Anticoagulant proteins in childhood venous and arterial thrombosis: a review

Large Left Ventricular Thrombus in a Patient with Systemic and Venous Thromboembolism Secondary to Protein C and S Deficiency

58-year-old Hispanic female presented with an altered mental status. A CT scan of the head demonstrated multiple scattered infarcts and a large right temporal lobe infarct. We also diagnosed the patient with right popliteal and femoral vein thrombosis, bilateral pulmonary embolism, and a transient right radial artery occlusion. Her 12-lead EKG showed lateral ST elevation. Emergent coronary angiogram revealed normal coronaries. Echocardiogram demonstrated a large mobile mass attached to the anterolateral free wall with overall normal contractility of the left ventricle. The patient underwent surgical embolectomy to prevent further systemic embolization. Coagulability workup returned positive for protein C and S deficiency. The patient did well after surgery. Following her surgery, we initiated chronic oral anticoagulation. The presentation with intracardiac thrombus in a normal heart should raise a concern of a probable thrombophilia.

Long-term follow-up of homozygote protein C deficiency after multimodal therapy

Homozygous protein C deficiency is an extremely rare condition presenting in the neonatal period with purpura fulminans, with very high rates of morbidity and mortality. Optimal treatment for this condition is highly complex, poorly understood, and often limited by cost and product supply. We report a child who presented 2 days after birth with purpura fulminans and severe prenatal eye damage, but no cerebral lesions. He was treated with novel multimodal therapy culminating in liver transplant at 3 years of age. The patient is now 12 years of age, well, with blindness as his only long-term deficit.

Thromboembolism in childhood nephrotic syndrome: A rare but serious complication

The main clinical features of nephrotic syndrome (NS) are heavy proteinuria, hypoalbuminemia, hyperlipidemia and edema. In addition, multiple abnormalities in the coagulation pathway may be a consequence of the NS. Both arterial and venous thromboembolic complications (TEC) are relatively common and serious consequences of NS. In addition, arterial and venous thrombosis might be unexpected events during an exacerbation of NS. Embolic episodes may manifest in different regions of the body such as the brain or the lung. Hence, predisposing factors, personal and family history of TEC, thrombosis location and evolution should be always investigated in children with NS.

Incidence of and risk factors for childhood thrombosis: a single-center experience in Ankara, Turkey

This study was conducted to analyze the incidence of and risk for thrombosis in thrombotic children monitored in the Department of Pediatric Hematology of our hospital at the time of diagnosis, in addition to the clinical characteristics of those patients. The clinical and laboratory findings of 122 patients diagnosed with thrombosis from 1997 to 2006 were retrospectively analyzed. The incidence of thrombosis was 88.6/10,000 hospital admissions. The authors found that 31.1% of the patients studied had a thrombosis in more than 1 region. The incidence of thrombosis by anatomic site was as follows: 42 thromboses in the peripheral arterial system, 39 in an intracardiac region, 38 in the abdominal venous system, 36 in the deep peripheral venous system, and 28 in the cerebral vascular system. The mean age of the patients at the time of diagnosis was 4.9 years. Of the patients studied, 10.7% were neonates, 35.3% were infants younger than 1 year, and 48.4% were younger than 2 years. Most of the patients had a congenital cardiac disease and spontaneous thrombosis, and 66.1% had at least 1 acquired risk factor, the most common of which were having undergone surgery (42%) or wearing a central venous catheter (39%). A hereditary factor for the development of thrombosis was present in 54% of the patients. The most frequently observed hereditary risk factor was the MTHFR 677C-T mutation, and the second most common was the factor V Leiden mutation. Thrombosis should be considered a systemic disorder, and thrombotic patients should be evaluated with appropriate methods. Acquired and hereditary risk factors should be analyzed systematically in thrombotic patients.

Treatment of endothelium with the chemotherapy agent vincristine affects activated protein C generation to a greater degree in newborn plasma than in adult plasma

INTRODUCTION

Activated protein C (APC) is well-established as a physiologically important anticoagulant. During development, plasma concentrations of protein C and alpha(2)macroglobulin, factors involved in APC generation, differ from adult levels. Chemotherapy drugs can perturb endothelial expression of PC-activating receptors. This study examines the effect of chemotherapy treatment of endothelium on APC generation in newborn and adult plasma.

MATERIALS AND METHODS

APC generations were initiated on endothelial cells treated with vincristine or media by recalcifying defibrinated plasma with buffer containing thromboplastin. APC generation was terminated by mixing timed subsamples into FFRCMK-EDTA or heparin, followed by EDTA. APC-PCI and APC-alpha(1)AT were assayed by ELISA. APC-alpha(2)M was measured chromogenically. Since heparin converts free APC to APC-PCI, the difference between APC-PCI detected in heparin subsamples and APC-PCI detected in FFRCMK-EDTA subsamples gave the free APC. Cellular expression of EPCR and TM were measured by flow cytometry and Western blot.

