What Is Factor I (Fibrinogen) Deficiency?

Factor I (fibrinogen) deficiency is an inherited bleeding disorder caused by a defect or lack of a protein in the blood (fibrinogen) which plays an important role in blood clotting. Fibrinogen is also found on the surface of platelets (the blood cells that make a plug to patch holes in arteries, veins and capillaries) and helps platelets stick to each other. When fibrinogen is not functioning properly or when it is absent or at a very low level, it is difficult for a blood clot to form. People with factor I deficiency have a combined bleeding disorder, which means that both platelets and clotting are abnormal.

Factor I deficiency is a very rare inherited bleeding disorder often found in people whose parents are blood relatives. Factor I deficiency is the umbrella term for several rare clotting disorders known as congenital fibrinogen defects. Either the quantity of the protein may be abnormal or it may not function well (qualitative abnormality). Two fibrinogen disorders – afibrinogenemia (a complete absence of fibrinogen) and hypofibrinogenemia (low levels of fibrinogen) – are known as quantitative abnormalities because they result from an absence or low quantity of fibrinogen. The third disorder – dysfibrinogenemia – is called a qualitative abnormality because it results from the fibrinogen not working well.

Of the three main types, afibrinogenemia is an autosomal recessive disorder, meaning that both parents must carry the defective gene in order to pass it on. Hypofibrinogenemia and dysfibrinogenemia can be either recessive (both parents carry the gene) or dominant (only one parent is a carrier). The genes are found on chromosome 4. Factor I deficiency disorder affects males and females in equal numbers.

Symptoms

Symptoms of factor 1 deficiency differ depending on which form of factor I deficiency is present. People with factor 1 deficiency may experience:

• bleeding from the gums
• nose bleeds
• excessive bleeding in the gut (gastrointestinal hemorrhage)
• excessive bleeding in the genito-urinary tract (kidneys, ureters, bladder, and urethra)
• excessive bleeding in the brain (intracranial hemorrhage)
• rupture of the spleen and prolonged bleeding in the spleen
• bleeding in the central nervous system
• bleeding from umbilical cord stump at birth
• miscarriage
• blood clot in a blood vessel (thrombosis)

Afibrinogenemia: People with afibrinogenemia are usually discovered at birth. It can cause bleeding from the umbilical cord.

Hypofibrinogenemia: People with hypofibrinogenemia may be more likely to have a miscarriage. They may have little or excess bleeding depending on the level of factor I in the blood. The lower the level of fibrinogen, the more severe the bleeding.

Dysfibrinogenemia: There are many identified types. People with dysfibrinogenemia have very few symptoms, although some may develop a blood clot in a blood vessel (thrombosis), experience prolonged bleeding, or both.

Diagnosis

Factor I (fibrinogen) deficiency is diagnosed by a variety of laboratory tests to see if there is a bleeding disorder. Special testing will determine which one of the factor I (fibrinogen) types is present.

Treatment

Many people with hypofibrinogenemia or dysfibrinogenemia do not need treatment. When treatment is needed, factor I (fibrinogen) deficiency is treated with:

• fibrinogen concentrates
• cryoprecipitate
• fresh frozen plasma (FFP)

Content reviewed by Dr. Paula Bolton-Maggs
Consultant Haemotologist
Manchester Haemophilia Comprehensive Care
Manchester Royal Infirmary
Manchester, UK.

Last updated December 2007