Molecular analysis of the genotype-phenotype relationship in factor VII deficiency

Factor VII (FVII) deficiency is a rare haemorrhagic condition, normally inh erited as an autosomal recessive trait, in which clinical presentation is h ighly variable and correlates poorly with laboratory phenotype. The FVII (F 7) gene was sequenced in 48 unrelated individuals with FVII deficiency, yie lding a total of 23 novel lesions including 15 missense mutations, 2 micro- deletions, 5 splice junction mutations and a single base-pair substitution in the 5' untranslated region. Family studies were performed in order to di stinguish the contributions of individual mutant F7 alleles to the clinical and laboratory phenotypes. Specific missense mutations were evaluated by m olecular modelling in the context of the FVIIa-tissue factor crystal struct ure. Single base-pair substitutions in splice sites and the 5' untranslated region were studied by in vitro splicing assay and luciferase reporter gen e assay, respectively. All probands were also typed for four previously rep orted F7 polymorphisms. In the majority of cases of FVII deficiency studied here, consideration of both mutational and polymoryhism data permitted the derivation of plausible explanations for the FVII activity and antigen lev els measured in the laboratory. Inter-familial variation in FVII activity a nd the antigen levels of heterozygous relatives of probands was found to be significantly higher than intra-familial variation, consistent with the vi ew that the nature of the F7 gene lesion(s) segregating in a given family i s a prime determinant of laboratory phenotype. Although no relationship cou ld be discerned between laboratory phenotype and polymorphism genotype, the frequencies of the A2 and M2 polymorphic alleles were significantly higher in the FVII-deficient individuals tested than in controls. This suggests t hat the presence of these alleles may have served to increase the likelihoo d of pathological F7 gene lesions coming to clinical attention.