MOLECULAR-DETECTION OF A COMMON MUTATION IN COAGULATION-FACTOR-V CAUSING THROMBOSIS VIA HEREDITARY RESISTANCE TO ACTIVATED PROTEIN-C

More than half of all patients with familial or recurring venous throm bosis have hereditary resistance to activated protein C (HRAPC) as the result of a specific missense mutation in the gene for coagulation fa ctor V. Because the mutant factor Va (with an Arg to Gin substitution at codon 506) cannot be cleaved and inactivated by activated protein C , carriers of this mutation are at significantly increased risk of ven ous thrombosis. We have recently introduced a direct polymerase chain reaction (PCR)-based clinical diagnostic test for the factor V codon 5 06 mutation based on the destruction of an Mnl I restriction site by t he causative nucleotide substitution. To assess the accuracy of this P CR-based assay, we compared a functional clotting time test for HRAPC with the direct mutation test. Of 47 patients dually tested, only five had discrepant values for the functional test versus the DNA test. Ei ther of these two complementary assays is useful for the accurate diag nosis of HRAPC. The DNA-based test is, however, specifically recommend ed for evaluation of anticoagulated patients or patients with borderli ne functional tests and confirmation of genotype in HRAPC families. In an additional analysis of 287 normal individuals, we found an extreme ly high prevalence of the mutated codon 506 allele-similar to 4% in ea ch of two different populations. The absence of disease in the majorit y of heterozygous carriers suggests that symptomatic thrombosis requir es the simultaneous presence of both a mutated factor V protein and ad ditional synergistic factors.