Sickle Cell Disease SICKLE CELL DISEASE The sickle cell diseases
are a group of disorders that have in common the propensity of
the red blood cells to become deformed when oxygen tension in
the blood is lowered, causing anemia, occlusion of blood vessels
by misshapen cells, and various associated clinical
consequences, including death. In sickle cell disease, a
mutation of the beta-globin gene results in the substitution of
valine for glutamic acid in the sixth amino acid of the chain,
producing a hemoglobin, designated hemoglobin S, that has less
solubility than does normal hemoglobin A. Inheriting one gene
for hemoglobin S, together with a normal gene, results in the
formation of red cells that contain approximately 40 percent of
the abnormal hemoglobin and 60 percent of the normal hemoglobin,
an essentially harmless state that is designated as sickle cell
trait. But if the gene inherited together with the sickle gene
is not normal, then the sickle cell disease may develop. The
most common hemoglobin that i