Afibrinogenemia

Afibrinogenemia is a genetic disorder where there is a total absence of fibrinogen in the blood.

Fibrinogen is a protein produced in the liver with an essential role in the formation of blood clots, a process required to stop bleeding. Fibrinogen is present in the blood as the precursor of fibrin, a protein necessary for clot formation.

Fibrinogen is also known as coagulation factor I and the lack of fibrinogen makes it difficult to stop the bleeding in case of hemorrhage.

Afibrinogenemia results from homozygous mutation in genes FGA (4q31.3), FGB (4q31.3) or FGG (4q32.1) located on chromosome 4 that encoded fibrinogen information.

It is an autosomal recessive condition, where both genes, one from each parent, must be mutated to suffer the disorder.

Congenital afibrinogenemia is an extremely rare disorder with an estimated incidence of 1 case per 1.000.000.

Afibrinogenemia has a variable bleeding tendency, ranging from life-threatening or spontaneous bleeding events to long periods without any bleeding episodes.

The most common symptoms are:

• Epistaxis (nosebleed)
• Hemarthroses (articular bleeding for example in the knee)
• Menorrhagia (prolonged menstrual bleeding)
• First-trimester recurrent spontaneous abortion in women

The appearance of spontaneous intracranial hemorrhage and intraabdominal bleeding have been reported as the worst-case scenario.

Bleeding from the umbilical cord is the most common presentation in the neonatal period.

In afibrinogenemia, the fibrinogen level is undetectable (<2 mg/dl) using both a functional assay and an immunoassay. Fibrinogen usually circulates in the plasma at a concentration of approximately 200 to 400 mg/dl.

The screening tests for prothrombin time (PT) and partial and thromboplastin time (PTT) are also prolonged.

As there is no presence of fibrinogen in the blood, people with afibrinogenemia need fibrinogen supplementation to achieve the objective of 50 mg/dl to 100 mg/dl of fibrinogen in the blood.

For this purpose, it is available:

• Fibrinogen concentrate: RiaSTAP, Haemocomplettan, FIBRYGA are prepared from pooled human plasma and are available as lyophilized powders. The dose depends on the weight of the patient.
• Cryoprecipitate. A plasma-derive blood product that may be a good source of fibrinogen but is not first-line therapy because it is not virally inactivated.