Human missense variants in F3 impair the initiation of blood coagulation Available to Purchase

• Rare human missense variants in tissue factor impede the activation of blood coagulation

• These variants disrupt either the: 1) Tissue factor interaction with factor VIIa or 2) Tissue factor exosite for macromolecular substrates

Tissue factor (TF), encoded by F3, binds factor VII/VIIa to initiate blood coagulation. Because standard clinical assays do not measure endogenous TF directly, the extent to which human F3 variants impact blood coagulation is unknown. We sought to determine the effect of the human TF missense variants with the highest allele frequency as well as additional rare variants occurring at sites predicted to perturb the initiation of blood coagulation. The variants with the highest allele frequency did not impact coagulation activation. By contrast, some rare human TF missense substitutions did profoundly impact TF-initiated plasma clotting time and the activation of factors IX and X by two distinct mechanisms: by precluding TF interaction with factor VIIa or by altering the TF exosite to prevent macromolecular but not amidolytic substrate cleavage. Individuals heterozygous for the rare p.Gly196Arg variant have reduced basal factor VIIa-antithrombin complex and D-dimer levels but no major differences in TF or factor VII levels. Gly196Arg supported impaired factor VII autoactivation in vitro. These data demonstrate that rare missense variants in F3 can impair the activation of factors VII, IX and X and suggest these variants impair the basal activation of blood coagulation in humans.