Genetic Welfare Problems of Companion Animals

An information resource for prospective pet owners

British shorthaired cat

British Shorthair (BSH)

Haemophilia B

Related terms: Factor IX deficiency; Haemophilia B, coagulation disorder; Christmas disease

VeNom term: Haemophilia (VeNom code: 924).

Related conditions: Haemophilia A

Outline: Haemophilia B is a rare blood disorder in which the blood is unable to clot properly, leading to excessive bleeding. It is caused by a hereditary deficiency of the blood clotting protein, factor IX, one of the substances responsible for blood clotting. Haemophilia B is reported to be inherited in British shorthair cats, although it is uncommon.

Clinical signs usually appear in affected cats before 6 months of age. Prolonged bleeding can be initiated from injury, trauma and surgery. Internal bleeding may occur in the organs. The clinical signs of haemophilia B include episodes of lameness, swelling and bruising under the skin, weakness, lack of appetite, fever and depression. Anaemia may also occur due to the loss of blood, contributing to weakness, lethargy, irregular heartbeats and shortness of breath.


Summary of Information

(for more information click on the links below)

1. Brief description

Haemophilia B is a rare blood disorder in which the blood is unable to clot properly, leading to excessive bleeding. Coagulation is the process of clot formation, when blood transforms from a free flowing liquid into a thickened gel like state, or clot. This process is critically important to seal open wounds, allowing them to stop bleeding and heal. Haemophilia B is caused by a hereditary deficiency of the blood clotting protein, factor IX, one of the substances responsible for blood clotting. Typically, the problem shows after wounds caused by injury, trauma or surgery or through gum disease which causes bleeding. Under these circumstances, affected animals show abnormally prolonged bleeding, because clot formation is ineffective.  

The clinical signs of haemophilia B include episodes of lameness, swelling and bruising under the skin that resolve with no treatment, weakness, lack of appetite, fever and depression. Affected cats may show small spots of bleeding under the skin (only readily apparent in areas that are hairless and unpigmented) or inside the tissues of the mouth. Internal bleeding may occur in organs or body cavities, resulting in bloody or dark vomit or stools, rectal or vaginal bleeding, nose bleeds, breathing difficulties, abnormal heart rhythm, swollen or distended abdomen and/or excessive thirst. Bleeding inside the eyes and into the brain can occur, and this can lead to blindness or neurological signs (signs of abnormal brain function). Regular episodes of bleeding may cause regenerative anaemia, due to loss of blood, and this may cause weakness, lethargy, irregular heartbeats and shortness of breath.

Cats with haemophilia B can be severely affected if the activity of factor IX is very low; extremely affected cats (<1% activity of factor IX) usually die at birth or shortly thereafter. Severely affected cats (<5% activity of factor IX) bleed spontaneously and will usually die due to severe bleeding or anaemia. If affected cats have adequate factor IX activity (eg 25-30%), they may have no symptoms until surgery or injury where prolonged bleeding occurs, though this can still be life-threatening.

2. Intensity of welfare impact

Severely affected animals (those with factor IX activity less than 1%) may die at birth due to excessive umbilical bleeding or they may die shortly after due to body cavity haemorrhage.  

For animals that are not so severely affected, the clinical signs may be less obvious, but they may suffer intermittently from anaemia, weakness, periodic lameness or fever. Affected cats may also lose bodyweight as a result of inappetance. If bleeding occurs into confined body cavities, such as within the eyeball, skull or joints, this can cause severe pain due to the increased pressure within the cavity. Severe bleeding following trauma or surgery causes weakness, malaise, nausea, and severe anaemia can be life threatening.

Owners of affected cats can reduce the risk of trauma and injury in their cat, eg by restricting opportunities to get involved in fights with other cats or risks of falls, and by maintaining good dental hygiene to avoid excessive bleeding of the gums (eg with gingivitis). There is no curative treatment for the condition. Antifibrinolytic agents can be given by a veterinarian to stem bleeding, eg after surgical procedures. If anaemia is severe, transfusions of fresh whole blood transfusions may be required.

3. Duration of welfare impact

Affected cats are born with defects in haemostasis (blood clotting) and the clinical signs of haemophilia usually appear before 6 months of age. At this time, bleeding and bruising or haematomas at the site of injections may be noticed following routine procedures, such as vaccination, castration, or spaying). Severe cases of haemophilia B are lethal due to severe bleeding (external or internal) or anaemia. For cases which are less severe, animals may still experience clinical signs – such as bruising, nosebleeds or blood-tinged vomit, urine or faeces, weakness, lameness – intermittently throughout their lives.

