Stuart clotting defect. I. Segregation of an hereditary hemorrhagic state from the heterogeneous group heretofore called stable factor (SPCA, proconvertin, factor VII) deficiency

Development and characterization of Factor Xa-responsive materials for applications in cell culture and biologics delivery

Stimuli-responsive biomaterials may be used to better control the release of bioactive molecules or cells for applications involving drug delivery and controlled cell release. In this study, we developed a Factor Xa (FXa)-responsive biomaterial capable of controlled release of pharmaceutical agents and cells from in vitro culture. FXa-cleavable substrates were formed as hydrogels that degraded in response to FXa enzyme over several hours. Hydrogels were shown to release both heparin and a model protein in response to FXa. Additionally, RGD-functionalized FXa-degradable hydrogels were used to culture mesenchymal stromal cells (MSCs), enabling FXa-mediated cell dissociation from hydrogels in a manner that preserved multicellular structures. Harvesting MSCs using FXa-mediated dissociation did not influence their differentiation capacity or indoleamine 2,3-dioxygenase (IDO) activity (a measure of immunomodulatory capacity). In all, this FXa-degradable hydrogel is a novel responsive biomaterial system that may be used for on-demand drug delivery, as well as for improving processes for in vitro culture of therapeutic cells.

Congenital Factor X-Riyadh (Stuart-Prower) Deficiency With Isolated Prothrombin Time Prolongation: A Case Report

Factor X (FX) deficiency is an extremely rare autosomal recessive inherited coagulation defect. We report a case of congenital Factor X-Riyadh deficiency discovered during a routine workup before a dental procedure. During routine work-up for dental surgery, prothrombin time (PT) and the international normalized ratio (INR) were prolonged. The prothrombin time (PT) was found to be 78.4 (normal 11-14 seconds) with an international normalized ratio (INR) of 7.83; the activated partial thromboplastin time (APTT) was 30.7 (normal 25-42 seconds). Specific coagulation factor assays confirmed an FX deficiency (<10 % of normal activity) and a mild factor VII deficiency 37% (normal 48%-124%). Molecular genetic analysis of the whole exome sequence (WES) confirmed the diagnosis of FX deficiency (homozygous pathogenic variant c. 271G>A p {Glu91Lys} chr13:113793685). The patient is currently on regular follow-up and is advised to take oral antifibrinolytic medications for any superficial or mucosal bleeding.

[Congenital factor X deficiency: a retrospective analysis of 11 cases]

Objective: To analyze the clinical characteristics, laboratory examination, diagnosis, treatment, and outcome of hereditary factor Ⅹ (FⅩ) deficiency. Methods: Clinical data of 11 patients with congenital FⅩ deficiency were retrospectively analyzed from July 2009 to February 2021. Results: There were 3 males and 8 females. Median age was 39 (5-55) years. The media duration of follow-up was 81.67 (1.87-142.73) months. Of the 11 patients, 10 had bleeding symptoms, 7 had ecchymosis or hemorrhage after skin bump, 7 had nosebleed, 6 had gingival hemorrhage, and 1 had muscle hematoma. Among the female patients, 6 had menorrhagia and 1 experienced bleeding after vaginal delivery. Family history of FⅩ deficiency was found in one case. Eight patients had a history of surgery, and four had postoperative bleeding. Laboratory findings were characterized by significantly prolonged activated partial thromboplastin time, prothrombin time, and decreased FⅩ activity (FⅩ∶C) . Four cases underwent gene mutation analysis and five new mutations were found. Four cases were treated with prothrombin complex concentrates (PCC) and seven cases with fresh frozen plasma (FFP) . One female patient had significantly reduced menstrual volume after PCC prophylactic therapy. One patient received FFP for prophylactic infusion with no bleeding during and after the operation. Conclusion: Most patients with congenital FⅩ deficiency had bleeding symptoms and there was no significant correlation between severity of bleeding symptoms and FⅩ∶C. Prophylaxis should be applied in patients with severe bleeding tendencies. Gene mutation test is significant for screening, diagnosis, and prognosis prediction of congenital FX deficiency.

