In vitro and ex vivo rescue of a nonsense mutation responsible for severe coagulation factor V deficiency

BACKGROUND

Coagulation factor V (FV) deficiency is a rare bleeding disorder that is usually managed with fresh-frozen plasma. Patients with nonsense mutations may respond to treatment with readthrough agents.

OBJECTIVES

To investigate whether the F5 p.Arg1161Ter mutation, causing severe FV deficiency in several patients, would be amenable to readthrough therapy.

METHODS

F5 mRNA and protein expression were evaluated in a F5 p.Arg1161Ter-homozygous patient. Five readthrough agents with different mechanisms of action, i.e. G418, ELX-02, PTC-124, 2,6-diaminopurine (2,6-DAP), and Amlexanox, were tested in in vitro and ex vivo models of the mutation.

RESULTS

The F5 p.Arg1161Ter-homozygous patient showed residual F5 mRNA and functional platelet FV, indicating detectable levels of natural readthrough. COS-1 cells transfected with the FV-Arg1161Ter cDNA expressed 0.7% FV activity compared to wild-type. Treatment with 0-500 μM G418, ELX-02, and 2,6-DAP dose-dependently increased FV activity up to 7.0-fold, 3.1-fold, and 10.8-fold, respectively, whereas PTC-124 and Amlexanox (alone or in combination) were ineffective. These findings were confirmed by thrombin generation assays in FV-depleted plasma reconstituted with conditioned media of treated cells. All compounds except ELX-02 showed some degree of cytotoxicity. Ex vivo differentiated megakaryocytes of the F5 p.Arg1161Ter-homozygous patient, which were negative at FV immunostaining, turned positive after treatment with all 5 readthrough agents. Notably, they were also able to internalize mutant FV rescued with G418 or 2,6-DAP, which would be required to maintain the crucial platelet FV pool in vivo.

CONCLUSION

These findings provide in vitro and ex vivo proof-of-principle for readthrough-mediated rescue of the F5 p.Arg1161Ter mutation.

Molecular and clinical characterization of two unrelated families with factor V deficiency, including a novel nonsense variant (p.Gln1532*)

BACKGROUND

Factor V (FV) is an essential cofactor in the coagulation cascade. The characterization of novel mutations is advantageous for the clinical management of FV-deficient patients.

METHODS

Coagulation screening and thrombin generation assay were performed with the plate-poor plasma. All 25 exons of the F5 gene were amplified and sequenced. The ClustalX-2.1 software was applied to the multiple sequence alignment. The possible adverse effects of mutations were investigated with online bioinformatics software and protein modeling.

RESULTS

Two unrelated families with FV deficiency were under investigation. Proband A was an 18-year-old youth with recurrent epistaxis. Proband B was a 29-year-old woman who did not present with any bleeding symptoms. Three heterozygous mutations (p.Gln1532*, p.Phe218Ser, and p.Asp2222Gly) were detected. Interestingly, they were compound heterozygotes and both contained the p.Asp2222Gly, a polymorphism. The thrombin generation assay showed that both patients had impaired ability of thrombin generation, and in particular, proband A was more severe. Conservation, pathogenicity and protein modeling studies all indicated that these three mutations could cause deleterious effects on the function and structure of FV.

CONCLUSION

These three mutations are responsible for the FV-deficient in two pedigrees. Moreover, the nonsense variant p.Gln1532* is first reported in the world.

Clinical Characterization and Molecular Analysis of Fourteen Chinese Patients with Factor V Deficiency

INTRODUCTION

 Coagulation factor V (FV) functions as a vital cofactor that performs procoagulant roles in the coagulation system. We investigated 14 unrelated patients whose plasma FV levels were all below the reference range.

METHODS

 FV activity (FV:C) and FV antigen were detected by one-stage clotting and ELISA, respectively. All 25 exons of the F5 gene in patients were amplified by the PCR, and they were sequenced directly. Haplotype analysis was performed with different polymorphisms on F5. Protein modeling was applied to analyze the potential molecular mechanisms.

RESULTS

 Of five patients with higher FV levels (FV:C > 10%), only one had minor bleeding symptoms. In contrast, of the remaining eight patients with lower FV levels (FV:C < 10%), six showed various bleeding manifestations. A total of 10 mutations were detected from 14 patients (6 were novel mutations). Interestingly, the homozygous p.Phe190Ser was found in five pedigrees, and haplotype analysis showed that they shared almost the same haplotype, indicating the common origin rather than a hotspot mutation. In silico analysis preliminarily investigated the potential pathogenic mechanism of the mutation. Modeling analysis showed that all six missense mutations would lead to conformational alterations in the FV protein. Among them, three (p.Gly1715Ser, p.Ser1753Arg, and p.Asp68His) would decrease hydrogen bonds.

CONCLUSION

 This is the largest genetic analysis of a single cohort of FV deficiency in Chinese. The study demonstrated that FV levels tended to be correlated with the probability of hemorrhage. The identification of a large number of unique FV-deficient pedigrees highlighted the screening for mutations in F5.

