Predisposing factors

General

• An autosomal recessive disorder of domestic shorthairs and domestic longhairs.

• Also reported in Siamese and Himalyan cats.
  Likely to be potentially identified in any breed.

Pathophysiology

• An autosomal recessive genetic trait.

• The exact defect is not known in cats. Factor XII is a zymogen that is converted into the active enzyme by proteolysis. This should happen when it is exposed to negatively charged surfaces such as collagen in the subendothelial matrix or antigen-antibody complexes. Activated factor XII is one element that can initiate the intrinsic pathway of coagulation.
• Because the intrinsic pathway can be stimulated in other ways, eg by tissue factor, factor III or factor VII, factor XII seems not to be essentialin vivo. Indeed many species seem not to have factor XII.
• Thus factor XII deficiency is asymptomatic despite prolongation of clotting timesin vitro.
• Factor XII deficiency has also been detected in FIV positive cats Feline immunodeficiency virus. It is not clear whether this is coincidental or connected with the virus.

Epidemiology

• Factor XII deficiency has been reported in combination with factor VIII:C deficiency (combined hemophilia A and Hageman factor deficiency). This is a condition that is expected to cause some bleeding problems after challenge from trauma or surgery. It has been reported in domestic shorthaired cats and results in a normal prothrombin time Hematology: prothrombin time and a prolonged activated partial thromboplastin time Hematology: activated partial thromboplastin time.
• Combined hemophilia B and Hageman factor deficiency has also been reported in Siamese cats and domestic shorthaired cats. These cats have deficiencies of factor IX and XII and are expected to have quite serious bleeding tendencies after surgery or trauma. They will have a prolonged activated partial thromboplastin time.