Single nucleotide polymorphisms and the risk of venous thrombosis: results from a Danish case‐cohort study

A number of single nucleotide polymorphisms (SNP) have been linked to higher risk of venous thromboembolism (VTE). We investigated the VTE risk associated with SNPs in the GP6 (rs1613662), SERPINC1 (rs2227589), F11 (rs2036914 and rs2289252), FGG (rs2066865), and F12 (rs1801020) genes. In F11, the CC genotype for rs2036914 and the CT and TT genotypes for rs2289252 were associated with a significantly higher VTE risk. A trend toward a thrombogenic effect was observed for the risk alleles of the GP6 and FGG SNPs. Risk estimates were unaffected by adjustments for blood type and F5 rs6025 (Factor V Leiden) mutation.     

High factor VIII antigen levels increase the risk of venous thrombosis but are not associated with polymorphisms in the von Willebrand factor and factor VIII gene

High factor VIII levels increase the risk of venous thromboembolism, but the mechanisms that cause high factor VIII levels are unclear. In 301 thrombosis patients and 301 matched healthy controls, factor VIII antigen (VIII:Ag) levels > or = 150 IU/dl increased the thrombosis risk more than fivefold. We investigated whether high factor VIII:Ag levels result from a genetic variation in the factor VIII or von Willebrand factor (VWF) genes. Six polymorphisms in the VWF gene and two CA-repeats in the factor VIII gene were not associated with plasma VWF levels, factor VIII:Ag levels, or thrombosis risk. Our data do not support the hypothesis that a single functional sequence variation in the factor VIII or VWF gene explains the majority of high factor VIII levels and thrombotic risk.     

Protein C inhibitor (plasminogen activator inhibitor-3) and the risk of venous thrombosis

Protein C inhibitor (PCI), also known as plasminogen activator inhibitor-3, is a serine proteinase inhibitor that can inhibit enzymes in blood coagulation, fibrinolysis and fertility. The role of PCI in regulating the blood coagulation mechanism is not known, as it can inhibit both procoagulant (thrombin, factor Xa, factor XIa) and anticoagulant (activated protein C, thrombin-thrombomodulin, urokinase) enzymes. To determine the relevance of this inhibitor in thrombosis, PCI levels were assessed in the Leiden Thrombophilia Study, a case-control study of venous thrombosis in 473 patients with a first deep-vein thrombosis and 474 age- and sex-matched control subjects. PCI levels above the 95th percentile of the controls (136.1%) increased the risk 1.6-fold compared with PCI levels below the 95th percentile (95% confidence interval 0.9-2.8). There was a gradual increase in risk of thrombosis with further increasing levels of PCI. Adjustment for a number of possible confounders led to a reduction of the risk estimates associated with PCI. However, it is unclear whether adjustment for such factors in the risk models is justified. These results indicate that high levels of PCI may constitute a mild risk factor for venous thrombosis.     

Interleukin 8 and venous thrombosis: evidence for a role of inflammation in thrombosis

Elevated plasma levels of interleukin 8 (IL-8) were previously shown to be associated with recurrent venous thrombosis. To assess the risk of venous thrombosis, IL-8 plasma concentrations were measured in patients and control subjects of the Leiden Thrombophilia Study (LETS). This population based case-control study included 474 patients with a first deep-vein thrombosis and 474 age- and sex-matched controls. The risk of venous thrombosis for subjects with elevated IL-8 levels (above 90th percentile of controls) compared with subjects with IL-8 levels below the 90th percentile was increased 1.8-fold (95%CI 1.2-2.8). Adjusted for age and sex, the odds ratio was 1.9 (95%CI 1.3-2.8). IL-8 concentrations were weakly correlated with age, male sex, and concentrations of C-reactive protein, factor VIII coagulation activity and homocysteine, but adjustment for these factors did not substantially affect the association between IL-8 and venous thrombosis. Our results suggest that IL-8 is a risk factor for venous thrombosis.     

