Inherited resistance to activated protein C is corrected by anticoagulant cofactor activity found to be a property of factor V

Factor V Leiden related Budd-Chiari syndrome

BACKGROUND

The role of factor V Leiden as a cause of Budd-Chiari syndrome has only recently been described.

AIMS

To assess the specific features of factor V Leiden related Budd-Chiari syndrome.

PATIENTS

Sixty three consecutive patients with hepatic vein or terminal inferior vena cava thrombosis.

METHODS

Standardised chart review.

RESULTS

Factor V Leiden was found in 20 patients (31% (95% CI 20-43)). In the subgroup of patients with, compared with the subgroup without, factor V Leiden, a combination of prothrombotic states was more common (70% (95% CI 50-90) v 14% (95% CI 3-24)); inferior vena cava thrombosis was more frequent (40% (95% CI 19-61) v 7% (95% CI 0-14)); and distribution of initial alanine aminotransferase values was bimodal (almost normal or extremely increased) versus unimodal (p=0.003). Factor V Leiden accounted for four of five cases of massive ischaemic necrosis (transaminases >50-fold the upper limit of normal values) (p=0.014), and also for all three cases developing during pregnancy. Patients with and without factor V Leiden did not differ with regard to mortality, portosytemic shunting, or listing for liver transplantation. Hepatocellular carcinoma developed in two patients; both had factor V Leiden and indolent obstruction of the inferior vena cava.

CONCLUSIONS

In patients with Budd-Chiari syndrome, factor V Leiden (a) is common; (b) precipitates thrombosis mostly when combined with another risk factor; (c) is associated with one of two contrasting clinical pictures: indolent thrombosis-particularly of the inferior vena cava-or massive ischaemic necrosis; and (d) is a major cofactor of Budd-Chiari syndrome developing during pregnancy.

DNA technology for the detection of common genetic variants that predispose to thrombophilia

With the identification of common single locus point mutations as risk factors for thrombophilia, many DNA testing methodologies have been described for detecting these variations. Traditionally, functional or immunological testing methods have been used to investigate quantitative anticoagulant deficiencies. However, with the emergence of the genetic variations, factor V Leiden, prothrombin 20210 and, to a lesser extent, the methylene tetrahydrofolate reductase (MTHFR677) and factor V HR2 haplotype, traditional testing methodologies have proved to be less useful and instead DNA technology is more commonly employed in diagnostics. This review considers many of the DNA techniques that have proved to be useful in the detection of common genetic variants that predispose to thrombophilia. Techniques involving gel analysis are used to detect the presence or absence of restriction sites, electrophoretic mobility shifts, as in single strand conformation polymorphism or denaturing gradient gel electrophoresis, and product formation in allele-specific amplification. Such techniques may be sensitive, but are unwielding and often need to be validated objectively. In order to overcome some of the limitations of gel analysis, especially when dealing with larger sample numbers, many alternative detection formats, such as closed tube systems, microplates and microarrays (minisequencing, real-time polymerase chain reaction, and oligonucleotide ligation assays) have been developed. In addition, many of the emerging technologies take advantage of colourimetric or fluorescence detection (including energy transfer) that allows qualitative and quantitative interpretation of results. With the large variety of DNA technologies available, the choice of methodology will depend on several factors including cost and the need for speed, simplicity and robustness.

Severe digital necrosis in an elderly patient with heterozygous factor V Leiden mutation

We report an 81-year-old female with a heterozygous factor V Leiden mutation who developed purpura fulminans. Digital necrosis, a characteristic clinical feature of purpura fulminans was prominent. Purpura fulminans is more common in children and adult cases are rare. Of eight reported cases of purpura fulminans resulting from a heterozygous factor V Leiden mutation recorded in the literature, only two were in adults: 40 and 42 years of age, respectively. This is the first report of this condition arising in a patient in her eighties.

Modeling zymogen protein C

A solution structure for the complete zymogen form of human coagulation protein C is modeled. The initial core structure is based on the x-ray crystallographic structure of the gamma-carboxyglutamic acid (Gla)-domainless activated form. The Gla domain (residues 1-48) is modeled from the x-ray crystal coordinates of the factor VII(a)/tissue factor complex and oriented with the epidermal growth factor-1 domain to yield an initial orientation consistent with the x-ray crystal structure of porcine factor IX(a). The missing C-terminal residues in the light chain (residues 147-157) and the activation peptide residues 158-169 were introduced using homology modeling so that the activation peptide residues directly interact with the residues in the calcium binding loop. Molecular dynamics simulations (Amber-particle-mesh-Ewald) are used to obtain the complete calcium-complexed solution structure. The individual domain structures of protein C in solution are largely unaffected by solvation, whereas the Gla-epidermal growth factor-1 orientation evolves to a form different from both factors VII(a) and IX(a). The solution structure of the zymogen protein C is compared with the crystal structures of the existing zymogen serine proteases: chymotrypsinogen, proproteinase, and prethrombin-2. Calculated electrostatic potential surfaces support the involvement of the serine protease calcium ion binding loop in providing a suitable electrostatic environment around the scissile bond for II(a)/thrombomodulin interaction.

Occlusive vascular diseases in oral contraceptive users. Epidemiology, pathology and mechanisms

Despite being an unprecedented departure from normal physiology, the combined oral contraceptive is not only highly effective, but it also has a remarkably good safety record. Concerns over safety persist, though, particularly with regard to venous thromboembolism (VTE), stroke and myocardial infarction (MI). Epidemiological studies consistently show an increase in risk of VTE, but the results are more contentious with regard to arterial diseases. Despite 40 years of research, the mechanisms behind these adverse effects are not understood. In this review, we integrate information from published studies of the epidemiology and pathology of the occlusive vascular diseases and their risk factors to identify likely explanations for pathogenesis in oral contraceptive users. Oral contraceptives induce both prothrombotic and fibrinolytic changes in haemostatic factors and an imbalance in haemostasis is likely to be important in oral contraceptive-induced VTE. The complexity of the changes involved and the difficulty of ascribing clinical significance has meant that uncertainty persists. A seriously under-researched area concerns vascular changes in oral contraceptive users. Histologically, endothelial and intimal proliferation have been identified in women exposed to high plasma estrogen concentrations and these lesions are associated with thrombotic occlusion. Other structural changes may result in increased vascular permeability, loss of vascular tone and venous stasis. With regard to arterial disease risk, epidemiological information relating to dose effects and joint effects with other risk factors, and studies of pathology and changes in risk factors, suggests that oral contraceptive use per se does not cause arterial disease. It can, nevertheless, synergise very powerfully with subclinical endothelial damage to promote arterial occlusion. Accordingly, the prothrombotic effects of the oral contraceptive estrogen intervene in a cycle of endothelial damage and repair which would otherwise remain clinically silent or would ultimately progress - in, for example, the presence of cigarette smoking or hypertension - to atherosclerosis. Future work in this area should focus on modification of the effects of established risk factors by oral contraceptive use rather than modification of the supposed risk of oral contraceptive use by established risk factors. Attempts to understand vascular occlusion in oral contraceptive users in terms of the general features of VTE or with reference to atherosclerosis may be limiting, and future work needs to acknowledge that such occlusions may have unique features. Unequivocal identification of the mechanisms involved would contribute considerably to the alleviation of fears over vascular disease and to the development of even safer formulations.

