Human genetics. Bad blood by mutation

Admixture Has Shaped Romani Genetic Diversity in Clinically Relevant Variants

Genetic patterns of inter-population variation are a result of different demographic and adaptive histories, which gradually shape the frequency distribution of the variants. However, the study of clinically relevant mutations has a Eurocentric bias. The Romani, the largest transnational minority ethnic group in Europe, originated in South Asia and received extensive gene flow from West Eurasia. Most medical genetic studies have only explored founder mutations related to Mendelian disorders in this population. Here we analyze exome sequences and genome-wide array data of 89 healthy Spanish Roma individuals to study complex traits and disease. We apply a different framework and focus on variants with both increased and decreased allele frequencies, taking into account their local ancestry. We report several OMIM traits enriched for genes with deleterious variants showing increased frequencies in Roma or in non-Roma (e.g., obesity is enriched in Roma, with an associated variant linked to South Asian ancestry; while non-insulin dependent diabetes is enriched in non-Roma Europeans). In addition, previously reported pathogenic variants also show differences among populations, where some variants segregating at low frequency in non-Roma are virtually absent in the Roma. Lastly, we describe frequency changes in drug-response variation, where many of the variants increased in Roma are clinically associated with metabolic and cardiovascular-related drugs. These results suggest that clinically relevant variation in Roma cannot only be characterized in terms of founder mutations. Instead, we observe frequency differences compared to non-Roma: some variants are absent, while other have drifted to higher frequencies. As a result of the admixture events, these clinically damaging variants can be traced back to both European and South Asian-related ancestries. This can be attributed to a different prevalence of some genetic disorders or to the fact that genetic susceptibility variants are mostly studied in populations of European descent, and can differ in individuals with different ancestries.

State-of-the-Art Review: Activated Protein C Resistance: Clinical Implications

The discovery of inherited resistance to activated protein C (APC) as a major risk factor for venous thrombosis has dramatically improved our understanding of the pathogenesis of venous thrombosis. In a majority of cases, APC resistance is associated with a single point mutation in the factor V gene (FV) that results in substitution of arginine, R, at position 506 by glutamine, Q. (FV:Q506). The mutation renders factor Va partially resistant to degradation by APC. A functional APC resistance test, which includes predilution of the patient plasma with factor V-deficient plasma, is found to be 100% sensitive and specific for the presence of FV:Q506and is useful as a screening assay. Carriers of the FV:Q506allele have increased thrombin generation, resulting in hypercoagulability and a lifelong increased risk of venous thrombosis. In Western countries, APC resistance due to the FV mutation is present in 20-60% of thrombosis patients and in 1-15% of healthy controls, whereas the mutation is virtually absent from ethnic groups other than Caucasians. This may explain the high incidence of venous thrombosis in Western countries. The thrombotic risk in APC-resistant individuals may be further increased by other genetic defects, e.g., protein C or protein S deficiency, and by exposure to circumstantial risk factors, e.g., oral contraceptives, pregnancy, immobilization, and surgery. The question is thus raised as to whether general screening for APC resistance before circumstantial risk factors occur is warranted in Western countries. Key Words: Factor V—APC resistance-Protein C-Protein S—Thrombosis—Mutation.

Anticoagulant factor V: factors affecting the integration of novel scientific discoveries into the broader framework

Since its initial discovery in the 1940s, factor V has long been viewed as an important procoagulant protein in the coagulation cascade. However, in the later part of the 20th century, two different scientists proposed novel anticoagulant roles for factor V. Philip Majerus proposed the first anticoagulant function for factor V in 1983, yet ultimately it was not widely accepted by the broader scientific community. In contrast, Björn Dahlbäck proposed a different anticoagulant role for factor V in 1994. While this role was initially contested, it was ultimately accepted and integrated into the scientific framework. In this paper, I present a detailed historical account of these two anticoagulant discoveries and propose three key reasons why Dahlbäck's anticoagulant role for factor V was accepted whereas Majerus' proposed role was largely overlooked. Perhaps most importantly, Dahlbäck's proposed anticoagulant role was of great clinical interest because the discovery involved the study of an important subset of patients with thrombophilia. Soon after Dahlbäck's 1994 work, this patient population was shown to possess the factor V Leiden mutation. Also key in the ultimate acceptance of the second proposed anticoagulant role was the persistence of the scientist who made the discovery and the interest in and ability of others to replicate and reinforce this work. This analysis of two different yet similar discoveries sheds light on factors that play an important role in how new discoveries are incorporated into the existing scientific framework.

