ABSTRACT
Sickle cell anemia and its variants are inherited disorders of hemoglobin
(Hb) structure due to the substitution of valine for glutamic acid at position 6 of the beta globin chain. Upon deoxygenation of the erythrocyte, Hb S
undergoes intracellular polymerization with morphologic transformation
to the sickled shape. Repetitive sickling cycles induce a complex series of
abnormalities in the erythrocyte, including cytoplasmic andmembrane rigid-
ity, dehydration, and an increase in intracellular Hb concentration. The
circulating erythrocyte population is thus comprised of a heterogeneous
population of cells including low-density reticulocytes, very dense disco-
cytes, and irreversibly sickled cells. These dense, poorly deformable cells are ultimately responsible for the elevated whole blood viscosity and
microvascular occlusion in this disease (1,2). The clinical features of the
disease are the direct result of the beta 6 substitution and consist of
chronic hemolytic anemia, frequent infections, and microvascular obstruc-
tion producing acute and chronic ischemia and ultimately resulting in
organ damage from infarction and fibrosis (3).
