Clinical, Laboratory Aspects and Management of Factor X Deficiency.

Coagulation factor X (FX), originally named Stuart-Prower factor, plays a pivotal role in the coagulation cascade, activating thrombin to promote platelet plug formation and prevent excess blood loss. Genetic variants in F10 may lead to FX deficiency and to impaired coagulation. FX variants are phenotypically classified as being type I, with the concomitant reduction of FX coagulant activity and FX antigen levels or type II, corresponding to a reduction in activity with normal antigen plasma levels. Patients affected with FX deficiency tend to be one of the most seriously affected among those with rare bleeding disorders. They show a variable bleeding tendency strongly associated with FX coagulant activity levels in plasma and may present, in the severe form of the deficiency, life-threatening symptoms such as gastrointestinal and umbilical stump bleeding and intracranial hemorrhages or central nervous system bleeding. Treatment of FX deficiency was originally based on the replacement of the missing factor using fresh frozen plasma, cryoprecipitate and prothrombin complex concentrates; however, a plasma-derived concentrate, shown to be safe and effective in clinical trials, is now available. In addition, novel nonreplacement therapy such as small interference RNA, gene therapy, drug repurposing, and gene editing may also represent novel therapeutic approaches for FX deficiency, but further, much focused studies are needed before considering this emerging therapy in such patients.

Menegatti M ，Peyvandi F 《-》

Analysis of 180 Genetic Variants in a New Interactive FX Variant Database Reveals Novel Insights into FX Deficiency.

Coagulation factor X (FX), often termed as Stuart-Prower factor, is a plasma glycoprotein composed of the γ-carboxyglutamic acid (GLA) domain, two epidermal growth factor domains (EGF-1 and EGF-2), and the serine protease (SP) domain. FX plays a pivotal role in the coagulation cascade, activating thrombin to promote platelet plug formation and prevent excess blood loss. Genetic variants in FX disrupt coagulation and lead to FX or Stuart-Prower factor deficiency. To better understand the relationship between FX deficiency and disease severity, an interactive FX variant database has been set up at https://www.factorx-db.org , based on earlier web sites for the factor-XI and -IX coagulation proteins. To date (April 2021), we report 427 case reports on FX deficiency corresponding to 180 distinct F10 genetic variants. Of these, 149 are point variants (of which 128 are missense), 22 are deletions, 3 are insertions, and 6 are polymorphisms. FX variants are phenotypically classified as being type I or II. Type-I variants involve the simultaneous reduction of FX coagulant activity (FX:C) and FX antigen levels (FX:Ag), whereas type-II variants involve a reduction in FX:C with normal FX:Ag plasma levels. Both types of variants were distributed throughout the FXa protein structure. Analyses based on residue surface accessibilities showed the most damaging variants to occur at residues with low accessibilities. The interactive FX web database provides a novel easy-to-use resource for clinicians and scientists to improve the understanding of FX deficiency. Guidelines are provided for clinicians who wish to use the database for diagnostic purposes.

Harris VA ，Lin W ，Perkins SJ 《-》

Occurrence and management of severe bleeding episodes in patients with hereditary factor X deficiency.

Vitamin K-dependent factor X (FX) plays an important role in thrombin formation, and a deficiency in FX can cause impaired coagulation, the severity of which is usually correlated with the degree of deficiency. Due to the critical role that FX plays in the coagulation cascade, FX deficiency is associated with a higher risk of bleeding than deficiencies in other coagulation factors. Patients with the hereditary autosomal-recessive homozygous form of FX deficiency, which occurs in approximately 1:1,000,000 individuals worldwide, are often diagnosed when they present with spontaneous life-threatening haemorrhage (most often intracranial haemorrhage) during the first month of life. In addition to central nervous system bleeds, other severe bleeding types experienced by such patients may include umbilical cord bleeding, gastrointestinal or pulmonary haemorrhage, intramuscular haematomas and/or haemarthrosis. Delayed treatment or inadequate replacement of FX may result in developmental delays, musculoskeletal disabilities or death. The high risk of recurrent severe bleeding necessitates prophylactic replacement therapy for many individuals with severe FX deficiency. Available products for replacement therapy include plasma-derived FX concentrate and prothrombin complex concentrates. Fresh-frozen plasma may be used when concentrates are not available but is a less efficient means of FX replacement. This article reviews the literature on severe bleeding in individuals with hereditary FX deficiency and discusses current treatment options.

Tarantino MD 《-》

Factor X deficiency.

Menegatti M ，Peyvandi F 《-》

Blood product support for delivery in severe factor X deficiency: the use of thrombin generation to guide therapy.

van Veen JJ ，Hampton KK ，Maclean R ，Fairlie F ，Makris M ... -  《Blood Transfusion》