Hemophilia in dogs and cats: inheritance mechanisms and diagnosis

Hemophilia is the most common severe hereditary disorder of blood coagulation in animals and humans. In dogs and cats, the disease occurs as a result of spontaneous mutation. As soon as it appears in a particular population, the defect may manifest through many generations. In this article, we would like to discuss the main features of hemophilia, its clinical picture, etc.

Inheritance mechanisms

This in itself pathology is the result of a defect in one of the coagulation factors. More precisely, factor VIII, responsible for the formation of blood clots. If it does not work correctly, the platelets even in the presence of a serious wound remain intact (coagulation factor simply does not stand out), the formation of a blood clot does not occur, and the animal can bleed even from a trifle scratch itself.

Fortunately, the hemophilia gene inherited by the female line (by the way, this disease is practically not found in females) is very recessive. Only when offspring appear in parents, each of which is a carrier of a defective gene, is there a chance of the birth of sick animals. We discuss some features of the transfer:

  • When crossing a male with one defective recessive gene with a female who did not have hemophilia carriers in her ancestors, the gene in the first generation will not appear, but will go further to the descendants. Then hemophilia in dogs or cats can be a "surprise" in 10-20 years.
  • Males having one pathological gene, have hemophilia and will pass this pathological gene to all their daughtersbut not to one of his sons.
  • Females having one normal and one pathological gene are asymptomatic carriers and transmit the pathological gene, on average, 50% of male and 50% of female offspring (in other words, half of the litter will hurt, and the second will not).
  • If the X chromosome carrying the normal gene for factor VIII is represented as XH, then hereditary transmission of the disease can be expressed as follows:

Hemophilia usually occurs when a normal male crosses with a female carrierwhich has no clinical signs. Male puppies and kittens born in such a litter have a 50% chance of getting sick and a 50% chance of carriage of a defective gene. Average following 4 type categories descendants will be found in equal quantities:

Clinical signs and diagnosis

What are the symptoms of the disease? Hemophilicists very often experience spontaneous “swelling” of muscles and joint bags, developing against the background of microbleeds. In more sad cases, sudden death is possible with massive bleeding in the abdominal or chest cavity. Hematomas are regularly formed under the skin in sick animals. Sometimes it happens that a sick male dies after castration (occasionally because, as a rule, the owners usually know about the illness of their pet).

Various mutations responsible for hemophilia cause disease variability. Some forms of hemophilia are so severe that animals will die within the first few weeks of life. Other forms may be more sparing, and then sick pets will live, suffering from constant and unconditioned bleeding (most often this happens in animals).

How is hemophilia diagnosed in animals? For this, a special method is used that allows you to determine the degree of blood coagulation. It is called APTT, the method is a screening test for the determination of coagulation defects. But for an accurate diagnosis (especially in mild cases) DNA analysis is required. It is desirable that samples for him be taken not only from a sick animal, but also from parents and possibly as many of his ancestors.

Unfortunately, simple coagulation tests may not always help to distinguish between a carrier and healthy females. Generally female carriers show low levels of factor VIII, but there is a certain blurring of indicators between a healthy animal and doubtful cases of carriage. Detection accuracy can be improved by measuring the level of another blood protein associated with factor VIII (von Willebrand factor), followed by determining the ratio of these two proteins. Alas, even in this case, implicit and doubtful results are possible, and therefore, if the animal is of a certain breeding value, DNA analysis cannot be dispensed with.

By the way, is there a cure for this pathology? Unfortunately no. With the development of bleeding in sick individuals they are injected with calcium chloride 10%. This method is practiced in medicine and veterinary medicine almost from the moment the disease is described, and so far a simpler and more reliable method has not been developed.

Breeding recommendations

An assessment of the pedigrees can determine the status of the “carrier” for some asymptomatic females, will allow to assess the degree of risk of carriage, and will help confirm the laboratory diagnosis in case of doubtful results. All descendants of sick males, as well as female carriers, must be excluded from the reproduction process. It is strongly recommended that castration and sterilization be performed to completely eliminate the transmission of defective genes.

Siblings and maternal half-sisters in hemophilic males have a 50% chance of carriage. If possible, these animals should be completely excluded from the reproduction process. At the slightest suspicion of carriage, DNA testing material should be sent. Only when exactly the DNA analysis will show a clearly negative result, can males be used for reproduction. Here's how hemophilia manifests itself in cats and dogs.

Watch the video: Pedigree Analysis 1: How to solve a genetic pedigree No. 1 (December 2019).