Factor VII (F.VII) is a
vitamin-K-dependent
serine protease required in the early stages of blood coagulation. We describe here a patient with severe F.VII deficiency, with a normal plasma F.VII
antigen level (452 ng/mL) and F.VII activity less than 1%, who is homozygous for two defects: a G-->A transition at
nucleotide 6055 in exon 4, which results in an
Arg-->Gln change at
amino acid 79 (R79Q); and a G-->A transition at
nucleotide 8961 in exon 6, which results in an
Arg-->Gln substitution at
amino acid 152 (R152Q). The R79Q mutation occurs in the first
epidermal growth factor (
EGF)-like domain, which has previously been implicated in binding to
tissue factor. The R152Q mutation occurs at a site (Arg 152-Ile 153) that is normally cleaved to generate activated F.VII (F.VIIa). Analysis of purified F.VII from patient plasma shows that the material cannot be activated by F.Xa and cofactors. In addition, in an in vitro binding assay using relipidated recombinant
tissue factor, patient plasma showed markedly reduced binding to
tissue factor at all concentrations tested. In an effort to separate the contributions of the two mutations, three recombinant variants, wild-type, R79Q, and R152Q, were prepared and analyzed. The R152Q variant had markedly reduced activity in a clotting assay, whereas R79Q showed a milder, concentration-dependent reduction. The R152Q variant exhibited nearly normal binding in the
tissue factor binding assay, whereas the R79Q variant had markedly reduced binding. The time course of activation of the R79Q variant was slowed compared with wild-type. Our results suggest that the first
EGF-like domain is required for binding to
tissue factor and that the F.VII
zymogen lacks activity and requires activation for expression of
biologic activity.