vonWillebrands Disease

vonWillebrands Disease

Von Willebrand's Disease is the most common in a group of diseases known as "clotting disorders" or "bleeding disorders," which are often collectively referred to as hemophilia in humans (and the term "hemophilia" is commonly used in dogs as well). In order to understand von Willebrand's Disease (vWD), it's important to have a basic understanding of how blood normally clots.

When there is an injury or other trigger for bleeding, the body responds to "plug" the bleeding source in the injury. One major component of the response is the accumulation of platelets, cellular components that physically "plug the hole." A second part of the clot formation response is a series of chemical reactions involving specific molecules known as "clotting factors," which, to think of it simply, help glue the platelets together and to the tissue/blood vessel. Those clotting factors are numbered in sequence from I to XII (1 to 12 in Roman numerals), and they follow the numbered sequence in the way they react... Factor I interacts with Factor II, and the result interacts with Factor II, etc. Obviously, with so many components involved in creating the clot that stops bleeding, the failure of any single component could severely impair the clotting process. In fact, there are a wide variety of clotting disorders, each affecting a particular step in that process. In the case of von Willebrand's Disease, there is a reduction in the concentration of a protein known as von Willebrand's Factor, which stabilizes Factor VIII and helps the clot form.

Types of von Willebrand's Disease
There are actually three types of vWD. Type I is the most common, and it is the overall reduction in the concentration of von Willebrand's Factor, resulting in extended clotting time. Type II is characterized by the absence of the larger molecules of von Willebrand's Factor, which are the more important in clotting. Type III is the most severe, is the complete absence of von Willebrand's Factor, and results in extensive, typically fatal bleeding.

Genetic Inheritance
Type I von Willebrand's Disease is autosomal (not sex-linked) with partial dominance. This means that if a puppy inherits the gene from only one parent, they will be affected to a varying degree, with a reduction in von Willebrand's Factor. A puppy that inherits the gene from both parents will typically die before or right after birth.

Type II is autosomal recessive, meaning that a puppy would have to get the gene from each parent to fully express the disease, with a complete absence of vWF. This requires that both parents be carriers, who would show little or no symptoms except for a somewhat decreased level of vWF if it were measured.

Type III is also autosomal recessive.

Symptoms of von Willebrand's Disease
The fundamental symptom of vWD is a lengthening of the time it takes for a clot to form, which results in excessive bleeding. This is most commonly noticed after injury or surgery, when there is substantial bleeding to begin with. Additionally, there may be instances of more "spontaneous" bleeding, such as nosebleeds or bleeding from the gums. Bleeding into the digestive system and/or urinary tract can also occur, leading to bloody or black stools and bloody or brown urine. In some cases, bleeding into joint capsules can occur, producing arthritis-like symptoms.

There also seems to be an increased instance of hypothyroidism in dogs with von Willebrand's Disease.

Diagnosis
Typically, the initial diagnosis of a clotting disorder is on the observation of excessive bleeding after injury or surgery. As von Willebrand's Disease is the most common of the clotting disorders, that is often the first condition suspected. Often, the first diagnostic procedure is called a "mucosal bleeding time" test, where a vet will make one or more standardized incisions on the inner lip, then blot at regular intervals while measuring the clotting time. This is a basic test to identify the presence of a clotting disorder, but it doesn't pinpoint von Willebrand's Disease exactly, as some other clotting disorders can have the same clot-delaying effect. Actually diagnosing von Willebrand's Disease requires either (1) a laboratory blood analysis to measure the concentration of von Willebrand's Factor, or (2) a genetic test to identify the causative gene, in breeds where the test is available.

Breeds Affected
Different breeds are more commonly affected by the different types of von Willebrand's Disease. Type I is most prevalent in the Doberman Pinscher, Shetland Sheepdog, Airedale Terrier, Scottish Terrier, Golden Retriever, Poodle varieties, German Shepherd, Basset Hound, Dachshund varieties, and Rottweiler, among others, but it can occur in most breeds.

Type II predominantly affects the German Shorthaired Pointer.

Type III is very rare, and occurs most commonly in the Chesapeake Bay Retriever and Scottish Terrier.

Treatment
There is no "cure" for von Willebrand's Disease, but it can often be managed in mild to moderate cases. Ideally, when bleeding is expected, such as surgery, a transfusion of blood or blood products may be done. This may also be done after trauma. The best blood product for such a transfusion is called "cryoprecipitate," but it isn't always available, so whole blood or blood plasma may be used.

Simply being aware that a dog has the condition can be very important, so that extra care can be practiced if there is any bleeding wound, including direct pressure on the wound and more urgent veterinary care.

Additionally, some vets may recommend thyroid supplementation in vWD-affected dogs who are also hypothyroid, or use of intranasal desmopressin acetate during a bleeding eposide.