Blood Group, Chido/rodgers System

A number sign (#) is used with this entry because the Chido/Rodgers blood group system is based on variation in 2 closely linked genes, C4A (120810) and C4B (120820).

Description

The blood groups Chido (Ch) and Rodgers (Rg) are epitopes on the C4 protein, and polymorphisms associated with these epitopes may lead to the formation of antibodies to the Ch or Rg antigens in transfused patients. Identification of anti-Ch or anti-Rg is based on antibody neutralization with plasma from Ch-positive or Rg-positive individuals and lack of reactivity with qualified Ch-negative or Rg-negative red blood cells. The C4 protein occurs in 2 forms, C4A and C4B, which are encoded by 2 closely linked genes. C4A and C4B are expressed as single-chain precursors of 1,744 amino acids that are nearly identical, with amino acids differences at residues 1101 to 1106 distinguishing C4A from C4B. C4A and C4B are also distinguished by their expression of either the Ch antigen or the Rg antigen at residues 1188 to 1191, where the Ch1 epitope has ADLR and the Rg1 epitope has VDLL. C4A proteins usually carry the Rg antigens, and C4B proteins usually carry the Ch antigens, although in some haplotypes these associations are switched. Nine antigens have been described for the Ch/Rg system: 6 of high prevalence for Ch, 2 of high prevalence for Rg, and 1 of low prevalence, WH. Eight phenotypes of the Ch/Rg system have been established, with 88.2% of individuals having the Ch(1,2,3) Chido phenotype and 95.0% of individuals having the Rg(1,2) Rodgers phenotype (review by Mougey (2010)).

Molecular Genetics

Awdeh and Alper (1980) introduced a typing system that allowed them to detect 6 common structural alleles at the Rodgers (C4A) locus or 2 or 3 at the Chido (C4B) locus in whites.

History

The Chido blood group, which was discovered by Harris et al. (1967), is an antigenic characteristic of C4B. Chido has a low frequency of negatives (2%) and is tightly linked to HLA (Middleton and Crookston, 1972), closer to HLA-B (142830) than to HLA-A (142800). The Chido antigen resembles the HLA antigens in molecular structure.

Like Chido, Rodgers has a low frequency of negatives (about 3%) and is closely linked to HLA (Giles et al., 1976).