von Willebrand Disease

Von Willebrand Disease (or von Willebrand's Disease) is the most common canine bleeding disorder. Platelets or thrombocytes (blood cells) normally form the first line of defense against excessive bleeding whenever a blood vessel is ruptured. There are several abnormalities attributable to failure of the platelets to function as they should. One of them is when genetic mutation results in premature termination of von Willebrand factor (VWF) protein synthesis.

Von Willebrand factor is a plasma glycoprotein that is synthesized by endothelial cells of the blood vessels. Von Willebrand factor performs two main functions: it binds to the injured vessel wall creating a surface to which platelets adhere, and it carries and protects coagulation factor VIII.

Types of von Willebrand Disease

There are three subtype classifications which are dependent on the severity of clinical signs, mode of inheritance, and biochemical abnormalities of von Willebrand factor (VWF):

1. Type 1 has been observed in many canine breeds and in cats. There is a mild bleeding tendency.
2. Type 2 has been observed in German shorthaired and wirehaired pointers. There is a moderate bleeding tendency.
3. Type 3 has been observed in Scottish terriers, Chesapeake Bay retriever and Shetland sheepdog. There is a moderate bleeding tendency. Von Willebrand factor is usually 0 percent.

The abnormal gene can be inherited from one or both parents. If both parents pass on the gene, most of the puppies will fail to thrive and die. In most cases, the puppies inherits a relative lack of blood clotting ability, which is quite variable. For instance, one dog may have 15% of the clotting factor, while another might have 60%.

The higher the amount, the less likely it will be that the bleeding will be readily evident, since spontaneous bleeding is usually only seen when dogs have less than 30% of the normal level of von Willebrand clotting factor. Thus, some dogs don't get diagnosed until they are neutered or spayed, in which case they end up bleeding uncontrollable or they develop pockets of blood (hematomas) at the surgical site.

Signs

Bleeding from mucous membranes, nose or mouth, skin bruising, and prolonged bleeding from sites of trauma or surgery. Bleeding can be mild (common) or severe (uncommon). Bleeding can become worse because of using non-steroidal anti-inflammatory drugs.

Treatment

Although the clotting time can be corrected to some extent by blood transfusion from healthy dogs, there is no cure for this disease.

Any dog that requires surgery should be pre-tested for this problem.

Breeds at Risk

Von Willebrand Disease has been reported in many (over 50) breeds, which include:

Doberman Pinscher, French Bulldog, Great Danes, Shih Tzu, Poodle (all sizes), German shorthaired and wirehaired pointers, Scottish terriers, Chesapeake Bay retriever, Rottweilers, and Shetland sheepdog.

Different breeds have different subtypes of VWF deficiency. Von Willebrand Disease in the Scottish Terrier breed is a serious, often fatal, hereditary bleeding disorder. Elimination of the mutated gene by selective breeding is an important goal for the health of this breed. Although the standard protein-based tests are accurate for identification of affected Scottish Terriers, they are not reliable for the identification of carriers of the mutant gene unless multiple replicate assays are performed.

Testing for von Willebrand Disease

There are tests available to determine the amount of von Willebrand factor in the blood and they are accurate and reasonably priced.

Carriers should not be used for breeding even though they appear normal. Since hypothyroidism can be linked to von Willebrand disease, thyroid profiles can also be a useful part of the screening procedure for predisposed breeds.

References

1. Lowell Ackerman. Dr. Ackerman's Book of the Great Dane
2. Denis CV. Molecular and cellular biology of von Willebrand factor
3. Sabino EP, Erb HN, Catalfamo JL. Development of a collagen-binding activity assay as a screening test for type II von Willebrand disease in dogs
4. Venta PJ, Li J, Yuzbasiyan-Gurkan V, Brewer GJ, Schall WD. Mutation causing von Willebrand's disease in Scottish Terriers