4. Number of animals affected

Haemophilia is rare in cats, although the exact prevalence is unknown. Haemophilia B is reported to be inherited in British shorthair cats. Male cats are more commonly affected than female cats, since the genetic defect is on a sex-linked chromosome.

5. Diagnosis

Blood can be tested for platelet count, and activated clotting time; cats with haemophilia B have a slower clotting time and a deficiency of factor IX protein activity.

6. Genetics

A mutation in the gene that codes for the expression of Factor IX protein is responsible for haemophilia B in cats. Haemophilia B is a sex-linked recessive disorder, and the mutated gene is found on the X sex chromosome. Females have two X chromosomes; males have one X and one Y. If a male, inherits an X chromosome carrying the mutated gene then it will be affected by the haemophilia B disorder. For females to be affected they have to be homozygous for the condition, that is both X chromosomes have to carry the mutated gene; but this is less common. Heterozygous females, which carry one copy of the genetic mutation, are therefore unaffected carriers for the disorder. Mating of a female carrier with an affected male will result in half of male offspring being affected and the other half of male offspring being clear. Half of female offspring will be affected and the other half will be carriers (unaffected but able to pass on the condition to their offspring).

7. How do you know if an animal is a carrier or likely to become affected?

To our knowledge, there is no genetic test to detect the mutation responsible for Haemophilia B in cats, although the genetic mutation is known and a test may be developed in the future (Lyons 2012). Cats with haemophilia B can be diagnosed using measures of blood clotting, where abnormal clotting times and a deficiency of factor IX are found. In particular, male cats should be tested.

8. Methods and prospects for elimination of the problem

Although the condition is considered to be rare, breeding from affected cats should be avoided since it will result in both affected cats and carriers (females only).

Without a specific genetic test, the best advice that can be offered to prospective breeders is to seek testing for haemophilia B in cats showing clinical signs, via a veterinarian, before breeding. Breeding between affected cats or from cats with affected relatives, including grandparents, siblings, previous offspring and siblings of parents should be avoided.


For further details about this condition, please click on the following:
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1.  Clinical and pathological effects

Haemophilia B is a rare blood disorder in which the blood is unable to clot properly, leading to excessive bleeding. Coagulation is the process of clot formation, when through a series of steps, blood transforms from a free flowing liquid into a thickened gel like state, a clot. This process is critically important to seal open wounds, allowing them to stop bleeding and to begin to heal.

Platelets are cell-like particles that start the process of blood clotting. They are produced in the bone marrow and circulate in the blood. When an injury occurs, the wall of the blood vessel breaks and bleeding occurs. The blood vessel narrows so that there is a slower blood supply to the broken vessel. Platelets rush to the broken wall where exposure to certain proteins causes the shape of these cells to change from round to spiny. This allows the platelets to clump together, and with other blood cells, at the site of the damage to the blood vessel. Other proteins form fibrin strands, creating a net that holds together the platelets and blood cells, creating a clot that plugs the break in the vessel wall, stopping the loss of blood.

Defects in the blood clotting proteins, usually referred to as factors, cause delayed coagulation and leads to prolonged bleeding (Maggio-Price & Dodds 1993). Haemophilia B is caused by a hereditary deficiency of clotting factor IX, one of the substances responsible for blood clotting under a process called the coagulation cascade. Factor IX forms links between platelets and collagen fibrils and promotes binding of the platelets to the extracellular matrix of the blood vessel wall. Typically, haemophilia is noticed after wounds caused by injury, trauma or surgery or as a result of gum disease, which causes bleeding. Under these circumstances, affected animals show abnormally prolonged bleeding, because clot formation is ineffective. Affected cats may show small spots of bleeding under the skin (only readily apparent in areas that are hairless and unpigmented) or inside the tissues of the mouth. These blood spots within the tissues are called petechiae, when small, and purpura or ecchymoses when larger. The prolonged bleeding in haemophilia B is usually milder than found in haemophilia A, which is a result of factor XI deficiency (Cotter 2013).

