Resistance to Activated Protein C

Abstract

The article by Svensson and Dahlback on resistance to activated protein C (APC) (Feb. 24 issue)¹ postulates that there is a genetically determined defect in anticoagulation characterized by resistance to APC. The authors subsequently found the anticoagulant cofactor that corrects inherited APC resistance to be identical to unactivated factor V. I believe that these findings could also be due to hyperhomocysteinemia. It has been demonstrated that hyperhomocysteinemia is an independent risk factor for vascular disease^2,3. It was previously demonstrated that homocysteine induced a vascular-endothelial-cell activator that led to the activation of factor V⁴. I feel that serum homocysteine levels should have been measured by Svensson and Dahlback, and that elevated homocysteine levels may explain their findings.