Cumulative flying time and risk of venous thromboembolism

The risk of venous thromboembolism (VTE) associated with cumulative flying time remains uncertain. In a case-control study in general practices throughout the UK, participants comprised 550 VTE cases identified from practice records and 1971 age- and gender-matched controls. Participants returned identical questionnaires asking for information including air travel details. Compared to not flying, cumulative flying time >12 h within the previous 4 weeks was associated with a threefold increase in the risk of VTE [odds ratio (OR) 2·75, 95% confidence interval (CI), 1·44-5·28]. Those who had flown >4 h in a single leg in the previous 4 weeks had twice the risk of VTE (OR 2·20, 95% CI, 1·29-3·73). These risks were no longer evident by 12 weeks and were similar to those of day-case or minor surgery (OR 5·35, 95% CI, 2·15-13·33). Equivalent risks for moderate and high-risk surgery were over 30-fold (OR 36·57, 95% CI, 13·05-102·52) and 140-fold (OR 141·71, 95% CI, 19·38-1036·01) respectively. The temporary nature of the association of cumulative and long-haul air travel with VTE suggests a causal relationship. The risks of VTE in those with a higher baseline risk due to surgery, previous VTE or obesity are further increased by air travel.     

Clinical features of venous insufficiency and the risk of venous thrombosis in older people

Venous thrombosis is common in older age, with an incidence of 0·5–1% per year in those aged >70 years. Stasis of blood flow is an important contributor to the development of thrombosis and may be due to venous insufficiency in the legs. The risk of thrombosis associated with clinical features of venous insufficiency, i.e., varicose veins, leg ulcers and leg oedema, obtained with a standardized interview was assessed in the Age and Thrombosis Acquired and Genetic risk factors in the Elderly (AT‐AGE) study. The AT‐AGE study is a case–control study in individuals aged 70 years and older (401 cases with a first‐time venous thrombosis and 431 control subjects). We calculated odds ratios (ORs) and corresponding 95% confidence intervals (CI) adjusted for age, sex and study centre. Varicose veins and leg ulcer were associated with a 1·6‐fold (95% CI 1·2–2·3) and 3·3‐fold increased risk of thrombosis (95% CI 1·6–6·7), respectively, while the risk was increased 3·0‐fold (95% CI 2·1–4·5) in the presence of leg oedema. The risk of thrombosis was highest when all three risk factors occurred simultaneously (OR: 10·5; 95% CI 1·3–86·1). In conclusion, clinical features of venous insufficiency, i.e., varicose veins, leg ulcers and leg oedema, are risk factors for venous thrombosis in older people.     

How I manage venous thromboembolism in pregnancy

In pregnancy, the combination of altered coagulation factors, stasis and vascular damage heightens the thrombotic risk and venous thromboembolism (VTE) is a major cause of maternal morbidity and mortality. In women presenting with pregnancy-related VTE, the wellbeing of both mother and fetus must be considered, necessitating a multidisciplinary approach. The risk of VTE is present throughout the pregnancy and is maximal during the postpartum period. Diagnosis may be difficult because the symptoms might mimic those of pregnancy and prospectively validated diagnostic protocols are lacking. Compression ultrasound is the test of choice for deep vein thrombosis and perfusion scan and computerized tomography pulmonary angiography are the imaging options for diagnosis of pulmonary embolism. Low molecular weight heparin does not cross the placenta and is a safe and effective treatment for the majority of cases of pregnancy-related VTE. This review provides a practical approach to diagnosis and treatment of VTE in pregnancy.     

The risk of pregnancy-related venous thromboembolism in women who are homozygous for factor V Leiden

The risk of venous thromboembolism (VTE) is increased in pregnancy and during the post-partum period. The absolute risk for pregnancy-related VTE in heterozygous women with the factor V Leiden mutation is approximately 2%, but studies on this risk for homozygous women show conflicting results. In a retrospective family study, we found that the risk of pregnancy-related VTE in women with a symptomatic first-degree relative was 17% per pregnancy (95%CI 4.7-37.4). Anticoagulant prophylaxis during the post-partum period appears to be indicated in asymptomatic homozygous women from symptomatic kindred, whereas this could be decided on an individual basis during pregnancy.     