Hemophilia A and factor V deficiency in a girl with Turner syndrome: a case report

BACKGROUND

Hemophilia is an X-linked, recessive inherited disease caused by a defect or deficiency of one of the coagulation factors (VIII or IX). It is considered a rare disease in females. One of the reasons that hemophilia affects females is Turner syndrome. Hemophilia with Turner syndrome is a very rare case, but the combination of Turner syndrome, hemophilia, and factor V deficiency is an isolated case that has never been recorded in the medical literature.

CASE PRESENTATION

In our case, a 5-year-old Syrian girl presented with hemorrhage of gum, epistaxis, and short stature. The lab tests showed: prolonged activated partial thromboplastin time and prothrombin time with deficiency of factor V (1%) and factor VIII (1%). We diagnosed hemophilia A with factor V deficiency. In addition to short stature, the patient was noted to have spaced nipples and winged neck. We performed karyotyping that showed deletion of one X chromosome (45X0), Turner syndrome. There is no family history of hemophilia or any other genetic disease.

CONCLUSIONS

In females affected with hemophilia, karyotyping should be performed. It is very important not to exclude the possibility of a combination of deficiency of more than one clotting factor, and to note that deficiency of more than one factor does not necessarily increase the severity of bleeding compared with deficiency of a single factor.

Clinical Phenotype and Genetic Analysis of Twins With Congenital Coagulation Factor V Deficiency

OBJECTIVE

The aim was to investigate the clinical characteristics and molecular pathogenic mechanism of twins with congenital factor V (FV) deficiency.

METHODS

We comprehensively analyzed the clinical manifestations and laboratory test results of a set of twins and their parents and performed point mutation analysis with direct high-throughput exon sequencing.

RESULTS

The prothrombin time and activated partial thromboplastin time were prolonged for both probands, and the FV activity levels were 13.0% and 9.8%. Next-generation sequencing showed that the affected individuals harbored a paternal c.5113A>C (p.S1705R) and a maternal c.4949C>T (p.A1650V) heterozygous variants in the FV gene, which conformed to an autosomal recessive inheritance pattern. This is the first report of these point mutations. The older boy also had a congenital patent foramen ovale.

CONCLUSION

In this set of twins, missense mutations of the FV gene were related to congenital FV deficiency but unrelated to the patent foramen ovale observed in the older boy.

Hereditary factor V deficiency from heterozygous mutations with a novel variant p.Pro798Leufs∗13 in the F5 gene

To explore the causative mutation for autosomal recessive inheritance factor V (FV) deficiency in a Chinese family. Relative coagulation indexes and the FV antigen were tested by the one-stage clotting method and ELISA, respectively. At the same time, the calibrated automated thrombogram (CAT) was used to analyze the mutant protein function. All 25 exons, flanking sequences, 5' and 3' untranslated regions of the F5 were amplified by PCR and sequenced directly, while each suspected variant was verified by reverse sequencing. The possible impact of the mutant was analyzed by the corresponding bioinformatics software. The phenotypic tests showed that the proband's FV activity has decreased to 24%, whereas the FV antigen has also reduced to 28%. The genetic analysis revealed that she was a compound heterozygote for a frameshift variant from small deletion in the exon 13 (c.2390_2390delC, p.Pro798Leufs∗13) and a missense mutation in the exon 25 (c.6665A>G, p.Asp2222Gly). Meanwhile, the online bioinformatics software indicated that the frameshift variant was disease-causing. The pathogenic variant p.Pro798Leufs∗13 and the benign variant p.Asp2222Gly largely account for the decrease of the FV deficiency in this Chinese family, of which the pathogenic variant is firstly reported in the world.

[Clinical and genetic analyses of hereditary factor Ⅴ deficiency cases]

Objective: To analyze the clinical phenotype and molecular pathogenesis of nine patients with hereditary factor Ⅴ (FⅤ) deficiency. Methods: Nine patients with hereditary FⅤ deficiency who were admitted to the Institute of Hematology and Blood Diseases Hospital from April 1999 to September 2019 were analyzed. The activated partial thromboplastin time, prothrombin time, and FⅤ procoagulant activity (FⅤ∶C) were measured for phenotypic diagnosis. High-throughput sequencing was employed for the F5 gene mutation screening, Sanger sequencing was adopted to confirm candidate variants and parental carrying status, Swiss-model was used for three-dimensional structure analysis, and ClustalX v.2.1 was used for homologous analysis. Results: The FⅤ∶C of the nine patients ranged from 0.1 to 10.6. Among them, eight had a hemorrhage history, with kin/mucosal bleeding as the most common symptom (three cases, 37.5%) , whereas one case had no bleeding symptom. There were five homozygotes and four compound heterozygotes. A total of 12 pathogenic or likely pathogenic mutations were detected, of which c.6100C>A/p.Pro2034Thr, c.6575T>C/p.Phe2192Ser, c.1600_1601delinsTG/p. Gln534*, c.4713C>A/p.Tyr1571*, and c.952+5G>C were reported for the first time. Conclusion: The newly discovered gene mutations enriched the F5 gene mutation spectrum associated with hereditary FⅤ deficiency. High-throughput sequencing could be an effective method to detect F5 gene mutations.

