RHD positive haplotypes in D negative Europeans.

BACKGROUND: Blood group genotyping is increasingly utilized for prenatal diagnosis and after recent transfusions, but still lacks the specificity of serology. In whites, the presence of antigen D is predicted, if two or more properly selected RHD-specific polymorphism are detected. This prediction must fail, if an antigen D negative RHD positive allele is encountered. Excluding RHDpsi and CdeS frequent only in individuals of African descent, most of these alleles are unknown and the population frequency of any such allele has not been determined. METHODS: We screened 8,442 antigen D negative blood donations by RHD PCR-SSP. RHD PCR positive samples were further characterized by RHD exon specific PCR-SSP or sequencing. The phenotype of the identified alleles was checked and their frequencies in Germans were determined. RESULTS: We detected 50 RHD positive samples. Fifteen samples harbored one of three new Del alleles. Thirty samples were due to 14 different D negative alleles, only 5 of which were previously known. Nine of the 14 alleles may have been generated by gene conversion in cis, for which we proposed a mechanism triggered by hairpin formation of chromosomal DNA. The cumulative population frequency of the 14 D negative alleles was 1:1,500. Five samples represented a D+/- chimera, a weak D and three partial D, which had been missed by routine serology; two recipients transfused with blood of the D+/- chimera donor became anti-D immunized. CONCLUSION: The results of this study allowed to devise an improved RHD genotyping strategy, the false-positive rate of which was lower than 1:10,000. The number of characterized RHD positive antigen D negative and Del alleles was more than doubled and their population frequencies in Europe were defined.

Weak D alleles express distinct phenotypes.

The weak D phenotype is caused by many different RHD alleles encoding aberrant RhD proteins, raising the possibility of distinct serologic phenotypes and of anti-D immunizations in weak D. We reported 6 new RHD alleles, D category III type IV, DIM, and the weak D types 4.1, 4.2.1, 4.2.2, and 17. The immunohematologic features of 18 weak D types were examined by agglutination and flow cytometry with more than 50 monoclonal anti-D. The agglutination patterns of the partial D phenotypes DIM, D(III) type IV, and D(IV) type III correlated well with the D epitope models, those of the weak D types showed no correlation. In flow cytometry, the weak D types displayed type-specific antigen densities between 70 and 4000 RhD antigens per cell and qualitatively distinct D antigens. A Rhesus D similarity index was devised to characterize the extent of qualitative changes in aberrant D antigens and discriminated normal D from all tested partial D, including D category III. In some rare weak D types, the extent of the alterations was comparable to that found in partial Ds that were prone to anti-D immunization. Four of 6 case reports with anti-D in weak D represented auto-anti-D. We concluded that, in contrast to previous assumptions, most weak D types, including prevalent ones, carry altered D antigens. These observations are suggestive of a clinically relevant potential for anti-D immunizations in some, but not in the prevalent weak D types, and were used to derive an improved transfusion strategy in weak D patients. (Blood. 2000;95:2699-2708)