Prevalence of factor V Leiden and prothrombin variant G20210A in patients age <50 years with no significant stenoses at angiography three to four weeks after myocardial infarction

OBJECTIVES

We sought to determine the frequencies of factor V Leiden and prothrombin variant G20210A in patients age <50 years with no significant coronary stenoses three to four weeks after myocardial infarction (MI).

BACKGROUND

Factor V Leiden and prothrombin variant G20210A occur frequently in patients with venous thromboembolism. However, the contribution of these mutations to the development of MI requires clarification.

METHODS

The frequencies of factor V Leiden and prothrombin variant G20210A were determined in 41 patients age <50 years who had "normal" or "near normal" coronary arteries (no stenosis >50%) at angiography three to four weeks after MI (the study group) and compared with those in 114 patients who had at least one angiographic stenosis >50% after MI (the control group). Patients age > or =50 years with, or without, stenoses were also studied.

RESULTS

The frequency of factor V Leiden was 14.6% in patients age <50 years in the study group compared with 3.6% in patients in the control group (odds ratio [OR] 4.7 [95% confidence interval (CI) 1.3-17.7], p = 0.02). The frequency of the prothrombin variant G20210A was 7.3% in the study group compared with 1.8% in the control group (OR 4.4 [95% CI 0.7-27.5], p = 0.12). One or both mutations were present in 8 of the 41 patients (19.5%) age <50 years in the study group compared with 6 of the 114 patients (5.5%) in the control group (OR 4.4 [95% CI 1.4-13.5], p = 0.01). In all 271 patients (irrespective of age) with normal arteries, the frequency of factor V Leiden was 11.7% (7/60) compared with 4.3% (9/211) in patients with at least one >50% stenosis (OR 2.9 [95% CI 1.1-8.3], p = 0.04), and the frequency of prothrombin variant G20210A was 6.7% (4/60) compared with 1.4% (3/211) (OR 4.9 [95% CI 1.1-22.8], p = 0.04), respectively.

CONCLUSIONS

The frequencies of factor V Leiden and/or prothrombin variant G20210A are increased in patients age <50 years with normal or near normal coronary arteries after MI.

Combinations of 4 mutations (FV R506Q, FV H1299R, FV Y1702C, PT 20210G/A) affecting the prothrombinase complex in a thrombophilic family

The study of the molecular bases of thrombophilia in a large family with 4 symptomatic members is reported. Three thrombophilic genetic components (FV R506Q, FV H1299R, and PT 20210G/A), all affecting the activity of the prothrombinase complex, were detected alone and in combination in various family members. In addition, a newly identified missense mutation (factor V [FV] Y1702C), causing FV deficiency, was also present in the family and appeared to enhance activated protein C (APC) resistance in carriers of FV R506Q or FV H1299R by abolishing the expression of the counterpart FV allele. The relationships between complex genotypes, coagulation laboratory findings, and clinical phenotypes were analyzed in the family. All symptomatic family members were carriers of combined defects and showed APC resistance and elevated F1 + 2 values. Evidence for the causative role of the FV Y1702C mutation, which affects a residue absolutely conserved in all 3 A domains of FV, factor VIII, and ceruloplasmin, relies on (1) the absolute cosegregation between the mutation and FV deficiency, both in the family and in the general population; (2) FV antigen and immunoblot studies indicating the absence of Y1702C FV molecules in plasma of carriers of the mutation, despite normal levels of the FV Y1702C messenger RNA; and (3) molecular modeling data that support a crucial role of the mutated residue in the A domain structure. These findings help to interpret the variable penetrance of thrombosis in thrombophilic families and to define the molecular bases of FV deficiency.

Combinations of 4 mutations (FV R506Q, FV H1299R, FV Y1702C, PT 20210G/A) affecting the prothrombinase complex in a thrombophilic family

The study of the molecular bases of thrombophilia in a large family with 4 symptomatic members is reported. Three thrombophilic genetic components (FV R506Q, FV H1299R, and PT 20210G/A), all affecting the activity of the prothrombinase complex, were detected alone and in combination in various family members. In addition, a newly identified missense mutation (factor V [FV] Y1702C), causing FV deficiency, was also present in the family and appeared to enhance activated protein C (APC) resistance in carriers of FV R506Q or FV H1299R by abolishing the expression of the counterpart FV allele. The relationships between complex genotypes, coagulation laboratory findings, and clinical phenotypes were analyzed in the family. All symptomatic family members were carriers of combined defects and showed APC resistance and elevated F1 + 2 values. Evidence for the causative role of the FV Y1702C mutation, which affects a residue absolutely conserved in all 3 A domains of FV, factor VIII, and ceruloplasmin, relies on (1) the absolute cosegregation between the mutation and FV deficiency, both in the family and in the general population; (2) FV antigen and immunoblot studies indicating the absence of Y1702C FV molecules in plasma of carriers of the mutation, despite normal levels of the FV Y1702C messenger RNA; and (3) molecular modeling data that support a crucial role of the mutated residue in the A domain structure. These findings help to interpret the variable penetrance of thrombosis in thrombophilic families and to define the molecular bases of FV deficiency.

