A novel JK ‐null allele due to splicing variant

The absence of JK antigens carried by the erythroid urea transporter due to null alleles is well documented. To date, over 50 alleles have been identified and registered by the International Society of Blood transfusion (ISBT Blood Group Database). An elderly woman of European ancestry developed anti-JK1 (Jka) 3 days after the transfusion of two units of packed red blood cells (RBCs), one of which was from a JK: 1 (or Jk (a+) ) donor. The JK phenotype of the other unit was unknown. We report the identification of a novel JK*01 allele carrying the c. 151+1G>C variant in the SLC14A1 gene that was shown to be responsible for the lack of JK1 (Jka) expression by functional analysis. Antibody identification was done using standard methods. The patient's plasma was tested with native or papain or trypsin-treated RBC. A direct antiglobulin test (DAT) was performed on the patient's RBC. Subsequently, the eluate using Gamma ELU-KIT II (Werfen, Norcross, USA) was tested in an indirect agglutination test (IAT) to identify a potential alloantibody. Genomic DNA was isolated from whole blood with NucleoMag (Macherey-Nagel, Hoerdt, France) according to the manufacturer's instructions. Genotyping was performed using the HEA BeadChip array (BioArray Solutions/Immucor-Werfen, Warren, New Jersey, USA) and Sanger sequencing (SLC14A1 coding exons 3 to 10 and flanking regions; 3500 Dx genetic analyzer, Thermo Fisher), as previously described. 1 The effect of the variant was predicted in silico using SpliceAI2 and SPIP3 and reporter minigene splicing assay was performed to further investigate the effect of the variant in an in vitro model. 4, 5 Anti-JK1 was identified in the patient's plasma by IAT. The DAT was 2+ with anti-C3d, and the eluate also contained anti-JK1, consistent with an allo-antibody due to a recent RBC transfusion. By the HEA Beadchip, the sample was found to be heterozygous (G/A) at position c. 838 defining the JK1/JK2 antigen specificity, which is consistent with a JK*01/JK*02 genotype. According to the reference sequence NM₀15865, Sanger sequencing of SLC14A1 confirmed c. 838G/A in exon 8, and additionally detected the c. 151+1G>C single nucleotide variant, which is located within the consensus donor splice site of intron 3, at the heterozygous state. This variant was predicted to disrupt splicing by in silico investigation (SpliceAI score: 0. 71 donor loss; SPiP v2. 1 score: 0. 986 Alter by SPiCE). The deleterious effect was confirmed in vitro by the minigene splicing assay demonstrating the complete disruption of the constitutive donor splice site and the full skipping of SLC14A1 exon 3 (Figure 1, black arrowhead). Very importantly, this exon carries the methionine initiation codon. Therefore, it is thought that translation initiation cannot occur and no normal protein can be expressed from the novel allele carrying the c. 151+1G>C variant. In this work, we describe the novel JK*01 N c. 151 + 1 G>C null allele (Genbank accession number: PX849538) that disrupts the expression of the JK1 antigen in a patient of European descent who made anti-JK1 after being transfused with JK: 1 RBC. This demonstrates, once again, that caution must be exercised when interpreting targeted genotyping results when antibodies are present. ISBT Blood Group Database (JK blood group system): blooddatabase. isbtweb. org/system/JK (accessed on January 12, 2026). Open access publication funding provided by COUPERIN CY26. The authors have nothing to report. The authors have disclosed no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.