This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Anatomy
[{'content': 'All the following are true about sickle cell anemia except \nSelect and explain. \nA. Mutation in alpha chain, B. Symptoms ameliorated by Hbf, C. Venoocclusive cries is cause of morbidity, D. Bone pain is presenting feature', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ref Harrison 19 th ed pg 634 The sickle cell syndromes are caused by a mutation in the b-globin gene that changes the sixth amino acid from glutamic acid to valine. HbS (a2 b2 6 Glu-Val) polymerizes reversibly when deoxygenated to form a gelatinous network of fibrous polymers that stiffen the RBC membrane, increase viscosity, and cause dehydration due to potas- sium leakage and calcium influx.', 'role': 'assistant'}]