Von Willebrand Disease Testing in Whippets
copyright 2003, Adele C. Monroe, DVM, MSPH

(published in The Whippet Watch, volume 4, issue 6, 2003)

Note: Excellent information on canine von Willebrand disease can be found at the web site for the Comparative Coagulation Section of Cornell veterinary school's diagnostic laboratory: see Background, Laboratory Diagnosis (see the link to standard sampling technique), and Inheritance & Breeding Recommendations. (http://web.vet.cornell.edu/public/coaglab/clinical_topics/vWD.htm)

Von Willebrand disease (vWD) is an inherited blood clotting disorder characterized by reduced production of von Willebrand factor (vWF), a complex protein that is essential to blood clotting. Three types of von Willebrand disease have been identified in purebred dogs. Type I, the most common form, has variable severity and occurs in many breeds including the Doberman Pinscher. In type I vWD, the dog produces low concentrations of vWF that has normal structure. In Type II vWD, a dog produces low concentrations of vWF that has an abnormal structure, which adds to the severity of the disease. In type III vWD, dogs produce little or no vWF. Dogs with type II and type III vWD experience severe clinical disease. The type found in whippets has not been verified, largely because whippets with a clinical bleeding problem are uncommon. Because type I vWD is the most common form of the disease and clinical severity varies from mild to more serious, it is reasonable to presume that whippets have type I vWD until evidence to the contrary is found.

vWD is caused by a mutation in a single gene. In type I vWD, each normal gene directs the production of vWF with a normal structure. Clear dogs, those with two normal genes, produce normal amounts of vWF. Carriers, dogs with one normal gene and one defective gene make intermediate amounts of vWF; they typically produce enough to prevent symptoms of a bleeding disorder. Depending on the specific mutation causing vWD, affected dogs (those with two defective genes) may make small amounts of vWF. However, affected dogs are at significant risk of potentially life-threatening bleeding if injured or if they undergo elective surgery such as spaying or neutering.

Two clear parents will produce only clear offspring. If a clear dog is bred to a vWD carrier, each pup has a 50% chance of being clear and a 50% chance of carrying one defective gene—none of the pups will be affected. See Clear to Carrier chart. If two carriers are bred together (not recommended as a general practice), each pup has a 25% chance of being clear (two normal genes), a 50% chance carrying one defective gene and one normal gene, and a 25% chance of being affected (two defective genes). See Carrier to Carrier chart. Type I vWD carriers, with one defective gene, typically live completely normal lives without any restrictions on their activity. They can participate in the full range of performance sports available to dogs. Therefore, in a carrier-to-carrier breeding, each puppy has a 75% chance of living a perfectly normal life. However, the breeder of a carrier-to-carrier mating must be prepared for the birth of one or more affected puppies.

Possible genetic combinations produced in the offspring when at least one parent is a carrier. F = normal gene; f = defective gene; FF = clear; Ff = carrier; ff = affected.

Clear to Carrier. Column headers represent individual genes contributed by the clear parent. Row labels represent individual genes contributed by the carrier parent.

 

F

F

F

FF

FF

f

Ff

Ff

Carrier to Carrier. Column headers and row labels represent individual genes contributed by the parents: both are carriers.

 

F

f

F

FF

Ff

f

Ff

ff

 

Interpreting vWF:Ag Assay Results

The von Willebrand factor antigen (vWF:Ag) assay, which measures the amount of vWF in the blood, is the test most commonly used to diagnose von Willebrand disease. The amount of vWF can vary within an individual dog on a daily basis and the manner in which blood is collected, processed, and stored can influence test results. Predicting genetic status (clear, carrier, or affected) using vWF:Ag assay results is not an exact science. However, the test provides important information that breeders can use in making decisions. The vWF:Ag test is the ONLY test available to evaluate von Willebrand status in breeds for which a DNA test has not yet been developed, including whippets.

