Lack of Activated Protein C Resistance in Healthy Hong Kong Chinese Blood Donors - Correlation with Absence of Arg506-Gln Mutation of Factor V Gene

Factor V Leiden

Factor V Leiden (FVLeiden ) is a common hereditary thrombophilia that causes activated protein C (APC) resistance. This review describes many of the most fascinating features of FVLeiden , including background features, mechanisms of hypercoagulability, the founder mutation concept, the "FVLeiden paradox," synergistic interaction with other thrombotic risk factors, the intertwined relationship between FVLeiden and APC resistance testing, and other, uncommon mutations implicated in causing APC resistance. In addition, there are several conditions where laboratory tests for APC resistance and FVLeiden are or can be discrepant, including lupus anticoagulants, anticoagulants such as direct thrombin inhibitors (dabigatran, argatroban, and bivalirudin) and rivaroxaban, as well as pseudohomozygous, pseudo-wildtype, liver transplant, and bone marrow transplant patients. The laboratory test error rate for FVLeiden is also presented.

Factor V Leiden mutation in women with early recurrent pregnancy loss: a meta-analysis and systematic review of the causal association

BACKGROUND

Recently, the interest has focused on the increased prevalence of thrombophilic defects in women with gestational complications.

OBJECTIVE

To explore whether women with early recurrent pregnancy loss (RPL) are at increased risk of being carriers of the Factor V Leiden (FVL) mutation compared to those who have a normal reproductive history.

METHODS

A manual and electronic literature search was undertaken to identify studies with a case-control population of women with two or more first trimester RPLs of undetermined origin and age- and ethnicity-matched control group with normal reproductive history and at least one full-term delivery. Both groups were screened for FVL mutation. A quality assessment was performed according to the pre-established validity criteria and using the Cochrane handbook guidelines for observational studies. The combinability of studies was assessed by clinical and statistical methods (Breslow-Day's test of homogeneity). Quantitative data were abstracted with regard to the prevalence of FVL mutation in the case and control group, and 2 × 2 tables were created. The ratio comparing the odds of FVL mutation in women with early RPL with the odds of FVL mutation in women with normal reproductive outcome was calculated with its 95% confidence interval (CI) by Mantel-Haenszel method.

RESULTS

Nine studies met the inclusion criteria and were selected for review. A total of 2,147 women were screened for the FVL mutation, 1,305 women with early RPL, and 842 women with no gestational complications. Women with early RPL had indeed a statistically significantly increased carrier frequency of FVL mutation, the common OR being 1.68 (95% CI: 1.16-2.44).

CONCLUSION

FVL carrier state may increase the susceptibility for early RPL. Testing for FVL mutation should be considered in women with unexplained early RPL and thrombophylaxis has been suggested in women with unexplained RPL associated with FVL mutation.

Thrombotic risk factors in Chinese nonmalignant and noncirrhotic patients with portal vein thrombosis: an observational study with a systematic review of the literature

BACKGROUND

Until now, no data on the routine screening for thrombotic risk factors in Chinese nonmalignant and noncirrhotic patients with portal vein thrombosis (PVT) have been reported.

METHODS

A total of 141 nonmalignant and noncirrhotic patients with PVT who underwent screening tests for thrombotic risk factors between September 2009 and August 2012 were included in this study.

RESULTS

The JAK2 V617F mutation was found in 35 of the 141 patients tested. Neither the JAK2 exon 12 mutation nor the MPL W515 L/K mutation was found in any of the 50 patients tested. Overt myeloproliferative neoplasms (MPNs) were diagnosed in 13 patients (polycythemia vera, n=1; essential thrombocythemia, n=9; idiopathic myelofibrosis, n=3). Latent MPNs were considered in 23 patients with the JAK2 V617F mutation but without any significant abnormalities, as determined through regular blood tests. Anticardiolipin IgG antibodies were positive in none of the 136 patients tested. Paroxysmal nocturnal hemoglobinuria was not found in any of the 141 patients tested. Neither the factor V G1691A mutation nor the factor II G20210A mutation was found in any of the 72 patients tested. The C677T mutation in 5,10-methylenetetrahydrofolate reductase (MTHFR) was found in 29 of the 38 patients tested. Hyperhomocysteinemia was detected in eight of the 39 patients tested.

