<prompt> Leiden factor is -Factor VIFactor VIIIFactor IVFactor V  <response>: Approximately 2 to 15 of whites carry a specific factor V mutation called the Leiden mutation, after the Dutch city where it was first described. The mutation alters an amino acid residue in factor V and renders it resistant to protein C. Thus, an impoant antithrombotic counter-regulatory mechanism is lost. Heterozygotes carry a 5-fold increased risk for venous thrombosis, with homozygotes having a 50-fold increased risk. Robbins Basic Pathology, 9 th edition, page 87 