Factor IX
Factor IX (EC 3.4.21.22), also known as Christmas factor, is one of the serine proteases involved in coagulation; it belongs to peptidase family S1. Deficiency of this protein causes haemophilia B.
It was discovered in 1952 after a young boy named Stephen Christmas was found to be lacking this exact factor, leading to haemophilia.[5] Coagulation factor IX is on the World Health Organization's List of Essential Medicines.[6]
Deficiency of factor IX causes Christmas disease (hemophilia B).[5] Over 3000 variants of factor IX have been described, affecting 73% of the 461 residues;[21] 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.[22]
Recombinant factor IX is used to treat Christmas disease. Formulations include:
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.[35]
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.[36]
A list of all the mutations in Factor IX is compiled and maintained by EAHAD.[37]
Coagulation factor IX is on the World Health Organization's List of Essential Medicines.[6]