The association of sickle cell anemia with heterozygous and homozygous α-thalassemia-2 : in vitro HB chain synthesis

Abstract

The in vitro synthesis of hemoglobin chains was investigated in 34 scikle cell anemia (SS) patients and five patients with Hb S‐βo‐thalassemia. Incubations were made for 30 minutes and for 120 minutes. Hematological and family data were also obtained. Although the 30‐minute α/non‐α total activity ratios were more widely distributed than the ratios at 120 minutes, a distinct classification of SS patients into groups without an α‐thalassemia, with a heterozygous α‐thal‐2, or with a homozygous α‐thal‐2 could not be made. Family studies indicated that four patients who had 30‐minute α/non‐α ratios below 0.82 and mean corpuscular volume (MCV) values below 70 fl had a homozygosity for both α‐thal‐2 and Hb S. They had mild hematological features of SS disease. Many SS patients with 30‐minute α/non‐α ratios between 0.8 and 1.0 and MCV values above 70 fl had an associated α‐thal‐2 heterozygosity. Their hematological features were similar to those of SS patients with four active α chain genes. It appears that an α‐thal‐2 heterozygosity (−α/αα; βS/βS) does not alter the hematological expression of SS disease. An α‐thal‐2 homozygosity −α/−α;βS/βS results in a microcytosis similar to that seen in Hb S‐βo‐thalassemia patients. The diagnosis of these α chain deficiencies in association with SS disease (by in vitro chain synthesis analyses) leaves several uncertainties.