COPRESENCE 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 (G PD). 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 an d/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-n egative 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 compati ble siblings as compared with controls. in contrast, titrations of mou se and rat monoclonal antibodies specific for GPC/GPD showed no differ ences. Western blotting of RBC membranes using GPC/GPD specific monocl onal antibodies showed a broad diffuse band corresponding to GPC.Ge in addition to GPC and GPD. Blotting of membranes from trypsin-treated R BCs from these individuals revealed an increase of 1500 in M-r of memb rane-bound tryptic fragment over that in the membranes from typsin-tre ated RBCs from persons with normal GPC/GPD. In RT-PCR, two products we re obtained for RW and her compatible siblings: one had a complete del etion 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 po int mutation has resulted in the loss of restriction enzyme Tth111 I-s ensitive site in the mutant GYPC. CONCLUSION: The specificity of antib ody in RW's serum was serologically anti-Ge2. Two genetic events occur red in exon 3 in GYPC of RW and her compatible siblings. The exon 3 de letion confirmed a Ge:-2,-3,4 haplotype. The abnormal tryptic fragment obtained was due to the (A(173)-->T) base change in exon 3 that resul ted in Asp(58)-->Val in the deduced amino acid sequence at the membran e boundary.