Does factor V Asp79His (409 G/C) polymorphism influence factor V and APC resistance levels?

Gene Dosage of F5 c.3481C>T Stop-Codon (p.R1161Ter) Switches the Clinical Phenotype from Severe Thrombosis to Recurrent Haemorrhage: Novel Hypotheses for Readthrough Strategy

Inherited defects in the genes of blood coagulation essentially express the severity of the clinical phenotype that is directly correlated to the number of mutated alleles of the candidate leader gene (e.g., heterozygote vs. homozygote) and of possible additional coinherited traits. The F5 gene, which codes for coagulation factor V (FV), plays a two-faced role in the coagulation cascade, exhibiting both procoagulant and anticoagulant functions. Thus, defects in this gene can be predisposed to either bleeding or thrombosis. A Sanger sequence analysis detected a premature stop-codon in exon 13 of the F5 gene (c.3481C>T; p.R1161Ter) in several members of a family characterised by low circulating FV levels and contrasting clinical phenotypes. The propositus, a 29 y.o. male affected by recurrent haemorrhages, was homozygous for the F5 stop-codon and for the F5 c.1691G>A (p.R506Q; FV-Leiden) inherited from the heterozygous parents, which is suggestive of combined cis-segregation. The homozygous condition of the stop-codon completely abolished the F5 gene expression in the propositus (FV:Ag < 1%; FV:C < 1%; assessed by ELISA and PT-based one-stage clotting assay respectively), removing, in turn, any chance for FV-Leiden to act as a prothrombotic molecule. His father (57 y.o.), characterised by severe recurrent venous thromboses, underwent a complete molecular thrombophilic screening, revealing a heterozygous F2 G20210A defect, while his mother (56 y.o.), who was negative for further common coagulation defects, reported fully asymptomatic anamnesis. To dissect these conflicting phenotypes, we performed the ProC®Global (Siemens Helthineers) coagulation test aimed at assessing the global pro- and anticoagulant balance of each family member, investigating the responses to the activated protein C (APC) by means of an APC-sensitivity ratio (APC-sr). The propositus had an unexpectedly poor response to APC (APC-sr: 1.09; n.v. > 2.25), and his father and mother had an APC-sr of 1.5 and 2.0, respectively. Although ProC®Global prevalently detects the anticoagulant side of FV, the exceptionally low APC-sr of the propositus and his discordant severe-moderate haemorrhagic phenotype could suggest a residual expression of mutated FV p.506QQ through a natural readthrough or possible alternative splicing mechanisms. The coagulation pathway may be physiologically rebalanced through natural and induced strategies, and the described insights might be able to track the design of novel treatment approaches and rebalancing molecules.

The effect of FV-426 G/A gene variation on the occurrence of thrombosis

Factor V (FV) plays a crucial role in both procoagulant and anticoagulant pathways. It was indicated that -426G/A change in the promoter of the FV gene may have an effect on the occurrence of thrombosis. We aimed to investigate the effect of -426G/A gene variation on thrombus formation in the thrombosis patients of age 0 and 18 years and 70 years and older. The study included 179 patients with the diagnosis of thromboembolism and also 221 healthy individuals as controls. The Polymerase chain reaction-restriction fragment length polymorphism method was used to detect -426G/A. It was observed that carrying AA genotype does not have a significant risk of thrombosis between the patients and controls (for 0-18 age group P = .96, odds ratio [OR]: 1.13 [0.38-3.30], for ≥70 age P = .94, OR: 0.69 [0.11-4.28]). The same results were obtained when FV Leiden mutation carriers were excluded (for 0-18 age group P = .95, OR: 1.15 [0.35-3.78], for ≥70 age P = .89, OR: 0.73 [0.11-4.56]). In this study, an effect on thrombosis of -426G/A polymorphism was not determined.