Lower plasma creatinine and urine albumin in individuals at increased risk of type 2 diabetes with factor v leiden mutation

The factor V Leiden (FVL) mutation is the most frequent genetic cause of venous thrombosis in Caucasians. However, protective effects have been suggested to balance the disadvantages. We have recently observed protective effects of FVL mutation on experimental diabetic nephropathy in mice as well as an association with reduced albuminuria in two human cohorts of diabetic patients. In the present study we aimed to reevaluate these findings in an independent, larger cohort of 1905 Caucasians at risk of developing type 2 diabetes and extend possible associations to earlier disease stages of nephropathy. Carriers of FVL mutation had a significantly lower urine albumin excretion (P = 0.03) and tended to have lower plasma creatinine concentrations (P = 0.07). The difference in plasma creatinine concentrations was significant after adjustment for the influencing factors: age, gender, and lean body mass (P = 0.048). These observations at a very early "disease" stage are an important extension of previous findings and suggest that modification of glomerular dysfunction by FVL mutation is relevant during very early stages of diabetic nephropathy. This makes the underlying mechanism an interesting therapeutic target and raises the question whether FVL mutation may also exert protective effects in other glomerulopathies.

The evolving plasticity of coagulation protease-dependent cytoprotective signalling

Coagulation proteases control cellular homeostasis beyond haemostasis. While the role of coagulation proteases in regulating vascular healing and thrombosis is well established, the mechanism underlying the receptor-dependent regulation of cellular function remain incompletely understood. In particular, the opposing effects of the protease-activated receptor 1 (PAR-1), dependent on the activating proteases thrombin or activated protein C generated a conundrum researchers only recently have begun to decipher. The net-effect (cellular perturbation vs. cellular protection) depends on co-receptors involved, the concentration of the activating protease, the temporal context of receptor activation, and a dynamic process of receptor rearrangement upon receptor activation. The latter scenario recruits receptors to a cytoprotective signalling pathways. Recent insights into these mechanisms are summarized in this article.

Low but sustained coagulation activation ameliorates glucose-induced podocyte apoptosis: protective effect of factor V Leiden in diabetic nephropathy

Whereas it is generally perceived to be harmful, enhanced coagulation activation can also convey salutary effects. The high prevalence of the prothrombotic factor V Leiden (FVL) mutation in whites has been attributed to a positive selection pressure (eg, resulting from reduced blood loss or improved survival in sepsis). The consequences of enhanced coagulation activation, as observed in FVL carriers, on microvascular diabetic complications remain unknown. We therefore investigated the role of FVL in diabetic nephropathy. In heterozygous or homozygous diabetic FVL mice, albuminuria and indices of diabetic nephropathy were reduced compared with diabetic wild-type mice. This was associated with reduced glomerular apoptosis and preservation of podocytes in diabetic FVL-positive mice. In vitro, low-dose thrombin (50pM) prevented, whereas high-dose thrombin (20nM) aggravated, glucose-induced apoptosis in podocytes. In diabetic patients, the FVL mutation, but not the plasminogen activator inhibitor-1 4G/5G polymorphism, is associated with reduced albuminuria, which is consistent with a nephroprotective role of low but sustained thrombin generation. Consistently, anticoagulation of diabetic FVL-positive mice with hirudin abolished the nephroprotective effect. These results identify a nephroprotective function of low but sustained thrombin levels in FVL carriers, supporting a dual, context-dependent function of thrombin in chronic diseases.

Impact of the factor V Leiden mutation on the outcome of pneumococcal pneumonia: a controlled laboratory study

INTRODUCTION

Streptococcus (S.) pneumoniae is the most common cause of community-acquired pneumonia. The factor V Leiden (FVL) mutation results in resistance of activated FV to inactivation by activated protein C and thereby in a prothrombotic phenotype. Human heterozygous FVL carriers have been reported to be relatively protected against sepsis-related mortality. We here determined the effect of the FVL mutation on coagulation, inflammation, bacterial outgrowth and outcome in murine pneumococcal pneumonia.

METHODS

Wild-type mice and mice heterozygous or homozygous for the FVL mutation were infected intranasally with 2*106 colony forming units of viable S. pneumoniae. Mice were euthanized after 24 or 48 hours or observed in a survival study. In separate experiments mice were treated with ceftriaxone intraperitoneally 24 hours after infection and euthanized after 48 hours or observed in a survival study.

RESULTS

The FVL mutation had no consistent effect on activation of coagulation in either the presence or absence of ceftriaxone therapy, as reflected by comparable lung and plasma levels of thrombin-antithrombin complexes and fibrin degradation products. Moreover, the FVL mutation had no effect on lung histopathology, neutrophil influx, cytokine and chemokine levels or bacterial outgrowth. Remarkably, homozygous FVL mice were strongly protected against death due to pneumococcal pneumonia when treated with ceftriaxone, which was associated with more pronounced FXIII depletion; this protective effect was not observed in the absence of antibiotic therapy.