RESULTS

Vincristine-treated endothelium decreased free APC generation in newborn plasma to a greater degree than in adult plasma. APC-PCI levels in both adult and newborn plasma were unaffected by chemotherapy. Vincristine treatment reduced levels of APC-alpha(1) AT and APC-alpha(2) M to a greater degree in newborn plasma versus adult plasma. Expression of EPCR was reduced in cells treated with vincristine. Conversely, TM was reduced on the cell surface, but increased in whole cell lysates.

CONCLUSIONS

The differential response of newborn and adult plasma PC components to chemotherapy-mediated changes in cell surface components may be a factor in the increased risk of thrombosis in children receiving chemotherapy.

Treatment of massive cardiac thrombi in a patient with protein C and protein S deficiency

Myocarditis and dilated cardiomyopathy is characterized by dilatation of all four cardiac chambers and decreased systolic function of the heart, especially in the left ventricle. In this report we presented a patient with myocarditis or dilated cardiomyopathy and deficiency of protein C and protein S with biventricular multiple intracardiac thrombi. Standard heparin infusion and acetyl salicylic acid was begun. On the 10th day of hospitalization the right ventricular thrombus disappeared, and on the 24th day all thrombi in the left ventricle disappeared. During the treatment we did not observe any complication such as hemorrhagia or embolism. We think that patients with dilated cardiomyopathy or myocarditis should be evaluated for hemostatic disorders, and should be anticoagulated if any of these disorders are presented.

Low Arterial Saturation Is Associated With Increased Sensitivity to Activated Protein C in Children With Congenital Heart Disease

OBJECTIVES

Children with congenital heart disease experience both hemorrhagic and thrombotic complications. In this report the authors test the hypothesis that hypoxemia is associated with altered sensitivity to activated protein C (aPC) in pediatric patients with congenital heart lesions.

DESIGN

A retrospective genetic registry review, with statistical evaluation of factors contributing to the aPC ratio.

SETTING

Large university hospital.

PARTICIPANTS

Cohort of 92 children with congenital heart disease undergoing cardiac catheterization procedures.

INTERVENTIONS

The authors measured the aPC ratio at cardiac catheterization and evaluated the contribution of independent variables using linear regression and classification tree approaches. Independent variables included age, gender, use of aspirin, history of thrombosis, room air arterial saturation, factor VIII:C levels, presence of congestive heart failure, and heterozygosity for factor V Leiden.

MEASUREMENTS AND MAIN RESULTS

At univariate analysis, factor V Leiden, female gender, room air arterial saturation, age greater than 6 months, and plasma factor VIII:C levels were associated with a lower aPC ratio (resistance to aPC). At stepwise linear regression, arterial saturation, factor VIII:C level, female gender, and factor V Leiden were independently associated with a lower aPC ratio, and these variables explained about 49% of the variability in aPC ratio. The classification tree approach confirmed the dependence of aPC ratio on factor V genotype and arterial saturation.

CONCLUSIONS

The aPC ratio in this population is associated with hypoxemia, independent of factors previously observed in adults. Further studies are under way to determine how aPC resistance or sensitivity may independently affect perioperative hemostasis in this population.

Coagulation Parameters in the Patients with Fournier’s Gangrene

AIM

In this prospective study, we aimed to determine the coagulation parameters in the patients with Fournier's gangrene.

METHODS

The study group is consisted of 12 consecutive Fournier's gangrene patients (11 men and 1 woman) and control group is consisted of patients with periurethral abscess (n = 2), scrotal abscess (n = 4) and epididimorchitis (n = 4). Fibrinogen, protein C, protein S, antithrombin III, lupus anticoagulant, cardiolipin IgG and IgM, prothrombin time-international normalized ratio, activated partial thromboplastin time, platelet count, proaccelerin, antihemophilic globulin (FVIII), albumin, and calcium were evaluated in all subjects. Tissue specimens were taken from Fournier's gangrene patients. These specimens were tested for arterial and venous thrombosis using light microscopy.

RESULTS

All of the patients with Fournier's gangrene had both arterial and venous thrombosis in tissue specimens. The levels of fibrinogen and FVIII were high, the level of protein C was low in 12 patients. Lupus Anticoagulant was positive 11 of 12 patients.

CONCLUSIONS

According to our findings, we think that some coagulation parameters (FVIII, Lupus anticoagulant, protein C, fibrinogen) may be diagnostic for Fournier's gangrene.

Clopidogrel use in children

OBJECTIVES

To review a pediatric experience with the antiplatelet agent clopidogrel and suggest a dosage regimen.

STUDY DESIGN

A retrospective chart review of all infants and children treated with clopidogrel at The Hospital for Sick Children, Toronto between January 2001 and April 2004. Clopidogrel dosages, duration of therapy, complications, and adverse effects in a pediatric population were explored.

