Antithrombin III Deficiency and Thromboembolism

Characterization of two novel mutations of the antithrombin gene observed in Japanese thrombophilic patients

We investigated the molecular basis of reduced functional levels of antithrombin (AT) in two individuals suffering from thromboembolic events. In each case direct sequencing of amplified DNA revealed 13,260-13,262 del in one patient and 2511C>A in the other patient, predicting a heterozygous E381del and P16H, respectively. Both patients had no 20210A allele and factor V Leiden mutation. To understand the molecular mechanism responsible for antithrombin deficiency, stable expression experiments were performed using HEK293 cells transfected with the expression vector containing the wild-type or the mutated recombinant cDNA. In these experiments, the media levels of the two mutated antithrombins were the same as that of wild type, but the specific activity of the E381del mutant decreased significantly compared with that of wild type. These results showed that the E381del mutation was responsible for type II deficiency, whereas the other mutation, P16H, did not produce any definite abnormality which could contribute to antithrombin deficiency.

Argatroban therapy for antithrombin deficiency and mesenteric thrombosis: case report and review of the literature

Antithrombin deficiency is a hypercoagulable state that can increase the risk for thrombosis, especially in the presence of other procoagulant triggers. Unfractionated heparin and low-molecular-weight heparins may not provide effective anticoagulation since they require antithrombin for activity. Direct thrombin inhibitors, however, work independently of antithrombin. A 21-year-old man with a history of heavy alcohol consumption had thrombosis of the superior mesenteric vein. Infusion with unfractionated heparin was started, and despite repeated boluses and increases to 21 U/kg/hour, the maximum activated partial thromboplastin time reached was 39 seconds. The unfractionated heparin was discontinued, and the direct thrombin inhibitor argatroban was infused at rates of 0.4-0.5 microg/kg/minute. Over the course of several weeks, the patient had numerous operations to remove and repair necrotic bowel. When no further surgery was anticipated, warfarin therapy was started; the argatroban infusion was discontinued when the patient reached the therapeutic target international normalized ratio with warfarin. No recurrent thrombosis or major bleeding occurred. Direct thrombin inhibitors, such as argatroban, seem to be suitable alternatives for acute anticoagulation in patients with antithrombin deficiency.

Genetically Determined Procoagulant States and Heparin Use

The propensity for both arterial and venous thrombotic disorders involves a genetic predetermination that operates In concert with environmental factors or triggers. Appropriate clinical assessment and therapeutic recommendations for patients with thrombosis requires a thorough knowledge of genetic variables that influence this propensity. This review focuses on the pathophysiology, natural history, and molecular biology of defined thrombophilic risk factors relevant to the care of patients with thrombotic disorders.

Hypercoagulable states and central retinal vein occlusion

Central retinal vein occlusion is a common cause of permanent visual loss. Work up and laboratory evaluation of patients requires the clinician to rule out hypertension, diabetes, hyperlipidemia, and glaucoma. Patients without an identifiable risk factor are often subject to extensive testing for primary and secondary thrombophilias. The purpose this paper is to review the literature to determine which of these tests is associated with central retinal vein occlusion. Antiphospholipid antibodies and elevated plasma homocysteine levels appear to be the tests associated most commonly in patients with central retinal vein occlusion in most controlled studies. Primary thrombophilias are found rarely when screening patients with central retinal vein occlusion. Extensive testing for thrombophilias is not warranted in the vast majority of patients with central retinal vein occlusion. Older patients with any of the common vascular risk factors do not require thrombophilic screening. By carefully selecting the patients who are evaluated for thrombophilias, the likelihood of finding true-positive tests is increased.

Manufacturing process of anti-thrombin III concentrate: viral safety validation studies and effect of column re-use on viral clearance

A manufacturing process for the production of Anti-thrombin IIII concentrate is described, which is based primarily on Heparin Sepharose affinity chromatography. The process includes two sequential viral inactivation/removal procedures, applied to the fraction eluted from the column, the first by heating in aqueous solution at 60 degrees C for 10 h and the second by nanofiltration. Using viral validation on a scaled-down process both treatments proved to be effective steps; able to inactivate or remove more than 4 logs of virus, and their combined effect (>8 logs) assured the safety of the final product. Viral validation studies of the Heparin Sepharose chromatographic step demonstrated a consistency of the affinity of the resin for viruses over repeated use (16 runs), thus providing evidence of absence of cross-contamination from one batch to the next. It was concluded that the process of ATIII manufacturing provides a high level of confidence that the product will not transmit viruses.

Risk factors for venous thromboembolism

Until the 1990s, venous thromboembolism (VTE) was viewed primarily as a complication of hospitalization for major surgery (or associated with the late stage of terminal illness). However, recent trials in patients hospitalized with a wide variety of acute medical illnesses have demonstrated a risk of VTE in medical patients comparable with that seen after major general surgery. In addition, epidemiologic studies have shown that between one quarter and one half of all clinically recognized symptomatic VTEs occur in individuals who are neither hospitalized nor recovering from a major illness. This expanding understanding of the population at risk challenges physicians to carefully examine risk factors for VTE to identify high-risk patients who could benefit from prophylaxis. Factors sufficient by themselves to prompt physicians to consider VTE prophylaxis include major surgery, multiple trauma, hip fracture, or lower extremity paralysis because of spinal cord injury. Additional risk factors, such as previous VTE, increasing age, cardiac or respiratory failure, prolonged immobility, presence of central venous lines, estrogens, and a wide variety of inherited and acquired hematological conditions contribute to an increased risk for VTE. These predisposing factors are seldom sufficient by themselves to justify the use of prophylaxis. Nevertheless, individual risk factors, or combinations thereof, can have important implications for the type and duration of appropriate prophylaxis and should be carefully reviewed to assess the overall risk of VTE in each patient.

