Breeds Affected: Lhasa Apso
Samples Accepted: Blood, Buccal Swabs
Disease Information: This severe bleeding disorder is caused by a mutation in the F9 gene. The blood cannot coagulate properly, leading to uncontrolled bleeding from even small injuries.
Inheritance Information: Factor IX Deficiency is X-linked recessive, because the F9 gene is located on the X-chromosome. Male animals with the mutation (which have only one X chromosome) are affected. Females may have one normal and one mutated version and be asymptomatic carriers.
The possible genotypes are:
XX This dog is a normal female.
XXf This dog is a carrier female. She is clinically normal, but will pass the mutation (Xf) to 50% of her offspring. When bred to a normal male, she can have pups of all four genotypes: normal female (XX), carrier female (XXf), normal male (XY), and affected male (XfY).
XY This dog is a normal male.
XfY This dog is an affected male. If he lives long enough to reproduce, when bred to a normal female, all daughters will be carriers (XXf), but all sons will be normal (XY).
– Female offspring of a carrier female should be genetically tested to determine if they are normal or carriers (XX or XXf).
– Carrier females (XXf) should not be bred, because affected males can be produced.
– Affected males (XfY) are unlikely to live long enough to reproduce. If they do, they should only be bred to normal females, and all female offspring should be tested to determine if they are normal or carriers (XX or XXf).
Test Information: This mutation test identifies a mutation in the F9 gene.
Mauser, A.E., Whitlark, J., Whitney, K.M., Lothrop, C.D.: A deletion mutation causes hemophilia B in Lhasa Apso dogs Blood 88:3451-3455, 1996. Pubmed reference: 8896410.
Further information is available at the Online Mendelian Inheritance in Animals website.