Exclusion of the First EGF Domain of Factor VII by a Splice Site Mutation Causes Lethal Factor VII Deficiency

Molecular Characterization of Two Homozygous Factor VII Variants Associated with Intracranial Bleeding

Clinical parameters have been extensively studied in factor (F) VII deficiency, but the knowledge of molecular mechanisms of this disease is scarce. We report on three probands with intracranial bleeds at an early age, one of which had concomitant high titer of FVII inhibitor. The aim of the present study was to identify the causative mutations and to elucidate the underlying molecular mechanisms. All nine F7 exons were sequenced in the probands and the closest family members. A homozygous deletion in exon 1, leading to a frame shift and generation of a premature stop codon (p.C10Pfs*16), was found in proband 1. Probands 2 and 3 (siblings) were homozygous for a missense mutation in exon 8, resulting in a glycine (G) to arginine (R) substitution at amino acid 240 (p.G240R). All probands had severely reduced FVII activity (FVII:C < 1 IU/dL). Treatment consisted of recombinant FVIIa and/or plasma concentrate, and proband 1 developed a FVII inhibitor shortly after initiation of treatment. The FVII variants were overexpressed in mammalian cell lines. No FVII protein was produced in cells expressing the p.C10Pfs*16 variant, and the inhibitor development in proband 1 was likely linked to the complete absence of circulating FVII. Structural analysis suggested that the G to R substitution in FVII found in probands 2 and 3 would destabilize the protein structure, and cell studies demonstrated a defective intracellular transport and increased endoplasmic reticulum stress. The molecular mechanism underlying the p.G240R variant could be reduced secretion caused by protein destabilization and misfolding.

Biochemical, molecular and clinical aspects of coagulation factor VII and its role in hemostasis and thrombosis

Activated factor VII (FVIIa), the first protease of clotting, expresses its physiological procoagulant potential only after complexing with tissue factor (TF) exposed to blood. Deep knowledge of the FVIIa-TF complex and F7 gene helps to understand the Janus-faced clinical findings associated to low or elevated FVII activity (FVIIc). Congenital FVII deficiency, the most frequent among the recessively inherited bleeding disorders, is caused by heterogeneous mutations in the F7 gene. Complete FVII deficiency causes perinatal lethality. A wide range of bleeding symptoms, from life-threatening intracranial hemorrhage to mild mucosal bleeding, is observed in patients with apparently modest differences in FVIIc levels. Though clinically relevant FVIIc threshold levels are still uncertain, effective management, including prophylaxis, has been devised, substantially improving the quality of life of patients. The exposure of TF in diseased arteries fostered investigation on the role of FVII in cardiovascular disease. FVIIc levels were found to be predictors of cardiovascular death and to be markedly associated to F7 gene variation. These genotype-phenotype relationships are among the most extensively investigated in humans. Genome-wide analyses extended association to numerous loci that, together with F7, explain >50% of FVII level plasma variance. However, the ability of F7 variation to predict thrombosis was not consistently evidenced in the numerous population studies. Main aims of this review are to highlight i) the biological and clinical information that distinguishes FVII deficiency from the other clotting disorders and ii) the impact exerted by genetically predicted FVII level variation on bleeding as well as on the thrombotic states.

Prenatal diagnosis in rare bleeding disorders-An unresolved issue?

Intracranial haemorrhage (ICH) is the most dreadful complication, and the main cause of death among patients with rare bleeding disorders (RBD) and prenatal diagnosis (PND) is a preventative lifesaving program. A total of 39 PNDs were reported in the literature through a search on PubMed, EMBASE, SCOPUS and Web of Science databases, most often for congenital factor (F) XIII and FVII deficiencies and rarely in FX, FV deficiencies and afibrinogenemia. The main cause to request a PND is ICH and related morbidity and mortality. Different molecular methods including direct sequencing and linkage analysis as well as polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) for a specific mutation are the most common used methods for PND, while factor assay and combination of molecular and factor assay also were used. In this research, 7 severely affected foetuses were identified during PND including 3 foetuses with FXIII deficiency, 3 with FVII deficiency and 1 with FX deficiency. Out of these 7 cases, intrauterine ICH occurred in 1 case with FXIII deficiency, 1 was electively aborted and 1 case with severe FVII deficiency received intrauterine factor transfusion. Postdelivery ICH was reported for 1 patient with severe FVII deficiency within the first month of life. All other pregnancies were uneventful.