The effects of hormone replacement therapy on thrombin generation, fibrinolysis inhibition, and resistance to activated protein C: prospective cohort study and review of literature

Recent studies have found that hormone replacement therapy (HRT) is associated with a two- to fourfold increased risk of venous thromboembolism, but the thrombogenic mechanism of HRT remains unclear. To investigate whether HRT use induces a procoagulant state, we undertook a prospective cohort study in postmenopausal women to investigate the effects of 3 months of treatment with oral HRT (conjugated equine estrogen 0.625 mg daily and medroxyprogesterone 2.5 mg daily) on markers of thrombin generation (prothrombin fragment 1+2, thrombin-antithrombin complexes), fibrinolytic potential (plasminogen activator inhibitor-1 (PAI-1) activity), and activated protein C (APC) resistance. In addition, we reviewed the literature for studies investigating the effects of HRT on markers of thrombin generation and fibrinolytic potential. In 12 patients who received HRT for a mean of 3.8 months, there was no significant effect of HRT on levels of F1+2, thrombin-antithrombin complexes, or the APC ratio. HRT use had the greatest effect on PAI-1 activity (mean difference = -3.75 UI/mL; 95% confidence interval: - 8.9, 1.1) compared to other coagulation parameters, but this did not attain statistical significance (p = 0.12). In the literature review, the effects of HRT on markers of thrombin generation were inconsistent across studies. There was a consistent pattern of increased fibrinolytic potential with HRT use associated with one marker (PAI-1), but not with another marker (tissue plasminogen activator antigen). We conclude that there is a lack of consistent evidence that the increased risk of venous thromboembolism associated with HRT use is due to a procoagulant state related to increased thrombin generation, decreased fibrinolytic potential, or acquired APC resistance.

Prothrombotic phenotype of protein Z deficiency

Protein Z (PZ) is a vitamin K-dependent plasma protein whose function has been uncertain. The structure of PZ is very similar to that of the coagulation-related factors VII, IX, and X and PC, but PZ differs from these other proteins in that it is not the zymogen of a serine protease. We have shown recently that PZ forms a calcium ion-dependent complex with activated factor X at phospholipid surfaces and that this interaction leads to the inhibition of activated factor X activity through, in part, the action of a previously unidentified plasma protein named PZ-dependent protease inhibitor. Herein, we report that the presence of PZ dampens the coagulation response in human plasma and that concomitant PZ deficiency dramatically increases the severity of the prothrombotic phenotype of factor V(Leiden) mice. The results indicate that PZ plays a physiologically important role in the regulation of coagulation.

A pilot study of the possible role of familial defects in anticoagulation as a cause for terminal limb reduction malformations

Terminal limb deficiency defects affect between three and eight babies per 10000 births and are an important cause of disability. Established causes for these malformations include single gene disorders, chromosome abnormalities, teratogens, and amniotic bands. However, the etiology remains unknown in a significant proportion of cases. Several authors have hypothesized that vascular accidents, either bleeds or vessel occlusions, may underlie a substantial number of cases; but, for the most part, the origin of such events remains obscure. Over the past several years, an increasing number of genetic thrombophilias have been recognized and have been associated with increased risks of peri- and post-natal occlusive disease, and with higher rates of recurrent pregnancy loss. The hypothesis to be examined in this pilot study was whether the inherited thrombophilias might be associated with a vascular cause of some terminal limb deficiency defects. Towards that end, protein C, protein S, antithrombin III, factor V Leiden mutation, prothrombin (G20210A) variant, methylenetetrahydrofolate reductase variant, plasma homocysteine, anticardiolipin IgM and IgG antibodies, and lipoprotein (a) were measured in 24 mother-child pairs in which the child had a terminal limb defect. The results provided some evidence that there may be an excess of thrombophilias present in such families and that they may play some etiological role in a subset of these types of limb malformations.

Obstetric implications of activated protein C resistance and factor V Leiden mutation

An increasing number of reports have focused on activated protein C resistance (APCR) as it has been shown not only to be the most common genetic factor predisposing patients to thromboembolic disease but the most common identifiable cause overall. More than 90 percent of the cases of APCR are caused by the factor V Leiden mutation, in which a guanine to adenine substitution in the factor V gene at nucleotide position 1691 results in a glutamine to arginine switch at position 506. Recent studies have also pointed to evidence of an association between APCR/factor V Leiden mutation and hypertensive disorders of pregnancy, first and second trimester miscarriage, placental infarction, and placental abruption.

Advances toward gene therapy for hemophilia at the millennium

Hemophilia A and hemophilia B are both X chromosome-linked recessive bleeding disorders that affect about 1 in 5000 males and result from a deficiency in the coagulation factors VIII and IX, respectively. Severely affected individuals require frequent administration of factor VIII or factor IX preparations derived from human plasma, and more recently, from recombinant DNA technology. Although these preparations have greatly reduced the contamination with blood-borne pathogens, there still exist significant limitations with protein replacement therapy. As we elucidate more about the expression, structure, and function of these coagulation factors new avenues will open for the development of novel genetically improved coagulation factors. Several aspects of the hemophilias A and B make these diseases attractive candidates for gene therapy. These advantages include the following: (1) these proteins are readily delivered into the circulation from a variety of different cell types; (2) low levels of expression would significantly improve the management of bleeding episodes in these patients; (3) it is unlikely that regulated expression of these proteins will be required; and (4) there are excellent animal models for these diseases. Although progress with gene transfer of factor IX has proceeded at a greater rate than factor VIII, success with both molecules has demonstrated partial persistent correction in mouse and canine models of hemophilia A and B. The information gained from these animal studies has provided new insights into gene therapeutic approaches for genetic diseases. In addition, several gene therapy clinical studies for the treatment of hemophilia A and B were initiated in 1999.

High prevalence of activated protein C resistance due to factor V leiden mutation in cases of intrauterine fetal death

OBJECTIVE

To test a possible association between activated protein C resistance and intrauterine fetal death.

METHODS

The activated protein C anticoagulant activity and factor V R506Q mutation were assessed in 14 nonpregnant women with a history of intrauterine fetal death and 14 healthy controls.

RESULTS

Four women in the study group were heterozygotes for the factor V mutation and none of the controls. The mean activated protein C activity of the study group was statistically significantly lower than that of the controls (P = 0.013).

CONCLUSION

Resistance to activated protein C activity may be of etiologic importance in some cases of intrauterine fetal death.

The role of inherited thrombophilia in venous thromboembolism associated with pregnancy

Venous thromboembolism is an important cause of maternal morbidity and mortality. The puerperium should be regarded as the period of greatest risk. However, fatalities in early pregnancy emphasise the need to assess thrombotic risk at all stages of pregnancy. In many cases those at increased risk are potentially identifiable on clinical grounds alone such as those with a personal or family history of venous thromboembolism, obesity, or surgery. Identification of women with multiple clinical risks for thrombosis during pregnancy remains the key to reducing the incidence of this condition. In women who present with a personal or family history of proven venous thromboembolism, thrombophilia screening should be performed in early pregnancy, since the results may influence subsequent management during pregnancy. The investigation and management of patients considered at increased risk of venous thrombosis during pregnancy requires close liaison between obstetricians and haematologists familiar with this rapidly expanding and complex field of thrombophilia.

