First report of Rhnullindividuals in the Indian population and characterization of the underlying molecular mechanisms

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.

Rhnull phenotype caused by a novel RHAG mutation, c.945+1G>A, in the Japanese population

BACKGROUND

The Rh complex contributes to cell membrane structural integrity of erythrocytes. Rh_null syndrome is characterized by the absence of the Rh antigen on the erythrocyte membrane, resulting in chronic hemolytic anemia. We recently came across 3 Rh_null phenotype probands within two families with the same novel RHAG mutation in the Japanese population.

MATERIALS AND METHODS

Detailed Rh phenotyping by hemagglutination was performed using monoclonal and polyclonal anti-D, -C, -c, -E, and -e; monoclonal and polyclonal anti-Rh17 antibodies; and polyclonal anti-Rh29 antibodies. RHAG mRNA transcripts were analyzed by reverse transcription-polymerase chain reaction, and the mutation was verified by genomic sequencing.

RESULTS

The genomic region spanning exon 6 contained a G > A transition in the invariant GT motif of the 5' donor splice-site of Intron 6 (c.945+1G>A). The Rh_null phenotype was caused by an autosomal recessive mutation in Probands 1 and 2, determined by family history. Regarding clinical features, the degree of hemolysis varied slightly between these individuals, with Proband 3 displaying acute hemolytic anemia with an infection. While no standard therapy has been established, the condition of the patient in this study improved with conservative treatment, including hydration and antibiotics.

CONCLUSION

The mechanisms of hemolysis due to the Rh_null phenotype can vary, but our findings indicate that acute hemolytic crisis caused by the Rh_null syndrome could be associated with infection.