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Factor VII central. A novel mutation in the catalytic domain that reduces tissue factor binding, impairs activation by factor Xa, and abolishes amidolytic and coagulant activity.

Factor VII is a vitamin K-dependent zymogen of a serine protease that participates in the initial phase of blood coagulation. A factor VII molecular variant (factor VII Central) was identified in a 24-year-old male with severe factor VII deficiency and whose plasma factor VII antigen was 38% of normal, but expressed <1% factor VII procoagulant activity. DNA sequence analysis of the patient's factor VII gene revealed a thymidine to cytidine transition at nucleotide 10907 in exon VIII that results in a novel amino acid substitution of Phe328 to Ser. The patient was homozygous for this mutation, whereas each parent of the patient was heterozygous for this mutation. To investigate the molecular properties of this variant, a recombinant F328S factor VII mutant was prepared and analyzed in relation to wild-type factor VII. F328S factor VII exhibited <1% factor VII procoagulant activity and a 2-fold decreased affinity for tissue factor and failed to activate factor X or IX in the presence of tissue factor following activation by factor Xa. In addition, F328S factor VIIa exhibited no detectable amidolytic activity in the presence of tissue factor. The rate of F328S factor VII activation by factor Xa was markedly decreased relative to the rate of wild-type factor VII activation as revealed by densitometry scanning of SDS gels. Temporal analysis of this reaction by SDS-polyacrylamide gel electrophoresis also revealed the formation of two novel F328S factor VII degradation products (40 and 9 kDa) resulting from factor Xa proteolysis of the Arg315-Lys316 peptide bond in intact F328S factor VII. Computer modeling and molecular dynamics simulations of the serine protease domain of factor VIIa suggested that the inability of F328S factor VIIa to cleave substrates may result from the apparent formation of a hydrogen bond between Tyr377 and Asp338, a residue at the bottom of the substrate-binding pocket important for the interaction of substrate arginine side chains with the enzyme. These findings suggest that Phe328, which is conserved in prothrombin, factor IX, factor X, factor VII, and trypsin, is important for factor VIIa catalysis.

Adult↗

Inherited bleeding disorders in the Eastern Province of Saudi Arabia.

Thirty-four cases of inherited bleeding disorders are reported. All are Saudi patients from the Eastern Province of Saudi Arabia. There were 15 haemophiliacs, 1 factor VII deficiency, 1 factor X deficiency, 12 Glanzmann's thrombasthenia, and 5 unidentified platelet function disorders. Consanguinity was common among the families of these patients. Different age groups were affected and the severity of bleeding varied in the different conditions reported.

Adenosine Diphosphate↗

Challenges in the therapeutic use of a "so-called" universal hemostatic agent: recombinant factor VIIa.

Recombinant factor VIIa (rFVIIa) was developed in the early 1990s to provide "bypassing" hemostatic therapy for hemophilia A and B patients with inhibitors. More recently, it has been licensed for use in patients with inherited deficiency of factor VII. Since it was licensed for use in hemophilia with inhibitors in the US, Europe, and other countries for these specific indications, it has been used selectively but in a wide array of clinical settings for uncontrolled hemorrhage in individuals without an inherited bleeding disorder. Many of these uses have been described in the medical literature as case reports or small, uncontrolled series. Several randomized clinical trials (RCT) for these "off-label" medical uses have been published in recent months and will serve as the focus of this review. In particular, a review of an RCT for spontaneous intracranial hemorrhage that has demonstrated clinical efficacy in reducing both mortality and volume of central nervous system hemorrhage will be offered. A brief discussion of hypothesized physiologic mechanisms of supraphysiologic doses of rFVIIa will introduce the clinical discussion of these broad off-label uses. Since rFVIIa is a very expensive therapy, possible strategies for optimizing its use in the these settings will be presented.

Factor VII↗