Activated factor VII (FVIIa), the first protease of clotting, expresses its physiological procoagulant potential only after complexing with tissue factor (TF) exposed to blood. Deep knowledge of the FVIIa-TF complex and F7 gene helps to understand the Janus-faced clinical findings associated to low or elevated FVII activity (FVIIc). Congenital FVII deficiency, the most frequent among the recessively inherited bleeding disorders, is caused by heterogeneous mutations in the F7 gene. Complete FVII deficiency causes perinatal lethality. A wide range of bleeding symptoms, from life-threatening intracranial hemorrhage to mild mucosal bleeding, is observed in patients with apparently modest differences in FVIIc levels. Though clinically relevant FVIIc threshold levels are still uncertain, effective management, including prophylaxis, has been devised, substantially improving the quality of life of patients. The exposure of TF in diseased arteries fostered investigation on the role of FVII in cardiovascular disease. FVIIc levels were found to be predictors of cardiovascular death and to be markedly associated to F7 gene variation. These genotype-phenotype relationships are among the most extensively investigated in humans. Genome-wide analyses extended association to numerous loci that, together with F7, explain >50% of FVII level plasma variance. However, the ability of F7 variation to predict thrombosis was not consistently evidenced in the numerous population studies. Main aims of this review are to highlight i) the biological and clinical information that distinguishes FVII deficiency from the other clotting disorders and ii) the impact exerted by genetically predicted FVII level variation on bleeding as well as on the thrombotic states.

The study of the molecular bases of thrombophilia in a large family with 4 symptomatic members is reported. Three thrombophilic genetic components (FV R506Q, FV H1299R, and PT 20210G/A), all affecting the activity of the prothrombinase complex, were detected alone and in combination in various family members. In addition, a newly identified missense mutation (factor V [FV] Y1702C), causing FV deficiency, was also present in the family and appeared to enhance activated protein C (APC) resistance in carriers of FV R506Q or FV H1299R by abolishing the expression of the counterpart FV allele. The relationships between complex genotypes, coagulation laboratory findings, and clinical phenotypes were analyzed in the family. All symptomatic family members were carriers of combined defects and showed APC resistance and elevated F1 + 2 values. Evidence for the causative role of the FV Y1702C mutation, which affects a residue absolutely conserved in all 3 A domains of FV, factor VIII, and ceruloplasmin, relies on (1) the absolute cosegregation between the mutation and FV deficiency, both in the family and in the general population; (2) FV antigen and immunoblot studies indicating the absence of Y1702C FV molecules in plasma of carriers of the mutation, despite normal levels of the FV Y1702C messenger RNA; and (3) molecular modeling data that support a crucial role of the mutated residue in the A domain structure. These findings help to interpret the variable penetrance of thrombosis in thrombophilic families and to define the molecular bases of FV deficiency.

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Objective—Functional polymorphisms contributing to coagulation factor levels are preferential markers for association studies aimed at identifying prothrombic genetic components.Methods and Results—Factor V (FV) microsatellite genotypes were found to be associated with FV levels (P=0.003). Single nucleotide polymorphisms analysis and sequencing of the promoter and of coding regions identified two polymorphisms (Met2120Thr, Asp2194Gly) present in 20% of the population (n=1013) that are responsible for genotype-phenotype associations. The effect of the Met2120Thr polymorphism, both in plasma (mean reduction of FV level in the heterozygous condition: 25%) and in recombinant FV studies (34% reduction), was comparable to that of the Asp2194Gly change (20% and 34%, respectively). The study of 10 subjects with a rare genotype indicated that the Asp2194Gly substitution is the functional determinant of the reduced FV levels associated with the FVHR2 haplotype. Among Leiden carriers, the doubly heterozygous condition for FV2120Thr was found to be associated with a significantly increased activated protein-C resistance (APCR) (P<0.05), and the doubly heterozygous condition for FV2194Gly was found to be more frequent (P=0.009) in symptomatic than in asymptomatic subjects.Conclusions—Extensive analysis of FV polymorphisms indicated that changes in the C2 domain modulate FV levels and might increase APCR and thrombotic risk in FV Leiden carriers through a pseudohomozygous mechanism.

Summary: The short half‐life of coagulation factor IX (FIX) for haemophilia B (HB) therapy has been prolonged through fusion with human serum albumin (HSA), which drives the neonatal Fc receptor (FcRn)‐mediated recycling of the chimera. However, patients would greatly benefit from further FIX‐HSA half‐life extension. In the present study, we designed a FIX‐HSA variant through the engineering of both fusion partners. First, we developed a novel cleavable linker combining the two FIX activation sites, which resulted in improved HSA release. Second, insertion of the FIX R338L (Padua) substitution conferred hyperactive features (sevenfold higher specific activity) as for FIX Padua alone. Furthermore, we exploited an engineered HSA (QMP), which conferred enhanced human (h)FcRn binding [dissociation constant (K_D) 0·5 nM] over wild‐type FIX‐HSA (K_D 164·4 nM). In hFcRn transgenic mice, Padua‐QMP displayed a significantly prolonged half‐life (2·7 days, P < 0·0001) versus FIX‐HSA (1 day). Overall, we developed a novel FIX‐HSA protein with improved activity and extended half‐life. These combined properties may result in a prolonged functional profile above the therapeutic threshold, and thus in a potentially widened therapeutic window able to improve HB therapy. This rational engineering of both partners may pave the way for new fusion strategies for the design of engineered biotherapeutics.