Globin biosynthesis in sickle cell, Hb SC, and Hb C diseases

Molecular analysis of the beta-thalassemia phenotype associated with inheritance of hemoglobin E (alpha 2 beta2(26)Glu leads to Lys)

Inheritance of the gene for betaE-globin is associated with hypochromia and microcytosis, reminiscent of typical heterozygous beta-thalassemia. Patients with hemoglobin (Hb)E-beta-thalassemia exhibit clinical phenotypes of severe beta-thalassemia, a circumstance not encountered in other compound heterozygous states for structural beta-chain mutations and beta-thalassemia. We have analyzed the kinetics of globin synthesis and the levels of globin messenger (m) RNA accumulation in patients with Hb E-beta-thalassemia and Hb E trait. The initial rate of beta-globin synthesis (betaE/alpha=0.20-0.34) was less than expected on the basis of gene dosage, or comparable studies of other compound heterozygous states for beta-thalassemia and structurally abnormal beta-chains. betaE-globin synthesis was not only reduced during short-term incubations (1-5 min), but also remained relatively unchanged during long-term pulse or chase incubations up to 5h. