Red Blood Cell Membrane Disorders

The process of erythropoiesis, which produces around 2 million red blood cells (RBCs) per second, is intricate. These RBCs deform their normal shape to pass through the 3-μm diameter capillaries and the 1-μm to 2-μm-wide endothelial slits in the spleen. Normal RBCs are 7–8 μM in size with a complexly regulated ratio of their membrane surface area to cytoplasmic volume, which gives them the classic biconcave disc shape. The RBC membrane consists of an array of lipids and proteins. The membrane proteins can be classified into two general groups: (1) integral proteins: band 3, aquaporin 1, GLUT1, PIEZO1, glycophorins; and (2) peripheral proteins: ankyrin, spectrin, band 4.2, actin, tropomyosin, and tropomodulin, protein 4.1, adductin, sematin. Conditions that can interfere with normal membrane deformability and stability of RBCs can decrease the normal surface membrane area-to-volume ratio, thereby altering RBC shape, inducing hemolysis, and shortening the lifespan of the RBC. Hemolytic anemias resulting from defects in the RBC membrane are an important group of hereditary anemias.