Clinical and molecular characterization of 6 patients affected by severe deficiency of coagulation factor V: Broadening of the mutational spectrum of factor V gene and in vitro analysis of the newly identified missense mutations

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.

Nuclear Progestin Receptor-mediated Linkage of Blood Coagulation and Ovulation

Ovulation is a dramatic remodeling process that includes rupture of blood capillaries and clotting, but coagulation is not thought to directly regulate this process. Herein, we report remarkable increases of coagulation factors V (f5, ~3145-fold) and tissue factor (f3a, ~120-fold) in zebrafish ovarian follicle cells during ovulation. This increase was mediated through the nuclear progestin receptor (Pgr), which is essential for ovulation in zebrafish, and was totally abolished in ovarian follicular cells from pgr-/- mutants. In addition, promoter activities of f5 and f3a were significantly enhanced by progestin (DHP) via Pgr. Similar regulation of human F5 promoter activity was induced via human PGRB, suggesting a conserved mechanism. Site-directed mutagenesis of the zebrafish f5 promoter further demonstrated a direct regulation of coagulation factors via progestin response elements. Moreover, a stark increase of erythrocytes occurred in capillaries meshed in wild-type preovulatory follicles but was absent in pgr-/- mutants. Interestingly, anticoagulants significantly inhibited ovulation both in vitro and in vivo, respectively. Furthermore, reduced fecundity was observed in f5+/- female zebrafish. Taken together, our study provides plausible evidence for steroid regulation of coagulation factors, and a new hypothesis for blood clotting-triggered ovulation in vertebrates.

High Mutational Heterogeneity, and New Mutations in the Human Coagulation Factor V Gene. Future Perspectives for Factor V Deficiency Using Recombinant and Advanced Therapies

Factor V is an essential clotting factor that plays a key role in the blood coagulation cascade on account of its procoagulant and anticoagulant activity. Eighty percent of circulating factor V is produced in the liver and the remaining 20% originates in the α-granules of platelets. In humans, the factor V gene is about 80 kb in size; it is located on chromosome 1q24.2, and its cDNA is 6914 bp in length. Furthermore, nearly 190 mutations have been reported in the gene. Factor V deficiency is an autosomal recessive coagulation disorder associated with mutations in the factor V gene. This hereditary coagulation disorder is clinically characterized by a heterogeneous spectrum of hemorrhagic manifestations ranging from mucosal or soft-tissue bleeds to potentially fatal hemorrhages. Current treatment of this condition consists in the administration of fresh frozen plasma and platelet concentrates. This article describes the cases of two patients with severe factor V deficiency, and of their parents. A high level of mutational heterogeneity of factor V gene was identified, nonsense mutations, frameshift mutations, missense changes, synonymous sequence variants and intronic changes. These findings prompted the identification of a new mutation in the human factor V gene, designated as Jaén-1, which is capable of altering the procoagulant function of factor V. In addition, an update is provided on the prospects for the treatment of factor V deficiency on the basis of yet-to-be-developed recombinant products or advanced gene and cell therapies that could potentially correct this hereditary disorder.

Analysis of factor V in zebrafish demonstrates minimal levels needed for early hemostasis

In humans, coagulation factor V (FV) deficiency is a rare, clinically heterogeneous bleeding disorder, suggesting that genetic modifiers may contribute to disease expressivity. Zebrafish possess many distinct advantages including high fecundity, optical clarity, external development, and homology with the mammalian hemostatic system, features that make it ideal for genetic studies. Our aim was to study the role of FV in zebrafish through targeted mutagenesis and apply the model to the study of human F5 variants. CRISPR-mediated genome editing of the zebrafish f5 locus was performed, generating mutants homozygous for a 49 base pair deletion in exon 4. Thrombus formation secondary to vascular endothelial injury was absent in f5 ^-/- mutant embryos and larvae. Despite this severe hemostatic defect, homozygous mutants survived before succumbing to severe hemorrhage in adulthood. Human F5 variants of uncertain significance from patients with FV deficiency were evaluated, and the causative mutations identified and stratified by their ability to restore thrombus formation in larvae. Analysis of these novel mutations demonstrates variable residual FV function, with minimal activity being required to restore hemostasis in response to laser-induced endothelial injury. This in vivo evaluation may be beneficial for patients whose factor activity levels lack correlation with bleeding symptomatology, although limitations exist. Furthermore, homozygous mutant embryos tolerate what is a severe and lethal defect in mammals, suggesting the possibility of species-specific factors enabling survival, and allowing further study not possible in the mouse. Identification of these factors or other genetic modifiers could lead to novel therapeutic modalities.

