The JR blood group system (ISBT 032): molecular characterization of three new null alleles

Evaluating the TaqMan Jra-Genotyping Method for Rapidly Predicting the Presence of Anti-Jra Antibodies

Background

The Jra antigen is a high-prevalence red blood cell (RBC) antigen. Reports on cases of fatal hemolytic disease of the fetus and newborn and acute hemolytic transfusion reactions suggest that antibodies against Jra (anti-Jra) have potential clinical significance. Identifying anti-Jra is challenging owing to a lack of commercially available antisera. We developed an alternative approach to rapidly predict the presence of anti-Jra using the TaqMan single-nucleotide polymorphism (SNP)-genotyping method.

Methods

Residual peripheral blood samples from 10 patients suspected of having the anti-Jra were collected. Two samples with confirmed Jr(a-) RBCs and anti-Jra were used to validate the TaqMan genotyping assay by comparing the genotyping results with direct sequencing. The accuracy of the assay in predicting the presence of anti-Jra was verified through crossmatching with in-house Jr(a-) O+ RBCs.

Results

The TaqMan-genotyping method was validated with two Jr(a-) RBC- and anti-Jra-confirmed samples that showed concordant Jra genotyping and direct sequencing results. Jra genotyping for the remaining samples and crossmatching the serum samples with inhouse Jr(a-) O+ RBCs showed consistent results.

Conclusions

We validated a rapid, simple, accurate, and cost-effective method for predicting the presence of anti-Jra using a TaqMan-based SNP-genotyping assay. Implementing this method in routine practice in clinical laboratories will assist in solving difficult problems regarding alloantibodies to high-prevalence RBC antigens and ultimately aid in providing safe and timely transfusions and proper patient care.

Hemolytic disease of the newborn due to anti-Jra from a Chinese mother with one novel and one classic heterozygous mutation

OBJECTIVE

Investigation of a Jr(a-) family samples, identification of the mutant and assessment of the differences of Jr antigen density of the Jr(a-) family members, random adult and newborn individuals' RBCs.

BACKGROUND

The anti-Jra antibody is generated when a Jr(a-) individual pregnant or transfused with Jr(a+) blood unit, which can lead to mild-to-moderate hemolytic disease of the foetus and newborn (HDFN) or hemolytic transfusion reaction (HTR). Several mutations had been identified. The anti-Jra caused HDFN is not rare in East Asia, but due to the lack of antibody and molecular background, it is likely to lead missed detection.

METHODS AND MATERIALS

One G4P1 woman had been detected as IAT positive during prenatal examination. Suspected as anti-Jr^a after the laboratory serological testing, the maternal sample was further assessed by molecular analysis. The antigen density was detected by flow cytometry after reacting with anti-Jr^a serum in family members and the normal individuals.

RESULTS

One novel frameshift mutation c.717delC and one previously identified mutation c.706C > T in ABCG2 was identified on proband. The infant haemoglobin(Hb) and bilirubin increased significantly after exchange transfusion and the severe HDFN was relieved. Flow cytometry results showed that the Jr^a antigens on adult RBCs were significantly less than those on the infant.

CONCLUSION

The c.717delC mutation can lead to the shortening of protein ABCG2 in the site of p.Leu307Stop, result in the loss of Jr^a antigen. The difference in antigen density between adult and infant RBCs may be a possible reason that leads to severe HDFN but not transfusion reaction. Breastfeeding may lead to slower recovery from HDFN.