Genetic modulation of the FV(Leiden)/normal FV ratio and risk of venous thrombosis in factor V Leiden heterozygotes

BACKGROUND AND OBJECTIVES

The factor (F)V Leiden mutation causes activated protein C (APC) resistance by decreasing the susceptibility of FVa to APC-mediated inactivation and by impairing the APC-cofactor activity of FV in FVIIIa inactivation. However, APC resistance and the risk of venous thromboembolism (VTE) vary widely among FV Leiden heterozygotes. Common F5 genetic variation probably contributes to this variability.

PATIENTS/METHODS

APC resistance was determined in 250 FV Leiden heterozygotes and 133 normal relatives using the prothrombinase-based assay, which specifically measures the susceptibility of plasma FVa to APC. The effects of 12 F5 single-nucleotide polymorphisms (SNPs) on the normalized APC sensitivity ratio (nAPCsr) and on FV levels were determined by multiple regression analysis.

RESULTS

In FV Leiden heterozygotes,VTE risk increased with increasing nAPCsr, reaching an odds ratio (OR) of 9.9 (95% confidence interval [CI] 1.2–80.5) in the highest nAPCsr quartile. The minor alleles of several F5 SNPs, including 327 A/G (Q51Q), 409 G/C (D79H), 2663 A/G(K830R, T2 haplotype), 6533 T/C (M2120T) and 6755 A/G (D2194G, R2 haplotype), increased the nAPCsr in FV Leiden heterozygotes, but not in their normal relatives. Most of these effects could be attributed to a shift in the FV(Leiden)/normal FV ratio. Four FV Leiden heterozygotes with extremely high nAPCsr turned out to be pseudo-homozygotes, i.e. they carried a deleterious mutation on the non-Leiden allele.

CONCLUSIONS

In FV Leiden heterozygotes, the prothrombinase-based nAPCsr is a marker of VTE risk and is modulated by common F5 SNPs that affect the FV(Leiden)/normal FV ratio in plasma.

Variable plasma levels of Factor V Leiden correlate with circulating platelet microparticles in carriers of Factor V Leiden

INTRODUCTION

Inheritance of Factor V Leiden (FVL) is associated with an increased but variable level of risk for thrombosis. We have previously shown that FVL heterozygotes have elevated levels of circulating pro-coagulant microparticles (MP). Here we sought to determine if these subjects differed in their plasma levels of FVL and if this was related to MP concentrations and/or history of thrombosis.

MATERIALS AND METHODS

The Hemoclot Quanti. V-L clotting assay was used to specifically measure FVL in plasma samples from 44 known carriers (12M, 32F; aged 46±13years). Circulating MP were quantified by flow cytometry using fluorochrome conjugated antibodies to platelet (CD41a), leukocyte (CD45), and endothelial (CD62e) surface markers, and MP prothrombinase activity was determined by ELISA.

RESULTS

The cohort was found to have a mean FVL of 49.5±5.6% and this was positively correlated to the total number of circulating CD41a+MP (R=0.31, p=0.03) but not to other MP subsets or to MP prothrombinase activity. The amount of FVL relative to normal factor V (FVL/FV clotting ratio) was calculated and found to be highly variable, ranging from 0.37 to 0.69, and significantly correlated with a history of thrombosis (n=14; p=0.04).

CONCLUSIONS

This is the first study to investigate the relationship between varying levels of FVL and plasma derived MP. These results are consistent with our previous findings of an increase in MP levels in carriers of FVL as compared to controls, and suggest a role for FVL/FV ratio in predicting risk of thrombosis in carriers of FVL.

Inherited defects of coagulation Factor V: the thrombotic side

DNA variations in the Factor V gene have played a major role in thrombosis research ever since the discovery of Factor V Leiden. Here, all relatively common DNA variations in the coding regions of the Factor V gene are discussed. Many of them have been associated with venous thrombosis or related diseases. However, most variations have been studied separately, without taking the presence of other variations in the same gene into account. This means that their association with disease should be interpreted with caution, as it may reflect linkage with another variation. An approach in which a haplotype-based analysis of the Factor V gene is combined with in vitro assays of recombinant proteins is advocated. Finally, a possible reason for the relatively polymorphic nature of the Factor V protein is discussed.