Understanding the Impact of Aberrant Splicing in Coagulation Factor V Deficiency

Rare inherited coagulation disorders (RICDs) are congenital deficiencies of the plasma proteins that are involved in blood coagulation, which generally lead to lifelong bleeding manifestations. These diseases are generally qualitative and/or quantitative defects that are associated with monoallelic or biallelic mutations in the relevant gene. Among RICDs, factor V (FV) deficiency is one of the least characterized at the molecular level. Here, we investigated four unrelated patients with reduced plasma FV levels (three severe, one mild), which were associated with a moderately severe bleeding tendency. Sequence analysis of the FV gene identified seven different variants, five hitherto unknown (p.D1669G, c.5789-11C>A, c.5789-12C>A, c.5789-5T>G, and c.6528G>C), and two previously reported (c.158+1G>A and c.5789G>A). The possible pathogenic role of the newly identified missense variant was studied by in silico approaches. The remaining six genetic defects (all putative splicing mutations) were investigated for their possible effects on pre-mRNA splicing by transient transfection experiments in HeLa cells with plasmids expressing appropriate hybrid minigenes. The preparation of minigene constructs was instrumental to demonstrate that the two adjacent variants c.5789-11C>A and c.5789-12C>A are indeed present in cis in the analyzed FV-deficient patient (thus leading to the c.5789-11_12CC>AA mutation). Ex vivo experiments demonstrated that each variant causes either a skipping of the relevant exon or the activation of cryptic splice sites (exonic or intronic), eventually leading to the introduction of a premature termination codon.

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.

Functional characterization of a novel missense mutation identified in a Turkish patient affected by severe coagulation factor V deficiency

Factor V (FV) deficiency is a rare coagulation disorder, characterized by a bleeding phenotype varying from mild to severe. To date, 115 mutations have been described along the gene encoding for FV (F5) but only few of them have been functionally characterized. Aim of this study was the identification and the molecular characterization of genetic defects underlying severe FV deficiency in a 7-month-old Turkish patient. Mutation detection was performed by sequencing the whole F5 coding region, exon-intron boundaries and about 300 bp of the promoter region. Functional analysis of the identified missense mutation was conducted by transient expression of wild-type and mutant FV recombinant molecules in COS-1 cells. Two novel mutations: a missense (Pro132Arg) and a 1-bp deletion (Ile1890TyrfsX19) were identified in the F5 gene. While the frameshift mutation is responsible for the introduction of a premature stop codon, likely triggering F5 mRNA to nonsense-mediated mRNA degradation, the demonstration of the pathogenic role of the Pro132Arg mutation required an experimental validation. Expression experiments showed that the missense mutation causes a significant reduction in FV secretion and in the specific activity of the residual secreted molecule (77% and 78% decrease, respectively). This paper reports the identification of two novel mutations responsible for FV deficiency, thus widening the mutational spectrum of the F5 gene. The Pro132Arg mutation adds to the only other two functionally characterized missense defects in the FV A1 domain.

Ser234Leu missense mutation in the A1 domain of factor V causing moderate factor V deficiency in a Chinese family

AIMS

To investigate the molecular defects in a Chinese pedigree with inherited factor V (FV) deficiency.

METHODS

Laboratory studies including activated partial thromboplastin time (APTT), prothrombin (PT), and thrombin time (TT) were tested in a patient and his family members. FV antigen (FV:Ag) and FV activity (FV:C) were measured by both ELISA and one-stage clotting assays. All the exons, exon-intron boundaries and promoter regions of FV gene were analysed by direct sequencing. The detected mutations were introduced independently by site-directed mutagenesis into a pMT2/FV mammalian expression plasmid containing the full-length FV cDNA and the wild-type and mutant FV proteins were expressed in COS-7 and CHO cells.

