The risk of venous thromboembolism attributed to established prothrombotic genotypes

Background: The proportion of venous thromboembolism (VTE) events that can be attributed to established prothrombotic genotypes has been scarcely investigated in the general population. We aimed to estimate the proportion of VTEs in the population that could be attributed to established prothrombotic genotypes using a population-based case-cohort. Methods: Cases with incident VTE (n=1,493) and a randomly sampled sub-cohort (n=13,069) were derived from the Tromsø Study (1994-2012) and the Nord-Trøndelag Health (HUNT) Study (1995-2008). DNA-samples were genotyped for 17 single nucleotide polymorphism (SNPs) associated with VTE. Hazard ratios with 95% confidence intervals (CIs) were estimated in Cox regression models. Population attributable fraction (PAF) with 95% bias-corrected CIs (based on 10,000 bootstrap samples) were estimated using a cumulative model where SNPs significantly associated with VTE were added one-by-one in ranked order of the individual PAFs. Results: Six SNPs were significantly associated with VTE (rs1799963 [Prothrombin], rs2066865 [FGG], rs6025 [FV Leiden], rs2289252 [F11], rs2036914 [F11] and rs8176719 [ABO]. The cumulative PAF for the six-SNP model was 45.3% (95% CI 19.7-71.6) for total VTE and 61.7% (95% CI 19.6-89.3) for unprovoked VTE. The PAF for prothrombotic genotypes was higher for DVT (52.9%) than for PE (33.8%), and higher for those aged <70 years (66.1%) than for those aged ≥70 years (24.9%). Conclusions: Our findings suggest that 45-62% of all VTE events in the population can be attributed to known prothrombotic genotypes. The PAF of established prothrombotic genotypes was higher in DVT than in PE, and higher in the young than in the elderly.

Factor V H1299r (Hr2) Heterozygosity: A Risk Factor For Recurrent Implantation Failure Particularly In Non-Carriers For Factor V Leiden Mutation-A Case-Control Study

Objective: The association between recurrent implantation failure and thrombophilia is still controversial depending on the published reports with conflicting results. In this study, we aimed to assess the clinical relevance of screening women with recurrent implantation failure for some thrombophilic variants including factor V H1299R (FV HR2) haplotype. Study Design: A total of 279 women were recruited in this case-control study. 229 women with a history of recurrent implantation failure and 50 fertile control with no history of pregnancy losses were screened for eight specific gene mutations, regarding factor V G1691A gene (FV Leiden), FV HR2, factor II prothrombin G20210A, factor XIII V34L, PAI-1 4G/5G, MTHFR C677T, MTHFR A1298C and A3 haplotype of the endothelial cell protein C receptor gene. Results: Recurrent implantation failure group displayed a significantly higher prevalence of FV HR2 heterozygosity than fertile controls while the frequency of FV Leiden mutation was comparable between groups (p=0.011; p=0.619). Additionally, the difference in the prevalence of other specific or total gene mutations among women with recurrent implantation failure was also insignificant. Discussion: The primer outcome of this study was the co-existence of the higher prevalence of FV HR2 haplotype and the insignificant percentage of FV Leiden mutation in women with recurrent implantation failure. Thus, we emphasize that the HR2 haplotype may be associated with recurrent implantation failure particularly in non-carriers for FV Leiden mutation. In the necessity of screening for thrombophilia in recurrent implantation failure, HR2 haplotype should be involved in the searched gene panel particularly in the absence of FV Leiden mutation. Further large-scale prospective studies are needed to investigate whether screening or treatment for HR2 haplotype has any detrimental impact on implantation success in cases of recurrent implantation failure.

Rare Defects: Looking at the Dark Face of the Thrombosis

Venous thromboembolism (VTE) constitutes a serious and potentially fatal disease, often complicated by pulmonary embolism and is associated with inherited or acquired factors risk. A series of risk factors are known to predispose to venous thrombosis, and these include mutations in the genes that encode anticoagulant proteins as antithrombin, protein C and protein S, and variants in genes that encode instead pro-coagulant factors as factor V (FV Leiden) and factor II (FII G20210A). However, the molecular causes responsible for thrombotic events in some individuals with evident inherited thrombosis remain unknown. An improved knowledge of risk factors, as well as a clear understanding of their role in the pathophysiology of VTE, are crucial to achieve a better identification of patients at higher risk. Moreover, the identification of genes with rare variants but a large effect size may pave the way for studies addressing new antithrombotic agents in order to improve the management of VTE patients. Over the past 20 years, qualitative or quantitative genetic risk factors such as inhibitor proteins of the hemostasis and of the fibrinolytic system, including fibrinogen, thrombomodulin, plasminogen activator inhibitor-1, and elevated concentrations of factors II, FV, VIII, IX, XI, have been associated with thrombotic events, often with conflicting results. The aim of this review is to evaluate available data in literature on these genetic variations to give a contribution to our understanding of the complex molecular mechanisms involved in physiologic and pathophysiologic clot formation and their role in clinical practice.

