The erythrocyte membrane accounts for 1 percent of total weight of the red cell.
It plays an integral role in the maintenance of erythrocyte integrity.
The lipid bilayer of the membrane and its associated skeletal proteins provide the flexibility, durability, and tensile strength for the erythrocyte to undergo large deformations during repeated passages through narrow microcirculatory channels.
Hereditary spherocytosis (HS) is the most common inherited anemia of persons of northern European descent. It is characterized by hemolysis of variable intensity, spherocytosis, and increased osmotic fragility of red blood cells. There is a favorable response to splenectomy.
Accelerated red cell destruction results from deficiency or abnormality of one or more of the red cell membrane proteins, resulting in release of membrane lipids, decreased surface area, and formation of poorly deformable spherocytes.
The underlying molecular defects are heterogeneous and defects affecting the same protein may produce different phenotypes, such as spherocytosis and elliptocytosis or ovalocytosis.
Table 14–1 summarizes the relationship between red cell membrane proteins and disease phenotype.
TABLE 14–1RED CELL MEMBRANE PROTEIN DEFECTS IN INHERITED DISORDERS OF RED CELL SHAPE |Favorite Table|Download (.pdf) TABLE 14–1 RED CELL MEMBRANE PROTEIN DEFECTS IN INHERITED DISORDERS OF RED CELL SHAPE
|Protein ||Disorder ||Comment |
|Ankyrin ||HS ||Most common cause of typical dominant HS |
|Band 3 ||HS, SAO, NIHF, HAc ||"Pincered" HS spherocytes seen on blood film presplenectomy; SAO results from 9 amino acid deletion |
|β-Spectrin ||HS, HE, HPP, NIHF ||"Acanthocytic" spherocytes seen on blood film presplenectomy; location of mutation in β-spectrin determines clinical phenotype |
|α-Spectrin ||HS, HE, HPP, NIHF ||Location of mutation in α-spectrin determines clinical phenotype; α-spectrin mutations most common cause of typical HE |
|Protein 4.2 ||HS ||Primarily found in Japanese patients |
|Protein 4.1 ||HE ||Found in certain European and Arab populations |
|GPC ||HE ||Concomitant protein 4.1 deficiency is basis of HE in GPC defects |
With spectrin deficiency, larger areas of lipid bilayer are unsupported by the submembranous skeleton, causing loss of lipid in submicroscopic vesicles.
The red cell membrane is more permeable to sodium, which activates the Na+, K+-ATPase pump and leads to K+ loss and dehydration.
A decrease in the surface area-to-volume ratio and an increase in internal viscosity make spherocytes less deformable and unable to penetrate the slits between splenic cords and sinuses.
While retained in the spleen, the red cells undergo a "conditioning effect," which renders the cells more spherical (loss of membrane surface area) and more osmotically fragile (lower surface area to volume ratio).
Ultimately, the cells are engulfed by splenic macrophages ...
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