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