RESULTS

Fifteen infants and children with congenital and acquired heart disease were treated with clopidogrel (median age, 3.5 years; range, 6 weeks to 16 years). Dosages ranged from 1 to 6 mg/kg/day for periods between 1 month and 6 months. Although no thrombotic events were reported, 1 child had a bleeding complication (gastrointestinal) while on triple antithrombotic therapy. Other complications reported in adults, including rash and clinical thrombocytopenia, were not noted in this pediatric series.

CONCLUSIONS

Clopidogrel was well tolerated. We suggest a starting dose of 1 mg/kg/day for children.

Tissue-specific hemostasis in mice

Blood coagulation is essential to maintain hemostasis in organisms with a vascular network. Formation of a fibrin-rich clot at a site of vessel injury is a highly complex process that is orchestrated by the coagulation protease cascade. This cascade is regulated by 3 major anticoagulant pathways. Removal of a clot is mediated by the fibrinolytic system. Defects in the regulation of clot formation lead to either hemorrhage or thrombosis. Tissue factor, the primary cellular initiator of blood coagulation, is a transmembrane receptor that is expressed in a tissue-specific manner. The 3 major anticoagulants are tissue factor pathway inhibitor, antithrombin, and protein C, the latter requiring a transmembrane receptor called thrombomodulin for its activation. Tissue factor pathway inhibitor and thrombomodulin are expressed by endothelial cells in a tissue-specific manner, whereas antithrombin and protein C circulate in the plasma. Fibrinolysis requires the activation of plasminogen to plasmin, which is mediated by tissue-type plasminogen activator and urokinase-type plasminogen activator. Interestingly, tissue-type plasminogen activator is expressed by a subset of endothelial cells of discrete size and location. These observations, together with the phenotypes of mice that have defects in the procoagulant, anticoagulant, and fibrinolytic pathways, indicate that hemostasis is regulated in a tissue-specific manner.

Liver transplantation as definitive treatment for a factor V Leiden mutation

Liver transplantation (LT) was achieved for factor V Leiden-induced thrombophilia in a neonate with hepatic veno-occlusive disease. Initial LT was performed with a liver segment removed from a child with primary oxalosis. Four months later, a second, definitive LT was performed. The child remains well without recurrent thrombosis.

Excellent outcome in infants and small children with thrombophilias undergoing kidney transplantation

One of the most common causes of early graft failure in children undergoing renal transplantation is vascular thrombosis. Numerous risk factors for graft thrombosis have been previously described. Children with various types of thrombophilias such as protein C, protein S and factor V Leiden deficiencies are at an increased risk for vascular thrombosis. Infants and small children with these disorders undergoing renal transplantation have not been well documented in the literature. We reviewed our experience in the diagnosis, peri-operative management and follow up of these patients at our institution. A retrospective analysis of all children undergoing renal transplantation at our institution, using data obtained from the Pediatric Transplant Registry at our institution since May 2000 was performed. The indications for renal transplant included focal segmental glomerulosclerosis, renal dysplasia and reflux nephropathy. One patient had factor V Leiden mutation and two patients had protein S deficiency. Patients were anticoagulated in the peri-operative and post-transplant period. All index transplants were performed with living donor kidneys. There were no adverse outcomes in children with thrombophilias despite having significantly lower weight at the time of transplant vs. children without thrombophilia. The incidence of graft thrombosis in the pediatric renal transplant recipients is high. We identify a potential cause of thrombosis in children not well documented in the literature. A high index of suspicion combined with preoperative screening and diagnosis of thrombophilias and an appropriate treatment plan may decrease the incidence of graft thrombosis in infants and small children undergoing renal transplantation.

Sex-specific changes in platelet aggregation and secretion with sexual maturity in pigs

Cardiovascular disease may begin early in adolescence. Platelets release factors contributing to vascular disease. Experiments were designed to test the hypothesis that hormonal transitions associated with sexual maturity differentially affect platelet aggregation and secretion in males and females. Platelets were collected from juvenile (2-3 mo) and sexually mature (adult; 5-6 mo) male and female pigs (n=8/group). Maturation was evidenced by increased weight of reproductive tissue and changes in circulating levels of gonadal hormones. Aggregation to ADP (10 microM) and collagen (6 microg/ml) and ATP secretion to 50 nM thrombin were determined by turbidimetric analysis and bioluminescence, respectively. Total platelet counts, platelet turnover, and mean platelet volume did not change with maturity. Platelet aggregation and ATP secretion decreased in females but increased in males with maturity, whereas total ATP content remained unchanged in platelets from females but increased in platelets from males. Platelet fibrinogen receptor, P-selectin expression, and receptors for sex steroids did not change with sexual maturation. Plasma C-reactive protein and brain-type natriuretic peptide also did not change. Results indicate that changes in platelet aggregation and secretion change with sexual maturity differently in females and males. These observations provide evidence on which clinical studies could be designed to examine platelet characteristics in human children and young adults.

