A 29-year-old man with a history of elevated creatine kinase and necrotizing 
myopathy was reviewed. Prominent red cell acanthocytosis in association with 
reduced Kell antigen expression was present, findings consistent with the McLeod 
syndrome. Investigation of the patient's XK gene revealed a novel TGG- to-TAG 
transition at position 1023 in exon 3. This point mutation creates an in-frame 
stop codon (W314X), and predicts a truncated XK protein of 313 amino acids, 
compared with 444 amino acids in the normal XK protein. The mutation was not 
identified in the patient's mother or sister indicating that this mutation was 
spontaneous.