Von Willebrand's Disease (vWD)
Von Willebrand's disease has been identified in a wide range of canine breeds, and is the most common of the inherited bleeding disorders. As with humans, there are three classifications of this disease, Types I, II, and III. These are based on the concentration and nature of plasma vWF. Type I vWD is characterized by abnormally low concentrations of structurally normal vWF, and tends to be a milder and more variable form. Type II vWD is characterized by structurally abnormal vWF, which impedes function and results in severe bleeding in affected animals. Type III vWD is found in animals that have essentially no plasma vWF. The disease has been reported in many breeds of dog, and is generally diagnosed by an ELISA test for plasma vWF following a bleeding event.
Five mutations have been identified that cause vWD in canines. Direct DNA tests have been developed for all five of these mutations that allow unambiguous delineation of the genetic status of the animal, which is not always possible with the ELISA test due to temporal variations in the amount of circulating vWF. These five mutations are responsible for the vast majority of vWD in at least the fifteen breeds discussed in this poster, and probably others, which have yet to be tested. All five may be classified as recessively inherited resulting in clear, carrier, or affected status.
While carriers do exhibit a reduction in the amount of plasma vWF, it is not enough to make them symptomatic. It should be noted that affected status in the case of these tests means the animal carries two copies of the mutant allele, not necessarily that the disease is manifest. In the case of the severe Type II and III diseases any "affected" animal will almost certainly experience a severe bleeding incident. In the case of the milder and more variable Type I disease, "affected" animals are obviously at risk, but may or may not have a severe bleeding incident.
VetGen has now being offering DNA testing for vWD for more than ten years, and has tested over 20,000 dogs.
Canine: vWD Patents
US Patent No. 6,040,143 and 6,074,832
Canadian Patent No. CA 2261015
European Patent No. EP 0961836
Licensed Exclusively by The Board of Regents of the
University of Michigan (Ann Arbor, MI) System to VetGen LLC