Genetic susceptibility to venous thrombosis

[Duration of oral anticoagulant therapy in deep venous thrombosis of the lower limbs]

The optimal duration of oral anticoagulant therapy is a matter of debate. It is essential to balance the desired effect of the anticoagulants in reducing recurrences against the risk of major bleeding. Recent data suggest that it is necessary to tailor the duration of anticoagulation individually according to the topography of deep vein thrombosis (DVT) and the presence of risk factors. A six-week treatment for patients with isolated calf DVT is sufficient. For proximal DVT and/or pulmonary embolism, a short anticoagulant course seems sufficient in patients with temporary risk factors (three months) and a longer anticoagulant course (six months at least) is recommended for cases with permanent risk factors or idiopathic DVT. The inherited or acquired hypercoagulable states can be divides into those that are common and associated with a modest risk of recurrence (i.e. isolated factor V Leiden or G20210A prothrombin gene) and those are uncommon but associated with a high risk of recurrence (i.e. antithrombin, protein C or S deficiencies and anticardiolipin antibodies). Thus, the presence of one of these last abnormalities favours more prolonged anticoagulant therapy. For the high-risk of recurrence patients, there is a paucity of evidence based medicine particularly for patients with biological thrombophilia, and randomised controlled trials in this population are required. An assessment of low- or fixed-dose oral anticoagulation is also necessary in order to reduce the bleeding risk.

Evaluation of women with clinically suspected thrombotic thrombocytopenic purpura-hemolytic uremic syndrome during pregnancy

Thrombotic thrombocytopenic purpura-hemolytic uremic syndrome (TTP-HUS) is more common in women, and commonly occurs during pregnancy and the immediate postpartum period. An important clinical issue is the distinction of TTP-HUS from the more common obstetric complications, preeclampsia and HELLP syndrome (hemolysis, elevated liver function tests, low platelets). Clinical suspicion of TTP-HUS requires urgent intervention with plasma exchange treatment, a procedure with substantial risk, while preeclampsia and HELLP syndrome typically resolve spontaneously following delivery. Since clinical features of these syndromes can be similar, especially if preeclampsia becomes severe or if seizures (defining eclampsia) occur, the differential diagnosis may be arbitrary. This review addresses the evaluation and management of these syndromes and describes a clinical approach for determining when plasma exchange is appropriate.

Laboratory thrombophilias and venous thromboembolism

Inherited abnormalities of coagulation are increasingly recognized in patients with venous thromboembolism. Common causes of hypercoagulability, also known as thrombophilia, include factor V Leiden, the prothrombin gene mutation, hyperhomocysteinemia, and antiphospholipid antibodies. Thrombophilia should be suspected in patients who develop idiopathic venous thromboembolism at a young age, recurrent thrombosis, thromboses at unusual sites, recurrent unexplained pregnancy loss, or if there is a family history of thrombotic disorders. The most cost-effective approach is to initially screen for factor V Leiden, the prothrombin gene mutation, hyperhomocysteinemia, and antiphospholipid antibodies because these are the most common defects causing thrombophilia. Long-term anticoagulation is controversial but should be considered if unprovoked venous thromboembolism recurs.

[Coronary thrombosis on patient with the factor V Leiden mutation]

We report a documented observation of coronary thrombosis occurring in a 25-year-old patient with no risk factor, presenting a hereditary thrombophilia (facteur V Leiden) diagnosed a few months earlier in a context of venous thrombosis. This patient had a spread out anterior myocardial infarction with cardiac arrest due to a ventricular fibrillation; although he was quickly rescued by the mobile intensive Care Unit, the patient died 48 hours later, after cerebral anoxia. The mutation called factor V Leiden is a widely spread hereditary family thrombophilia (5 to 6% of the population) and is characterized by a resistance to activated C protein provoking a hypercoagulable state. The unexpected arterial thrombosis, very rare in that case, can be extremely serious and raises the question of a preventive medication such as antiplatelet agent or low-molecular-weight heparin as soon as the genetic abnormally has been proved to be symptomatic.

Protein S gene mutation in a young woman with type III protein S deficiency and venous thrombosis during pregnancy

BACKGROUND

We attempted to identify a gene defect in a young woman with type III protein S deficiency and venous thrombosis during pregnancy.

METHODS

Measurements of total and free PS antigen levels in plasma were carried out using an enzyme-linked immunosorbent assay. Plasma PS cofactor activity was determined by a clotting assay using activated factor V as the substrate. Genomic DNA prepared from peripheral blood was amplified by polymerase chain reaction (PCR) with PROS1-specific oligonucleotide primers. PCR products were sequenced on both strands using specific oligonucleotide primers.

RESULTS

Plasma PS cofactor activity was undetectable in every measurement at 36 weeks of gestation, as well as at 2 weeks and 4 months after delivery. Plasma total PS antigen levels were 70% and 67% at 2 weeks and 4 months after delivery, respectively. Free PS antigen level was 24% at 4 months after delivery. Of all exons analyzed, codon 295 of GGC in exon 10 was substituted for AGC. This missense mutation predicted an amino acid change of glycine to serine.

