Which is the most common red cell defect without Hb abnormality

On smears, spherocytes are dark red and lack central pallor (Fig. 11-2). The excessive red cell destruction and resultant anemia lead to a compensatory hyperplasia of red cell progenitors in the marrow and an increase in red cell production marked by reticulocytosis. Splenomegaly is more common and prominent in hereditary spherocytosis than in any other form of hemolytic anemia. The splenic weight usually is between 500 and 1000 g. The enlargement results from marked congestion of the splenic cords and increased numbers of tissue macrophages. Phagocytosed red cells are seen within macrophages lining the sinusoids and, in paicular, within the cords. In long-standing cases there is prominent systemic hemosiderosis. The other general fea- tures of hemolytic anemias also are present, including cho- lelithiasis, which occurs in 40% to 50% of patients with hereditary spherocytosis. Hereditary spherocytosis is caused by abnormalities in the membrane skeleton, a network of proteins that underlies lipid bilayer of the red cell (Fig. 11-1). The major membrane skeleton protein is spectrin, a long, flexible het- erodimer that self-associates at one end and binds sho actin filaments at its other end. These contacts create a two- dimensional meshwork that is linked to the overlying mem- brane through ankyrin and band 4.2 to the intrinsic membrane protein called band 3, and through band 4.1 to glycophorin. The mutations in hereditary spherocytosis most frequently involve ankyrin, band 3, and spectrin, but mutations in other components of the skeleton have also been described. Ref Robbins 9/e pg 410