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
All are true about the Etiology of primary myelofibrosis , EXCEPT: 
Select and explain. 
A. 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%
D: Mutations in the thrombopoietin receptor Mpl occur in 50%
Answer: D: Mutations in the thrombopoietin receptor Mpl occur in 50% 
Explanation: 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.