[Identification of a novel variant of F5 gene in a consanguineous pedigree affected with inherited coagulation factor V deficiency]

OBJECTIVE

To explore the genetic basis for a consanguineous pedigree affected with inherited coagulation factor V deficiency.

METHODS

Genomic DNA was extracted from peripheral blood samples from the pedigree and subjected to next generation sequencing for screening variants of the F5 gene. Suspected pathogenic variant was verified by using Sanger sequencing. Pathogenicity of the variant was evaluated according to ACMG guidelines.

RESULTS

A homozygous frameshifting variant, c.4096delC (p.Leu1366Phefs*3), was identified in the F5 gene in the proband, which was confirmed to be derived from her consanguineous parents. This variant was absent in all databases including 10 000 in-house Chinese exome sequences. Based on the ACMG guidelines, the c.4096delC was predicted to be a pathogenic variant.

CONCLUSION

A novel pathogenic variant has been identified in the F5 gene in a consanguineous pedigree with inherited coagulation factor V deficiency, which has enriched the spectrum of F5 gene variants.

[Clinical phenotype and variantal analysis of a pedigree affected with hereditary coagulation factor V deficiency]

OBJECTIVE

To explore the molecular basis for a pedigree affected with coagulation factor V (FV) deficiency.

METHODS

Clinical data of the patient and his family members was analyzed. Targeted capture and next-generation sequencing (NGS) and Sanger sequencing were carried out to detect potential variant of the FV gene.

RESULTS

The patient presented with jaundice and prolonged prothrombin time (PT) and activated partial thromboplastic time (APTT). V factor activity measured only 0.1% of the normal level, though the patient had no sign of bleeding. A paternal heterozygous variant c.653T>C (p.F218S) and a maternal heterozygous variant c.3642_3643del (p.P1215Rfs*175) were identified in the FV gene of the patient. His elder brother was a heterozygous carrier of the c.653T>C (p.F218S) variant. c.653T>C(p.F218S) was a known pathogenic variant, while the c.3642_3643del (p.P1215Rfs*175) variant was unreported previously.

CONCLUSION

Mutations of the FV gene probably underlie the hereditary coagulation factor V deficiency in this patient. NGS combined with Sanger sequencing has detected potential variant with efficiency and provided a reliable basis for clinical and prenatal diagnosis for this family.

Congenital factor V deficiency from compound heterozygous mutations with a novel variant c.2426del (p.Pro809Hisfs*2) in the F5 gene: A case report

INTRODUCTION

Congenital factor V deficiency (FVD) is a rare bleeding disorder characterized by low or undetectable plasma factor V (FV) levels leading to mild to severe bleeding symptoms. Currently, more than 100 mutations have been reported in F5. We herein report a patient with FVD from mutations in the F5 gene.

PATIENT CONCERNS

A 52-year-old man with prolonged prothrombin time and activated partial thromboplastin time corrected by mixing test on preoperative screening. His past medical or family history was not remarkable.

DIAGNOSIS

Factor assays revealed a markedly reduced FV activity at 7%. Other factors were not decreased. DNA sequencing analysis to detect F5 gene mutations showed the patient was compound heterozygous for c.286G>C (p.Asp96His) and c.2426del (p.Pro809Hisfs*2). Asp96His was previously described missense mutation and Pro809Hisfs*2 was a novel deleterious mutation.

INTERVENTIONS

Fresh-frozen plasma was administered to supplement FV before surgery.

OUTCOMES

Subsequent factor assays revealed temporarily increased FV activity at 33%.

CONCLUSION

As was the case in our patient, genotype-phenotype correlations are poor in FVD, and molecular genetic test is necessary to confirm the diagnosis.

[Phenotypic and genetic analysis of a pedigree affected with hereditary FV deficiency due to a novel deletional variant of F5 gene]

OBJECTIVE

To analyze the phenotype and F5 gene variant in a pedigree affected with hereditary coagulation factor V (FV) deficiency.

METHODS

All of the exons, flanking sequences, and 5' and 3' untranslated regions of the F5 gene were subjected to PCR and direct sequencing. Suspected variant sites were confirmed by clone sequencing. Influence of the variants was predicted by using software including ClustalX and Mutation Taster.

RESULTS

The prothrombin time (PT) and activated partial thromboplastin time (APTT) of the proband were prolonged to 20.3 s and 59.2 s, respectively, while FV activity (FV:C) and FV antigen (FV:Ag) were reduced by 13% and 17%, respectively. The FV:C and FV:Ag of his father, sister and daughter were decreased to 35%, 37%, 29% and 42%, 46%, 35%, respectively. The proband was found to carry a heterozygous c.2851delT variant in exon 13 of the F5 gene, which caused a frameshift and resulted in a truncated protein (p.Ser923LeufsX8). In addition, a heterozygous c.1538G to A (p.Arg485Lys) variant was found in exon 10. The father, sister and daughter of the proband all carried the p.Ser923LeufsX8 variant, while his mother and son carried the heterozygous p.Arg485Lys polymorphism. His younger brother and wife were of the wild type. Bioinformatic analysis showed that p.Ser923 was highly conserved across various species. Mutation Taster scored 1.00 for the p.Ser923LeufsX8 variant, and the result has predicted a corresponding disease.

