VARIABILITY OF THROMBOSIS AMONG HOMOZYGOUS SIBLINGS WITH RESISTANCE TO ACTIVATED PROTEIN-C DUE TO AN ARG-]GLN MUTATION IN THE GENE FOR FACTOR-V

The most frequent laboratory abnormality in patients with idiopathic deep-vein thrombosis is resistance to activated protein C1. Depending on the selection criteria, in vitro resistance to activated protein C can be identified in 20 to 50 percent of patients2–6. Protein C, a key element in the regulation of coagulation, circulates in plasma as an inactive precursor. On contact with thrombin bound to the thrombomodulin receptors on vascular endothelial cells, protein C rapidly becomes activated. Activated protein C enzymatically lyses two cofactors of the coagulation cascade, factor VIIIa and factor Va. It is thus a natural anticoagulant that… © 1994, Massachusetts Medical Society. All rights reserved.