CONCLUSION

MPNs are an important thrombotic risk factor in Chinese patients with PVT. However, the extreme rarity of paroxysmal nocturnal hemoglobinuria, anticardiolipin IgG antibodies, and factor V G1691A and factor II G20210A mutations has precluded any support for the implementation of routine screening for these thrombotic factors in such patients. Additional case-control studies should confirm the role of the MTHFR C677T mutation and hyperhomocysteinemia in the pathogenesis of PVT.

Acquired activated protein C resistance, thrombophilia and adverse pregnancy outcomes: a study performed in an Irish cohort of pregnant women

The combination of thrombophilia and pregnancy increases the risk of thrombosis and the potential for adverse outcomes during pregnancy. The most significant common inherited risk factor for thrombophilia is activated protein C resistance (APCR), a poor anticoagulant response of APC in haemostasis, which is mainly caused by an inherited single-nucleotide polymorphism (SNP), factor V G1691A (FV Leiden) (FVL), referred as inherited APCR. Changes in the levels of coagulation factors: FV, FVIII, and FIX, and anticoagulant factors: protein S (PS) and protein C (PC) can alter APC function causing acquired APCR. Prothrombin G20210A and methylenetetrahydrofolate reductase (MTHFR) C677T are prothrombotic SNPs which in association with APCR can also increase the risk of thrombosis amongst Caucasians. In this study, a correlation between an acquired APCR phenotype and increased levels of factors V, VIII, and IX was demonstrated. Thrombophilic mutations amongst our acquired APCR pregnant women cohort are relatively common but do not appear to exert a severe undue adverse effect on pregnancy.

The Role of Factor V Leiden in Adult Patients With Venous Thromboembolism: A Meta-Analysis of Published Studies from Turkey

Factor V Leiden (FVL) is the most common inherited risk factor for venous thromboembolism (VTE). The frequency of FVL in patients with VTE has been reported from different parts of Turkey. A meta-analysis was performed to estimate the risk of VTE associated with FVL in Turkish population. Published studies were retrieved from Pubmed and Science Citation Index/Expanded. We selected studies comparing the prevalence of FVL in patients with VTE with controls. The analysis was performed by the software comprehensive meta-analysis. The analysis consisted of 10 studies including 1202 patients with VTE and 1283 controls. The pooled frequency of FVL was significantly higher in patients with VTE (22.8%) than controls (7.6%). The pooled odds ratio (OR) was 3.4 (95% confidence interval [CI], 2.6-4.5). The study showed homogeneity ( Q value, 9.955). No publication bias was observed in any comparison model. Our meta-analysis showed an association of FVL with VTE in Turkey.

Antithrombin Cambridge II(A384S) mutation frequency and antithrombin activity levels in 120 of deep venous thrombosis and 150 of cerebral infarction patients in a single center in Southern China

Antithrombin Cambridge II(A384S) mutation shows a relatively high frequency in western population. Some studies suggest that the mutation is an independent genetic risk factor both for deep vein thrombosis (DVT) and for arterial thrombosis, but whether the mutation has racial difference or has a general significance for thrombophilia remains unclear. In this study we performed an analysis of the prevalence of the mutation in Chinese southern population; Also, the antithrombin activity levels were evaluated in each investigated individual. The studies included 120 patients with DVT, 150 patients with cerebral infarction, and 110 controls. The mutation was detected using polymerase chain reaction/PvuII restrictive fragment length polymorphism procedures. Antithrombin activity assay was done using chromogenic substrate method. The results showed that no antithrombin Cambridge II mutation was detected in all three groups (DVT, cerebral infarction and controls), the incidence was 0/380. Plasma antithrombin activity was 91.37% +/- 16.15% in the DVT patients and 102.68% +/- 13.10% in the controls; the antithrombin activity was significantly reduced in the DVT group (P < 0.0001). In DVT patients, eight cases were identified as primary antithrombin deficiency, accounting for an incidence of 6.7%. No significant difference was found for antithrombin activity between cerebral infarction group and controls. These results suggest that antithrombin Cambridge II mutation has a racial difference, and may not be a valuable risk factor of thrombophilia in Asian population, and antithrombin deficiency remains a major genetic risk factor for DVT patients in China.

