A novel factor V compound heterozygous mutation associated with thrombosis (Y1961C; FV-Kanazawa, together with 1982_1983del)

Background

Factor (F)V is pivotal in both procoagulant and anticoagulant mechanisms. The present report describes a novel F5 mutation in a FV-deficient patient (FV activity, 6 IU/dL; FV antigen, 32 IU/dL) complicated by recurrent deep vein thrombosis. The patient demonstrated activated protein C resistance (APCR) with compound heterozygous mutations consisting of FV-Y1961C (FV_Kanazawa) and FV-1982_1983del.

Objectives

To clarify thrombotic mechanisms associated with this FV abnormality.

Methods and Results

Levels of FV-1982_1983del were below the detection sensitivity in our expression experiments using human embryonic kidney 293T cells, and analyses were targeted, therefore, on the FV-Y1961C mutation. Activated partial thromboplastin time–based clotting assays demonstrated that FV-Y1961C exhibited APCR and that the reduced activated protein C (APC) susceptibility in FVa-Y1961C resulted in a marked depression of APC-catalyzed inactivation with delayed cleavage at Arg506 and little cleavage at Arg306 with or without protein S. The APC cofactor activity of FV-Y1961C in APC-catalyzed FVIIIa inactivation promoted by Arg336 cleavage in FVIII was impaired. The binding affinity of FVa-Y1961C to phospholipid membranes was reduced in reactions involving APC/protein S–catalyzed inactivation and in prothrombinase activity. Furthermore, the addition of FVa-Y1961C to plasma failed to inhibit tissue factor–induced procoagulant function. These characteristics were similar to those of FV-W1920R (FV_Nara) and FV-A2086D (FV_Besançon).

Conclusion

We identified a compound heterozygous FV-Y1961C mutation in the C1 domain representing a novel FV mutation (FV_Kanazawa) resulting in not only APCR due to impaired FVa susceptibility and FV cofactor activity for APC function but also impaired inhibition of tissue factor–induced procoagulant function. These defects in anticoagulant function associated with FV in FV-Y1961C contributed to a prothrombotic state.