Poll Dorset sheep carrying the gene for factor IX, was produced by Dr Ian Wilmut at the Roslin Institute in 1997. Role in disease Deficiency of factor IX causes Christmas disease (hemophilia B). Over 3000 variants of factor IX have been described, affecting 73% of the 461 residues; some cause no symptoms, but many lead to a significant bleeding disorder. The original Christmas disease mutation was identified by sequencing of Christmas' DNA, revealing a mutation which changed a cysteine to a serine. Recombinant factor IX is used to treat Christmas disease. Formulations include: nonacog alfa (brand name BeneFix) albutrepenonacog alfa (brand name Idelvion) eftrenonacog alfa (brand name Alprolix) nonacog beta pegol (brand name Refixia) Some rare mutations of factor IX result in elevated clotting activity, and can result in clotting diseases, such as deep vein thrombosis. This gain of function mutation renders the protein hyperfunctional and is associated with familial early-onset thrombophilia. Factor IX deficiency is treated by injection of purified factor IX produced through cloning in various animal or animal cell vectors. Tranexamic acid may be of value in patients undergoing surgery who have inherited factor IX deficiency in order to reduce the perioperative risk of bleeding. A list of all the mutations in Factor IX is compiled and maintained by EAHAD. Coagulation factor IX is on the World Health Organization's List of Essential Medicines. References Further reading External links GeneReviews/NCBI/NIH/UW entry on Hemophilia B The MEROPS online database for peptidases and their inhibitors: S01.214 Coagulation system EC 3.4.21 Peripheral membrane proteins Pfizer brands Zymogens Sanofi World Health Organization essential medicines