Thrombophilia: disorders predisposing to venous thromboembolism

Activation of Protein C in Human Trophoblasts in Culture and Downregulation of Trophoblast Endothelial Protein C Receptor by TNF-α

In mice, trophoblasts are equipped with a potent anticoagulant mechanism, the protein C pathway. In human placenta, no functional studies of the protein C pathway are available. Human first-trimester trophoblasts (CK(++) HLA-G(+/-) Vim(-)) were isolated and kept in culture for a maximum of 48 hours. Activation of protein C on trophoblasts was at least as efficient as in endothelial cells (4.43 × 10 (-) (7) nmol/L/min/cell). Endothelial protein C receptor (EPCR) was expressed in syncytiotrophoblasts and extravillous trophoblasts. Downregulation of the messenger RNA of trophoblast EPCR occurred when trophoblasts were challenged with tumor necrosis factor α, and it could be prevented by unfractionated heparin but not by low-molecular-weight heparin at therapeutic doses. In conclusion, there is a functional protein C pathway on human first-trimester trophoblasts which can be modulated by inflammation. This finding has implications for the pathogenesis and prevention of placenta-mediated obstetric complications.

Thrombophilia in children with venous thromboembolic disease

Venous thromboembolic events (VTEs) in children are usually associated with underlying clinical conditions such as central venous line, cancer and cardiac diseases. The objective of this review is to present the importance of thrombophilia to the occurrence of childhood VTE. The reported prevalence of thrombophilia in children with VTE varies extremely between 10% and 78% in different registries. The variation in the reported prevalence most probably reflects differences in the clinical characteristics of the children studied and differences in study designs. The initial management of children with thrombophilia and VTE is similar to those individuals who do not have a specific inherited thrombophilic risk factor, except in the rare events of homozygous deficiencies of prothrombotic coagulation proteins. The impact of thrombophilic markers on long-term therapy and outcome of children with VTE has not been completely clarified. According to the current guidelines for thrombophilia, all children with VTE should be tested for a full panel of genetic and acquired prothrombotic traits. However, re-evaluation of co-morbid risk factors other than thrombophilic markers and careful consideration of the prognostic value of thrombophilic markers might help to change future attitude from the rigidity of current guidelines to more rational schemes.

Prothrombotic conditions in an unselected cohort of children with venous thromboembolic disease

Venous thromboembolic events (VTEs) in children are usually associated with underlying clinical conditions. The added contribution of prothrombotic conditions to the occurrence of VTEs in children is not clear. This study reports the prevalence of prothrombotic conditions in 171 consecutive children with VTE followed in the Hospital for Sick Children Thrombosis Outpatient Clinic. The median age of the children at the time of VTE was 2.3 months (range 1 day to 16.5 years). An underlying medical condition and a central venous line (CVL) were present in 156 (91%) and 132 (77%) of 171 children, respectively. A positive family history was present in 8% of children. The prevalence of factor V Leiden was 4.7%, prothrombin G20210A polymorphism was 2.3%, protein S deficiency was 1.2%, protein C deficiency was 0.6% and increased plasma lipoprotein (a) concentration (>30 mg dL-1) was 7.5% (tested in 107 children). The overall frequency of inherited prothrombotic coagulation proteins was 13% (95% confidence interval 7 to 19%) and the frequency was not significantly different between neonates and older children with VTE. Inherited prothrombotic coagulation proteins were not associated with gender, CVL-related VTE, a positive family history of thrombosis or spontaneous VTE in neonates. Increased frequency of inherited prothrombotic coagulation proteins was, however, found in older children with spontaneous VTE (60%) compared with older children with VTEs secondary to an underlying medical condition (10%) (P = 0.02). In conclusion, this study indicates that inherited prothrombotic coagulation proteins do not contribute significantly to the pathogenesis of VTEs in neonates and children, in whom the most significant etiological factors are the presence of a CVL and/or other medical conditions.

Thromboembolic diseases of childhood

Over the last decade, pediatric thrombophilia programs have emerged around the world as a new discipline in pediatric hematology. These programs specialize in the diagnosis, prevention and treatment of children with thromboembolic events (TEs) in both the venous and arterial systems. The need for separate pediatric programs has been discussed previously. (J Pediatr Hematol Oncol 1997; 19: 7-22.) The following article will update previous reviews (Hematol Oncol Clin North Am 1998; 12: 1283-1312; Thromb Haemost 1997; 78: 715-725) and will concentrate on three aspects: (1) The risk factors for acquiring TEs; (2) The confirmatory diagnostic tests used in children with TEs; and (3) The different antithrombotic agents used for prevention and treatment. The current knowledge in respect to the above points is only the "tip of the iceberg". Well-designed prospective trials are required to establish the contribution of congenital prothrombotic disorders, appropriate diagnostic strategies, and optimal therapy for children with TEs.