Laboratory Methods in the Assessment of Hereditary Hemostatic Disorders

In patients presenting with a suspect hereditary bleeding disorder a detailed bleeding history is first obtained. Testing proceeds in a tiered manner with platelet count, platelet morphology, platelet histogram, PFA-100, fibrinogen, prothrombin time, and activated partial thromboplastin time. More detailed testing includes von Willebrand factor, individual clotting factor assays, and platelet function testing. Next, testing for a dysfibrinogenemia, FXIII, or a fibrinolytic defect is considered. Hemostatic abnormality is not demonstrated in a fraction of patients. An approach to management in these patients, such as desmopressin or antifibrinolytic therapy, may be required and empiric use of blood component therapy is discouraged.

Rare Coagulation Factor Deficiencies (Factors VII, X, V, and II)

Although rare clotting factor deficiencies primarily referred to as rare bleeding disorders (RBD), including factors II, V, VII, and X, make up ∼5% of all inherited bleeding disorders worldwide, each of these clotting factors play a critical role in the coagulation cascade. Incomplete bleeding evaluation or misinterpretation of laboratory studies can result in delayed diagnoses that ultimately affect patient outcomes. Bleeding manifestations can range from mild to severe, but the most common are mucocutaneous bleeding. The ideal treatment in RBD is dedicated single-factor concentrates that can be used for acute bleeding events, surgical management, and prophylaxis.

Blood coagulation factor X: molecular biology, inherited disease, and engineered therapeutics

Blood coagulation factor X/Xa sits at a pivotal point in the coagulation cascade and has a role in each of the three major pathways (intrinsic, extrinsic and the common pathway). Due to this central position, it is an attractive therapeutic target to either enhance or dampen thrombin generation. In this brief review, I will summarize key developments in the molecular understanding of this critical clotting factor and discuss the molecular basis of FX deficiency, highlight difficulties in expressing recombinant factor X, and detail two factor X variants evaluated clinically.

Structure and function of factor X: properties, activation, and activity in prothrombinase. A retrospective in a historical context

The evolution of our understanding of the formation of thrombin from the postulated thrombokinase of Morawitz to activated Factor X and prothrombinase occurred during a period of nearly 100 years. During this time structure-function relationships have emerged and the roles of phospholipid surfaces, the accessory factor, Factor V and its activated form have been clarified. This paper summarizes this story with particular acknowledgement of the seminal contributions of Haskell Milstone.

The Effect of Polyphenols on Hypercholesterolemia through Inhibiting the Transport and Expression of Niemann-Pick C1-Like 1

The Niemann-Pick C1-like 1 (NPC1L1) protein is a cholesterol transporter that is expressed in the small intestine. This report describes the discovery of NPC1L1, its transport properties, and the inhibitory effects of polyphenols on NPC1L1. NPC1L1 was identified in 2004 while searching for ezetimibe molecular targets. Excessive synthesis of cholesterol results in hyperlipidemia, which increases the amount of bile cholesterol excreted into the duodenum. The inhibition of NPC1L1 decreases blood cholesterol because food and bile cholesterol are also absorbed from NPC1L1 in the intestine. Some polyphenols, particularly luteolin, have been reported as NPC1L1-mediated anti-dyslipidemia constituents. Luteolin affects NPC1L1 through two mechanisms. Luteolin directly inhibits NPC1L1 by binding to it, which occurs in a short timeframe similar to that for ezetimibe. The other mechanism is the inhibition of NPC1L1 expression. Luteolin reduced the binding of Sterol-regulatory element-binding protein 2 (SREBP2) in the promoter region of the NPC1L1 gene and decreased mRNA levels of SREBP2 and hepatocyte nuclear factor 4α. These data suggest that luteolin decreases the expression of NPC1L1 through regulation of transcription factors. This review also explores the effect of other polyphenols on NPC1L1 and hypercholesterolemia.

Factor X Deficiency Due to a Compound Heterozygosis Between a New Mutation (Gla72Asp) in Exon 2 and an Already Known one (Gly154Arg) in Exon 5: Factor X Mar Del Plata1)

BACKGROUND

Investigation of rare bleeding disorders in Latin-America.

