Human missense variants in <i>F3</i> impair the initiation of blood coagulation

Tissue factor (TF), encoded by F3, binds factor VII (FVII)/activated factor VII (FVIIa) to initiate blood coagulation. Because standard clinical assays do not measure endogenous TF directly, the extent to which human F3 variants affect 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 affect coagulation activation. By contrast, some rare human TF missense substitutions did profoundly affect TF-initiated plasma clotting time and the activation of FIX and FX by 2 distinct mechanisms: by precluding TF interaction with FVIIa, 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 FVIIa-antithrombin complex and D-dimer levels but no major differences in TF or FVII levels. Gly196Arg supported impaired FVII autoactivation in vitro. These data demonstrate that rare missense variants in F3 can impair the activation of FVII, FIX, and FX, and suggest these variants impair the basal activation of blood coagulation in humans.