Molecular characterization of Hb S(C) β‐thalassemia in American blacks

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Abstract
An extension of previous reports describing the molecular defects and hematological abnormalities in black patients with Hb S(C) β-thalassemia living in the Southeastern United States is presented. As many as 58 patients with Hb S-β+-thalassemia, 16 with Hb C-β+-thalassemia and 12 with Hb S-β°-thalassemia have been studied. Patients with Hb S(C) β+-thalassemia type 2 (high Hb A values) were most common; the thalassemia was due to mutations in the promoter of the β-globin gene [−88 (C → T) and −29 (A → G)] or at the polyadenylation signal (T → C). Two patients with lower Hb A values (type 1) carried a mutation in the first intron of the β-globin gene (IVS-1-5: G → T). The simultaneous presence of an α-thalassemia −2( −αl) resulted in some modifications of the hematological parameters, but had a minimal effect on the clinical condition. Patients with Hb S-β°-thalassemia had lower hemoglobin values, lower number of red blood cells, and lower MCHC values and suffered more frequently from complications than the patients with Hb S-β+ -thalassemia. A total of 17 different β-thalassemia mutations were observed in 128 chromosomes; two mild β+ -thalassemia mutations [−88(C → T) and −29(A → G)] account for more than 80% of the thalassemic chromosomes.