Congenital Afibrinogenemia, Factor I Deficiency
Inherited coagulation disorders have been diagnosed in many breeds of dogs as well as in mongrels and cat. Congenital afibrinogenemia (also called factor I deficiency) is a relative lack of fibrinogen in the blood due to the defective fibrinogen synthesis. It may be the result of a congenital (primary) blood abnormality or an acquired disorder. Deaths attributable to afibrinogenemia are associated with bleeding, most commonly postoperative bleeding and intracranial bleeding.
Fibrinogen is a glycoprotein that circulates in plasma. The primary physiological role of fibrinogen is in maintaining normal blood clotting. In the final step of the coagulation process, fibrinogen is converted to fibrin, with formation of a fibrin clot. The fibrin clot has an essential role in limiting bleeding at sites of blood vessel injury; it also provides the structure for assembly and activation of the fibrinolytic proteins. 1 Fibrinogen is synthesized by liver cells which explains a large number of defective or abnormally low number of fibrinogens known to occur in underlying liver disorders.
Hereditary fibrinogen deficiencies are autosomal incompletely dominant or recessive traits. Inherited hypofibrinogenemia (low fibrinogen levels) has been detected in Vizsla, Lhasa Apso and Collie. Hypofibrinogenemia is associated with mild bleeding episodes triggered by stress, trauma or surgery.
Signs of Congenital Afibrinogenemia
In afibrinogenemia bleeding manifestations range from mild to severe. Umbilical cord bleeding frequently provides an early alert to the abnormality. To prevent excessive bleeding during surgical procedures, prophylactic treatment to raise fibrinogen levels during the procedure is performed. Replacement is continued for 4-14 days following surgery, depending on the nature of the surgical procedure and time to complete healing.
Factor I Deficiency has been reported in goats and dogs. In dogs, the disorder is manifested by severe bleeding episodes and low fibrinogen levels in plasma. It is characterized by bleeding from mucous membranes into the joints and muscle tissues. The disease has been described in Saint Bernard dogs but it also occurs in other breeds. 2 The treatment of choice for severe fibrinogen defects is fresh-frozen plasma. 3
Adapted from
'1. Sara J Israels, MD, FRCPC. Inherited Abnormalities of Fibrinogen. emedicine.comNov 8, 2007
'2. Thomas Carlyle Jones, Ronald Duncan Hunt, Norval W. King. Veterinary Pathology. p.166
'3. Bernard F. Feldman, Joseph G. Zinkl, Nemi Chand Jain. Schalm's Veterinary Hematology. p. 1031
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