Analysis of RHD genes in Taiwanese RhD-negative donors by the multiplex PCR method

Weak D types in the Egyptian population

Patients with the most common weak D types 1, 2, and 3 can be safely considered D positive. We evaluated 1,113 Rh-negative Egyptian samples for weak D expression to propose a cost-effective strategy related to D variant testing. D variants were tested using polymerase chain reaction with sequence-specific priming. Fifty samples were D variants (4.5%): weak D type 4.2 (32%), weak D type 4.0/4.1 (16%), and weak D type 15 (2%). Fifteen (62.5%) of 24 samples were identified serologically as partial D. We also studied the probability of the development of anti-D in 52 Rh-negative children with thalassemia who were receiving units for which weak D was not tested. Anti-D alloimmunization was observed in 63.5% of patients with thalassemia. It is prudent to implement weak D typing in Egyptian donors. Weak D variants of Egyptians are significantly different compared with Caucasians. Ethnicity must be taken into consideration when developing clinical and prenatal strategies related to D variants.

Molecular bases of unexpressed RHD alleles in Chinese D- persons

BACKGROUND

The aim of this study was to use a systematic survey to analyze RHD alleles in Chinese D- donors who do not express D antigen or who lack functional RhD protein.

STUDY DESIGN AND METHODS

A total of 733 D-Chinese donors, not including Del phenotypes, were investigated by RHD polymorphism–specific polymerase chain reaction (PCR), Rhesus box PCR-PstI digestion, and RHD sequencing. The frequencies of identified alleles were calculated.

RESULTS

Three genetic mechanisms and eight alleles were found associated with the Chinese D- phenotype. One new RHD/CE hybrid allele and one novel mutation were also found. The rates of total deletion and the most frequent hybrid allele RHD(1)-CE(2-9)-D(10) were similar to those found in previous studies. A previously reported mutation RHD(711delC) was found to be the predominant cause of aberrant RHD alleles.

CONCLUSION

Informative population-based data for improving molecular diagnostic strategies for Chinese D- persons are suggested by this study. This type of systematic knowledge is important for the development of typing and transfusion strategies for the Chinese population.

Non-invasive foetal RHD genotyping via real-time PCR of foetal DNA from Chinese RhD-negative maternal plasma

BACKGROUND

A majority of studies predicting the foetal RhD blood group in free foetal DNA from RhD-negative maternal plasma have been conducted in Caucasian populations, whereas limited data have been accumulated for Asian populations. In this study, we assessed the feasibility of prenatal genotyping of RHD in RhD-negative Chinese pregnant women.

MATERIALS AND METHODS

Cell-free plasma DNA was extracted from 78 RhD-negative Chinese women carrying a singleton foetus (gestation between 14 and 40 weeks). Foetal DNA was confirmed by testing SRY or nine different polymorphic STR loci in the maternal plasma and buffy coat. Foetal RHD exons 5, 7 and 10 and intron 4 were successfully amplified with RQ-PCR. The RHD1227A allele was examined in all RhD-positive individuals. The foetal RHD genotyping results were compared with the infant cord blood serological analysis.

RESULTS

Among the 78 specimens, RHD genotyping results of 70 cases were in complete concordance with serological results from foetal umbilical cord blood. Sixty of these cases were identified as RhD-positive, and 10 cases were typed as RhD-negative. In addition, five cases were 'false-positives', while three cases were considered inconclusive. The detection rate was 89.7% (70/78). In four of the five 'false-positive' cases, the RhDel phenotype was assessed by detecting the RHD1227A allele. Thus, this method yielded a 94.9% (74/78) accuracy rate.

CONCLUSIONS

The correct foetal RhD phenotype may be accurately predicted from RhD-negative maternal plasma in Chinese subjects. The RHD1227A allele proved to be an important genetic marker in the RhDel Chinese population.

