Congenital coagulation factor X deficiency: Genetic analysis of five patients and functional characterization of mutant factor X proteins

Congenital factor X (FX) deficiency is a rare bleeding disorder that is inherited as an autosomal recessive trait. In this study, a genetic analysis of the FX gene was performed in five families with this disorder. Four heterozygous mutations [p.Gly154Arg, p.Val236Met, p.Gly263Val and p.Arg387Cys] and one pair of compound heterozygous FX gene mutations consisting of p.Gly406Ser and p.Val424Phe were identified. Mutant FX proteins containing the identified amino acid substitutions were also expressed in cultured cells. These proteins were analysed by enzyme‐linked immunosorbent assay and pulse‐chase experiments. The results demonstrated normal intracellular synthesis and extracellular secretion of mutant FX proteins carrying the p.Val236Met, p.Arg387Cys and p.Gly406Ser amino acid substitutions. However, the results also showed that the p.Gly154Arg, p.Gly263Val and p.Val424Phe proteins were secreted less efficiently than the wild‐type protein, although they were synthesized normally in the cell. Collectively, these observations suggest that the amino acid substitutions p.Gly154Arg, p.Gly263Val and p.Val424Phe induce protein misfolding, leading to the intracellular degradation of many FX proteins containing any of these mutations, and ultimately to the development of FX deficiency. On the other hand, for the p.Val236Met, p.Arg387Cys and p.Gly406Ser mutant proteins, we hypothesize that secreted FX proteins have impaired coagulant activities due to functional defects caused by these amino acid substitutions.     

A novel type I factor X variant (factor X Cys350Phe) due to loss of a disulfide bond in the catalytic domain.

We report a novel mutation within the coagulation factor X (FX) that we have designated FX Padua 4. The phenotype and genotype of the proband and family members were studied. The proband was a child affected by a complex neurological syndrome who, after birth, experienced severe bleeding. The proband showed a laboratory pattern characterized by a severe reduction of FX activity and FX antigen, suggesting a true deficiency. Molecular analysis disclosed a new FX mutation localized in the catalytic domain responsible for a Cys350Phe substitution. The proband was homozygous for this mutation. The proband's mother and father showed a heterozygous pattern and had approximately one-half the normal FX activity and FX antigen. Residual purified FX Cys350Phe had an identical behavior to normal FX as showed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Molecular modeling confirms that the mutation leads to the disruption of a disulfide bridge in the catalytic region of FX. Comparison with other topologically equivalent mutations in other vitamin K-dependent proteins suggests that this disruption could adversely affect protein folding/stability, accounting for the cross-reactive material negative phenotype.     

Human factor VII deficiency caused by S339C mutation located adjacent to the specificity pocket of the catalytic domain

This report documents our identification of a novel factor VII (FVII) gene mutation in a Japanese boy with FVII deficiency. The proband's FVII activity was 34% and his FVII antigen level was 40% of normal controls. DNA sequence analysis of the proband's FVII gene identified a C to G point mutation at nucleotide position 10 933 in exon 8, which results in the substitution of Cys (TGC) for Ser339 (TCC). Hinf I digestion results indicate the proband and his mother were heterozygous for the mutation. Both wild-type and mutant FVIIs were transiently expressed in COS-1 cells. FVII levels measured in the culture medium of FVII Ser339Cys mutants were markedly reduced as compared to those of cells with FVII wild-type. The amount of intracellular FVII in FVII Ser339Cys mutants was 80% of that in wild-type. In the wild-type FVII, Ser339 is juxtaposed to Asp338, which is positioned at the bottom of the substrate-binding pocket in the protease domain and located adjacent to FVII Cys340, that forms a disulphide bond with Cys368. We suspect that the creation of a novel unpaired cysteine through this mutation leads to abnormal disulphide bonding during protein folding, thereby reducing the secretion of FVII.     

Factor XDebrecen: Gly204Arg mutation in factor X causes the synthesis of a non-secretable protein and severe factor X deficiency

Due to a homozygous Gly204Arg mutation in the factor X (FX) gene no detectable FX antigen was found in the plasma of a one-year old patient with severe bleeding diathesis. The amino acid replacement destabilized the disulfide bond that holds the two FX chains together, decreasing the interaction between the Cys201-Cys206 loop region and the region connecting the EGF2 and serine protease domains. Both Gly204 FX and Arg204 FX were synthesized in transfected cells, but only the wild type protein became secreted. The mutant protein was diverted from the normal secretory pathway and retained at the trans Golgi-late endosome level.     