APCR, factor V gene known and novel SNPs and adverse pregnancy outcomes in an Irish cohort of pregnant women

Background

Activated Protein C Resistance (APCR), a poor anticoagulant response of APC in haemostasis, is the commonest heritable thrombophilia. Adverse outcomes during pregnancy have been linked to APCR. This study determined the frequency of APCR, factor V gene known and novel SNPs and adverse outcomes in a group of pregnant women.

Methods

Blood samples collected from 907 pregnant women were tested using the Coatest^® Classic and Modified functional haematological tests to establish the frequency of APCR. PCR-Restriction Enzyme Analysis (PCR-REA), PCR-DNA probe hybridisation analysis and DNA sequencing were used for molecular screening of known mutations in the factor V gene in subjects determined to have APCR based on the Coatest^® Classic and/or Modified functional haematological tests. Glycosylase Mediated Polymorphism Detection (GMPD), a SNP screening technique and DNA sequencing, were used to identify SNPs in the factor V gene of 5 APCR subjects.

Results

Sixteen percent of the study group had an APCR phenotype. Factor V Leiden (FVL), FV Cambridge, and haplotype (H) R2 alleles were identified in this group. Thirty-three SNPs; 9 silent SNPs and 24 missense SNPs, of which 20 SNPs were novel, were identified in the 5 APCR subjects. Adverse pregnancy outcomes were found at a frequency of 35% in the group with APCR based on Classic Coatest^® test only and at 45% in the group with APCR based on the Modified Coatest^® test. Forty-eight percent of subjects with FVL had adverse outcomes while in the group of subjects with no FVL, adverse outcomes occurred at a frequency of 37%.

Conclusions

Known mutations and novel SNPs in the factor V gene were identified in the study cohort determined to have APCR in pregnancy. Further studies are required to investigate the contribution of these novel SNPs to the APCR phenotype. Adverse outcomes including early pregnancy loss (EPL), preeclampsia (PET) and intrauterine growth restriction (IGUR) were not significantly more frequent in subjects with APCR compared to normal pregnant women however Pregnancy induced hypertension (PIH) was found to be associated with FVL in our study group.

Ethnic differences in coagulation factor abnormalities after the Fontan procedure

We tested the hypothesis that Chinese patients have a coagulation profile that is less prothrombotic than that of Caucasian counterparts after the Fontan procedure by determining the type and prevalence of anticoagulant and procoagulant deficiencies in Chinese patients and comparing the findings to those previously reported in Caucasian series. The liver function and coagulation factors were assessed in 21 ethnic Chinese patients, aged 17.0 +/- 5.6 years, at 10.7 +/- 4.0 years after the Fontan procedure. The results were compared to those of 21 age-matched Chinese controls with minor congenital heart disease. The prevalence of coagulation factor deficiencies in our patients was further compared to that reported in Caucasian patients. When compared with controls, patients had significantly lower protein C (p = 0.014), factors II (p = 0.024), V (p < 0.001), VII (p < 0.001), IX (p = 0.036), and X (p < 0.001), and higher bilirubin (p = 0.001) levels. The prevalence of protein C deficiency was 9.5%, whereas those of factor II, V, VII, IX, and X deficiencies were 0, 66.7, 9.5, 0, and 57.1%, respectively. When compared with Caucasian data, our data showed a significantly lower prevalence of protein C, total protein S, antithorombin III, factor II, and factor VII deficiencies. Furthermore, the previously reported increase in factor VIII levels was not found. In contrast, the prevalence of factor X deficiency was higher in our patients. This study provides the first evidence of ethnic differences in coagulation factor abnormalities after the Fontan procedure. The imbalance between procoagulant and anticoagulant pathways in Chinese patients favors a bleeding, rather than a thrombotic, tendency.

Influence of methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism, B vitamins and other factors on plasma homocysteine and risk of thromboembolic disease in Chinese

BACKGROUND

Thromboembolic disease is a major cause of morbidity and mortality in many countries. Our previous study found that Chinese subjects carried the same polymorphism of the methylenetetrahydrofolate reductase (MTHFR) gene as described in Western studies. The aim of the present study was to determine the influence of MTHFR polymorphism, B vitamins and other factors on plasma homocysteine (Hcy) levels and risk of thromboembolic disease in Chinese.

METHODS

One hundred and six subjects were enrolled into the study. They were categorized into 4 groups: healthy individuals (n = 42); those with diabetes mellitus (n = 20); those with deep vein thrombosis (DVT) (n = 11); and those with coronary artery disease (CAD) (n = 33). Plasma levels of folic acid, vitamins B6 and B12, Hcy, and fasting blood sugar were measured; total cholesterol, triglycerides, complete blood count, and 677 C-->T mutation in MTHFR were determined.

RESULTS

Plasma Hcy was lowest in the healthy subjects, higher in diabetics, followed by patients with DVT, and highest in patients with CAD (p < 0.001, ANOVA). MTHFR C677T polymorphism was the common factor affecting plasma logHcy levels in all 4 groups of subjects. Triglycerides affected plasma logHcy in the CAD patients. For the 4 groups as a whole, MTHFR polymorphism, triglycerides, and vitamin B12 were the most significant factors influencing plasma Hcy.

CONCLUSION

We suggest that high plasma Hcy is an important risk factor for CAD. Other factors including MTHFR polymorphism, vitamin B12, triglycerides, total cholesterol, and gender might affect Hcy levels in different diseases and conditions.

Long-term anticoagulation therapy and thromboembolic complications after the Fontan procedure

BACKGROUND

The necessity for chronic anticoagulation of Fontan patients remains controversial. We determined the prevalence of thromboembolic complications after the Fontan procedure in relation to different long-term anticoagulation strategies.

METHODS

The clinical outcomes, postoperative anticoagulation strategies and occurrence of thromboembolic complications in 102 ethnic Chinese patients who had undergone Fontan procedure between 1980 and 2002 were reviewed.

RESULTS

The early and late surgical mortalities, all unrelated to thromboembolism, were 10.8% (11/102) and 5.8% (6/104), respectively. Of the 85 survivors, 46 (54%) were maintained on long-term warfarin therapy, 8 (9%) on aspirin prophylaxis while 31 (37%) were not on chronic anticoagulation. Four (4.5%) patients, two with and two without warfarin prophylaxis, developed thromboembolic complications at 0.14 to 7.7 years after the Fontan procedure (0.74%/patient-year). Three had a grossly dilated right atrium after atriopulmonary connection, two of whom had atrial fenestrations. The other had atrial tachycardia. Freedom from development of thromboembolic complications (mean+/-S.E.) at 1, 5 and 10 years after surgery was 97+/-19%, 96+/-2.5% and 92+/-4.2%, respectively. When compared with those on long-term warfarin therapy, patients without chronic anticoagulation were followed-up longer (p=0.001), more likely to have undergone atriopulmonary connection (p<0.001), less likely to have fenestrations (p=0.02) and cardiac arrhythmias (p=0.02) but not predisposed to increased risk of thromboembolism (p=1.00).

CONCLUSION

The study supports the contention that chronic anticoagulation may not be required for majority of ethnic Chinese Fontan patients. Nonetheless, it may perhaps be considered in those with grossly dilated right atrium, cardiac arrhythmias and residual right-to-left shunts.

Epidemiology of venous thromboembolism in a Chinese population

BACKGROUND

Deep vein thrombosis (DVT) is uncommon in Asians and routine thromboprophylaxis for surgery is controversial. Despite recent reports of higher incidences in some Asian countries, population-based data are lacking.

METHODS

Information from 2000 to 2001 was retrieved from a centralized computer public healthcare database serving an ethnic Chinese population of 6.7 million. The incidence, demographics and hospital mortality rates of DVT and pulmonary embolism (PE) were obtained, and analysed for different surgical categories.

RESULTS

The overall annual incidences of DVT and PE were 17.1 and 3.9 per 100000 population respectively. Venous thromboembolic disease was more common with increasing age in both sexes. The annual age-specific incidences of DVT and PE were 81.1 and 18.6 per 100000 for those aged 65 years and over. Hospital mortality rates associated with DVT and PE were 7.3 and 23.8 per cent respectively. Among 120940 surgical operations a year, the mean incidence of postoperative DVT and PE was only 0.13 and 0.04 per cent respectively. No high-risk surgical group was identified.

CONCLUSION

Venous thromboembolism is not as common in Chinese as in Caucasians, but it is certainly not rare. The majority of DVTs and PEs, however, were not associated with surgery, so routine thromboprophylaxis may not be required.

The incidence of proximal deep vein thrombosis following total knee arthroplasty in an Asian population: a Doppler ultrasound study

PURPOSE

To investigate the incidence of deep vein thrombosis (DVT) following total knee arthroplasty in an Asian population.

