Factor IX
（重定向自Nonacog alfa）
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![The blood coagulation and Protein C pathway.](/Images/godic/202501/30/Coagulation_full.svg4351.png")
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Factor IX (or Christmas factor) (EC3.4.21.22) is one of the serine proteases of the coagulation system; it belongs to peptidase family S1. Deficiency of this protein causes hemophilia B. It was discovered in 1952 after a young boy named Stephen Christmas was found to be lacking this exact factor, leading to hemophilia.