Molecular and family analyses revealed two novel RHD alleles in a survey of a Chinese RhD-negative population

BACKGROUND AND OBJECTIVES

RHD alleles are considered variable in the Chinese RhD-negative persons. The purpose of the present work was to elucidate the molecular bases of two novel RHD alleles identified in a survey of a Chinese RhD-negative population.

MATERIALS AND METHODS

A total of 163 RhD-negative blood samples were investigated. The sequences of RHD exons were examined by RHD exon specific multiplex polymerase chain reaction (PCR) and PCR with sequence-specific primers (PCR-SSP). Characterizations of RHD intron 2 and Rhesus box were performed by PCR-PstI digestion. The DNA and cDNA sequences of the novel alleles were determined by PCR and reverse transcriptase-PCR (RT-PCR) sequencing analysis. A family study was performed to investigate the segregation of a novel RHD allele.

RESULTS

One hundred and twenty-nine samples (79.1%) had no RHD gene. Twenty-seven samples (16.6%) carried RHD-CE-D hybrid alleles. The remainder seven samples (4.3%) appeared to have an intact RHD gene. Three of them were sequenced for RHD gene and two novel alleles, RHD 325del and RHD intron 2 1A, were identified. The deletion of a nucleotide A at position 325 in the allele RHD 325del resulted in a stop codon at amino acid position 118. The RHD intron 2 1A allele was generated from a splice mutation and its transcript sequence had no exon 2. Family study indicated that the RHD 325del allele was inherited with a Ce haplotype.

CONCLUSION

This study provides the molecular bases of RHD alleles RHD 325del and RHD intron 2 1A. The existences of RHD 711del, RH (D1 CE2-9 D10), and RH (D1 CE2-9 D10) alleles in the Chinese population were confirmed. A PCR-SSP-based assay for rapid detection of RHD 325del and RHD intron 2 1A alleles was established and it could be used to predict the RHD genotype in the Chinese RhD-negative subjects.

An easy RHD genotyping strategy for D- East Asian persons applied to Korean blood donors

BACKGROUND

In East Asian populations RHD alleles are known to occur frequently among D- donors, requiring suitable genotyping strategies. The molecular basis of the "RHD(el)" allele previously reported in Taiwan to harbor a genomic 1013-bp deletion was questioned by several authors.

STUDY DESIGN AND METHODS

The presence of the RHD gene was investigated in 126 random serologic D- blood donors from Gwangju, southwest Korea. Four donors who typed weakly positive for the D antigen were also analyzed. RH alleles were determined by polymerase chain reaction (PCR) with sequence-specific priming (PCR-SSP) or nucleotide sequencing.

RESULTS

Seventy-five percent of the serologically D- samples lacked the RHD gene, 10 percent carried the hybrid RHD-CE(2-9)-D2 or RHD-CE(2-7)-D2 alleles, 13 percent represented the RHD(K409K), and 2 percent were weak D type 15 and type 17. Among the four donors typing weak D, two carried weak D type 15, one RHD(K409K), and one the novel weak D type 43. Critical molecular characteristics of RHD(K409K) and its population frequencies were indistinguishable to those reported for the RHDel allele.

CONCLUSION

Korean RHD allele frequencies are comparable to Chinese and Japanese frequencies. It is concluded that the RHDel allele may actually not exist but is identical to RHD(K409K). A practical RHD genotyping strategy applicable to D- donors in all East Asian populations was devised. The strategy requires four PCR-SSP procedures only for RHD intron 4 and exon 7 as well as RHD(K409K) and non-RHD(K409K).

