The molecular genetic background leading to the formation of the human erythroid-specific Xg/CD99 blood groups.

The Xg and CD99 antigens of the human Xg blood group system show a unique and sex-specific phenotypic relationship. The phenotypic relationship is believed to result from transcriptional coregulation of the and genes, which span the pseudoautosomal boundary of the X and Y chromosomes. However, the molecular genetic background responsible for these blood groups has remained undetermined. During the present investigation, we initially conducted a pilot study aimed at individuals with different Xg/CD99 phenotypes; this used targeted next-generation sequencing of the genomic areas relevant to and This was followed by a large-scale association study that demonstrated a definite association between a single nucleotide polymorphism (SNP) rs311103 and the Xg/CD99 blood groups. The G and C genotypes of SNP rs311103 were associated with the Xg(a+)/CD99H and Xg(a-)/CD99L phenotypes, respectively. The rs311103 genomic region with the G genotype was found to have stronger transcription-enhancing activity by reporter assay, and this occurred specifically with erythroid-lineage cells. Such activity was absent when the same region with the C genotype was investigated. In silico analysis of the polymorphic rs311103 genomic regions revealed that a binding motif for members of the GATA transcription factor family was present in the rs311103[G] region. Follow-up investigations showed that the erythroid GATA1 factor is able to bind specifically to the rs311103[G] region and markedly stimulates the transcriptional activity of the rs311103[G] segment. The present findings identify the genetic basis of the erythroid-specific Xg/CD99 blood group phenotypes and reveal the molecular background of their formation.