Molecular defects in CRM+ factor VII deficiencies: modelling of missense mutations in the catalytic domain of FVII

Summary. The molecular defects causing CRM+ factor VII deficiency were investigated in seven unrelated subjects and several members of their families.
Four missense mutations located in the catalytic domain of factor VII were found. The previously reported ³⁰⁴ArgGln substitution was present in the homozygous and heterozygous forms, with different polymorphic haplotypes, thus demonstrating that it is recurrent and frequent in the Italian population. The ³¹⁰Cys Phe substitution was found in the homozygous form and in the compound heterozygous condition with the nonsense mutation ³⁵⁶Trpstop. Two missense mutations, ²⁹⁸MetIle and ³⁴²GlyArg, were found in the homozygous and in the heterozygous condition respectively.
Molecular heterogeneity was further increased by finding of the ³⁵³ArgGln polymorphism in the doubly heterozygous condition with the 304 and 342 mutations.
Plausible explanations for loss of FVII function were found by inspecting a model of the serine protease domain of factor VIIa. Inefficient activation of the catalytic site is predicted for ²⁹⁸MetIle. ³⁴²GlyArg would directly distort the geometry of the 'oxyanion hole'preventing formation of a substrate enzyme intermediate. ³¹⁰Cyshe is predicted to have an adverse effect on tissue factor interaction. These mutations point to important regions of the factor VII molecule.