CONCLUSIONS

Measurements of total and free PS antigen levels along with PS activity indicated that this was a case of type III PS deficiency. DNA analysis identified a heterozygous missense mutation of codon 295 in the PS gene, substituting glycine for serine.

Management and outcome of pregnancy in women with thrombophylic disorders and past cerebrovascular events

OBJECTIVE

To evaluate the maternal and fetal outcome in a cohort of women undergoing a subsequent pregnancy after a previous cerebrovascular event in the presence of thrombophilia.

PATIENTS

Fifteen pregnancies were followed up in 12 women with past cerebrovascular events and thrombophilic disorders. The cerebrovascular events occurred during a previous pregnancy in five patients. Six patients had a bad obstetric history including intrauterine fetal death in four cases, early onset of severe preeclampsia in two cases and one infant that was small for gestational age. THE THROMBOPHILIC DISORDERS INCLUDED: anti-phospholipid syndrome, protein C, S or antithrombin III deficiencies, mutations of the methyltetrahydrofolate reductase (MTHFR). All patients received prophylactic treatment with low molecular weight heparin and low dose aspirin.

RESULTS

Thromboembolic complications occurred in four pregnancies. Postpartum complications occurred in one patient; deep vein thrombosis and pulmonary emboli after stopping anticoagulation treatment. No patient had long-term neurologic damage. All pregnancies except one resulted in live births. (mean gestational age at delivery 36 +/- 3. 7 weeks, mean birth weight 2656 +/- 811 g). The one remaining pregnancy was electively terminated. There was one neonatal death due to the complications of severe prematurity in a woman with severe HELLP syndrome.

CONCLUSION

This preliminary data suggests that women with a history of cerebrovascular events and thrombophilic disorders receiving prophylactic treatment, have a relatively favorable pregnancy outcome; however, they remain at significant risk during pregnancy. Further studies are necessary to determine the optimal prophylactic treatment.

Oral contraceptives and the risk of thrombosis and atherosclerosis

Oral contraceptives containing synthetic oestrogens have been used successfully as birth control for > 40 years and are currently prescribed to > 100 million women worldwide. Several new progestins have been introduced and the third generation of progestins has now been available for two decades. Oral contraceptives are prescribed over a prolonged period of time and therefore substantially impact on hormonal, metabolic and plasmatic functions. Oral contraceptives increase the risk for venous thrombosis and pulmonary embolism, particularly if associated with confounding factors, such as genetic predisposition, smoking, hypertension or obesity. The risk of developing coronary artery disease is also increased in users with cardiovascular risk factors. This article discusses mechanistic and clinical issues and reviews the need for novel approaches targeting the considerable side effects in order to reduce cardiovascular morbidity in women using oral contraceptives.

Inherited thrombophilia and stillbirth

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

Pharmacogenetics, pharmacogenomics, and cardiovascular therapeutics: the way forward

The completion of sequencing of the human genome will be the vanguard for numerous advances in medicine. The first discernible application is likely to occur in pharmacogenomics, a field focused on the influence of genetic differences on the variability in patients' response to medications. While an inherited basis for drug response has been recognized for some time, it is the confluence of molecular biology, high-throughput genotyping, and bioinformatics that has made it practical to study the genetic basis of variability to medications on a large scale. Pharmacogenomics may enable clinicians to prospectively identify patients most likely to derive benefit from a drug, with minimal likelihood of adverse events. This DNA-based approach to predicting clinical drug efficacy and toxicity would shift the current prescribing paradigm from its empirical nature to a more patient-specific model, ushering in a new era of personalized medicine. Polymorphisms in drug metabolizing enzymes, drug targets, and disease pathogenesis genes are associated with therapeutic effect to cardiovascular pharmacotherapy. Moreover, pharmacogenomics and functional genomics are expected to have a profound impact on the process of drug discovery and development. Finally, pharmacogenomics is likely to transform the way clinical trials are conducted by allowing for the selection of a more homogeneous study population, thereby reducing the size and cost of clinical investigation.

Update on selected inherited venous thrombotic disorders

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

Pathophysiology of venous thromboembolism

Venous thromboembolism remains an important cause of morbidity and mortality for surgical and non-surgical patients, and its pathophysiology in acutely ill, non-surgical patients is not well understood. The clinically silent nature of thromboembolism makes it a significant threat to hospital patients.

[Duration of oral anticoagulant therapy in venous thromboembolism]

PURPOSE

The optimal duration of oral anticoagulant therapy after a first episode of venous thromboembolism is still a matter of debate. It is essential to balance the desired effect of the anticoagulants in reducing recurrences against the risk of major bleeding. The aims of this paper are to describe the current concepts in this field.

CURRENT KNOWLEDGE AND KEY POINTS

Recent data, based on randomised controlled trials, suggest that it is necessary to tailor the duration of anticoagulation individually according to the topography of venous thromboembolism and the presence of risk factors. A 6-week treatment for patients with isolated calf vein thrombosis is sufficient. For proximal thrombosis and/or pulmonary embolism, a short anticoagulant course seems sufficient in patients with temporary risk factors (3 months) and a longer anticoagulant course (6 months at least) is recommended for cases with permanent risk factors or idiopathic venous thromboembolism. The inherited or acquired hypercoagulable states can be divided into those that are common and associated with a modest risk of recurrence (i.e., isolated factor V Leiden or G20210A prothrombin gene) and those that are uncommon but associated with a high risk of recurrence (i.e., antithrombin, protein C or S deficiencies and anticardiolipin antibodies). Thus, the presence of one of these last abnormalities favours more prolonged anticoagulant therapy.

FUTURE PROSPECTS AND PROJECTS

1) For patients at high risk of recurrence, there is a paucity of evidence-based medicine, particularly for patients with biological thrombophilia, and randomised controlled trials in this population are required. An assessment of low- or fixed-dose oral anticoagulation is also necessary in order to reduce the bleeding risk. 2) It is not always possible to precisely determine the optimal duration with the available data. We have performed a meta-analysis on summary data which suggests that a long course of oral anticoagulant therapy is superior to a short course. An individual meta-analytic approach is needed to draw more precise conclusions on an interesting and important clinical topic and we propose to perform this analysis in a international collaborative group.

Using genetic variation to study human disease

The generation of a draft sequence of the human genome has spawned a unique opportunity to investigate the role of genetic variation in human diseases. The difference between any two human genomes has been estimated to be less than 0.1% overall, but still, this means that there are at least several million nucleotide differences per individual. The study of single nucleotide polymorphisms (SNPs), the most common type of variant, is likely to contribute substantially to deciphering genetic determinants of common and rare diseases. The effort to identify SNPs has been accelerated by three developments: the availability of sequence data from the genome project, improved informatic tools for searching the former and high-throughput genotype platforms. With these new tools in hand, dissecting the genetics of disease will rapidly move forward, although a number of formidable challenges will have to be met to see its promise realized in clinical medicine.

Factor V Leiden and prothrombin gene mutation in inflammatory bowel disease in a Mediterranean area

BACKGROUND

Thromboembolism has been reported to be associated with inflammatory bowel disease.

AIM

To evaluate the association of factor V Leiden and prothrombin gene mutation with inflammatory bowel disease in a population of patients with thromboembolic events and inflammatory bowel disease and in a control population of patients with inflammatory bowel disease without thromboembolic events.

PATIENTS AND METHODS

A series of 18 patients with inflammatory bowel disease and a history of arterial or venous thrombosis and 45 patients with inflammatory bowel disease without thromboembolic events were evaluated for the presence of factor V Leiden and prothrombin gene mutation. Frequency of gene mutation was compared with its occurrence in 100 healthy controls.

RESULTS

One patient with inflammatory bowel disease without thromboembolic events was heterozygous for factor V Leiden mutation. whereas no patient with a thromboembolic event had factor V Leiden mutation. No patients (either cases or controls) had prothrombin gene mutation. In the healthy population the frequency of factor V Leiden and prothrombin mutation was 5% and 2%, respectively.

CONCLUSIONS

Data emerging from the present study do not support any role of factor V Leiden and prothrombin gene mutation as the cause of thromboembolism in inflammatory bowel disease.

Extended outpatient therapy with low molecular weight heparin for the treatment of recurrent venous thromboembolism despite warfarin therapy

PURPOSE

The optimal management of patients who have recurrent thromboembolism while being treated with oral anticoagulation therapy is unknown. This study reports managing such patients with extended duration low molecular weight heparin therapy.

SUBJECTS AND METHODS

This study was a retrospective review of the prospective databases of three tertiary care teaching hospitals over a 27-month period. All patients who had recurrent symptomatic thromboembolism while being treated with warfarin were identified. All patients were treated with low molecular weight heparin (dalteparin), 200 U/kg daily. Data were collected for recurrent venous thromboembolism, bleeding, and survival.

RESULTS

Eight hundred eighty-seven patients were managed for acute thromboembolism. In 32 patients, symptomatic, objectively documented thromboembolism recurred while they were taking warfarin; 63% of the patients with recurrence had cancer, compared with 30% of patients without recurrence. All recurrences were treated with dalteparin. In 3 patients (9% [95% confidence interval: 2% to 25%]), symptomatic recurrence developed while they were being treated with low molecular weight heparin. Nineteen patients (59%) died while receiving anticoagulation therapy; all deaths but 1 were due to malignancy, and none was due to pulmonary embolism or bleeding.

CONCLUSIONS

These results suggest that recurrent venous thromboembolism is more likely to develop in cancer patients while being treated with warfarin and that long-term therapy with low molecular weight heparin may be effective in managing warfarin-failure thromboembolic disease.