Protein C and protein S deficiencies are the most important risk factors associated with thrombosis in Chinese venous thrombophilic patients in Taiwan

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.

Genetic thrombophilia

The genetic thrombophilias are an important cause of venous thrombotic events. Much has been learned about the natural history of these disorders, their genetics, and, to a lesser degree, their treatment. This article provides an overview of the genetics of thrombophilia. Specific information on the factor V Leiden mutation;the prothrombin G20210A mutation; and protein C, proteinS, and antithrombin deficiency is reviewed. Current testing and treatment options for the genetic thrombophilias also are discussed.

R147W mutation of PROC gene is common in venous thrombotic patients in Taiwanese Chinese

We analyzed the genetic defects of 21 unrelated patients with venous thrombosis in whom hereditary protein C deficiency was diagnosed. Eleven mutations were detected in 18 families, while no mutation was detectable in the other three families. Among these mutations, a common genetic mutation of protein C (PROC) gene recurred in 43% (nine propositi from these 21 families). This C6152T mutation at exon 7 resulted in a missense mutation, Arg147Trp (R147W). Each propositus or family carrier had another specific polymorphism T66C at exon 2, which did not change the proline at position (-21). The haplotype analysis strongly suggested a founder effect. The first thrombotic attack was significantly younger in patients with multiple genetic defects or combined with other risk factors than those without precipitating factors. We further studied the prevalence rate of R147W mutations in normal populations through PCR amplification and dot hybridization. Three different cohorts got similar results. The prevalence rate of R147W in health controls is 0.85% [95% confidence interval (CI) 0.35-1.35]. Analysis of plasma protein C levels of all patients or carriers suggested that R147W was a type II deficiency. The odds ratio of thrombosis of R147W is 5.1 (95% CI 1.7-14.8). Taken together, R147W mutation is a significant thrombotic risk factor and is the most common defect of PROC gene in Taiwanese patients with protein C deficiency. This finding is important for screening thrombophilic families in Chinese populations.

Incidence of thrombophilia detected in southern Taiwanese patients with venous thrombosis

In order to analyze the incidence of thrombophilia in southern Taiwan, we studied the prevalence of antithrombin (AT), protein C (PC), and protein S (PS) deficiencies, the prevalence of factor V Leiden mutation, and the presence of acquired lupus anticoagulant (LA) and anticardiolipin antibody (ACA) in 56 patients < or =65 years old with deep venous thrombosis (DVT). Of 56 patients, 30 were male, 26 female, and the mean age of the patients was 43 years (18-65 years). None had factor V mutation or activated PC resistance; 21 patients (37.5%) showed abnormal results: 4 (7.1%) had AT deficiencies, 6 (10.7%) PC deficiencies, 6 (10.7%) PS deficiencies, 2 (3.6%) a combined PC and PS deficiency, and 3 (5.4%) LA and ACA. Only PC and PS deficiencies were significantly associated with increased risk for the development of thrombosis with an odds ratio of 4.2 (95% confidence interval: 1.2-15.0, P=0.018) and 8.1 (95% confidence interval: 1.6-40.6, P=0.003), respectively. We concluded that the prevalence of heritable thrombophilia (34.0%) in Taiwan is higher than that in Western countries, but that it is lower than previously reported in Hong Kong and Taiwan. We attribute this to selection bias.

Factor V gene G1691A mutation, prothrombin gene G20210A mutation, and MTHFR gene C677T mutation are not risk factors for pulmonary thromboembolism in Chinese population

A mutation in coagulant factor V gene, a substitution in the 3' untranslated region of prothrombin gene, and a variant in 5,10-methylenetetrahydrofolate reductase (MTHFR) gene have been reported to be related to venous thromboembolism in Caucasians, but this relationship remains in debate in other populations. In this case-control study, we aimed to determine the prevalence of these three mutations in the Chinese population and investigate whether they are associated with pulmonary thromboembolism. The subjects consisted of 90 patients with pulmonary thromboembolism and 143 age- and sex-matched healthy controls. Traditional risk factors for venous thrombosis and pulmonary thromboembolism were investigated as well. We found that the frequencies of varicose vein, phlebitis, trauma, and surgery were significantly higher in cases than in controls. Of all subjects, none was a carrier of coagulant factor V gene G1691A mutation or prothrombin gene G 20210A mutation, which are common point mutations in Caucasians, while the frequency of MTHFR gene 677T allele exceeded 55% in cases (56.7%), controls (55.2%), and all subjects (55.8%) studied. The homozygous mutation rate of MTHFR gene was over 30% in both cases (33.3%) and controls (32.2%), but no significant difference was found in genotype distribution (chi(2)=0.100, P=0.951). Model fitting using logistic regression did not find that MTHFR gene C677T mutation was associated with pulmonary thromboembolism, consistent with the results of stratification analysis. In conclusion, coagulant factor V gene G1691A mutation and prothrombin G20210A mutation are very rare, while MTHFR C677T mutation is very common, and all of them are not associated with pulmonary thromboembolism in the Chinese population.

Age, sex and vitamin status affect plasma level of homocysteine, but hyperhomocysteinaemia is possibly not an important risk factor for venous thrombophilia in Taiwanese Chinese

The biological effects of age, sex and vitamin status on plasma total homocysteine (tHcy), and association of hyperhomocysteinaemia with venous thromboembolism in Taiwanese Chinese individuals, were investigated. Eighty patients (16-85 years) with venous thrombophilia and 123 healthy subjects (15-85 years) without history of vascular thrombosis were studied for plasma levels of tHcy, folate and vitamin B12. A multivariate analysis in healthy subjects revealed that plasma tHcy levels tended to increase with age (P < 0.001) and with decreasing plasma levels of folate (P=0.001) or vitamin B12 (P < 0.029); men tended to have higher plasma tHcy levels than women (P=0.006). Thrombotic risk assessment in a case-control study demonstrated that neither plasma level of tHcy [odds ratio (OR), 1.07; 95% confidence interval (CI), 0.96-1.18; P=0.210] nor hyperhomocysteinaemia (OR, 1.65; 95% CI, 0.50-5.49; P=0.415) was significantly associated with venous thrombophilia. The relationship between hyperhomocysteinaemia and recurrence of episode remained insignificant (P=0.560). We conclude that age, sex and vitamin status affect plasma tHcy but hyperhomocysteinaemia is possibly not an important risk factor for venous thrombophilia in Taiwanese Chinese.