Fatal hemolytic disease of the fetus and newborn caused by anti-Jra antibody: A case report and literature review

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.

Generation of a human induced pluripotent stem cell line (YUCMi020-A) from peripheral blood mononuclear cells derived from a female with the Jr(a-) blood type

The Jra antigen, the only antigen within the JR blood group system, is a high-prevalence red blood cell (RBC) antigen found in over 99 % of the global population. An induced pluripotent stem cell line (YUCMi020-A) was generated from peripheral blood drawn from a Jr(a-) phenotype individual, who was homozygous for a null mutation of ABCG2*01N.01 (rs72552713, c.376C>T; p.Gln126*). The generated line exhibited pluripotent characteristics and no chromosomal aberrations. This cell line will serve as a cell source, enabling us to produce RBCs with the Jr(a-) phenotype in vitro, which can be used for transfusing individuals with anti-Jra antibodies.

Prevalence and molecular basis of null blood group phenotypes in the Korean population: Analysis using a public database

BACKGROUND

Null phenotypes are characterized by complete absence of all antigens within a blood group system and caused by null variants (e.g., nonsense, frameshift, initiation codon, and canonical splice site variants) in the genes encoding the antigens. Knowing the prevalence and molecular basis of null phenotypes is essential to establish a rare donor program, and the aim of this study was to reveal the prevalence and molecular basis of null phenotypes using the Korean Reference Genome Database (KRGDB) containing whole-genome sequences of 1722 Korean individuals.

STUDY DESIGN AND METHODS

Population allele frequencies of null alleles in 39 blood group systems except ABO, MNS, Rh, Lewis, and FORS were obtained from the KRGDB. The prevalence of null phenotypes was calculated using Hardy-Weinberg equation.

RESULTS

The prevalence of null phenotypes were estimated to be less than 0.001% in all blood group systems except JR and SID. The prevalence of the Jr(a-) and Sd(a-) phenotypes were estimated to be 0.0453% and 0.2323%, respectively. The most frequent null allele of the JR system was ABCG2*01N.01, accounting for approximately 85% of null alleles.

DISCUSSION

Our approach using a public database allowed us to investigate the prevalence and molecular basis of null phenotypes in the Korean population, which will serve as a guide for establishing a rare donor program in Korea. Considering the clinical significance, Jr(a-) is an important null phenotype that should be typed in the Korean population, and molecular assays targeting the most frequent allele ABCG2*01N.01 may be useful in detecting this phenotype.

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.

Severe fetal anemia caused by anti-Jra : Burst forming unit-erythroid colony formation inhibition assay suggesting possible erythroid suppression mechanism

BACKGROUND

The Jr blood group system includes a single, high-prevalence antigen, Jr^a , encoded by the ABCG2 gene. The impact of anti-Jr^a in pregnancy is variable, ranging from no clinical effect to severe anemia including some fetal deaths. Case reports have postulated that anti-Jr^a mediated fetal anemia is poorly hemolytic, suggesting other mechanisms of anemia may be involved.

STUDY DESIGN AND METHODS

We describe the case of severe anti-Jr^a mediated fetal anemia. At Canadian Blood Services laboratories, maternal anti-Jr^a was tested for phagocytic activity via a monocyte monolayer assay (MMA) and erythroid suppression via inhibition of burst forming unit-erythroid (BFU-E) colony formation assays. The New York Blood Center sequenced exons 4 and 7 of the ABCG2 gene.

RESULTS AND DISCUSSION

Sequencing of exons 4 and 7 of the ABCG2 gene revealed maternal compound heterozygosity for two nonsense mutations at exon 7 (c.706 C > T and c.784G > T). Fetal sequencing revealed the c.706C > T polymorphism. The MMA showed a borderline phagocytic index (around the cutoff of five for both donor segments tested [5 ± 1 and 7 ± 3]). The BFU-E colony formation inhibition assay suggested a dose-dependent inhibition of BFU-E colony formation with inhibition percentages of 4%, 11%, and 43% at maternal serum concentrations of 2%, 5%, and 10%, respectively. Our findings support the hypothesis that anti-Jr^a may impair erythropoiesis leading to clinically significant fetal/neonatal anemia. A referral to maternal fetal medicine is recommended if anti-Jr^a is detected in pregnancy, regardless of the titer.

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.