This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood, Subject name: Pathology
Most common type of inherited disease of hypercoagulobility is? 
Select and explain. 
A. Protein C deficiency, B. Leiden mutation, C. DIC, D. Antithrombin III deficiency
B: Leiden mutation
Answer: B: Leiden mutation 
Explanation: Ans. is 'b' i.e., Leiden mutation * Of the inherited causes of hypercoagulability, mutation in factor V gene is the most common.* Factor V mutations (called the leiden mutation) causes subsitution of arginine residue (at position 506) by glutamine.* This mutation makes factor V resistant to cleavage by protein 'C* (normally protein 'C is one of the factor that regulates coagulation by inactivating factor V & VIII).* This results in unchecked coagulation.