Deficiency Of Vitamin K-dependent Clotting Factors Research Articles

Rare inherited coagulation and fibrinolytic defects that challenge diagnostic laboratories.

Coagulation factors, anticoagulants, and fibrinolytic proteins are important for hemostasis, and mutations affecting these proteins causes some rare inherited bleeding disorders that are particularly challenging to diagnose. This review provides current information on rare inherited bleeding disorders that are difficult to diagnose. A review of the literature was conducted for up to date information on rare and difficult to diagnose bleeding disorders. Some rare bleeding disorders cause an inherited deficiency of multiple coagulation factors (F), such as combined FV and FVIII deficiency and familial vitamin K-dependent clotting factor deficiency. Additionally, congenital disorders of glycosylation can affect a variety of procoagulant and anticoagulant proteins and also platelets. Some bleeding disorders reflect mutations with unique impairments in the procoagulant/anticoagulant balance, including those caused by F5 mutations that secondarily increase the plasma levels of tissue factor pathway inhibitor as well as THBD mutations that increase functional thrombomodulin in plasma or cause a consumptive coagulopathy due to thrombomodulin deficiency. Some bleeding disorders accelerate fibrinolysis due to loss-of-function mutations in SERPINE1 and SERPINF2 or in the case of Quebec platelet disorder, a duplication mutation that rewires PLAU and selectively increases expression in megakaryocytes, resulting in a unique platelet-dependent gain-of-function defect in fibrinolysis. Current information on rare and difficult to diagnose bleeding disorders indicates they have unique clinical and laboratory features, and pathogenic characteristics to consider for diagnostic evaluation. Laboratories and clinicians should consider rare inherited disorders, and difficult to diagnose conditions, in their strategy for diagnosing bleeding disorders.

Partial research progress of GGCX pathogenic variation associated phenotypes

γ-glutamyl carboxylase (GGCX), also known as vitamin K-dependent glutamyl carboxylase, catalyzes the posttranslational modification of specific glutamate residues in vitamin K-dependent proteins (VKDPs), and participates multiple biological functions including blood coagulation, bone metabolism, vascular calcification, and cell proliferation. It has been reported originally that GGCX pathogenic variation causes blood coagulation deficiency, which is called as vitamin K-dependent coagulation factor deficiency 1 (VKCFD1). Recently, it has been found that GGCX gene variation results in multiple clinical phenotypes, including dermatological, ophthalmological, skeletal or cardiac abnormalities. Among them, dermatological phenotype is the most common, which is known as pseudoxanthoma elasticum-like syndrome. This paper has reviewed the GGCX pathogenic variation associated phenotypes, in order to increase the recognition of GGCX-related genetic diseases and to help its diagnosis and treatment.

Congenital Combined Bleeding Disorders, a Comprehensive Study of a Large Number of Iranian Patients

Congenital combined bleeding disorders (CBDs) are extremely rare disorders which mainly occur in regions with a high rate of consanguineous marriage. These disorders can present with a variety of symptoms ranging from mucocutaneous bleeding to life-threatening episodes. This study aims to evaluate the prevalence and clinical course of Iranian patients with congenital CBDs. This study is conducted on 450 patients with CBDs who were referred to the Iranian Comprehensive Hemophilia Care Center (ICHCC) between 2010 and 2020. All these patients were diagnosed through evaluation of past medical history and coagulation laboratory investigation. Out of 450 patients, 33 were entered in this study. Having excluded cases with factor (F) V and FVIII deficiency, as well as those with hereditary combined Vitamin K dependent clotting factor deficiency (VKCFD), We found the most common CBDs to be FV-FVII deficiency (n: 6, 18.1%), together with FVII and FX deficiency (n: 6, 18.1%). The most common reason for referral of these patients to ICHCC was postoperative bleeding (14.3%). The mean of The International Society on Thrombosis and Hemostasis-Bleeding Assessment Tool (ISTH-BAT) and condensed MCMDM-1VWD bleeding assessment tool were 9.6 ± 4.79 and 9.1 ± 4.87, respectively (P < 0.005). In 10 females of reproductive age, the mean of Pictorial Bleeding Assessment Chart (PBAC) score was 649.3 ± 554. Among all patients, 23 (69.7%) received on-demand replacement therapy, whereas 5 patients (15.1%) received prophylaxis. In Iran, the coinheritance of bleeding disorders is surprisingly higher than expected. Moreover, patients with congenital CBDs may experience serious bleeding manifestations.