Activation of a cryptic splice site in a potentially lethal coagulation defect accounts for a functional protein variant

Changes at the invariable donor splice site + 1 guanine, relatively frequent in human genetic disease, are predicted to abrogate correct splicing, and thus are classified as null mutations. However, their ability to direct residual expression, which might have pathophysiological implications in several diseases, has been poorly investigated. As a model to address this issue, we studied the IVS6 + 1G > T mutation found in patients with severe deficiency of the protease triggering coagulation, factor VII (FVII), whose absence is considered lethal. In expression studies, the IVS6 + 1G > T induced exon 6 skipping and frame-shift, and prevented synthesis of correct FVII transcripts detectable by radioactive/fluorescent labelling or real-time RT-PCR. Intriguingly, the mutation induced the activation of a cryptic donor splice site in exon 6 and production of an in-frame 30 bp deleted transcript (8 ± 2%). Expression of this cDNA variant, lacking 10 residues in the activation domain, resulted in secretion of trace amounts (0.2 ± 0.04%) of protein with appreciable specific activity (48 ± 16% of wt-FVII). Altogether these data indicate that the IVS6 + 1G > T mutation is compatible with the synthesis of functional FVII molecules (~ 0.01% of normal, 1 pM), which could trigger coagulation. The low but detectable thrombin generation (352 ± 55 nM) measured in plasma from an IVS6 + 1G > T homozygote was consistent with a minimal initiation of the enzymatic cascade. In conclusion, we provide experimental clues for traces of FVII expression, which might have reverted an otherwise perinatally lethal genetic condition.

Using a minigene approach to characterize a novel splice site mutation in human F7 gene causing inherited factor VII deficiency in a Chinese pedigree

Factor VII deficiency which transmitted as an autosomal recessive disorder is a rare haemorrhagic condition. The aim of this study was to identify the molecular genetic defect and determine its functional consequences in a Chinese pedigree with FVII deficiency. The proband was diagnosed as inherited coagulation FVII deficiency by reduced plasma levels of FVII activity (4.4%) and antigen (38.5%). All nine exons and their flanking sequence of F7 gene were amplified by polymerase chain reaction (PCR) for the proband and the PCR products were directly sequenced. The compound heterozygous mutations of F7 (NM_000131.3) c.572-1G>A and F7 (NM_000131.3) c.1165T>G; p.Cys389Gly were identified in the proband's F7 gene. To investigate the splicing patterns associated with F7 c.572-1G>A, ectopic transcripts in leucocytes of the proband were analyzed. F7 minigenes, spanning from intron 4 to intron 7 and carrying either an A or a G at position -1 of intron 5, were constructed and transiently transfected into human embryonic kidney (HEK) 293T cells, followed by RT-PCR analysis. The aberrant transcripts from the F7 c.572-1G>A mutant allele were not detected by ectopic transcription study. Sequencing of the RT-PCR products from the mutant transfectant demonstrated the production of an erroneously spliced mRNA with exon 6 skipping, whereas a normal splicing occurred in the wide type transfectant. The aberrant mRNA produced from the F7 c.572-1G>A mutant allele is responsible for the factor VII deficiency in this pedigree.

