Factor ix

The activated factor IX forms a complex together with cofactor VIIIa as well as with calcium ions and platelet factor 3, which activates factor X. This complex is called tenase. Factor IX has a molecular weight of 55 kD and is a single-chain molecule. It carries 12 Ca++-binding sites.

The lack of factor IX is the cause of haemophilia B, an inherited X-linked disorder. Factor IX or Christmas factor is synthesized in the liver, whereby the synthesis is vitamin K-dependent. It can be detected in normal serum, the concentration is 3 ug/mg. 60% of factor IX is extravascular. Its half-life is between 18 and 30 hours. It is determined by a chromogenic subtrate test, immunologically or by the so-called one-step test.

In 1952, Aggeler and Schulman described patients with symptoms similar to those of haemophilia, but not identical to classic haemophilia A. Aggeler called this hitherto unknown factor Plasmathromboplastin Component (PTC). Schulman called it plasma factor X, but this was changed because the number X had already been assigned to another factor. The publications of Aggeler and Schulman both appeared at intervals of one week. Factor IX was given the name Christmas factor because a report on six patients with a factor IX deficiency was published in the Christmas issue of the British Medical Journal in 1952.

1. HA Neumann (2014) The coagulation system. ABW-Wissenschaftsverlag GmbH Berlin S. 62f.