Multiplexed measurement of variant abundance and activity reveals VKOR topology, active site and human variant impact.

Vitamin K epoxide reductase (VKOR) drives the vitamin K cycle, activating vitamin K-dependent blood clotting factors. VKOR is also the target of the widely used anticoagulant drug, warfarin. Despite VKOR's pivotal role in coagulation, its structure and active site remain poorly understood. In addition, VKOR variants can cause vitamin K-dependent clotting factor deficiency or alter warfarin response. Here, we used multiplexed, sequencing-based assays to measure the effects of 2,695 VKOR missense variants on abundance and 697 variants on activity in cultured human cells. The large-scale functional data, along with an evolutionary coupling analysis, supports a four transmembrane domain topology, with variants in transmembrane domains exhibiting strongly deleterious effects on abundance and activity. Functionally constrained regions of the protein define the active site, and we find that, of four conserved cysteines putatively critical for function, only three are absolutely required. Finally, 25% of human VKOR missense variants show reduced abundance or activity, possibly conferring warfarin sensitivity or causing disease.

Development of a cell-based diagnostic system for vitamin K-dependent coagulation factor deficiency 1

To develop a cell-based system for the diagnosis of vitamin K-dependent coagulation factor deficiency 1 (VKCFD1). In HEK293 cells stably expressing the reporter gene FIX-Gla-PC, the gamma-glutamyl carboxylase (GGCX) gene was knocked out by using CRISPR/Cas9 technology. Enzyme-linked immunosorbent assay (ELISA), DNA sequencing and Western blotting were used to identify the GGCX gene knockout cells. A quickchange point variant method was used to construct the GGCX variant. ELISA was used to assess the influence of GGCX variant on the activity of reporter gene. Two monoclonal cell lines with no reporter activity by ELISA was identified. Edition and knockout of the GGCX gene was confirmed by DNA sequencing and Western blotting. The activity of the reporter gene was recovered by transfection of the wild-type GGCX gene. Thereby two monoclonal cells with GGCX knockout were obtained. By comparing the wild-type and pathogenic GGCX variants, the reporter activity was decreased in the pathogenic variants significantly. A cell-based system for the detection of GGCX activity was successfully developed, which can be used for the diagnosis of VKCFD1 caused by GGCX variants.

Fat-soluble vitamin deficiency and subsequent coagulopathy in a cat with exocrine pancreatic insufficiency

This report describes the clinical signs, diagnostic findings and treatment of a female spayed Domestic Shorthair with exocrine pancreatic insufficiency (EPI) who presented in shock due to severe gastrointestinal haemorrhage...

Autosomal recessive inherited bleeding disorders in Pakistan: a cross-sectional study from selected regions

BackgroundAutosomal recessive bleeding disorders (ARBDs) include deficiencies of clotting factors I, II, V, VII, X, XI, XIII, vitamin K dependent clotting factors, combined factor V & VIII, Von Willebrand Disease (vWD) type 3, Glanzmann’s thrombasthenia (GT) and Bernard–Soulier syndrome. Patients with primary bleeding disorders from all the major provincial capitals of Pakistan were screened for ARBDs. Prothrombin (PT), activated partial thromboplastin time (APTT), bleeding time (BT) and fibrinogen levels were measured. Cases with isolated prolonged APTT were tested for factors VIII and IX using factor assays This was followed by FXI:C level assessment in cases with normal FVIII and FIX levels. vWD was screened in patients with low FVIII levels. Factors II, V and X were tested in patients with simultaneous prolongation of PT and APTT. Peripheral blood film examination and platelet aggregation studies were performed to assess platelet disorders. Urea clot solubility testing was done to detect Factor XIII levels where platelet function tests were normal. Descriptive analysis was done using SPSS version 16.ResultsOf the 429 suspected bleeding disorder patients, 148 (35%) were diagnosed with hemophilia A and 211 (49.1%) patients had ARBDs. 70 patients (16.3%) remained undiagnosed. Out of 211 patients with ARBD; 95 (33.8%) had vWD type 3. Fibrinogen deficiency was found in 34 patients (12%), GT in 27 (9.6%), factor XIII deficiency in 13 (4.6%), factor VII deficiency in 12 (4.3%), factor V deficiency in 9 (3.2%). Eight patients (2.8%) had vitamin K-dependent clotting factor deficiency, Bernard–Soulier syndrome was diagnosed in seven patients (2.5%), factor X deficiency in 2 (0.7%), factor II deficiency in 2 (0.7%), factor XI deficiency and combined factor V and VIII deficiency in 1 (0.4%) patient each.ConclusionvWD type 3 was the most common ARBD found in our sample of patients in Pakistan, followed by fibrinogen deficiency and GT in respective order.

