Koenraad Mertens

Association of idiopathic venous thromboembolism with single point-mutation at Arg506 of factor V

Abnormal coagulation factor V may underlie the thrombotic events associated with resistance to activated protein C (APC). We analysed 27 consecutive patients with documented idiopathic (recurrent) thromboembolism for the occurrence of point mutations within the APC sensitive regions of blood coagulation factor V. In 10 patients we observed a single basepair mutation resulting in a substitution of Arg506 to Gln. This mutation was significantly linked to in-vitro resistance to APC in these subjects. This mutation at Arg506 of factor V may form the molecular basis for the thrombotic events associated with APC resistance.

Biological activity of recombinant factor VIII variants lacking the central B-domain and the heavy-chain sequence Lys713-Arg740: discordant in vitro and in vivo activity.

Summary. Recombinant factor VIII variants with overlapping deletions spanning the region Lys713‐Ile1668 have been expressed in mammalian cells, and analysed for biological activity both in vitro and in vivo. Two distinct assay systems were used to measure the activity in vitro. The one‐stage coagulation assay served to assess factor VIII procoagulant activity while a spectrophotometric assay was used for the quantification of factor VIII cofactor activity in factor IXa‐dependent factor X activation. Deletion of the entire B‐domain (Ser741‐Arg1648) resulted in a protein with similar procoagulant and cofactor activity. In contrast, factor VIII‐del(713–163 7), which has a deletion that also comprises the heavy‐chain sequence Lys713‐Arg740, had lost factor VIII procoagulant activity while factor VIII cofactor activity was retained. This functional inconsistency was further addressed by comparing purified factor VIII‐del(713–1637) with factor VIII‐del(868–1562). a mutant with normal in vitro activity.