CONCLUSIONS

Homozygosity for the FVL mutation protects against lethality due to pneumococcal pneumonia in mice treated with antibiotics.

A follow-up study of a genome-wide association scan identifies a susceptibility locus for venous thrombosis on chromosome 6p24.1

To identify genetic susceptibility factors conferring increased risk of venous thrombosis (VT), we conducted a multistage study, following results of a previously published GWAS that failed to detect loci for developing VT. Using a collection of 5862 cases with VT and 7112 healthy controls, we identified the HIVEP1 locus on chromosome 6p24.1 as a susceptibility locus for VT. Indeed, the HIVEP1 rs169713C allele was associated with an increased risk for VT, with an odds ratio of 1.20 (95% confidence interval 1.13-1.27, p = 2.86 x 10(-9)). HIVEP1 codes for a protein that participates in the transcriptional regulation of inflammatory target genes by binding specific DNA sequences in their promoter and enhancer regions. The current results provide the identification of a locus involved in VT susceptibility that lies outside the traditional coagulation/fibrinolysis pathway.

Maternal thrombophilias are associated with specific placental lesions

Maternal floor infarction (MFI), massive perivillous fibrin deposition (MPVFD), and fetal thrombotic vasculopathy (FTV) are specific placental lesions with associations to recurrent adverse fetal outcomes and with maternal thrombophilia. We studied the frequency of a range of acquired and genetic maternal thrombophilias in MFI (40 cases), MPVFD (87 cases), FTV (7 cases), and FTV+MPVFD (4 cases). Thrombophilias were identified in 16 (40%), 20 (23%), 5 (71%), and 2 (50%) of these lesions, respectively. Seventy-seven percent of the identified thrombophilias were genetic, and 23% were acquired. The most common genetic thrombophilia was protein S deficiency, which constituted 14 of the 36 genetic thrombophilias (39%). We advocate full maternal thrombophilia testing when the diagnosis of MFI, MPVFD, and FTV is made by placental pathology examination. Because of the possible contribution of paternal thrombophilic mutations to the fetal genotype, it would be desirable to test the whole family as well.

The hemostatic balance revisited through the lessons of mankind evolution

Under physiologic conditions, a hemostatic balance is achieved through the effects of natural procoagulant and anticoagulant factors which, in equilibrium with each other, provide hemostasis at the sites of vascular injury. Abnormalities of these hemostasis factors can result in a tendency toward hemorrhagic or thrombotic events. In this review the influence of inherited prothrombotic risk factors--especially the more frequent factor V Leiden and prothrombin gene mutations--on normal and abnormal hemostasis is analyzed from an evolutionary point of view. The effect of inherited bleeding disorders on the development of thrombotic or atherosclerotic processes is also discussed.

Role of the factor V Leiden mutation in septic peritonitis assessed in factor V Leiden transgenic mice

OBJECTIVE

The factor V Leiden (FVL) mutation (Arg506Glu) results in the production of an FV protein that when activated is relatively resistant to inactivation by activated protein C and thereby leads to predisposition to thrombosis. The rather high prevalence of the FVL mutation in the general population prompted speculation about a potential survival benefit for individuals carrying the FVL allele. Indeed, both clinical and experimental animal data suggest that a heterozygous FVL genotype might protect against the lethal consequences of sepsis. We sought to confirm the survival advantage of heterozygous FVL mice in septic disease.

DESIGN

Controlled animal experiment.

SETTING

Academic research laboratory.

SUBJECTS

Wild-type, heterozygous, and homozygous FVL mice subjected to 1 x 10 live bacteria as model for septic peritonitis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The intraperitoneal injection of E. coli led to growth and dissemination of bacteria and provoked an inflammatory response as evident from elevated cytokine levels (interleukin-6, interleukin-10, and tumor necrosis factor-alpha), induced thrombin-antithrombin complex levels, increased granulocyte influx into the peritoneal cavity, liver necrosis, and adhesion of leukocytes to the vessel wall, resulting in approximately 50% mortality after 72 hrs. The FVL genotype had no significant effect on bacterial outgrowth, markers of inflammation (i.e., tumor necrosis factor-alpha levels of 152 [96.2-200], 152 [99.7-1745], and 110 [99.7-177] pg/mL in peritoneal lavage fluid at t = 20 hrs for wild-type, heterozygous, and homozygous FVL mice, respectively), thrombin generation (i.e., thrombin-antithrombin complex levels of 19.9 [9.31-37.4], 10.4 [6.55-15.8], and 12.6 [8.24-29.0] ng/mL in peritoneal lavage fluid at t = 6 hrs for wild-type, heterozygous, and homozygous FVL mice, respectively), and/or survival (50%, 36%, and 50% for wild-type, heterozygous, and homozygous FVL mice, respectively).