Cornell's vWF:Ag assay results are expressed as a percentage. The amount of vWF in each test sample is compared to the amount in a standard reference sample, which is assigned a value of 100%. If the test sample contains more vWF than the standard reference, the results are greater than 100%. Cornell has developed the following categories for test results: normal, 70 to 180%; borderline, 50 to 69%; and abnormal, 0 to 49%.

In theory, carriers produce about half as much vWF as clear dogs. However, the amount of vWF produced by clear, carrier, and affected dogs can vary widely. The following data are from the article "Temporal variation and factors affecting measurement of canine von Willebrand factor" by Moser, Meyers, et al (American Journal of Veterinary Research 1996;57:1288-1293). This article can be downloaded from the VetGen web site (http://www.vetgen.com). Although expressed as units/dl, the numbers in the following tables correspond to Cornell's percentages because the researchers arbitrarily assigned a value of 100 units/dl to their standard reference sample.

Table 1. Affected. Plasma vWF assay results from samples taken daily from dogs affected with type I vWD. (from Table 1 in article)

 

Dog
Number

Average vWF
(U/dl)

Range
(U/dl)

Number of
Samples

1

24

22-30

19

2

16

13-19

17

3

18

15-22

18

4

16

12-23

13

5

20

12-24

17

   

Total

84

Affected dogs, overall range: 12 to 30

 

Table 2. Carrier. Plasma vWF assay results from six pups who were carriers of type I vWD (sire was affected, dam was normal). Blood was drawn from the jugular vein in the neck at 3, 10, 20, 30, 45, 60, and 180 days of age. (from Table 3 in article)

 

Pup
Number

Average vWF
(U/dl)

Range
(U/dl)

Number of
Samples

1

53

37-62

7

2

62

45-71

7

3

74

64-80

7

4

66

62-71

7

5

56

46-66

7

6

59

42-77

7

   

Total

42

Carrier dogs, overall range: 37 to 80

 

Table 3. Normal (presumed clear). Plasma vWF assay results from daily samples taken from six mixed-breed dogs with high vWF values. (from Table 1 in article) This category included only dogs for whom the average vWF assay result was greater than 75. Because they tested consistently high, these dogs are presumed to have two normal genes for vWF. However, genetic testing was not performed.

 

Dog
Number

Average vWF
(U/dl)

Range
(U/dl)

Number of
Samples

1

88

79-106

12

2

125

88-152

13

3

113

93-144

13

4

79

74-91

13

5

79

71-93

13

6

143

118-172

13

   

Total

77

Normal dogs, overall range: 71 to 172

 

The overall ranges indicate the lowest and highest individual values within each group of dogs. Note that the overall range for affected dogs (based on 84 individual samples) did NOT overlap the overall range for carriers. Pay particular attention to the individual ranges. Notice how much variation individual dogs exhibited in this study. In the Carrier table, individual results for pups 2 and 6 spanned all three of Cornell's categories, from abnormal to normal. The average for Carrier pup 3 was 74, and this pup's highest result was 80, well within Cornell's "normal" range (>70%). In addition, carrier pups 2, 4, and 6 each had at least one test result in the "normal" range, although they were known to carry one normal gene and one defective gene.

Intelligent Use of vWF:Ag Assay Results

With so much variation possible, one might question the value of a single assay result in an individual dog. Here's how I look at testing.

Using vWF:Ag results to estimate genetic status is imprecise at best, but that does not mean the test is without value. Cornell's normal range is from 70 to 180%. Because the overall range of carrier pups in the Moser et al study went to 80% and the range is based on only 42 total samples, I feel more confident considering a dog to be clear (probably has two normal genes) if the results of a single test are close to 100% or higher. However, breeding and testing offspring is the only way to determine a whippet’s genetic status. Based on the results of a single test, it is possible that a breeder could breed a dog and bitch with vWF:Ag results in the 70 to 100 range, thinking both parents are clear, when both parents could be carriers, or one could be a carrier and one could be clear, or both could be clear. In one study of Poodles, one of the breeds for which a DNA test is available, one dog with vWF:Ag results in the 100 to 109 range and another with results in the 90 to 100 range tested as carriers on the DNA test (see http://www.vetgen.com/correlat.html).

I am not recommending that whippet breeders "throw out the baby with the bath water" and exclude from breeding all whippets that do not test normal (regardless of where one draws the "normal" line). Clinical von Willebrand disease is not common enough in whippets to warrant such an extreme measure. I suspect this is because most whippets with two defective genes either do not survive puppyhood or they make enough functioning vWF that they do not develop a clinical bleeding problem, although there may be another explanation. If the defective gene is widespread in whippets, as is the case in Dobermans, excluding whippets with subnormal test results from breeding could dangerously restrict the gene pool. However, dogs testing very low (see the Affected table) are at a high risk of developing a clinical bleeding disorder—they should never be bred. Because affected dogs have two defective genes, they will pass along only defective genes to their offspring. Even if bred to a mate that tests high normal (presumed clear), all the offspring of an affected dog will carry one defective gene. Also, pregnancy and whelping could be life-threatening for an affected bitch.

I strongly recommend that whippet breeders test both parents and all the pups in a litter before the pups are placed. Testing parents will give the breeder some idea of what types of test results to expect in the pups. Testing parents and pups will help clarify the genetic status of the parents. Cornell recommends breeding dogs that test in the borderline range (50 to 69%) only to dogs that test in the normal range and then testing the pups. If the normal testing parent is in fact clear, the test results of the pups will help clarify the actual status of the borderline parent (clear or carrier).

Testing pups will enable the breeder to consider vWF along with other factors when deciding which pups to keep as potential breeding stock for the next generation. If a breeder wants to reduce the occurrence of the defective gene in her or his breeding program, keeping a pup that tests 100% (probably clear) is preferable to keeping a pup of comparable quality that tests 56% (likely to have one defective gene).

To develop a DNA test for von Willebrand disease in whippets, VetGen needs samples from whippets that test 20% or lower on the vWF:Ag assay. If whippet breeders are not testing pups and whippet owners are not testing adults, VetGen will not obtain the samples they need to develop a test that can more accurately determine genetic status.

Perhaps the most compelling reason for testing pups is that doing so will enable a breeder to identify pups that are at high risk for developing a clinical bleeding disorder—before they are placed in homes. In this day and age, placing a pup that is later diagnosed with a disorder that is known to be genetic is a liability that most breeders will not want to take on. In a study of Dobermans, pups that tested less than 22% were at higher risk of excessive bleeding during and after ear trimming compared to pups that tested above 38%. Based on the Moser et al study, pups testing 30% or less should be considered affected, with two defective genes (see the Affected table). In this situation, at least two or three tests are highly recommended to confirm the pup's status.

Testing pups makes it possible for a breeder to responsibly breed together two quality dogs with less than normal test results, although this is not recommended as a general practice. Dogs testing in Cornell's borderline range (and dogs testing low in the normal range, see Carrier table), might be clear or they might be carriers with one defective gene. In this situation, the breeder is wise to assume that both dogs are carriers until puppy test results prove otherwise. Also, the breeder must be prepared to deal responsibly with any puppy that tests in the affected range. For a glimpse into the life of an affected dog, read "Life with a Bleeder," "Bleeding Always Stops," and other articles on the Canine References page at VetGen's web site (http://www.vetgen.com) and "Treatment" on Cornell's web site (http://web.vet.cornell.edu/public/coaglab/clinical_topics/vWD.htm).

