Abstract: Objective To study the RhD epitope pattern and molecular mechanism of a volunteer blood donor whose phenotype is partial D. Methods Serological methods were used for weak D test and CE phenotyping for one blood sample which was identified as D-negative initially; and D-screen kit was used to analyze RhD epitopes. All exons of RHD were sequenced by Sanger sequencing method. We developed a method to determine RHD zygosity based on droplet digital PCR and analyzed the sample. Robetta modeling was used to compare the conformations of RhD protein between wild type and the sample. Results It was identified as partial D phenotype serologically,and the CE type was CcEe. The c.492C>G base change of exon 4 of RHD gene was identified by sequencing. The results of ddPCR showed that RHD genotype of the sample was D+/D-. Aspartic acid replaced by glutamic acid may influence the conformation of the third extracellular loop of RhD protein according to Robetta modeling results. Conclusion This is the first domestic report of the variant allele RHD*492G, which results in partial D phenotype with lack of some D epitopes. Compared with RT-PCR,the ddPCR method showed better repeatability and accuracy when used for determining RHD zygosity.

Key words: RhD antigen, Partial D phenotype, Droplet digital PCR, Homology modeling