CONCLUSIONS

The FVL allele has no beneficial effect in mouse septic peritonitis, and the general protective effect of FVL in sepsis needs further investigation.

Effect of factor V Leiden polymorphism in severe sepsis and on treatment with recombinant human activated protein C

OBJECTIVE

Coagulation activation is part of the acute innate host response to infection that, when uncontrolled, may contribute to organ dysfunction and death. Activated protein C limits excessive coagulation activation by inactivating factors Va and VIIIa. The factor V Leiden mutation (R506Q), a prothrombotic gene polymorphism, disrupts the activity of this natural anticoagulant by rendering factor Va partially resistant to inactivation by activated protein C. Previous findings in the mouse factor V Leiden endotoxemia model and in patients with severe sepsis suggest that factor V Leiden constitutes a rare example of a balanced gene polymorphism that may provide a survival advantage for heterozygous carriers with severe sepsis. We sought to confirm that carriers of this prothrombotic factor V Leiden mutation do not have an increased risk of developing severe sepsis and that carriers with severe sepsis derive similar treatment benefit from recombinant human activated protein C (drotrecogin alfa [activated]) as non-factor V Leiden carriers.

DESIGN

Prospective collection of factor V Leiden status from two clinical studies of severe sepsis (PROWESS and ENHANCE).

SETTING

: A total of 447 clinical sites across 25 countries.

PATIENTS

A total of 3894 adult patients with severe sepsis.

INTERVENTION

Either 24 microg x kg x hr drotrecogin alfa (activated) (n = 3063) or placebo (n = 800) for 96 hrs or no exposure to the study drug (n = 31).

MAIN RESULTS

The effect of the factor V Leiden carrier status in severe sepsis in the PROWESS study has been previously reported. The combined data on factor V Leiden status from 3894 adult patients with severe sepsis from the PROWESS and ENHANCE (a single-arm, open-label study of drotrecogin alfa [activated]) studies are reported here. At study entry, 3.9% of patients (150/3894) presenting with severe sepsis were heterozygous carriers. No homozygous factor V Leiden carriers were identified. The proportion of factor V Leiden carriers in patients with severe sepsis differs slightly from that predicted (allelic frequency of 2.5%) by the Hardy-Weinberg equation for the general white population (p =.05). There was no significant difference in baseline disease severity (Acute Physiology and Chronic Health Evaluation II score or number of organ dysfunctions) between heterozygous carriers and non-Leiden carriers. There was no significant difference in serious bleeding or thrombotic event rates with drotrecogin alfa (activated) treatment between heterozygous carriers and non-Leiden carriers. The 28-day mortality rates for heterozygous carriers and non-Leiden carriers with drotrecogin alfa (activated) treatment were 20.3% and 24.9%, respectively (risk ratio, 0.82; 95% confidence interval, 0.57-1.17).

CONCLUSIONS

: Compared with non-Leiden carriers, factor V Leiden heterozygous carriers may have a slightly decreased risk of developing severe sepsis from infection, do not seem to have increased mortality in severe sepsis, and derive similar benefit and risk profiles from drotrecogin alfa (activated) treatment. Therefore, factor V Leiden carriers should not be excluded from this new sepsis therapy.

Factor V Leiden polymorphism modifies sepsis outcome: Evidence from animal studies

OBJECTIVE

The high prevalence of the factor V Leiden mutation in certain populations has prompted speculation that the mutation may have been subject to positive selection during evolution, either by providing a survival benefit or by directly enhancing reproductive performance. We investigated the hypothesis that heterozygous factor V Leiden carrier status might protect against the lethal consequences of severe inflammatory disease.

DATA SOURCE

Two mouse models (thrombomodulin-deficient TMPro mice and factor V Leiden mice), in which the endogenous protein C anticoagulant pathway is disrupted either at the level of protein C activation (TMPro mice) or at the level of factor V proteolysis by activated protein C (factor V Leiden mice), were employed. The mutant mouse strains were subjected to lethal doses of bacterial lipopolysaccharide. The effects of these two mutations on coagulation activation and inflammatory cytokine elaboration were observed and compared with those in wild-type mice.