Multidrug efflux transporter ABCG2: expression and regulation

The adenosine triphosphate (ATP)-binding cassette efflux transporter G2 (ABCG2) was originally discovered in a multidrug-resistant breast cancer cell line. Studies in the past have expanded the understanding of its role in physiology, disease pathology and drug resistance. With a widely distributed expression across different cell types, ABCG2 plays a central role in ATP-dependent efflux of a vast range of endogenous and exogenous molecules, thereby maintaining cellular homeostasis and providing tissue protection against xenobiotic insults. However, ABCG2 expression is subjected to alterations under various pathophysiological conditions such as inflammation, infection, tissue injury, disease pathology and in response to xenobiotics and endobiotics. These changes may interfere with the bioavailability of therapeutic substrate drugs conferring drug resistance and in certain cases worsen the pathophysiological state aggravating its severity. Considering the crucial role of ABCG2 in normal physiology, therapeutic interventions directly targeting the transporter function may produce serious side effects. Therefore, modulation of transporter regulation instead of inhibiting the transporter itself will allow subtle changes in ABCG2 activity. This requires a thorough comprehension of diverse factors and complex signaling pathways (Kinases, Wnt/β-catenin, Sonic hedgehog) operating at multiple regulatory levels dictating ABCG2 expression and activity. This review features a background on the physiological role of transporter, factors that modulate ABCG2 levels and highlights various signaling pathways, molecular mechanisms and genetic polymorphisms in ABCG2 regulation. This understanding will aid in identifying potential molecular targets for therapeutic interventions to overcome ABCG2-mediated multidrug resistance (MDR) and to manage ABCG2-related pathophysiology.

Genomic coordinates and continental distribution of 120 blood group variants reported by the 1000 Genomes Project

BACKGROUND

The 1000 Genomes Project provides a database of genomic variants from whole genome sequencing of 2504 individuals across five continental superpopulations. This database can enrich our background knowledge of worldwide blood group variant geographic distribution and identify novel variants of potential clinical significance.

STUDY DESIGN AND METHODS

The 1000 Genomes database was analyzed to 1) expand knowledge about continental distributions of known blood group variants, 2) identify novel variants with antigenic potential and their geographic association, and 3) establish a baseline scaffold of chromosomal coordinates to translate next-generation sequencing output files into a predicted red blood cell (RBC) phenotype.

RESULTS

Forty-two genes were investigated. A total of 604 known variants were mapped to the GRCh37 assembly; 120 of these were reported by 1000 Genomes in at least one superpopulation. All queried variants, including the ACKR1 promoter silencing mutation, are located within exon pull-down boundaries. The analysis yielded 41 novel population distributions for 34 known variants, as well as 12 novel blood group variants that warrant further validation and study. Four prediction algorithms collectively flagged 79 of 109 (72%) known antigenic or enzymatically detrimental blood group variants, while 4 of 12 variants that do not result in an altered RBC phenotype were flagged as deleterious.

CONCLUSION

Next-generation sequencing has known potential for high-throughput and extended RBC phenotype prediction; a database of GRCh37 and GRCh38 chromosomal coordinates for 120 worldwide blood group variants is provided as a basis for this clinical application.

International Society of Blood Transfusion Working Party on red cell immunogenetics and blood group terminology: Cancun report (2012)

The International Society of Blood Transfusion Working Party on red cell immunogenetics and blood group terminology convened during the International congress in Cancun, July 2012. This report details the newly identified antigens in existing blood group systems and presents three new blood group systems.

Molecular analysis of immunized Jr(a-) or Lan- patients and validation of a high-throughput genotyping assay to screen blood donors for Jr(a-) and Lan- phenotypes

BACKGROUND

Individuals with anti-Jr(a) or anti-Lan are ideally transfused with rare Jr(a-) or Lan- red blood cells. We characterized mutations in Dutch Jr(a-) and Lan- individuals and developed a high-throughput genotyping assay to detect Jr(a-) and Lan- donors.

STUDY DESIGN AND METHODS

Six Jr(a-) and seven Lan- persons, who all made anti-Jr(a) or anti-Lan, were sequenced for ABCG2 or ABCB6 and the copy number of ABCG2 and ABCB6 was determined. A total of 3366 Caucasian, 621 black, and 333 Chinese donors were screened with a high-throughput screening assay targeting frequently occurring mutations causing the Jr(a-) or Lan- phenotype.

RESULTS

In the six tested Jr(a-) individuals previously described, c.376C > T, c.706C > T, and c.736C > T nonsense mutations in ABCG2 were detected. In the seven Lan- individuals 12 different mutations, of which 10 underlie the Lan- phenotype, were detected. No copy number variation was detected for ABCG2 and ABCB6. The high-throughput screening assay detected five Caucasian donors heterozygous for the c.706C > T or 736C > T mutation in ABCG2 and nine Caucasian donors heterozygous for the 574C > T mutation in ABCB6. No black or Chinese donors were found positive for a mutation.

