Co-presence of a point mutation and a deletion of exon 3 in the glycophorin C gene and concomitant production of a Gerbich-related antibody.

BACKGROUND

Antigens of the human blood group system Gerbich (Ge) are located on sialoglycoproteins glycophorin C (GPC) and glycophorin D (GPD).

CASE REPORT

The Ge+ proposita (RW) produced an alloanti-Ge after receiving 2 units of red cells (RBCs) during surgery. Further studies were carried out to characterize the antibody specificity, RBC GPC and/or GPD (GPC/GPD), and the glycophorin C gene (GYPC) from RW and her compatible siblings. RW's serum contained an alloanti-Ge that did not react with RBCs from RW or four of her siblings or with RBCs with Ge-negative phenotypes. An eluate of RW's antibody reacted weakly with GPC in Western blotting. RW's RBCs were positive with 20 alloanti-Ge2, 1 autoanti-Ge2, 4 alloanti-Ge3, and 1 alloanti-Ge4. Titrations revealed weak expression of these antigens on her RBCs and those of her compatible siblings as compared with controls. In contrast, titrations of mouse and rat monoclonal antibodies specific for GPC/GPD showed no differences. Western blotting of RBC membranes using GPC/GPD specific monoclonal antibodies showed a broad diffuse band corresponding to GPC.Ge in addition to GPC and GPD. Blotting of membranes from trypsin-treated RBCs from these individuals revealed an increase of 1500 in M(r) of membrane-bound tryptic fragment over that in the membranes from typsin-treated RBCs from persons with normal GPC/GPD. In RT-PCR, two products were obtained for RW and her compatible siblings: one had a complete deletion of exon 3 and the other had a base change (A-->T) in nucleotide 173 in exon 3 (confirmed by genomic DNA sequencing of exon 3). This point mutation has resulted in the loss of restriction enzyme Tth111 I-sensitive site in the mutant GYPC.

CONCLUSION

The specificity of antibody in RW's serum was serologically anti-Ge2. Two genetic events occurred in exon 3 in GYPC of RW and her compatible siblings. The exon 3 deletion confirmed a Ge:-2,-3,4 haplotype. The abnormal tryptic fragment obtained was due to the (A173-->T) base change in exon 3 that resulted in Asp58-->Val in the deduced amino acid sequence at the membrane boundary.