GGCX-Associated Phenotypes: An Overview in Search of Genotype-Phenotype Correlations.

Gamma-carboxylation, performed by gamma-glutamyl carboxylase (GGCX), is an enzymatic process essential for activating vitamin K-dependent proteins (VKDP) with important functions in various biological processes. Mutations in the encoding GGCX gene are associated with multiple phenotypes, amongst which vitamin K-dependent coagulation factor deficiency (VKCFD1) is best known. Other patients have skin, eye, heart or bone manifestations. As genotype–phenotype correlations were never described, literature was systematically reviewed in search of patients with at least one GGCX mutation with a phenotypic description, resulting in a case series of 47 patients. Though this number was too low for statistically valid correlations—a frequent problem in orphan diseases—we demonstrate the crucial role of the horizontally transferred transmembrane domain in developing cardiac and bone manifestations. Moreover, natural history suggests ageing as the principal determinant to develop skin and eye symptoms. VKCFD1 symptoms seemed more severe in patients with both mutations in the same protein domain, though this could not be linked to a more perturbed coagulation factor function. Finally, distinct GGCX functional domains might be dedicated to carboxylation of very specific VKDP. In conclusion, this systematic review suggests that there indeed may be genotype–phenotype correlations for GGCX-related phenotypes, which can guide patient counseling and management.

Pseudoxanthome élastique variant avec déficit en facteurs de coagulation vitamine K-dépendants et perte d’élasticité cutanée

Pseudoxanthoma elasticum (PXE)-like syndrome is characterized by the association of PXE and cutis laxa (CL) features with a deficiency of vitamin K-dependent clotting factors. It was first described in 1971 and was identified as a distinct genetic entity in 2007 with analysis of the GGCX (γ-glutamyl carboxylase) gene, which is involved in congenital deficiency in vitamin K-dependent clotting factors. Here we report a new case of this extremely rare syndrome. A 23-year-old female patient was seen for the emergence of loose and redundant skin following extensive weight loss. She also presented a deficiency of vitamin K-dependent clotting factors. Physical examination revealed excessive, leathery skin folds in the axillary and neck regions. A skin biopsy revealed polymorphous and fragmented elastic fibers in the reticular dermis. These were mineralized, as was demonstrated by Von Kossa staining. The clinical features of CL associated with the histopathological features of PXE and vitamin K-dependent clotting factor deficiency led us to a diagnosis of PXE-like syndrome. A molecular study of the GGCX gene showed compound heterozygosity. The GGCX gene is usually responsible for PXE-like syndrome. GGCX encodes a γ-glutamyl carboxylase necessary for activation of gla-proteins. Gla-proteins are involved both in coagulation factors in the liver and in the prevention of ectopic mineralization of soft tissues. Uncarboxylated forms of gla-proteins in fibroblast would thus enable mineralization and fragmentation of elastic fibers.

Retrospective Study of Twenty-Four Patients With Prolonged Coagulopathy Due to Long-Acting Anti-Vitamin K Rodenticide Poisoning

Second generation anticoagulant rodenticides are now the most common rat killers used in China; however, poisoning incidents are frequently reported. The authors retrospectively reviewed 24 patients with vitamin K-dependent coagulation factor deficiency caused by rodenticide poisoning in the past 2 years. The main clinical presentation was hemorrhage, although intracranial bleeding and life-threatening symptoms were not seen. All patients responded to vitamin K, the specific antidote, along with fresh frozen plasma and cryoprecipitate, although prolonged treatment was sometimes required. To avoid such incidents, rodenticide should be safely stored and protective measures used during production and application. once poisoning has occurred, vitamin K should be administered as soon as possible along with fresh frozen plasma and cryoprecipitate.

