The delicate, complex balance between coagulation and anticoagulation attracts both admiration and some wonderment that things do not go wrong more often. The protein C anticoagulant pathway is part of the story.
Papers No. 3 and No. 5 show how a substantial proportion of venous thrombosis that is not otherwise explained is caused by resistance to activated protein C (APC). How big a fraction depends on the selection criteria for the study up to a fifth, maybe, but more when there is a familial history.
In February 1994, Peter J. Svensson and Bjorn Dahlbäck (paper No. 3) suggested that APC was caused by a single gene, but they did not say where that defect might lie. In fact, a recent paper from their group had just revealed that defective factor V was involved. A slightly earlier paper, No. 5, from the Leiden Thrombophilia Study, also referred to "as yet unknown ...