Risk factors for venous thromboembolism in pregnancy

Venous thromboembolism remains the leading cause of maternal mortality in the United Kingdom. In this review we highlight studies that have documented the incidence of objectively confirmed venous thromboembolism in pregnancy, consider the effect of pregnancy on the coagulation and fibrinolytic systems, and examine in detail current knowledge of the risk factors for the development of this condition.

Cleavage of Factor V at Arg 506 by Activated Protein C and the Expression of Anticoagulant Activity of Factor V

Activated protein C (APC) inhibits coagulation by cleaving and inactivating procoagulant factor Va (FVa) and factor VIIIa (FVIIIa). FV, in addition to being the precursor of FVa, has anticoagulant properties; functioning in synergy with protein S as a cofactor of APC in the inhibition of the FVIIIa-factor IXa (FIXa) complex. FV:Q506 isolated from an individual homozygous for APC-resistance is less efficient as an APC-cofactor than normal FV (FV:R506). To investigate the importance of the three APC cleavage sites in FV (Arg-306, Arg-506, and Arg-679) for expression of its APC-cofactor activity, four recombinant FV mutants (FV:Q306, FV:Q306/Q506, FV:Q506, and FV:Q679) were tested. FV mutants with Gln (Q) at position 506 instead of Arg (R) were found to be poor APC-cofactors, whereas Arg to Gln mutations at positions 306 or 679 had no negative effect on the APC-cofactor activity of FV. The loss of APC-cofactor activity as a result of the Arg-506 to Gln mutation suggested that APC-cleavage at Arg-506 in FV is important for the ability of FV to function as an APC-cofactor. Using Western blotting, it was shown that both wild-type FV and mutant FV was cleaved by APC during the FVIIIa inhibition. At optimum concentrations of wild-type FV (11 nmol/L) and protein S (100 nmol/L), FVIIIa was found to be highly sensitive to APC with maximum inhibition occurring at less than 1 nmol/L APC. FV:Q506 was inactive as an APC-cofactor at APC-concentrations ≤ 1 nmol/L and only partially active at higher APC concentrations. Our results show that increased expression of FV anticoagulant activity correlates with APC-mediated cleavage at Arg-506 in FV, but not with cleavage at Arg-306 nor at Arg-679.

Cleavage of Factor V at Arg 506 by Activated Protein C and the Expression of Anticoagulant Activity of Factor V

Activated protein C (APC) inhibits coagulation by cleaving and inactivating procoagulant factor Va (FVa) and factor VIIIa (FVIIIa). FV, in addition to being the precursor of FVa, has anticoagulant properties; functioning in synergy with protein S as a cofactor of APC in the inhibition of the FVIIIa-factor IXa (FIXa) complex. FV:Q506 isolated from an individual homozygous for APC-resistance is less efficient as an APC-cofactor than normal FV (FV:R506). To investigate the importance of the three APC cleavage sites in FV (Arg-306, Arg-506, and Arg-679) for expression of its APC-cofactor activity, four recombinant FV mutants (FV:Q306, FV:Q306/Q506, FV:Q506, and FV:Q679) were tested. FV mutants with Gln (Q) at position 506 instead of Arg (R) were found to be poor APC-cofactors, whereas Arg to Gln mutations at positions 306 or 679 had no negative effect on the APC-cofactor activity of FV. The loss of APC-cofactor activity as a result of the Arg-506 to Gln mutation suggested that APC-cleavage at Arg-506 in FV is important for the ability of FV to function as an APC-cofactor. Using Western blotting, it was shown that both wild-type FV and mutant FV was cleaved by APC during the FVIIIa inhibition. At optimum concentrations of wild-type FV (11 nmol/L) and protein S (100 nmol/L), FVIIIa was found to be highly sensitive to APC with maximum inhibition occurring at less than 1 nmol/L APC. FV:Q506 was inactive as an APC-cofactor at APC-concentrations ≤ 1 nmol/L and only partially active at higher APC concentrations. Our results show that increased expression of FV anticoagulant activity correlates with APC-mediated cleavage at Arg-506 in FV, but not with cleavage at Arg-306 nor at Arg-679.

Phenotype and genotype expression in pseudohomozygous factor VLEIDEN : the need for phenotype analysis

The presence of a DNA mutation is frequently used to define a disease or a risk state. Because DNA typing has become easy and convenient in contrast to protein characterization, it is generally assumed that a mutation if present (or not) at the DNA level will be also present (or not) in the corresponding protein. However, discrepancies between phenotype and genotype can occur. A point mutation in the coagulation factor V gene (G1691-->A, resulting in an Arg506-->Gln amino acid substitution in the factor V molecule [factor VLEIDEN], leading to activated protein C resistance) is the most common genetic risk factor for familial thrombophilia. A pseudohomozygous factor VLEIDEN phenotype would occur if a heterozygous individual for factor VLEIDEN also did not express the "normal" (non-Leiden) factor V allele. However, to date, no data have been available to confirm the presence of only the factor VLEIDEN form in the plasma of these individuals. Platelet mRNA from 2 presumed pseudohomozygous patients and their family members was isolated, the amplified partial cDNAs were sequenced or restricted, and the allelic bands were quantified. Both patients were found to be heterozygous for the G1691-->A substitution at both the DNA and mRNA levels. The presence of either the normal or mutated form of factor V in the patients' plasmas was investigated using a monoclonal antibody to factor V that recognizes an epitope located between residues 307 and 506 of the factor Va heavy chain. No normal factor V could be detected in the plasmas of the 2 propositi. The present data demonstrate absence of a correlation between genotype at position 1691 (at the DNA and mRNA levels) and the corresponding phenotype data found in the plasmas of patients with pseudohomozygous factor VLEIDEN. Overall, these data suggest the existence of heterogeneous genetic "lesions," which interfere with factor V expression, processing, secretion, and/or stability. Because the presence of the factor VLEIDEN molecule in plasma is directly related to pathology, identification and quantification of the circulating forms of factor V in plasma may be required for the diagnosis of individuals with activated protein C resistance.

Polymorphisms of coagulation factor genes--a review

Common genetic variants of coagulation factor genes associated with differences in concentration and/or function of coagulation factors have been studied in search of variability that could explain the individual susceptibility to thrombosis and atherothrombotic diseases. The more outstanding polymorphisms in genes of factors involved in coagulation and fibrinolysis described in the literature (such as fibrinogen, factor XIII, glycoprotein IIb/IIIa, von Willebrand factor, factors VII, VIII and IX, factor V, ATIII and protein C system factors, prothrombin, PAI-1 and fibrinolytic system) are reviewed in the context of factor's structure and function and also in its proposed relevance for thrombotic and atherothrombotic risk definition.

