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The Rh blood group system: RHCE update.

While the previous review encompassed the Rh blood group system (Chou ST, Westhoff CM. The Rh and RhAG blood group systems. Immunohematology. 2010;26:178-86), this update focusses on the RHCE gene and its variants. Four new antigens- PARG, CEVF, CEWA, and CETW (RH60 to RH63)-were reported since the last update. RHCE*cEMI (RHCE*03.31) was amended from a null allele to an allele encoding very weak antigen expression. The following topics are discussed: cross-reactive alleles [such as RHCE*ceHAR (*01.22.01) and RHCE*ceCF (*01.20.06) which may type D+ with some monoclonal anti-D reagents], issues with hybrid alleles and allele dropout, common haplotypes (association between RHCE alleles and specific RHD alleles), and clinical considerations. While the detailed description of new Rh antigens has become rare, many RHCE alleles have been reported since the previous review, a result of increased adoption of DNAbased testing for red blood cell antigens in immunohematology laboratories. The Rh blood group system has fascinated generations of immunohematologists and is likely to continue to do so for decades to come.

Rh-Hr Blood-Group System

The 2 breakpoint regions of an RHCE-D(2-9)-CE allele causing a D phenotype and its RhAG antigen density.

BACKGROUND: Among 195 known RHCE alleles, 10 have evolved to form hybrid RHCE-D-CE alleles encoding aberrant RhCE proteins lacking CE antigen expression. The resulting D-- phenotype predisposes to anti-Hro alloimmunization (anti-Rh17). Although hybrid alleles may appear identical at the mRNA level, distinct breakpoint configurations can result in diverse D phenotypes or Rh antigens. We determined the molecular structure of a D-- phenotype. An unrelated RHD allele, DMA had been observed once without serology. We tested Rh antigen densities. MATERIALS AND METHODS: Genomic DNA and cDNA were analyzed using a combination of molecular techniques and commercial red cell genotyping assays targeting the RHD and RHCE genes. A flow cytometric method was developed to quantify RhAG antigen expression. Red cell antigen densities were determined for RhAG and RhD in the D-- and DMA/DAU3 samples serologically. RESULTS: Nucleotide sequencing of the RHCE gene and its cDNA identified a homozygous CE-D(2-9)-CE hybrid allele in an individual of Afghan origin. The 5' and 3' breakpoint regions included 131 and 4,287 nucleotides. The new allele was linked in a haplotype to the normal RHD allele (RHD*01). Quantitative flow cytometry demonstrated antigen densities of 92,297 RhD and 52,907 RhAG molecules per red cell for the D-- sample (12,465 RhD and 117,871 RhAG for DMA/DAU3). DISCUSSION: We describe the breakpoint regions of a Ce-D(2-9)-Ce allele that encoded a D-- phenotype. Our results underscore the importance of breakpoint characterization for identifying clinically relevant RH variants and advancing personalized transfusion medicine. The second DMA observation, in trans to a DAU3 allele, aligned with a weak D phenotype for DMA.

Journal Article

Rhesus blood group haplotype determination by nanopore sequencing and adaptive sampling enables the precise determination of complex allele combinations that could not be accurately determined by standard methods.

BACKGROUND: Patients with chronic transfusion needs such as those with sickle cell disease face a high risk of developing antibodies against high-prevalence antigens in the RH blood group system, complicating transfusion therapy and potentially necessitating stem cell transplantation. Molecular characterization of the RH system is hindered by hybrid alleles and high sequence homology between RHD and RHCE, limiting the effectiveness of conventional short-read sequencing. STUDY DESIGN AND METHODS: We analyzed 11 control and 20 patient samples, some of which could not be reliably genotyped by standard methods. RESULTS: Nanopore sequencing with adaptive sampling enables targeted, amplification-free long-read sequencing of the RH locus, resolving homologous and complex hybrid structures and enabling complete haplotype phasing for all samples, including samples that could not be accurately determined by standard methods like serology and short-read sequencing. Four new alleles were identified and for 13 out of 20 patients the results led to a change in the transfusion regimen. DISCUSSION: These findings show that nanopore sequencing with adaptive sampling allows unambiguous genotyping of the RH system, improves detection of complex variants, and supports better-matched transfusion strategies for chronically transfused patients.

Rh-Hr Blood-Group System