الفهرس 
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Abstract
Sickle cell disease (SCD) was the first human monogenic disorder to be characterized at the molecular level. Sickle cell disease (SCD) and its variants are genetic disorders of mutant haemoglobin (Hb). The most common form found worldwide is homozygous HbS disease. Hemoglobins are the major oxygen-carrying pigments of the body. The α- and β-globin gene clusters and protein products are tightly regulated to ensure that at any stage of development there is a correct balance in the availability of α-like and β-like globin chains. The molecular genetic basis for SCD is a single base substitution in the second position of codon 6 in the β-globin gene, located inside a cluster of genes called the β-globin gene cluster on the short arm of chromosome 11. The result of this mutation is the production of sickle hemoglobin. The pathogenesis of sickle cell disease (SCD) primarily derives from the polymerization of deoxygenated hemoglobin S (HbS) in the red cells. Polymerization of hemoglobin leads to the distortion of the red blood cell (RBC) and, consequently, its adoption of a sickle shape and reduced deformability. The clinical manifestations of SCA result from two main pathophysiological processes. One of these is chronic hemolytic anemia, resulting in deficient oxygen-carrying capacity, increased cardiac workload and increased metabolic demands. The other feature is vaso-occlusion or obstruction of the microvasculature by sickled red cells, resulting in tissue ischemia and infarction.