DATA SUMMARY

As has already been shown, heterozygous factor V Leiden carrier status improves the survival of mice subjected to endotoxemia induced by bacterial lipopolysaccharide. The survival of homozygous factor V Leiden mice did not differ from that of normal mice. The survival benefit derived from heterozygous factor V Leiden carrier status was only evident at doses of lipopolysaccharide producing death in approximately 50% of wild-type animals. At higher (LD90) or lower (LD10) doses of lipopolysaccharide, the survival of heterozygous factor V Leiden mice did not differ from that of wild-type mice. Concomitant administration of an LD90 dose of lipopolysaccharide and therapeutic heparin abolished the relative survival advantage of heterozygous factor V Leiden mice. Analysis of systemic coagulation and cytokine variables failed to provide conclusive evidence for altered coagulation activation or inflammatory cytokine production as the basis for the survival advantage associated with heterozygous factor V Leiden carrier status.

CONCLUSIONS

The improved survival of mice heterozygous for the factor V Leiden mutation complements results from the analysis of the factor V Leiden subgroup of patients enrolled in the PROWESS trial. Such convergent findings in two different species strongly suggest that the factor V Leiden mutation is indeed a potent modifier of the response to severe inflammatory disease. The striking magnitude of the factor V Leiden survival benefit in the initial PROWESS population, and in mice, suggests that the as-yet unknown mechanism conferring this benefit is a rather potent endogenous modifier of the pathogenic pathways engaged in sepsis. Delineation of this pathway will be important for understanding the therapeutic mechanisms, or absence thereof, of agents designed to act at the interface of coagulation and inflammation.

Survival advantage associated with heterozygous factor V Leiden mutation in patients with severe sepsis and in mouse endotoxemia

Sepsis is associated with systemic inflammation, coagulopathy, and disrupted protein C (PC) pathway function. The effect of prothrombotic polymorphism, factor V Leiden (Arg506Gln; FV Leiden), was examined in a large clinical trial (PROWESS) of severe sepsis and a mouse endotoxemia model. In PROWESS, 4.1% (n = 65) of patients were heterozygous FV Leiden (VL+/-) carriers. The 28-day mortality was lower in VL+/- (13.9%) than in non-FV Leiden (VL-/-; 27.9%) patients (P =.013). The mortality benefit of recombinant human activated PC (rhAPC) treatment was similar in VL+/- (placebo, 15.6%; rhAPC,12.1%) and VL-/- patients (placebo, 31.0%; rhAPC, 24.7%; interaction P =.981). VL+/- status did not appear to influence baseline biomarkers of coagulopathy and inflammation or disease severity, with the exception that vasopressor usage was less in VL+/- patients (46.2% versus 63.0%; P =.009). In a median lethal dose (40 mg/kg) endotoxin mouse model, VL+/- mice had lower mortality than wild-type mice (19% versus 57%; P =.008), whereas the mortality of homozygous (VL+/+) mice was almost identical to that of wild-type mice (65% versus 57%; P =.76). The findings suggest that FV Leiden constitutes a rare example of a balanced gene polymorphism that maintains the FV Leiden mutation in the general gene pool due to a survival advantage of VL+/- in severe sepsis.

Selection pressure for the factor-V-Leiden mutation and embryo implantation

The factor-V-Leiden mutation is seen in high frequencies in white people, despite its contribution to second-trimester abortion, preterm birth, and deep-vein thrombosis. The reason for its high frequency is not known. We investigated 102 mother-child pairs who had had successful in-vitro fertilisation by intracytoplasmic sperm injection as a model for human implantation. In 90% (9 of 10) of mother-child pairs who carried factor-V-Leiden mutation, the first embryo transfer was successful, compared with 49% (45 of 92) in factor-V-Leiden negative pairs (p=0.018, Fisher's exact test). Furthermore, the median number of unsuccessful transfers was lower in pairs who were positive for the mutation (0, range 0-2) than those who were negative (1, 0-8) (p=0.02, Mann Whitney U test) suggesting that improved implantation rate is an important genetic advantage of the factor-V-Leiden mutation.

Polymorphisms of clotting factors modify the risk for primary intracranial hemorrhage