CONCLUSION

A heterozygous deletional mutation c.2851delT in exon 13 of the F5 gene and a heterozygous c.1538G to A polymorphism harbored by the proband may be associated with the decreased FV level in this pedigree.

Inherited disorders of the fibrinolytic pathway

Deficiencies or excessive activation of the  fibrinolytic system can result in severe, lifelong bleeding disorders. The most severe clinical phenotype is caused by α2-Antiplasmin (α2-AP) deficiency which results in excess fibrinolysis due to the inability to inhibit plasmin. Another bleeding disorder due to a defect in the fibrinolytic pathway results from Plasminogen activator inhibitor-1 (PAI-1) deficiency causing enhanced fibrinolysis due to the decreased inhibition of plasminogen activators resulting in increased conversion of plasminogen to plasmin. Both these disorders are rare and have an autosomal recessive pattern of inheritance. They can remain undetected as routine coagulation and platelet function tests are normal. A unique gain-of-function defect in fibrinolysis causes the Quebec platelet disorder (QPD) which is characterized by profibrinolytic platelets containing increased urokinase-type plasminogen activator (uPA) in the α-granules. A high index of suspicion based on clinical phenotype along with the availability of specialized hemostasis testing is required for timely and accurate diagnosis. Antifibrinolytic agents, such as tranexamic acid or ε-aminocaproic acid, are the mainstays of treatment which inhibit fibrinolysis by preventing the binding of plasminogen to fibrin and thereby stabilizing the fibrin clot. The purpose of this review is to summarize the pathogenesis, clinical phenotype, approaches to diagnosis and treatment for these three major disorders of fibrinolysis.

[Phenotypic and mutational analysis of a pedigree affected with hereditary coagulation factor Ⅴ deficiency]

OBJECTIVE

To explore the molecular pathogenesis for a pedigree affected with coagulation factor Ⅴ (FⅤ) deficiency.

METHODS

Prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen (FIB), coagulation factor Ⅱ activity (FⅡ: C), FⅤ activity (FⅤ: C), coagulation factor Ⅶ activity (FⅦ: C), and coagulation factor Ⅹ activity (FⅩ: C) were determined with a STAGO automatic coagulometer. FⅤ antigen (FⅤ: Ag) was detected with enzyme linked immunosorbent assay (ELISA). All exons and their flanking regions, and 5' and 3' untranslated regions of the F5 gene were analyzed by direct sequencing. Suspected mutation was verified by reverse sequencing as well as testing of family members. ClustalX software was used to analyze the conservative property of the mutation sites. PROVEAN and MutationTaster online software was used to predict the effect of the mutation on the protein function. Swiss-pdbViewer was used to analyze the protein model and interaction of amino acids.

RESULTS

The PT and APTT of the proband were slightly prolonged to 15.2 s and 41.8 s, respectively. And the FⅤ: C and FⅤ: Ag measured 55% and 62%, respectively. The FⅤ: C and FⅤ: Ag of his father and son were decreased to various extent (60%, 65% and 31%, 40%, respectively). A c.911G>A heterozygous mutation (Gly276Glu) was detected in exon 6 of the proband, for which her father and son were heterozygotes. The same mutation was not found in her mother, brother and husband. Conservation analysis showed that the Gly276 is highly conserved across various species. By bioinformatic analysis, the PROVEAN (scored -6.214) indicated Gly276Glu was harmful, and MutationTaster (scored 0.976) suggested that it is pathogenic. Model analysis suggested there are two hydrogen bonds between Gly276 and Ile298 in the wild type protein. When Gly276 was replaced by Glu276, the original hydrogen bond did not change, but the side chain of Glu was extended, which added steric hindrance with the surrounding amino acids, which resulted in decreased protein stability.

CONCLUSION

The heterozygous c.911G>A (Gly276Glu) mutation of the F5 gene probably underlies the decreased level of FⅤin the proband.

The duplication mutation of Quebec platelet disorder dysregulates PLAU, but not C10orf55, selectively increasing production of normal PLAU transcripts by megakaryocytes but not granulocytes

