Hemophilia B (Variant 1)

Hemophilia B is a clotting disorder characterized by a deficiency of factor IX, which is essential for the formation of blood clots. This condition results in hemostatic problems that can trigger severe bleeding. The genetic variant responsible is located in the F9 gene, responsible for encoding coagulation factor IX.

Symptoms

Hemophilia B in cats presents with various symptoms such as intermittent loss of appetite, fatigue, fever and difficulty walking. These signs may appear in different combinations. Severely affected individuals may die at birth as a result of umbilical hemorrhage, while those who survive the neonatal period may suffer from clotting problems such as hemorrhage and hematoma formation.

Disease Management

Treatment of hemophilia B focuses primarily on managing and preventing bleeding episodes caused by clotting factor IX deficiency. Options include transfusions of Fresh Frozen Plasma (FFP) and hemostatic medications to control active bleeding.

Genetic basis

This disease follows an X-linked recessive mode of inheritance. Recessive X-linked inheritance means that females must receive two copies of the mutation or pathogenic variant (one from each parent) to develop the disease, whereas males need only one copy of the mutated gene or variant from the mother to develop the disease. Male cats usually show symptoms of the disease. Each male kitten born to a mother carrying the mutation has a 50% chance of inheriting the mutation and thus the risk of developing the disease. Females that do not carry the mutation are not at increased risk of having affected kittens. Breeding between cats carrying genetic variants that can cause disease, even if they do not show symptoms, is not recommended.

Technical report

Hemophilia B, also known as Christmas disease, is an X-linked inherited clotting disorder manifested by a deficiency of functional clotting factor IX. This factor is crucial in the blood coagulation cascade, facilitating clot formation to stop bleeding. In the F9 gene, responsible for the production of coagulation factor IX, two genetic variants associated with hemophilia B have been identified in domestic cats. Here, we analyzed the variant consisting of a single nucleotide change in exon 4, which is crucial for encoding the first domain of epidermal growth factor. The specific change, c.383G>A, substitutes at the amino acid level a cysteine for a tyrosine, which probably affects the structure and function of factor IX, thus contributing to the manifestation of the disease.

Most affected breeds

Domestic Longhair

Bibliography

Goree M, Catalfamo JL, Aber S, et al. Characterization of the mutations causing hemophilia B in 2 domestic cats. J Vet Intern Med. 2005 Mar-Apr.