Cornell has a special rate for testing litters: the charge to the veterinarian is $60, compared to $24 for testing an individual dog. This discount applies if the following information is submitted with the litter's samples: pedigree of the litter and copies of both parents' test results (or Cornell laboratory's accession number from the parents' test result forms). If the parents had not been tested previously, samples from the parents can be included with the litter shipment. All individual and litter test results are handled confidentially. Once or twice a year, Cornell compiles litter data from all breeds that have tested litters during the past year. Cornell will share compiled data—which contains NO information identifying individual dogs—and summaries with interested individuals or breed groups. The litter data are very useful for helping to plan future matings. If data from enough litters are compiled, Cornell will be able to predict inheritance patterns accurately and to provide better informed recommendations for breeders. By participating in Cornell's litter testing program, whippet breeders can provide important information for the breed as a whole while gaining information for use in their own breeding programs.

Cornell states that healthy pups can be tested as early as six to eight weeks of age. Blood should be drawn only when pups are feeling at their best. If pups are quiet for a day or two after vaccination or deworming, wait until they have regained their usual puppy vigor before drawing blood. In the Moser et al study, pups were tested as early as 3 days of age. Theoretically, blood could be drawn for vWF:Ag testing when whippet pups have their front dewclaws removed. If a breeder chooses this option, blood must be drawn BEFORE dewclaw removal because surgery will change test results. The bottom line is that pups can be tested before they are placed in their new homes and that test results can be used, along with other criteria, in deciding which pups will be potential breeding stock for the next generation.

Some Comments on Testing Procedures

Results of the vWF:Ag assay can be affected by how the blood sample is drawn and processed. Careful technique is required. I recommend that you have your veterinarian send samples directly to Cornell for vWF:Ag testing. See Cornell's Standard Sampling Technique page (link from the Laboratory Diagnosis page) for instructions that you can print and take to your veterinarian. Be sure that your veterinarian has, or can obtain, the required collection tubes before your appointment.

I recommend that your veterinarian draw blood for vWF:Ag testing only from the jugular vein in the neck, not from a leg vein. Pups are so small that the jugular vein is by far the most reliable location for the veterinarian to get a "clean stick" on the first try. While leg veins of adult whippets are large enough to draw blood easily, if you are comparing test results of pups and adults, using consistent technique in all age groups is preferable. The Moser et al study looked at the influence of the vein used on test results. Although results did not reach statistical significance, they suggested that vWF concentrations measured following collection from the cephalic vein in the front leg might be somewhat higher than concentrations from samples obtained from the jugular vein in the neck. A falsely elevated test result obtained from blood drawn from a leg vein might give a breeder a sense of security, but it will not advance knowledge of von Willebrand status in the breeder's dogs or the breed.

Drawing blood from the jugular vein of puppies is greatly facilitated by using a 23 gauge butterfly catheter with a vaccutainer. Once the butterfly catheter is in the vein, a bit of wiggling by the puppy does not interfere with the blood drawing process. (Your veterinarian may need to special order vaccutainer adapters to connect the butterfly catheters to the vaccutainer sleeves.)

The Bottom Line

In whippets, von Willebrand disease is a bump in the road, but not a disaster. It is a condition for which breeders can obtain useful information. Carriers live completely normal lives without any restrictions on their activity or a need for special care. Dogs that test in the normal range can be carriers, especially those with vWF:Ag test results lower than the high 90s. Dogs testing in the borderline range can be either carriers or can be clear of the defective gene; their status can only be determined by breeding them. Prior to breeding, breeders can test prospective breeding partners using Cornell’s vWF:Ag test to get an idea about what might be expected in the pups.

Puppies can be tested before they are placed in new homes. Testing puppies will allow the breeder to select high testing pups as potential breeding stock and will provide information about the genetic status of the parents. Cornell uses information from litters to refine recommendations to breeders. Testing puppies will ensure that a puppy at a high risk of developing a clinical bleeding disorder will not be placed in an unsuspecting home. Cornell offers a substantial discount compared to individual testing when litter samples are submitted together with a pedigree and test results of the parents (or samples from the parents).



Copyright 2003 by Adele C. Monroe, DVM, MSPH. Except for printing single copies for personal use, reproduction of this article, either electronically or in print, without prior written permission of the author is prohibited.

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