This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pathology, Subject name: Pathology
Leiden factor is - 
Select and explain. 
A. Factor VI, B. Factor VIII, C. Factor IV, D. Factor V
D: Factor V
Answer: D: Factor V 
Explanation: 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 )