Compound heterozygous mutations in severe factor VII deficiency including a novel nonsense mutation

A 26-year-old man who had a history of recurrent spontaneous nasal bleeding was admitted to our hospital with uncontrolled traumatic subdural hemorrhage. His plasma factor VII activity was less than 10% of normal. DNA sequence analysis revealed that the proband had a compound heterozygote for a novel nonsense mutation (F7 NM_000131.2 c.345C > A; p.Cys115X) in exon 4 encoding the EGF1 domain and a known missense mutation (F7 NM_000131.2 c.1027G > A; p.Gly343Ser) in exon 8 encoding the serine protease domain of F7. The same F7 Gly343Ser mutation was present in the asymptomatic father, who exhibited a modest reduction in the plasma level of factor VII activity (48%).     

In vitro activity of daptomycin and tigecycline against coagulase‐negative staphylococcus blood isolates from bone marrow transplant recipients

The presence of gene lesions in blood coagulation factor X (FX) was investigated in eight FX-deficient patients with severe bleeding symptoms, originating from five unrelated Algerian families (FX coagulant activity <1%, FX antigen ranging from 2% to 16%). A missense mutation (p.Phe31Ser) in the Gla domain was found in homozygous form for all patients but one, who is a compound heterozygote for the Phe31Ser mutation and for a non-sense mutation, Tyr130Term in EGF-2 domain. The haplotypes of FX alleles were determined by the following allelic variants located in the promoter: g.1323_1330delTTGTGA (A1/A2), g.1449T>C, g.1451C>A, upstream to exon 3: g.17257C>T and downstream to exon 3: g.17396A>C. The A1-C-A-T-C haplotype was found on each allele bearing the Phe31Ser mutation in the eight FX deficient patients contrasting with its low frequency (8%) in a control Algerian population (in which the Phe31Ser substitution was absent). The patients came from the same geographical area of Algeria (5/8 are certainly from Kabyle origin) and the haplotype analysis suggests a founder effect. Transient expression study reveals that, for the mutant FX-Phe31Ser, FX antigen level was 60% in conditioned media and 140% in cell lysates compared with the wild type FX. The partial retention and intracellular accumulation of the mutant FX might be due to impaired folding and/or conformational changes, and the discrepancies observed between the FX antigen level in COS-7 cell supernatant (60%) and in the patients plasma (2-16%) to an in vivo increased clearance of the secreted unstable FX mutant.     

A novel two base pair deletion in the factor V gene associated with severe factor V deficiency

We studied a family in which the proband, a 13-year-old boy, had unmeasurable plasma levels of coagulation factor V antigen and activity. Clinical symptoms were severe, with several episodes of haemorrhages in the mucosal tracts (gastrointestinal, nose and urinary) and recurrent haemarthroses that caused permanent arthropathy. Sequence analysis of the factor V gene demonstrated the presence of a novel 2 base pair (bp) homozygous deletion in exon 13 at positions 2833-2834. This mutation, present in the heterozygous state in the asymptomatic mother and absent in the healthy brother, introduced a frameshift and a premature stop at codon 900. This would predict the synthesis of a truncated factor V molecule, lacking part of the B domain and the complete light chain. Because of the existence of a surveillance mechanism that selectively recognizes and degrades mRNA molecules carrying premature termination codons, we analysed the relative abundance of mutant vs. wild-type mRNA molecules in the platelets of the heterozygous proband's mother. The mutant mRNA was significantly reduced in amount (mutant/wild-type ratio 0.35). This is the first reported mutation in the factor V gene causing severe factor V deficiency, the effect of which was quantitatively analysed at mRNA level.     