Quebec Platelet disorder (QPD) is a unique bleeding disorder that markedly increases urokinase plasminogen activator (uPA) in megakaryocytes and platelets but not in plasma or urine. The cause is tandem duplication of a 78 kb region of chromosome 10 containing PLAU (the uPA gene) and C10orf55, a gene of unknown function. QPD increases uPA in platelets and megakaryocytes >100 fold, far more than expected for a gene duplication. To investigate the tissue-specific effect that PLAU duplication has on gene expression and transcript structure in QPD, we tested if QPD leads to: 1) overexpression of normal or unique PLAU transcripts; 2) increased uPA in leukocytes; 3) altered levels of C10orf55 mRNA and/or protein in megakaryocytes and leukocytes; and 4) global changes in megakaryocyte gene expression. Primary cells and cultured megakaryocytes from donors were prepared for quantitative reverse polymerase chain reaction analyses, RNA-seq and protein expression analyses. Rapidly isolated blood leukocytes from QPD subjects showed only a 3.9 fold increase in PLAU transcript levels, in keeping with the normal to minimally increased uPA in affinity purified, QPD leukocytes. All subjects had more uPA in granulocytes than monocytes and minimal uPA in lymphocytes. QPD leukocytes expressed PLAU alleles in proportions consistent with an extra copy of PLAU on the disease chromosome, unlike QPD megakaryocytes. QPD PLAU transcripts were consistent with reference gene models, with a much higher proportion of reads originating from the disease chromosome in megakaryocytes than granulocytes. QPD and control megakaryocytes contained minimal reads for C10orf55, and C10orf55 protein was not increased in QPD megakaryocytes or platelets. Finally, our QPD megakaryocyte transcriptome analysis revealed a global down regulation of the interferon type 1 pathway. We suggest that the low endogenous levels of uPA in blood are actively regulated, and that the regulatory mechanisms are disrupted in QPD in a megakaryocyte-specific manner.

Platelet-delivered therapeutics

We have proposed that modified platelets could potentially be used to correct intrinsic platelet defects as well as for targeted delivery of therapeutic molecules to sights of vascular injury. Ectopic expression of proteins within α-granules prior to platelet activation has been achieved for several proteins, including urokinase, factor (F) VIII, and partially for FIX. Potential uses of platelet-directed therapeutics will be discussed, focusing on targeted delivery of urokinase as a thromboprophylactic agent and FVIII for the treatment of hemophilia A patients with intractable inhibitors. This presentation will discuss new strategies that may be useful in the care of patients with vascular injury as well as remaining challenges and limitations of these approaches.

[Analysis of a consanguineous pedigree featuring hereditary coagulation factor Ⅴ deficiency]

OBJECTIVE

To screen potential mutation and explore the underlying mechanism for a consanguineous pedigree featuring hereditary coagulation factor Ⅴ (FⅤ) deficiency.

METHODS

Clinical diagnosis was validated by coagulant parameter assays of prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen (FIB), FⅤ procoagulant activity (FⅤ:C) and FⅤ antigen (FⅤ:Ag). Potential mutations of the F5 gene in the proband and his family members were analyzed by direct DNA sequencing of PCR products of all exons, exon-intron boundaries and 3', 5' untranslated regions. Suspected mutation was confirmed by reverse sequencing.

RESULTS

The PT and APTT in the proband were significantly prolonged, which measured 23.5 s (reference range 11.8-14.8 s) and 50.5 s (reference range 27.0-41.0 s), respectively. FⅤ activity and FⅤ antigen of the proband were significantly reduced to 8% and <1%, respectively. PT and APTT in the younger sister of the proband were also significantly prolonged (24.1 s and 62.4 s, respectively). Her FⅤ activity and FⅤ antigen were also significantly decreased (7% and <1%, respectively). PT and APTT of other family members were within the normal range. The homozygous missence mutation causing T→C transition at position 29170 in exon 5 of F5 gene has resulted in a Phe190Ser substitution in the proband. His younger sister was also homozygous for Phe190Ser. Heterozygosity for Phe190Ser was confirmed in his elder brother, elder sister, two daughters and niece, and their FⅤ activity were slightly decreased (57%, 73%, 72%, 66% and 75%, respectively). A normal wild type was observed in two younger brothers of the proband, and their FⅤ activity and FⅤ antigen were in the normal range.

CONCLUSION

Homozygous missence mutation of Phe190Ser has been found in above family featuring hereditary FⅤ deficiency. The homozygous missence mutation was inherited from the parents by consanguineous marriage. Phe190Ser probably underlies may underlie the pathogenesis of hereditary FⅤ deficiency in this pedigree.

Homozygous F5 deep-intronic splicing mutation resulting in severe factor V deficiency and undetectable thrombin generation in platelet-rich plasma

BACKGROUND

Coagulation factor (F) V deficiency is associated with a bleeding tendency of variable severity, but phenotype determinants are largely unknown. Recently, we have shown that three patients with undetectable plasma FV and mild bleeding symptoms had sufficient residual platelet FV to support thrombin generation in platelet-rich plasma (PRP). Therefore, we hypothesized that FV-deficient patients with severe bleeding manifestations may lack platelet FV.

OBJECTIVES

To characterize a FV-deficient patient with a severe bleeding diathesis.

PATIENTS/METHODS

We performed FV mutation screening and functional studies in a 31-year-old male (FV:C < 1%) with umbilical bleeding at birth, recurrent hemarthrosis and muscle hematomas, and a recent intracranial hemorrhage.

RESULTS

The proband was homozygous for a deep-intronic mutation (F5 IVS8 +268A→G) causing the inclusion of a pseudo-exon with an in-frame stop codon in the mature F5 mRNA. Although platelet FV antigen was detectable by immunoprecipitation followed by Western blotting, no FV activity could be demonstrated in the proband's plasma or platelets with a prothrombinase-based assay. Moreover, no thrombin generation was observed in PRP triggered with 1-50 pm tissue factor (even in the presence of platelet agonists), whereas an acquired FV inhibitor was excluded. Clot formation in the proband's whole blood, as assessed by thromboelastometry, was markedly delayed but not abolished.

