[Elucidation of an altered anticoagulant function due to Factor V abnormality and development of a simple screening...

Coagulation factor V (FV) is both procoagulant and anticoagulant functions. Congenital FV abnormality, which are caused by mutations in the FV gene, are characterized by a tendency to bleed. However, FV-R506Q (FV_Leiden) is the most common FV abnormality that eliminates an activated protein C (APC) cleavage site, resulting in the occurrence of deep venous thrombosis (DVT). In Japan, the thrombotic predisposition caused by FV_Leiden and FV molecular abnormalities was believed to be nonexistent. We did, however, report the first case in Japan of a young patient with FV abnormality-related thrombosis. The recurrent DVT in this case was caused by a novel mutation of FV-W1920R (FV_Nara), located in the C1 domain and far from the APC cleavage sites. We considered the possibility that there were cases of FV-related thrombotic predisposition that had gone undetected in Japan. We thoroughly examined FV-related anticoagulant function to understand the pathogenesis of thrombosis caused by FV abnormality. Furthermore, using recombinant thrombomodulin, we successfully developed a novel assay with clot waveform analysis for the rapid detection of FV deficiency with APC resistance. Other FV abnormality-related thrombosis has been reported in Japan in recent years, and we hope to further clarify the FV-related thrombotic predisposition in the future.