Coagulation factor IX

General Information

Coagulation factor IX, or antihemophilic factor B, or Christmas factor, is a glycoprotein that is synthesized in hepatocytes (liver cells) with the participation of vitamin K and consists of the fraction: FIX-C and FIX-C Ag.

FIX-C is responsible for activation of coagulation and is synthesized by genes located on the X (sex) chromosome.

FIX-C Ag is an inactive protein element that promotes coagulation and has antigenic properties.

Functionally, factor IX is an enzyme that interacts with activated factor VIII in the presence of calcium ions. This complex then activates factor X.

In turn, factor IX is activated by the tissue factor VIIa complex at the beginning of coagulation. At a later stage, an additional amount of factor IX is produced by activated factor XI (FXIa) to subsequently activate factor X and thrombin generation.

FIX-C deficiency, i.e. hemophilia B, i.e. Christmas disease, is a recessive genetic disease linked to the X chromosome (genes synthesizing the ninth factor are located on the sex X chromosome). A number of mutations of these genes have been described, most of which are point mutations. The disease is transmitted from the mother carrying the mutated gene to her son on the X chromosome.

Cases of hemophilia B caused by spontaneous mutation of the FIX gene have also been described.

In pregnant women, the amount of factor IX is lower than in the rest of the population, although it is sufficient to prevent bleeding.

Females with Turner syndrome (X0 karyotype, i.e. absence of 1 sex X chromosome) may present with hemophilia when carrying the FIX gene.

Symptoms

The clinical picture of hemophilia is represented by bleeding, which most often appears within 1 year after birth:

• External bleeding from various organs develops within a few hours after the injury.
• Internal bleeding is more severe. Hemorrhages develop in tissues or cavities (abdominal cavity, pleura, joints, pericardium, subarachnoid spaces).

Depending on the severity of hemorrhagic syndrome, there are three clinical forms of hemophilia B:

Heavy: with spontaneous hemorrhages (factor IX level <1%)

Medium: Hemorrhages develop in response to minor injuries (factor IX level 1-5%)

light: Bleeding occurs only as a result of massive trauma or surgery (Factor IX level 5-25%)

Acquired factor IX deficiency is associated with vitamin K deficiency, liver disease, which also causes decreased levels of all coagulation factors.

Hemophilia B patients on replacement therapy may develop inhibitors in up to 3% of cases due to the development of antibodies.

In factor IX deficiency, coagulation tests show the following changes: prolonged activated partial thromboplastin time (APTT), which is corrected after administration of normal plasma. At the same time, thrombin time and bleeding time are within normal limits.

Factor IX activity is expressed as a percentage of the normal value. The current indicator confirms the diagnostics of hemophilia B and limits the form of the disease (mild, moderate, severe)

Preliminary preparation: The study is conducted on an empty stomach

Material for examination: Venous blood

Reference norm:  70-130%