Novel intronic RHD variants identified in serologically D-negative blood donors

Blood group genotyping is used to predict RhD phenotype in transfusion and obstetric medicine. Prediction of antigen D is based on molecular techniques which targets most common RHD-specific polymorphism. However, inactive RHD variants can suggest false-positive RhD phenotype. Their types and frequencies vary among ethnicities. Our study aimed to identify RHD variants among Moroccan blood donors who are serologically D negative.

DNA from 53 blood donors who are serologically D negative RhC and/or RhE positive were screened for RHD exon 10 by PCR-SSP. RHD-positive samples were further tested by multiplex PCR covering exons 3, 4, 5, 6, 7 and 9 and then sequenced by targeted next-generation sequencing method. Mutations' impact on mRNA splicing was predicted using alamut software version 2·0.

PCR-SSP revealed 9 of 53 (16·9%) RHD-positive samples. Five of nine samples were positive for all tested exons, two of nine were positive for exon 9, and two of nine were undetermined. Sequencing revealed four novel RHD variants based on six mutations in introns 1, 3, 5 and 6. In silico analysis revealed aberrant splicing of three mutations (RHD c.487-1024delG, RHD c.487-256T>G and RHD c.940-187_940-188del), while three other mutations (RHD c.149-682C>A, RHD c.802-37delA and RHD c.939 + 1151dup) had no effect on splicing compared to wild type.

All identified RHD variants contain at least one mutation that probably affects splicing to generate D-negative phenotype. Hence, ethnic RhD antigen background must be considered when developing transfusion and obstetric strategies.