We report a novel mutation in the XK gene (XK) in a Japanese patient with McLeod 
syndrome. A 50-year-old man showed progressive muscular atrophy, choreic 
movement, elevated level of serum creatinine kinase, and acanthocytosis. The 
expression level of all the Kell antigens in erythrocyte was decreased and 
molecular analysis revealed a single-base (T) deletion at the nucleotide 
position 1095 in XK. This deletion caused a frameshift in translation, leading 
to a premature stop codon at the amino acid position 408. We conclude this 
single-base deletion causes defective Kx protein, which is responsible for the 
McLeod phenotype in this patient.