CONCLUSIONS

This is the first report of a pathogenic deep-intronic mutation in the F5 gene. Our findings indicate that the minimal FV requirement for viability is extremely low and suggest that thrombin generation in PRP may predict bleeding tendency in patients with undetectable plasma FV.

Analysis of newly detected mutations in the MCFD2 gene giving rise to combined deficiency of coagulation factors V and VIII

Combined deficiency of coagulation factor V (FV) and factor VIII (FVIII) (F5F8D) is a rare autosomal recessive disorder characterized by mild-to-moderate bleeding and reduction in FV and FVIII levels in plasma. F5F8D is caused by mutations in one of two different genes, LMAN1 and MCFD2, which encode proteins that form a complex involved in the transport of FV and FVIII from the endoplasmic reticulum to the Golgi apparatus. Here, we report the identification of a novel mutation Asp89Asn in the MCFD2 gene in a Tunisian patient. In the encoded protein, this mutation causes substitution of a negatively charged aspartate, involved in several structurally important interactions, to an uncharged asparagine. To elucidate the structural effect of this mutation, we performed circular dichroism (CD) analysis of secondary structure and stability. In addition, CD analysis was performed on two missense mutations found in previously reported F5F8D patients. Our results show that all analysed mutant variants give rise to destabilized proteins and highlight the importance of a structurally intact and functional MCFD2 for the efficient secretion of coagulation factors V and VIII.

Estimating the cost of redundancy in molecular diagnostics: the case of activated protein C resistance and factor V Leiden

BACKGROUND

The activated protein C resistance--sensitivity ratio in the presence of Factor V deficient plasma (APC-SR/Factor V) exhibits a high sensitivity for factor V Leiden mutation and has been proposed as the diagnostic approach of choice, as an alternative to genetic tests, to evaluate activated protein C resistance. A survey, including 4969 requests, was performed on the activity of a typical Molecular Diagnostics Laboratory in order to estimate the costs due to reagents, instrumentation and personnel.

METHODS

The global costs of three hypothetical diagnostic approaches were compared: (A) exclusive molecular test for FV Leiden; (B) APC-SR alone; (C) APC-SR and the exclusive confirmation of positive results with molecular test.

RESULTS

The global cost for each patient with the three approaches investigated were respectively 42.20 euros (A), 1.09 euros (B), and 433 euros (C). The cost for finding a patient with factor V Leiden mutation was 549.00 euros for A, 14.18 euros for B, and 56.32 euros for C. It was calculated that a decrease of 97.42% and 89.74% can be obtained using the approaches B and C, respectively. The difference in cost between B and C can be justified by the avoidance of false positive cases (6%) and by the impossibility of distinguishing homozygous from heterozygous patients using APC-SR exclusively (B).

CONCLUSIONS

In the case of suspected phenotype APC resistance, we suggest a laboratory approach, which provides the combined and sequential use of ProCGlobal/FV analysis and a subsequent genetic test for positive patients.

[Inherited bleeding disorders common in Jews]

Four inherited disorders of hemostasis have been identified in Jews with a relatively high frequency: Factor XI deficiency, factor VII deficiency, combined factor V and VIII deficiency and GLanzmann thrombasthenia. During the past decades, the bleeding manifestations of these disorders, the diagnosis, the molecular-genetic basis and therapy have been discerned. Furthermore, the prevalence of the respective mutant genes have been delineated in various Jewish Communities. Each one of the disorders can serve as a model enabling better understanding of the pathophysioLogy of the coagulation systems. On the basis of data obtained from the research of Glanzmann thrombasthenia, several widely used drugs have been developed as effective antithrombotic agents.

Structural basis for the cooperative interplay between the two causative gene products of combined factor V and factor VIII deficiency

Combined deficiency of coagulation factors V and VIII (F5F8D), an autosomal recessive disorder characterized by coordinate reduction in the plasma levels of factor V (FV) and factor VIII (FVIII), is genetically linked to mutations in the transmembrane lectin ERGIC-53 and the soluble calcium-binding protein MCFD2. Growing evidence indicates that these two proteins form a complex recycling between the endoplasmic reticulum (ER) and the ER-Golgi intermediate compartment and thereby function as a cargo receptor in the early secretory pathway of FV and FVIII. For better understanding of the mechanisms underlying the functional coordination of ERGIC-53 and MCFD2, we herein characterize their interaction by x-ray crystallographic analysis in conjunction with NMR and ultracentrifugation analyses. Inspection of the combined data reveals that ERGIC-53-CRD binds MCFD2 through its molecular surface remote from the sugar-binding site, giving rise to a 11 complex in solution. The interaction is independent of sugar-binding of ERGIC-53 and involves most of the missense mutation sites of MCFD2 so far reported in F5F8D. Comparison with the previously reported uncomplexed structure of each protein indicates that MCFD2 but not ERGIC-53-CRD undergoes significant conformational alterations upon complex formation. Our findings provide a structural basis for the cooperative interplay between ERGIC-53 and MCFD2 in capturing FV and FVIII.

