Molecular basis of the Kell (K1) phenotype

Area of Science:

• Immunogenetics
• Molecular Biology
• Blood Group Serology

Background:

• The Kell blood group system, particularly the K1 antigen, is a significant immunogen.
• K1 antibodies can lead to severe transfusion reactions and hemolytic disease of the newborn.
• The Kell system comprises over 20 antigens, with K1 and K2 (k) being antithetical alleles.

Purpose of the Study:

• To elucidate the molecular basis of the K1/K2 polymorphism in the Kell blood group system.
• To identify the genetic variation responsible for the K1 and K2 antigen expression.
• To develop a diagnostic method for K1/K2 genotyping.

Main Methods:

• Sequencing of the 19 exons of the Kell gene (KEL) from genomic DNA of a K1/K1 individual.
• Polymerase chain reaction (PCR) amplification and sequencing of KEL gene products.
• Restriction enzyme analysis (Bsm I) to confirm the identified genetic variation.

Main Results:

• A single C to T base substitution was identified in exon 6 of the KEL gene.
• This substitution results in an amino acid change from threonine to methionine at residue 193.
• The C to T substitution creates a Bsm I restriction site, enabling differentiation of K1/K1, K2/K2, and K1/K2 genotypes.

Conclusions:

• The identified C to T substitution in the KEL gene is the molecular basis for the K1/K2 polymorphism.
• This genetic change likely affects N-glycosylation at residue 193, altering the K1 antigen phenotype.
• The Bsm I restriction site provides a reliable method for K1/K2 genotyping, crucial for prenatal diagnosis of K1-related hemolytic disease.