Hereditary Acanthocytosis Associated with the McLeod Phenotype of the Kell Blood Group System

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Abstract
Summary. Some boys with X‐linked chronic granulomatous disease (CGD) have red cells of the rare McLeod phenotype in the Kell blood group system. Only one example of this phenotype has previously been described in a non‐CGD subject. We have studied a 10‐year‐old boy and a maternal brother who do not have CGD and whose red cells are of the McLeod type. The boy presented as a haematological problem with red‐cell abnormalities. These were acanthocytosis, anisocytosis and ‘tailing’ in the osmotic fragility curve, changes now known to occur with the McLeod phenotype. Subsequent studies revealed his rare blood group.A family study has established that an uncle also has acanthocytic red cells and the McLeod phenotype. In addition the boy's sister, mother and maternal grandmother all show red‐cell mosaicism with double populations of McLeod acanthocytes and normal red cells of common Kell type. The gene that determines inheritance of the McLeod phenotype is X‐linked and the mosaicism present in female carriers is believed to result from X chromosome inactivation by the Lyon effect. The study provides further evidence that the McLeod phenotype arises by inheritance of a variant X‐linked modifying gene and not through inheritance of a variant gene at the Kell autosomal locus. It also represents the first occasion that a person of rare blood group has been recognized because of an associated anomaly in red cell morphology.