Elevated factor VIII levels and risk of venous thrombosis

Modern thrombophilia testing fails to identify any underlying prothrombotic tendency in a significant number of patients presenting with objectively confirmed venous thromboemboembolism (VTE). This observation has led to a search for other novel inherited or acquired human thrombophilias. Although a number of putative mechanisms have been described, the evidence behind many of these candidates remains weak. In contrast, an increasing body of work supports the hypothesis that increased plasma factor VIII (FVIII) levels may be important in this context. An association between elevated plasma FVIII levels and VTE was first described in the Leiden Thrombophilia Study (LETS). Subsequently, these conclusions have been supported by an increasing number of independent case-control studies. Cumulatively, these studies have clearly demonstrated that high FVIII levels constitute a prevalent, dose-dependent risk factor for VTE. Furthermore, more recent studies have shown that the risk of recurrent venous thrombosis is also significantly increased in patients with high FVIII levels. In this review, we present the evidence supporting the hypothesis that elevated FVIII levels constitute a clinically important thrombophilia. In addition, we examine the biological mechanisms that may underlie persistently elevated FVIII levels, and the pathways through which high FVIII may serve to increase thrombotic risk.     

Inferior vena cava malformation as a risk factor for deep venous thrombosis in the young

Conditions which result in hypercoagulable blood or venous stasis may predispose to the development of deep vein thrombosis (DVT). Most of the recently described risk factors for DVT induce a hypercoagulable state. Over a 3-year period we have observed anomaly of the inferior vena cava (IVC) in four young patients presenting with spontaneous unprovoked DVT. This is a greater than expected rate (5% observed versus 0.5% expected). Further, bilateral DVT, which constitutes less than 10% of cases in most series, was present in three of the four cases. Anomaly of the IVC is a rare example of a prevalent congenital condition that predisposes to DVT, presumably by favouring venous stasis. This diagnosis should be considered in young patients with spontaneous and bilateral DVT.     

Deep venous thrombosis and previous myocardial infarction in mild factor XII deficiency: a risk factor for both venous and arterial thrombosis

Factor XII deficiency is associated with increased risk for both arterial and venous thrombosis. We describe a case of DVT involving superficial femoral and popliteal vein occurred following total hip replacement and despite prophylaxis with low molecular weight heparin in a subject with previous acute myocardial infarction (AMI). Tests of haemostasis documented a slightly prolonged activated partial thromboplastin time (APTT) (45′′) due to mild factor XII deficiency (clotting activity 32%). A therapeutic dose of enoxaparin was started, together with warfarin therapy. The patient was advised to continue oral anticoagulation indefinitely. Although cases of both venous and arterial thrombosis in carriers of severe factor XII deficiency have been already reported, to our knowledge this is the first case in the literature occurred in a carrier of partial factor XII deficiency. In conclusion, factor XII deficiency should be suspected if a patient presents with recurrent arterial and/or venous thrombosis and prolonged APTT. If this defect is diagnosed, in the presence of a history of thrombotic events, lifelong anticoagulation could be considered.     

High risk of pregnancy-related venous thromboembolism in women with multiple thrombophilic defects

