Evaluation of targeted exome sequencing for 28 protein-based blood group systems, including the homologous gene systems, for blood group genotyping.

BACKGROUND: Blood group single nucleotide polymorphism genotyping probes for a limited range of polymorphisms. This study investigated whether massively parallel sequencing (also known as next-generation sequencing), with a targeted exome strategy, provides an extended blood group genotype and the extent to which massively parallel sequencing correctly genotypes in homologous gene systems, such as RH and MNS. STUDY DESIGN AND METHODS: Donor samples (n = 28) that were extensively phenotyped and genotyped using single nucleotide polymorphism typing, were analyzed using the TruSight One Sequencing Panel and MiSeq platform. Genes for 28 protein-based blood group systems, GATA1, and KLF1 were analyzed. Copy number variation analysis was used to characterize complex structural variants in the GYPC and RH systems. RESULTS: The average sequencing depth per target region was 66.2 ± 39.8. Each sample harbored on average 43 ± 9 variants, of which 10 ± 3 were used for genotyping. For the 28 samples, massively parallel sequencing variant sequences correctly matched expected sequences based on single nucleotide polymorphism genotyping data. Copy number variation analysis defined the Rh C/c alleles and complex RHD hybrids. Hybrid RHD*D-CE-D variants were correctly identified, but copy number variation analysis did not confidently distinguish between D and CE exon deletion versus rearrangement. CONCLUSION: The targeted exome sequencing strategy employed extended the range of blood group genotypes detected compared with single nucleotide polymorphism typing. This single-test format included detection of complex MNS hybrid cases and, with copy number variation analysis, defined RH hybrid genes along with the RHCE*C allele hitherto difficult to resolve by variant detection. The approach is economical compared with whole-genome sequencing and is suitable for a red blood cell reference laboratory setting.

A D+ blood donor with a novel RHD*D-CE(5-6)-D gene variant exhibits the low-frequency antigen RH23 (D(W) ) characteristic of the partial DVa phenotype.

BACKGROUND: Blood donors whose red blood cells (RBCs) exhibit a partial RhD phenotype, lacking some D epitopes, present as D+ in routine screening. Such phenotypes can exhibit low-frequency antigens (LFAs) of clinical significance. The aim of this study was to describe the serologic and genetic profile for a blood donor with an apparent D+ phenotype carrying a variant RHD gene where D Exons 5 and 6 are replaced by RHCE Exon (5-6). STUDY DESIGN AND METHODS: Anti-D monoclonal antibodies were used to characterize the presentation of RhD epitopes on the RBCs. RHD exon scanning and DNA sequencing of short- and long-range polymerase chain reaction amplicons were used to determine the RHD structure and sequence. Extended phenotyping for LFAs RH23 (D(W) ) and Rh32 was performed. RESULTS: The donor serology profile was consistent with partial RhD epitope presentation. The donor was hemizygous for an RHD variant allele described as RHD*D-CE(5-6)-D hybrid. The RHCE gene insert is at least 3.868 kb with 5' and 3' breakpoints between IVS4 + 132-c.667 and IVS6 + 1960-IVS6 + 2099, respectively. The sequence for this hybrid was assigned GenBank Accession Number KT099190.2. The RBCs were RH23 (D(W) )+ and Rh32-. CONCLUSION: A novel RHD*D-CE(5-6)-D hybrid allele encodes a partial RhD epitope and carries the LFA RH23 (D(W) ). This and the epitope profile resemble the partial DVa phenotype. Given that RBCs from this individual lack some RhD epitopes, there is an alloimmunization risk if the donor is exposed to D+ RBCs. Conversely, transfusions of RH23 (D(W) )+ cells to RH23 (D(W) )- recipients also pose an alloimmunization risk.