Von Willebrand disease type I (VWDI) is an inherited bleeding disorder affecting many breeds of dog. Dogs affected with VWDI have less than half of the normal level of von Willebrand coagulation factor (vWf), which is an essential protein needed for normal blood clotting. There is variability in the amount of vWf such that not all dogs with two copies of the Mutation are equally affected. Dogs that have less than 35% of the normal amount of vWf generally have mild to moderate signs of a bleeding disorder. Affected dogs may bruise easily, have frequent nosebleeds, bleed from the mouth when juvenile teeth are lost, and experience prolonged bleeding after surgery or trauma. Less often, the bleeding may be severe enough to cause death. Due to the variable severity of the disorder, affected dogs may not be identified until a surgery is performed or trauma occurs at which time excessive bleeding is noted. Veterinarians performing surgery on known affected dogs should have ready access to blood banked for transfusions. Most dogs will have a normal lifespan with this condition despite increased blood clotting times.
Breed-Specific Information for the Brazilian Terrier
The Mutation of the VWF gene associated with von Willebrand disease I has been identified in Brazilian terriers. Though the exact frequency in the overall Brazilian terrier population is unknown, 1 out of 107 Brazilian terriers tested were carriers of the mutation.
Genetic testing of the VWF gene in Brazilian terriers will reliably determine whether a dog is a genetic Carrier of von Willebrand disease I. Von Willebrand disease I is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs rarely have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the VWF gene mutation. Reliable genetic testing is important for determining breeding practices. Because symptoms may be mild in affected dogs, genetic testing should be performed before breeding. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Brazilian terriers that are not carriers of the mutation have no increased risk of having affected pups.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
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