Factor VII deficiency: clinical manifestation of 717 subjects from Europe and Latin America with mutations in the factor 7 gene

The congenital FVII deficiency (FVIID) is a rare haemorrhagic disorder with an autosomal recessive pattern of inheritance. Data on phenotype and the genotype from 717 subjects in Central Europe (six countries), Latin America (Costa Rica, Venezuela) and United States, enrolled in the Greifswald Registry of FVII Deficiency were analysed. We detected 131 different mutations in 73 homozygous, 145 compound heterozygous and 499 heterozygous subjects. Regional differences were observed in the mutation pattern and the clinical profile of the evaluated patients. Seventy-one per cent of homozygous and 50% of compound heterozygous subjects were symptomatic. The clinical manifestations of the homozygous subjects were characterized by intracranial haemorrhage (2%), gastrointestinal bleeding (17%), haemarthrosis (13%), epistaxis (58%), gum bleeding (38%), easy bruising (37%), haematoma (15%), haematuria (10%) and menorrhagia (19 of 26 females, 73%). The clinical variability and genotype-phenotype correlation was evaluated in the homozygous subjects. The pattern of bleeding symptoms among compound heterozygous patients was severe and similar to that of the homozygous patients. The large-scale analysis of 499 heterozygous subjects shows that 93 (19%) presented with spontaneous bleeding symptoms such as haemarthrosis (4%), epistaxis (54%), gum bleeding (14%), easy bruising (38%), haematoma (23%), haematuria (5%) and menorrhagia (19 of 45 females; 42%). The severe haemorrhages - intracranial and gastrointestinal - were not reported in heterozygous subjects. The clinical variability and the regional differences in the mutation pattern are discussed regarding care and treatment.

Japanese collaborative study to assess inter-laboratory variation in factor VII activity assays

BACKGROUND

The clinical phenotype manifest by patients with factor VII (FVII) deficiency correlates poorly with that predicted by laboratory tests. Despite its importance, there are no data on the variability of inter-laboratory determinations of low to very low plasma FVII activity (FVII:C).

METHODS

We distributed three FVII-deficient plasma samples, prepared by immunoaffinity chromatography, to 58 laboratories in Japan. All samples were assayed using standardized reference plasma as a calibrator. Recombinant thromboplastin was also supplied as a common reagent.

RESULTS

In the case of sample A, which had a very low FVII:C, the use of standardized reference plasma and thromboplastin, lowered the variability of inter-laboratory measurements, when compared with the variability observed when samples were assayed using the respective laboratory's routine method.

CONCLUSIONS

The data obtained indicated that results for samples with a very low FVII:C were greatly influenced by the number of plasma dilutions used in constructing a standard activity curve, and also by the type of calibrator and thromboplastin. Such variability was not seen for samples with moderate FVII:C. We conclude that it is necessary to develop a more sensitive and accurate FVII:C measurement system for the diagnosis and treatment of FVII deficiency.

Intracellular readthrough of nonsense mutations by aminoglycosides in coagulation factor VII

BACKGROUND

Nonsense mutations in coagulation factor (F) VII potentially cause a lethal hemorrhagic diathesis. Readthrough of nonsense mutations by aminoglycosides has been studied in a few human disease models with variable results.

OBJECTIVES

We investigated the K316X and W364X FVII mutations, associated with intracranial hemorrhage, and their correction by aminoglycosides. The rare nonsense mutations in FVII represent favorite models to test this strategy, because even tiny increases in the amount of functional full-length protein in patients could ameliorate hemorrhagic phenotypes.

RESULTS

A FVII-green fluorescent protein (GFP) chimaera provided us with a fluorescent model of FVII expression in living cells. Appreciable fluorescence in cells transfected with nonsense FVII-GFP mutants was detected upon geneticin treatment, thus demonstrating suppression of premature translation termination. To investigate the rescue of FVII function, nonsense variants of the native FVII without GFP (p316X-FVII and p364X-FVII) were transfected and found to secrete low amounts of FVII (approximately 1% of Wt-FVII activity), thus suggesting a spontaneous stop codon readthrough. Geneticin treatment of cells resulted in a significant and dose-dependent increase of secreted FVII molecules (p316X-FVII, 24 +/- 12 ng mL(-1), 3.6 +/- 0.8% of Wt-FVII activity; p364X-FVII, 26 +/- 10 ng mL(-1), 3.7+/-0.6%) characterized by reduced specific activity, thus indicating the synthesis of dysfunctional proteins. Similar results were observed with gentamicin, a commonly used aminoglycoside of potential interest for patient treatment.

