Blood Group AB, blood types A, AB, B
and the alleles A, a^AB, and b in the cat

 

Phenotypes and biochemistry:

The major blood group in the cat is the AB group, responsible for three blood serotypes:

Blood type A: the most common, frequency of 73-99.7% depending on the breed and the region

Blood type AB: the least common, frequency of 0.2-20%

Blood type B: frequency of 0.3-30%

Blood group AB cats have sugars on the surface of their red blood cells, which 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-type sugar found on the surface of red blood cells.  A blood type A cat has a Neu5Gc sialic acid sugar on the surface of its red blood cells, while a blood type B cat has a Neu5Ac sialic acid sugar on the surface of its red blood cells.  It is the enzyme CMAH that makes the conversion between the Neu5Ac and Neu5Gc sugars.

Genetics and alleles:

The gene responsible for the AB blood group is CMAH.  The CMAH gene encodes for the enzyme cytidine monophospho-N-acetylneuraminic hydroxylase.  The three alleles responsible are the allele A, the allele a^AB and the allele b of the CMAH gene.  The dominance relationship between the alleles is as follows:

A > a^AB > b

The allele A gives a functional enzyme whereas the allele b gives an enzyme which is not functional due to an insertion of 18bp into exon1.  In addition, the CMAH gene has SNPs that correlate with the A/b status: c.139 G> A, c.265 T> A, c.1600 G> A.  The a^AB allele with a c.364 C>T mutation gives an enzyme with partial function.

Neonatal isoerythrolysis (red blood cell rupture at birth):

Cats with blood type A (A/- alleles) have natural anti-B antibodies in the blood at low levels.  Cats with blood type B (b/b alleles) have natural anti-A antibodies in the blood at high levels.  A situation of neonatal isoerythrolysis can occur when a blood type B female (with b/b alleles) is bred with a blood type A male (with A/A or A/b or even A/a^AB alleles).  Gestation is normal but after birth, the kittens with blood type A (A/b allele) absorb maternal anti-A antibodies in the colostrum, precipitating the destruction of red blood cells (isoerythrolysis) which can be lethal to kittens.  It is better not to use Blood type B (alleles b/b) female cats for breeding.

Blood group AB and the cat’s breed:

Most cats are blood type A with A/A alleles.  Breeds that are almost fixed for the A allele include Siamese, Tonkinese, and Burmese.  The b allele is seen in the British Shorthair, Birman, Devon Rex and Cornish Rex races at a frequency between 25-50%.  Twenty percent of Ragdoll cats are blood type AB, because of the a^AB allele.

Blood group AB phenotypes and genotypes:

The concordance between the blood type (phenotype) and the genotype is as follows:

Phenotype:                             Genotype:
Blood type A                          A/A or A/a^AB or A/b
Blood type AB                       a^AB/a^AB or a^AB/b
Blood type B                          b/b

 

References:

Labgenvet blog

Anderson H, Davison S, Lytle KM et al. (2022) Genetic epidemiology of blood type, disese and trait variants, and genome-wide genetic diversity in over 11,000 domestic cats.  PLoS Genet 18(6):e1009804.  [pubmed/35709088]

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]

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]

https://www.vgl.ucdavis.edu/services/abblood.php