Taken from the September 1994 issue of the Weimaraner Magazine

Inherited and acquired von Willebrand’s Disease is now recognized as secondary to familial auto-immune thyroid disease. Presently 47 of the 59 dog breeds known to have von Willebrand’s also transmit this form of thyroid disease which results in hypothyroidism. The prevalence of both diseases has increased rapidly over the last decade despite the collective efforts of conscientious breeders to test and screen out carriers from their breed programs.

Inherited or Congenital von Willebrands Disease

This is the primary inherited problem from one or both parents. Carriers of this genetic defect may show no symptoms until some other stress event further comprises the ability of the body to form clots. The most common form of Willebrands is classified as Type 1, and is autosomal or non-sex linked incomplete dominant trait. This means it has ovariable expression within affected families. Both homozygotes who have inherited a double dose of the gene, one from each parent, and heterozygotes that carry a dose from either parent can manifest a bleeding tendency. Homozygosity is rarely seen because affected puppies usually die during fetal development or shortly after birth. The other types of Willebrands are type II which is rare and usually seen in German Shorthaired Pointers, and type III which is an autosomal recessive disease seen in Scottish Terriers, Chesapeake Bay Retrievers, and occasionally Shetland Sheepdogs (usually when two dogs effected with type I).

Willebrands affects many animals, although few develop severe problems and even fewer die. The bleeding episodes become worse from physical, emotional and physiological stresses and other diseases. Typical clinical signs include: recurrent gastrointestinal hemorrhage (with or without diarrhea); bleeding from the gums, vagina or penis; lameness that mimics eosinophilic panosteitis; still-births or neonatal deaths with evidence of bleeding at necropsy; prolonged bleeding at estrus or after whelping; bruises or blood-filled lumps on the surface of the body, limbs, or head; excessive umbilical cord bleeding at birth; excessive bleeding from toenails cut too short, after elective procedures such as ear cropping and dewclaw removal. Affected dogs may even bleed to death from surgical procedures. Diagnostic tests require specialized assays as routine screening coagulation tests are non-diagnostic. Affected individuals have long bleeding times. Definitive diagnosis is made by finding reduced levels (less than 50%) of the Willebrand factor antigen (vWF:Ag).

Acquired vWD

Because the production of Willebrands disease in the body arises almost exclusively from the endothelial cells lining blood vessels, any disease process altering the endothelial metabolism and protein synthesis can affect Willebrands levels. Auto-immune disease, especially thyroid disease, can disrupt Willebrands production and function. The disruption causes a secondary, acquired form of Willebrands. A classic situation arises when an animal develops auto-immune thyroid disease later in life. Platelets are small cells involved in helping the body form clots and Willebrands acts on the platelet surface, making it more sticky or adhesive. The disease acts on the platelets, impairing their clotting function.

In dogs with the congenital form of Willebrands disease, their bleeding tendency becomes clinically severe when hypothyroidism is present. Frequently, dogs developing thyroid disease have lower levels of Willebrands. Hypothyroid dogs also may exhibit low platelet counts (thrombocyopenia) which can cause mucosal bleeding. Finding low or low-normal levels of Willebrands and/or platelet numbers may be early indications of thyroid dysfunction in your stock.

It is generally impossible with currently available techniques to distinguish between the inherited and the acquired types of Willebrands disease in an individual patient.Therefore, it is important to screen for both Willebrands disease and thyroid function to assess susceptibility to these interrelated disorders.

Recommendations to Breeders

• Blood test animals for Willebrands disease that are related to those bloodlines known to have the problem.
• Ideally, all dogs affected by Willebrands disease and carriers of the genes should not be used for breeding purposes. It may not be feasible, however, to remove all carriers from a breeding program. If breeding a Willebrands disease carrier is necessary to preserve important bloodlines or type, breed symptom-free disease carriers to normal mates and blood test the puppies. On average, one half of the litter should be normal and the other half will be carriers.
• Do not mate carries of Willebrands disease together. One quarter of the litter on average will be affected “bleeders”.
• Never breed an affected animal as its puppies are likely to be carriers of Willebrands disease. Also, severely affected females may not survive pregnancy or the postpartum period.

Several commercial veterinary testing laboratories offer testing and use validated methods based on the Laurell eletroimmuno assay, radioimmuno assay, or enzyme-linked immunosorbent assay (ELISA) techniques.