Background and Objectives-In the Rh blood group system, partial D, C, and e antigens are well-known, but a partial c antigen resulting in the production of alloanti-c in a c+ individual is rare. One example of an alloanti-c in a c+ person was an anti-Rh26, which can appear as anti-c, and another was an alloanti-c in a c+ person with a presumed R 1 r phenotype. The finding of an apparent alloanti-c in a transfused c+ patient initiated this investigation.

Antigens in the Gerbich blood group system are expressed on glycophorin C (GPC) and glycophorin D (GPD), which are both encoded by a single gene, GYPC. The GYPC gene is located on the long arm of chromosome 2, and Gerbich antigens are inherited as autosomal dominant traits. There are 11 antigens in the Gerbich blood group system, six of high prevalence (Ge2, Ge3, Ge4, GEPL [Ge10*], GEAT [Ge11*], GETI [Ge12*]) and five of low prevalence (Wb [Ge5], Ls a [Ge6], An a [Ge7], Dh a [Ge8], GEIS [Ge9]). GPC and GPD interact with protein 4.1R, contributing stability to the RBC membrane. Reduced levels of GPC and GPD are associated with hereditary elliptocytosis, and Gerbich antigens act as receptors for the malarial parasite Plasmodium falciparum. Anti-Ge2 and anti-Ge3 have caused hemolytic transfusion reactions, and anti-Ge3 has produced hemolytic disease of the fetus and newborn (HDFN).

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A new RHCE-D structure is associated with altered expression of C and e antigens in this family and the generation of a novel low-prevalence antigen (CENR).