Rare coagulation factor deficiencies: a countrywide screening data from India

As compared to haemophilia, although the clinical features and the management strategies for rare coagulation factor deficiencies are discussed, little is known about them. This study was undertaken to assess the distribution, clinical presentation and treatment of patients with rare coagulation factor deficiency disorders in a cross-sectional population of India. Blood samples and other clinical details from patients suspected of rare coagulation factor deficiencies were collected by the Haemophilia Treatment Centers across India and were diagnosed at National Institute of Immunohaematology, Mumbai. A total of 321 cases of rare clotting factor deficiencies were diagnosed, of which 88% were severe, 10% moderate and 2% mild. Commonest deficiency encountered was factor XIII (FXIII) (30%) followed by FX (15.6%), FVII (15%), fibrinogen (12.1%), FXI (9%), combined V and VIII deficiency (5.6%) and congenital multiple vitamin K-dependent coagulation factor deficiency (MCFD, 2.1%). Major representation of these deficiencies was from Southern and Western India (82%). Mucocutaneous bleeding was the commonest clinical presentation (59%); intracranial (IC) haemorrhage was seen in 18% of the patients; menorrhagia was an important clinical pointer in women in the reproductive age group (78%); 8% of the severe cases had no history of bleeding and 73% of the FXIII deficiency cases had umbilical stump bleeding. The major therapeutic products used was fresh frozen plasma (64%), cryoprecipitate (15%), whole blood (15%), antifibrinolytics (5%) and recombinant FVIIa (1%). A distinct pattern in the distribution of rare clotting factor deficiencies was observed which was based on multiple factors that include ethnicity and the available diagnostic facilities in different regions of this vast country.

Vitamin K‐dependent coagulation factor deficiency in trauma: a comparative analysis between international normalized ratio and thromboelastography (CME)

The use of international normalized ratio (INR) to diagnose vitamin K-dependent coagulation factor (VitK-CF) deficiency in trauma has limitations (inability to predict bleeding and long turnaround times). Thromboelastography (TEG) assesses the entire coagulation process. With TEG, reaction time (TEG-R) is used to assess global coagulation factor activity and takes less than 10 minutes. We assessed the ability of TEG-R to detect VitK-CF deficiency in trauma, compared to the INR. A total of 219 trauma patients with INR, TEG, and all VitK-CF measured at admission were included. Demographics and laboratory tests, drugs, blood transfusions, and severity scores were analyzed. Specificity, sensitivity, positive predictive value (PPV), and negative predictive value (NPV) of INR (≥1.3 and ≥1.5) and TEG-R (>8 min) to diagnose VitK-CF deficits (≤50%) were calculated. Secondary outcomes included time to INR and TEG results. Overall, TEG-R performed worse than INR. TEG-R had a sensitivity of 33% (95% CI, 16%-55%), specificity of 95% (95% CI, 91%-98%), PPV of 47% (95% CI, 23%-72%), and NPV of 92% (95% CI, 87%-95%). An INR of 1.5 or greater had a sensitivity of 67% (95% CI, 45%-84%), specificity of 98% (95% CI, 96%-99.7%), PPV of 84% (95% CI, 60%-97%), and NPV of 96% (95% CI, 92%-98%). An INR of 1.3 or greater also had better sensitivity, PPV, and NPV. For patients on warfarin, the times to INR results and TEG completion were 58 (±23) and 92 (±40) minutes (p=0.07), respectively. TEG-R was abnormal in only one patient on warfarin. Our study suggests that TEG-R is not superior at identifying VitK-CF deficiency compared to INR in trauma.

Relationship between acquired deficiency of vitamin K-dependent clotting factors and hemorrhage

This study examined the changes of activities of vitamin K-dependent clotting factors (VKDCF) under various pathological conditions and explored the relationship between acquired deficiency of VKDCFs and hemorrhage. Clinical data of 35 patients who were diagnosed as having acquired deficiency of VKDCF were retrospectively analyzed. Coagulation factors involved in the intrinsic and extrinsic pathways were detected in these patients and 41 control subjects. The results showed that the average activities of VKDCFs were decreased in the patients in comparison to the control subjects and significantly increased after treatment of these patients with vitamin K and blood products. Multivariate regression analysis indicated that decreased activity of VKDCF was not an independent risk factor for bleeding disorders owing to deficiency or metabolic disturbance of vitamin K. It was concluded that acquired deficiency of VKDCF occurs under a variety of pathologic conditions and is closely associated with hemorrhagic events. Administration of vitamin K and transfusion of blood products containing high concentrations of VKDCFs helps alleviate the hemorrhagic diseases.

