THE GENETIC-BASIS OF A NEW PARTIAL D-ANTIGEN - D-DBT

The Rh system, the most polymorphic system on red cells, is geneticall y controlled by two different but highly homologous genes on chromosom e 1. The RHCE gene encodes different RhCeEe polypeptides and the RHD g ene encodes D antigens. It is well established that in D negative indi viduals the RHD gene is either absent or grossly deleted. The D antige n comprises at least nine serologically defined D epitopes. The D anti gen can be divided into different partial D categories, reflecting a d ifferent pattern of specific D epitopes. In this study an newly define d partial D antigen, D-DBT, was studied. D epitope mapping revealed th e presence of D epitopes 6/7 and 8 and the absence of the other D epit opes. The molecular basis of this phenotype was studied by Southern bl otting, by RHD typing using the polymerase chain reaction (RHD-PCR) an d by sequence analysis of Rh transcripts. The DBT phenotype appeared t o be encoded by a hybrid RHD gene, in which exons 5, 6 and 7 (and poss ibly and identical exon 8) were replaced by the corresponding exons of the RHCE gene. From this study it may be concluded that D epitopes 1, 2, 3, 4, 5 and 9 are dependent on the presence of RHD exons 5, 6, and 7.