A functional AQP1 allele producing a Co(a–b–) phenotype revises and extends the Colton blood group system

Abstract

The Co(a-b-) phenotype can be generated by a functional AQP1 allele, that is, AQP1 140G encoding AQP1 (Q47R) and allowing the development of a novel Colton alloantibody. This study also shows that the Co(b) antigen can be produced by at least two different substitutions at Amino Acid Position 45, that is, A45V and A45T.

Colton Blood Group System

“…Her antibody did not react with Co(a − b − ) cells, but could not be anti -Co3 as it did not react with her own Co:3 red cells [40] . Two other Co(a − b − ) individuals with the Gln47Arg are reported [40,41] . − 04 ).…”

“…Her phenotype was not Co null as her red cells expressed normal levels of Co3, normal quantities of AQP1, and exhibited normal water permeability. Transfection experiments in K562 cells demonstrated that Gln47 is also required for Co b expression [40] . She was homozygous for 140A > G encoding Gln47Arg ( CO * 01.…”

Immunohematology, Blood Groups

“…The function of AQP-1 in RBCs may be to rehydrate rapidly after shrinking in the hypertonic environment of the renal medulla (Smith et al, 1993). Co a has a prevalence of 99.9%, its antithetical antigen Co b has a prevalence of 10%, and Co3 and Co4 are present on all RBCs except on those of the very rare Co(aÀbÀ) null phenotype (Arnaud et al, 2010). Apparently healthy individuals with the Co(aÀbÀ) phenotype and AQP-1 deficiency have RBCs with an 80% reduction in the ability to transport water.…”

International Society of Blood Transfusion Working Party on red cell immunogenetics and blood group terminology: Berlin report

“…Molecular analysis of AQP1 revealed homozygosity for 140A>G, encoding the amino acid change Gln47Arg, in close proximity to the Co a /Co b polymorphism at residue 45. Samples from a second Co(a–b–) proband homozygous for the same 140A>G mutation were investigated following detection of an antibody to a high incidence antigen initially identified as anti-Co3 [15]. Unexpectedly, her RBCs were shown to have functional aquaporin 1.…”

“…Expression studies with AQP1 encoding Arg47 demonstrated a loss of Co a antigen expression despite the presence of the Co a -specific Ala45, consistent with the observed phenotype. Arnaud and colleagues [15] also re-evaluated three antisera classified as anti-Co3 in their collection and re-identified one of the three sera as anti-Co4. PCR-RFLP analysis revealed that this sample also was homozygous for AQP1 140G.…”