Definition
Von Willebrand disease (vWD) is an inherited disorder that causes there to be too little of a certain adhesive protein, called von Willebrand factor (“vWF”), in the bloodstream. Von Willebrand factor is necessary for normal platelet-collagen binding at sites of injury to small blood vessels – in other words, dogs need sufficient vWF in order for their blood to clot properly. Dogs with von Willebrand disease have bleeding disorders that range from mild to very severe.
How von Willebrand Disease Affects Dogs
Von Willebrand disease is the most common hereditary blood clotting disorder in dogs. The condition is found in males and females alike, and a number of breeds are predisposed. Severe forms of the disease usually are evident by one year of age and typically include recurrent episodes of spontaneous bleeding, normally from mucosal areas such as the gums and in the form of “nose bleeds” or internal gastrointestinal bleeding. Dogs with severe disease also tend to have prolonged bleeding when they lose their “baby teeth” and also from minor wounds and surgical incisions. Dogs with mild to moderate forms of the disease may not be diagnosed for many years – and even then, often only after surgery or traumatic injury such as lacerations, bites or being hit by a car. Intact females may bleed excessively during their heat cycles. Regenerative anemia is a common consequence of these bleeding episodes in affected animals.
Causes of von Willebrand Disease in Dogs
Von Willebrand disease is caused by genetic mutations that impair the synthesis, release, function or stability of von Willebrand factor. Males and females express and transmit the genetic mutation to their offspring with equal frequency. There are three recognized classifications of vWD, and affected breeds tend to separate into one of those three categories. Type 1 vWD is a quantitative reduction in the amount of circulating vWF and typically causes mild to moderate disease. It is the most common form of the condition, affecting many breeds. Type 2 vWD is both a quantitative and a functional defect in vWF and causes severe signs primarily in German wireharied and shorthaired pointers. Type 3 vWD also causes severe disease and predominates in Chesapeake retrievers, Dutch Kooikers, Scottish terriers, Shetland sheepdogs and occasionally in other breeds. It is a complete absence of detectable vWF in the dog’s blood.
Preventing von Willebrand Disease
Because of the strong genetic component to this disease, the only realistic way to prevent it is to remove clinically affected animals from breeding programs. To prevent the abnormally profuse bleeding caused by vWD, dogs in predisposed breeds should be screened before surgery to ascertain whether they are deficient in von Willebrand factor.
Special Notes
Veterinarians have several fairly non-invasive ways to diagnose vWD. A DNA test is also available that can give valuable information to breeders. Dogs known to be affected can be given certain clotting factors and medications intravenously before surgery to prevent dangerous bleeding episodes; blood transfusions are available as well. Most dogs with vWD have a good prognosis, and with diligence and the proper precautions, surgery and treatment of incidental trauma can be performed safely.