The prevalence of thrombophilia in patients with chronic venous leg ulceration

BACKGROUND

Thrombophilia is increasingly recognized as a risk factor for deep venous thrombosis (DVT), which in turn is a major risk factor for chronic venous ulceration (CVU). However, the relationship between thrombophilia and CVU remains unknown. The aim of this study was to define the prevalence of thrombophilia in patients with CVU and to determine whether this is associated with a history or duplex scan evidence of DVT.

METHODS

Eighty-eight patients with CVU were prospectively studied. The patients underwent clinical assessment and duplex ultrasound scanning. Blood was drawn for antithrombin, proteins C and S, activated protein C resistance, factor V Leiden, prothrombin 20210A, lupus anticoagulant, and anticardiolipin antibodies.

RESULTS

The study included 35 men with a median age of 61 years (interquartile range, 45 to 72 years) and 53 women with a median age of 76 years (interquartile range, 69 to 82 years). Thirty-six percent of the patients had either a history or duplex scan evidence suggestive of previous DVT. The following abnormalities were detected: four, five, and six cases of antithrombin, protein C, and protein S deficiencies, respectively; 14 cases of activated protein C resistance; 11 cases of factor V Leiden mutation; three cases of prothrombin 20210A mutation; eight cases of lupus anticoagulant; and 12 cases of anticardiolipin antibodies. Thrombophilia was not significantly related to previous DVT, deep reflux, or disease severity.

CONCLUSION

Patients with CVU have a 41% prevalence rate of thrombophilia. This rate is two to 30 times higher than the rate of the general population but is similar to that reported for patients with previous DVT. However, in patients with CVU, thrombophilia does not appear to be related to a history of DVT, a pattern of reflux, or severity of disease. Many patients with CVU may have unsuspected postthrombotic disease.

Importance of hyperhomocysteinemia as a risk factor for venous thromboembolism in a Taiwanese population. A case-control study

OBJECTIVE

To determine the current status of hyperhomocysteinemia, which is a known risk for venous thrombosis (DVT), in Taiwan.

SUBJECTS

101 unselected patients with a minimum of one episode of deep leg DVT, either initial inpatients or current compliant outpatients in a teaching hospital.

METHODS

Various thrombophilic risks, gene polymorphism and clinical predisposition were evaluated.

RESULTS AND CONCLUSIONS

Patients presented higher fast total plasma homocysteine (hcy) levels than age- and sex-matched controls did (14.1 vs. 9.94 microM). Based on the 95th percentile of control values, hyperhomocysteinemia had a four- to nine-fold risk for DVT, irrespective of clinical predisposition, as well as other thrombophilic risks surveyed. Polymorphism of a metabolizing enzyme, methylenetetrahydrofolate reductase (MTHFR), was not associated with DVT, although homozygous thermolabile mutation tended to have higher plasma hcy levels. Factor V Leiden was absent in analysis of 80 patients. In complete evaluation (hcy, antithrombin (AT), protein S (PS), protein C (PC), lupus anticoagulant (LA), anticardiolipin antibody) of a subset of 83 patients hyperhomocysteinemia was the most prevalent risk (33.7%), with PC or PS deficiencies following (22.9%). Thus, hyperhomocysteinemia is a prominent risk for DVT in Taiwan.

Clinical management of protein C deficiency

Protein C (PC) is a vitamin K-dependent plasma protein that is structurally similar to other coagulation factors such as prothrombin and Factor X. PC is converted to its active anticoagulant form by a thrombin-thrombomodulin complex on the surface of capillary endothelial cells. Activated PC (APC) prevents the formation of blood clots by specifically inactivating factors Va and VIIIa in the clotting cascade. Both acquired and hereditary forms of PC deficiency exist, with hereditary further categorised as heterozygous, homozygous as well as doubly heterozygous. Patients suffering from symptomatic heterozygous PC deficiency present with purpura fulminans, venous thrombosis and/or pulmonary embolism. Homozygous PC deficiency is usually associated with the development of severe and often fatal, purpura fulminans and disseminated intravascular coagulation (DIC) during the neonatal period. Various therapeutic options have been described for long-term management of severe heterozygous and homozygous PC deficiencies. For the treatment of heterozygous PC deficiency, oral anticoagulation with a coumarin derivative or heparin therapy remains standard therapy. Homozygous patients may be treated with fresh frozen plasma (FFP) and iv. PC concentrate or coumarin derivatives. Other therapeutic options for the treatment of hereditary PC deficiency include the use of low-molecular weight heparin (LMWH), steroids and liver transplantation. Maintenance of a symptom-free life depends on response to therapy. Patients responding well to treatment can expect normalisation of haemostasis as well as improvement of microcirculation and resolution of purpura fulminans.