N-linked oligosaccharide processing, but not association with calnexin/calreticulin is highly correlated with endoplasmic reticulum-associated degradation of antithrombin Glu313-deleted mutant

Previously we showed that two antithrombin mutants were degraded through an endoplasmic reticulum (ER)-associated degradation (ERAD) pathway [F. Tokunaga et al., FEBS Lett. 412 (1997) 65]. Here, we examined the combined effects of inhibitors of glycosidases, protein synthesis, proteasome, and tyrosine phosphatase on ERAD of a Glu313-deleted (DeltaGlu) mutant of antithrombin. We found that kifunensine, an ER mannosidase I inhibitor, suppressed ERAD, indicating that specific mannose trimming plays a critical role. Cycloheximide and puromycin, inhibitors of protein synthesis, also suppressed ERAD, the effects being cancelled by pretreatment with castanospermine. In contrast, kifunensine suppressed ERAD even in castanospermine-treated cells, suggesting that suppression of ERAD does not always require the binding of lectin-like ER chaperones-like calnexin and/or calreticulin. These results indicate that, besides proteasome inhibitors, inhibitors of ER mannosidase I and protein synthesis suppress ERAD of the antithrombin deltaGlu mutant at different stages, and processing of N-linked oligosaccharides highly correlated with the efficiency of ERAD.

Prothrombin G20210A mutation, antithrombin, heparin cofactor II, protein C, and protein S defects

These defects are not as common as factor V Leiden, but they are more common than many other hereditary procoagulant defects. The incidence of the prothrombin gene (G20210A) mutation is not yet known with certainty, but it may approach or even exceed that of factor V Leiden. These defects also seem less common than hereditary sticky platelet syndrome; however, they are all common enough that they always should be considered in any individual with unexplained thrombosis and should be part of the work-up for patients with thrombotic disorders. Of the defects discussed herein, prothrombin G20210A mutation seems, thus far, to be more common than AT, protein C, protein S, or HC-II defects. Assessment of prothrombin gene mutation should be part of the primary evaluation of patients with unexplained thrombosis.

A Model Incorporating Some of the Mechanical and Biochemical Factors Underlying Clot Formation and Dissolution in Flowing Blood

Multiple interacting mechanisms control the formation and dissolution of clots to maintain blood in a state of delicate balance. In addition to a myriad of biochemical reactions, rheological factors also play a crucial role in modulating the response of blood to external stimuli. To date, a comprehensive model for clot formation and dissolution, that takes into account the biochemical, medical and rheological factors, has not been put into place, the existing models emphasizing either one or the other of the factors. In this paper, after discussing the various biochemical, physiologic and rheological factors at some length, we develop a model for clot formation and dissolution that incorporates many of the relevant crucial factors that have a bearing on the problem. The model, though just a first step towards understanding a complex phenomenon, goes further than previous models in integrating the biochemical, physiologic and rheological factors that come into play.

Intracellular accumulation of antithrombin Morioka (C95R), a novel mutation causing type I antithrombin deficiency

Antithrombin (AT) is a major plasma protease inhibitor with three intramolecular disulfide bonds, and its deficiency is associated with increased venous thrombosis. Recently, we found a novel missense mutation named AT Morioka (C95R), which causes the loss of one of the three disulfide bonds. In this study, we prepared Chinese hamster ovary cells stably overexpressing wild type or mutant AT and examined the intracellular fate of the ATs. In pulse-chase experiments, newly synthesized wild type AT was secreted into the medium with a half-life of approximately 1.5 h. In contrast, most of the mutant type AT was not secreted during the chase period of 9 h and, surprisingly, was not degraded in the cells. The kinetics of the secretion suggests that the mutant was secreted about 50 times more slowly into the medium. Most of the mutant AT in the cells had high mannose type oligosaccharides, suggesting that it was retained in the endoplasmic reticulum (ER). In addition, half of the mutant AT existed in a dimeric form with an intermolecular disulfide bond. On immunoelectron microscopy, the mutant AT was found to have accumulated in variously sized structures surrounded by a single membrane in the cytoplasm. Immunogold particles exhibiting calnexin immunoreactivity were detected on the membranes. Ribosomes were attached to some of the small structures that had accumulated the mutant AT. Further, we prepared Chinese hamster ovary cells stably overexpressing another mutant AT in which two cysteine residues at 21 and 95, responsible for disulfide bond formation, were substituted for arginines. In pulse-chase experiments, the mutant AT (C21C,C95R) was secreted faster than that of AT Morioka (C95R) into the medium. These results suggest that AT Morioka remained for a long time in ER without being degraded and accumulated in newly formed membrane structures derived from the ER. The dimerization of AT Morioka (C95R) through Cys-21 seems to be critical for its intracellular accumulation.

