Type II protein C deficiency: identification and molecular modelling of two natural mutants with low anticoagulant and normal amidolytic activity

Two mutations in exons 3 and 9 of the protein C gene were identified by amp lification and sequencing from symptomatic probands referred for venous thr omboembolism and thrombophilia screening. The phenotype associated with the mutations is a type II protein C deficiency with normal amidolytic activit y In one family, the mutation in exon 3 (G3545-->A), which predicts an R9 t o H substitution in the Gla domain, was identified. A mutation in exon 9 (G 10899-->A), which predicts an R352 to W substitution in the catalytic site, was identified in the second family and has been reported previously in as sociation with type II deficiency with low amidolytic activity. Western blo tting of the purified proteins from the probands' plasma did not show any a bnormal migratory pattern. Molecular modelling suggested a possible impairm ent in the recently described Na+ binding pocket for the R352-->W mutant. N o conclusions could be drawn relative to the R9-->H mutant.