Factor V Leiden and pulmonary embolism in a young woman taking an oral contraceptive

A 34-year-old woman with a history of asthma and oral contraceptive use died suddenly. Autopsy examination showed chronic pulmonary emboli with an acute pulmonary saddle embolus. An underlying congenital thrombophilic disorder was considered. Molecular studies on DNA isolated from blood using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis revealed coagulation factor V Leiden mutation. The incidence of venous thromboembolism in patients with factor V Leiden mutation and associated activated protein C (APC) resistance is discussed.

Venous thrombosis in older people: prevalence of the factor V gene mutation Q506

OBJECTIVES

Old age is usually considered to be a risk factor for venous thromboembolism, in conjunction with other factors such as heart failure, major surgery, cancer, long-term immobilization, and antiphospholipid antibodies. Genetic risk factors, especially inherited deficiencies in coagulation inhibitors, also play a role in the pathogenesis of thrombosis, but these are usually diagnosed in thrombophilic patients before the age of 50. The factor V Q506 mutation, responsible for activated protein C resistance, was recently linked to thromboembolic disease. We therefore investigated the prevalence of biological risk factors in older hospital patients with venous thromboembolism.

DESIGN

A 2-year study period.

SETTING

Ivry sur Seine (Paris), France.

PARTICIPANTS

Seventy-nine geriatric patients (60 women and 19 men, mean age 83+/-6.8 years, range 70-102 years) who had had at least one proven episode of venous thromboembolism were enrolled over a 2-year period.

MEASUREMENTS

Lupus anticoagulant and antithrombin (AT), protein C (PC), and protein S (PS) levels were determined in plasma. The factor V Q506 mutation was detected on genomic DNA.

RESULTS

Lupus anticoagulant was detected in two women, one of whom also had a high level of anticardiolipin IgG, leading to the diagnosis of an antiphospholipid syndrome. No hereditary deficiency in AT, PC, or PS was found, but one patient had an acquired AT deficiency. Interestingly, nine of the 79 patients (11.4%, six women and three men) were heterozygous for the factor V Q506 mutation, although none were homozygous. The only major risk factor for thrombosis identified in these patients was prolonged immobilization in four cases. Four of the nine patients who were heterozygous for the factor V Q506 mutation had recurrent thromboembolism, and two of these patients had been immobilized for long periods.

CONCLUSIONS

This study confirms that hereditary deficiencies in coagulation inhibitors, and the lupus anticoagulant, are rarely involved in the pathogenesis of venous thromboembolism in older subjects. In contrast, the factor V Q506 mutation was frequently associated with thrombosis (11.4% of our patients) and should, therefore, be considered an important risk factor in the older people.

Amino acid residues in thrombin-sensitive region and first epidermal growth factor domain of vitamin K-dependent protein S determining specificity of the activated protein C cofactor function

Human protein S (PS) potentiates the anticoagulant activity of human but not bovine activated protein C (APC), whereas bovine PS is a cofactor to APC from both species. The structural requirements for the specificity of the APC cofactor function of human PS are located in its thrombin-sensitive region (TSR) and the first epidermal growth factor (EGF1)-like module. To elucidate which residues in these two modules determine the specificity of the APC cofactor activity, 41 human PS mutants were expressed. All mutants were cofactors to human APC and some also to bovine APC. Residues in TSR (positions 49 and 52) and EGF1 (residues 97 and 106) together determined the specificity of the APC cofactor function, whereas substitution of individual residues did not change specificity. Bovine PS, and mutants expressing cofactor activity to bovine APC, stimulated phospholipid binding of bovine APC. In contrast, human PS and mutants lacking cofactor activity to bovine APC failed to support binding of bovine APC to phospholipids. These data indicate that residues in TSR and EGF1 cause the specificity of the APC cofactor activity and support the concept that key residues in these two modules interact with APC on the phospholipid surface.

Activated protein C resistance in patients with peripheral vascular disease

PURPOSE

The frequency of activated protein C (APC) resistance, caused by factor V R506Q gene mutation and abnormal APC ratio, in patients with peripheral vascular diseases was analyzed.

METHODS

All patients electively admitted to the vascular ward unit of our tertiary care academic medical center from January 1995 through October 1996 (n = 679) were prospectively analyzed using an APC-resistance screening test to determine the frequency of abnormal APC ratio (< or =2.6). Baseline activated partial thromboplastin time (APTT) and its prolongation after the addition of a standard amount of APC were determined. The factor V R506Q gene mutation (Leiden) was analyzed in patients with an APC ratio less than 3.0. Statistical comparisons were made to an age-matched control population (n = 278).

RESULTS

The factor V Leiden gene mutation or abnormal APC ratio was detected in 154 of the patients (22.7%), compared with 34 of 278 the control subjects (12.2%; t = 13.65; P < .001). The factor V Leiden gene mutation was found in 102 patients (15.2%), compared with 29 control subjects (10.4%; t = 4.64; P < .05); an abnormal APC ratio was found in 132 patients (19.8%), compared with 26 (9.8%) of controls (t = 14.56; P < .001). The frequency of the factor V Leiden gene mutation was significantly increased in patients with femoro-popliteal occlusive disease (n = 126), to 21.6% (t = 16.94; P< .001), and venous disease (n = 50), to 36.0% (t = 20.93; P< .001). Overall, 63% of the patients with abnormal APC ratios tested positive for the factor V Leiden gene mutation. A significantly increased frequency of APC resistance was demonstrated in patients undergoing aorto-iliac (n = 37) or femoro-crural graft reconstructions (n = 72); it was found in 41% and 35%, respectively (P < .001). In addition, a significantly increased frequency of APC resistance was found in patients who suffered from occlusion after reconstruction; 13 of 41 (32%) had the factor V Leiden gene mutation (P < .001), and 19 of 39 (49%) had an abnormal APC ratio (P < .001).

CONCLUSION

The factor V Leiden gene mutation and abnormal APC ratios are significantly increased in patients with lower extremity peripheral vascular disease and failed reconstructions. An abnormal APC ratio was seen without factor V Leiden gene mutation in 37% of patients with peripheral vascular diseases, suggesting additional causes of an abnormal APC ratio, exclusive of gene mutation.

Cerebral venous thrombosis and procoagulant factors--a case study

Cerebral venous thrombosis is a polymorphic clinical entity for which diagnosis has become more frequent with the advent of neuroradiology. The superior sagittal and transverse sinuses are frequently involved, whereas cavernous sinus thrombosis is much less frequent. Inherited resistance to the anticoagulant action of activated protein C (APC resistance), antithrombin deficiency, protein C and S deficiencies, and hyperhomocysteinemia seem to represent major causes of thrombophilia when unusual thromboembolic events (ie, before the age of 45 years) are observed. The authors present the combined occurrence of protein C and protein S deficiencies in a 32-year-old woman, manifested by extensive cerebral venous thrombosis.