Intracranial hemorrhage is the third most frequent cause of cerebrovascular disease, but few genetic risk factors have been associated with its development. Recently, it has been reported that some polymorphisms that affect clotting factors increase the risk for thrombosis. However, reports have analyzed the effect of polymorphisms influencing the hemostatic state in bleeding disorders insufficiently. A case-control study was conducted of 201 patients with spontaneous intracranial hemorrhage and 201 control subjects matched for age, race, sex, and selected risk factors (hypertension, smoking, and alcohol consumption). Genomic polymerase chain reaction was used to analyze the prevalence of 4 polymorphisms: factor V Leiden, prothrombin 20210A, factor VII-323 Del/Ins of a decanucleotide, and factor XIII V34L. Subjects with factor V Leiden had decreased risk for spontaneous intracranial hemorrhage (odds ratio, 0.19; 95% confidence interval, 0.03-0.95). The frequency of the prothrombin 20210A/G genotype was also lower among patients than controls (1.5% vs 3%, respectively). Moreover, carriers of the -323 Ins allele of factor VII had a 1.54-fold risk for intracranial hemorrhage (95% CI, 1.03-2.72). Finally, no significant differences were observed in the prevalence of factor XIII V34L polymorphism between patients and controls. Therefore, new genetic factors affecting the risk for spontaneous intracranial hemorrhage were identified. These data, together with the relevance of these polymorphisms in thrombotic diseases, support the idea that a polymorphism may play opposite roles in thrombosis and hemorrhage, suggesting an explanation for the high frequency of these polymorphisms in the general population.

The role of natural anticoagulant deficiencies and factor V Leiden in the development of idiopathic portal vein thrombosis

One of the causes of portal hypertension is portal vein thrombosis (PVT). The aim of this study was to determine whether natural anticoagulant deficiencies, activated protein C resistance (APCR), and factor V Leiden play a role in the development of PVT, leading to cavernous transformation of the portal vein (CTPV). Twenty-three patients with idiopathic CTPV (group 1) seen at Hacettepe University Hospital during the past 12 years were identified and prospectively studied. These 23 patients underwent a detailed hematological evaluation including measurement of protein S, protein C, antithrombin III, activated protein C resistance (APCR), and factor V Leiden gene mutation. Additionally, all patients were tested for anticardiolipin antibodies (ACA), IgG, IgM, and lupus anticoagulant (LA). Natural anticoagulants and APCR were measured using available commercial kits, and factor V Leiden mutation (R506Q) was detected by Mnl I digestion of an amplified factor V DNA fragment. All parameters were measured at least 6 months after the diagnosis of CTPV was established. No patient was on anticoagulant or antiaggregant treatment while tested. The findings in these 23 patients were compared with those in 20 healthy control subjects (group 2), in whom all tests mentioned above were also performed. In 23 patients (group 1), who had no recognizable factor for portal vein thrombosis, considerably natural anticoagulant deficiencies and factor V Leiden mutation positivity were found when we compare them to those healthy controls (group 2). The protein C levels of six patients (26%), the protein S levels of 10 patients (43.5%), and the antithrombin III levels of five patients (26%) were lower than in control subjects. Two patients were found to have combined protein S and antithrombin III deficiency, and one had combined protein S and C deficiency and APCR. APCR was detected in seven of the 23 patients, and six of these seven patients were found to have R506Q factor V Leiden mutations. In group 1, ACA IgG levels were higher in four patients (17%) and ACA IgM level was higher in one (4%) compared with the control group. LA was positive in only one patient in group 1. Natural anticoagulant deficiencies and factor V Leiden mutation are strongly associated with PVT. The natural anticoagulant deficiencies and APCR (almost totally caused by R506Q mutation) produce a favorable medium for thrombus generation. PVT seems to be related to the natural anticoagulant deficiencies and factor V Leiden R506Q mutation. A combination of these defects increases the incidence of PVT and these factors should be evaluated carefully in patients with idiopathic CTPV.

Plasma glutathione peroxidase deficiency and platelet insensitivity to nitric oxide in children with familial stroke

In a previous report by Freedman et al (J Clin Invest. 1996;97:979-987), plasma from 2 brothers with stroke or transient ischemic attack inactivated the antiplatelet effects of nitric oxide (NO), and this effect was found to be a consequence of a deficiency of plasma glutathione peroxidase (GSH-Px). In this study, we attempted to define the generalizability of this deficiency by studying NO-mediated antiplatelet effects in 7 families with familial childhood stroke. Seven families with familial childhood stroke that consecutively presented to a large referral center were included in the study. We monitored ADP-induced aggregation of normal gel-filtered platelets (GFP) in platelet-poor plasma (PPP) from normal individuals and from patients in the presence or absence of an NO donor (S-nitroso-glutathione). Surface P-selectin expression of normal GFP in patients' PPP was analyzed by flow cytometry after incubation with a P-selectin-specific monoclonal antibody in the presence or absence of the NO donor. We also measured GSH-Px activity in plasmas from family members and normal controls using standard methods. In 6 of 7 families, NO failed to inhibit platelet P-selectin expression and platelet aggregation in PPP from the affected family members and some of their relatives. Of 4 families studied, 3 probands and their corresponding affected parent had 50% decrease in plasma GSH-Px activity. In some patients with childhood stroke, impaired metabolism of reactive oxygen species as a result of reduced GSH-Px activity results in NO insufficiency that affects normal platelet inhibitory mechanisms and predisposes to arterial thrombosis.