OBJECTIVES

The report of a new case of FX deficiency due to a compound heterozygosis.

METHODS

Accepted clotting procedures were used. Sequencing of DNA was carried out by means of Applied Biosystems Instruments.

RESULTS

A compound heterozygote due to the association of a new mutation (Gla72Asp) with an already known mutation (Gly154Arg) of the FX gene is reported. The proposita is a 38 year old female who had a moderate bleeding tendency (menorrhagia, epistaxis, easy bruising). The proposita has never received substitution therapy but in the occasion of a uterine biopsy. The mother was asymptomatic but was a heterozygote for the new mutation. The father was asymptomatic but had deserted the family and could not be investigated. After this abandonment the mother of the proposita re-married with an asymptomatic man and she gave birth to a son who was asymptomatic but was also heterozygous for the new mutation (Gla72Asp). As a consequence it has to be assumed that the first husband of the mother of the proposita was heterozygous for the known mutation (Gly154Arg).

CONCLUSIONS

This is the third case of a new mutation in the FX gene reported, during the past few years, in Argentina.

Factor X Friuli Coagulation Disorder: Almost 50 Years Later

The story of factor X (FX) Friuli. Factor X Friuli was discovered in 1969 to 1970. However, the story of that disease was an international event since patients with this defect were studied in France and in Italy, and different diagnoses were reached-FVII; FX; combined prothrombin complex; and combined FII, FVII, and FX deficiencies. The diagnostic difficulties were due to the peculiar clotting pattern presented by these patients, namely, prolonged partial thromboplastin time, prolonged prothrombin time but normal Russell viper venom clotting time. Only suitable anti-FX antisera clarified the pattern. Altogether 12 homozygotes and 102 heterozygotes have been followed during 4 decades. Six homozygotes died, 2 of them due to HIV infection and 1 due to hepatitis B liver cirrhosis. The other 3 died of nontransfusion-related morbidity. Bleeding tendency has been moderate in agreement with the extrinsic or intrinsic system assay results-FX level of 4% to 5% is considered normal. Heterozygotes may present occasional bleeding manifestations usually during surgery or delivery. Molecular analysis have shown that the mutation responsible for the defect is a Pro343Ser substitution in exon 8. Chimeric FX Friuli mice have been useful in studying the effect of FX levels on embryonic or natal mortality of these animals. No new homozygote but several heterozygotes have been recently seen. The study of FX Friuli has revolutionized the diagnostic approach to FX deficiencies. The FX should be assayed by all assay systems. The FX Friuli has never been described in any other country, and all patients studied come from the Friuli Meduna River Valley.

Transporters for the Intestinal Absorption of Cholesterol, Vitamin E, and Vitamin K

Humans cannot synthesize fat-soluble vitamins such as vitamin E and vitamin K. For this reason, they must be obtained from the diet via intestinal absorption. As the deficiency or excess of these vitamins has been reported to cause several types of diseases and disorders in humans, the intestinal absorption of these nutrients must be properly regulated to ensure good health. However, the mechanism of their intestinal absorption remains poorly understood. Recent studies on cholesterol using genome-edited mice, genome-wide association approaches, gene mutation analyses, and the development of cholesterol absorption inhibitors have revealed that several membrane proteins play crucial roles in the intestinal absorption of cholesterol. Surprisingly, detailed analyses of these cholesterol transporters have revealed that they can also transport vitamin E and vitamin K, providing clues to uncover the molecular mechanisms underlying the intestinal absorption of these fat-soluble vitamins. In this review, we focus on the membrane proteins (Niemann-Pick C1 like 1, scavenger receptor class B type I, cluster of differentiation 36, and ATP-binding cassette transporter A1) that are (potentially) involved in the intestinal absorption of cholesterol, vitamin E, and vitamin K and discuss their physiological and pharmacological importance. We also discuss the related uncertainties that need to be explored in future studies.

Theories of Blood Coagulation

Although the concept of the coagulation cascade represented a significant advance in the understanding of coagulation and served for many years as a useful model, more recent clinical and experimental observations demonstrate that the cascade/waterfall hypothesis does not fully and completely reflect the events of hemostasis in vivo. The goal of this article is to review the evolution of the theories of coagulation and their proposed models to serve as a tool when reviewing the research and practice literature that was published in the context of these different theories over time.

