Serologic and molecular investigations of DAR1 (weak D Type 4.2), DAR1.2, DAR1.3, DAR2 (DARE), and DARA.

BACKGROUND

The partial D variant DAR1 (weak D Type 4.2) is caused by three single-point mutations, 602C>G, 667T>G, and 1025T>C. Here we report a molecular study on different D variants belonging to the DAR category (DAR1, DAR1.2, DAR1.3, and DAR2) and their serologic data.

STUDY DESIGN AND METHODS

A total of 42 samples belonging to the DAR category were screened for the presence of the silent mutations 744C>T and 957G>A. The samples were phenotyped for RhD and RhCE, characterized for RhD epitope expression, and sequenced for RHD exons. Flow cytometry was performed to determine RhD antigen density.

RESULTS

The silent mutation 744C>T was found in all six samples previously typed as RHDDAR2 (602C>G, 667T>G, 957G>A, 1025T>C). In addition to the three nucleotide changes originally reported for the RHDDAR1 allele, the silent mutations 744C>T and 957G>A were found in 14 of 16 samples previously typed as RHD*DAR1. In the remaining two samples one additional silent mutation, 744C>T, was found. Serologically the DAR1.2 and DAR1.3 samples analyzed in this study showed no distinct difference in their anti-D reaction pattern compared to each other. The anti-D reaction pattern of DARA/DAR2 showed some distinct differences compared to those of DAR1.2 and DAR1.3.

CONCLUSION

RHDDARA and RHDDAR2 are the same allele. Furthermore, the alleles RHDDAR1.2 and RHDDAR1.3 both exist; however, the silent mutation 957G>A (V319) showed no influence on the RhD phenotype.