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: Medicine
[{'content': 'All are true about the Etiology of primary myelofibrosis , EXCEPT: \nSelect and explain. \nA. JAK2 mutation is seen in 50 % cases, B. Overproduction of transforming growth factor, C. Overproduction of osteoprotegerin, D. Mutations in the thrombopoietin receptor Mpl occur in 50%', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Primary myelofibrosis ,Etiological features. The etiology is unknown. JAK2 V617F is present in approximately 50% of patients Mutations in the thrombopoietin receptor Mpl occur in about 5%. Fibrosis is associated with overproduction of transforming growth factor and tissue inhibitors of metalloproteinases Osteosclerosis is associated with overproduction of osteoprotegerin. Ref: Harrison, E-18,P-906.', 'role': 'assistant'}]