Neonatal onset of congenital factor X deficiency: a description of two novel mutations with 6-year follow-up

Factor X congenital deficiency is a rare coagulation disorder involving autosomal recessive transmission. The clinical situation depends on the extent of the defect and may appear at any age. We report a case of a term newborn who developed a life-threatening bleeding event on the first day of life because of a Factor X (FX) deficiency. Fresh frozen plasma and FX intravenous replacement therapy were administered with normalization of the coagulation test. Genetic analysis identified two novel mutations (c.517G>T; c.139delG) in heterozygous state in the proband that were confirmed in the parents. We also describe a 6-year follow-up during which the patient has been administered prophylactic replacement therapy. The description of these two novel mutations and the long clinical follow-up help to increase our knowledge of the genotype-phenotype correlation of congenital FX deficiency, and provide information on better ways of managing the replacement therapy in patients with similar mutations.

A family with factor X deficiency from Argentina: a compound heterozygosis because of the combination of a new mutation (Gln138Arg) with an already known one (Glu350Lys)

The objective was to investigate a family from Argentina. The proposita was a 51-year-old woman who had a moderate bleeding tendency. Some of her children showed a mild bleeding tendency. Her mother and the husband were asymptomatic. Clotting, immunological and molecular biology techniques were used. Partial thromboplastin, prothrombin, Russell Viper venom-clotting times were moderately prolonged in the proposita, whereas they were slightly prolonged in the children and in her mother. Factor X (FX) activity was about 2-3% of normal in all assay systems. FX antigen was less than 5%. Other clotting factors and platelet were normal. Genetic analysis showed a compound heterozygosis: combination of a 'new' mutation (Gln138Arg) with an already known mutation (Glu350Lys). The children had intermediate FX levels (35-63% of normal) and were carriers of one of the two mutations present in the proposita. This is the first observation of a FX deficiency in Argentina.

NPC1L1 is a key regulator of intestinal vitamin K absorption and a modulator of warfarin therapy

Vitamin K (VK) is a micronutrient that facilitates blood coagulation. VK antagonists, such as warfarin, are used in the clinic to prevent thromboembolism. Because VK is not synthesized in the body, its intestinal absorption is crucial for maintaining whole-body VK levels. However, the molecular mechanism of this absorption is unclear. We demonstrate that Niemann-Pick C1-like 1 (NPC1L1) protein, a cholesterol transporter, plays a central role in intestinal VK uptake and modulates the anticoagulant effect of warfarin. In vitro studies using NPC1L1-overexpressing intestinal cells and in vivo studies with Npc1l1-knockout mice revealed that intestinal VK absorption is NPC1L1-dependent and inhibited by ezetimibe, an NPC1L1-selective inhibitor clinically used for dyslipidemia. In addition, in vivo pharmacological studies demonstrated that the coadministration of ezetimibe and warfarin caused a reduction in hepatic VK levels and enhanced the pharmacological effect of warfarin. Adverse events caused by the coadministration of ezetimibe and warfarin were rescued by oral VK supplementation, suggesting that the drug-drug interaction effects observed were the consequence of ezetimibe-mediated VK malabsorption. This mechanism was supported by a retrospective evaluation of clinical data showing that, in more than 85% of warfarin-treated patients, the anticoagulant activity was enhanced by cotreatment with ezetimibe. Our findings provide insight into the molecular mechanism of VK absorption. This new drug-drug interaction mechanism between ezetimibe (a cholesterol transport inhibitor) and warfarin (a VK antagonist and anticoagulant) could inform clinical care of patients on these medications, such as by altering the kinetics of essential, fat-soluble vitamins.

