This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S., Subject name: Pediatrics
[{'content': 'Leiden mutation involves: \nSelect and explain. \nA. Factor V, B. Factor VI, C. Protein C, D. Protein S', 'role': 'user'}, {'content': "Answer: A \nExplanation: a. Factor V(Ref: Nelson's 20/e p 2384-2389, Ghai 8/e p 350-352)Factor V Leiden: glutamine arginine substitution at amino acid residue 506 that renders factor V resistant to cleavage and inactivation by protein C (also called Activated Protein C resistance)", 'role': 'assistant'}]