An unusual red cell antigen pattern seen when a patient inherits a deletion of a portion of the X chromosome carrying a gene for the Xk red cell protein. That protein carries the “Kx” antigen, which is tightly bound to the much larger Kell antigen structure. In the McLeod Phenotype, the RBCs lack the Kx antigen, and that absence leads to markedly decreased quantities of Kell system antigens, such as K, k, Kpb, and Jsb.
The McLeod Phenotype is rare in real life, but is popular on exams, especially given the other things associated with it. In particular, the McLeod Syndrome includes the red cell features of the phenotype, but it also includes a hemolytic anemia with acanthocytes, a movement disorder, cardiac problems, and most famously, an association with chronic granulomatous disease (CGD).
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