CONCLUSIONS

Our approach, extendable to other coagulation factors, represents an effective tool for a systematic study of the effects of aminoglycosides and neighboring sequences on nonsense codon readthrough. These results provide the rationale for a mutation-specific therapeutic approach in FVII deficiency.

Long-term FVII substitution in a preterm infant with severe gastrointestinal bleeding and FVII deficiency due to a homozygous donor splice mutation IVS4+1G-->A

Congenital FVII deficiency is a rare bleeding disorder. Clinical complications are similar to those seen in hemophilia A, and an increased incidence of intracerebral hemorrhage related to birth trauma has been reported. The authors report on an infant who presented at the second day of life with melaena and hematemesis caused by congenital FVII deficiency with minimal activity of 4%. A homozygous mutation IVS4+G-->A, formerly described in 2 siblings, who died of brain hemorrhage within the first month of life, was identified. Severe bleeding events were prevented with prophylactic treatment. Early identification of the underlying mutation helps to assess the risk of hemorrhage and prevent severe bleeding by prophylactic FVII therapy.

Molecular characterization of two novel mutations causing factor X deficiency in a Chinese pedigree

Factor X (FX) deficiency is a rare bleeding disorder inherited as an autosomal recessive trait. In this study, we investigated the molecular basis of FX deficiency in a Chinese pedigree. The proposita showed a markedly prolonged activated partial thromboplastin time and a mild prolongation of prothrombin time. The levels of FX antigen and FX activity were 58.6% and 2.5%, respectively. Molecular analysis revealed that the proposita was compound heterozygous for two novel mutations: IVS1 + 1G > A and G1185A (Arg347His). The aberrant transcripts from the IVS1 + 1G > A mutant allele were not detected by analyzing the splicing pattern of ectopic transcripts in leukocytes of the patient with nested polymerase chain reaction after reverse transcription. We thus hypothesize that the mRNA molecules originating from the IVS1 + 1G > A mutation were rapidly destroyed in vivo. Site-directed mutagenesis of FX cDNA was used to introduce FXG1185A mutation, and wild-type as well as mutant FX proteins were expressed by transient transfection in HEK 293 cells. Normal FX antigen levels both in the conditioned media of cells expressing the mutant and in cell lysates were detected by an enzyme-linked immunoadsorbent assay. Evaluation of wild-type and mutant coagulant activity demonstrated that the FX molecules carrying the Arg347His mutation have dramatically decreased activity.

Two novel mutations in severe factor VII deficiency

We have characterized the molecular defect in two families with severe factor VII (FVII) deficiency. In family I, the proband was found to be homozygous for a novel 18 bp deletion in exon 8 (g.10896-10913del) resulting in the in-frame deletion of six amino acids in the serine protease domain. Molecular modelling suggests the deletion is likely to disrupt folding of the FVII molecule. The reduced FVII antigen (21 U/dl) and negligible activity (0.4 U/dl) in the patient's plasma indicated that the deletion affected both the secretion/stability and function of the mutant protein. In family II, the proband was found to be a compound heterozygote for a novel missense mutation (g.7884G>A; FVII G117R) in exon 5 encoding the EGF2 domain of FVII and a nonsense mutation (g.8960C>T; FVII R152X) in exon 6. Extensive sequence comparison in a wide evolutionary context suggested that the Gly117 residue is critical for structure of FVII. The grossly reduced FVII antigen (1.1 U/dl) and activity (0.4 U/dl) plasma values indicate the mutation primarily affected the folding/secretion or stability of the protein.