Risk factors for thromboembolism in teens: when should I test?

The discoveries of the factor V Leiden mutation and the prothrombin gene variant 20210 in the last decade have markedly contributed to the understanding of the molecular pathophysiology of inherited risk factors for thrombophilia. Population studies in the adult literature have shown that although the overall prevalence of these defects is low, affected individuals are at increased risk of thrombosis particularly if acquired risk factors for thrombosis are also present. The use of combined hormonal oral contraceptive pills is a well-known acquired risk factor, and recent studies have shown significant increased risk of thrombosis for women who carry the factor V Leiden mutation and use oral contraceptive pills. Despite this significant increased risk, mass screening of asymptomatic women for factor V Leiden prior to prescribing oral contraceptive pills is not a cost-effective use of health care dollars and could result in unnecessarily preventing many women from the contraceptive and noncontraceptive benefits of this medication. Instead, clinicians can use thoughtful screening questions to identify potentially high-risk patients for thrombophilia and consider testing for inherited risk factors on a case-specific basis.

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.

Disseminated intravascular coagulation: a review of etiology, pathophysiology, diagnosis, and management: guidelines for care

The pathophysiologic mechanisms, clinical, and laboratory manifestations of DIC are complex in part due to interrelationships within the hemostasis system. Only by clearly understanding these extraordinarily complex pathophysiologic interrelationships can the clinician and laboratory scientist appreciate the divergent and wide spectrum of often confusing clinical and laboratory findings in patients with DIC. Many therapeutic decisions to be made are controversial and lack validation. Nevertheless, newer antithrombotic agents, and agents that can block, blunt, or modify cytokine activity and the activity of vasoactive substances appear to be of value. The complexity and variable degree of clinical expression suggests that therapy should be individualized depending on the nature of DIC, age, etiology of DIC, site and severity of hemorrhage or thrombosis and hemodynamics and other appropriate clinical parameters. At present, treatment of the triggering event, low-dose heparin or antithrombin concentrate and wise choice of components when indicated appear to be the most effective modes of therapy.

Two novel gene mutations in type I antithrombin deficiency

We studied the molecular basis of type I antithrombin (AT) deficiency in 2 Japanese families, in which affected persons had histories of recurrent venous thrombosis and low (about 50% of normal) levels of AT protein according to measurements by both functional and antigen assays. Southern blotting of DNA isolated from peripheral leukocytes revealed no abnormalities in all the cases examined. Direct sequencing of the polymerase chain reaction (PCR) products from case I suggested a novel heterozygous nonsense mutation in exon 4 (GAG-->TAG at nucleotide position 7627, leading to Glu306 stop). The sequencing of the subclones of the patient's exon 4 products confirmed the nonsense mutation. No other sequence abnormalities were detected in the rest of the PCR products. The same mutation was detected in this patient's brother, who had a history of recurrent venous thrombosis and a reduced level of AT activity. In case 2, the direct sequencing of PCR products suggested a novel heterozygous 9-bp deletion in exon 3a (-CACTTC at nucleotide position 5354-5362, leading to the deletion of 3 amino acids, His120, Phel21, and Phe122). The 9-bp deletion mutation in the region of a unique quasi palindrome was confirmed by sequencing several of the subclones of the patient's exon 3a from the PCR products. No other mutations were found by direct sequencing of the rest of the coding regions. The 2 mutations found in this study are novel. The use of PCR and the sequencing of the PCR product subclones has simplified and confirmed the detection and characterization of the various AT mutations.

Epidemiology of venous thromboembolic disease

From the information presented in this article, it can be concluded that clinical suspicion of VTE should be increased in patients with a history of VTE, recent surgery, spinal cord injury, trauma, or malignancy. A variety of medical illnesses also increase the risk of venous thrombosis, including congestive heart failure, myocardial infarction, stroke with paresis, nephrotic syndrome, cigarette smoking, and obesity. Hypercoagulable states, such as antithrombin III deficiency, protein C deficiency, protein S deficiency, or factor V Leiden mutation should be considered in those patients who develop VTE in the absence of known risk factors. Additionally, the presence of vena caval filters does not exclude the possibility of PE or recurrent DVT. With a careful assessment of risk, physicians can hope to increase the diagnostic yield of VTE and decrease the significant morbidity and mortality of caused by this disease.

Thrombosis in the intensive care unit: etiology, diagnosis, management, and prevention in adults and children

Venous thromboembolism, a well-recognized complication in postoperative patients, is emerging as a frequent complication in critically ill patients in intensive care units. Diagnosis can be particularly difficult in such patients because underlying systemic illnesses may mask common presenting signs and symptoms. Although numerous independent risk factors have been identified, the critical role of both central venous catheters and prothrombotic disorders as significant risk factors is a common theme in the pediatric and adult literature. Various diagnostic tests exist, with venography remaining the gold standard and newer, less invasive methods such as ultrasonography and impedance plethysmography becoming increasingly popular. Standard unfractionated heparin remains the mainstay of therapy and prophylaxis, although the use of low molecular weight heparins is becoming more commonplace. Thrombolytic therapy continues to be reserved for severe, life-threatening, acute thrombosis. In this article, we review the common risk factors, diagnostic modalities, and treatment options for venous thromboembolism in critically ill adult and pediatric patients.

