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

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.