Gla-Rich Protein Is a Novel Vitamin K-Dependent Protein Present in Serum That Accumulates at Sites of Pathological Calcifications

Mineralization of soft tissues is an abnormal process that occurs in any body tissue and can greatly increase morbidity and mortality. Vitamin K-dependent (VKD) proteins play a crucial role in these processes; matrix Gla protein is considered one of the most relevant physiological inhibitors of soft tissue calcification know to date. Several studies have suggested that other, still unknown, VKD proteins might also be involved in soft tissue calcification pathologies. We have recently identified in sturgeon a new VKD protein, Gla-rich protein (GRP), which contains the highest ratio between number of Gla residues and size of the mature protein so far identified. Although mainly expressed in cartilaginous tissues of sturgeon, in rat GRP is present in both cartilage and bone. We now show that GRP is a circulating protein that is also expressed and accumulated in soft tissues of rats and humans, including the skin and vascular system in which, when affected by pathological calcifications, GRP accumulates at high levels at sites of mineral deposition, indicating an association with calcification processes. The high number of Gla residues and consequent mineral binding affinity properties strongly suggest that GRP may directly influence mineral formation, thereby playing a role in processes involving connective tissue mineralization.

Compound Heterozygosity of a W493C Substitution and R704/Premature Stop Codon within the γ-Glutamyl Carboxylase in Combined Vitamin K-Dependent Coagulation Factor Deficiency in a French Family.

Abstract 1302Poster Board I-324Combined vitamin K-dependent (VKD) coagulation factor deficiency is an autosomal recessive bleeding disorder associated with defects in either the γ-carboxylase (GGCX) which carboxylates VKD proteins to render them active or the vitamin K epoxide reductase (VKORC1) which supplies the reduced vitamin K cofactor required for carboxylation. Such deficiencies are rare, and due to mutations within either gene. Of note some mutations within the GGCX gene have recently been found associated with the pseudoxanthoma elasticum (PXE) syndrome, suggesting a role for GGCX in skin development. We report a new case of combined VKD coagulation factor deficiency resulting from two mutations in the GGCX gene, and the first identified in a French child, who exhibited impaired function in hemostatic VKD factors. The propositus exhibited bleeding at sites of venipuncture at birth, and at the age of 3 months was admitted in emergency for spontaneous multiple hematomas of the chest and thighs; recently, at the age of 1 year, he exhibited a hematoma of the wrist following a casual fall. Coagulation and VKD factors were low [PT (Control/patient): 12.8/>100 sec; II : 3 % ; VII :2% ; X :3%] while the non-VKD factor V was normal (105%). Vitamin K infusion corrected the bleeding tendency as well as coagulation paramenters [PT (Control/patient): 12.8/14.8 sec; II :72% ; VII+X : 62%; factor V remained normal at 102%]. Family analysis revealed that both parents and one brother were unaffected, both clinically and biologically, but that a brother had died of an unexplained abdominal hemorrhage, in the neonatal period. Taken together the clinical family history is consistent with a recessive trait. No sign of PXE was found in the family. DNA sequence analysis of the propositus did not identify any mutations in the VKORC1 gene but revealed two new heterozygous mutations in the carboxylase gene: a G10233T transversion in exon 11 (G1565U in mRNA) that caused an W493C substitution and a C12078T transition in the last exon (15) (C2196U in mRNA) that caused a premature R704stop, presumably deleting the last 55 C-terminal amino acids. W493 is a highly conserved amino acid and its homozygous mutation (for S493) has recently been reported in a case of VKD coagulation factor deficiency associated with PXE. R704 mutation has never been reported previously. Family analysis showed that W493C was transmitted by the father, R704stop by the mother, that the deceased brother carried both mutations, while the unaffected brother carried neither. Mutational analysis was carried out by site-directed mutagenesis of the GGCX cDNA subsequently subcloned into the BacPak8 baculovirus-based vector, and GGCX was expressed in the virally-infected SF21 insect cell line. Protein expression level of the enzyme was assessed by western blotting, and enzymatic activity was evaluated by measuring the incorporation of [14]C-CO2 within the Boc-Glu-Glu-Leu-OMe peptide. No difference in expression level was detected for either mutant protein compared to the wild type protein. However, while no difference in molecular weight was seen between the W493C mutant and wild type on wertern blotting, the R704stop mutation generated a shorter form of carboxylase than wild type, consistent with the predicted shorter reading frame. W493C mutant exhibited a much lower activity than wild type, suggesting a functional role for W493. The activity of the R704stop mutant is currently being assessed, as well as the activity of the coexpressed mutants. Since PXE has been correlated with a W493S mutation, a role for the W493C mutation in future development of PXE in this young patient will be assessed during follow-up. DisclosuresNo relevant conflicts of interest to declare.