Crystal structure of the LMAN1-CRD/MCFD2 transport receptor complex provides insight into combined deficiency of factor V and factor VIII

LMAN1 is a glycoprotein receptor, mediating transfer from the ER to the ER-Golgi intermediate compartment. Together with the co-receptor MCFD2, it transports coagulation factors V and VIII. Mutations in LMAN1 and MCFD2 can cause combined deficiency of factors V and VIII (F5F8D). We present the crystal structure of the LMAN1/MCFD2 complex and relate it to patient mutations. Circular dichroism data show that the majority of the substitution mutations give rise to a disordered or severely destabilized MCFD2 protein. The few stable mutation variants are found in the binding surface of the complex leading to impaired LMAN1 binding and F5F8D.

[Combined deficiency of factors V and VIII caused by a novel compound heterozygous mutation of gene Lman1]

Combined deficiency of factor V and VIII (F5F8D) is a rare, autosomal recessive disorder caused by mutations of either lman1 or mcfd2. To identify mutations of these two genes in a Chinese F5F8D family, the samples of peripheral blood were collected from the proband and her parents. Coagulation tests were carried out, including activated partial thromboplastin time (APTT), prothrombin time (PT), thrombin time (TT), fibrinogen (Fg) and coagulate activity of FV, FVIII (FV:C, FVIII:C). The genomic DNA was extracted, then all the exons and intron/exon boundaries of these two genes were amplified by polymerase chain reaction (PCR). The products were finally analyzed by direct sequencing. The results showed that the proband's APTT, PT, TT, Fg, FV:C and FVIII:C were 82.2 sec, 19.6 sec, 18.6 sec, 2.9 g/L, 7.1% and 18.7% respectively, while those parameters of the parents were all within the normal range. Two pathogenic mutations were identified in lman1 gene of the proband: one was the heterozygous c.912_913insA in exon 8 resulting in a frameshift of p.Glu305fsX20; the other was the heterozygous c.1366C > T in exon 11 resulting in p.Arg456X. The proband's father and mother were heterozygous for c.1366C > T and c.912_913insA respectively. It is concluded that F5F8D of the proband is caused by a novel compound heterozygous mutation of the lman1 gene, which has never been reported.

A novel missense mutation causing abnormal LMAN1 in a Japanese patient with combined deficiency of factor V and factor VIII

Combined deficiency of coagulation factor V (FV) and factor VIII (FVIII) (F5F8D) is an inherited bleeding disorder characterized by a reduction in plasma concentrations of FV and FVIII. F5F8D is genetically linked to mutations in either LMAN1 or MCFD2. Here, we investigated the molecular basis of F5F8D in a Japanese patient, and identified a novel missense mutation (p.Trp67Ser, c.200G>C) in the LMAN1, but no mutation in the MCFD2. The amount of LMAN1 in Epstein-Barr virus-immortalized lymphoblasts from the patient was found to be almost the same as that in cells from a normal individual. Interestingly, an anti-MCFD2 antibody did not co-immunoprecipitate the mutant LMAN1 with MCFD2 in lymphoblasts from the patient, suggesting the affinity of MCFD2 for the mutant LMAN1 is weak or abolished by the binding of the anti-MCFD2 antibody. In addition, a Myc/6xHis-tagged recombinant form of wild-type LMAN1 could bind to D-mannose, but that of the mutant could not. The p.Trp67Ser mutation was located in the carbohydrate recognition domain (CRD), which is thought to participate in the selective binding of LMAN1 to the D-mannose of glycoproteins as well as the EF-motif of MCFD2. Taken together, it was suggested that the p.Trp67Ser mutation might affect the molecular chaperone function of LMAN1, impairing affinity for D-mannose as well as for MCFD2, which may be responsible for F5F8D in the patient. This is the first report of F5F8D caused by a qualitative defect of LMAN1 due to a missense mutation in LMAN1. Am. J. Hematol. 2009. (c) 2009 Wiley-Liss, Inc.

Modelling and expression studies of two novel mutations causing factor V deficiency

Human coagulation factor V (FV), a non-enzymatic cofactor of the prothrombinase complex, is required for the rapid generation of thrombin. FV deficiency is a rare autosomal recessive bleeding disorder. We describe two novel mutations, Tyr91Asn and Asp2098Tyr, found in two probands with a residual FV activity of 51% and 4%, respectively. Modelling and structural analysis of these mutations were performed following short-duration molecular dynamics (MD) simulation. Asp2098Tyr lead to abolishment of the highly conserved salt bridge Asp2098-Arg2171 presumably required for structural integrity of the C2 domain. MD studies suggest that additional conformational changes resulting from this mutation involve local rearrangements at Tyr2063 and Tyr2064 and so affect the phospholipid-membrane binding. MD modelling of the Try91Asn mutant revealed a conformational change nearby the Cu(2+) binding site that could affect overall stabilization of the heavy and light chains. These findings suggest that both mutations influence the structural integrity of FV protein. Transient expression data of wild-type and mutant FV variants in 293T human embryonic kidney cells showed FV-specific activity reduced to 26% for Asp2098Tyr and 56% for Tyr91Asn compared to that of wild-type. Thus, both the data from the short duration molecular dynamic simulation and from expression analysis indicate alterations of the FV protein variants that explain the clinical phenotype.

