von Willebrand's Disease Type I Overview
von Willebrand's Disease Type I
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Category: Haemolymphatic - Associated with the blood and lymph
Variant Detected: c.7437G>A
Severity: Scale 4 has a high degree of severity. It generally causes a decreased quality of life and may also decrease the life expectancy.
Mode of Inheritance: Autosomal Recessive with Incomplete Penetrance
Test Overview: Von Willebrand’s disease is the most common inherited bleeding disorder in dogs and occurs when there is a lack of functional von Willebrand factor. Von Willebrand factor is needed for the normal adhesion of platelets, and therefore clotting of blood. There are 3 types of von Willebrand’s disease, and type 1 von Willebrand’s disease is the most common. This type is where there is an overall lack of structurally normal von Willebrand factor. It has been reported in over 60 breeds, as well as mixed breed dogs. Not all pups are affected equally when they have von Willebrand’s disease, as the decrease in amount of von Willebrand factor can vary quite a lot. The genetic abnormality has also been described as autosomal dominant with incomplete penetrance, which leads to the high variability in expression. Different mutations have been reported. Some breeds are affected from birth, while others may not be affected until adulthood, or even middle age. DNA tests are available for some breeds, but some dogs that test “positive” may have severe disease, while others may never develop any bleeding tendency. Other dogs are diagnosed by a von Willebrand factor assay, which expresses the level of von Willebrand factor as a percentage. Levels of von Willebrand factor are less than 50% in affected animals, but animals have an increased risk of haemorrhage (i.e. abnormal bleeding tendency) when levels are less than 25-35%. Severe bleeding tendencies are usually associated with levels less than 10-20% (depending on breed). Von Willebrand factor assays are quite variable within an individual, and can be affected by a number of factors, hence repeat testing can be necessary. Signs of von Willebrand’s disease are generally those of abnormal bleeding or prolonged periods of bleeding. If undiagnosed, affected dogs can suffer life-threatening haemorrhage at times of routine surgery or after a traumatic event. Treatment can often be required with blood or plasma transfusions. It is generally recommended to test for this disease (or at least test bleeding times) prior to routine surgery in breeds with a high incidence of the disease (e.g. the Dobermann) and have appropriate transfusion products available in case of a bleeding episode.
Recommended Screening: 1. DNA testing of all breeding animals performed prior to breeding - e.g. at 1 year of age. 2. Recommend von Willebrand factor levels and/or BMBT measured prior to surgery (e.g. desexing).
Research Citation(s): Am J Vet Res. 2001 Mar;62(3):364-9; Moser, J., Meyers, K.M., Meinkoth, J.H., and Brassard, J.A. (1996). Temporal variation and factors affecting measurement of canine von Willebrand factor. American Journal of Veterinary Research 57, 1288–1293. Venta, P.J., Li, J., Yuzbasiyan-Gurkan, V., Brewer, G.J., and Schall, W.D. (2000). Mutation causing von Willebrand’s disease in Scottish Terriers. J. Vet. Intern. Med. 14, 10–19.
Associated Breed(s): Bernese Mountain Dog, Coton De Tulear, Dobermann, Goldendoodle, Kerry Blue Terrier, Labradoodle , Manchester Terrier , Papillon, Pembroke Welsh Corgi, Toy Poodle, Miniature Poodle, Standard Poodle, Scottish Terrier , Spoodle, West Highland White Terrier , White Swiss Shepherd, Australian Terrier, Mixed Breed, English Toy Spaniel , Australian Labradoodle , Groodle, Cavoodle, German Spitz ,