Normal levels of anticoagulant heparan sulfate are not essential for normal hemostasis

Endothelial cell production of anticoagulant heparan sulfate (HS(act)) is controlled by the Hs3st1 gene, which encodes the rate-limiting enzyme heparan sulfate 3-O-sulfotransferase-1 (3-OST-1). In vitro, HS(act) dramatically enhances the neutralization of coagulation proteases by antithrombin. The in vivo role of HS(act) was evaluated by generating Hs3st1(-/-) knockout mice. Hs3st1(-/-) animals were devoid of 3-OST-1 enzyme activity in plasma and tissue extracts. Nulls showed dramatic reductions in tissue levels of HS(act) but maintained wild-type levels of tissue fibrin accumulation under both normoxic and hypoxic conditions. Given that vascular HS(act) predominantly occurs in the subendothelial matrix, mice were subjected to a carotid artery injury assay in which ferric chloride administration induces de-endothelialization and occlusive thrombosis. Hs3st1(-/-) and Hs3st1(+/+) mice yielded indistinguishable occlusion times and comparable levels of thrombin.antithrombin complexes. Thus, Hs3st1(-/-) mice did not show an obvious procoagulant phenotype. Instead, Hs3st1(-/-) mice exhibited genetic background-specific lethality and intrauterine growth retardation, without evidence of a gross coagulopathy. Our results demonstrate that the 3-OST-1 enzyme produces the majority of tissue HS(act). Surprisingly, this bulk of HS(act) is not essential for normal hemostasis in mice. Instead, 3-OST-1-deficient mice exhibited unanticipated phenotypes suggesting that HS(act) or additional 3-OST-1-derived structures may serve alternate biologic roles.

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.

Thrombophilia and chronic venous ulceration

It is known that thrombophilia (TP) is a risk factor for deep venous thrombosis (DVT), and that DVT predisposes to chronic venous ulceration (CVU). However, the relationship between TP and CVU has not been well studied. Review of the literature reveals that the prevalence of TP in CVU patients is high--similar to the prevalence found in patients with a history of DVT. This is despite many patients with CVU having no clear history, or duplex evidence of previous DVT. TP may predispose to CVU by leading to macro- or micro-vascular thrombosis. This association raises several issues regarding the investigation, prevention and management of patients with venous disease.

Mice deficient in heparan sulfate 3-O-sulfotransferase-1: normal hemostasis with unexpected perinatal phenotypes

Heparan sulfate that contains antithrombin binding sites is designated as anticoagulant heparan sulfate (HS(act)) since, in vitro, it dramatically enhances the neutralization of coagulation proteases by antithrombin. Endothelial cell production of HS(act) is controlled by the Hs3st1 gene, which encodes the rate limiting enzyme-heparan sulfate 3-O-sulfotransferase-1 (Hs3st1). It has long been proposed that levels of endothelial HS(act) may tightly regulate hemostatic tone. This potential in vivo role of HS(act) was assessed by generating Hs3st1(-/-) knockout mice. Hs3st1(-/-) and Hs3st1(+/+) mice were evaluated with a variety of methods, capable of detecting altered hemostatic tone. However, both genotypes were indistinguishable. Instead, Hs3st1(-/-) mice exhibited lethality on a specific genetic background and also showed intrauterine growth retardation. Neither phenotypes result from a gross coagulopathy. So although this enzyme produces the majority of tissue HS(act), Hs3st1(-/-) mice do not show an obvious procoagulant phenotype. These results suggest that the bulk of HS(act) is not essential for normal hemostasis and that hemostatic tone is not tightly regulated by total levels of HS(act). Moreover, the unanticipated non-thrombotic phenotypes suggest structure(s) derived from this enzyme might serve additional/alternative biologic roles.

Systemic lupus erythematosus and antiphospholipid syndrome in children and adolescents

Systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS) can be associated with significant morbidity in children and adolescents. Renal involvement in SLE appears to be more severe and more frequent in the pediatric age group, with the major predictors for poor outcome being the severity of histopathologic lesions, severity of renal impairment at diagnosis, and hypertension. In addition to currently recognized cardiovascular and pulmonary involvement, accelerated atherosclerosis is of increasing concern in young individuals with SLE, because of both disease effects and medication usage. Neuropsychiatric SLE seen in childhood ranges from subtle cognitive dysfunction to severe central nervous system involvement; however, there is controversy over the value of different diagnostic studies. APS in children may be associated with SLE, idiopathic, or associated with viral infections. Systemic anticoagulation is recommended for patients with thrombotic events, but long-term management has not been well studied in children.