Syndromes of disseminated intravascular coagulation in obstetrics, pregnancy, and gynecology. Objective criteria for diagnosis and management

This article presents current understanding of the causes, pathophysiology, clinical, and laboratory diagnosis, and management of fulminant and low-grade DIC, as they apply to obstetric, pregnant, and gynecologic patients. General medical complications leading to DIC, which may often be seen in these patients, are also discussed. Considerable attention has been given to interrelationships within the hemostasis system. Only by clearly understanding these pathophysiologic interrelationships can the obstetrician/gynecologist appreciate the divergent and wide spectrum of often confusing clinical and laboratory findings in patients with DIC. Objective clinical and laboratory criteria for diagnosis of DIC have been outlined to eliminate unnecessary confusion and the need to make empiric decisions regarding the diagnosis. Particularly in the obstetric patient, if a condition is observed that is associated with DIC, or if any suspicion of DIC arises from either clinical or laboratory findings, it is imperative to monitor the patient carefully with clinical and laboratory tools to assess any progression to a catastrophic event. In most instances of DIC in obstetric patients, the disease can be ameliorated easily at early stages. Many therapeutic decisions are straightforward, particularly in obstetric and gynecologic patients. For more serious and complicated cases of DIC in these patients, however, efficacy and choices of therapy will remain unclear until more information is published regarding response rates and survival patterns. Also, therapy must be highly individualized according to the nature of DIC, patient's age, origin of DIC, site and severity of hemorrhage or thrombosis, and hemodynamic and other clinical parameters. Finally, many syndromes that are often categorized as organ-specific disorders and are sometimes identified as independent disease entities, such as AFE syndrome, HELLP syndrome, adult shock lung syndrome, eclampsia, and many others, either share common pathophysiology with DIC or are simply a form of DIC. These entities represent the varied modes of clinical expression of DIC and illustrate the diverse clinical and anatomic manifestations of this syndrome.

Thrombophilia in pregnancy

Thrombophilia can be defined as a predisposition to thrombosis. Abnormalities in haemostasis that are associated with clinical thrombophilia include heritable defects, such as mutations in the genes encoding the natural anticoagulants antithrombin, protein C, and protein S, or clotting factors prothrombin and factor V, and acquired defects, such as antiphospholipids. Women with thrombophilic defects have been shown to be at increased risk, not only of pregnancy associated thromboembolism, but also of other vascular complications of pregnancy, including pre-eclampsia and fetal loss. Routine thrombophilia screening of all women attending antenatal clinics is not recommended. Because some thrombophilic defects--for example, type 1 antithrombin deficiency and antiphospholipids--are associated with a high risk of recurrent thrombosis or other pregnancy complications, it is suggested that selected women (those with a personal or confirmed family history of venous thromboembolism or with a history of recurrent fetal loss) are screened for these defects to allow pregnancy management planning.

Pre-operative coagulopathy management of a neonate with complex congenital heart disease: a case study

Severe coagulation defects often develop in neonates undergoing cardiac surgery, both as a result of the surgical intervention, and as pre-existing defects in the hemostatic mechanisms. The following case report describes a newborn patient with complex congenital heart disease and respiratory failure whose pre-operative coagulopathy was aggressively managed prior to surgical correction. A 5-day-old, 2.5 kg child presented with interrupted aortic arch, ventricular septal defect, atrial septal defect, and patent ductus arteriosus. On admission, he was in respiratory arrest suffering from profound acidemia. In addition, the child was hypothermic (30.1 degrees C), septic (Streptococcus viridans), and coagulopathic (disseminated intravascular coagulation-DIC). The patient was immediately intubated and initial coagulation assessment revealed the following: prothrombin time (PT) 48.9 s (international normalized ratio (INR) 15.7), activated partial thromboplastin time (aPTT) >106 s, platelet count 30,000 mm(3), fibrinogen 15 mg dL(-1) and antithrombin III (AT-III) 10%. Before cardiac surgery could be performed, the patient's DIC was corrected with the administration of cryoprecipitate (15 ml), fresh frozen plasma (300 ml), and platelets (195 ml). In spite of the large transfusion of fresh frozen plasma, the AT-III activity, measured as a percentage, remained depressed at 33. Initial thromboelastographic (TEG) determination revealed an index of +2.02, and following 100 IU administration of an AT-III concentrate, declined to -2.32. Sequential TEG profiles were performed over several days, with the results used to guide both transfusion and medical therapy. The congenital heart defect correction was subsequently performed with satisfactory initial results, but the patient developed a fungal infection and expired on the 16th post-operative day. The present case describes techniques of coagulation management for a newborn with both a severe hemostatic defect and congenital heart disease.