The C-terminal region of the factor V B-domain is crucial for the anticoagulant activity of factor V

Factor V (FV) is recently shown to express anticoagulant activity. It functions as a synergistic cofactor with protein S to activated protein C (APC) in the degradation of factor VIIIa (FVIIIa). FV is composed of multiple domains, A1-A2-B-A3-C1-C2. Thrombin cleaves FV at Arg-709, Arg-1018, and Arg-1545 that leads to the generation of a procoagulant FV species which functions as a cofactor to factor Xa (FXa) in the activation of prothrombin to thrombin. During the activation process, the B-domain is released from the heavy (A1-A2) and light chains (A3-C1-C2) which constitute the active FV (FVa). To elucidate which effect the different thrombin cleavages in FV have on the ability of FV to express APC-cofactor activity, seven recombinant FV mutants containing all possible combinations of mutated and native thrombin cleavage sites were tested in a FVIIIa degradation assay. Thrombin cleavage at Arg-709 and/or Arg-1018 yielded FV molecules that were still able to function as APC cofactors, whereas cleavage at Arg-1545 led to a complete loss in APC-cofactor function. This suggests that the APC-cofactor function of FV depends on the B-domain remaining attached to the A3 domain. The importance of the FV B-domain for expression of APC-cofactor activity was further investigated using two B-domain deleted FV molecules, FV des-709-1545 (with the whole B-domain deleted) and FV des-709-1476 (with amino acids 710-1476 of the B-domain being removed). FV des-709-1476 expressed APC-cofactor activity, whereas the FV des-709-1545 was completely devoid of such activity. Thus, the C-terminal part of the B-domain (residues 1477-1545) was crucial for the APC-cofactor function. FV and factor VIII (FVIII) are homologous proteins having similar domain organization. A FV/FVIII chimera, harboring the B-domain from FVIII (FVBVIII) instead of the FV B-domain did not work as an APC cofactor, further illustrating the importance of the FV B-domain for the APC-cofactor function.

Structural investigation of the A domains of human blood coagulation factor V by molecular modeling

Factor V (FV) is a large (2,196 amino acids) nonenzymatic cofactor in the coagulation cascade with a domain organization (A1-A2-B-A3-C1-C2) similar to the one of factor VIII (FVIII). FV is activated to factor Va (FVa) by thrombin, which cleaves away the B domain leaving a heterodimeric structure composed of a heavy chain (A1-A2) and a light chain (A3-C1-C2). Activated protein C (APC), together with its cofactor protein S (PS), inhibits the coagulation cascade via limited proteolysis of FVa and FVIIIa (APC cleaves FVa at residues R306, R506, and R679). The A domains of FV and FVIII share important sequence identity with the plasma copper-binding protein ceruloplasmin (CP). The X-ray structure of CP and theoretical models for FVIII have been recently reported. This information allowed us to build a theoretical model (994 residues) for the A domains of human FV/FVa (residues 1-656 and 1546-1883). Structural analysis of the FV model indicates that: (a) the three A domains are arranged in a triangular fashion as in the case of CP and the organization of these domains should remain essentially the same before and after activation; (b) a Type II copper ion is located at the A1-A3 interface; (c) residues R306 and R506 (cleavage sites for APC) are both solvent exposed; (d) residues 1667-1765 within the A3 domain, expected to interact with the membrane, are essentially buried; (e) APC does not bind to FVa residues 1865-1874. Several other features of factor V/Va, like the R506Q and A221V mutations; factor Xa (FXa) and human neutrophil elastase (HNE) cleavages; protein S, prothrombin and FXa binding, are also investigated.

No correlation between activated protein C resistance and free flap failures in 100 consecutive patients

This study evaluates whether thrombophilic disorders contribute to failures in microvascular surgery. A recently discovered condition is focused on, i.e., activated protein C resistance, which is a highly prevalent functional defect of a crucial endogenous anticoagulant system--the protein C anticoagulant pathway (up to 15 percent of Caucasians affected). One hundred consecutive patients were operated on with 103 free tissue transfers during a 2.5-year period, all of which received perioperative intravenous anticoagulation, principally based on dextran (1 liter) and a heparin bolus at vascular reperfusion (80 to 100 IU/kg). The patients underwent extensive laboratory analysis with respect to conditions predisposing for thrombosis. Eleven patients were found to be activated protein C resistant, and one patient had congenital protein S deficiency. There were six total and five partial flap losses, which, however, in only one case coincided with the presence of a thrombophilic disorder (activated protein C resistance). By contrast, a substantial portion of flap necroses could be related to nonconstitutional factors (for example, pedicle kinking). It is concluded that routine screening for hypercoagulable states such as activated protein C resistance is not necessary in microvascular surgery.

[A young patient with multiple arterial occlusions]

BACKGROUND

Mild hyperhomocysteinemia due to genetic causes and nutrition factors is well known as an independent strong risk factor for premature arterial occlusive disease.

CASE REPORT

A 27-year-old female with a history of two episodes of small bowel ileus due to vascular causes presented with subacute pain in the left lower extremity. Angiography revealed a short segmental occlusion in the P III segment of the popliteal artery with small vessel collateralization and proximal occlusion of the superior mesenteric artery und the coeliac trunk. Vascular risk factors in this patient included smoking over a duration of 10 years, use of oral contraceptives (estrogen and gestagen combination) and elevated levels of homocysteine in the fasting state and after methionin loading. The patient was treated conservatively with intravenous application of prostaglandins, additionally she underwent training to improve her walking capability. After 4 weeks of the fasting state as well as after methionin loading were normalized by an oral substitution with folate and B vitamins. So far it was not possible to prove a genetic defect of the enzymes participating in the metabolism of homocysteine.

CONCLUSION

This clinical conference of a young female patient with occlusion of several arteries illustrates the differential diagnosis of premature occlusive vascular disease with special regard to mild hyperhomocysteinemia as an independent risk factor.

Changes of resistance to activated protein C in the course of pregnancy and prevalence of factor V mutation

The purpose of this study was to examine the changes in activated protein C (APC) anticoagulant activity during pregnancy and determine whether changes in APC could contribute to thrombosis in the placental bed in preeclampsia. We measured APC anticoagulant activity in 150 women with a normal pregnancy and 50 women with preeclampsia. There was a significant reduction in the mean APC sensitivity ratio (APC-SR) during pregnancy (p<0.001). APC resistance in preeclampsia was significantly higher than in normal pregnancy (p<0.01). Amongst women with APC resistance the presence of the factor V Leiden mutation was significantly higher in the preeclampsia group than in the normal pregnancy group (p<0.01). It seems that both factor V Leiden mutation and APC resistance may be associated with the development of preeclampsia. These results suggest that APC resistance may be an important mechanism underlying placental bed pathology in pregnancy and may be associated with an increased tendency to develop preeclampsia in some women. Assay of APC resistance and factor V Leiden mutation should be performed in women with preeclampsia.