Detection of RhD(el) in RhD-negative persons in clinical laboratory

The Rhesus (Rh) blood group is the most polymorphic human blood group system, and it is clinically significant in transfusion medicine. About 15% of Caucasoid people are RhD-negative, whereas in the Asian population, the RhD-negative blood type only occurs in 0.1% to 0.5%. However, approximately 30% of apparently RhD-negative Taiwanese people actually were RhD(el). Traditionally, we verify RhD(el) by a serologically adsorption-elution procedure with polyclonal anti-D. In our recent report, RhC phenotype is highly associated with RhD(el), and RHD1227A is a useful genetic marker for RhD(el). For setting up a rapid protocol to detect RhD(el) in clinical laboratory, a total number of 395 Taiwanese serological RhD-negative blood samples, those with RhC (+) phenotypes as selected by serological tests, were further screened by adsorption/elution tests and RHD1227A allele by specific sequence primer-polymerase chain reaction (SSP-PCR) for RhD(el). Among 395 blood samples collected from RhD-negative subjects, the incidence of RhC (+) was 43% (171/395). One hundred and twenty six of the 171 RhC (+) samples were positive for both adsorption/elution for RhD detection and SSP-PCR assay for RHD1227A. The sensitivity and specificity were 96.9% and 97.5%, respectively, for RHD1227A detection as compared with the traditional adsorption/elution test. Our results also indicated that RHD1227A was highly linked to Ce haplotypes (95.2%). In conclusion, combined RhC (+) phenotyping and RHD1227A analysis can be a simple and accurate laboratory screening protocol for RhD(el) detection in RhD-negative population.

Systemic analysis and zygosity determination of the RHD gene in a D-negative Chinese Han population reveals a novel D-negative RHD gene

BACKGROUND AND OBJECTIVES

The aim of this study was to systemically analyse the genetic background of D negativity in a Chinese Han population.

MATERIALS AND METHODS

DNA of 74 D-negative samples was analysed by using an RHD multiplex polymerase chain reaction (MPX PCR) for the presence of RHD and by PCR-restriction fragment length polymorphism (PCR-RFLP) for RHD zygosity determination. Sixty-five samples were additionally analysed by using real-time quantitative PCR on RHD exon 7. RHD exon-specific sequencing was performed on discrepant samples.

RESULTS

Forty-six samples (62%) showed the absence of RHD-specific exons by RHD MPX PCR and homozygous RHD negativity by PCR-RFLP. Twenty-two samples (30%) showed a 1227G>A mutation, characteristic for the Del phenotype. Five (7%) samples showed all characteristics of the RHD(1-2)-CE(3-9)-D(10) hybrid gene. One sample (1.4%) showed a novel 933C>A nonsense mutation in RHD exon 6, which resulted in a premature stop codon.

CONCLUSIONS

The RHD gene deletion, RHD-CE-D hybrid genes and one novel 93C>A mutation were found to be the three mechanisms that cause D negativity in our samples. The 1227G>A Del mutation was found to be the major cause of discrepant results between genotyping and phenotyping strategies, favouring genotyping of D-negative samples.

Presence ofRHDin serologically D-, C/E+ individuals: a European multicenter study

BACKGROUND

RHD blood group alleles with reduced or absent antigen expression are a clinically significant and heterogeneous group.

STUDY DESIGN AND METHODS

To detail population genetics data on apparently D- individuals in central Europe, a six-center study was performed with participants from Austria, Germany, Slovenia, Switzerland, and Russia. A total of 1700 serologically D- samples, positive for C and/or E, were investigated.

RESULTS

Observed unexpressed RHD alleles were 59 RHD-CE-D+ hybrid alleles, 9 apparently regular RHD, 1 new RHD(Y401X); DELs were 8 RHD(M295I), 6 RHD(IVS3+1G>A), and 1 new RHD(X418L); and weakly expressed RHDs were 2 weak D type 5, 1 weak D type 1, 1 RHD category VI type 1, and 1 novel weak D type 26. Although weak D type 26 was shown to have one of the lowest D antigen densities ever observed, it gave rise to anti-D immunization in a transfused D- individual.

CONCLUSION

The relative occurrence of RHD among serologically D- samples, positive for C and/or E, differed significantly in the investigated central European regions. Considering the growing use of molecular typing techniques, correct identification of blood group alleles with scarce or missing antigen expression is of utmost clinical importance and requires reliable population-based frequency data.