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: Biochemistry
[{'content': 'What is the cause of sickling of RBC in sickle cell disease? \nSelect and explain. \nA. Decreased Solubility, B. Decreased Stability, C. Altered Function, D. Altered 02 binding capacity', 'role': 'user'}, {'content': "Answer: A \nExplanation: In sickle cell disease glutamic acid is replaced by valine. The charge and location of this substitution cause HbS to be conveed from a soluble state into a polymer when it undergoes structural changes that accompany release of oxygen. Hypoxia, acidosis, and hypeonicity facilitate polymer formation. The polymerization of hemoglobin cause the red cell to transform from a deformable, biconcave disk into a rigid, sickle shaped cell. Ref: Rudolph's Fundamentals of Pediatrics By Abraham M. Rudolph, Pages 528-30", 'role': 'assistant'}]