BASICS
- Several rare inherited coagulation deficiencies occur in horses:
- vWD (vWF deficiency)—vWF is involved in platelet adhesion, and this defect results in abnormal platelet adhesion and platelet plug formation
- Glanzmann thrombasthenia is a deficiency/dysfunction of the platelet glycoprotein IIb/IIIa complex, critical to platelet adhesion and aggregation
- Hemophilia A (factor VIII deficiency) results in a defect in the intrinsic coagulation pathway, with deficient clot formation
- Prekallikrein deficiency leads to defective initiation of the intrinsic coagulation pathway as this glycoprotein stimulates activation of factor XII
- Protein C deficiency results in a hypercoagulable state and thrombotic events, as protein C is a critical coagulation inhibitor
- Most disorders are inherited in an autosomal recessive pattern and occur in young purebred horses
- Hemophilia A is most common, and has been diagnosed in Thoroughbred, Standardbred, Quarter Horse, Tennessee Walking Horse, and Arabian colts. It is an X-linked recessive chromosomal abnormality usually evident in colts <6 months of age (up to 3 years)
- Prekallikrein deficiency has been reported in families of American Miniature and Belgian horses, affecting males and females. Horses with signs are homozygous, while heterozygous horses are asymptomatic
- vWF deficiency has been reported in young Quarter Horses and Thoroughbreds
- Glanzmann thrombasthenia has been reported in young and adult horses (Thoroughbred cross; Quarter Horse; Peruvian Paso; Oldenburg)
- Protein C deficiency has been diagnosed in a Thoroughbred colt
There are 3 clinical forms:
- When the defect affects platelet function or primary hemostasis (e.g. vWF deficiency, Glanzmann thrombasthenia), signs are spontaneous epistaxis or bleeding involving mucosal surfaces and prolonged bleeding after trauma/surgery. Petechiae may be observed
- When the defect affects clot formation or secondary hemostasis (e.g. hemophilia A), signs are a bleeding tendency with spontaneous hemorrhages or prolonged bleeding after trauma/surgery. Bleeding into body cavities, joints, muscles, and subcutaneously is common
- When the defect is related to a coagulation inhibitor defect (e.g. protein C deficiency), signs are related to the subsequent hypercoagulable state (thrombosis)
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS