINDINGS

The majority of studies report an increased prevalence of genetic thrombophilic mutations in the female partner of couples with recurrent miscarriage. It is important to note, however, that this is not a uniform finding. A sub-group of women with recurrent miscarriage has been demonstrated to be in a prothrombotic state before pregnancy, and that women in such a state are at an increased risk of miscarriage in future untreated pregnancies. Furthermore, the long-term health implications of this hypercoaguability have been highlighted in a large retrospective study reporting an increased risk of ischaemic heart disease among women with a history of pregnancy loss.

SUMMARY

Although recurrent miscarriage is a heterogeneous condition and no single abnormality will account for all cases of pregnancy loss, the relationship between abnormalities in the haemostatic pathways and pregnancy outcome is increasingly recognized. The challenges we face are how to discriminate between women with a thrombophilic defect who are destined to miscarry from those whose pregnancy will be successful, the pathology of pregnancy loss associated with thrombophilic defects, the role of the fetal genotype in determining pregnancy outcome, and the management of women with thrombophilic defects both during and beyond their reproductive years.

Serum homocysteine, thermolabile variant of methylene tetrahydrofolate reductase (MTHFR), and venous thromboembolism: Longitudinal Investigation of Thromboembolism Etiology (LITE)

We sought to examine prospectively the association of serum homocysteine and the methylene tetrahydrofolate reductase (MTHFR) C677T gene polymorphism with risk of venous thromboembolism (VTE). We studied these relationships in a nested case-control study of 303 VTE cases and 635 matched controls from a population-based cohort of 21,680 adults from six U.S. communities. The highest quintile of serum homocysteine carried a non-statistically significant adjusted odds ratio of 1.55 (95% CI, 0.93-2.58) compared to the lowest quintile in the overall cohort but a significant association among adults aged 45-64 years (OR = 2.05, 95% CI, 1.10-3.83) and an inverse association in those > or = 65 years of age. Carriers of the MTHFR C677T polymorphism were not at higher risk for VTE than those with normal genotype (OR = 0.74, 95% CI = 0.56-0.98). Our prospective data showed, at most, a weak relationship between homocysteine and VTE risk, with associations larger among younger participants. MTHFR C677T was not a risk factor for VTE.

Hyperhomocysteinaemia as a Risk Factor for Venous Thrombosis: An Update of the Current Evidence

Classical homocystinuria is associated with arterial vascular diseases and venous thrombosis. In the last decade, many studies, including some prospective studies, have been published indicating that moderate hyperhomocysteinaemia is also a risk factor for venous thrombosis. The 677C>T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene is an important cause of mild hyperhomocysteinaemia. Recent metaanalyses show an elevated risk of venous thrombosis for subjects with the TT-genotype. Based on the concept of 'Mendelian randomisation', this observation supports the hypothesis that hyperhomocysteinaemia is a causal risk factor for venous thrombosis. The results of one homocysteine-lowering trial regarding venous thrombosis are awaited at the end of 2003. In this paper the current evidence for hyperhomocysteinaemia as a risk factor for venous thrombosis is being discussed.

Thermolabile methylenetetrahydrofolate reductase, homocysteine, and cardiovascular disease risk: the European Concerted Action Project

BACKGROUND

Homozygotes for the thermolabile mutation (TT genotype) of the methylenetetrahydrofolate reductase (MTHFR; EC 1.5.1.20) enzyme have elevated plasma concentrations of the cardiovascular disease risk factor homocysteine, particularly if folate depleted.

OBJECTIVE

We examined the relations between thermolabile MTHFR, plasma homocysteine, plasma folate, and vascular disease risk.

DESIGN

This was a case-control comparison in 711 vascular disease cases and 747 controls from 9 European countries.

