Genetic basis of the K(0) phenotype in the Swedish population

The absence of all Kell blood group antigens (K(0) phenotype) is very rare. K(0) persons, however, can produce clinically significant anti-Ku (K5) after transfusion and/or pregnancy and require K(0) blood for transfusion. Ten alleles giving rise to the K(0) phenotype have been reported: different populations were studied although none from Scandinavia.

Three K(0) samples were identified by blood banks in Sweden (Uppsala, Umeå, and Linköping) during a 20-year period. Kell antigen typing was performed with standard serologic techniques by the respective blood banks and K(0) status was confirmed by the International Blood Group Reference Laboratory in Bristol, England. Polymerase chain reaction and DNA sequencing of the KEL coding region (exons 1-19) was performed on genomic DNA.

The Uppsala K(0) was homozygous for a 1540C>T substitution in exon 13, leading to an immediate stop codon. The Umeå K(0) was homozygous for 1023delG in exon 8 that results in a frameshift and a premature stop codon in exon 9. In the Linköping K(0), a previously reported mutation g>a at +1 of intron 3 was found.

Two novel and one previously reported null alleles at the KEL locus are described. The identified nonsense mutations abolish expression of the Kell glycoprotein and are thus responsible for the K(0) phenotype in these Swedish families.