RESULTS

The proposita, a 52-year-old Chinese man, had no spontaneous bleeding syndrome. It was found that he had prolonged APTT and PT, 52 s and 22.8 s, respectively, a FV:C of 5.5% and a FV:Ag of 33.1%. Gene analysis showed the proposita was a compound heterozygote of FV mutations, carrying Ser234Leu and Arg413Cys. The FV antigen and activity levels of the Ser234Leu and Arg413Cys mutants are lower than wild type both in cell lysates and in culture media. Protein degradation inhibitor experiment in transfected COS-7 cells showed that Ser234Leu and Arg413Cys degraded intracellularly through the lysosomal pathway. CHO cells expressing either the wild-type or the mutant FV were subjected to immunofluorescence staining with the indicated antibodies and organelle markers, indicating that Ser234Leu and Arg413Cys can be transported to Golgi partially.

CONCLUSIONS

We identified the molecular pathological mechanism of the novel C785T mutation causing type I inherited FV deficiency for the first time.

A novel in-frame deletion in the factor V C1 domain associated with severe coagulation factor V deficiency in a Korean family

Hereditary coagulation factor V deficiency is a rare bleeding disorder characterized by extremely low levels of functional and immunoreactive factor V in plasma associated with moderate-to-severe bleeding symptoms. The genetic bases of factor V deficiency have been characterized only in a limited number of cases and the majority of causative mutations are truncating mutations providing only limited information about the function of subdomains and of individual residues. Here, we present the first report on a Korean family with inherited factor V deficiency. The proband is a 25-year-old man who showed normal coagulation factor levels except those for factor V antigen and activity (3 and 4%, respectively), and was only suffering from bleeding after tooth extraction. Direct sequencing of the factor V gene disclosed the already known nonsense mutation (R1133X) and a novel in-frame 6-bp deletion (6116-6121delGAACAG, corresponding to the amino-acid deletion N1982-S1983) located in the factor V C1 domain; both mutations were found in the heterozygous state. The structural and functional importance of the in-frame deletion was examined by constructing a molecular model based on the crystal structure of bovine activated factor V that has been inactivated by activated protein C. N1982 and S1983 are located on a loop that is exposed on the surface of the C1 domain, and are in close contact with another loop belonging to the A3 domain. Even though the detailed mechanism of the association of the in-frame deletion of our patient and factor V deficiency needs further investigation, this model suggests the possibility that the N1982-S1983 deletion could destabilize the C1-A3 interaction by preventing the potential formation of hydrogen bonds between K1980 and N1986 of the C1 domain with D1604 of the A3 domain. Also, because N1982 is strongly expected to be N-glycosylated judging from its structural homology to factor VIII, loss of this residue can influence proper folding of factor V, resulting in unstable structure, which is vulnerable to intracellular degradation.

Identification of four novel mutations in F5 associated with congenital factor V deficiency

Coagulation factor V (FV) deficiency is a rare bleeding disorder characterized by low coagulant and antigen levels of FV with bleeding symptoms ranging from mild to severe. Only a limited number of mutations have been reported because of the large size of the factor V gene (F5) as well as the low prevalence. In this study, we have identified four novel mutations in F5 in five unrelated patients with congenital FV deficiency. All the patients, including two with undetectable FV activity, were asymptomatic and were found to have prolonged prothrombin time and activated partial thromboplastin time during preoperative screening or routine examinations. All four mutations found in this study are either missense or in-frame deletion. This is in contrast with previous reports of a high frequency of mutations introducing premature termination codons in inherited FV deficiency. Missense mutations of F5 might produce a mild phenotype and are not frequently diagnosed. Although FV deficiency is a very rare disorder with a predicted incidence of one in 1 million, this study suggests that the numbers of F5 mutations, especially missense mutations, are higher than estimated.