Platelet-Derived Factor Va/VaLeiden Cofactor Activities Are Sustained on the Surface of Activated Platelets Despite the Presence of Activated Protein C

We investigated the role of the thrombin-activated platelet in modulating the rate and extent of activated protein C (APC)-catalyzed inactivation of platelet-derived factor Va and factor VaLeiden. Platelet-derived factor Va and factor VaLeiden were inactivated by APC at near identical rates; however, complete inactivation of the cofactors was never achieved. Greater residual cofactor activity remained when using thrombin-activated platelets compared with that observed with synthetic phospholipid vesicles and platelet-derived microparticles, suggesting that thrombin-activated platelets protect the cofactors from APC-catalyzed inactivation. This apparent protection was not due to (1) an insufficient number of membrane binding sites for APC or factor Va; (2) the destruction of these sites; or (3) the presence of a platelet-associated APC inhibitor. Results from a plasma-based clotting assay (with or without APC) with platelets or PCPS vesicles added to induce clot formation indicated that, even in the presence of high concentrations of APC, platelets offered protection of the cofactor by delaying cleavage at Arg506. This resulted in incomplete proteolysis of the heavy chain, suggesting that platelets can also protect plasma-derived factor Va from APC-catalyzed inactivation. However, additional experiments indicated that the plasma-derived cofactor, bound to thrombin-activated platelets, was completely inactivated by APC, suggesting that the plasma and platelet-derived cofactor pools represent different substrates for APC. Collectively, these results indicate that platelets sustain procoagulant events by providing a membrane surface that delays cofactor inactivation and by releasing a cofactor molecule that displays an APC resistant phenotype. Thus, at sites of arterial injury, the factor VLeidenmutation may not as readily predict arterial thrombosis, because the normal and variant platelet-derived cofactors are equally resistant to APC at the activated platelet surface.

Guidelines for antithrombotic therapy in pediatric patients

Because of the relatively low incidence of TEs in children, the diagnostic and therapeutic approaches used are largely extrapolated from guidelines for adults. Features that differ in children compared with adults include underlying disorders, high incidence of CVL-related DVT in the upper venous system, and response to SH, warfarin, and thrombolytic agents. There is a paucity of information on the risk/benefit ratio of the therapeutic interventions and long-term outcome. Clinical trials are urgently needed to clarify optimal management for pediatric patients with TEs.

[New causes of inherited thrombophilia]

Activated protein C resistance is the most frequent cause of thrombophilia. It is found in 20% of patients with an episode of deep vein thrombosis (DVT) and its prevalence in caucasian population is between 3-7%. Activated protein C resistance is secondary to an Arg 506 to Gln mutation of factor V (factor V Leiden). The relative risk of DVT for heterozygotes is 5 to 10, and for homozygotes 50 to 100. There is a 2- to 4-fold increase risk of recurrences in patients bearing the factor V Leiden mutation after a first episode of DVT. Recently a new mutation in the prothrombin gene (20210 G/A) was found to increase the relative risk of DVT by 2 to 4. Finally we also reviewed the association between DVT and hyperhomocysteinemia that is associated with a 2-fold increase risk of DVT.

Evaluation of a modified APTT-based method for determination of APC resistance in plasma from patients on heparin or oral anticoagulant therapy

An APTT-based kit method (Coatest APC Resistance), modified by predilution 1+4 of sample plasma in a plasma diluent containing a heparin antagonist (V-DEF plasma), has been evaluated on plasmas from patients treated with unfractionated (n = 110) or either of three different low molecular heparins (n=44), or with oral anticoagulants (n=147). Irrespective of treatment, no difference was observed in the APC response as compared to untreated individuals (n=62), and a complete discrimination was obtained between individuals with a normal factor V genotype and those carrying the FV:Q506 mutation. Furthermore, in contrast to the original, APTT-based kit method, where anticoagulant therapy results in a prolongation of the APTT, the modified kit provided APTT values within the normal range for orally anticoagulated (INR< or =6) and for all heparin treated (< or =1 IU/mL) patients except for one with a suspected presence of phospholipid antibodies. Due to the predilution in V-DEF plasma, contamination with platelets up to 1.5 x 10(4)/microL had a negligible effect on analysis of frozen plasmas regarding their classification as normal or abnormal. Analyses of fresh plasmas show no influence at platelet counts up to 6x10(4)/microL. Consequently, negligible differences in APC ratios were obtained between fresh and frozen plasmas. In conclusion, the modified kit method is applicable to plasmas from anticoagulated patients as well as from untreated individuals, allowing a safe assignment regarding the presence or absence of the FV:Q506 genotype.

Association of vitamin K-dependent coagulation proteins and C4b binding protein with triglyceride-rich lipoproteins of human plasma

The triglyceride (TG) concentration in plasma is an independent risk factor for coronary heart disease. There is evidence that TG-rich lipoprotein (TGRLP), ie, chylomicrons (CMs), chylomicron remnants (CMRs), and VLDLs associate with factor VII and prothrombin and that the association enhances a platelet factor Xa-mediated prothrombin activation when the CM-prothrombin complex is exposed to platelets. In this study, we examined the association of the vitamin K-dependent coagulation factors VII, IX, X, and prothrombin, as well as the anticoagulation protein C and its cofactor protein S, in plasma lipoproteins obtained from human fasting and postprandial plasma. We also analyzed some other proteins that are related to the coagulation system but not to vitamin K-dependent proteins, including factor V, serum amyloid P component (SAP), C4b binding protein (C4BP), and thrombomodulin (TM), and as a control, Ig G. Human TGRLP (d < 1.006 kg/L), LDL (d = 1.006 to 1.063 kg/L), and HDL (d = 1.063 to 1.210 kg/L) were separated from normal subjects both in fasting and 2 to 3 hours after the ingestion of a meal containing 100 g fat. The different coagulation proteins, SAP, C4BP, TM, and Ig G were determined by SDS-polyacrylamide gel electrophoresis combined with Western blotting, using specific polyclonal or monoclonal antibodies, and were visualized by peroxidase staining. All the vitamin K-dependent proteins associate with TGRLP in both fasting and postprandial plasma, but not with LDL or HDL. Factor V, SAP, TM, and Ig G were not found in any lipoprotein classes. C4BP, which is a regulatory protein of the classic pathway of the complement system and which binds protein S in vivo to regulate blood coagulation, was present in TGRLP, especially postprandial, but not in LDL or HDL. The amounts of prothrombin, protein S, and C4BP in postprandial TGRLP were larger than those in fasting TGRLP. Vitamin K-dependent procoagulation and anticoagulation proteins, as well as C4BP, could be associated with TGRLP in vivo. If the association enhances prothrombin activation, this effect may thus be counteracted by simultaneous binding of protein S.

