Hemophilia in Dogs

What is hemophilia A?

Hemophilia A is the most common inherited blood clotting disorder in dogs. It is caused by a gene mutation that creates a deficiency of blood clotting factor VIII (8).

A dog with this mutation cannot produce functional factor VIII, which means their blood cannot clot effectively, making it difficult to control bleeding.

How are dogs diagnosed with hemophilia A?

Dogs are often diagnosed with hemophilia based on signs of excessive bleeding. Dogs with hemophilia may:

• Bleed spontaneously
• Bleed into their skin, causing bruising (ecchymosis)
• Bleed into their joints or muscles, causing lameness
• Bleed into their chest cavity or abdomen, causing death
• Have excessive, unexpected bleeding during or after a surgery

Dogs can be screened for clotting disorders with a test called the APTT (activated partial thromboplastin time), but this test cannot distinguish among the various types of hemophilia. The APTT must be performed on a specially prepared blood sample.

A specific hemophilia A diagnosis is made by measuring the activity of factor VIII in the dog’s blood. In addition, several DNA tests are available to screen for hemophilia A.

Can a dog with hemophilia A be bred?

Hemophilia A (factor VIII deficiency) is an inherited disease, so it is important to understand the inheritance pattern. The gene for factor VIII is carried on the X chromosome, and it is recessive, which means that only one normal gene is needed to prevent hemophilia A. Male dogs (XY) inherit one X chromosome (from their mother), and female dogs (XX) inherit two X chromosomes (one from their mother and one from their father).

This sex-linked inheritance pattern shows up in breeding as follows:

• A male with one normal factor VIII gene is clear of hemophilia A and cannot pass the disease along to any offspring.
• A female with two normal factor VIII genes are completely clear of hemophilia A and cannot pass the disease along to any offspring.
• A male with one abnormal factor VIII gene (on his only X chromosome) will have hemophilia A, and will pass the abnormal gene to all female offspring, but no male offspring (they get their single X chromosome from the mother).
• A female dog with one abnormal factor VIII gene will not exhibit hemophilia A, but will pass the abnormal gene to 50% of her offspring (male and female), on average.

Most commonly, when hemophilia A is expressed in a line of dogs, it is passed along when asymptomatic females breed with normal males. From these pairings, about 50% of male offspring will have hemophilia A and about 50% of females will be carriers.

Because of the heritability pattern of hemophilia A, a laboratory analysis should be combined with a pedigree analysis to develop recommendations for breeding. Genetic tests can screen for the mutation in certain breeds.

What is hemophilia B?

Hemophilia B is caused by a deficiency of coagulation factor IX (9) and has been found in more than 25 dog breeds. As with hemophilia A, dogs with hemophilia B may spontaneously bleed into the skin, chest, abdomen, muscles, or joints. There may also be excessive bleeding from a surgery site. Hemophilia B tends to be a milder disease than hemophilia A. Hemophilia B is also rare compared to hemophilia A.

Hemophilia B is a sex-linked recessive disease, like hemophilia A. The gene for factor IX is carried on the X chromosome, so the inheritance pattern is the same as that for hemophilia A. The blood level of factor IX can be measured to make the diagnosis of hemophilia B. Genetic tests to screen for the hemophilia B mutations are available for several different breeds.

Can hemophilia be treated or prevented?

Affected dogs cannot be cured of hemophilia. Following trauma or surgery, these dogs may need blood transfusions of whole blood or blood products that provide clotting factors.

Hemophilia A and B are diseases that are best prevented, so it is vital to screen potential breeding animals. Carriers of hemophilia A and B do not exhibit symptoms of blood clotting deficiencies, but they should not be used in breeding programs.