Rearrangements of the blood group RhD gene associated with the D(VI) category phenotype

Abstract

The Rh (Rhesus) blood group antigens, D, Cc, and Ee, are carried by three unglycosylated membrane proteins of the human erythrocytes encoded by two highly related genes, D and CcEe. The major antigen, D, is a mosaic composed of at least nine determinants (epD1 through epD9). The lack of expression of some of these D epitopes at the surface of variant red blood cells defines the so-called D category phenotypes. In this report, we have determined the molecular basis of the D(VI) category phenotype characterized by the lack of epitopes D1, D2, D5, D6/7, and D8. Southern blot analysis and mRNA sequencing showed that the D(VI) phenotype is associated with two types of rearrangement of the D gene. Of 10 D(VI) genomes investigated, 8 exhibited a segmental DNA replacement (gene conversion) between the D fragment encompassing exons 4, 5, and 6 and the equivalent region of the CcEe gene. In the two other variants, these three exons are deleted. In both cases, the genomic rearrangement did not alter the reading frame of the variant RhD transcripts that are translated in 417 and 266 amino acid polypeptides, respectively. A heterogeneity of category D(VI) samples based on variable reactivity of the red blood cells with anti-D antibodies was previously found to be associated with the CD(VI)e or cD(VI)E haplotypes. Interestingly, our present results indicated that this serologic subdivision of the D(VI) category is correlated to two types of genomic rearrangements of the D gene.