Internal bleeding may also occur in organs and body cavities and this may present as blood in the vomit or stools, bleeding from the nose, rectum or vagina, breathing difficulties, abnormal heart rhythm, swollen or enlarged abdomen and/or excessive thirst (Fogh & Fogh 1988). Internal bleeding may cause the formation of haematomas (where blood outside of blood vessels collects locally), bleeding into joint spaces (hemarthrosis) and body cavity haemorrhage. Bleeding inside the eyes and into the brain can occur, and this can lead to blindness or neurological signs (signs of abnormal brain function).

Regular episodes of bleeding may cause regenerative anaemia (Barr & McMichael 2012), due to the loss of blood. New blood cells are produced by the bone marrow to replace those that are lost, but anaemia will occur when the speed at which the red blood cells are lost is greater than they can be replaced. This can be measured by an increased presence of immature red blood cells in the blood. The clinical signs of anaemia include weakness, lethargy, irregular heartbeats and shortness of breath. Pica – a compulsive eating behaviour – can also occur, where cats consume non-food materials in an attempt to balance a lack of minerals or vitamins (eg iron) from the loss of blood. Other possible signs include episodes of lameness, swelling and bruising under the skin that resolve with no treatment, weakness, lack of appetite, fever and depression (Maggio-Price & Dodds 1993).

The severity of the bleeding disorder is related to how active the factor IX is (Lutze et al 2005, Cotter 2013). Animals with extremely low Factor IX activity (less than 1%) usually die at birth or shortly thereafter. If the factor IX activity is very low (<5%), affected cats usually bleed spontaneously and will have a poor prognosis. If affected cats have adequate factor IX activity (eg 25-30%), they may have no symptoms until surgery or injury where prolonged bleeding occurs, though this can still be life-threatening.

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2. Intensity of welfare impact

Haemophilia B causes excessive bleeding after injuries and occasional spontaneous bleeding, but this does not usually cause pain except where bleeding occurs in confined body cavities, such as the eyeball, skull or joints. Excessive blood loss causes weakness, malaise, nausea, and in severe cases it can cause collapse, seizures and death. Affected cats may also lose bodyweight as a result of inappetance.     

For animals with severe haemophilia B, the condition is usually fatal. Cats with less than 1% factor IX activity may die at birth due to excessive umbilical bleeding or as surviving kittens due to body cavity haemorrhage. 

There is no curative treatment for the condition. Antifibrinolytic agents can be given by a veterinarian to stem bleeding, eg after surgical procedures. Owners of affected cats can reduce the risk of trauma and injury in their cat, eg by restricting their opportunities to get involved in fights with other cats or falls from heights, and maintain good dental hygiene to avoid excessive bleeding of the gums (gingivitis). If anaemia is severe, transfusions of fresh whole blood transfusions may be required. Intramuscular injections and certain drugs can impair haemostasis and should be avoided, and so appropriate veterinary care may be hindered.

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3. Duration of welfare impact

Affected cats are born with defects in haemostasis (blood clotting) and the clinical signs of haemophilia usually appear before 6 months of age. Bleeding and bruising or haematomas at the site of injections might be noticed for routine procedures, such as vaccination, castration, or spaying. Severe cases of haemophilia B are lethal and animals may die suddenly. For cases which are less severe, animals may not be diagnosed until they show abnormal bleeding after major surgery or trauma. However, these animals may still experience clinical signs – such as bruising, nosebleeds or blood-tinged vomit, urine or faeces, weakness, lameness – intermittently throughout their lives. These episodes are likely to last from days to weeks.

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4. Number of animals affected

Haemophilia is rare in cats (Barr & McMichael 2012), although the exact prevalence is unknown. Haemophilia B is reported to be inherited in British shorthair cats (Maggio-Price & Dodds 1993, Brooks & DeWilde 2006). Male cats are more commonly affected than female cats, since the genetic defect is on a sex-linked chromosome.

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5. Diagnosis

A diagnosis of haemophilia B is suspected when an animal has apparently abnormal and excessive bleeding eg from the mouth or elsewhere that is beyond what might be expected, or when there is excessive bleeding during surgery. The diagnosis can be confirmed by various blood tests that assess primary and secondary haemostasis (clotting) and by measurement of the concentration factor IX in the blood. An atraumatic venepuncture can be used to draw blood without excessive bleeding. Activated partial thromboplastin time is used as a measure of the time it takes for blood to clot; this is prolonged in cats with haemophilia B whereas other blood clotting parameters are normal (prothrombin time, thrombin clotting time, fibrinogen determination). Definitive diagnosis of the exact disorder depends on measurement of Factor VIII (haemophilia A) or Factor IX (haemophilia B) activity.