Surgical treatment for a paraplegic patient induced by congenital factor X deficiency

Congenital factor X (FX) deficiency is a rare disease which usually leads to coagulation disorders. We reported a case of paraplegic patient induced by traumatic spinal epidural hematoma which was associated with congenital FX deficiency. The treatments of this patient included elevating FX activity (FX: C) by adding fresh-frozen plasma (FFP) or prothrombin complex concentration (PCC) to improve his coagulation function, and doing operation to remove his spinal hematoma. Symptoms started to resolve after operation. Besides, we found one of his elder brother had the same disease as the patient himself via family follow-up. They can survive because their FX: C are relatively high enough to keep them away from fatal bleeding.

Successful treatment of a noninhibitory antibody-mediated acquired factor X deficiency in a patient with marginal-zone lymphoma

Prolonged clotting times were observed in a patient with spontaneous hemorrhage. Analysis showed severe factor X deficiency due to clearance by a noninhibitory antibody. Lymphadenopathy identified on imaging led to diagnosis of marginal B-cell lymphoma. Treatment of lymphoma with rituximab and chlorambucil resulted in complete disappearance of the bleeding disorder.

Epidemiologic and clinical data linking factors XI and XII to thrombosis

Currently available evidence supports the contention that elevated levels of factor XI (fXI) are associated with a greater risk of venous thromboembolism and ischemic stroke, but, less convincingly, with myocardial infarction. Conversely, reduced plasma levels of fXI seem to offer some protection from venous thromboembolism and stroke, but not myocardial infarction. Factor XI-deficient patients are at risk for certain types of bleeding, particularly posttraumatic hemorrhage on mucosal surfaces where there is a high endogenous fibrinolytic activity. In contrast, the situation with fXII in human thrombosis remains enigmatic. Deficiency of fXII is clearly not associated with any bleeding risk, but neither does it seem to be protective against thrombosis. The longstanding debate as to whether partial fXII deficiency represents a risk factor for thrombosis remains unresolved, with seemingly conflicting results depending on study design, type of assay used, and analyte evaluated. The possibility that elevated fXII levels represent a risk factor for thrombosis is not borne out in the literature.

Coagulation Factor Xa

The third edition of the Handbook of Proteolytic Enzymes aims to be a comprehensive reference work for the enzymes that cleave proteins and peptides, and contains over 800 chapters. Each chapter is organized into sections describing the name and history, activity and specificity, structural chemistry, preparation, biological aspects, and distinguishing features for a specific peptidase. The subject of Chapter 642 is Coagulation Factor Xa.

Keywords

Coagulation factor, prothrombin, thrombin, proconvertin, Stuart’s factor, Prower’s factor.

Historical perspective and future direction of coagulation research

Over the past 100 years, remarkable advances have been made in our understanding of the mechanisms of blood coagulation. Starting with the early clinical observations of rare patients with hereditary clotting disorders, our knowledge has increased in keeping pace with the introduction of new technologies: from simple laboratory tests to protein chemistry, to DNA technology, and to gene targeting technology. Advances in basic research have been successfully translated into improved methods for the diagnosis of bleeding disorders as well as thrombosis, and the development of recombinant clotting factors for replacement therapy in patients with haemophilia. New promising anticoagulants have also been developed for the treatment of thrombotic disorders. Based on the unique nature of blood coagulation research the close interactions and collaborations between basic scientists and clinicians have played a major role in these developments. It is anticipated that blood coagulation research will continue to play a leading role in promoting better care of the patients with bleeding disorders or thromboembolism.

Unexplained Discrepancies in the Activity—Antigen Ratio in Congenital FX Deficiencies With Defects in the Catalytic Domain

Studies on molecular biology have considerably enhanced our understanding of congenital coagulation disorders but have failed so far to supply tools for an adequate classification of defects. In fact, mutations in the same domain may give rise to different phenotypes. Conversely, mutations in different domains, controlled by different exons, may cause similar patterns. The 37 kindreds with congenital factor X (FX) deficiency, known to have a defect in the catalytic domain, have been evaluated in an attempt to investigate the genotype—phenotype relation. Discrepant results were obtained because about half kindreds showed a type I pattern, namely a concomitant decrease in FX activity and antigen. The other half showed a type II pattern, namely a decrease in FX activity with a normal or near normal FX antigen. In a few instances, the allocation of the kindred either to type I or to type II defect could not be reached, due to the lack of information about the antigen.

