Molecular defects underlying the Kell null phenotype

Molecular approaches to blood group identification

Allogeneic barriers to transfusion are caused by differences between those portions of the donor and recipient genomes that define the antigenicity and immune response to the transfused cells. Historically, a blood group antigen was identified when an immune response (alloantibody) was detected by hemagglutination in the serum of a transfused patient. There has been an astounding pace of growth over the past two decades in the field of molecular biology techniques and even more recently in the understanding of the basis of many blood group antigens and phenotypes. Identification of blood group antigens can now be performed in genetic terms, and identification of blood group antibodies can be performed using molecular approaches. This knowledge is being applied to help resolve some long-standing clinical problems that cannot be resolved by classical hemagglutination. This article reviews knowledge of molecular approaches for identifying blood group antigens and antibodies as applied to transfusion medicine practice.

Point mutations in KEL exon 8 determine a high-incidence (RAZ) and a low-incidence (KEL25, VLAN) antigen of the Kell blood group system

BACKGROUND AND OBJECTIVES

The molecular basis of two Kell blood group antigens, RAZ (provisionally KEL27) and VLAN (KEL25), were determined.

MATERIALS AND METHODS

The DNA sequences of the open reading frames and the flanking intron regions of the 19 KEL exons from RAZ and VLAN probands were compared with that of common KEL. Genotyping assays were designed to confirm and detect RAZ and VLAN phenotypes.

RESULTS

A homozygous G865A mutation, encoding lysine instead of glutamic acid at amino acid position 249 of Kell protein, defines the RAZ phenotype, while a heterozygous G863A mutation in KEL, encoding an arginine to glutamine substitution at amino acid 248, characterizes the VLAN phenotype.

CONCLUSION

Point mutations G865A and G863A, in adjacent codons of KEL exon 8, which cause amino acid substitutions, characterize the RAZ and VLAN Kell blood group phenotypes.