Molecular basis of serological weak D phenotypes and RhD typing discrepancies identified in the Korean population.

BACKGROUND: The molecular basis of RhD blood groups differs with race/ethnicity. This study aimed to investigate the molecular basis of serological weak D phenotypes and RhD typing discrepancies in the Korean population. MATERIALS AND METHODS: The RhD status of 188,852 Korean patients was initially determined using the automated microplate method and manual tile method. In case of no agglutination, weak D testing was further performed using the tube and gel methods. Serologically D-negative samples with C+ and/or E+ were tested using polymerase chain reaction-sequence specific primers for four RHD targets and/or exon 9 sequencing. Samples showing a serological weak D phenotype or an RhD typing discrepancy were subjected to full RHD gene sequencing. RESULTS: Of the 32 samples showing a serological weak D phenotype and 191 samples showing a serologically D-negative phenotype with C+ and/or E+, 23 and 50 were genotyped, respectively. Among the weak D samples, the most common alleles were RHD*15 (n=6), RHD*13.01 (n=4), and RHD*01W.25 (n=4), and no variant was found in two samples. RHD*01EL.01 (n=26) accounted for more than half of the D-negative samples. Of the seven samples that were typed as D-positive using the automated microplate method but showed weak reactivity using the tile method, four were genotyped, and the results were as follows: RHD*01W.33 (n=2), RHD*01W.43 (n=1), and no variant found (n=1). DISCUSSION: In our cohort, various D variant alleles including RHD*15 were identified; however, RHD*01W.1, RHD*01W.2, RHD*01W.3, RHD*09.03.01, and RHD*09.04, accounting for more than 95% of Caucasians with a serological weak D phenotype, were not found. Our study reaffirms that the distribution of D variant alleles differs between East Asians and Caucasians. Our findings also indicate that some D variants including RHD*01W.33 and RHD*01W.43 are at risk of being mistyped as D-positive by a highly sensitive RhD typing method such as an automated microplate method.