In sickle cell anemia all are true except -
Ans. is 'd' i.e., Ringed sideroblast Laboratory findings of sickle cell anemia :-o Moderate to severe anaemia,o Peripheral smear will showSickle cellsTarget cellsHowell-Jolly bodies because of autosplenctomy.o A postive sickling test with a reducing substance like sodium metabisulfite.o Sickle cell anemia is caused by replacement of normal Hemoglobin by sickled hemoglobin (HbS).o HbS is formed by replacement of Glutamine by Valine at position 6o This substitution replaces the polar Glutamine residue with a nonpolar Valine.o The replacement of Glutamine by Valine generates a sticky patch on the surface of HBS.o The sticky patch is present on both oxygenated and deoxygenated HbSo The deoxygenated HbS also contains a complementary site for the sticky patch.o In oxygenated hemoglobin this complementary site is masked.o When HbS is deoxygenated the sticky patch present on its surface binds to the complementary patch on another deoxygenated HbS molecules.o This binding leads to polymerization of deoxyhemoglobin S forming long fibrous precipitates,o These extend throughout the erythrocyte and mechanically distort it, causing lysis and multiple secondary clinical effect.So, if HbS can be maintained in an oxygenated state or if the concentration of deoxygenated HbS can be minimized, formation of these polymers will not occur and sickling can be prevented (Remember the complementary site for the sticky patch remains masked in case of Oxygenated HbS).Role of HbA in polymerization -o Unlike HbS, HbA does not contain any sticky patch, but it does have a binding site for the sticky patch of HbS.o Thus it can bind to HbS through its receptor site but this binding cannot extend the polymer because HbA does not contain any sticky patch to promote binding to still another hemoglobin molecule.o So HbA interferes with the polymerisation and aggreation of HbS and reduces the intensity of sickle cell anemia.
Sickle cells
Target cells
Howell jolly bodies
Ringedsideroblast
Hemolytic anemia