Novel therapeutic approach for hemophilia using gene delivery of an engineered secreted activated Factor VII

Hemophilia is a bleeding disorder caused by mutations in the genes encoding coagulation Factor VIII (FVIII) or FIX. Current treatment is through intravenous infusion of the missing protein. The major complication of treatment is the development of neutralizing Ab's to the clotting factor. Infusion of recombinant activated human Factor VII (rhFVIIa), driving procoagulant reactions independently of human FVIII (hFVIII) or hFIX, has been successful in such patients and could in theory provide hemostasis in all hemophilia patients. However, its high cost and short half-life have limited its use. Here, we report a novel treatment strategy with a recombinant adeno-associated virus vector delivering a modified FVII transgene that can be intracellularly processed and secreted as activated FVII (FVIIa). We show long-term expression, as well as phenotypic correction of hemophilia B mice following gene transfer of the murine FVIIa homolog, with no evidence of thrombotic complications at these doses. These data hold promise for a potential treatment for hemophilia and other bleeding disorders.

Factor VII deficiency

As yet, there have been neither systematic reviews nor reports of randomized, controlled trials involving factor VII (FVII) deficiency. Hence, a picture of this disorder can only be drawn by reviewing and summarizing the data that is available. This article provides an overview of the understanding of this rare, inherited disorder of coagulation. In particular, the status of current knowledge of the disorder's prevalence, clinical presentation, diagnostic characteristics and molecular genetics is reviewed, followed by a summary of currently available options for its treatment and management.

Prenatal exclusion of severe factor VII deficiency

A nonconsanguineous asymptomatic couple, were identified as carriers of factor VII (FVII) deficiency when two of their newborn children died of massive intracranial hemorrhage secondary to severe congenital FVII deficiency. Complete sequence analysis of the factor VII (F7) gene in this couple indicated that the mother was heterozygous for an A to G transition at position -2 of the exon 5 acceptor splice site, and the father was heterozygous for a G to T transversion at position +1 of the exon 6 donor splice site. This information allowed us to exclude a compound heterozygous deficiency state in a subsequent pregnancy using PCR/direct sequencing of the F7 gene using DNA obtained from chorionic villi at 10 weeks' gestation. Our experience with the family reported here further supports the conclusion that mutation-specific detection is reliable in the prenatal exclusion of severe bleeding disorders.

Two novel cases of cerebral haemorrhages at the neonatal period associated with inherited factor VII deficiency, one of them revealing a new nonsense mutation (Ser52Stop)

Factor VII (FVII) is a plasma glycoprotein that plays a key role in the initiation of blood coagulation cascade. Inherited FVII deficiency is a rare autosomal recessive disorder with a wide heterogeneous clinical pattern. The severe form may be associated with intracranial haemorrhages occurring closely to birth with a high mortality rate. In the present article, we report two novel cases of neonatal intracerebral bleeding associated with FVII activity levels below 1% of normal. FVII genotyping investigations revealed particular genotypes including the deleterious Cys135Arg mutation and a novel Ser52Stop nonsense mutation at the homozygous state. Both mutations, through different mechanisms, are expected to be inconsistent with the production of functional FVII. These putative mechanisms are discussed through a review of the literature on phenotypic and genotypic characteristics of cerebral haemorrhages in severe inherited FVII deficiency.

Two double heterozygous mutations in the F7 gene show different manifestations

We sequenced the factor VII gene (F7) in two unrelated Japanese patients with factor VII (FVII) deficiency. In the first (an asymptomatic 46-year-old man with FVII activity and antigen levels of 1.2% and 21% of normal respectively), novel E25K and H348Q mutations were identified in the doubly heterozygous state. In transiently transfected HEK293 cells, the level of FVII-E25K mutant activity in the culture media was significantly lower than that of FVII wild type, whereas the antigen levels of both proteins were similar. This suggests that the E25K mutation is associated with a dysfunctional FVII molecule. In the second patient (a 47-year-old woman with FVII activity and antigen levels of less than 1% and 6% respectively), an IVS4+1 mutation and a novel -96C to T transition were detected in the double heterozygous state. In electrophoretic mobility shift assays, the -96T mutation was shown to disrupt binding of Sp1.