Co-Existent Pseudoxanthoma Elasticum and Vitamin K-Dependent Coagulation Factor Deficiency: Compound Heterozygosity for Mutations in the GGCX Gene

Pseudoxanthoma elasticum (PXE) is a multisystem disorder characterized by ectopic mineralization of connective tissues with primary manifestations in the skin, eyes, and cardiovascular system. The classic forms of PXE are due to mutations in the ABCC6 gene that encodes the ABCC6 protein, a putative transmembrane transporter expressed primarily in the liver and the kidneys. PXE-like clinical findings have been encountered in association with vitamin K-dependent coagulation factor deficiency, an autosomal recessive disorder that is due to mutations in either the GGCX or VKORC1 genes. In this study, we investigated a family with two siblings with characteristic features of PXE and vitamin K-dependent coagulation factor deficiency. Mutation analysis identified two GGCX mutations in the affected individuals (p. R83W and p.Q374X); however, no mutations in either ABCC6 or VKORC1 could be found. GGCX encodes a gamma-glutamyl carboxylase necessary for activation of both coagulation factors in the liver and matrix gla protein, which, in fully carboxylated form, is able to prevent ectopic mineralization. Analysis of skin by specific antibodies demonstrated that matrix gla protein was found predominantly in undercarboxylated form and was associated with the mineralized areas in the patients' lesional skin. These observations pathomechanistically suggest that, in our patients, reduced carboxylase activity results in a reduction of matrix gla protein carboxylation, thus allowing peripheral mineralization to occur. Our findings also confirm GGCX as the second gene locus causing PXE.

Pseudoxanthoma elasticum: clinical phenotypes, molecular genetics and putative pathomechanisms.

Pseudoxanthoma elasticum (PXE), a prototype of heritable multisystem disorders, is characterised by pathologic mineralisation of connective tissues, with primary clinical manifestations in the skin, eyes and the cardiovascular system. The causative gene was initially identified as ABCC6 which encodes an ABC transporter protein (ABCC6) expressed primarily in the liver and the kidneys. The critical role of ABCC6 in ectopic mineralisation has been confirmed by the development of Abcc6(-/-) knock-out mice which recapitulate the features of connective tissue mineralisation characteristic of PXE. Over 300 distinct loss-of-function mutations representative of over 1000 mutant alleles in ABCC6 have been identified by streamlined mutation detection strategies in this autosomal recessive disease. More recently, missense mutations in the GGCX gene, either in compound heterozygous state or digenic with a recurrent ABCC6 nonsense mutation (p.R1141X), have been identified in patients with PXE-like cutaneous findings and vitamin K-dependent coagulation factor deficiency. GGCX encodes a carboxylase which catalyses gamma-glutamyl carboxylation of coagulation factors as well as of matrix gla protein (MGP) which in fully carboxylated form serves as a systemic inhibitor of pathologic mineralisation. Collectively, these observations suggest the hypothesis that a consequence of loss-of-function mutations in the ABCC6 gene is the reduced vitamin K-dependent gamma-glutamyl carboxylation of MGP, with subsequent connective tissue mineralisation. Further progress in understanding the detailed pathomechanisms of PXE should provide novel strategies to counteract, and perhaps cure, this complex heritable disorder at the genome-environment interface.