METHODS

A prospective study of 149 consecutive cases of total knee arthroplasty done for osteoarthritis was conducted over a 5-year period. All patients underwent duplex ultrasonographic assessment of the lower limbs within the first postoperative week.

RESULTS

The incidence of proximal DVT was found to be 4.38% in this study. Symptomology was statistically significant in predicting the presence of proximal DVT in all cases. General anaesthesia was associated with a statistically significant-higher incidence of DVT as compared with regional anaesthesia. There was a significant association between a sedentary lifestyle and the development of DVT.

CONCLUSION

The incidence of proximal DVT in Asian patients after total knee arthroplasty is higher than that previously reported for this demographic group.

Activated protein C resistance, the factor V Leiden mutation, and a laboratory testing algorithm

OBJECTIVES

To present the current understanding of factor V Leiden and activated protein C resistance, and to propose a laboratory testing algorithm.

DATA SOURCES

Publications on MEDLINE with the terms factor V Leiden or activated protein C resistance through mid 2001, as well as publications in the authors' files, were screened for inclusion in this report.

STUDY SELECTION

Original studies that report a novel finding on testing or clinical features of activated protein C resistance or factor V Leiden are included. Data Extraction.-The novel or key findings from the selected studies are analyzed.

DATA SYNTHESIS

Protein C and protein S are the integral components of an anticoagulation pathway that limits fibrinogen conversion to fibrin through the degradation of factors Va and VIIIa. When factor Va is resistant to degradation by activated protein C, this anticoagulation pathway does not operate properly, and patients have an increased risk for thrombosis. This report describes the protein C/protein S pathway, the significance of activated protein C resistance and the factor V Leiden mutation, and the clinical testing used to detect activated protein C resistance and the factor V Leiden mutation. A proposed laboratory testing algorithm is also provided.

CONCLUSIONS

Factor V Leiden is a risk factor for venous thrombosis and it is particularly common in white populations. A laboratory testing algorithm is proposed.

Retinal vein occlusion and factor V Leiden and prothrombin 20210 G:A mutations

PURPOSE

The aim of this study was to establish whether the factor V Leiden mutation and the prothrombin 20210 G:A mutation were risk factors for retinal vein occlusion.

METHODS

Blood samples were obtained from 40 patients with retinal vein occlusion and from 50 healthy normal volunteers as controls. Polymerase chain reaction assays were done to detect factor V Leiden and prothrombin 20210 G:A mutations, and the two groups were compared.

RESULTS

Two (5%) of 40 patients with retinal vein occlusion and three (6%) of 50 controls were heterozygous for factor V Leiden (p=0.84). None of the individuals in either group had the prothrombin 20210 G:A mutation.

CONCLUSIONS

There was no significant association between retinal vein occlusion and the factor V Leiden mutation.

Causes of venous thrombosis in fifty Chinese patients

In a whole year from July 1997 to June 1998, a total of 50 patients with sonogram-proved venous thrombosis who called on our hematology clinic consecutively entered into the study. Their mean age was 59.1 +/- 17.5 years, range 18-83 years, and 29 were male. A series of examinations were performed in order to find out the cause of venous thrombosis. These examinations included antithrombin, protein C, protein S, plasminogen, heparin cofactor II, activated protein C ratio, factor V Leiden mutation, fibrinogen, factors VIII and XII, euglobulin lysis time, 677 C-->T mutation of methylenetetrahydrofolate reductase (MTHFR), prothrombin 20210 (PT 20210) A allele mutation, lupus anticoagulant, anticardiolipin antibody, and complete blood count. Five patients (10%) were found to have malignancy; an inferior vena cava thrombosis in one patient was due to venous compression by hydronephrosis; two patients had lupus anticoagulant; two had varicose veins of legs; two had protein C deficiency; four had protein S deficiency; two had plasminogen deficiency; two had antithrombin deficiency. No activated protein C resistance, elevated factor VIII level, factor V Leiden, PT 20210 A allele or heparin cofactor II deficiency was found in the present study. Homozygous MTHFR 677 C-->T gene mutation was found in 7 patients (14%); one of them also had a plasminogen deficiency. No possible risk factor of venous thrombosis could be found in 24 patients (48%). In conclusion, malignancy and protein S deficiency were the most frequent acquired and congenital causes of venous thrombosis in the Chinese, respectively.