Prevalence of activated protein C resistance in the Chinese population

In 1996, a total of 1700 subjects, including 461 healthy subjects and 1239 clinic patients, were randomized and consecutively entered into our study. Their mean age was 49.30+/-18.71 years, range 1-99 years. Of them, 1117 were male, and 583 were female. The mean age of the male was 42.96+/-17.64 years, and of the female, 52.60+/-18.41 years. The mean activated protein C ratio in 1700 subjects was 2.96+/-0.69, range 2.00-7.93. None of them had activated protein C ratio <2.0. The mean activated protein C ratio in the male was 2.81+/-0.63, and in the female was 3.04+/-0.71. None of the subjects was found to have activated protein C resistance. DNA analysis for the Arg 506-Gln mutation was also performed on 492 out of the 1700 subjects; none of them had this mutation. We suggested that the Chinese is not a race with the trait of activated protein C resistance.

Methysergide-induced retroperitoneal fibrosis: successful outcome and two new laboratory features

A 25-year-old woman sought medical attention because of iliocaval manifestations of retroperitoneal fibrosis while she was taking methysergide. Laboratory studies yielded substantially increased serum procollagen III levels and anticardiolipin antibodies accompanied with anti-beta(2) glycoprotein I, findings not previously described with this disorder. Clinical and laboratory manifestations resolved after cessation of methysergide therapy.

Peripheral retinal neovascularization and retinal vascular occlusion associated with activated protein C resistance

PURPOSE

To describe a patient with peripheral retinal neovascularization and vascular occlusion associated with activated protein C resistance.

METHODS

Case report. A 63-year-old woman was examined for acute loss of vision in both eyes. She was noted to have macular edema in both eyes as well as a macular branch vein occlusion in the right eye and a central retinal vein occlusion in the left eye. Peripheral retinal neovascularization was present in both eyes.

RESULT

Extensive systemic evaluation disclosed a heterozygous state for the factor V Leiden indicating activated protein C resistance.

CONCLUSION

Activated protein C resistance may be associated with peripheral retinal neovascularization.

Molecular Genetics of Factor V Leiden: Genetic Origins and Modern DNA-Based Detection Strategies

It has been acknowledged that a prothrombotic tendency may result from a specific genetic defect. Resistance to activated protein C (APC) (factor V Leiden) is now recognized as the most prevalent cause of increased thrombogenicity, being found in 2% to 5% of the world population. The APC-resistant phenotype arises from a well-characterized transitional mutation, resulting in an arginine(R)-506-glutamine(Q) amino acid substitution. Much remains to be uncovered concerning the importance of this mutation and how it relates to other conditions on a broader basis. Relevant and accurate detection methods that quickly identify the genetic lesion will play a major part in this strategy. This article details recent advances in identifying the factor V Leiden mutation by modern molecular techniques.

Changes in activated protein C resistance during normal pregnancy

OBJECTIVE

The objective of this study was to determine the changes in activated protein C resistance that occur during normal pregnancy.

STUDY DESIGN

In this cross-sectional study activated protein C was measured in 128 women with normal pregnancies in the first, second, and third trimesters and in nonpregnant control subjects with 24 to 39 women in each group. In addition, factor V, factor VIII, free protein S, and functional protein C were measured and correlated with activated protein C levels. Polymerase chain reaction for factor V Leiden mutation was performed.

RESULTS

There was a significant fall in the activity of activated protein C in the second and third trimesters of pregnancy (p < 0.05). This was related to increased factor VIII and decreased free protein S levels (p = 0.002, R2 = 0.20). The prevalence of the factor V Leiden mutation was 7.3%.

CONCLUSION

Resistance to activated protein C is increased in the second and third trimesters of pregnancy. This is related to the alterations in other coagulation proteins, a phenomenon normally occurring during pregnancy.

Approaching the clinical application of xenotransplantation

Interspecies transplantation or xenotransplantation is seen increasingly as a potential approach to overcoming the severe shortage of human organs and tissues for transplantation. Much has been learned recently about the immunologic hurdles of transplanting porcine organs into humans. These hurdles can be addressed, in part, by the genetic engineering of donors and by specific therapies directed at the salient immune events. As we succeed in dealing with the immunologic aspects of xenotransplantation, other issues, including zoonosis, and regulatory aspects will need to be addressed.

Activated protein C resistance (factor V Leiden) associated with thrombosis in pregnancy

OBJECTIVE

Our purpose was to evaluate activated protein C resistance phenotype and genotype among patients with thrombosis during pregnancy and the puerperium.

STUDY DESIGN

This observational study was conducted prospectively during a 2-year period (July 1993 to June 1995) in a preselected population. All patients admitted to our high-risk pregnancy unit with a diagnosis of deep vein thrombosis, pulmonary emboli, transient ischemic attack, and cerebrovascular accident during pregnancy and the puerperium were included. Prothrombin time, partial thromboplastin time, fibrinogen levels, protein C, protein S, antithrombin III, functional test for activated protein C resistance, and factor V Leiden mutation by polymerase chain reaction were performed on each patient.

RESULTS

Fifteen patients were included. Seven (46.6%) patients were positive for activated protein C resistance (factor V Leiden). All other coagulation studies were negative for all patients. All patients with activated protein C resistance had a venous thrombotic event, deep vein thrombosis, or pulmonary emboli, and only one had a cerebrovascular accident on the basis of sagittal sinus thrombosis. Only two of the activated protein C resistance-negative patients had venous thrombosis (pulmonary emboli). The remaining six patients had transient ischemic attacks or cerebrovascular accidents. For the subgroup with venous thrombosis during pregnancy and the puerperium, the incidence of activated protein C resistance (factor V Leiden) was 78%.

CONCLUSION

This study demonstrates the incidence of factor V Leiden in a selected population in whom thrombotic events developed during pregnancy and the puerperium. This small-scale study provides justification for a large cohort study that will identify women with factor V Leiden and determine their risk for thrombosis during pregnancy and the puerperium. We believe that factor V Leiden should be evaluated in conjunction with thrombotic events in the pregnant woman.