Pregnancy is associated with an increased risk of venous thromboembolism, which probably varies according to the presence of single or multiple thrombophilic defects. This retrospective family cohort study assessed the risk of venous thromboembolism during pregnancy and puerperium, and the contribution of concomitant thrombophilic defects in families with hereditary antithrombin, protein C or protein S deficiencies. Probands were excluded. Of 222 female relatives, 101 were deficient and 121 non-deficient. Annual incidences of venous thromboembolism were 1.76% in deficient women versus 0.19% in non-deficient women [adjusted relative risk (RR) 11.9; 95% confidence interval (CI), 3.9-36.2]. Other single and multiple thrombophilic defects increased the risk in deficient women from 1.55% to 2.14% and 2.92%, and in non-deficient women from 0.16% to 0.09% and 0.54% respectively. Deficient women were at lower risk (1.37%; 0.80-2.19) than deficient women that had never been pregnant (2.96%; 1.53-5.18); RR 0.5 (0.2-0.99). This difference was due to the predominance of events related to oral contraceptives in deficient women that had never been pregnant (75%), while 71% of events in deficient women that had had at least one pregnancy were pregnancy-related. In conclusion, women with hereditary deficiencies of antithrombin, protein C or protein S are at high risk of pregnancy-related venous thromboembolism. This risk is increased by multiple additional thrombophilic defects.     

Risk factors for venous thrombosis – current understanding from an epidemiological point of view

Epidemiological research throughout the last 50 years has provided the long list of risk factors for venous thrombosis that are known today. Although this has advanced our current understanding about the aetiology of thrombosis, it does not give us all the answers: many people have several of these risk factors but never develop thrombosis; others suffer from thrombosis but have none. In this review, we discuss how risk factors for venous thrombosis can be interpreted with use of several epidemiological models. We comment on how to explain why risk factors for first venous thrombosis differ from recurrent venous thrombosis, and use a causal model to better understand risk of first and recurrent venous thrombosis.     

IL-10单核苷酸多态性与溃疡性结肠炎的相关性研究

目的探讨血清IL-10水平、IL-10启动子区3个位点(IL-10-1082/-819/-592)的单核苷酸多态性(SNPs)与溃疡性结肠炎之间的相关性。方法选择溃疡性结肠炎患者60例(溃疡性结肠炎组),轻度24例、中—重度36例,并设健康对照组。采用ELISA法检测血清中IL-10,采用PCR-RFLP检测IL-10启动子区SNPs。结果中—重度溃疡性结肠炎患者血清IL-10水平低于健康对照组(P<0.05)。溃疡性结肠炎组IL-10-592位点AA型及AC型-819位点TT型和TC型与健康对照组比较有统计学差异(P均<0.05);两组IL-10-592位点CC型及IL-10-819位点CC型比较差异有统计学意义(P均<0.05);-592位点和-819位点基因型高度连锁。两组IL-10-1082位点AA型及GG型比较有统计学意义(P均<0.05)。结论 IL-10启动子区SNPs影响IL-10表达。血清IL-10的表达水平及其启动子区的不同基因型可反映溃疡性结肠炎的发病敏感性或活动度。     

Pseudohomozygosity for activated protein C resistance is a risk factor for venous thrombosis

Pseudohomozygosity for activated protein C resistance (APC-r) is a rare condition due to the association of heterozygous FV Leiden mutation and partial type I FV deficiency. To assess the risk of venous thromboembolism in these subjects, seven families including 11 pseudohomozygotes and 45 relatives were examined. Among the relatives, 16 were heterozygous FV Leiden carriers, nine showed partial FV deficiency and 20 no abnormalities. Deep vein thrombosis occurred in 4/11 (36.3%) pseudohomozygous patients versus 6/16 (37. 4%) FV Leiden carriers and 1/20 (5%) normal relatives. Pseudohomozygotes and FV Leiden carriers had a significantly increased risk of venous thrombosis in comparison to normal relatives (RR 8.8 and 5.7, respectively). There was no difference between the thrombotic risk of pseudohomozygous subjects and of FV Leiden carriers (RR 1.6, 95% CI 0.43-5.7). Furthermore, there was no difference in thrombosis-free survival between pseudohomozygotes and 45 consecutive FV Leiden heterozygous outpatients, suggesting that a referral bias may explain the apparent younger age of thrombosis in the pseudohomozygotes in comparison to relatives with FV Leiden heterozygosity (27 years v 54 years; P = 0.01). Pseudohomozygosity for APC resistance carries a significantly higher risk for venous thromboembolism in comparison to normal subjects, but probably not in comparison to heterozygous FV Leiden carriers.