Genetic Disorders Affecting Equine Blood Cells and Coagulation Factors: A-State-of-The-Art Review

Genetic diseases that affect blood cells and clotting factors in the horse are uncommon. Unfortunately, the prognosis is reserved, because the treatment in many cases is only symptomatic and when it fails, euthanasia of the patient is the only viable option. The detection of carriers is of pivotal importance in order to prevent the spread of these disorders in the equine population. This manuscript reviews the current state of knowledge of genetic diseases that affect red blood cells, leukocytes, platelets and clotting factors in the horse. The genetic diseases that affect equine red blood cells are defects in the activity of enzymes and cofactors involved in erythrocytes metabolism, such as glucose 6 phosphate dehydrogenase, flavin adenine dinucleotide, glutathione reductase and glutathione. Therefore, their deficiency triggers methemoglobinemia and hemolytic anemia. Genetic disorders affecting granulocytes are rare in horses, but a Pelget-Hüet anomaly has been reported. Primary immunodeficiencies described in horses and arising from defects in the immune system are severe combined immunodeficiency, X-linked agammaglobulinemia and Fell pony immunodeficiency syndrome. Because of the immunodeficiency, foals usually develop fatal infections during the first weeks or months of life, caused for opportunistic organisms. Prognosis of these animals is poor. The most common genetic defect of platelet is Glanzmann thrombasthenia, which results in prolonged bleeding time and hematoma formation. Spontaneous bleeding or impaired hemostasis after trauma or surgery are clinical findings in types 1 and 2 von Willebrand disease. Hemophilia A, resulting from a decreased activity of coagulation factor VIII has also been described in male horses of different breeds, being the most common genetic disorder affecting coagulation factor in the horse. Prekallikrein deficit, although described in some horses, is a rare genetic coagulation factor deficiency.