The comparison of the kindreds in which the same mutation has been discovered by different investigations is not always possible also for lack of information.

The study analyzes the need to have a multipronged approach to the study of congenital FX deficiency. The indication of a mutation in a given domain does not provide clear information about the phenotype.

Congenital factor X deficiencies with a defect only or predominantly in the extrinsic or in the intrinsic system: a critical evaluation

Congenital Factor X deficiency is commonly classified as type I, in which there is a concomitant decrease of activity and antigen (CRM negative), and in type II, in which activity is low but antigen is normal or near normal (CRM positive). During the past decades it was shown that type II was by itself very heterogeneous. It was shown in fact that some forms showed a defect in all three assay systems (extrinsic, intrinsic, and RVV dependent), whereas others showed a defect only in two of the three systems. Molecular biology analysis, whenever available, has failed so far to supply clear explanations for these discrepancies. The purpose of the present article was an attempt to correlate the clotting activities seen in these two defects with other clotting, chromogenic, immunological assays, and molecular biology results. There are in the literature 10 families that show a predominant defect in the extrinsic system, and four families that show a predominant defect in the intrinsic system. All patients showed a normal, near normal, or reduced level of antigen that is always definitively higher than the clotting counterpart. Molecular biology studies revealed mutations in different exons, namely 2, 4, 5, 6, and 8. These mutations in different exons do not allow any clear genotype-phenotype conclusions, but indicate that mutations in different exons may give rise to the same phenotype. The study underlines the importance of a multipronged evaluation of all cases with Factor X deficiency. In fact only by this approach can an acceptable classification of the defect be reached.

Dietary fatty acids and the haemostatic system

Studies of the effects of dietary fatty acids on the haemostatic system, and their potential relevance for the thrombotic component of coronary heart disease (CHD), have a pedigree as long as those linking dietary fat, plasma lipoprotein metabolism and atheroma. Achievements have not been as impressive, however, partly owing to the relatively slow evolution of our understanding of the complicated physiology, biochemistry and pathology of haemostasis and fibrinolysis, which remains incomplete. Progress was also retarded up to 1980 by a general reluctance to acknowledge the pathogenic importance of thrombosis for myocardial infarction. Interest in dietary fat and the haemostatic mechanism re-emerged with reports of associations of haemostatic variables with plasma triacylglycerol levels and risk of CHD. This review summarises the history, focuses on evidence for dietary C18-unsaturated fatty acids as important determinants of factor VII (FVII) activation and plasminogen activator inhibitor type 1 (PAI-1) levels, and discusses possible underlying mechanisms involving ATP binding cassette (ABC) transporters and peroxisome proliferator-activated receptors. The potential relevance of these effects for CHD is discussed. In the presence of unstable atheromatous plaques, increased levels of activated FVII and PAI-1 induced by diets rich in mixtures of saturated and unsaturated fats may raise the risk of occlusive thrombosis in the event of plaque rupture.

Factor X deficiency

Factor X is one of the vitamin K-dependent serine proteases. It plays a crucial role in the coagulation cascade, as the first enzyme in the common pathway of thrombus formation. The gene for factor X maps to the long arm of chromosome 13, approximately 2.8 kb downstream of the factor VII gene. The gene consists of eight exons, each of which encodes a specific functional domain within the protein. Both the gene structure and the amino acid sequence show homology to other vitamin K-dependent clotting factors, suggesting their origin in a common ancestral protein. Factor X deficiency is one of the rarest of the inherited coagulation disorders. Inheritance is in an autosomal recessive manner. The clinical phenotype is of a variable bleeding tendency. Homozygous factor X deficiency has an incidence of 1:1,000,000 in the general population. Heterozygotes are often clinically asymptomatic. Acquired factor X deficiency is rare, but when it occurs it is usually in association with amyloidosis. Treatment of factor X deficiency involves replacement of the protein with either fresh frozen plasma or prothrombin complex concentrates, although the latter should be used with caution as infusion may be associated with an increased risk of thrombosis.

Structure and dynamics of zymogen human blood coagulation factor X

The solution structure and dynamics of the human coagulation factor X (FX) have been investigated to understand the key structural elements in the zymogenic form that participates in the activation process. The model was constructed based on the 2.3-A-resolution x-ray crystallographic structure of active-site inhibited human FXa (PDB:1XKA). The missing gamma-carboxyglutamic acid (GLA) and part of epidermal growth factor 1 (EGF1) domains of the light chain were modeled based on the template of GLA-EGF1 domains of the tissue factor (TF)-bound FVIIa structure (PDB:1DAN). The activation peptide and other missing segments of FX were introduced using homology modeling. The full calcium-bound model of FX was subjected to 6.2 ns of molecular dynamics simulation in aqueous medium using the AMBER6.0 package. We observed significant reorientation of the serine-protease (SP) domain upon activation leading to a compact multi-domain structure. The solution structure of zymogen appears to be in a well-extended conformation with the distance between the calcium ions in the GLA domain and the catalytic residues estimated to be approximately 95 A in contrast to approximately 83 A in the activated form. The latter is in close agreement with fluorescence studies on FXa. The S1-specificity residues near the catalytic triad show significant differences between the zymogen and activated structures.

A new factor X defect (factor X Padua 3): a compound heterozygous between true deficiency (Gly(380)-->Arg) and an abnormality (Ser(334)-->Pro)

We report a novel mutation in Factor X (FX) gene which results in a phenotype without any bleeding tendency. The proband has been found to be a compound heterozygote between a novel FX true deficiency (Gly(380)-->Arg) and a previously reported dysfunctional mutation Ser(334)-->Pro (FX Marsiglia). Prothrombin time (PT) and partial thromboplastin time (PTT) were moderately prolonged and were fully corrected by the addition of normal serum. Her FX activity level varied between 8% and 19% of normal according to the method used whereas the FX antigen level was 40% of the normal control value. All the exons and intron/exon junctions of the FX gene were studied using a combined approach of polymerase chain reaction and conformation sensitive gel electrophoresis. A transversion G to A in exon 8 resulting in the replacement of Gly380 by Arg was found in the proband, in the father and in a proband's brother, whereas heterozygous FX Marsiglia was present in the proband's mother and her sister. Gly380 is strictly linked to Ser379, a component of the catalytic triad. The substitution of Gly for Arg causes the introduction of a large charged amino acid which could affect the catalytic function of FX leading to secretion problem, accounting for the cross-reactive material (CRM) negative phenotype.

A dysfunctional factor X (factor X San Giovanni Rotondo) present at homozygous and double heterozygous level: identification of a novel microdeletion (delC556) and missense mutation (Lys(408)-->Asn) in the factor X gene. A study of an Italian family

Low levels of factor X (F.X) were detected in a 4-year-old boy who experienced acute lymphoblastic leukemia and bleeding manifestations. Laboratory data suggested the presence of a dysfunctional F.X molecule. Two novel F.X gene mutations were identified in the proband that was double heterozygous for both: a microdeletion (delC556) in exon VI resulting in a frameshift leading to a termination codon at position 226. This deletion was found in six family members with reduced F.X antigen and activity levels. A second mutation characterised by a G(1344)-->C transversion in exon VIII was detected in the proband resulting in a Lys(408)-->Asn substitution. This latter mutation was present in several asymptomatic family members from the paternal and the maternal side. The proband's sister was homozygous for the Lys(408)-->Asn substitution and exhibited low F.X activity with a normal antigen level. The naturally occurring F.X Lys(408)-->Asn (F.X(K408N)) variant was isolated from plasma of either homozygous or double heterozygous individuals. NH(2)-terminal sequencing of the heavy chain of F.X(K408N) failed to show any sequence abnormality in patients who were also carriers of the delC556, suggesting that this latter lesion accounted for the lack of F.X synthesis. Purified F.X Lys(408)-->Asn had an identical behaviour to normal F.X as judged by SDS-PAGE and immunoblotting. Clotting assay using purified F.X(K408N) and F.X-deficient plasma resulted in a laboratory phenotype similar to that observed in a homozygous subject for F.X Lys(408)-->Asn substitution. This is the first characterisation of a naturally occurring F.X variant with a mutation at the COOH-terminal end of the molecule.