Diversity of variant alleles encoding Kidd, Duffy, and Kell antigens in individuals with sickle cell disease using whole genome sequencing data from the NHLBI TOPMed Program

BACKGROUND

Genetic variants in the SLC14A1, ACKR1, and KEL genes, which encode Kidd, Duffy, and Kell red blood cell antigens, respectively, may result in weakened expression of antigens or a null phenotype. These variants are of particular interest to individuals with sickle cell disease (SCD), who frequently undergo chronic transfusion therapy with antigen-matched units. The goal was to describe the diversity and the frequency of variants in SLC14A1, ACKR1, and KEL genes among individuals with SCD using whole genome sequencing (WGS) data.

STUDY DESIGN AND METHODS

Two large SCD cohorts were studied: the Recipient Epidemiology and Donor Evaluation Study III (REDS-III) (n = 2634) and the Outcome Modifying Gene in SCD (OMG) (n = 640). Most of the studied individuals were of mixed origin. WGS was performed as part of the National Heart, Lung, and Blood Institute's Trans-Omics for Precision Medicine (TOPMed) program.

RESULTS

In SLC14A1, variants included four encoding a weak Jka phenotype and five null alleles (JKnull ). JKA*01N.09 was the most common JKnull . One possible JKnull mutation was novel: c.812G>T. In ACKR1, identified variants included two that predicted Fyx (FY*X) and one corresponding to the c.-67T>C GATA mutation. The c.-67T>C mutation was associated with FY*A (FY*01N.01) in four participants. FY*X was identified in 49 individuals. In KEL, identified variants included three null alleles (KEL*02N.17, KEL*02N.26, and KEL*02N.04) and one allele predicting Kmod phenotype, all in heterozygosity.

CONCLUSIONS

We described the diversity and distribution of SLC14A1, ACKR1, and KEL variants in two large SCD cohorts, comprising mostly individuals of mixed ancestry. This information may be useful for planning the transfusion support of patients with SCD.

Clinical Significance of an Alloantibody against the Kell Blood Group Glycoprotein

BACKGROUND

Kell null (K₀) individuals can produce anti-Ku, an antibody against many epitopes in the Kell glycoprotein, after transfusion and/or pregnancy. Since sensitized K₀ patients are rare, little is known about anti-Ku clinical relevance and in particular about its association to hemolytic disease of the fetus and newborn.

CASE REPORT

This work describes a case of neonatal hyperbilirubinemia due to immune-mediated erythrocyte destruction by an alloantibody directed against the Kell glycoprotein. Serologic and molecular approaches identified an anti-Ku alloantibody in maternal serum. A homozygous IVS3 + 1g>a point mutation (KEL*02N.06 allele) was found to be responsible for the lack of Kell antigen expression in the mother's red blood cell and subsequent alloimmunization after a previous pregnancy. Even though in most cases Kell antibodies are clinically severe and may cause suppression of erythropoiesis, in our case the newborn had a moderate anemia and hyperbilirubinemia that was successfully treated with phototherapy without requiring exchange transfusion. Serological and molecular studies performed in the proband's family members allowed us to provide them with proper counseling regarding alloimmunization after transfusion and/or pregnancy.

CONCLUSIONS

This case enlarges the understanding of the clinical significance of alloantibodies against Kell blood group antigens.

Molecular Basis of KELnull Phenotype in Brazilians

BACKGROUND

KELnull (K0) persons can produce clinically significant anti-KEL5 antibody after transfusion and/or pregnancy, requiring K0 blood transfusion when indicated. 37 K0 alleles have been reported in studies over different populations, but none in Amerindian-Caucasian descendants from South America. The aim of this study was to identify the molecular basis of K0 phenotype in Brazilians.

METHODS

We investigated three K0 samples from different Brazilian blood banks (Recife, Manaus, and Vila Velha) in women with anti-KEL5. KEL antigen typing was performed by serologic techniques, and the K0 status was confirmed by flow cytometry. PCR-RFLP and DNA sequencing of the KEL coding and exon-intron regions were also performed.

RESULTS

RBCs of the 3 patients were phenotyped as KEL:-1,-2,-3,-4,-7. The 3 patients had the same KEL*02/02 genotype and were negative for KEL*02.03 and KEL*02.06 alleles. The Recife K0 patient was homozygous for IVS16 + 1g>a mutation (KEL*02N.31 allele). The flow cytometry with anti-KEL1, anti-KEL2, anti-KEL3, anti-KEL4, and anti-CD238 confirmed the K0 phenotype. In addition, we found the c.10423C>T mutation (KEL*02N.04 allele) in both the Manaus K0 and the Vila Velha K0 patients.

CONCLUSION

This report represents the first study of K0 molecular basis performed in Amerindian-Caucasian descendants from South America.