Familial deficiency of vitamin K‐dependent clotting factors

Combined deficiency of vitamin K-dependent clotting factors II, VII, IX and X (and proteins C, S, and Z) is usually an acquired clinical problem, often resulting from liver disease, malabsorption, or warfarin overdose. A rare inherited form of defective gamma-carboxylation resulting in early onset of bleeding was first described by McMillan and Roberts in 1966 and subsequently has been termed 'vitamin K-dependent clotting factor deficiency' (VKCFD). Biochemical and molecular studies identify two variants of this autosomal recessive disorder: VKCFD1, which is associated with point mutations in the gamma-glutamylcarboxylase gene (GGCX), and VKCFD2, which results from point mutations in the vitamin K epoxide reductase gene (VKOR). Bleeding ranges in severity from mild to severe. Therapy includes high oral doses of vitamin K for prophylaxis, usually resulting in partial correction of factor deficiency, and episodic use of plasma infusions or prothrombin complex concentrate. Recent molecular studies have the potential to further our understanding of vitamin K metabolism, gamma-carboxylation, and the functional role this post-translational modification has for other proteins. The results may also provide potential targets for molecular therapeutics and pharmacogenetics.

VKORC1: molecular target of coumarins.

The genetic diagnosis of a single family with combined vitamin K-dependent clotting factor deficiency (VKCFD2, OMIM #607473) finally led to the identification and molecular characterization of vitamin K epoxide reductase (VKORC1). VKORC1 is the key enzyme of the vitamin K cycle and the molecular target of coumarins, which represent the most commonly prescribed drugs for therapy and prevention of thromboembolic conditions. However, coumarins are known to have a narrow therapeutic window and a considerable risk of bleeding complications caused by a broad variation of intra- and inter-individual drug requirement. Now, 3 years after its identification, VKORC1 has greatly improved our understanding of the vitamin K cycle and has led to the translation of basic research into clinical practise in at least three directions: (i) Mutations within VKORC1 have been shown to cause a coumarin-resistant phenotype and a single SNP (rs9923231) within the VKORC1 promoter region has been identified as the major pharmacodynamic determinant of coumarin dose. Together with the previously described CYP2C9 variants and other dose-influencing factors, such as age, gender and weight, individualized dosing algorithms have become available. (ii) Preliminary studies indicate that concomitant application of low-dose vitamin K (80-100 microg day(-1)) and warfarin significantly improves INR stability and time of INR within the therapeutic range. (iii) Co-expression studies of FIX and FX with VKORC1 have shown that VKOR activity is the rate-limiting step in the synthesis of biologically active vitamin K-dependent factors. Thus, co-expression of VKORC1 leads to a more efficient production of recombinant vitamin K-dependent coagulation factors such as FIX and FVII. This could improve production of recombinant factor concentrates in the future.

Compound Heterozygosity in the Novel Mutations W157R and T591K in the γ-Glutamyl Carboxylase Gene Causes Hereditary Combined Vitamin K-Dependent Coagulation Factor Deficiency in a Tunisian Family.

Combined deficiency in vitamin K-dependent (VKD) coagulation factors is an autosomal recessive bleeding disorder associated with defects in either the VKD carboxylase which converts Glus to Glas in VKD proteins to render them active or the vitamin K epoxide reductase (VKORC1) which supplies the reduced vitamin K cofactor required for carboxylation. Such defects are rare, and we now report the fourth case of deficiency caused by mutations in the carboxylase gene. The mutations were identified in a two year old Tunisian girl who exhibited impaired function in several VKD procoagulant and anticoagulant factors that was not restored by vitamin K administration. Sequence analysis of the propositus did not identify any mutations in the VKORC1 gene but, remarkably, revealed three heterozygous mutations in the carboxylase gene, D31N, W157R and T591K within exons 2, 4 and 13, respectively. None of these mutations have previously been reported. Family analysis showed that D31N and T591K were coallelic and transmitted by the mother while W157R was transmitted by the father. The mutations were not found in the genomes of 200 normal subjects, ruling out frequent polymorphisms. Mutational analysis indicated wild type activity for the D31N carboxylase. In contrast, the W157R and T591K enzymes had activities that were, respectively, 7% and 0% that of wild type carboxylase, and their compound heterozygosity can therefore account for defective carboxylation. Residues 157 and 591 are both highly evolutionarily conserved, and residue 157 lies within a region previously suggested to be important for carboxylase binding to VKD Glus or propeptide. However, the hydrophobic nature of this region and inability of vitamin K administration to restore VKD protein function alternatively suggests that residue 157 may be important for vitamin K binding.