vWDI is inherited in an autosomal dominant manner with incomplete penetrance, in the Kromfohrländer breed.

Background: Von Willebrand disorder type I (vWDI) is known as an inherited bleeding disorder in different dog breeds following an autosomal recessive inheritance. The Kromfohrländer is a rare dog breed with an increased incidence of unclear bleeding episodes and prolonged coagulation time during/after surgery or injuries, indicating a defect in one or more critical proteins of the coagulation cascade.

Objective: The objective of this study was to determine whether the c.7437G > A mutation in the VWF gene previously shown to cause von Willebrand disorder type I in Doberman Pinscher is also linked to this disease in the Kromfohrländer breed and to serum concentrations of vWF. Furthermore, establish a possible link between bleeding phenotype, vWF serum concentrations and VWF mutation status.

Results: Eighty-seven Kromfohrländer were genotyped for the G > A von Willebrand type I mutation. For detection of the associated mutation we used an endpoint genotyping method. We identified the G > A von Willebrand type I mutation in 80.5% of our study population. 65.5% were heterozygous (WT/MUT) and 15.0% were homozygous for the mutation (MUT/MUT). 21% of the overall study population exhibited bleeding symptoms. 45.5% of all homozygous dogs (MUT/MUT) showed bleeding symptoms. In contrast, wild-type homozygotes exhibited no bleeding symptoms, whereas 23.2% of the heterozygotes did. VWF serum concentrations varied from 28 to 137% in wild-type dogs while in heterozygous and homozygous dogs the concentration ranged from 3 to 77% and 1 to 23%, respectively ( p  < 0.05).

Conclusion: Based on our data, we found the G > A mutation in the VWF gene in the Kromfohrländer breed and the subsequent vWDI as the underlying cause for the bleeding episodes and delayed coagulation in heterozygous and homozygous dogs. Since both, heterozygotes and homozygotes show reduced vWF serum concentrations and exhibit to a certain percentage the vWD syndrome phenotype, we postulate that, in contrast to most other vWDI affected breeds, inheritance follows an autosomal dominant mode with incomplete penetrance.