Von Willebrand Disease (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. Clinical signs of vWD ranged from mild to severe bleeding tendency.
There are three forms of vWD (types 1, 2 and 3) that are defined by the quantity and structure of VWF in the blood plasma. Type 1 is characterised by a low concentration of vWF, but it has a normal structure and clinical severity of the disease is variable. These dogs are unlikely to bleed spontaneously but may be prone to excessive bleeding when undergoing surgery or in injured.
The single nucleotide variant in the gene called VWD that causes Von Willebrand Disease Type I in multiple breeds is autosomal dominant, with incomplete penetrance. This means that dogs that carry one or two copies of the mutation (heterozygotes and homozygotes respectively) have reduced levels of the vWF protein and may experience abnormal and severe bleeding due to Von Willebrand Disease type I during their lives. They will also pass the mutation on to all (for homozygotes) or about half (for heterozygotes) of any offspring they have. Breeding dogs that will not develop Von Willebrand Disease Type I should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Heterozygotes (“carriers”) should not be bred from, even if they are mated to a dog that has also been tested and is clear of the VWD mutation (i.e. carry no copies of the mutation). If a heterozygote is mated to a clear dog approximately half of the resulting puppies will also be heterozygous and may develop Von Willebrand Disease Type I caused by the VWD mutation during their lifetime.