Activated protein C resistance in patients with central retinal vein occlusion

AIM/BACKGROUND

A new defect in the anticoagulant system has recently been discovered--activated protein C resistance. The frequency of this disorder has been shown to be increased in young patients (< 50 years of age) with central retinal vein occlusion. This study was carried out to determine if there was any overrepresentation of activated protein C resistance in patients > 50 years of age with central retinal vein occlusion.

METHODS

Blood samples were obtained from 83 patients > 50 years of age and with a history of central retinal vein occlusion. The blood samples were analysed for activated protein C resistance with standard clinical laboratory methods.

RESULTS

In this material 11% of the patients were resistant to activated protein C. The normal incidence of activated protein C resistance in the same geographical area is 10-11%.

CONCLUSION

Activated protein C resistance does not seem to be a cause of central retinal vein occlusion in people older than 50 years.

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.

Toward molecular strategies for heart disease--past, present, future

The past two decades of cardiovascular biology and medicine have been based largely upon the consideration of the heart and vasculature as an integrated physiological system, a view that has resulted in major therapeutic advances. With the advent of developments of gene transfer, mouse and human genetics, genetic engineering of intact animals, and molecular and cellular technology, cardiovascular medicine is now on the threshold of a molecular therapeutic era. Major steps have been taken toward unraveling the molecular determinants of complex, integrative, and polygenic cardiovascular disease states, including atherogenesis, hypertension, cardiac hypertrophy and failure, congenital heart disease, and coronary restenosis following balloon angioplasty. Our improved understanding of the fundamental basis of these important cardiovascular disease processes has established a scientific foundation for diagnostic, prognostic, and therapeutic advances in the mainstream of cardiovascular medicine.

Factor V Leiden: should we screen oral contraceptive users and pregnant women?

The factor V Leiden mutation is the most common genetic risk factor for deep vein thrombosis: it is present in about 5% of the white population. The risk of deep vein thrombosis among women who use oral contraceptives is greatly increased by the presence of the mutation. The same seems to be true of the risk of postpartum thrombosis. Several authors have called for all women to be screened before prescription of oral contraceptives and during pregnancy. Such a policy might deny effective contraception to a substantial number of women while preventing only a small number of deaths due to pulmonary emboli. Moreover, in pregnancy the ensuing use of oral anticoagulation prophylaxis might carry a penalty of fatal bleeding that is equal to or exceeds the risk of death due to postpartum thrombosis. It might pay, however, to take a personal and family history of deep vein thrombosis when prescribing oral contraceptives or at a first antenatal visit to detect women from families with a tendency to multiple thrombosis.

Activated protein C resistance--low incidence in glaucomatous optic disc haemorrhage and central retinal vein occlusion

PURPOSE

Activated protein C (APC) resistance has recently been reported as conferring a sevenfold increase in the risk of venous thrombosis. It is linked to a genetic mutation in the factor V gene which occurs commonly (about 2% to 4% of the community have the mutation). Glaucoma patients with nerve fibre layer (NFL) haemorrhages on the optic disc and patients with central retinal vein occlusion (CRVO) were tested for APC resistance to determine if there was an association.

METHODS

Twenty-three patients with glaucomatous NFL haemorrhages and 23 patients with CRVO were tested. The CRVO cases included 11 with relatively young age of onset (mean 45.1 +/- 6.9 years) without conventional vascular risk factors. Eighty randomly selected Red Cross blood donor samples and 33 staff members were tested as controls. Clotting times with and without exogenous APC were recorded and an APC ratio determined. Cases with APC resistance were tested to confirm that they had the factor V Leiden gene.

RESULTS

No cases of APC resistance were identified in the glaucoma patients and only one of the younger CRVO patients tested positive, but four of 113 controls tested positive. The difference in prevalence between groups is not significant. The mean APC ratios for the three groups were very similar: NFL haemorrhages 5.46(+/- 1.62), CRVO 5.70(+/- 1.56), controls 5.34 ( +/- 1.19) p > 0.5.

CONCLUSION

There was not clear association detected between glaucomatous NFL haemorrhages or CRVO and APC resistance in this sample of patients. This negative finding is important due its known association with venous thrombosis elsewhere in the body.

