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

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.