Characterization of GYP(B-A-B) hybrid glycophorins among Thai blood donors with Mia-positive phenotypes.

Background: GYPA and GYPB genes encode the antigens of the MNS blood group system carried on glycophorin A (GPA) and glycophorin B (GPB), or on a hybrid molecule of GPA and GPB. GP hybrid variants are created through unequal crossing over and gene conversion, typically from the parent genes GYPA and GYPB. In the present study, we characterized the GYP(B-A-B) hybrid variants among Thai blood donors with Mi^a-positive phenotypes using PCR-based coupled to DNA sequencing techniques.

Materials and methods: Altogether, 1,020 samples from Thai blood donors were tested with anti-Mi^a by conventional tube technique (CTT). Polymerase chain reaction with sequence-specific primer (PCR-SSP) was initially used to differentiate normal GYPB, GYP*Vw and groups of GYP*Hut, GYP*Mur, GYP*Hop, GYP*Bun and GYP*HF alleles. Subsequently, GYP(B-A-B) hybrid variants were investigated using DNA sequencing.

Results: Among 1,020 blood donors, 127 (12.45%) were Mi(a+) phenotypes. The comparison Mi^a typing results between CTT and PCR-SSP were concordant. All Mi(a+) samples were positive with only group of GYP*Hut, GYP*Mur, GYP*Hop, GYP*Bun and GYP*HF alleles by PCR-SSP. Regarding the sequencing results, 115/1,020 (11.27%) donors carried the GYP*Mur, of which 111/1,020 (10.88%) were GYP*Mur/GYPB heterozygotes and the other 4/1,020 (0.39%) donors were GYP*Mur/GYP*Mur homozygotes. The remaining 12 donors included different GYP*Bun-like alleles; 11 of them (1.08%) were GYP*Thai/GYPB heterozygotes, and one (0.10%) was GYP*Thai II/GYPB heterozygotes. With 5.83% (119/2,040) of the total hybrid alleles, GYP*Mur was the predominant allele. The GYP*HF, GYP*Bun, GYP*Hop and GYP*Kip alleles were not observed in this study.

Discussion: Regarding the hybrid GP variants, a consensus of observed prevalent GYP*Mur and GYP*Bun-like alleles, respectively, was identified in the Thai population. The introduction of our strategy has allowed us to identify the zygosity for GYP hybrid variants, particularly GYP(B-A-B) hybrid genes, when antisera are unavailable and lacking adequate phenotypic features to determine GP variants.