Cis-Segregation of c.1171C>T Stop Codon (p.R391*) in SERPINC1 Gene and c.1691G>A Transition (p.R506Q) in F5 Gene and Selected GWAS Multilocus Approach in Inherited Thrombophilia

Inherited thrombophilia (e.g., venous thromboembolism, VTE) is due to rare loss-of-function mutations in anticoagulant factors genes (i.e., SERPINC1, PROC, PROS1), common gain-of-function mutations in procoagulant factors genes (i.e., F5, F2), and acquired risk conditions. Genome Wide Association Studies (GWAS) recently recognized several genes associated with VTE though gene defects may unpredictably remain asymptomatic, so calculating the individual genetic predisposition is a challenging task. We investigated a large family with severe, recurrent, early-onset VTE in which two sisters experienced VTE during pregnancies characterized by a perinatal in-utero thrombosis in the newborn and a life-saving pregnancy-interruption because of massive VTE, respectively. A nonsense mutation (CGA > TGA) generating a premature stop-codon (c.1171C>T; p.R391*) in the exon 6 of SERPINC1 gene (1q25.1) causing Antithrombin (AT) deficiency and the common missense mutation (c.1691G>A; p.R506Q) in the exon 10 of F5 gene (1q24.2) (i.e., FV Leiden; rs6025) were coinherited in all the symptomatic members investigated suspecting a cis-segregation further confirmed by STR-linkage-analyses [i.e., SERPINC1 IVS5 (ATT)5–18, F5 IVS2 (AT)6–33 and F5 IVS11 (GT)12–16] and SERPINC1 intragenic variants (i.e., rs5878 and rs677). A multilocus investigation of blood-coagulation balance genes detected the coexistence of FV Leiden (rs6025) in trans with FV HR2-haplotype (p.H1299R; rs1800595) in the aborted fetus, and F11 rs2289252, F12 rs1801020, F13A1 rs5985, and KNG1 rs710446 in the newborn and other members. Common selected gene variants may strongly synergize with less common mutations tuning potential life-threatening conditions when combined with rare severest mutations. Merging classic and newly GWAS-identified gene markers in at risk families is mandatory for VTE risk estimation in the clinical practice, avoiding partial risk score evaluation in unrecognized at risk patients.

Activated Protein C has a Regulatory Role in Factor VIII Function

Mechanisms thought to regulate activated factor VIII (FVIIIa) cofactor function include A2-domain dissociation and activated protein C (APC) cleavage. Unlike A2-domain dissociation, there is no known phenotype associated with altered APC cleavage of FVIII and biochemical studies suggest APC plays a marginal role in FVIIIa regulation. However, the in vivo contribution of FVIIIa inactivation by APC is unexplored. Here we compared wild-type B-domainless FVIII (FVIII-WT) recombinant protein to an APC resistant FVIII variant (FVIII-R336Q/R562Q; FVIII-QQ). FVIII-QQ demonstrated expected APC resistance without other changes in procoagulant function or A2-domain dissociation. In plasma-based studies, FVIII-WT/FVIIIa-WT demonstrated a dose-dependent sensitivity to APC with or without protein S, while FVIII-QQ/FVIIIa-QQ did not. Importantly, FVIII-QQ demonstrated approximately 5-fold increased procoagulant function relative to FVIII-WT in the tail clip and ferric chloride injury models in hemophilia A (HA) mice. To minimize the contribution of FV inactivation by APC in vivo, the tail clip assay was performed in homozygous HA/FV-Leiden mice infused with FVIII-QQ or FVIII-WT in the presence or absence of mAb1609, an antibody that blocks murine PC/APC hemostatic function. FVIII-QQ again demonstrated enhanced hemostatic function in HA/FV-Leiden mice; however, FVIII-QQ and FVIII-WT performed analogously in the presence of the PC/APC inhibitory antibody, supporting the increased hemostatic effect of FVIII-QQ was APC specific. Our data demonstrate APC contributes to the in vivo regulation of FVIIIa, which has the potential to be exploited to develop novel HA therapeutics.

