Factor X Deficiency with Heterozygous Mutations of Novel p.G435S and Known p.G244R in a Patient Presenting with Severe Umbilical Hemorrhage

(1R,3S)-THCCA-Asn: To show the discovery of selective inhibitor of thrombin by successfully combining virtual screening and biological assay

Thrombin is the most potent platelet aggregator. To discover the selective inhibitor of thrombin that is important to curing platelet aggregation-related diseases, docking experiments were performed to dock (1R,3S)-2,3,4,9-tetrahydro-β-carboline-3- carboxylic acid, [(1R,3S)-THCCA], and (1S,3S)-2,3,4,9-tetrahydro-β-carboline-3- carboxylic acid, [(1S,3S)-THCCA], into the p pocket of bovine thrombin. The ideal match supported that (1R,3S)-THCCA could be used as a potential lead compound. In this case 20 natural amino acids were theoretically introduced into the 3-carboxyl of (1R,3S)-THCCA and 20 derivatives, (1R,3S)-THCCA-amino acids, were docked into p pocket of bovine thrombin to perform virtual screening. The screening revealed that comparing to (1R,3S)-THCCA itself the DockScores of 16 derivatives were higher, and (1R,3S)-THCCA-Asn (4j) got the highest DockScore. Thus, 16 derivatives were synthesized for experimental study. The in vitro anti-platelet aggregation assay showed that at 100 μM of concentration the 16 derivatives failed to inhibit the platelet aggregation induced by both adenosine diphosphate and arachidonic acid. On the other hand, however, the IC₅₀ value of the 16 derivatives inhibiting the platelet aggregation induced by platelet activating factor and thrombin ranged from 9.44 μM to 194.64 μM and from 0.07 μM to 9.56 μM, respectively. The in vitro anti-platelet aggregation assay suggested that the 16 derivatives selectively inhibited the platelet aggregation induced by thrombin. In particular, the IC₅₀ of (1R,3S)-THCCA-Asn (4j) had the lowest value. On rat model at 1 nmol/kg of dosage the 16 derivatives effectively prevented thrombus formation. It is worth pointing out that even at 0.01 nmol/kg of dosage, 4j still effectively prevented thrombus formation. 4j hardly has effects on the proliferation of mammalian cells and rat tail bleeding time. In conclusion, the combination of virtual screening and biological assays successfully lead to the discovery of 4j as a promising candidate of selective inhibitor of thrombin.

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.

Rare bleeding disorders and advances in gene therapy

: Rare bleeding disorders usually begin in childhood and manifest as varying degrees of bleeding, which can be life-threatening in severe cases. With the development of gene editing technology, it is expected that hereditary coagulation factor disorders will someday be fundamentally cured by gene therapy. On account of their rarity, comprehension of these diseases is essential for the application of new treatment strategies. We have compiled the features of some newly discovered mutations of prothrombin, factor VII, and factor X in recent years. In addition, this review introduces the advances and obstacles in gene therapy.

Genetic analysis of a compound heterozygous patient with congenital factor X deficiency and regular replacement therapy with a prothrombin complex concentrate

Congenital factor X (FX) deficiency is a rare bleeding disorder with an incidence of one in one million. The proband, a 2-year-old girl, exhibited easy bruising and a history of umbilical cord bleeding at birth. Prothrombin time (> 40 s) and activated partial thromboplastin time (65.0 s) were prolonged. Marked declines in FX activity (< 1%) and FX antigen levels (5%) were also observed. Genetic analysis of the proband identified two types of single-base substitutions, c.353G>A (p.Gly118Asp) and c.1303G>A (p.Gly435Ser), indicating compound heterozygous congenital FX deficiency. Genetic analysis of family members revealed that her father and older sister (5-year-old) were also heterozygous for p.Gly118Asp, and that her mother was heterozygous for p.Gly435Ser. To improve the bleeding tendency, the proband received regular replacement of 500 units of PPSB-HT, a prothrombin complex concentrate (PCC). Following continued regular replacement of 500 units of PPSB-HT once per week, the proband has exhibited no bleeding tendencies and no new bruises have been observed. There are no previous report of the use of PPSB-HT for regular FX replacement. Regular replacement therapy with PPSB-HT may be an effective method for preventative control of bleeding tendencies in FX deficiency.