Clinical and laboratory update on the DEL variant

A Bioinformatically Initiated Approach to Evaluate GATA1 Regulatory Regions in Samples with Weak D, Del, or D- Phenotypes Despite Normal RHD Exons

Introduction

With over 360 blood group antigens in systems recognized, there are antigens, such as RhD, which demonstrate a quantitative reduction in antigen expression due to nucleotide variants in the non-coding region of the gene that result in aberrant splicing or a regulatory mechanism. This study aimed to evaluate bioinformatically predicted GATA1-binding regulatory motifs in the RHD gene for samples presenting with weak or apparently negative RhD antigen expression but showing normal RHD exons.

Methods

Publicly available open chromatin region data were overlayed with GATA1 motif candidates in RHD. Genomic DNA from weak D, Del or D- samples with normal RHD exons (n = 13) was used to confirm RHD zygosity by quantitative PCR. Then, RHD promoter, intron 1, and intron 2 regions were amplified for Sanger sequencing to detect potential disruptions in the GATA1 motif candidates. Electrophoretic mobility shift assay (EMSA) was performed to assess GATA1-binding. Luciferase assays were used to assess transcriptional activity.

Results

Bioinformatic analysis identified five of six GATA1 motif candidates in the promoter, intron 1 and intron 2 for investigation in the samples. Luciferase assays showed an enhancement in transcription for GATA1 motifs in intron 1 and for intron 2 only when the R 2 haplotype variant (rs675072G>A) was present. GATA1 motifs were intact in 12 of 13 samples. For one sample with a Del phenotype, a novel RHD c.1-110A>C variant disrupted the GATA1 motif in the promoter which was supported by a lack of a GATA1 supershift in the EMSA and 73% transcriptional activity in the luciferase assay. Two samples were D+/D- chimeras.

Conclusion

The bioinformatic predictions enabled the identification of a novel DEL allele, RHD c.1-110A>C, which disrupted the GATA1 motif in the proximal promoter. Although the majority of the samples investigated here remain unexplained, we provide GATA1 targets which may benefit future RHD regulatory investigations.

RHD Genotypes in a Chinese Cohort of Pregnant Women

RHD variants in D¯ Chinese pregnant women arose difficulties in management during pregnancy. Therefore, this study aims to precisely manage D¯ pregnant women by evaluating the spectrum of RHD mutations in D¯ pregnant women and getting insight into the possible rare alleles of RHD. A total of 76 D¯ pregnant women were analyzed by performing polymerase chain reactions with sequence-specific primers (PCR-SSP), the 10 RHD exons Sanger sequencing, RHD zygosity detection, and mRNA sequencing (mRNA-seq). About 40% of alleles are variations of RHD, including RHD 1227A homozygous, RHD-CE(2-9)-D, et al. Therefore, we developed a molecular diagnostic strategy for Chinese women, and most D¯ pregnant women can be diagnosed with this simple decision tree. After RHD genotyping for D¯ pregnancy women, we eliminated at least 15% unnecessary ante- and postpartum injections of Rh immunoglobulin (RhIG). As the first pedigree study and the first functional analysis under physiological conditions, mRNA-seq revealed that c.336-1G>A mutation mainly led to the inclusion of the intron 2, which indirectly explained the D¯ phenotype in this family. We also developed a robust protocol for determining fetal RhD status from maternal plasma. All 31 fetuses were predicted as RhD positive and confirmed the RhD status after birth.

DEL in China: the D antigen among serologic RhD-negative individuals

BACKGROUND

Providing RhD-negative red cell transfusions is a challenge in East Asia, represented by China, Korea, and Japan, where the frequency of RhD-negative is the lowest in the world.

