Genetic background of anti-Xg^a producers in Japanese blood donors

The Xg blood group is composed of two antigens, Xg^a (XG1) and CD99 (XG2 and MIC2). The XG and CD99 are homologous genes located on pseudoautosomal region 1 of the X and Y chromosomes. The expressions of Xg^a and CD99 are co-regulated by a single nucleotide polymorphism (rs311103) in the GATA-1 binding region. Another mechanism of the Xg(a-) phenotype is the genomic deletion of approximately 114 kb, including the XG gene. Anti-Xg^a seems to be naturally occurring by detection in males who have never been transfused.

In this study, we identified 23 anti-Xg^a producers among 580,115 donors (0.004%). Additional 12 anti-Xg^a producers were also identified from a separate cohort.

All 35 anti-Xg^a producers were male. Genomic DNA was obtained from 34 of 35 producers, and all 34 producers were confirmed to carry the XG-gene-deficient allele (XGdel). The breakpoints of all 34 producers were identical. The XGdel was also identified in 12 non-producers of anti-Xg^a among 860 donors who have no antibodies against RBCs, and the breakpoints were also identical with the anti-Xg^a producers.

Our results will serve as the basis for a more complete understanding of Xg blood group polymorphisms.