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What Is It?
Fibrinogen, also known as factor I, is needed for most types of platelet
aggregation. It's the last step in the clotting process, the "glue" that
holds the clot together. People who have a factor I deficiency have a
combined bleeding and clotting disorder, meaning that both platelets and
clotting are abnormal. Since its discovery in 1920, there have only been
about 200 cases of this disorder.
Included under factor I deficiency are several rare coagulation disorders
known as congenital fibrinogen defects. They include:
• afibrinogenemia
• hypofibrinogenemia
• 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.
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.
Inheritance Pattern
The disorder is not sex-linked as is hemophilia. It affects both males and
females with equal frequency. It is autosomal recessive, which means if the
clotting defect is inherited from a parent, the child will be a genetic
carrier of the condition, but may or may not have symptoms.
Symptoms & Diagnosis
Few people who have any of these disorders suffer symptoms, although some
are predisposed to form blood clots (thrombosis).
Treatments
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. The goal of treatment is to raise the patient's fibrinogen level
to 100 mg/dL for minor bleeding and up to 200 mg/dL for surgery or severe
bleeding. (One unit of fresh frozen plasma has about 450 mg of fibrinogen.)
Complications
Plasma levels of fibrinogen exceeding 1000 mg/dL have been reported to
possibly increase the risk of thrombosis. In women, menstrual bleeding can
be a severe problem and must be controlled.
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