Haemophilia B (Rhodesian Ridgebacks)


 

Haemophilia B is a condition affecting the blood clotting process by lack of biologically active coagulation factor IX. Canine haemophilia B represents a naturally occurring hereditary coagulopathy with a range in severity of clinical signs and coagulant activity in different breed variants. It has been reported in many breeds. In Rhodesian Ridgebacks, a severe form of haemophilia B with pronounced clinical signs was first described in 2000.

A G→A missense mutation in exon 7 of the canine factor IX gene was identified as the likely mutation responsible for severe haemophilia B in Rhodesian Ridgebacks. This mutation results in a glycine (GGA) to glutamic acid (GAA) exchange in the catalytic domain of the haemophilic factor IX.

Haemophilia B is a sex-linked disorder (x-chromosomal recessive). Male dogs express the disease when they have one mutated x-chromosome. The mutated x-chromosome comes from the bitch. In most cases female dogs are carrier of one mutated x-chromosome without being diseased (conductor). Female dogs will be diseased when they have two mutated x-chromosomes (one from the mother, one from the father).

Without a known genetic background, diagnosis of female carriers of a defect is difficult. For this purpose, Vetogene developed a genetic test to diagnose diseased dogs and identify genetically affected and carrier dogs.


Results and interpretation:

Male   (1 copy of the X chromosome)

wt: homozygous wild type, no mutation of F9 gene on the X chromosome

(0/1 allele carrying G→A transversion) →   Healthy Rhodesian 

mut: hemizygous affected for the transversion on the F9 gene on the X chromosome

(1/1 allele carrying carrying G→A transversion) →   Affected Rhodesian 
 

Female    (2 copies of the X chromosome)

wt/wt: homozygous wild type, no mutation on the F9 gene on the X chromosome

(0/2 alleles carrying G→A transversion) →   Healthy Rhodesian 

wt/mut: Heterozygous for the transversion on the F9 gene on the X chromosome

(1/2 allele carrying carrying G→A transversion) →   Carrier Rhodesian

mut/mut: homozygous for the deletion on the F9 gene on the X chromosome

(2/2 alleles carrying carrying G→A transversion) →   Affected Rhodesian  


Reference publication:

G244E in the canine factor IX gene leads to severe haemophilia B in Rhodesian Ridgebacks. Mischke et al. The Veterinary Journal 187 (2011) 113–118.