Thrombophilia-associated pregnancy wastage

OBJECTIVE

To critically review the literature regarding inherited thrombophilia and recurrent fetal loss.

DESIGN

English-language literature review.

PATIENT(S)

Women who experienced repeated pregnancy wastage.

INTERVENTION(S)

Aspirin, glucocorticoids, heparin, and IV immunoglobulin for the prevention of miscarriage.

MAIN OUTCOME MEASURE(S)

Live birth, miscarriage, preeclampsia, and pregnancy loss.

RESULT(S)

Recurrent fetal loss and other placental vascular pathologies of pregnancy have long been associated with antiphospholipid syndrome, an acquired autoimmune thrombophilic state. The number of known heritable thrombophilic disorders has grown rapidly in recent years with the identification of activated protein C resistance, factor V Leiden mutation, and hyperhomocysteinemia as major causes of thrombosis. Data accumulated over the past 2 years suggest that heritable thrombophilia is associated with an increased risk of fetal loss and preeclampsia. The present review discusses potential pathogenetic mechanisms for this association and evaluates reported therapeutic regimens for the prevention of fetal loss in women with thrombophilia.

CONCLUSION(S)

Placental thrombosis may be the final common pathophysiologic pathway in most women with habitual abortions and repeated pregnancy wastage. Prophylactic antithrombotic therapy is indicated in women with heritable thrombophilia and antiphospholipid syndrome and probably is more effective than the previously used modalities of prednisone, aspirin, and IV immunoglobulin.

Retinal vascular occlusion and deficiencies in the protein C pathway

PURPOSE

To report abnormalities in the protein C pathway and other vascular occlusion risk factors in patients with retinal vascular occlusion.

METHODS

In a study, we investigated 76 consecutive patients who had in-patient evaluation of venous or arterial retinal vascular occlusion. All patients underwent comprehensive tests for coagulation disorders including determinations of protein C, protein S, lupus anticoagulants, and resistance to activated protein C and were screened for vascular disease risk factors. Resistance to activated protein C was confirmed by a polymerase chain reaction method to detect the specific factor V R506Q mutation. For comparative purposes, we also screened 209 consecutive inpatients with deep vein thrombosis from the same geographic region for resistance to activated protein C as well as protein C and protein S deficiencies.

RESULTS

Ten (29%) of 35 patients with central retinal vein occlusion (CRVO) had factor V R506Q mutation. The factor V R506Q mutation was detected in four (19%) of 21 patients with branch retinal vein occlusion. The higher frequency in factor V R506Q mutation compared with the expected 9% mutation prevalence in a white population was highly significant for the central retinal vein occlusion group but not for the branch retinal vein occlusion group. In all patients with resistance to activated protein C, the factor V R506Q mutation was detected; 16 were heterozygous, one homozygous. No cases of lupus anticoagulants, protein C, or protein S deficiencies were detected. Forty (19%) of 209 patients with deep vein thrombosis were carriers of the factor V R506Q mutation.

CONCLUSIONS

The prevalence of the factor V R506Q mutation is similar in patients with central retinal vein occlusion and patients with deep vein thrombosis and represents a relevant risk factor. Screening for this mutation is therefore recommended in all patients with central retinal vein occlusion.

Laboratory evaluation of hypercoagulable states

The number of well-characterized hereditary and acquired hypercoagulable conditions is increasing, such that in many thrombophilic patients, the laboratory can now identify a hypercoagulable condition. This review describes the currently known hypercoagulable states that predispose patients to venous, and in some instances, arterial thrombosis. For each condition, the discussion includes the incidence, magnitude of the thrombotic risk in the general population in comparison with symptomatic families, synergistic interactions among the various hypercoagulable conditions, molecular pathogenesis, and interpretation of laboratory test results. In addition, recommendations for laboratory testing are summarized.

