G244E in the canine factor IX gene leads to severe haemophilia B in Rhodesian Ridgebacks.

Haemophilia B in Rhodesian Ridgebacks is currently the most important canine haemophilia in Germany. The aim of this study was to define the underlying genetic defect. Genetic studies were performed including six phenotypically affected male dogs (factor IX activity: approximately 1%), four suspected carriers (factor IX activity 48-69%, one confirmed by affected offspring), and 12 healthy dogs. Comparison of the entire coding region of the canine factor IX DNA sequences and exon-intron junctions from affected dogs with the wild type canine factor IX DNA revealed a G-A missense mutation in exon 7. This mutation results in a glycine (GGA) to glutamic acid (GAA) exchange in the catalytic domain of the haemophilic factor IX. All affected dogs were hemizygous for the detected mutation and carriers were heterozygous, whereas none of the Rhodesian Ridgebacks with normal factor IX activity showed the mutation. No further alterations in the sequences between affected dogs and the healthy control group could be observed. None of the Rhodesian Ridgebacks with undefined haemophilia B status (n=30) and no individual of three other dog breeds (Doberman Pinscher: n=20; German Wire haired Pointer: n=20; Labrador: n=25) showed the presence of the mutation. Amino acid sequence alignment and protein structural modelling analysis indicate that the detected mutation causes a relevant functional defect. The results of this study suggest that the detected mutation is responsible for a severe form of haemophilia B in Rhodesian Ridgebacks.

Prevalence of a 23bp insertion in exon 3 of the endothelial cell protein C receptor gene in venous thrombophilia.

BACKGROUND: The endothelial cell protein C receptor (EPCR) enhances protein C activation by the thrombin-thrombomodulin complex. As evidence is accumulating that EPCR is an important component of the protein C anticoagulant pathway, polymorphisms in the EPCR gene might be candidate risk factors predisposing to venous thromboembolism (VTE). Recently, a 23bp insertion in exon 3 of the EPCR gene has been identified, which duplicates the preceding 23 bases and results in a STOP codon downstream from the insertion point. However, the clinical significance of this mutation in VTE remains to be clarified. METHODS AND RESULTS: In this study we evaluated the EPCR 23bp insertion in 889 patients with documented VTE and in 500 healthy controls. The prevalence of the EPCR insertion among patients was 0.1%, which was not significantly different compared to controls (0.6%, p = 0.1). CONCLUSIONS: Our findings showed that the EPCR 23bp insertion is very rare in both patients with VTE and the general population and failed to support an association between the EPCR 23bp insertion and an increased risk of VTE.