Rh_null blood group caused by novel base deletion and comprehensive pedigree analysis

The objective of this study was to rigorously investigate and elucidate the genetic mechanisms underlying the formation of the RH_null blood group in a specific case and to systematically analyse the RH blood group genes among the family members of the proband.

Serological methods were used to determine the RH blood group phenotype of the proband. To elucidate the underlying genetic mechanism responsible for the RH_null phenotype, a comprehensive approach was undertaken, including RHCE genotyping, sequencing of RHD and RHCE genes, and exon sequencing of RHAG. For a comparative analysis, the same methodologies were applied to two family members of the proband.

The genotype of the proband was determined as CcDEe. Subsequent RHAG exon sequencing analysis revealed a homozygous frameshift mutation in exon 5. Specifically, a nucleotide deletion at position c.732 in RHAG resulted in an amino acid substitution from phenylalanine to serine, followed by a frameshift and premature termination at codon 245 (p.Phe245Serfs*16). This mutation was confirmed as a novel genetic variant in the NCBI database. Furthermore, serological findings, genotyping results, and RHAG exon sequencing data obtained from the proband's sister were identical to those of the proband. In contrast, the proband's son exhibited a serological phenotype of CCDee with a corresponding genotyping result for CCDee. RHAG exon sequencing of the son revealed a heterozygous frameshift mutation, which was consistent with the findings observed in the proband.

A novel mutation, specifically c.732delC, was identified in RHAG. The RH_null phenotype observed in this subject was attributed to a homozygous frameshift mutation in this gene. This mutation results in a truncated and nonfunctional RHAG protein, which subsequently disrupts the expression of other RH antigens on the cell membrane. Therefore, the serological phenotype associated with this genetic anomaly was classified as RH_null.