Characterization of two novel splice site mutations in human factor VII gene causing severe plasma factor VII deficiency and bleeding diathesis

The molecular basis of severe type I factor (F)VII deficiency was investigated in two Algerian patients. One patient, a 13-year-old-girl who has suffered from severe bleeding since birth, was homozygous for a 7-bp deletion (nt 7774-7780) and a 251-bp insertion (nt 7773-7781) of mitochondrial origin, in IVS 4 acceptor splice site. The other patient, an infant who died from massive intracranial haemorrhage, was homozygous for a transversion in the IVS 7 donor splice site (T9726+2-->G) and a missense mutation in exon 8 (G10588-->A; Arg224-->Gln). In both cases, the deleterious mutations are probably the splice site junction abnormalities impairing mRNA processing. These three lesions have not yet been reported.

Severe factor VII deficiency with recurrent intracranial haemorrhages owing to double heterozygosity for a splice site mutation of an IVS4 and a novel nonsense mutation in exon 8 (Gln211-->Term)

Genetic analysis of a 10-month-old Japanese baby boy with recurrent intrathoracic bleeding, cerebral haemorrhages and gastrointestinal bleeding secondary to severe factor VII (FVII) deficiency revealed evidence of two distinct mutations of FVII: a splice site mutation of G-->A at nucleotide 6071 in the IVS4 splice site and a novel nonsense mutation (Gln211-->Term) in exon 8. His bleeding was difficult to control without prophylactic infusion of FVII. We detected a heterozygous splice site mutation of the IVS4 in his mother and a heterozygous nonsense mutation in exon 8 (Gln211-->Term) in his father. The parents' FVII levels are both 50% of normal controls. The FVII:C in plasma from the proband was < 1.5% of normal controls. FVII:antigen (Ag) was < 1% of normal controls, using a monoclonal antibody (mAb) hVII-B101/1 that specifically reacts with FVII epidermal growth factor 1 (EGF-1), and 5% of normal controls, using a rabbit polyclonal antibody against human FVII. After immunoadsorption with mAb hVII-B101/B1-Sepharose 4B, FVII levels of both the proband and his mother were 5% of normal controls; after immunoadsorption the FVII levels of normal subjects were < 1%. We hypothesize that secretion of a small amount of dysfunctional FVII lacking EGF-1 into the circulation accounts for this observation.

Molecular basis of the Kell-null phenotype: a mutation at the splice site of human KEL gene abolishes the expression of Kell blood group antigens

The Kell blood group system is polymorphic, and 23 antigens have been defined to date. The Kell antigens are located on a single red cell transmembrane glycoprotein, encoded by the 19 exons of the KEL gene. The different Kell phenotypes result from point mutations leading to amino acid changes in the Kell glycoprotein. An unusual phenotype, which is defined as the complete lack of all of the Kell antigens, has been identified and designated as the Kell-null or Ko phenotype. The coding region of the KEL gene of the Ko individual showed a normal KEL2/KEL4/KEL7 gene sequence; nevertheless, a G to C mutation at the splice donor site (5' splice site) of intron 3 was found to be present as a homozygote in the individual. The mutation destroys the conserved GT sequence of the splice donor site. Reverse transcription-polymerase chain reaction analysis showed the absence of the complete KEL mRNA. Instead, a major transcript with the exon 3 region skipped was found. The exon 3 of the KEL gene encodes the transmembrane domain of the Kell glycoprotein, and a transcript without exon 3 is predicted to have a premature stop codon that abolishes the translation of C-terminal segment. The segment contains all of the known positions responsible for characterizing different Kell antigens, and this explains the lack of all Kell antigens in Ko red cells.

