BACKGROUND: Kx is lacking in the RBCs of patients with the McLeod syndrome. This 
condition is sometimes associated with chronic granulomatous disease (CGD). If 
given allogeneic RBCs, CGD patients with the McLeod phenotype may produce 
anti-Kx and anti-Km, and only phenotypically matched McLeod blood would be 
compatible. McLeod phenotype persons without CGD have made anti-Km but not 
anti-Kx (2 examples), and thus both McLeod and K(O) blood would be compatible.
CASE REPORT: RBCs from a transfused patient with the McLeod phenotype but not 
with CGD (non-CGD McLeod) were typed for the Kell blood group antigens, and the 
plasma was analyzed for the presence of antibody by agglutination. The molecular 
basis was determined by analyzing for XK protein on RBC membranes by Western 
immunoblotting, by sequencing the XK gene, and by RFLP.
RESULTS: The RBCs did not react with anti-Kx + anti-Km and showed weakening of 
Kell system antigens. The patient's plasma reacted moderately (2+) with RBCs of 
common Kell type and strongly (4+) with K(O) RBCs and RBCs of common Kell type 
treated with dithiothreitol, and did not react with McLeod RBCs. XK protein was 
absent from the RBC membranes. The XK gene had a point mutation in the donor 
splice site of intron 1 (G>C).
CONCLUSION: This is the first report describing the molecular alteration in a 
non-CGD McLeod patient who has made anti-Kx. The immune response of people with 
the McLeod phenotype can vary, and K(O) blood may not always be compatible.