Splenectomy and proximal lieno-renal shunt in a factor five deficient patient with extra-hepatic portal vein obstruction

BACKGROUND

The clinico-surgical implication and successful management of a rare case of factor five (V) deficiency with portal hypertension and hypersplenism due to idiopathic extra-hepatic portal venous obstruction is presented.

CASE PRESENTATION

A 16-year old boy had gastro-esophageal variceal bleeding, splenomegaly and hypersplenism. During preoperative workup prolonged prothrombin time and activated partial thromboplastin time were detected, which on further evaluation turned out to be due to factor V deficiency. Proximal lieno-renal shunt and splenectomy were successfully performed with transfusion of fresh frozen plasma during and after the surgical procedure. At surgery there was no excessive bleeding. The perioperative course was uneventful and the patient is doing well on follow up.

CONCLUSION

Surgical portal decompressive procedures can be safely undertaken in clotting factor deficient patients with portal hypertension if meticulous surgical hemostasis is achieved at operation and the deficient factor is adequately replaced in the perioperative period.

A case of coagulation factor V deficiency caused by compound heterozygous mutations in the factor V gene

We investigated the molecular basis of a severe factor V (FV) deficiency in a Japanese female, and identified two distinct mutations in the FV gene, a novel cytosine insertion (1943insC) and a previously reported point mutation (A5279G). We expected the patient to be a compound heterozygote for those mutations, as a 1943insC, but not an A5279G, was found in the mother and a sibling. The 1943insC will cause a frame-shift after 590Gln, resulting in amino acid substitutions with two abnormal residues followed by a stop codon in the FV A2 domain (FS592X). The A5279G will cause an amino acid alteration in the FV A3 domain (Y1702C), which has been observed in several ethnic groups. We found that both mutant mRNAs were detected by reverse transcriptase polymerase chain reaction (RT-PCR) in the patient's platelets, whereas no FV antigen and activity were detected in plasma. On the one hand, the RT-PCR signal from the FS592X-FV mutant mRNA was markedly reduced, suggesting that the RNA surveillance system would eliminate most of the abnormal FS592X-FV transcripts with a premature termination. On the other hand, expression analyses revealed that only small amounts of Y1702C-FV with a low specific activity were secreted, and that the FS592X-FV was not detected in cultured media. These data indicated that both mutant FV molecules would be impaired, at least in part, during the post-transcriptional process of protein synthesis and/or in secretion. Taken together, it seems to suggest that each gene mutation could be separately responsible for severe FV deficiency, while this phenotype is due to the in-trans combination of the two defects.

Inherited defects of coagulation factor V: the hemorrhagic side

Coagulation factor V (FV) is the protein cofactor required in vivo for the rapid generation of thrombin catalyzed by the prothrombinase complex. It also represents a central regulator in the early phases of blood clot formation, as it contributes to the anticoagulant pathway by participating in the downregulation of factor VIII activity. Conversion of precursor FV to either a procoagulant or anticoagulant cofactor depends on the local concentration of procoagulant and anticoagulant enzymes, so that FV may be regarded as a daring tight-rope walker gently balancing opposite forces. Given this dual role, genetic defects in the FV gene may result in opposite phenotypes (hemorrhagic or thrombotic). Besides a concise description on the structural, procoagulant and anticoagulant properties of FV, this review will focus on bleeding disorders associated with altered levels of this molecule. Particular attention will be paid to the mutational spectrum of type I FV deficiency, which is characterized by a remarkable genetic heterogeneity and by an uneven distribution of mutations throughout the FV gene.

Recessively inherited coagulation disorders

Deficiencies of coagulation factors other than factor VIII and factor IX that cause bleeding disorders are inherited as autosomal recessive traits and are rare, with prevalences in the general population varying between 1 in 500 000 and 1 in 2 million for the homozygous forms. As a consequence of the rarity of these deficiencies, the type and severity of bleeding symptoms, the underlying molecular defects, and the actual management of bleeding episodes are not as well established as for hemophilia A and B. We investigated more than 1000 patients with recessively inherited coagulation disorders from Italy and Iran, a country with a high rate of recessive diseases due to the custom of consanguineous marriages. Based upon this experience, this article reviews the genetic basis, prevalent clinical manifestations, and management of these disorders. The steps and actions necessary to improve the condition of these often neglected patients are outlined.