Identification of a new mutation (Gly420Ser), distal to the active site, that leads to factor XIII deficiency

The molecular defects of the factor XIII A subunit gene were studied in a patient with factor XIII deficiency. Mutation analysis was performed on amplified DNA from each exon of this gene by single-strand conformation polymorphism (SSCP) and DNA sequencing techniques. A substitution of guanine by adenine at nucleotide 1258 in exon 10 of the coagulation factor XIII A subunit gene has been identified in the patient. The mutation results in the replacement of Gly420 by Ser in the core domain of the enzyme. Restriction enzyme analysis of amplified exon 10 DNA confirmed that the patient was homozygous for this mutation. A family study revealed that the mutation was inherited from both parents, who were first cousins. The potential effects of the mutation were predicted by molecular modeling of the amino acid substitution within the coordinates of the crystal structure. The substitution occurred within the core domain of the enzyme at a residue completely conserved among all known members of the transglutaminase family. The model of the mutant protein suggests that although the substitution of Gly420 by Ser causes only minor readjustment of the residues and does not appear to be particularly deleterious in terms of structure, the mutation is, however, likely to decrease the molecule's ability to undergo the conformational change that is thought to be required for full transglutaminase activity. Our data strongly support the previously published information about the functional significance of the residues surrounding, but not forming, the catalytic pocket in the A subunit of factor XIII.     

Of four mutations in the factor VII gene in Tunisian patients, one novel mutation (Ser339Phe) in three unrelated families abrogates factor X activation.

Hereditary factor VII (FVII) deficiency is a rare bleeding disorder. Dysfunctional FVII variants characterized by normal or reduced levels of FVII antigen and discordantly low FVII activity have been described. In this study, seven unrelated Tunisian patients with FVII deficiency were examined. Molecular analysis revealed that three probands harbored a novel Ser339Phe mutation, one proband was inferred to have a novel splice site mutation in intron 2, c.226-2 A>G and three probands had two previously described mutations, Arg304Gln and Cys310Phe. Expression of Ser339Phe in baby hamster kidney cells yielded secretion of FVII antigen at a concentration of 225+/-50 ng/ml, compared with 181+/-47 ng/ml in cells transfected with wild-type FVII but with no demonstrable FVII activity. FVII Ser339Phe bound to tissue factor similarly to the binding of commercial recombinant activated FVII or recombinant wild-type FVII and was normally activated by activated factor X. The major defect of FVII Ser339Phe was its inability to activate factor X in the presence of tissue factor. Modeling predicted that the substitution of Ser339 by Phe abrogated substrate docking.     

A Japanese patient with lipoprotein lipase deficiency homozygous for the Gly188Glu mutation prevalent worldwide.

We studied the molecular basis of familial lipoprotein lipase (LPL) deficiency in a new Japanese kindred. The proband was a four-month-old infant with severe hyperchylomicronemia. In postheparin plasma, LPL activity was virtually absent, although LPL mass was detectable. Single strand conformational polymorphism (SSCP) analysis showed an abnormal band with exon 5 of the LPL gene that was amplified by PCR from the proband's genomic DNA. DNA sequence analysis of the amplified fragment demonstrated that the proband was homozygous for a G-to-A change at nucleotide position 818 resulting in the substitution of glutamic acid for glycine at codon 188. Although this is among the first Gly188Glu mutations identified in Japanese, the missense mutation has previously been reported as a prevalent cause of familial LPL deficiency worldwide and has been proposed to have a common origin. However, DNA haplotype analysis with either restriction fragment length polymorphism (RFLP) or microsatellite markers revealed that the DNA haplotype of the proband was not identical to the haplotype previously reported as common to the other patients with the Gly188Glu mutation. These results add the Gly188Glu mutation to the growing list of LPL gene mutations underlying familial LPL deficiency in Japanese and indicate that the origin of the Gly188Glu mutation is not necessarily common but would be multicentric at least in part.     

Gene mutations and three-dimensional structural analysis in 13 families with severe factor X deficiency

Factor X (FX) deficiency is a rare autosomal recessive disorder. The phenotype and genotype of 15 Iranian patients with FX deficiency from 13 unrelated families with a high frequency of consanguinity were analysed. Five different assays identified four patients from three families with a discrepancy between low-FX coagulant activity (FX:C) and higher-FX antigen (FX:Ag) (a type II deficiency). The remaining 11 patients had parallel reductions of FX:C and FX:Ag (a type I deficiency). Nine different homozygous candidate mutations were identified, of which eight were novel. The four type II cases were associated with an Arg(-1)Thr missense mutation in the prepropeptide: Arg(-1) is highly conserved in all vitamin K-dependent proteins. Four type I mutations (Gly78Asp, Cys81Tyr, Gly94Arg and Asp95Glu) were localized to the EGF-1 and EGF-2 domains, for which molecular views showed that the protein folding would be disrupted. The type I mutation Gly222Asp was localized in the catalytic domain of FX, and is sufficiently close to the Asp-His-Ser catalytic triad to disrupt its correct protein folding. The two type I splice site mutations were IVS1+3, A-->T and IVS2-3, T-->G. These novel homozygous FX mutations were consistent with their phenotypes and agree with experimental data from knockout mice, indicating that FX is an essential protein for survival.     