Gene-Gene and Gene-Environment Interactions Determine Risk of Thrombosis in Families With Inherited Antithrombin Deficiency

To analyze inherited antithrombin deficiency as a risk factor for venous thromboembolism in various conditions with regard to the presence or absence of additional genetic or acquired risk factors, we compared 48 antithrombin-deficient individuals with 44 nondeficient individuals of 14 selected families with inherited antithrombin deficiency. The incidence of venous thromboembolism for antithrombin deficient individuals was 20 times higher than among nondeficient individuals (1.1% v 0.05% per year). At the age of 50 years, greater than 50% of antithrombin-deficient individuals had experienced thrombosis compared with 5% of nondeficient individuals. Additional genetic risk factors, Factor V Leiden and PT20210A, were found in more than half of these selected families. The effect of exposure to 2 genetic defects was a 5-fold increased incidence (4.6% per year; 95% confidence interval [CI], 1.9% to 11.1%). Acquired risk factors were often present, determining the onset of thrombosis. The incidence among those with exposure to antithrombin deficiency and an acquired risk factor was increased 20-fold (20.3% per year; 95% CI, 12.0% to 34.3%). In conclusion, in these thrombophilia families, the genetic and environmental factors interact to bring about venous thrombosis. Inherited antithrombin deficiency proves to be a prominent risk factor for venous thromboembolism. The increased risks among those with exposure to acquired risk factors should be considered and adequate prophylactic anticoagulant therapy in high-risk situations seems indicated in selected families with inherited antithrombin deficiency.

Tissue factor pathway

Blood coagulation is initiated in response to vessel damage in order to preserve the integrity of the mammalian vascular system. The coagulation cascade can also be initiated by mediators of the inflammatory response, and fibrin deposition has been noted in a variety of pathological states. The cascade of coagulation zymogen activations which leads to clot formation is initiated by exposure of flowing blood to Tissue Factor (TF), the cellular receptor and cofactor for Factor VII (FVII). FVII binds to the receptor in a I:I stoichiometric complex and is rapidly activated. FVIIa undergoes an active site transition upon binding TF in the presence of calcium which enhances the fundamental properties of the enzyme. This results in rapid autocatalytic activation of FVII to FVIIa, thereby amplifying the response by generating more TF-FVIIa complexes. The TF-FVIIa activates both FIX and FX. Further FXa generation by the FIXa-FVIIIa-Ca2+-phospholipid complex is required to sustain the coagulation mechanism, since the TF-FVIIa complex is rapidly inactivated by Tissue Factor pathway inhibitor (TFPI). TFPI circulates in plasma, is associated with vascular cell surface and is released from platelets following stimulation by thrombin. TFPI requires the formation of an active TF-FVIIa complex and FXa generation before inhibition can occur. TFPI prevents further participation of TF in the coagulation process by forming a stable quaternary complex, TF-FVIIa-FXa-TFPI.

Venous thromboembolic events in pediatric patients. Diagnosis and management

Venous thromboembolism is a rapidly increasing secondary complication in children being treated for serious, life-threatening, primary diseases. Most current management guidelines and recommendations for imaging techniques have been extrapolated from the results of trials in adults. This may be less than optimal for children as there are important differences. The purpose of this article is to summarize the information on venous thromboembolism in children, and offer some guidelines for diagnosis, prophylaxis, and therapeutic intervention based on the best available evidence.

Thrombophilia: disorders predisposing to venous thromboembolism

Venous thromboembolism continues to present a challenge to clinicians. Over the years, a number of risk factors which predispose to venous thromboembolism have been identified, and these risk factors are taken into account in the formulation of recommendations for the prevention and treatment of these disorders. In more recent years, there have been major advances in our understanding of congenital or acquired defects that predispose to thrombosis leading to these so-called acquired or inherited forms of thrombophilia. The list of acquired forms of thrombophilia now includes anti-thrombin, protein C, protein S, activated protein C resistance, the prothrombin 20210A mutant, homocysteinemia and a number of rare defects which either enhance coagulation or interfere with fibrinolysis. In spite of these advances, there are numerous families with thrombophilia in whom none of the known defects can be demonstrated. The challenge for the future is to discover some of these as yet unknown factors and to determine the most appropriate methods for the prevention and treatment of venous thromboembolism in susceptible individuals with thrombophilia.

Syndromes of thrombosis and hypercoagulability. Congenital and acquired causes of thrombosis

Blood coagulation protein and platelet defects are now known to account for up to ninety percent of unexplained venous thrombosis and up to seventy percent of unexplained arterial thrombotic or ischemic events. This article summarizes the common and uncommon blood protein and platelet defects which should be suspected, and searched for, in patients with such events. Defining such defects will have major impact on secondary prevention and duration of antithrombotic therapy in the afflicted patient and impact on primary prevention for identified family members in those harboring hereditary defects.

Activated protein C resistance due to a common factor V gene mutation is a major risk factor for venous thrombosis

Inherited resistance to activated protein C (APC) was recently discovered to be a cause of familial thrombophilia and is now known to be the most common genetic risk factor for venous thrombosis. It is caused by a single point mutation in the gene for factor V, which predicts substitution or arginine (R) at position 506 with a glutamine (Q). Accordingly, the activated form of mutated factor V (FVa:Q506) is more slowly degraded by activated protein C than normal FVa (FVa:R506) is, resulting in hypercoagulability and a lifelong 5- to 10-fold increased risk of venous thrombosis. Previously known inherited hypercoagulable states, i.e. deficiencies of the anticoagulant proteins antithrombin III, protein S, and protein C, are found fewer than 10-15% of thrombosis patients in western countries, whereas inherited APC resistance is present in 20-60% of such patients. The FV mutation is common in populations of Caucasian origin, with prevalences ranging from 1-15%, whereas it is not found in certain other ethnic groups such as Japanese and Chinese. The high prevalence of APC resistance, in combination with the availability of simple laboratory tests, will have a profound influence on the development of therapeutic and prophylactic regimens for thrombosis and will, it is hoped, result in a decreased incidence of thromboembolic events.