RESULTS

The TT genotype was associated with higher homocysteine and lower plasma folate than the CC and CT genotypes in both cases and controls and a nonsignificant increase in vascular disease risk (1.26; 95% CI: 0.88, 1.81; P = 0.20). The frequency of the TT genotype in cases was not significantly different from that in controls (12.8% compared with 10.8%). After adjustment for traditional risk factors, the TT genotype was associated with an odds ratio of 1.48 (1.0, 2.20) for risk of vascular disease. This risk was attenuated after further adjustment for homocysteine. In subgroups with homocysteine concentrations >or= 9 micro mol/L, risk tended to be higher in CC than in TT subjects. However, CC subjects were characterized by a higher prevalence of the conventional risk factors associated with both elevated plasma homocysteine and serum creatinine. After adjustment, the risk of vascular disease associated with each genotype was not significantly different.

CONCLUSIONS

There was a strong graded association between homocysteine and vascular risk in all genotypes. MTHFR genotype is a key determinant of plasma total homocysteine concentrations. The initially nonsignificant risk estimate associated with the TT genotype was strengthened after adjustment for conventional cardiovascular disease risk factors but was attenuated after adjustment for plasma folate and total homocysteine. The modest risk increase conferred by the TT genotype is mediated mainly by increased total homocysteine and low plasma folate concentrations.

The epidemiology of venous thromboembolism in Caucasians and African-Americans: the GATE Study

The aim of this study was to assess, comprehensively, medical and genetic attributes of venous thromboembolism (VTE) in a multiracial American population. The Genetic Attributes and Thrombosis Epidemiology (GATE) study is an ongoing case-control study in Atlanta, Georgia, designed to examine racial differences in VTE etiology and pathogenesis. Between 1998 and 2001, 370 inpatients with confirmed VTE, and 250 control subjects were enrolled. Data collected included blood specimens for DNA and plasma analysis and a medical lifestyle history questionnaire. Comparing VTE cases, cancer, recent surgery, and immobilization were more common in caucasian cases, while hypertension, diabetes, and kidney disease were more prevalent in African-American cases. Family history of VTE was reported with equal frequency by cases of both races (28-29%). Race-adjusted odds ratios for the associations of factor V Leiden and prothrombin G20210A mutations were 3.1 (1.5, 6.7) and 1.9 (0.8, 4.4), respectively. Using a larger external comparison group, the odds ratio for the prothrombin mutation among Caucasians was a statistically significant 2.5 (1.4, 4.3). A case-only analysis revealed a near significant interaction between the two mutations among Caucasians. We found that clinical characteristics of VTE patients differed across race groups. Family history of VTE was common in white and black patients, yet known genetic risk factors for VTE are rare in African-American populations. Our findings underscore the need to determine gene polymorphisms associated with VTE in African-Americans.

Hyperhomocyst(e)inemia and Thrombophilia

OBJECTIVE

To review the role of an elevated total plasma homocysteine level (hyperhomocyst[e]inemia) in patients with venous or arterial thrombosis, as reflected by the medical literature and the consensus opinion of recognized experts in the field.

DATA SOURCES

Review of the medical literature, primarily from the last 10 years.

DATA EXTRACTION AND SYNTHESIS

The literature was reviewed to identify key points defining the condition, and the clinical study design of each article was examined. A draft manuscript was prepared and circulated prior to the conference to every participant in the College of American Pathologists Conference XXXVI: Diagnostic Issues in Thrombophilia. Each of the key points and associated recommendations was then presented for discussion at the conference. Recommendations were accepted if a consensus of the 70% of the experts attending the conference was reached. The results of the discussion were used to revise the manuscript into its final form.

CONCLUSIONS

Consensus was reached on 9 recommendations concerning the criteria for diagnosis, the method of testing, and the approach for clinical management. A major point of consensus was that no causal role of hyperhomocyst(e)inemia in venous or arterial thrombosis is yet established. Testing methods used to measure homocysteine directly are sensitive and reliable, and provide more information than does genotyping for markers linked to abnormal plasma homocysteine.