Three molecular structures cause rhesus D category VI phenotypes with distinct immunohematologic features

Rhesus D category VI (D-VI) is the clinically most important partial D, D-VI red blood cells were assumed to possess very low RhD antigen density and to be caused by two RHD-CE-D hybrid alleles, Because there was no population-based workup, we screened three populations in central Europe for D-VI. Twenty-six D-VI samples were detected and examined by exon-specific RHD polymerase chain reaction with sequence-specific primers (PCR-SSP). A new genotype, hereby designated D category VI type Ill, was characterized as a RHD-Ce(3-6)-D hybrid allele by sequencing of the cDNA, parts of intron 1, and by PCR-restriction fragment length polymorphism (PCR-RFLP) of intron 2. Rhesus introns 5 and 6 were sequenced and the 3' breakpoints of all known D-VI types shown to be distinct. We differentiated the 5' breakpoints of D-VI type land D-VI type II by a newly devised RHD-PCR. Thus, the D-VI phenotype originated in at least three independent molecular events. Each D-VI type showed distinct immunohematologic features in flow cytometry. The number of RhD proteins accessible on the red blood cells' surface of D-VI type III was normal(about 12,000 antigens/cell; D-VI type 1,500; D-VI type II, 2,400) based on the determination of an RhD epitope density profile. D-VI type II and D-VI type III occurred as CDe haplotypes, and D-VI type I as a cDE haplotype, The distribution of the D-VI types varied significantly in three German-speaking populations. Genotyping strategies should take account of allelic variations in partial RhD. The reconsideration of previous serologic and clinical data for partial D in view of the underlying molecular structures may be worthwhile, (C) 1998 by The American Society of Hematology.