Coagulation studies, factor V Leiden, and anticardiolipin antibodies in 40 cases of cerebral venous thrombosis

BACKGROUND AND PURPOSE

Cerebral venous thrombosis (CVT) is an infrequent condition with a large variety of causes. However, in 20% to 35% of cases, no cause is found. We studied coagulation parameters, including activated protein C resistance associated with factor V gene mutation (factor V Leiden) and anticardiolipin antibodies, in a large series of patients with CVT with or without identified cause or risk factor.

METHODS

Forty patients (30 women and 10 men) aged 19 to 71 years (mean age, 36.2 years) with CVT diagnosed by angiography and/or MRI were studied 1 to 18 years after thrombosis. No known cause was found in 10 idiopathic cases. Coagulation studies included the following tests: fibrinogen, antithrombin, protein C, protein S, plasminogen, anticardiolipin antibodies, activated protein C resistance, and factor V Leiden.

RESULTS

Six cases of thrombophilia (15%) were found: 1 protein C deficiency, 1 protein S deficiency, and 4 activated protein C resistance with heterozygous factor V Leiden mutation (10%). Only 1 case (protein S deficiency) was found in the group of 10 patients with idiopathic CVT. In the other 5, there was another cause or risk factor. Three patients (8%) had increased anticardiolipin antibodies: 1 with systemic lupus and 2 with primary antiphospholipid syndrome; 2 of these 3 patients also had factor V Leiden mutation.

CONCLUSIONS

Although present in a number of CVT cases, acquired (anticardiolipin) or congenital varieties of thrombophilia (factor V Leiden being the most frequent) are almost invariably associated with other predisposing factors. This suggests that (1) these abnormalities should be looked for in patients with CVT, whether a cause is found or not, and (2) their presence should not deter the search for other potential causes. The detection of such abnormalities has major practical consequences on the long-term management of patients to prevent further thrombotic episodes.

Thrombotic risk in hereditary antithrombin III, protein C, or protein S deficiency. A cooperative, retrospective study. Gesellschaft fur Thrombose- und Hamostaseforschung (GTH) Study Group on Natural Inhibitors

A cooperative, retrospective study was performed on data from 8 coagulation laboratories and thrombosis units in Austria, Germany, and Switzerland to assess the risk for thrombosis in patients with hereditary antithrombin III (AT-III), protein C (PC), and protein S (PS) deficiencies; to compare the clinical manifestations of these 3 deficiency states; and to estimate the risk for development of thrombosis in high-risk situations. Two hundred thirty patients from 71 families with a documented hereditary deficiency of a natural coagulation inhibitor were included in the study. The patient group comprised 69 patients from 25 families with AT-III deficiency, 86 patients from 27 families with PC deficiency, and 75 patients from 19 families with PS deficiency. Diagnosis of the deficiency state was made at each participating center. Clinical data were documented in a questionnaire that was completed during each patient's visit to the participating center. The questionnaires were sent to the coordinating center (Vienna) and analyzed centrally. The probability of developing thrombosis was 80% to 90% for all deficiency states by 50 to 60 years of age, and this figure did not change considerably after data from the propositi were excluded. AT-III-deficient females developed thrombosis earlier in life compared with PC- and PS-deficient females due to a high thrombotic risk during pregnancy (40% in patients with AT-III deficiency) and oral contraceptive use. The clinical features of thromboembolism were similar in the three deficiency states except for a higher frequency of superficial thrombophlebitis in patients with PC and PS deficiencies. Mesenteric vein thromboses occurred in 4% to 10% of patients and in 2 of 8 patients as a recurrent event. The recurrence rate was 63% (60% of recurrent events occurred spontaneously) and did not differ significantly among the three deficiency states. Before 14 years of age only 1 of 80 surgical procedures and 0 of 21 leg injuries were followed by thrombosis. After 14 years of age thromboembolic events occurred after abdominal surgery or leg injury in one third of patients. Between 40% and 50% of symptomatic patients reported that they felt handicapped by a postthrombotic syndrome. We conclude that diagnosis of a coagulation inhibitor deficiency state should be made before 14 years of age. During childhood thrombosis prophylaxis cannot be regularly recommended but should be instituted after 13 years of age during/after abdominal surgery, including appendectomy, and after leg injury in AT-III-, PC-, and PS-deficient patients. The high recurrence rate (60% spontaneous recurrence) and the relatively high frequency of mesenteric vein thrombosis as a recurrent event favor introduction of long-term oral anticoagulant treatment after the first thrombotic event in patients with a documented hereditary deficiency of AT-III, PC, or PS.

Molecular genetics of antithrombin deficiency

Antithrombin is the major proteinase inhibitor of thrombin and other blood coagulation proteinases. Antithrombin has two functional domains, a heparin binding site and a reactive centre (that complexes and inactivates the proteinase). Its deficiency results in an increased risk of venous thromboembolism. Appreciable progress has been made in recent years in understanding the structure and function of this protein, the genetic cause of inherited deficiency and its clinical consequence. The structure of antithrombin is now considered in terms of the models derived from X-ray crystallography, which have provided explanations for the function of its heparin interaction site and of its reactive loop. The structural organization of the antithrombin gene has been defined and numerous mutations have been identified that are responsible for antithrombin deficiency: these may reduce the level of the protein (Type I deficiency), alter the function of the protein (Type II deficiency, altering heparin binding or reactive sites), or even have multiple or 'pleiotropic effects' (Type II deficiency, altering both functional domains and the level of protein).

