Complete RHD next-generation sequencing: establishment of reference RHD alleles

The Rh blood group system (ISBT004) is the second most important blood group after ABO and is the most polymorphic one, with 55 antigens encoded by 2 genes, RHD and RHCE This research uses next-generation sequencing (NGS) to sequence the complete RHD gene by amplifying the whole gene using overlapping long-range polymerase chain reaction (LR-PCR) amplicons. The aim was to study different RHD alleles present in the population to establish reference RHD allele sequences by using the analysis of intronic single-nucleotide polymorphisms (SNPs) and their correlation to a specific Rh haplotype. Genomic DNA samples (n = 69) from blood donors of different serologically predicted genotypes including R₁R₁ (DCe/DCe), R₂R₂ (DcE/DcE), R₁R₂ (DCe/DcE), R₂R_Z (DcE/DCE), R₁r (DCe/dce), R₂r (DcE/dce), and R₀r (Dce/dce) were sequenced and data were then mapped to the human genome reference sequence hg38. We focused on the analysis of hemizygous samples, as these by definition will only have a single copy of RHD For the 69 samples sequenced, different exonic SNPs were detected that correlate with known variants. Multiple intronic SNPs were found in all samples: 21 intronic SNPs were present in all samples indicating their specificity to the RHD*DAU0 (RHD*10.00) haplotype which the hg38 reference sequence encodes. Twenty-three intronic SNPs were found to be R₂ haplotype specific, and 15 were linked to R₁, R₀, and R_Z haplotypes. In conclusion, intronic SNPs may represent a novel diagnostic approach to investigate known and novel variants of the RHD and RHCE genes, while being a useful approach to establish reference RHD allele sequences.

Frequency and characterization of RHD variants in serologically D- Surinamese pregnant women and D- newborns

BACKGROUND

Numerous RHD variant genes affect the expression of D on the red blood cell surface. In Suriname, 4.3% of pregnant women were D-, ranging from virtually zero to 7% among ethnic groups. Characterization of RHD variants, which are associated with a variable potential to induce anti-D, is of practical clinical importance especially in case of limited access to preventive measures. Here we report on the occurrence of RHD variant genes in Surinamese serologically D- pregnant women and their D- newborns from different ethnic groups.

STUDY DESIGN AND METHODS

The RheSuN study is a cross-sectional cohort study in D- pregnant women and their newborns, who visited hospitals in Paramaribo, Suriname, during routine pregnancy care. The presence of RHD variants was investigated using quantitative polymerase chain reaction targeting RHD Exons 5 and 7 and RH-multiplex ligation-dependent probe amplification.

RESULTS

Seven RHD variant genes were detected in 35 of 84 women and four RHD variant genes in 15 of 36 newborns. The RHD*03 N.01 and RHD*08 N.01 variants represented 87% of a total of 62 variant genes. Variants were comparably frequent among ethnicities. In four cases genotyping would have changed anti-D prophylaxis policy: one woman with a RHD*01EL.01 variant, not associated with anti-D formation and three D- newborns with RHD*09.01 and RHD*09.03.01 variants, potentially capable of inducing anti-D.

CONCLUSION

RHD variants at risk for anti-D are common among serologic D- individuals from African descent in Suriname. While genotyping D- women has limited added value, it may be considered in newborns from D- women.

A novel double-variant RHAG allele leads to Rhmod phenotype

AIMS/OBJECTIVES

We aimed to analyse the molecular backgrounds and red blood cell (RBC) antigen expression of a male blood donor with Rh_mod phenotype and his family members.

BACKGROUND

Rh deficiency phenotypes are rarely found worldwide and are characterised by the lack of Rh antigen expression on RBCs. During routine screening, we found a blood donor who seemingly lacked Rh antigens. Therefore, we recruited the donor and his family for further investigation.

METHODS

RBC serotyping and antibody screening/identification were performed for each sample. A routine blood examination was also conducted. RHD, RHCE and RHAG were sequenced at the genomic DNA or RNA level. Eleven antigens or proteins associated with Rh complex were tested using flow cytometry analysis.

RESULTS

The proband and one of his brothers showed extremely weak D antigen and Rh expression levels but did not manifest anaemia. Most of the expressed RBC antigens of the two Rh-deficient individuals were similar to the previously reported cases but with some exceptions. Molecular analyses demonstrated homozygous expression of a novel RHAG allele, namely, c.[572G>A;707A>C], both in the proband and one of his brothers.

CONCLUSIONS

To our knowledge, we identified the second double-variant RHAG allele and the first one related to Rh_mod phenotype. The novel allele was also confirmed to be heritable by family analyses.

Overhydrated stomatocytosis associated with a complex RHAG genotype including a novel de novo mutation

Overhydrated stomatocytosis is a rare autosomal dominant disorder known to cause variably severe haemolytic anaemia due to heterozygous mutations in the RHAG gene. We report a 26-year-old man with recurring jaundice, splenohepatomegaly and mild chronic haemolytic anaemia with significant stomatocytosis. Extensive haemolytic work-up including flow cytometry for eosin-5′-maleimide and CD47 expression levels was carried out. Targeted resequencing revealed two probably causative heterozygous mutations in RHAG (Leu336Ser and Ile149Met) and one heterozygous mutation in ANK1 (Glu1046Lys). RHAG involvement was confirmed by decreased RhAG macrocomplex component indicated by the reduced CD47 expression on erythrocytes. In silico analysis concordantly flagged RHAG:Leu336Ser and ANK1:Glu1046Lys as likely deleterious mutation, whereas RHAG:Ile149Met was reported as likely neutral by PROVEAN. Family screening by Sanger sequencing revealed RHAG:Leu336Ser in a mother and ANK1:Glu1046Lys in a father who were both asymptomatic, excluding them as causative dominant events, thus establishing RHAG:Ile149Met, novel de novo mutation as probably causative. This case illustrates the importance of family screening in interpreting next-generation sequencing (NGS) data, as in silico analysis alone can be misleading. Erudite generation of diagnostic possibilities based on a thorough baseline clinical and laboratory work-up remains as important as ever, even as NGS brings about a paradigm shift in the diagnostic work-up of rare haemolytic anaemias.