Canine von Willebrand Disease
- Clinical Signs
- Laboratory Diagnosis
- Inheritance & Breeding Recommendations
- Breed Summaries
von Willebrand Disease (abbreviated vWD) is an inherited bleeding disorder caused by lack of von Willebrand factor protein (vWF). This protein circulates in the blood stream and must be present at the site of blood vessel injury in order to control bleeding from that vessel. Von Willebrand disease is a distinct disorder, it is not hemophilia.
There are three variants or forms of vWD (types 1,2,3) defined by the quantity and structure of plasma von Willebrand factor (abbreviated vWF) in affected dogs. Within each breed a single form of vWD predominates. Characteristic biochemical and clinical findings have been described in a number of breeds with high prevalence and/or severe forms of vWD.
|Classification||vWF concentration/ structure||Clinical Severity||Affected Breeds|
|Type 1||low concentration/ normal structure||variable||Airedale, Akita, Bernese Mountain Dog, Dachshund, Doberman Pinscher, German Shepherd, Golden Rertiever, Greyhound, Irish Wolfhound, Manchester Terrier, Schnauzer, Pembroke Welsh Corgi, Poodle, Shetland Sheepdog and others|
|Type 2||low concentration/ abnormal structure||severe||German Shorthaired Pointer, German Wirehaired Pointer|
|Type 3||vWF markedly reduced or absent||severe||
Chesapeake Bay Retriever, Dutch Kooiker, Scottish Terrier, Shetland Sheepdog
Blue Heeler, Border Collie, Bull Terrier, Cocker Spaniel, Labrador Retriever, mixed breed, Pomeranian and others
Clinical signs of vWD range from a mild to severe bleeding tendency. Dogs may "carry" the vWD trait without expressing a bleeding tendency. Severe vWD causes spontaneous bleeding from the nose, mouth, and urinary, reproductive or intestinal tracts. Uncontrollable bleeding may occur after surgery. Dewclaw removal and teething may cause excessive bleeding in vWD-affected pups. Infections, endocrine disorders, and certain medications may exacerbate signs of bleeding in vWD-affected dogs.
Shetland sheepdog affected with
severe (type 3) vWD
Severe bruising along incision line after
ovariohysterectomy (spay). Bruising occurred in
spite of pre-operative transfusion.
Treatment of a severe bleeding episode requires transfusion of canine blood products. There is no drug, vitamin, hormone, or dietary modification that can induce production of vWF. Bleeding from minor injuries may be controlled using sutures, bandages or wound glue. Affected dogs should not be given drugs that interfere with normal blood clotting mechanisms. These drugs include aspirin, sulfa-type antibiotics, and heparin.
Laboratory diagnosis of vWD is most often based on results of von Willebrand factor antigen assay (abbreviated vWF:Ag). This test measures the amount or concentration of vWF in a blood sample. The Comparative Coagulation Section reports each dog's result as %vWF:Ag compared to a 100% standard. Dogs having low plasma vWF:Ag (below 50%) are at risk for transmitting or expressing the vWD trait. In general, the most severely affected dogs have marked reduction in plasma vWF:Ag, with values of less than 15%.
The methods used to draw, process, and ship samples are important for accurate results. Samples containing clots or hemolysis (red cell breakdown) are the most likely to yield inaccurate or unreproducible results. Use of a standard sampling technique ensures optimum sample quality.
Plasma vWF levels fluctuate from day to day in normal, healthy dogs. This fluctuation is exaggerated during pregnancy or heat in bitches, and in any dog having a systemic illness (especially liver disease or inflammatory disorders). Baseline values of vWF:Ag are more accurate genetic predictors for vWD status, therefore samples for genetic screening should be drawn from healthy dogs and bitches not pregnant or in heat. Puppies can be sampled as young as 6 to 8 weeks of age.
Diagnostic ranges of vWF:Ag are used to identify vWD-affected dogs and as an aid for predicting genetic status for the vWD trait in asymptomatic dogs.
|Normal||70 to 180|
|Borderline||50 to 69|
|Abnormal||0 to 49|
Dogs testing in the normal range are considered clear of the vWD trait, and at low risk for expressing or transmitting vWD.
Dogs testing in the borderline range can not be accurately classified as carrier or clear on the basis of that measurement. This is an overlap region of plasma vWF:Ag, where some individuals are clear and some carriers of vWD. On a second test, some dogs fall in the normal or abnormal range, thereby enabling a prediction of their genetic status. A test mating can be performed by breeding a borderline range dog to a high-testing clear mate. If the borderline parent is clear of vWD, then all pups in the litter are predicted to be clear. The presence of 1 or more abnormal range pup indicates that the borderline parent is a carrier of vWD. Dogs testing in the borderline range are not expected to have a bleeding tendency. They need no restriction on activity or special management.
Dogs testing in the abnormal range are considered carriers of the vWD trait. They are at risk for transmitting an abnormal vWF gene to offspring, and some will express a bleeding tendency. Dogs affected with the most severe form of vWD (type 3 vWD) have very low values of vWF:Ag (1% or less). Severely affected dogs should not undergo surgical procedures without transfusion.
Inheritance and expression patterns of vWD differ between breeds. All males and females have 2 vWF genes, one inherited from dam and one from sire. In many breeds, the presence of 1 abnormal vWF gene appears sufficient to cause abnormal bleeding in some (but not all) dogs. Dogs having 2 abnormal genes express the most severe forms of vWD.
Breeding Recommendations Use vWD diagnostic ranges as guidelines to reduce the prevalence of vWD within a family or line, without discriminating against all dogs in that line. Screening for vWD will ensure that no severely affected puppies are produced.
Dogs that test in the normal range (vWF:Ag greater than 70%) are ideal for use in breeding programs. Matings between 2 vWD test-clear parents are predicted to produce only vWD clear pups. Progeny testing (testing parents and entire litter) is useful for confirming predicted genetic status based on a single vWF:Ag value. Progeny testing can help clarify the status of a borderline range parent.
In some cases, dogs that test in the vWD abnormal range (provided they do not express a bleeding tendency) may also be used for breeding. Carriers should be bred to test-clear, and ideally progeny test proven clear mates. Some puppies in these matings will test in the normal range. By increasing the number of clear to clear matings in subsequent generations, the proportion of vWD carriers in a line will be gradually reduced, without losing desirable traits. Carrier to carrier matings are undesirable, because these crosses are likely o produce the most severe form of vWD in offspring. Do not breed any dog that expresses abnormal or excessive hemorrhage.
Bernese mountain dog