Guidelines for the management of thrombophilia. Department of Haematology, The Royal London Hospital, Whitechapel, London, UK

Although there are numerous risk factors for venous thromboembolic disease, the term 'thrombophilia' refers only to those familial or acquired disorders of the haemostatic system that result in an increased risk of thrombosis. The inherited thrombophilias include antithrombin III deficiency, resistance to activated protein C (factor V Leiden), protein C and protein S deficiencies as well as some rare forms of dysfibrinogenaemia. It is possible that other inherited conditions might also predispose to thrombosis. In contrast, when using the above definition, the antiphospholipid syndrome is the only genuine acquired thrombophilic state. Patients who have thromboembolic disease at a young age with no provoking event or who have a positive family history or whose thrombosis involves an unusual site should be investigated for thrombophilia. The management of a patient identified as having a laboratory abnormality associated with thrombophilia will depend on a variety of factors such as the patient's individual and family thrombotic history, the site of the thrombosis and the presence of other prothrombotic risk factors. The use of prophylactic anticoagulation during pregnancy and the puerperium requires particularly careful consideration in thrombophilic women. As more becomes known about the thrombophilias it will become possible to formulate more exact guidelines as to the management of these conditions.

Familial thrombophilia: clinical and molecular analysis of Swedish families with inherited resistance to activated protein C or protein S deficiency

This report describes the characterization of Swedish families with inherited resistance to activated protein C (APC resistance) and/or protein S deficiency, two genetic disorders associated with functional impairment of the protein C anticoagulant pathway. The APC resistance phenotype was linked to the factor V gene locus in a kindred with independent inheritance of APC resistance and protein S deficiency. A point mutation changing Arg506 to a Gln (FV:Q506) in the factor V gene was the cause of APC resistance. In studies of 50 families with hereditary APC resistance, the FV:Q506 mutation was identified in 94% (47/50) of the families, and the thrombotic risk was found to be dependent on the factor V genotype. Moreover, 18 families with hereditary deficiency of free protein S were investigated. Type I protein S deficiency (low free and total protein S) and type III deficiency (low free but normal total protein S) coexisted in 78% (14/18) of the families, suggesting the two types to be phenotypic variants of the same genetic disorder. Deficiency of free protein S was caused by equimolar relationship between protein S and beta-chain containing isoforms of C4BP. Though protein S deficiency was a strong risk factor for thrombosis, the FV:Q506 mutation was identified as an additional genetic risk factor in 39% of the families. Thus, familial thrombophilia is a multiple gene disorder. The thrombophilic tendency associated with APC resistance or protein S deficiency was related to increased levels of prothrombin fragment 1 + 2, reflecting increased activation of the common coagulation pathway.

Molecular genetics of human antithrombin deficiency

Human antithrombin is the major plasma inhibitor of thrombin both in the presence and absence of heparin. Its physiological importance is emphasised by the recurrent thromboses that individuals with a deficient or functionally abnormal protein are prone to develop. Such deficiencies are estimated to affect as many as 1:630 of the general population and between 3% and 5% of patients with thrombotic disease. The gene for antithrombin (AT3) has been cloned and shown to map to the long arm of chromosome 1 at 1q23-25. The gene consists of seven exons and six introns and spans 13,477bp of DNA. Advances in molecular genetic techniques have facilitated identification of the underlying DNA mutation(s) in > 80 families with antithrombin deficiency. Such work has proved invaluable in structure-function studies and in helping to provide informed genetic counselling to "at-risk" individuals based upon the natural history of similar variants.

The investigation of a patient with unexpected venous thrombosis

Over recent years a number of hereditary and acquired defects of the circulation's natural anticoagulant mechanisms have been characterised and shown to predispose affected individuals to thrombosis. It is important to attempt to diagnose a thrombophilia state in patients with a thrombotic tendency in order to provide appropriate management, especially during at-risk situations, both for themselves and asymptomatic relatives identified through family studies. This review defines the patients who should be investigated for an underlying thrombophilia state and describes the hereditary and acquired disorders which should be screened for within an investigation profile. The recently identified factor V Leiden mutation which appears to be the most common hereditary cause of a thrombotic tendency is described in detail and descriptions of the more established thrombophilia states are included. Although the factor V Leiden mutation accounts for a significant proportion of cases fulfilling the criteria for thrombophilia screening, a predisposing cause for thrombosis remains unidentifiable in a large number of patients making it likely that over the years to come new thrombophilia states will continue to be identified.

