Hemoglobin Sβ thalassemia, SC disease and sd disease: Clinical and laboratorial aspects

Abstract

Sickle cell disorders are inherited hemolytic anemias, associated with the presence of Hemoglobin S. This group of disorders comprises homozygotes (HbSS), compound heterozygotes for hemoglobin C (HbSC) or β-thalassemia (Sβ thalassemia) (the most frequent associations) and, uncommonly, hemoglobin D (HbSD) and hemoglobin E (HbSE). This abnormal phenotype is caused by mutations in the Beta globin genes of both chromosomes 11. Thus, these disorders are recessively inherited and abnormalities in both alleles lead to structural defects in the betaglobin chain (HbS, HbC, HbD, HbE), or a reduction in its expression (thalassemia and HbE). Consequently, normal HbA, which is an α2 β2 tetramer, is absent and substituted by the mutated hemoglobins, containing an α2 β2 Mutated tetramer. Ultimately, the clinical phenotype is caused by the relatively high amounts of the α 2 β 2 sickle tetramer, which allows hemoglobin polymerization and, in turn, leads to vasoocclusion, the hallmark of all sickle cell disorders. In this chapter, we will discuss clinical and laboratorial aspects of the compound sickle cell disorders SC, SD and Sβ thalassemia. In this book, sickle cell anemia is a synonymous for the homozygote state and it is approached elsewhere.