Molecular basis for protein C hereditary deficiency.

The clinical presentation of hereditary protein C deficiency is highly variable. Homozygosity and compound heterozygosity have been linked to severe thrombotic complications early in the life. Heterozygous patients have a moderate form of the disease with deep venous thrombosis during adulthood. In the French population, we found 53 different mutations in 90 families. The amount of the protein C produced by the mutant allele as well as the genetic status partly account for the variable clinical expression. Other gene may also be involved: Arg 506 to Gln factor V mutation shows a frequency of 10 to 20% in symptomatic protein C deficient patients. Some protein C gene mutations are associated with a non functional circulating protein; most of them are located in the GLA domain and in the serine protease domain. The biochemical characterization of a few of theses variants has shown the important role of some amino acids on the activation and the mechanism of action of protein C.