Comprehensive analysis of RHD splicing transcripts reveals the molecular basis for the weak anti-D reactivity of Del -red blood cells.

BACKGROUND: Of the Rh blood type, Del is a rare variant that elicits the weakest anti-D reactivity. In this study, we revisit the genetic changes of Del allele and characterise the RHD splicing transcripts to realise the molecular basis of Del formation in the Taiwanese population. STUDY DESIGN AND METHODS: The RHD exons from Del and D-positive individuals were amplified by polymerase chain reaction (PCR) using different primer pairs followed by sequencing analyses. In addition, full-length RHD transcripts were reversed transcribed and amplified by nested-PCR. The type and frequency of the RHD splicing transcripts were analysed after sequencing the PCR products that were subcloned into a cloning vector. RESULTS: All Del individuals had a characteristic 1227G>A mutation. No deletion of the exon sequences was found. At least nine types of RHD splicing transcripts including exons 7/8/9 deletion, 7/9 deletion, 8/9 deletion, 9 deletion, 2/3/7/9 deletion, 2/3/7/8/9 deletion, exons 7/8/9 deletion with replacement of exon 3 with RHCE exon 3, exon 9 deletion with cryptic insertion of 170 bp of intron 7 and exons 7/8/9 deletion with cryptic insertion of 117 bp of intron 3 were identified in the Del -RBC. These aberrant splicing transcripts led to production of frame shift or truncated D antigen. Notably, no full-length RHD transcript was identified in the Del -RBC. CONCLUSION: The RHD 1227G>A mutation contributes to the molecular basis of Del phenotype in the Taiwanese population. The point mutation results in aberrant frame shift or exon deletion transcripts and generates D protein with weak antigen presenting function.