Factor I Deficiency
(Fibrinogen)
Included under this heading are several rare coagulation disorders known as congenital fibrinogen defects. They include afibrinogenemia and hypofibrinogenemia, and dysfibrinogenemia. The first two are called quantitative abnormalities because they have to do with an absent or low quantity of fibrinogen. The third is called a qualitative abnormality because the fibrinogen does not work well.

Fibrinogen, also known as Factor I, is needed for most types of platelet aggregation. People who have a Factor I deficiency have a combined bleeding disorder, meaning that both platelets and clotting are abnormal. Afibrinogenemia is the complete absence of fibrinogen. Hypofibrinogenemia is a low level of fibrinogen - less than 100mg in 1dL of blood. Both conditions are inherited in an autosomal fashion and can affect males and females.

The severity of the disorder is related to the amount of fibrinogen. Afibrinogenemia is usually discovered in newborns and can cause bleeding from the umbilical cord, genitourinary tract, or central nervous system. People with hypofibrinogenemia may have little, moderate, or severe bleeding.

Dysfibrinogenemias are due to variations in the Factor I molecule. More than 70 different types of dysfibrinogenemia have been identified. Few people who have any of these disorders suffer symptoms, although some are predisposed to form blood clots (thrombosis).

Many people with hypofibrinogenemia or dysfibrinogenemia need no treatment. Those who require treatment may be given cryoprecipitate or fresh frozen plasma. Anticoagulants are sometimes prescribed to reduce the risk of thrombosis.

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