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.1042C>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.