Interpreting DNA Test Results for Von Willebrands Disease

(Information via Vet-Gen)                                                                  
  
 

What is von Willebrand's disease?

Von Willebrand's disease (vWD) is a common, usually mild, inherited bleeding disorder in people and in dogs. It is caused by a lack of von Willebrand factor (vWF), which plays an essential role in the blood clotting process.

Normally the body responds to an injury causing bleeding through a complex defence system. This consists of local changes in the damaged blood vessels, activation of blood cells called platelets, and the coagulation process. A reduction in von Willebrand factor leads to abnormal platelet function and prolonged bleeding times. 

Three forms of the disease are distinguished based on vWF concentration and function. Dogs with Type I vWD (by far the most common) have mild to moderate bleeding abnormalities, depending on the level of vWF. The much rarer types II and III vWD cause severe bleeding disorders.

von Willebrand's Disease: 

Unfortunately, there is no such thing as a perfect dog of ANY breed. Canine geneticists estimate that the average purebred dog is carrying at least 4-5 defective genes, even grand champions. Today’s breeders make the best breeding decisions they can based upon testing results, conformation, temperament, working ability, pedigree, etc. A good breeder is open and honest about the health status of all their dogs and is always willing to help and guide the new puppy owner.

von Willebrand's Disease is one of the least destructive diseases inherited by Dobermans but it should not be ignored. It is a genetically inherited autosomal recessive bleeding disorder much like hemophilia and is the most common bleeding disorder in canines and in humans. It affects some 60 different breeds of dogs including the Doberman Pinschers and Sheltie's and because it is genetic in nature, there is no cure only eradication by deliberate breeding strategies. It is passed on directly from one generation to the next and will affect offspring to varying degrees. 

Although Dobermans are one of the breeds most commonly affected by von Willebrand's, they usually have only the milder form (Type I). Other breeds suffer from type II (moderate to severe form and extremely rare being found only in German Shorthaired Pointers and German Wirehaired Pointers) and still others are well known to suffer from type III (severe but rare). 

Under normal circumstances, type I means that bleeding will clot normally. However, in times of stress or with major blood loss during surgery or as a result of trauma, the defect may become “clinically” apparent with the inability to clot. Bleeding tendencies can be exacerbated by medications or by stress such as illness, particularly viral disease since viral infections can prolong clotting times by impairing platelet cohesiveness and/or endothelial cell production in the blood vessel walls (the endothelial cells produce the protein called von Willebrand's factor which is necessary for normal clotting). Because Parvovirus attacks the gastrointestinal tract where it causes bleeding, it is especially dangerous to Dobermans. Live virus vaccines can have the same effect.

There are 3 classifications of type I vWD dogs: Clear, Carrier and Affected. As of January 2004, VetGen states that of the Dobermans it has tested, 25% of Dobermans were classified as clear, 49% were carriers and 26% were classified as affected.

What breeds are affected by von Willebrand's disease?

Type I vWD: This is by far the most common form. The gene for the condition is widespread in the Doberman pinscher population, and is also relatively common in the Scottish terrier and Shetland sheep dog.  There is an increased risk of the disorder in the Golden retriever, standard and miniature poodle, Welsh Pembroke corgi, miniature Schnauzer, basset hound, German shepherd, Rottweilers, Manchester terrier, Keeshond, and standard and miniature dachshund. This disease occurs in most other breeds and in mixed-breed dogs as well.

Type II: extremely rare, German short-haired pointer 

Type III: rare, occurs in the Scottish terrier, Shetland sheepdog, and very sporadically.

What does von Willebrand's disease mean to your dog & you?

Although many dogs are affected by vWD, only a small proportion have any problems.  Some dogs with vWD are prone to nose bleeds, bleeding from the gums, and prolonged bleeding during heat or after whelping. There may be prolonged bleeding from the umbilical cord at birth or when your pup sheds its baby teeth. Excessive bleeding after surgery or trauma is common, and may be the first sign of this condition in your dog. You may see blood in your dog's urine or stool. 

Most dogs with vWD lead normal lives (and many are un-affected by these syptoms) with occasional bleeding episodes that may go unnoticed or can be treated appropriately. 

How is von Willebrand's disease diagnosed?

There are specialized tests available to make the diagnosis of von Willebrand's disease. One is a genetic test and the other measures blood levels of von Willebrand factor. 

The trait for von Willebrand's disease is widespread, particularly in Doberman pinschers but also in several other breeds. An accurate genetic test has been developed for the Doberman pinscher, Scottish terrier, Shetland sheepdog, Manchester terrier, poodle, and Pembroke Welsh corgi. Testing can reliably identify dogs with vWD, dogs that are carriers, or dogs that are clear. 

 

There are three possible test results: Clear, Carrier, and Affected.  
Below is a description of what each result means to you as a owner/breeder.

CLEAR: This finding indicates that the gene is not present in your dog.  
Therefore, when used for breeding, a Clear dog will not pass on the disease gene.

CARRIER:  This finding indicates that one copy of the disease gene is present in your dog, but that it will not exhibit disease symptoms. Carriers will not have medical problems as a result. Dogs with Carrier status can be enjoyed without the fear of developing medical problems but when bred will pass on the disease gene to 50% of thier offspring.

AFFECTED:  This finding indicates that two copies of the disease gene are present in the dog. These dogs always have a potential to bleed given the right circumstance and will always pass on the disease gene (mutation) to their progeny. 

Please see the following page, and follow all the links for more detailed information. http://www.vetgen.com/vwdrpt.html  Also, inform your veterinarian and consult with him/her regarding this test result.

Breeding Strategies… 

VetGen's DNA test findings can be extremely valuable when developing and implementing your breeding plans.  
The chart provided below outlines the implications of various breeding pair combinations. Remember, it is always best to breed "Clear to Clear". If followed by all breeders, these strategies will ensure a significant reduction in the frequency of the targeted disease gene in future generations of dogs. However, to maintain a large enough pool of good breeding stock, it is necessary for some breeders to breed "Clear" to "Carriers" (see below). 
 

Breeding Pair Combinations: 
 

 

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Ideal Breeding Pair. Puppies will not have the disease gene (neither as Carrier nor as Affected).

Breeding Is Safe. No Affected puppies will be produced. However, some or all puppies will be Carriers. Accordingly, it is recommended that Carrier dogs which are desirable for breeding be bred with Clear dogs in the future, which will produce 50% carrier and 50% clear animals, to further reduce the disease gene frequency. These offspring should be tested by VetGen's test for this defective gene, and if possible, only the clear animals in this generation should be used.

High Risk Breeding. Some puppies are likely to be Carriers and some puppies are likely to be Affected. Even though it is possible that there will be some clear puppies when breeding "Carrier to Carrier", in general, neither this type of breeding pair nor "Carrier to Affected" are recommended for breeding. 

Breeding Not Recommended. All puppies will be genetically Affected.