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

Abstract

Rhesus D category VI (D(VI)) is the clinically most important parital D. D(VI) red blood cells were assumed to possess very low RhD antigen density and top 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 bu exon-specific RHD polymerase chain reaction with sequence-specific primers (PCR-SSP). A new genotype, hereby designated D category VI type III, 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 lenght 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 I and 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 distint immunonohematologic 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) density profile. D(VI) type II and D(VI) type III occured as CDe haplotypes, and D(VI) type I as 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 partiak D in view of the underlying molecular structures may be worthwhile.