Hemophilia is a bleeding disorder of varying severity that is due to a deficiency in specific clotting factors. Normally the body responds to an injury that causes bleeding through a complex defence system. This consists of local changes in the damaged blood vessels, activation of blood cells called platelets, and the coagulation (clotting) process. Most inherited bleeding disorders are the result of abnormal platelet function or a deficiency in one or more of the factors involved in the blood clotting system.
Hemophilia is the most common inherited coagulation factor deficiency. Hemophilia A is a result of a deficiency of factor VIII, and hemophilia B of factor IX. Hemophilia A is more common than hemophilia B, and varies in severity depending on the level of factor VIII activity. Hemophilia B is often a severe bleeding disorder.
Hemophilia is an X-linked,recessive disorder. It is one of the few sex-linked traits in dogs. Because males have only 1 X chromosome, a male dog is either affected or clear of the defect. Females, with 2 X chromosomes, may be affected (abnormal gene on both chromosomes), clear, or a carrier with no clinical signs (one gene affected). In effect, the disease is carried by females but affects mostly males. The disease occurs in many different breeds and in mixed breed dogs as well. The German shepherd is the breed most commonly affected.
Dogs with mild forms of hemophilia may experience few or no signs, and may never require treatment until/unless surgery or trauma is followed by excessive bleeding.
Where hemophilia is more severe, you may see signs of a problem at a fairly early age. Your pup may have prolonged bleeding associated with the loss of baby teeth, or unexplained areas of bleeding under the skin. Bleeding into muscles or joints will often cause lameness.
Once the condition is diagnosed, your veterinarian will discuss ways to manage this lifelong problem. These include being alert for signs of bleeding episodes in your dog, and tips on housing and maintenance so as to minimize risks of bleeding. Periodic blood transfusions will generally be required. Unfortunately, dogs with severe hemophilia often die or are euthanized because of recurrent or uncontrollable bleeding problems.
The clinical signs associated with hemophilia vary widely, based on the severity of the bleeding disorder and where in the body the bleeding occurs. Because this is a sex-linked disorder, dogs with hemophilia are almost always male. Affected dogs are commonly brought to the veterinarian for problems such as bloody diarrhea that is difficult to control, areas of bleeding under the skin, or lameness (due to bleeding into muscles or joints). Bleeding under the skin or into the muscle may occur after routine vaccination, or there may be prolonged or severe bleeding at surgery (such as when your dog is neutered.) Other less common problems include respiratory difficulties due to bleeding into the chest or around airways, or weakness, paralysis, or even sudden death due to bleeding into the brain or spinal cord.
Once a bleeding disorder is suspected, specialized laboratory tests are carried out to diagnose the specific disorder. If your pup is diagnosed with hemophilia, it is important that you inform the breeder so that he or she can have your dog's parents tested. (The mother is likely a carrier and the father free of the defect.)
For the veterinarian:
CLINICAL: Signs are highly variable and often non-specific: unthriftiness, acute blood loss anemia, unexplained sub-cutaneous masses, hematomas (often at injection sites), refractory bloody diarrhea. Other signs depend on the local physiologic impact of hemorrhage: for example bleeding into the brain or around nerve trunks will cause neurologic signs, and bleeding around airways or into the pleural cavity will cause respiratory signs. Lameness is commonly associated with hemorrhage into muscles or joints, especially in larger breeds.
LABORATORY: normal PT (prothrombin time) and prolonged aPTT (activated partial thromboplastin time); definitive diagnosis requires a specific assay for factors VIII and IX. Factor activity will be markedly decreased. Specific factor assays are also required to screen for female carriers (heterozygotes), who usually have about 40 to 60% of normal factor activity. Consult your diagnostic laboratory for specific information about sample collection and submission.
There is no cure for this disorder. Mildly affected dogs may never require treatment, or only after surgery or trauma.
With more severe hemophilia, your dog will require periodic transfusions when bleeding occurs, to replace the deficient coagulation factor activity. Strict cage rest is important along with transfusion, to decrease further hemorrhage.
For the veterinarian:
Administer fresh plasma, fresh frozen plasma, or cryoprecipitate (factor VIII) or cryosupernatant (factor IX) plasma. Transfused factors have a relatively short half-life so plasma may need to be transfused every 8 to 12 hours until the bleeding stops. Fresh whole blood may be used but it must be carefully cross-matched to prevent future transfusion reactions.
Because hemophilia is a sex-linked recessive trait and the carrier state can be detected by testing, this disorder can be controlled. German shepherd females and females from lines of other breeds where hemophilia has been diagnosed, should be tested for the carrier state. Males used for breeding should be screened for the disorder.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Brooks,M. 1998. Hereditary bleeding disorders. ACVIM-Proceedings of the 16th Annual Veterinary Medical Forum: 424-426.
Brooks MB. Hemophilias and other hereditary coagulation factor deficiencies. In: Côté E, ed. Clinical Veterinary Advisor Dogs and Cats. Missouri: Mosby Elsevier, 2007:482-3.
Sargan DR. Coagulation disorders in IDID - Inherited diseases in dogs:web-based information for canine inherited disease genetics. Mamm Genome. 2004 Jun;15(6):503-6.