Coagulation factor V

The coagulation cascade involves sequential enzymatic activations of serine protease zymogens that converge on the generation of thrombin. Factor V (FV) takes part in this process as a component of the prothrombinase complex. Besides its role as procoagulant factor, it is also involved in the physiologic anticoagulant pathway, by participating in the inactivation of activated factor VIII (FVIIIa). Given the dual role of FV, genetic defects in FV gene may result in opposite hemorrhagic or thrombotic phenotypes. This review focuses on the structure, function (procoagulant and anticoagulant), regulation (activation and inactivation) of FV as well as on the genetic defects associated with mutations in the FV gene.

Characterization of an immunologic polymorphism (D79H) in the heavy chain of factor V

BACKGROUND

During the study of a family with hereditary factor (F)V deficiency (FV Amersfoort, 1102 A > T in exon 7) we identified an individual with 5% FV heavy chain antigen (FV(HC)) and 50% FV light chain antigen (FV(LC)). Further testing revealed that apart from the FV Amersfoort allele a second variant FV allele was segregating in this family, which encodes for a FV molecule with a reduced affinity for mAb V-23 used in the FV heavy chain ELISA (ELISA(HC)).

OBJECTIVE

Identification and characterization of the molecular basis responsible for the reduced affinity of the variant FV for mAb V-23.

METHODS

Family members of the proband were screened for mutations in the exons coding for the heavy chain of FV, after which the recombinant variant FV could be generated and characterized. Next, the cases and controls of the Leiden Thrombophilia Study (LETS) were genotyped for carriership of the variant FV.

RESULTS

In the variant FV allele a polymorphism in exon 3 (409G > C) was identified, which predicts the replacement of aspartic acid 79 by histidin (D79H). Introduction of this mutation in recombinant FV confirmed that it reduces the affinity for binding to mAb V-23. The substitution has no effect on FV(a) stability and Xa-cofactor activity. In Caucasians the frequency of the FV-79H allele is approximately 5%. Analysis of the LETS revealed that the FV-79H allele is not associated with FV levels (FV(LC)), activated protein C sensitivity (using an activated partial thromboplastin time-based test) or risk of venous thrombosis (OR 1.07, CI 95: 0.7-1.7).

CONCLUSION

The D79H substitution in FV should be considered as a neutral polymorphism. The monoclonal antibody V-23, which has a strongly reduced affinity for FV-79H, is not suitable for application in diagnostic tests.

Identification of three F5 gene mutations associated with inherited coagulation factor V deficiency in two Chinese pedigrees

To investigate the molecular defects in two Chinese pedigrees with inherited factor V (FV) deficiency. A 37-year-old male (proband 1) and an 18-month-old boy (proband 2) were diagnosed as inherited coagulation FV deficiency by severely reduced plasma levels of FV activity and antigen. All 25 exons and their flanking sequence of F5 gene were amplified by polymerase chain reaction (PCR) for both probands and the PCR products were directly sequenced. Total RNA was extracted from the peripheral lymphocytes of proband 1 for detecting the changes at mRNA level. The homozygous deletion IVS8 -2A>G was identified in the F5 gene of proband 1 and complementary DNA (cDNA) analysis revealed the abolishment of the canonical splicing site by the mutation and the activation of the cryptic acceptor site 24 bp upstream instead. The insertion introduced eight additional amino acids (AA) into the FV protein. Two heterozygous mutations of F5 gene were discovered in proband 2. The 2238-9del AG in exon 13 introduced a premature termination code at 689 AA and the substitution of G6410 by T in exon 23 lead to the missense mutation Gly2079Val. Three F5 gene mutations, IVS8 -2A>G, 2238-9del AG and G6410T, have been identified in two Chinese pedigree with congenital FV deficiency, respectively.