Factor VII deficiency and the FVII mutation database

Factor VII (FVII) is a zymogen for a vitamin K-dependent serine protease essential for the initiation of blood coagulation. It is synthesized primarily in the liver and circulates in plasma at a concentration of approximately 0.5 microg/ml (10 nmol/L). The FVII gene (F7) is located on chromosome 13 (13q34), consists of 9 exons, and spans approximately 12kb. It encodes a mature protein of 406 amino acids, which has an N-terminal domain (Gla) post-translationally modified by gamma-carboxylation of glutamic acid residues, two domains with homology to epidermal growth factor (EGF1 and 2), and a C-terminal serine protease domain. The single chain zymogen is activated by proteolytic cleavage at Arg152-Ile153. There are 238 individuals described in the world literature with mutations in their F7 genes (FVII mutation database; europium.csc. mrc.ac.uk). Complete absence of FVII activity in plasma is usually incompatible with life, and individuals die shortly after birth due to severe hemorrhage. The majority of individuals with mutations in their F7 gene(s), however, are either asymptomatic or the clinical phenotype is unknown. In general, a severe bleeding phenotype is only observed in individuals homozygous for a mutation in their F7 genes with FVII activities (FVII:C) below 2% of normal, however, a considerable proportion of individuals with a mild-moderate bleeding phenotype have similar FVII:C by in vitro assay. The failure of in vitro tests to differentiate between these groups may be due to lack of sensitivity in the assays to the very low amounts of FVII:C, which are sufficient to initiate coagulation in vivo. A number of polymorphisms have been identified in the F7 gene and some have been shown to influence plasma FVII antigen levels.

Analysis of the genotypes and phenotypes of 37 unrelated patients with inherited factor VII deficiency

Severe inherited factor VII (FVII) deficiency is a rare autosomal recessive disorder with a poor relationship between FVII coagulant activity and bleeding tendency. Both clinical expression and mutational spectrum are highly variable. We have screened for mutations the FVII gene of 37 unrelated patients with a FVII coagulant activity less than 5% of normal pooled plasmas. The nine exons with boundaries and the 5' flanking region of the FVII gene were explored using a combination of denaturing gradient gel electrophoresis and direct DNA sequencing. This strategy allowed us to characterise 68 out of the 74 predicted FVII mutated alleles. They corresponded to a large panel of 40 different mutations. Among these, 18 were not already reported. Genotypes of the severely affected patients comprised, on both alleles, deleterious mutations which appeared to be related to a total absence of activated FVII. We suggest that this absence of functional FVII can explain the severe clinical expression. Whether a small release of FVII is sufficient to initiate the coagulation cascade and to prevent the expression of a severe phenotype, requires further investigations.

Mechanism underlying factor VII deficiency in Jewish populations with the Ala244Val mutation

We investigated a Sephardic Jewish patient with a mild bleeding diathesis whose plasma levels of factor VII coagulant activity and factor VII antigen were 7% and 9% of normal, respectively. Sequencing demonstrated homozygosity for the Ala244Val mutation and the Arg353Gln polymorphism, which is associated with a modest decrease in factor VII levels. To elucidate the mechanism by which Ala244Val reduced factor VII levels in this patient, transient transfections were performed in COS-1 cells with wild type and mutant factor VII cDNAs and factor VII antigen levels in cell lysates and conditioned media were measured. The secretion of the mutant protein (FVII244V) into the media was 20% of wild type (FVIIwt), and intracellular levels of FVII244V were 60% of FVIIwt. A construct encoding Ala244Val along with the Arg353Gln polymorphism decreased the factor VII level in the media to that observed in the patient's plasma. Pulse-chase experiments demonstrated that FVII244V did not accumulate intracellularly and that low levels of the abnormal protein were maintained throughout the chase. To test the hypothesis that FVII244V results in an unstable molecule, amino acids with smaller (Gly) or larger (Phe) side chains were substituted for Val244 by site-directed mutagenesis. Transient transfection assays with these constructs demonstrated that the side chain of amino acid 244 is crucial in maintaining a proper conformation of the molecule. We conclude that Ala244Val results in a factor VII molecule that is unstable and is probably degraded intracellularly.