Evaluation of factor V mRNA to define the residual factor V expression levels in severe factor V deficiency

We evaluated FV mRNA in severe factor V deficiency caused by the -12T/A IVS18 mutation, activating a cryptic splice site and leading to premature translation termination. Quantitative evaluation of factor V cDNA from homozygous and heterozygous subjects, and correction for nonsense mediated decay, suggested the presence of 0.1% of normal factor V mRNA.

[Gene analysis of five inherited factor V deficiency cases]

OBJECTIVE

To identify gene mutations involved in five cases of inherited factor V (FV) deficiency.

METHODS

Activity of FV was determined by one-stage clotting assay using FV-deficiency plasma, and FV antigen by an ELISA assay. All the exons and exon-intron boundaries of FV gene were amplified by PCR and then DNA sequencing. Restriction enzyme analysis was used to analyze the probands, their family members and healthy volunteers.

RESULTS

Both activity and antigen of FV in the 5 patients were extremely lower compared with that of normal mixed plasma. Six mutations were identified in these 5 patients, G69969T (G2079V), C45533T (R712Ter), C46796T (R1133Ter), G45366A (C656Y), C46253T (R952C) and G16088C (D68H), the latter three were novel mutations reported for the first time and the C46253T (R952C) was the first missense mutation reported in B domain. The result of sequencing or restriction enzyme analysis showed that the three novel missense mutations were not caused by single nucleotide polymorphisms.

CONCLUSION

Gene mutations in 5 type I inherited FV deficiency of patients including 2 nonsense mutations and 4 missense mutations identified which led to the instability of FV protein and the reducing of FV: Ag in the plasma.

Mutations in the MCFD2 gene are predominant among patients with hereditary combined FV and FVIII deficiency (F5F8D) in India

Combined FV and FVIII deficiency (F5F8D) is a rare (1:1.000.000) autosomal recessive disorder caused by a defect in the LMAN1 or MCFD2 genes, encoding for a FV and FVIII cargo receptor complex. We report the phenotype and genotype analyses in nine unrelated Indian patients with low FV and FVIII coagulant activity [FV:C, range: 5.6-22.4% and FVIII:C, range: 8.3-27.1%]. Four homozygous mutations, including two frame shift, one missense and one splice site, were identified in all the nine patients. Three of them, a 72-bp deletion in LMAN1 (c.813_822 + 62del72, p.K272fs), a 35-bp deletion in MCFD2 (c.210_244del35) and a missence mutation in MCFD2 (p.D122V), identified in four patients, were novel mutations. A previously reported c.149 + 5G > A transition in MCFD2 was identified in the remaining five patients. Haplotype analysis of MCFD2 gene in patients with p.E71fs and c.149 + 5G > A defects suggested an independent origin of both these mutations. The identification of two common mutations (p.E71fs, c.149 + 5G > A) in MCFD2 gene in seven of nine patients, particularly the c.149 + 5G > A (55,6% of patients), suggests that this gene could be the first to be analysed during the genetic diagnosis of F5F8D in this population. This is the first report describing the molecular analysis of a consistent number of F5F8D patients of South Indian origin, a population with a high frequency of such recessive bleeding disorders.

A new case of combined factor V and factor VIII deficiency further suggests that the LMAN1 M1T mutation is a frequent cause in Italian patients

Combined factor V and factor VIII deficiency (F5F8D) is an extremely rare worldwide congenital hemorrhagic disorder that is more prevalent in the Mediterranean area. We report the clinical presentations and the identification of a LMAN1 mutation in a 3-year-old Italian boy who was diagnosed with F5F8D. The mutation identified (M1T) has already been found in several Italian patients. Since the LMAN1 M1T mutation has been identified in most patients with F5F8D, we suggest that the search for this mutation should be the first step in the molecular characterization of patients from an Italian ethnic background.

[Identification of two novel mutations of human blood coagulation factor V gene in a Chinese family with congenital factor V deficiency]

OBJECTIVE

To discover the mutations of human blood coagulation factor V (FV) gene in a Chinese family with congenital factor V deficiency, and to explore the molecular mechanism associated with the congenital factor V deficiency.

METHODS

PCR and DNA sequencing were used to look for the FV gene mutations in the proband. And the novel mutation were testified by PCR restriction fragment length polymorphism technique or reverse DNA sequencing. One hundred healthy volunteers were chosen as controls at random.

RESULTS

Two novel mutations were discovered in the FV gene of proband, which were the A1763C missense mutation in exon 11 and the splicing site mutation in the 3' terminal of intron 16 (G-->T). The pedigree analysis showed that the two mutations inherited from his parents respectively: the A1763C came from his father, and the G-->T from his mother. The A1763C missense mutation in exon 11 was not found in each of 100 healthy volunteers.

CONCLUSION

The congenital deficiency of FV in the proband might be caused by the A1763C missense mutation in exon 11 and the splicing site mutation in the 3' terminal of intron 16, which jointly caused the proband to be a double heterozygote.