CONCLUSION

We describe eight new mutations in ABCB6 of which seven, including three missense mutations, underlie the Lan- phenotype and determine that a complete gene deletion of ABCG2 or ABCB6 is not responsible for the Jr(a-) or Lan- phenotype, respectively. The extended heterogeneity of mutations causing the Jr(a-) or Lan- phenotype in most populations makes genetic screening for the Jr(a-) and Lan- phenotype inefficient in those populations.

Defining the Jr(a-) phenotype in the Japanese population

BACKGROUND

The Jr(a-) phenotype is rare in European and North American populations but is not so rare in Japanese and other Asian populations. Recently, two groups have established the connection between the Jr(a-) phenotype and the ATP-binding cassette, member G2 (ABCG2) gene and concluded that ABCG2-null alleles encode the Jr(a-) phenotype. In Japanese Red Cross Blood Centers, the Jr(a-) phenotype is found with a prevalence of 0.05% among blood donors, and we applied DNA-based genotyping to investigate the molecular basis of the Jr(a-) phenotype in Japan, in addition to serologic typing.

STUDY DESIGN AND METHODS

Purified genomic DNA extracts of Japanese donor samples [500 Jr(a+) and 85 Jr(a-) phenotypes] were amplified using specific amplification primers for the c.376C>T mutation, which is the most common mutation in the Asian JRnull allele. Polymerase chain reaction products were examined by high-resolution melt techniques and DNA sequence analyses.

RESULTS

Seventy-nine of 85 Jr(a-) samples were homozygous for the single-nucleotide polymorphism c.376C>T (Gln126Stop) change. In other samples, two novel null alleles were detected: c.2T>C and c.421C>A: c.1515delC.

CONCLUSION

In this study, more than 90% of the Japanese Jr(a-) phenotypes had c.376C>T (Gln126Stop) nucleotide change. In the other Jr(a-), a new mutation (c.2T>C) in the start codon encoding Thr instead of Met, c.1515delC encoding Ala505AlafsStop and heterozygous for c.337C/T and c.736C/T were detected. DNA-based genotyping is accurate and useful for Jr(a-) donor typing.

Emily Cooley lecture 2012: Emily Cooley and techniques that have been applied to characterize DO and JR blood groups

Emily Cooley was a well-respected medical technologist and morphologist with a remarkable skill set. She was highly regarded both professionally and personally. The "Emily Cooley Lectureship and Award" was established to honor her in particular and medical technologists in general. This article first reviews the history of the Emily Cooley award and provides some of the reasons why it carries her name. Then, using two blood group systems, DO and JR, it illustrates how many discoveries regarding blood groups were dependent on access to techniques.

The JR blood group system: identification of alleles that alter expression

BACKGROUND

The ABCG2 gene encodes antigens of the JR blood group system. Red blood cells (RBCs) from individuals homozygous for ABCG2 null alleles are nonreactive with polyclonal and monoclonal anti-Jr(a) . However, some RBCs have been defined as Jr(a+(W) /-) or Jr(a-), particularly when tested with polyclonal anti-Jr(a) . In an effort to resolve these apparent serologic ambiguities, the current study was undertaken.

STUDY DESIGN AND METHODS

Hemagglutination of RBCs from two individuals known to express a single copy of functional ABCG2 were compared to RBCs from eight unrelated, previously characterized, Jr(a+(W) /-) donors. Standard polymerase chain reaction-based methods were used to characterize ABCG2 alleles.

RESULTS

Two monoclonal anti-Jr(a) clones agglutinated RBCs from the eight Jr(a+(W) /-) study subjects. Two of these subjects were homozygous for a missense ABCG2 change (c.1858A; Asp620Asn). Two were heterozygous for two missense changes; one was c.1858G>A and c.421C>A (Asp620Asn; Gln141Lys), and the other was c.1714A>C and c.421C>A (Ser572Arg; Gln141Lys). The remaining four subjects were heterozygous for c.421C>A (Gln141Lys), and for one of four null alleles.

CONCLUSIONS

We have identified three ABCG2 alleles that are newly associated with weakened Jr(a) expression. One of these is novel, the missense allele c.1714A>C (Ser572Arg) and two that have been previously described c.421C>A (rs2231142; Gln141Lys) and c.1858G>A (rs34783571; Asp620Asn). In addition, we found a novel, presumed null allele, c.1017_1019delCTC (Ser340del).