Factor IX

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Coagulation factor IX (plasma thromboplastic component, Christmas disease, hemophilia B)
PBB Protein F9 image.jpg
PDB rendering based on 1cfh.
Symbol(s) F9; FIX; GLA domain; HEMB; MGC129641; MGC129642; PTC
External IDs OMIM: 306900 MGI88384 Homologene106
RNA expression pattern

PBB GE F9 207218 at tn.png

More reference expression data

Human Mouse
Entrez 2158 14071
Ensembl ENSG00000101981 ENSMUSG00000031138
Uniprot P00740 A0JLY3
Refseq NM_000133 (mRNA)
NP_000124 (protein)
NM_007979 (mRNA)
NP_032005 (protein)
Location Chr X: 138.44 - 138.47 Mb Chr X: 56.35 - 56.38 Mb
Pubmed search [1] [2]

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Editors-In-Chief: John Alexander, M.D. [3], Duke Clinical Research Institute; C. Michael Gibson, M.S., M.D. Duke Clinical Research Institute [4]

Factor IX (or Christmas factor) is one of the serine proteases (EC of the coagulation system; it belongs to peptidase family S1. Deficiency of this protein causes hemophilia B. It was discovered after a young boy named Stephen Christmas was found to be lacking this exact factor, leading to hemophilia, in 1952.[1]


Factor IX is inactive unless activated by factor XIa (of the contact pathway) or factor VIIa (of the tissue factor pathway). When activated into factor IXa, it acts by hydrolysing one arginine-isoleucine bond in factor X to form factor Xa. It requires calcium, membrane phospholipids, and factor VIII as cofactors to do so.


The gene for factor IX is located on the X chromosome (Xq27.1-q27.2). It was first cloned in 1982 by Kotoku Kurachi and Earl Davie.[2]

Role in disease

Deficiency of factor IX causes Christmas disease (hemophilia B). Over 100 mutations of factor IX have been described; some cause no symptoms, but many lead to a significant bleeding disorder.


  1. Biggs RA, Douglas AS, MacFarlane RG, Dacie JV, Pittney WR, Merskey C, O'Brien JR. Christmas disease: a condition previously mistaken for haemophilia. Br Med J 1952;2:1378-1382. PMID 12997790.
  2. Kurachi K, Davie E (1982). "Isolation and characterization of a cDNA coding for human factor IX". Proc Natl Acad Sci U S A. 79 (21): 6461–4. PMID 6959130. 

Further reading

  • Davie EW, Fujikawa K (1975). "Basic mechanisms in blood coagulation.". Annu. Rev. Biochem. 44: 799–829. PMID 237463. doi:10.1146/annurev.bi.44.070175.004055. 
  • Sommer SS (1992). "Assessing the underlying pattern of human germline mutations: lessons from the factor IX gene.". FASEB J. 6 (10): 2767–74. PMID 1634040. 
  • Lenting PJ, van Mourik JA, Mertens K (1999). "The life cycle of coagulation factor VIII in view of its structure and function.". Blood. 92 (11): 3983–96. PMID 9834200. 
  • Lowe GD (2002). "Factor IX and thrombosis.". Br. J. Haematol. 115 (3): 507–13. PMID 11736930. 
  • O'Connell NM (2004). "Factor XI deficiency--from molecular genetics to clinical management.". Blood Coagul. Fibrinolysis. 14 Suppl 1: S59–64. PMID 14567539. 
  • Du X (2007). "Signaling and regulation of the platelet glycoprotein Ib-IX-V complex.". Curr. Opin. Hematol. 14 (3): 262–9. PMID 17414217. doi:10.1097/MOH.0b013e3280dce51a.