A Novel Mutation of Arg306 of Factor V Gene in Hong Kong Chinese

We have analyzed 83 unrelated Hong Kong Chinese for the presence of genetic variants of factor V gene. Forty-three of them had a history of deep vein thrombosis. The DNA sequence variations of exons 7, 10, and 13, where the codons for Arg306, Arg506, and Arg679 are located, respectively, were studied by denaturing gradient gel electrophoresis. The G1691→A (Arg 506→Gln) mutation in exon 10 was not detectable in any of the 83 subjects. However, a high allelic frequency for the G1628→A (Arg 485→Lys) substitution was detectable in the same exon. We have also identified a novel DNA sequence mutation (A1090→G) in exon 7 that resulted in Arg 306→Gly substitution in 2 thrombotic patients and 1 nonthrombotic subject. Fresh blood samples were available from one of them for analysis of activated protein C resistance and the result was negative. Variation of DNA sequence was not found in exon 13 in any of our 83 subjects. The results of this study showed that, although the Arg 506→Gln mutation was rarely found in the Hong Kong Chinese population, a different mutation site such as A 1090→G in exon 7 of the factor V gene (Arg 306) may be of clinical importance.

Prevalence of activated protein C resistance in the Chinese population

In 1996, a total of 1700 subjects, including 461 healthy subjects and 1239 clinic patients, were randomized and consecutively entered into our study. Their mean age was 49.30+/-18.71 years, range 1-99 years. Of them, 1117 were male, and 583 were female. The mean age of the male was 42.96+/-17.64 years, and of the female, 52.60+/-18.41 years. The mean activated protein C ratio in 1700 subjects was 2.96+/-0.69, range 2.00-7.93. None of them had activated protein C ratio <2.0. The mean activated protein C ratio in the male was 2.81+/-0.63, and in the female was 3.04+/-0.71. None of the subjects was found to have activated protein C resistance. DNA analysis for the Arg 506-Gln mutation was also performed on 492 out of the 1700 subjects; none of them had this mutation. We suggested that the Chinese is not a race with the trait of activated protein C resistance.

Molecular Genetics of Factor V Leiden: Genetic Origins and Modern DNA-Based Detection Strategies

It has been acknowledged that a prothrombotic tendency may result from a specific genetic defect. Resistance to activated protein C (APC) (factor V Leiden) is now recognized as the most prevalent cause of increased thrombogenicity, being found in 2% to 5% of the world population. The APC-resistant phenotype arises from a well-characterized transitional mutation, resulting in an arginine(R)-506-glutamine(Q) amino acid substitution. Much remains to be uncovered concerning the importance of this mutation and how it relates to other conditions on a broader basis. Relevant and accurate detection methods that quickly identify the genetic lesion will play a major part in this strategy. This article details recent advances in identifying the factor V Leiden mutation by modern molecular techniques.

Clinicopathological pattern of pulmonary thromboembolism in Chinese autopsy patients: comparison with Caucasian series

The clinicopathological data of adult Chinese patients identified to have 'significant pulmonary thromboembolism (PTE)' at autopsy in Queen Mary Hospital (QMH) Hong Kong, from 1990 to 1994 inclusive, were analysed retrospectively. The prevalence of PTE was documented and data were compared with published series of Caucasian patients. The parameters studied included sex-age distribution, associated diseases, symptomatology, site of venous thrombosis, duration of admission and intervals between surgery and death. The rate of PTE was 4.7% (4.5% in males and 5.2% in females). The mean age of PTE patients was significantly higher than that of non-PTE patients (p < 0.001). Two clinicopathological features worthy of note are: (1) as in Caucasian patients, most Chinese patients with 'significant PTE' do not present with leg symptoms although many of them are found to have deep vein thrombosis (DVT) at postmortem; and (2) DVT in these patients is found in the calf veins rather than in the more proximal deep veins. The recently identified racial differences in hemostasis that may contribute to the differences between Chinese and Caucasian people are discussed.

A Single Genetic Origin for a Common Caucasian Risk Factor for Venous Thrombosis

A common genetic risk factor for venous thrombosis among Caucasoid subpopulations is a polymorphism, nt G1691A, in blood coagulation factor V that replaces Arg506 with Gln and imparts resistance of factor Va to the anticoagulant, activated protein C. Haplotype analyses using six dimorphic sites in the factor V gene for 117 Caucasian subjects of Jewish, Arab, Austrian, and French origin who were homozygous for nt A1691 compared with 167 controls (nt G1691) support a single origin for this polymorphism. The nt G1691A mutation is estimated to have arisen circa 21,000 to 34,000 years ago, ie, after the evolutionary divergence of Africans from non-Africans and of Caucasoid from Mongoloid subpopulations.