Role of Factor V R2 Haplotype and Common Thrombophilia Markers as Genetic Risk Factors for Ischemic Stroke

Background: Uncertainties remain about the role of common thrombophilia markers as determinants of the ischemic stroke (IS) risk. Polymorphism His1299Arg in the FV gene, named R2 haplotype (FVHR2), has been poorly investigated. The aim of the present study was to assess the prevalence of common thrombophilia markers and of FVHR2 in a cohort of IS patients compared to a nonmatched group of healthy individuals. Methods: We studied 156 consecutive patients survivors of a first ever IS and 124 healthy controls. All subjects were investigated for the gene polymorphisms factor V (FV) Leiden, prothrombin (PTH) G20210A, MTHFR C677T, and FVHR2. Protein C (PC), protein S (PS), antithrombin (ATIII), and lupus anticoagulant (LAC) activity was measured. Homocysteinemia was assessed within 48 hours and after 30 days from stroke onset. Univariate and multivariate analyses were performed. Results: Compared with controls, patients were significantly older (mean [SD] age, 50.5 [12.9] vs 37.5 [15.5] years, P < .001), less frequently females (48.1% vs 67.7%, P = .001) and had more frequently hyperhomocysteinemia (45.9% vs 11.0%) only in the acute phase (OR 6.899, CI 95% 2.993-15.899; P < .001). No differences were found in the prevalence of FV Leiden, PTH G20210A, and MTHFR C677T between patients and controls, whereas FVHR2 was present in 34/156 (22%) stroke patients and in 5/124 (4%) controls (OR 6.632, 95% CI 2.509-17.535, P < .001). In a multivariate logistic regression analysis, the FVHR2 resulted independently associated with the occurrence of IS (OR 6.071, 95% CI 1.762-20.923; P = .004). Conclusions: In our study, hyperhomocysteinemia was confirmed to be a transient consequence of the thrombotic event. FVHR2 seems to be a possible candidate prothrombotic condition related to arterial IS irrespective of age and sex in an Italian sample population.

Impedimetric Sensing of Factor V Leiden Mutation by Zip Nucleic Acid Probe and Electrochemical Array

A carbon nanofiber enriched 8-channel screen-printed electrochemical array was used for the impedimetric detection of SNP related to Factor V Leiden (FV Leiden) mutation, which is the most common inherited form of thrombophilia. FV Leiden mutation sensing was carried out in three steps: solution-phase nucleic acid hybridization between zip nucleic acid probe (Z-probe) and mutant type DNA target, followed by the immobilization of the hybrid on the working electrode area of array, and measurement by electrochemical impedance spectroscopy (EIS). The selectivity of the assay was tested against mutation-free DNA sequences and synthetic polymerase chain reaction (PCR) samples. The developed biosensor was a trustful assay for FV Leiden mutation diagnosis, which can effectively discriminate wild type and mutant type even in PCR samples.

Feature of distribution of polymorphic options of genes associated with thrombophilia and arterial hypertension in children with hemolytic-uremic syndrome

INTRODUCTION. The basis of hemolytic-uremic syndrome (HUS) is the pathology of hemostasis with the development of a condition that threatens the patient's life. Violations of the hemostatic system are probably largely due to a hereditary predisposition to thrombophilia.THE AIM. To study the characteristics of allelic polymorphism of genes associated with hereditary thrombophilia in 15 children with hemolytic-uremic syndrome.PATIENTS AND METHODS. A study was conducted of 15 children with HUS from the age of 1 to 4 years who were treated in the nephrology department of the clinic of St. Petersburg State Medical University. A typical HUS was diagnosed in 14 children. One child was diagnosed with atypical HUS confirmed by laboratory tests (increased levels of antibodies to protein H). At the Research Institute of Hematology and Transfusiology of the FMBA of Russia, PCR for all 15 patients and two parents analyzed the polymorphism of genes associated with thrombophilia.RESULTS. In all examined children, polymorphism of genes associated with various links of hemostasis was found. Two patients showed a mutation in the factor V gene (FV Leiden). In 7 patients out of 15 subjects, the homozygous state of the plasminogen activator inhibitor (PAI-1 - 675 4G / 5G) was revealed.CONCLUSION. The FV Leiden mutation, as the main reason for the resistance of activation of protein C (an inhibitor of the formation of thrombin), was found in two children, one with a typical HUS, and one with an atypical HUS. In 7 children out of 15 subjects, a homozygous state of plasminogen activator inhibitor (PAI-1 - 675 4G / 5G) was revealed, which may indicate insufficient fibrinolytic activity in these children, as an important factor contributing to the development of TMA.