Factor IX Deficiency

Factor IX is a single-chain, vitamin K-dependent glycoprotein serine protease with a molecular weight of approximately 55,400 and a plasma concentration of 3 – 5 μg/mL. Factor IX is encoded by a 34-kb gene located near the terminal end of the long arm of the X chromosome. Factor IX is activated by factor XIa, factor VIIa, or by Russell's viper venom. Activated factor IX (IXa) forms a complex with activated factor VIII, calcium and phospholipid which activates factor X. Most inherited abnormalities of factor IX are caused by a true deficiency, but a few patients with a dysfunctional form of the molecule have been identified. Factor IX disease is extremely heterogenous, with nearly 700 point mutations, additions, deletions, and other molecular abnormalities identified in different patients.