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6. Genetics

A mutation in the gene that codes for the expression of Factor IX protein is responsible for haemophilia B in cats (Goree et al 2005). Haemophilia B is a sex-linked recessive disorder, as the mutated gene is found on the X sex chromosome (Maggio-Price & Dodds 1993, Goree et al 2005). Females have two X, males only one X and another sex chromosome Y.  For males, inheritance of an X chromosome carrying the mutated gene causes haemophilia B to be expressed, since they only have one X chromosome, and therefore only require one copy of the gene mutation to be affected. For females to be affected, they have to inherit two copies of the mutated gene – ie they have to inherit one copy  of the mutation from the mother and the father, but this occurs much less commonly as breeding from affected cats is unusual). Females are therefore more usually unaffected carriers (heterozygous) for the disorder, that is, they carry one copy of the genetic mutation on one of their X chromosomes.  Mating of a female carrier with a hemizygous affected male will result in half of male offspring being affected and the other half of male offspring being clear. Half of female offspring will be affected and the other half will be carriers (unaffected) but able to pass on the condition to their offspring).

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7. How do you know if an animal is a carrier or likely to become affected?

To our knowledge, there is no genetic test to detect the mutation responsible for Haemophilia B in cats, though this test is available for dogs. The genetic mutation responsible for haemophilia B in cats is known, and therefore a genetic test could be developed in the future (Lyons 2012). 

Cats with haemophilia B can be diagnosed using measures of blood clotting, and where abnormal clotting times and a deficiency of factor IX are found, these cats should not be used for breeding. In particular, male cats should be tested.

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8. Methods and prospects for elimination of the problem

Although the condition is considered to be rare, breeding from affected cats should be avoided since it will result in both affected cats and carriers (females only). Without a known genetic background, diagnosis of female carriers of a defect is difficult. Assessment of littermates and relatives showing clinical signs may identify potential carrier status in females. Female carriers should not be bred from since they are likely to produce affected male offspring.

Without a specific genetic test, the best advice that can be offered to prospective breeders is to seek testing for haemophilia B in cats showing clinical signs, via a veterinarian, before breeding. Breeding between affected cats or from cats with affected relatives, including grandparents, siblings, previous offspring and siblings of parents should be avoided.

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9. Acknowledgements

UFAW thanks Dr Emma Buckland (BSc PhD), Dr David Brodbelt (MA VetMB PhD DVA DipECVAA MRCVS) and Dr Dan O’Neill (MVB BSc MSc PhD MRCVS) for their work in compiling this section.

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10. References

Barr JW and McMichael M (2012) Inherited disorders of hemostasis in dogs and cats. Topics In Companion Animal Medicine 27: 53–8

Brooks M and DeWilde L (2006) Feline Factor XII Deficiency. Compendium on Continuing Education for the Practicing Veterinarian 28: 148–155

Cotter SM (2013) Coagulation Protein Disorders. Merck Veterinary Manual. Found 10/03/2016: http://www.merckvetmanual.com/mvm/circulatory_system/hemostatic_disorders/coagulation_protein_disorders.html

Fogh JM and Fogh IT (1988) Inherited coagulation disorders. The Veterinary Clinics of North America: Small Animal Practice 18: 231–43

Goree M, Catalfamo JL, Aber S and Boudreaux MK (2005) Characterization of the Mutations Causing Hemophilia B in 2 Domestic Cats. Journal of Veterinary Internal Medicine 19: 200–204

Lutze G, Kutschmann K, Fürst K and Schneppenheim R (2005) Hemophilia B (factor IX deficiency) with concomitant factor XII degradation in a male crossbreed cat. Berliner und Mu╠łnchener tiera╠łrztliche Wochenschrift [Berlin and Munich Veterinary Weekly] 118: 255–60

Lyons LA (2012) Genetic testing in domestic cats. Molecular and Cellular Probes 26: 224–30

Maggio-Price L and Dodds WJ (1993) Factor IX deficiency (hemophilia B) in a family of British shorthair cats. Journal of the American

© UFAW 2016


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http://depositphotos.com/18317879/stock-photo-british-shorthair-cat-portrait.html ©Depositphotos.com/FotoJagodka