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Haemophilia B / Factor IX (Cairn Terrier Type) Overview

Haemophilia B / Factor IX (Cairn Terrier Type)
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Category: Haemolymphatic - Associated with the blood and lymph

Gene: F9 on Chromosome X

Variant Detected: Base Substitution G>A

Severity: Scale 3 has a moderate degree of severity, as it is not a fatal disease, though it can decrease the quality of life.

Mode of Inheritance: Autosomal X-Linked

Test Overview: This is reported to be the second most common inherited coagulopathy (blood clotting disorder) of dogs and has been reported in a number of breeds.  It is an X-linked recessive trait, which means it is almost always seen in male dogs (as they carry only one copy of the X chromosome).  Many different genetic mutations can lead to haemophilia B, making development of a DNA test across breeds very difficult. Factor IX is a clotting factor essential to normal blood clotting.  The level of factor IX that occurs in the blood of an affected dog can vary quite a lot, and depending on this level, clinical signs may be inapparent, mild, or severe enough to cause uncontrolled and life-threatening episodes of spontaneous bleeding.  In general however, severe episodes of bleeding may be seen following relatively minor trauma, or bleeding may be seen into joints or muscles, causing lameness for no obvious reason.  Following even minor surgery bleeding may be profuse and life-threatening.  Treatment is via transfusion of blood or plasma, in order to provide adequate amounts of factor IX for normal clotting to occur, and for bleeding to be controlled. There is no cure for haemophilia B.  Current testing identifies the activity of factor IX in the blood, with levels between 5-10% usually being able to be tolerated with minimal signs, while levels below 3% can be associated with spontaneous haemorrhage, and levels below 1% are associated with severe clinical signs or neonatal death (i.e. death at or around the time of birth).  There is a DNA test available for several breeds to identify affected and carrier animals, however the genetic test will not be able to tell how severely affected an animal will be.  Recent research suggests that there may be more than one gene responsible for the expression of haemophilia B within a given breed.

Recommended Screening: 1. PT/APTT testing (i.e. coagulation profile at local laboratory) – APTT prolonged and PT normal with haemophilia (good screening test prior to desexing etc) 2. Factor IX activity testing for all male breeding animals prior to breeding (e.g. at 1 year of age). 3. Factor IX testing can be carried out on any male animal if owner is concerned. Ensure testing done prior to desexing (also if coagulation profile is abnormal, recommend this).

Research Citation(s):
Blood. 1973 Apr;41(4):577-85. [PubMed: 4688873]
Proc Natl Acad Sci U S A. 1989 Dec; 86(24):10095-9. [PubMed: 2481310]
Thromb Haemost. 1996 Mar; 75(3):450-455 [PubMed: 8701406]


Associated Breed(s): Cairn Terrier,  Mixed Breed,