Von Willebrand Disease

In 1926, Finnish physician Erik von Willebrand reported a new type of inherited bleeding disorder that was distinct from hemophilia A.6 Thirty years later, the plasma protein that is central to the disease was identified and was named von Willebrand factor (VWF).5 Von Willebrand factor is a plasma glycoprotein that is synthesized by endothelial cells of the blood vessels. It performs two main functions: binding to the injured vessel wall creating a surface to which platelets adhere, and carrying coagulation factor VIII. The defect in von Willebrand factor is caused by a genetic abnormality in thrombocytes (platelets) that normally form the first line of defense against excessive bleeding whenever a blood vessel is ruptured. 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.

>von Willebrand Disease, also known as von Willebrand's Disease, is the most common canine bleeding disorder that has been reported in over 50 breeds. There are three subtype classifications, which are dependent on the severity of clinical signs, mode of inheritance, and biochemical abnormalities of von Willebrand factor. The 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. In most cases, the puppies inherit 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%. There is a mild bleeding tendency. Type 1 has been observed in many canine breeds and in cats. Type 2 is seen in the German Shorthaired and Wirehaired Pointers and characterized by moderate bleeding. Type 3 has been observed in the Scottish Terrier, Chesapeake Bay Retriever, and Shetland Sheepdog. There is a moderate bleeding tendency with VWF 0 percent.



Any dog that requires surgery should be pre-tested for this problem. 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 has been linked to von Willebrand disease, thyroid profiles may 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
  5. von Willebrand factor: an emerging target in stroke therapy




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