Correlation 16: Hereditary spherocytosis

The small round red blood cells seen here on a peripheral blood smear with Wright-Giemsa stain are much smaller than the lymphocyte nucleus at the left and bottom. These abnormal RBCs lack central pallor.

This condition is known as spherocytosis, because RBCs should be biconcave, distensible structures, not small and round. This is an uncommon inherited condition in which there is an abnormal spectrin gene. Spectrin is a structural protein that binds to actin and helps form the cytoskeletal network that supports the RBC membrane. The abnormal spectrin leads to the abnormal RBC shape, because the unstable membrane assumes the shape with the least volume and stress--a sphere. These abnormal RBCs do not survive as long as normal RBCs, and persons with hereditary spherocytosis have anemia. The abnormal spectrin gene is most often seen in persons of northern European ancestry.