Activated protein C-resistant factor V

Resistance to the anticoagulant effects of activated protein C (APC) (Factor V Leiden heterozygous*) is common (1):

• 5% of the general population
• 25-50% of patients with venous thromboembolism
• 50% of patients with thrombosis who have a family or personal history of thrombosis

APC resistance is usually due to a single point mutation in one or both of the protein C genes. The mutation reduces the susceptibility of factor V to cleavage by APC.

There is increasing evidence that individuals with two or more laboratory characterisable thrombophilic abnormalities (or who are homozygous for either factor V Leiden or prothrombin G20210A) are at a greater risk of thrombosis than those in whom there is a single gene abnormality (1).

* Factor V Leiden homozygous individuals have an 80x risk of venous thromboembolism

Reference:

(1) British Heart Foundation (Factfile 2/2002). Thrombophilia

(2) Rogier, MB. et al. (1994). Mutation in blood coaulation factor V associated with resistance to activated protein C. Nature, 369, 64-7.

(3) Drugs and Therapeutics Bulletin (1995), 33 (1), 6-8.