The xerocytosis of Hb SC disease
SK Ballas, J Larner, ED Smith, S Surrey, E Schwartz and EF Rappaport
Patients with Hb SC disease were found to have microcytic and hyperchromic
red cell indices despite mild reticulocytosis. Iron deficiency anemia was
ruled out by the finding of normal serum ferritin levels. In order to
determine whether the microcytosis was due to coexistent alpha-thalassemia,
restriction endonuclease mapping was performed on genomic DNA extracted
from peripheral blood leukocytes. Patients with Hb SC disease had
microcytic indices despite the presence of a full complement of four
alpha-genes (alpha alpha/alpha alpha), suggesting that the microcytosis may
be due to cellular dehydration (or xerocytosis), since the mean corpuscular
hemoglobin concentration in Hb SC disease patients was significantly higher
than in controls. This possibility was investigated further by the
determination of RBC cation content. RBC Na levels were similar in SC and
normal red cells. Hb SC RBCs, however, had significantly reduced K levels.
These findings show that RBC cation content, and thus cell water, is
decreased in Hb SC disease. The decreased RBC K level in the presence of
normal cellular Na concentration suggests selective K loss that is not due
to inhibition of the Na K pump. Ouabain-insensitive K+ efflux was increased
to four times normal in SC cells. Cell dehydration was confirmed by the
demonstration of increased high-density RBCs on discontinuous Stractan
density gradients and by osmotic gradient ektacytometry. Cellular
dehydration and its sequelae were worse in CC erythrocytes and milder in AC
cells than in Hb SC red cells. Taken together, these data indicate that in
Hb SC disease the RBCs are severely dehydrated and typically microcytic and
hyperchromic. Hb SC RBCs seem to be dehydrated due to selective K loss.
These findings suggest a functional interrelationship between Hb SC, the
red cell membrane, and cation regulation.
Volume 69,
Issue 1,
pp. 124-130,
01/01/1987
Copyright © 1987 by The American Society of Hematology