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Hemophilia B (FIX Deficiency) - Lhasa Apso Type
| Acronym: | HFIX |
| Gene: | F9 |
| Mutation: | c.548_553delinsT |
| Inheritance: | X-linked recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Haemophilia B also known as Factor IX Deficiency is a common genetic coagulation factor disorder in humans and various animal species including dogs. There are numerous inherited bleeding disorders known to affect dogs and all of them show a defect in primary hemostasis, coagulation, or breakdown of clots and are almost always caused by variants in genes interfering with platelet function. This type of haemophilia is a consequence of variants within the F9 gene coding for Factor IX causing the lack of its biological activity. Factor IX plays an important role in the coagulation pathway and its deficiency in affected dogs usually causes signs such as bleeding in joints, mouth, and gums and bleeding that is hard to stop. The type of Haemophilia B that has been reported in - Lhasa Apso dogs is caused by a complex deletion mutation at nucleotides 772-777.
As the F9 gene lies on the X chromosome, hemophilia B found in Lhasa Apso dogs shows an X chromosomal recessive mode of inheritance, meaning the specific mutation that causes the disease is located on the sex chromosome. Since male dogs have just one X chromosome, if they carry the mutation, they will develop a bleeding disorder. Female dogs have two X chromosomes and hence, dogs with only one copy of the mutated gene will act as carriers, and dogs carrying both mutated genes will show signs of the disease. Early genetic testing can help identify dogs that carry the gene with the specific mutation and prevent their further breeding by the proper selection of mating pairs.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (female) or hemizygous state (male) (i.e. only healthy allele on X chromosome). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has mutated allele in homozygous state (female) or hemizygous state (male) (i.e. only mutated allele on X chromosome). It is likely the animal will experience a genetic disorder due to this mutation.**It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Penetrance of tested mutation, and potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Mauser, A. E., Whitlark, J., Whitney, K. M., Lothrop, C. D., Jr (1996). A deletion mutation causes hemophilia B in Lhasa Apso dogs. Blood, 88(9), 3451–3455.
Nichols, T. C., Hough, C., Agersø, H., Ezban, M., Lillicrap, D. (2016). Canine models of inherited bleeding disorders in the development of coagulation assays, novel protein replacement and gene therapies. Journal of thrombosis and haemostasis : JTH, 14(5), 894–905. https://doi.org/10.1111/jth.13301