Resistance to activated protein C: role in venous and arterial thrombosis

Activated protein C resistance is the most prevalent cause of thrombophilia: it is found in 20 to 30% of patients with a deep venous thrombosis history. Activated protein C resistance is due to an arginine 506 to glutamine mutation in factor V. This mutation prevents normal inactivation of activated factor V by activated protein C. The estimated increase in relative risk of venous thrombosis is 5- to 10-fold in heterozygotes, and 50- to 100-fold in homozygotes. Activated protein C resistance does not seem to play a role in arterial thrombosis and in the occurrence of myocardial infarction.

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.

Heparin-induced thrombocytopenia and fatal thrombosis in a patient with activated protein C resistance

We report a 20-year-old woman who developed heparin-induced thrombocytopenia (HIT) associated with devastating and fatal multiorgan thrombosis. The patient, her mother, and her brother were found to have resistance to activated protein C (APC), and the congenital thrombophilia in this family was verified by the finding of the Arg506 Gln mutation in factor V. This is the first case of HIT and APC resistance. The consequences of this association are discussed.

Activated protein c resistance (APC) and inherited factor V (FV) mis-sense mutation in patients with venous and arterial thrombosis in a haematology clinic

BACKGROUND

Inherited factor V (FV) mis-sense point mutation has recently been identified as a major cause of familial venous thrombosis. The incidence of this congenital haemostatic disorder in Australia is unknown.

AIM

To examine the incidence of this congenital defect in patients with thrombosis attending a haematology clinic.

METHODS

Individuals investigated or treated for venous and arterial thrombosis over a four month period, as well as those who were on anticoagulant for valvular replacement or arrhythmia were studied for the presence of FV mis-sense point mutation, FV Q506 (G to A at nucleotide position 1691) by a polymerase chain reaction based test, and activated protein C (APC) resistance using an APTT based coagulation assay.

RESULTS

Forty-five patients with venous thromboembolism (VTE), 20 patients with coronary artery disease and 25 patients with valvular replacement or arrhythmia who were on anticoagulant were examined. The frequency of FV mis-sense point mutation in these three groups was 26.7%, 15% and 4% respectively. In this study, patients with FV Q506 were of a younger age and had a higher incidence of extensive thrombosis or recurrence as compared to those with the normal factor V gene. This mutation was found in a diverse group of people (four of the 12 patients were of non-European origin). Nearly 50% of these patients had other risk factors for VTE. The number of patients with a family history of VTE was similar for those with the FV mutation and the normal FV.

CONCLUSION

This study confirms the high incidence of FV Q506 mutation in patients with VTE reported overseas. Several clinical features, i.e. young age of onset of VTE, high recurrence rate, diverse ethnic background and importance of associated risk factors are highlighted. The findings in this study also raise the possibility that this mutation may be a risk factor for arterial thrombosis. Large studies are required to substantiate these findings.

Molecular genetics of venous thromboembolism

Venous thrombosis is often familial, but until recently well-defined genetic defects were only found in a minority of patients. The situation changed with the discovery of inherited resistance to activated protein C (APC) as a novel mechanism for familial thrombophilia. It is caused by a single point mutation in the factor V gene, which predicts replacement of Arg506 in the APC-cleavage site with a Gln. APC resistance is found in a majority of patients with familial thrombosis as well as in 3-7% of the general population. It afflicts affected individuals with a life-long increased risk of thrombosis. The factor V gene mutation is the most prevalent single gene defect associated with thromboembolic disease so far described.

Factor V gene mutation causing inherited resistance to activated protein C as a basis for venous thromboembolism

Venous thromboembolism is often familial, suggesting that genetic risk factors are involved. Until recently, genetic defects known to predispose for thrombosis (deficiencies of antithrombin III, protein C, and protein S) had not been shown to account for more than 5-10% of the cases. Inherited resistance to the anticoagulant function of activated protein C (APC) in the last year has been identified as a major basis for familial thrombosis. Unlike other genetic risk factors for thrombosis, APC resistance is highly prevalent in the general population (2-5%). In more than 90% of cases, the APC-resistance phenotype is associated with a point mutation in the factor V gene, which predicts replacement of arginine at position 506 with a glutamine. As APC inhibits factor Va by cleavage at arginine 506, mutated factor V is resistant to APC. In its heterozygous state, the mutation is associated with a 5-10-fold increased risk of thrombosis. Homozygocity is associated with more severe APC resistance, and with a higher risk of thrombosis. Because of its high prevalence in the population, individuals with deficiencies of other anticoagulant proteins occasionally carry the factor V gene mutation. People with such combinations of mutations have a higher risk of thrombosis than those with the single mutations. In conclusion, in the majority of familial thrombosis cases it is now possible to identify an underlying genetic risk factor. APC resistance caused by a single, factor V gene mutation, is the most frequent risk factor and it is at least ten times more common than any of the other genetic defects associated with thrombosis.