Hemophilia in Dogs and Cats
Occasionally, an animal’s ability to clot blood is diminished. This is called a coagulation disorder or a coagulopathy. Coagulopathies can be life threatening, as they can lead to hemorrhage and bleeding into a major organ, which may cause an animal to rapidly decompensate.
Hemophilia is caused by a lack of certain proteins that allow blood to clot properly. These proteins are referred to as clotting or coagulation factors. These factors are produced in the liver and circulate in the bloodstream. When a blood vessel or tissue is injured, the thirteen factors work together in a specific order to form the coagulation cascade, a complex process designed to slow and eventually stop bleeding. These specific proteins work in conjunction with platelets to help the body make blood clots and stop bleeding.
Hemophilia A is the most common clotting disorder in both humans and animals. It has been observed in cats, dogs, horses, and cattle. It is caused by a mutation of the gene that produces Factor VIII, which is an important clotting protein. Once this mutation has occurred, it can then be passed down through generations. Hemophilia is a sex-linked recessive gene, meaning that it is carried on the X chromosome and will be dormant in the presence of a dominant gene. All males have one X gene, which they inherit from their mothers, and all females have two, one which is inherited from the mother and one from the father. As it is a recessive gene, the existence of just one normal X gene is enough to keep the disorder from manifesting. Since females have two X genes, they can have one normal X gene and one mutated gene, making them carriers. As carriers, they will not show any signs of hemophilia themselves, but can still pass the disorder to their offspring and should not be bred.
What Are the Symptoms?
The severity of clinical signs will depend on the severity of disease. Normal animals show activity of Factor VIII at greater than 60%, whereas carriers show activity at 40 – 60%. Animals with mild disease show 6 – 20% activity. Most animals show less than 6% of activity and can be defined as having moderate to severe disease.
Signs of Hemophilia A include bleeding spontaneously into muscles or joints (causing lameness or swelling), bleeding under the skin (hematoma), and hemorrhaging into the chest or abdominal cavity. If the hemorrhage is severe enough, it can be fatal. Hemophilia A is typically not diagnosed until an animal undergoes surgery or experiences trauma. It is usually suspected in young animals who have extreme bleeding after routine procedures, such as vaccines or spay/neuter surgeries. There may also be abnormal bleeding of the gums when growing teeth. Puppies and kittens who have a severe deficiency of Factor VIII may be stillborn or die shortly after birth due to extreme hemorrhaging.
Hemophilia B is less common than Hemophilia A. Similar to Hemophilia A, Hemophilia B is a mutation in the gene that produces a certain clotting factor. In this case, it is Factor IX, which is also known as the Christmas Factor. It has been noted in Labrador Retrievers, German Shepherds, mixed-breed dogs, British short-haired cats, and Siamese mix cats. Hemophila B is also a sex-linked gene on the X chromosome. Carriers are female and most are asymptomatic, but they should not be bred to prevent passing the gene to offspring.
What Are the Symptoms?
Hemophilia B has many of the same clinical symptoms as A, though it tends to be a milder disease. Animals may spontaneously bleed into the thorax, abdomen, or brain. These bleeding episodes may not be noticed until they become an emergency. Bleeding that is unchecked can cause muscle necrosis, seizures, and/or shock. Often, there is no problem until there is surgery or trauma that causes extreme bleeding.
Hemophilia C is an extremely rare deficiency of Factor XI. It has been recognized in the Springer Spaniel, Great Pyrenees, Weimaraner, and Kerry Blue Terrier breeds. Like A and B, this disorder is also linked to a gene. Unlike A and B, it is an autosomal inheritance, meaning it is not connected to a sex chromosome and not passed by any specific gender. It is unknown if it is a dominant or recessive gene.
What Are the Symptoms?
In Hemophilia C, bleeding is induced by trauma or surgery. The animal appears to be recovering normally until 24 – 48 hours post surgery, when hemorrhaging begins. Bleeding can be delayed for up to 4 days. Research in humans shows that there may be a relation between Hemophilia C and the early breakdown of clots, due to the lack of a preventative enzyme. Though clots are initially formed, they are quickly destroyed, explaining the delayed bleeding.
How Is Hemophilia Diagnosed?
As hemophilia is a disorder of the coagulation of blood, the main tests performed are blood tests. The activated partial thromboplastin time test (aPTT) screens for coagulation disorders. aPTT measures how long it takes for blood to form a clot. In animals with hemophilia, this time will be increased. Many specialty clinics will have the machine necessary to run this test in hospital.
An activated coagulation time (ACT) may also be run. For this test, blood is placed into a tube, which contains a substance called diatomaceous earth that activates coagulation factors. If the factors are low, it will take longer for the blood in these tubes to clot. While these tests reveal that there is a clotting disorder, they do not tell us specifically which disorder is present. In order to discover which factor is deficient, the blood must be sent to an outside lab where they can measure the coagulation factor levels.
Testing is not always definitive in animals younger than 6 months old, as they often have a lower level of coagulation factor activity.
How Is Hemophilia Treated?
Treatment for all three types of hemophilia involves transfusions of blood products. There are many products that can be used, but fresh frozen plasma and cryoprecipitate are preferred. Fresh frozen plasma (FFP) is the fluid portion of blood that is frozen within 8 hours. FFP contains all coagulation factors. Cryoprecipitate is prepared from fresh frozen plasma that has been run through a centrifuge to separate and gather the solid parts of the fluid. This is then mixed with a small amount of plasma and frozen or freeze dried. When using freeze-dried cryoprecipitate, it needs to be reconstituted with sterile saline. Cryoprecipitate contains most coagulation factors, but has a large amount of Factor VIII, so it is most useful for hemophilia A.
These blood products are used because, unlike whole blood which contains all elements found in blood, they do not contain red blood cells (RBCs). RBCs contain antigens, which are substances that are recognized as foreign by the body, leading to an immune response. By transfusing products that do not contain RBCs, a reaction is less likely. Animals may need multiple transfusions of plasma or cryoprecipitate to curb bleeding. They may also need multiple transfusions throughout their lifetimes. Since you are only transfusing the parts of blood that the animal needs, less is necessary than if utilizing whole blood.
Is Hemophilia Curable?
There is no cure for hemophilia. It is an inherited disease and part of the animal’s genetic makeup. Animals will exhibit a life-long bleeding tendency, and it is important for owners to be aware and careful in relation to this condition. With proper care, animals with hemophilia can live long and normal lives.