FINDINGS

Among 56 ethnic groups in China, the RhD-negative frequency in Han, the prevalent ethnicity, is 0.5% or less, similar to most other ethnic groups. The Uyghur ethnic group has the highest reported RhD-negative frequency of up to 4.7%, as compared to 13.9% in the US. However, an estimated 7.15 million RhD-negative people live in China. The RhD-negative phenotype typically results from a loss of the entire RHD gene, causing the lack of the RhD protein and D antigen. The DEL phenotype carries a low amount of the D antigen and types as RhD-negative in routine serology. The DEL prevalence in RhD-negative individuals averages 23.3% in the Han, 17% in the Hui and 2.4% in the Uyghur ethnicities. The Asian type DEL, also known as RHD*DEL1 and RHD:c.1227G > A allele, is by far the most prevalent among the 13 DEL alleles observed in China.

CONCLUSION

The purpose of this review is to summarize the data on DEL and to provide a basis for practical strategy decisions in managing patients and donors with DEL alleles in East Asia using molecular assays.

Serological Detection of Rh-Del Phenotype among Rh-Negative Blood Donors at National Blood Center, Yangon, Myanmar

Background

Red cell Rhesus (Rh) antigen expression is influenced by the genetic polymorphism of RHD and RHCE genes and reveals serologically different reactions of RhD variants such as partial D, weak D, and Rh-Del. Serologically, Rh-Del type can only be detected by an adsorption-elution technique, and it might be mistyped as Rh-negative. The prevalence of Rh-Del has not been reported yet in Myanmar.

Method

A total of 222 Rh-negative blood donors in the National Blood Center were tested for weak D and Rh-Del by indirect antihuman globulin and adsorption-elution method, respectively. RhCE typing was performed among Rh-negative and Rh-Del.

Results

Of them, 75.2% (167/222) were Rh-negative, 15.8% (35/222) were Rh-Del, and 9% (20/222) were weak D. Of 202 blood donors (167 true Rh-negative and 35 Rh-Del), all of the Rh-Del positives were C-antigen-positive with 94.3% Ccee phenotype (33/35) and 5.7% CCee (2/35). Most of the Rh-negative donors (80.2%) were ccee phenotype (134/167).

Conclusion

About half of Rh-Del subjects were repeated donors, and attention was needed to avoid transfusion of truly Rh-negative patients to prevent alloimmunization. It is recommended to do Rh-Del typing of Rh-negative donors who are C-antigen-positive and consider moving them to the Rh-positive pool. Further study is needed to clarify the alloimmunization status for transfusion of Rh-Del blood to Rh-negative recipients. Molecular markers for RhD-negative and D variants should be established in the Myanmar population to improve selection of antisera for Rh typing and enhance safety of the transfusion services.

Recommendations Regarding Practical DEL Typing Strategies for Serologically D-Negative Asian Donors

Background

DEL, the weakest D variant, is mistyped as D-negative by routine serological assays. Transfusion of red blood cells expressing the DEL phenotype has the potential to elicit anti-D alloimmunization in D-negative recipients. The goal of this study was to recommend DEL typing strategies for serologically D-negative Asian donors.

Methods

RhCE phenotyping and the adsorption-elution test were performed on 674 serologically D-negative samples. RHD genotyping using real-time polymerase chain reaction and melting curve analysis were also undertaken to identify DEL alleles. Costs and turnaround time of RhCE phenotyping, the adsorption-elution test, and RHD genotyping were estimated.

Results

Sensitivity and specificity of the adsorption-elution test for serologically D-negative samples were 94.9% (93/98) and 91.5% (527/576), respectively. C+ phenotypes were detected in all 98 samples with DEL alleles. Despite comparable costs, RHD genotyping was more accurate and rapid than the adsorption-elution test.

Conclusions

Two practical DEL typing strategies using RhCE phenotyping as an initial screening method were recommended for serologically D-negative Asian donors. Compared with DEL typing using RHD genotyping, serological DEL typing using adsorption-elution test is predicted to increase the incidence of anti-D alloimmunization and decrease the D-negative donor pool without having any cost-competitiveness but can be used in laboratories where molecular methods are not applicable.