This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Factor V Leiden is caused due to a mutation that results in a substitution at position 506 glutamine to which of the following: 
Select and explain. 
A. Alanine, B. Arginine, C. Glycine, D. Glutamine
B: Arginine
Answer: B: Arginine 
Explanation: Mutation in factor V (called the Leiden mutation, after the city in the Netherlands where it was discovered) causes recurrent DVTs. The mutation results in a glutamine to arginine substitution at position 506 that renders factor V resistant to cleavage by protein C. As a result, an impoant antithrombotic counter-regulatory pathway is lost Ref: Robbins 8th edition Chapter 4.