Gene analysis and prenatal diagnosis for two families of congenital factor V deficiency

Summary. We studied two families in which the probands had severe bleeding tendency and showed low plasma levels of coagulation factor V (FV) antigen and activity. Sequence analysis of the FV gene on proband 1 demonstrated a novel G16088C homozygous missense mutation in exon 3 resulting in an Asp 68 to His substitution and on proband 2, a C69969T homozygous missense mutation in exon 23 leading to Gly2079Val. The parents of both families were each heterozygous for the corresponding FV gene defect. During their second pregnancy, the two families requested prenatal diagnosis. Chorionic villi were analysed at 12 weeks of gestation and cord blood samples were tested at 22 weeks. Microsatellite analysis performed in family 1 showed that the foetus sample was not contaminated by maternal tissue. The foetus 1 was found to be heterozygous for the familiar G16088C mutation with lower FV activity in the cord blood; the foetus 2 was a normal one. The diagnosis was confirmed after the birth. This is the first report of prenatal diagnosis for FV deficiency.     

Molecular characterization of factor X deficiency associated with borderline plasma factor X level

Borderline plasma factor X (FX) levels might complicate the diagnosis of FX deficiency. An asymptomatic individual with 73% FX activity was identified to be heterozygous for the Val342Ala mutation. Expression studies suggested that this substitution is responsible for a CRM+ FX variant with normal activation but modestly reduced catalytic function.     

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.     

Two novel factor VII gene mutations in a Chinese family with factor VII deficiency

We report two novel factor VII (FVII) gene mutations in a Chinese family with FVII deficiency. The proband, a 55-year-old woman. was incidentally found to have right shoulder arthritis consistent with chronic haemophilic arthropathy. FVII studies showed a FVII activity of 0.02 iu/ml and a FVII antigen of 49%. Molecular analysis showed a double heterozygous state, with an exon 4 nonsense mutation (C6003-->A; Cys61-->Term) and an exon 8 missense mutation (T10902-->G; Cys329-->Gly) that disrupted a Cys310/Cys329 disulphide bond. The genotypes and phenotypes were correlated in the patient's daughters. Two daughters were heterozygous for the Cys61-->Term mutation and showed a type 1 FVII gene mutation phenotype consistent with a nonsense mutation. One daughter was heterozygous for the Csy329-->Gly mutation and showed a type 2 mutation phenotype consistent with a missense mutation. These are the first reported FVII gene mutations in the Chinese people.     

Low frequency of the TEL/AML1 fusion gene in acute lymphoblastic leukaemia in Spain

The molecular defect of a congenitally dysfunctional form of prothrombin, prothrombin Segovia, was identified in a patient with a severe bleeding tendency, reduced prothrombin coagulant activity, and normal antigen level. Nucleotide sequencing of amplified DNA revealed a G --> A change at nucleotide 7539 of exon 9 of the prothrombin gene. This resulted in the substitution of Gly319 by Arg. The proband was homozygous for this mutation, his father and brother were heterozygous. We surmised that the substitution, which occurs near the site of cleavage of prothrombin by factor Xa (Arg320-Ile321), altered the conformation of the protein making the cleavage site inaccessible.     

Two novel factor X gene mutations in a Chinese family with factor X deficiency

We report a factor X (FX)-deficient Chinese family with two novel FX gene (F10) mutations. Two sibling probands had a bleeding tendency since childhood. Both had very low FX:C (<0.01 IU/ml) and FX:Ag (5–6%) levels and were heterozygous for two novel F10 mutations, a 2-bp GC deletion involving nucleotides 33 and 34, leading to premature chain termination at residue 45, and a T237C mutation, leading to Phe71Ser. A family study confirmed that the mother had the 2-bp GC deletion and a type I FX deficiency. The father had the Phe71Ser mutation. Interestingly, a type I FX deficiency was also observed, suggesting that Phe71Ser, occurring at a site sandwiched between two Gla residues, might perturb FX protein stability.