A COMBINATION OF THE EFFECTS OF RARE GENOTYPES AT THE XK AND KEL BLOOD-GROUP LOCI RESULTS IN ABSENCE OF KELL SYSTEM ANTIGENS FROM THE RED-BLOOD-CELLS

The 22 antigens of the Kell blood group system are located on a red bl ood cell (RBC) membrane glycoprotein that shows sequence homology with a family of metalloendopeptidases. Expression of the Kelt system anti gens is partially governed by XK, an X-linked gene that encodes the Kx protein: absence of Kx results in reduced Kell antigen expression. Al most total absence of Kelt antigens from the RBCs of a German man with no symptoms of neuroacanthocytosis could not be due to the Kell-null phenotype, K-0, because his RBCs had very weak expression of Kx antige n and his three children were Kp(a + b +). Kell antigens were normal o n the RBCs of his son but weak on those of his two daughters. An Nla I II restriction fragment-length polymorphism within the KEL gene showed the Kp(a)/Kp(a) genotype in the propositus, Sequencing of his XK gene showed a single base change within the donor splice consensus sequenc e of intron 2. A BsaAl restriction fragment-length polymorphism showed the mutation in both of his daughters but not in his son. The extreme depression of the Kelt antigens of the propositus must be due to a co mbination of effects, ie, homozygosity for Kp(a) and deficiency of Kx protein, each of which is capable of causing some degree of weakening of Kell antigens. (C) 1996 by The American Society of Hematology.