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

Abstract

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 1 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 serological 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, 6 weak D type 4.2.2 (DAR), and 1 weak D type 4.1. Another 4 donors had 1 variant allele each: DVII, weak D type 1, weak D type 3, and weak D type 100, while 3 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 positive transfusions for patients with weak D type 4.0 in Tunisia.

High frequency of variant RHD genotypes among donors and patients of mixed origin with serologic weak‐D phenotype

“…Arnoni et al have previously published an interesting strategy to investigate D variants among Brazilians using the same multiplex PCR which was also the cornerstone of the molecular investigation workflow proposed by the present study. The main differences between the two protocols are that our focused on investigating only individuals with serologic weak‐D phenotype, aiming to determine the best transfusion protocol in a relatively short period of time, while the other protocol is more extensive and focusing on the evaluation of all samples with suspected variant D phenotype.…”

“…Similar to what have been published by other groups, the recommendation to transfuse D-positive units to some weak-D genotypes was based on the lack of adverse clinical reports, rather than on the presence of studies ensuring the impossibility of anti-D formation. 8,26 In conclusion, nearly half of the Brazilian patients and donors with serologic weak-D phenotype were eventually classified as partial D and, consequently, at risk of alloimmunization. The recommendation is that blood recipients of mixed origin be transfused with D-negative units and receive RhIG in case of pregnancy until the molecular investigation is complete, differing from current guidelines directed to the European population.…”

Implementation of Molecular <b><i>RHD</i></b> Typing at Two Blood Transfusion Institutes from Southeastern Europe

“…Serological methods depend on immunohematological technique and test reagents are not capable of always unequivocally detecting RhD variants (weak D, such as weak D type 11, partial D or DEL) [38]. Therefore, RHD molecular typing is recommended to identify and confirm RHD variants [39]. Transfusion of D-positive RBCs to partial D individuals or the pregnancy of partial D women with D-positive fetuses could induce alloimmunisation against the missing epitopes [3, 8, 33, 36].…”

Genotyping in Sickle Cell Disease Patients: The French Strategy

“…In our experience, the anti-RH5 antibodies associated with these molecular backgrounds are auto-antibodies, and patients are therefore no more prone to the formation of anti-RH4 or anti-RH5 antibodies when exposed to non-genotype-matched pRBCs. The status of the RH1 antigen associated with weak D type 4.0 (RHD*09.03) is also under scrutiny [41,42,43]. …”