Background/Case Studies: The Gerbich (GE) blood system consists of 13 antigens: 8 high-prevalence and 5 low-prevalence. The antigens are located on glycophorin (GP) C and/or GPD encoded by GYPC. The high-prevalence GE10, GE11, GE12, GE13 and GE14 each result from a single nucleotide change in GYPC. The rare GE:-2,3,4 or GE:-2,-3, 4 phenotypes arise from deletions involving exon 2 or 3 and probands can make alloanti-Ge2 and/or -Ge3, respectively. We investigated a sample from a 26-year-old Mexican woman (postpartum G2 P2) whose plasma contained an antibody to a high-prevalence antigen.
Study
Design/Methods: Serologic testing was by tube hemagglutination. Rare RBCs and antibodies were from our in-house collection.RBCs were treated with papain, trypsin or dithiothreitol (DTT). Genomic DNA was isolated from WBCs. Sanger sequencing of GYPC exons 1-4 and flanking introns and long-range PCR of GYPC exons 2-3 was done.
Results/Findings: Patient plasma reacted 2+ to 3+ in the IAT with all RBCs tested; autocontrol was negative. Plasma reacted with papain, trypsin or DTT treated RBCs and anti-Dib, -Coa, -Vel, -Yta, -Lub and -U were ruled out. Patient ethnicity and plasma pattern with enzyme or DTT RBCs suggested an antibody to a GE system antigen. Plasma reacted 2+ with GE:-2,3,4, but GE:-2,-3,4 RBCs did not react, suggesting anti-Ge3. The plasma did not react with 3 additional GE:-2,-3,4 RBCs. Interestingly the patient’s RBCs were neg to micro+ with anti-Ge2 (n=4) , neg to 2+ with anti-Ge3 (n=3) and 2+ with mAb anti-Ge4 (pos control=4+).Although initial results were consistent with anti-Ge3, additional results suggested an antibody to a high-prevalence GE antigen lacking on GE:-2,-3,4 RBCs, but not anti-Ge3.GYPC sequencing identified heterozygous change c.333A >G (p.Gly111=), and hemi- or homozygous novel change c.190G >C (p.Gly64Arg) not found in gnomAD v.4.01.01. Long-range PCR and sequencing detected exon 3 deletion and confirmed c.190C, for a GE*01.-03.01,GE*01(190C) genotype. Conclusions: We report a compound heterozygote with novel GE*01(190C) in trans to GE*01.-03.01 (Gerbich type). Baby’s RBCs were DAT– and no evidence of HDFN was noted. The plasma reactivity pattern and the target antigen characteristics, combined with GYPC sequencing, indicates the alloantibody in her plasma recognizes a novel high prevalence GE antigen, provisionally named GEGA. Interestingly, p.64Arg encoded by c.190C is predicted in the transmembrane region of the RBC; the change from Gly to Arg, which is positively charged, may alter the protein conformation. Similar to Ge3 this novel high-prevalence antigen is resistant to treatment with papain, trypsin or DTT, in contrast to the high-prevalence antigens GE10, GE11, GE12, GE13 and GE14, which are sensitive to treatment with papain or both papain and trypsin.