Activated protein C resistance: from phenotype to genotype and clinical practice

The anticoagulant protein C system is an important regulator of the blood coagulation process. Its targets are the procoagulant cofactors factor Va and factor VIIIa, which are cleaved and inactivated by activated protein C, protein S and intact factor V working as cofactors. Genetic defects of protein C or protein S were, together with antithrombin III deficiency, the previously established major causes of familial venous thromboembolism. However, these abnormalities are found in less than 5-10% of patients with thrombosis. Inherited resistance to activated protein C was recently identified as a major risk factor for venous thromboembolism. The activated protein C-resistance phenotype is found in 20-60% of the patients with venous thrombosis, depending on selection criteria and on the prevalence of activated protein C-resistance in the population. The frequency of activated protein C-resistance is 2-10% in the normal populations studied so far. In more than 90% of cases, the molecular background for the activated protein C-resistance is a single point mutation in the factor V gene, which predicts substitution of an arginine at position 506 by a glutamine. Mutated factor V is activated by thrombin or factor Xa in the normal way, but impaired inactivation of mutated factor Va by activated protein C results in a life-long hypercoagulability. Owing to the high prevalence of activated protein C-resistance in the population, it occasionally occurs in patients with deficiency of protein S, protein C or antithrombin III. Individuals with combined defects suffer more severely from thrombosis, and often at a younger age, than those with single defects, suggesting thrombophilia to be a multigenetic disease.

Two antithrombin mutations in a compound heterozygote: Met20Thr and Tyr166Cys

The molecular basis for a family with Type I antithrombin deficiency has been established. Amplification and sequencing of the antithrombin gene identified two mutations: Met20Thr (2523T-->C) within exon 2 and Tyr166Cys (5493A-->G) within exon 3a. Further analysis indicated that the propositus was a compound heterozygote but in addition provided evidence for phase disruption during the amplification and/or cloning procedure. The Met20Thr mutation appears to be a neutral mutation with no functional consequences. In contrast, the Tyr166Cys mutation is associated with a Type I phenotype.

Reporting standards in venous disease: an update. International Consensus Committee on Chronic Venous Disease

At the request of the Ad Hoc Committee on Reporting Standards of the Joint Council of the Society for Vascular Surgery and the North American Chapter of the International Society for Cardiovascular Surgery, this report updates and modifies "Reporting standards in venous disease" (J Vasc Surg 1988;8:172-81). As in the initial document, reporting standards for publications dealing with (1) acute lower extremity venous thrombosis, (2) chronic lower extremity venous insufficiency, (3) upper extremity venous thrombosis, and (4) pulmonary embolism are presented. Numeric grading schemes for disease severity, risk factors, and outcome criteria present in the original document have been updated to reflect increased knowledge of venous disease and advances in diagnostic techniques. Certain recommendations of necessity remain arbitrary. These standards are offered as guidelines whose observance will in our opinion improve the clarity and precision of communications in the field of venous disorders.

Modulation of hemostatic balance with antithrombin III replacement therapy in a case of liver cirrhosis associated with recurrent venous thrombosis

Patients with liver failure can present both thrombotic and hemorrhagic complications because of the deficiency in coagulation factors and inhibitors (protein C and S, antithrombin III) and impairment of fibrinolytic balance. Here we report the case of a 63-year-old man with liver cirrhosis, recurrent thrombosis, and features of low-grade consumption coagulopathy, showing severe antithrombin III deficiency (about 30% of normal values). Treatment with antithrombin III (2000 U/day) and low doses of heparin (5000 U b.i.d.) was successful in modulating the coagulation system toward an antithrombotic effect. After discharge from hospital the ambulatory treatment with antithrombin III concentrates (2000 U twice a week) allowed the attainment of antithrombin III activity of about 60% and prevented the patient from recurrence of venous thrombosis.

Prevalence of lupus anticoagulant in patients with cirrhosis: relationship with beta-2-glycoprotein I plasma levels

We have previously demonstrated that patients with cirrhosis may be positive for lupus anticoagulant and anticardiolipin antibodies. The prevalence and clinical value of antiphospholipid antibodies in cirrhosis have never been described. Besides, it has not yet been determined if serum levels of beta-2-glycoprotein I, which is synthesized by the liver and mediates the interaction between cardiolipin and anticardiolipin antibodies affects lupus anticoagulant detectability in cirrhosis. We evaluated the prevalence of lupus anticoagulant in 63 patients with cirrhosis and related it to beta-2-glycoprotein I serum levels. We also analyzed whether lupus anticoagulant and anticardiolipin antibodies were associated with previous thrombotic complications. Eleven patients (18%) were lupus anticoagulant positive; 14 (22%) had high values of anticardiolipin antibodies. Fourteen patients had a previous history of splanchnic venous thrombosis (n = 9) or thrombophlebitis (n = 5). A significant association between lupus anticoagulant (p = 0.0001), anticardiolipin antibodies (p = 0.0001) and venous thrombosis was found. Patients with severe liver failure had significantly lower beta-2-glycoprotein I levels than those with moderate (p < 0.01) or low (p < 0.001) hepatic insufficiency. Among 14 anticardiolipin antibodies positive patients, six with severe liver failure were lupus anticoagulant negative and had beta-2-glycoprotein I values below 100 micrograms/ml. In four of these, basal values of dilute activated partial thromboplastin time were not modified by the addition of 50 micrograms/ml of exogenous beta-2-glycoprotein I. This study shows that antiphospholipid antibodies are relatively frequent in cirrhosis and that beta-2-glycoprotein I levels are not so low as to affect lupus anticoagulant detectability.(ABSTRACT TRUNCATED AT 250 WORDS)