Factor I Deficiency

Factor I deficiency, also known as fibrinogen deficiency, is a rare inherited bleeding disorder related to fibrinogen function in the blood coagulation cascade. It is typically subclassified into three distinct disorders: afibrinogenemia, hypofibrinogenemia, or dysfibrinogenemia. Afibrinogenemia is defined as a lack of fibrinogen in the blood, clinically <20 mg/deciliter of plasma. The frequency of this disorder is estimated at between 0.5 and 2 per million. Hypofibrinogenemia is defined as a partial deficiency of fibrinogen, clinically 20–80 mg/deciliter of plasma. Estimated frequency varies from <0.5 to 3 per million. Dysfibrinogenemia is defined as malfunctioning or non-functioning fibrinogen in the blood, albeit at normal concentrations: 200–400 mg/deciliter of plasma. Hypodysfibrinogenemia is a partial deficiency of fibrinogen that is also malfunctioning. Estimated frequency varies from 1 to 3 per million. Within the United States, afibrinogenemia accounts for 24% of all inherited abnormalities of fibrinogen, while hypofibrinogenemia and dysfibrinogenemia account for 38% each.

Causes

The disorders associated with Factor I deficiency are generally inherited, although certain liver diseases can also affect fibrinogen levels and function (e.g. cirrhosis). Afibrinogenemia is a recessive inherited disorder, where both parents must be carriers. Hypofibrinogenemia and dysfibrinogenemia can be dominant (i.e. only one parent needs to be a carrier) or recessive. The origin of the disorders is traced back to three possible genes: FGA, FGB, or FGG. Because all three are involved in forming the hexameric glycoprotein fibrinogen, mutations in any one of the three genes can cause the deficiency.

Symptoms

Afibrinogenemia is typically the most severe of the three disorders. Common symptoms include bleeding of the umbilical cord at birth, traumatic and surgical bleeding, GI tract, oral and mucosal bleeding, spontaneous splenal rupture, and rarely intracranial hemorrhage and articular bleeding. Symptoms of hypofibrinogenemia varies from mild to severe, but can include bleeding of the GI tract, oral and mucosal bleeding, and very rarely intracranial bleeding. More commonly it presents during traumatic bleeding or surgical procedures. Most cases (60%) of dyfibrinogenemia are asymptomatic, but 28% exhibit hemorrhaging similar to that described above while 20% exhibit thrombosis (i.e. excessive clotting).

Treatment

The most common type of treatment is cryoprecipitate or fibrinogen concentrate drip to increase fibrinogen levels to normal during surgical procedures or after trauma. RiaSTAP, a factor I concentrate, was approved by the U.S. FDA in 2009 for use in cases where the fibrinogen level was below 50 mg/deciliter of plasma. Recently, antifibrinolytics have also been used to inhibit fibrinolysis (breaking down of the fibrin clot). In the case of dysfibrinogenemia that manifests by thrombosis, anticoagulants can be used. Due to the inhibited clotting ability associated with a- and hypofibrinogenemia, physicians advise against the use of Aspirin as it is known to inhibit platelet function.