IDENTIFICATION OF MUTATIONS IN THE CANINE VON-WILLEBRAND-FACTOR GENE ASSOCIATED WITH TYPE-III VON-WILLEBRAND-DISEASE

In humans, type III von Willebrand disease is caused by deletions or n onsense mutations. In dogs, the underlying genetic defects have nor be en determined yet. We searched for the genetic defect in four related type III deficient Dutch Kooiker dogs obtained from one breeder. Mutat ion analysis was performed with total RNA isolated from platelets or w hole blood. The complete coding region of the vWf gene was amplified b y RT-PCR and sequenced by the cycle sequencing technique. Two homozygo us mutations were found, a G-->A transition at the first position of t he donor splice site sequence of intron 16 (TGgtaagt-->TGataagt) and a missense mutation at nt 208 (G-->A) (1). The splice site defect resul ted in the generation of a transcript containing 46bp of intron sequen ce and a stop codon at amino acid position 729 in the propeptide regio n of the vWf protein. This mutation seems to be causative for the type III phenotype. The effect of the missense mutation in exon 3 which ca uses a change of Val to Ile on the vWD phenotype is unclear. Probably, this transition represents a polymorphism occurring in Dutch Kooiker dogs. Both mutations were not present in 5 healthy mongrel dogs.