Blood group AB (variant 4)

Blood grouping is based on the identification of the presence or absence of certain antigens (glycoproteins) on the surface of red blood cells. The feline blood group system is composed of type A, B and AB (also called C).

Definition

The blood group is determined by the surface antigens expressed on the membrane of red blood cells or erythrocytes. In cats, the AB blood group system has been identified as consisting of two antigens A and B and is composed of blood group type A, blood group type B and blood group type AB (or type C). Against these antigens, antibodies can be created naturally or acquired (after transfusion). The enzyme cytidine monophospho-N-acetylneuraminic acid hydroxylase (CMAH) is responsible for converting N-acetylneuraminic acid (NeuAc) into N-glycolylneuraminic acid (NeuGc), thus determining the sugar bound to red blood cells and the type of antigen. Type A erythrocytes express NeuGc, type B erythrocytes express NeuAc, and type AB erythrocytes express both NeuGc and NeuAc. Several variants have been identified in the CMAH gene that have been linked to the three blood group types, however, by four of these variants (c.179G>T, c.268T>A, c.364C>T and c.1322delT) can be used to estimate all blood group types in a wide range of breeds. The three variants c.179G>T, c.268T>A and c.1322delT seem to be mainly responsible for the defective conversion of NeuAc to NeuGc, thus also responsible for blood type B. Whereas, the c.364C>T variant is estimated to reduce CMAH activity, leading to the presence of NeuAc and NeuGc, and thus resulting in blood type C. If the CMAH gene function is not altered, blood type A is expressed. In this case, we analyzed the c.364C>T variant.

Genetic basis

The CMAH locus has three alleles that make up the following allelic series A>Ac>b. Therefore, type A cats can be A/A, A/b and A/Ac, type AB cats are either Ac/Ac or Ac/b and type B cats can only be b/b. The A allele is associated with the absence of the four variants and as it is the dominant allele, even if there is a copy of one of the four variants, the cat will be of the A group. The b allele is linked to the presence of any of the three variants: c.179G>T, c.268T>A or c.1322delT. If a cat has two copies of any of these or one copy of two different variants, the cat will be group B. The Ac allele is identified when the cat has the variant c.364C>T, associated with group AB.

Other relevant information

When antibodies are created in an acquired form following an incompatible blood transfusion, the resulting symptomatology varies depending on the blood type of the recipient and the donor. In the case of a blood transfusion to a type B cat with type A blood, severe symptoms such as lethargy, bradycardia, cardiac arrhythmia, respiratory distress, vomiting and even neurological disorders can occur. On the other hand, when a type A cat receives type B blood, reactions tend to be less severe, but may still include restlessness, tachycardia and tachypnea.

Bibliography

Bighignoli B, Niini T, Grahn RA, et al. Cytidine monophospho-N-acetylneuraminic acid hydroxylase (CMAH) mutations associated with the domestic cat AB blood group. BMC Genet. 2007 Jun 6