Paternal RHD zygosity determination in Tunisians: evaluation of three molecular tests

RHD Genotyping by Molecular Analysis of Hybrid Rhesus box in RhD-Negative Blood Donors from Iran

D antigen is the most important and immunogenic antigen of the Rh blood group. The RhD-negative phenotype has different genetic backgrounds with variable distribution in different populations. Hybrid Rhesus box, resulting from RHD gene deletion, is used in genotyping studies of the Rh blood group as a marker to identify the RHD gene deletion. This study for the first time identified genetic mechanisms for the occurrence of RhD-negative phenotype among the Iranian population. 200 RhD-negative blood donors were randomly selected from Tehran Blood Transfusion Center. The phenotype of D, C, Ε, e and c antigens was serologically identified, and DNA was extracted from buffy coat. The molecular analysis of hybrid Rhesus box was performed by PCR-SSP and PCR-RFLP. Moreover, the presence of different exons of RHD gene was investigated by real-time PCR on extracted DNA. Hybrid Rhesus box was detected in all samples, and PCR-RFLP confirmed that 198 (99%) were homozygous for an RHD gene deletion and 2 were heterozygous for hybrid Rhesus box in which one (0.5%) had a weak D type 11 and the other one (0.5%) had a RHD-CE (2-9)-D₂ hybrid allele. Similar to Caucasians, the frequency of RHD gene deletion was high among the Iranian population studied in this investigation, so hybrid Rhesus box can be used as an efficient marker to detect RHD gene deletion in our population.

Transfusion strategy for weak D Type 4.0 based on RHD alleles and RH haplotypes in Tunisia

BACKGROUND

With more than 460 RHD alleles, this gene is the most complex and polymorphic among all blood group systems. The Tunisian population has the largest known prevalence of weak D Type 4.0 alleles, occurring in one of 105 RH haplotypes. We aimed to establish a rationale for the transfusion strategy of weak D Type 4.0 in Tunisia.

STUDY DESIGN AND METHODS

Donors were randomly screened for the serologic weak D phenotype. The RHD coding sequence and parts of the introns were sequenced. To establish the RH haplotype, the RHCE gene was tested for characteristic single-nucleotide positions.

RESULTS

We determined all RHD alleles and the RH haplotypes coding for the serologic weak D phenotype among 13,431 Tunisian donations. A serologic weak D phenotype was found in 67 individuals (0.50%). Among them, 60 carried a weak D Type 4 allele: 53 weak D Type 4.0, six weak D Type 4.2.2 (DAR), and one weak D Type 4.1. An additional four donors had one variant allele each: DVII, weak D Type 1, weak D Type 3, and weak D type 100, while three donors showed a normal RHD sequence. The weak D Type 4.0 was most often linked to RHCE*ceVS.04.01, weak D Type 4.2.2 to RHCE*ceAR, and weak D Type 4.1 to RHCE*ceVS.02, while the other RHD alleles were linked to one of the common RHCE alleles.

CONCLUSIONS

Among the weak D phenotypes in Tunisia, no novel RHD allele was found and almost 90% were caused by alleles of the weak D Type 4 cluster, of which 88% represented the weak D Type 4.0 allele. Based on established RH haplotypes for variant RHD and RHCE alleles and the lack of adverse clinical reports, we recommend D+ transfusions for patients with weak D Type 4.0 in Tunisia.