Haemophilia B in Rhodesian Ridgeback Dogs

Haemophilia is an inherited disorder of blood coagulation. It is manifests itself by bleeding into muscles or joints and a limited ability of the organism to stop bleeding. The underlying pathomechanism of haemophilia B is a lack or decreased activity of coagulation factor IX that plays a critical role in the coagulation cascade. Affected dogs present haemorrhage that varies from mild to severe depending on the degree of the disease.

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Clinical symptoms of haemophilia B:

Frequently occurring clinical symptoms were excessive bleeding from gums, when getting adult teeth, and haematomas in the regions of the proximal hindlimb, the knee joints as well as the chest or abdominal wall, respectively. Affected dogs have shown signs of limping and joint swelling after strenuous exercise, prolonged bleeding from minor wounds and haemorrhagic complications after surgery. Although Haemophilia B impacts on quality of life and performance of a dog, virtually all affected dogs survive to adulthood.

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Inheritance pattern of Haemophilia B:

Haemophilia B is a sex-linked recessive trait (X-chromosome recessive). That means that males are much more frequently affected than females as the males have only a single chromosome X. If this X chromosome carries a mutant gene, the dog is affected with haemophilia B. In female dogs the disease develops only if they inherit two chromosomes X with a mutant gene. Female dogs having only one mutant gene in one chromosome X are carriers of haemophilia B and the disease does not develop.
One half of their male offsprings inherit the mutant gene and they develop haemophilia B and the other half of female offsprings will be carriers of the mutation.

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Haemophilia B in Rhodesian Ridgeback is caused by mutation c.731G>A in exon 7 CFIX gene (canine factor IX gen) (Mischke et al. 2011). The mutation causes exchange of glycine for glutamic acid (p.G244E) in the catalytic domain of the coagulation factor IX.

The genetic test is used for early diagnosis of the disease in affected dogs and contributes to reduction of occurrence of this disease in the population. Female carriers cannot be identified without a genetic test.

References:

R. Mischke, P. Kühnlein, A. Kehl, I. Langbein-Detsch, F. Steudle, A. Schmid, T. Dandekar, A. Czwalinna, E. Müller: G244E in the canine factor IX gene leads to severe haemophilia B in Rhodesian Ridgebacks; The Veterinary Journal 187 (2011) 113-118