Cat Genetic Profile – Feline Blood Groups
Written by Dr. Chloé Fradet, DVM. (Translation DR)
As in humans and other mammals, cats, have blood groups very specific to their species. In cats, the major blood group is AB which is made up of subgroups A, B and AB. Blood groups are defined by antigens, often specific sugars that are found on the surface of red blood cells (erythrocytes) in the blood, and which work to develop (or not) an immune response against red blood cells. Blood typing is of major importance in order to avoid cases of reactive hemolysis during blood transfusion and for cases of neonatal isoerythrolysis in kittens.
Blood Group Frequencies
In the feline population, blood group A is found at the highest frequency (73 to 99.7%), blood group B is in second place (0.3 to 30%) and blood group AB has a fairly rare occurrence (0.2 to 20%). The prevalence of each group is highly dependent on cat breed and region. For example, breeds such as the Abyssinian, British Shorthair, Birman, Devon Rex, Himalayan, Persian, Scottish Fold and Somali have a higher frequency of blood group B than other breeds while Ragdoll cats have a higher frequency of blood group AB (18%) compared to other breeds.
Blood Typing
Blood typing can be done in several ways. The blood typing methods performed in veterinary clinics use antibodies against blood types to perform agglutination or immunochromatography tests. These two tests determine the cat’s blood group, either A, B or AB. In a genetic laboratory, it is possible to determine the blood group of the animal, but also to determine the exact versions (alleles) of the gene in the genome. The AB blood system includes 3 different gene alleles: A, aAB and b. The A is dominant over the other two alleles, while the aAB is co-dominant with b. Therefore, a cat with blood group A can have the genotypes A/A, A/aAB or A/b, a cat with blood group AB can be aAB/aAB or aAB/b, while a cat with blood group B has alleles b/b.
Feline Neonatal Isoerythrolysis
The vast majority of cats have natural antibodies against the blood group that they do not have. In general, cats in blood group B have very strong antibodies against antigens for blood group A, while cats in blood group A have weak anti-B antibodies.
A mating between a female in blood group B (alleles b/b) and a male in blood group A (alleles A/A, A/aAB or A/b) is highly likely to cause neonatal isoerythrolysis in any kittens of blood group A.
In fact, with the first feeding of colostrum (first milk) , the mother transmits a lot of antibodies to her babies, including anti-A antibodies. These anti-A antibodies in babies of blood group A will destroy the kitten’s red blood cells, a situation called neonatal isoerythrolysis. This is a phenomenon similar to our Rh (Rhesus) system, although the antigen and antibodies are different.
This isoerythrolysis reaction can be fatal in kittens of blood group A, so it is not recommended to keep females of blood group B (gene alleles b/b) for breeding, unless they are bred with a male of blood group B. Conversely, there is no danger of mating a female of blood group A with a male of blood group B since, as mentioned above, the antibodies against the antigens of blood group B are found at a low level in the blood.
Mating of a male in blood group A with a female in blood group B
Here are the theoretical results obtained by mating males in blood group A (alleles A/A, A/aAB or even A/b) with a female in blood group B (alleles b/b). This demonstrates the importance of having parents genetically tested before mating them.
Blood Transfusion
Since cats naturally have antibodies against the blood group that they do not have, it is of utmost importance to know the cat’s blood group before performing a blood transfusion. Even if blood group A is the most common in cats, a blood transfusion of even a few milliliters of group A blood to a cat with blood group B could result in a severe destruction of red blood cells (hemolytic reaction) and could lead to the death of the animal. The clinical signs of a severe hemolytic reaction are signs of hypotension, vomiting, vocalization, lethargy as well as jaundice (yellowish mucous membranes). However, transfusion of group B blood to a cat with group A blood will provoke a much milder reaction that will take place over a longer period of time, approximately 48 hours. In this case, signs of discomfort, restlessness, tachycardia, tachypnea, hemoglobinemia and hemoglobinuria may be observed.
Mutation Frequencies
Among the cats tested at Labgenvet for alleles associated with blood groups, 71.5% were females and 28.5% were males. About 85% of the cats were blood group A, of which 59% had alleles A/A (clear for allele b) and 26% had alleles A/b (carrier for allele b). 15% of the cats tested were blood group B (alleles b/b).
Among these cats, the most common breeds are shown in the table below.
Genetic Laboratory Test
The AB blood group system involves sugars on the surface of red blood cells, function as antigens to stimulate (or not) an immune response. The enzyme cytidine monophospho-N-acetylneuraminic hydroxylase (CMAH) is responsible for the synthesis of sialic acid-like sugars found on the surface of red blood cells.
A cat in blood group A has a sialic acid sugar type Neu5Gc on the surface of red blood cells, while a cat in blood group B has a sialic acid sugar type Neu5Ac on the surface of red blood cells. The CMAH enzyme converts Neu5Ac to Neu5Gc if it is functional. Allele A therefore gives a functional enzyme while allele b gives an enzyme which is not functional due to the insertion of 18bp into exon1 of the gene. In addition, the CMAH gene has SNPs which correlate with A/b status: c.139 G> A, c.265 T> A, c.1600 G> A. The aAB allele has a c.364 C> T mutation which gives a partially functional enzyme. The DNA test used by Labgenvet consists of detecting the mutation associated with the b allele. The aAB allele can be detected by a separate test.
References:
- Lien OMIA [000119-9685]
- Bighignoli B, Niini T, Grahn RA et al. (2007) Cytidine monophospho-N-acetylneuraminic acid hydroxylase (CMAH) mutations associated with the domestic cat AB blood group. BMC Genetics 8:27. [pubmed/17553163]
- Gandolfi B, Grahn RA, Gustafson NA, et al. (2016) A Novel Variant in CMAH Is Associated with Blood Type AB in Ragdoll Cats. PLoS One. 11(5):e0154973. [pubmed/27171395]
- Omi T, Nakazawa S, Udagawa C, Tada N et al. (2016) Molecular Characterization of the Cytidine Monophosphate-N-Acetylneuraminic Acid Hydroxylase (CMAH) Gene Associated with the Feline AB Blood Group System. PLoS One. 11(10):e0165000. [pubmed/27755584]
- Kehl A, Heimberger K, Langbein-Detsch I et al. (2018) Molecular characterization of blood type A, B, and C (AB) in domestic cats and a CMAH genotyping scheme. PLoS One. 20;13(9):e0204287. [pubmed/ 30235335]
- Kehl A, Mueller E, Giger U (2019) CMAH genotyping survey for blood types A, B and C (AB) in purpose-bred cats. Anim Genet 50 (3):303-306. [pubmed/30854707]
- Corlouer. Groupes sanguins chez le chat [En ligne]. Paris. [Cité le 20 décembre 2019]. Disponible : Fregis, Groupes sanguin chez le chat.
- UC Davis. AB blood group in felines [En ligne]. Californie. . [Cité le 20 décembre 2019]. Disponible : UC Davis, AB blood group in felines.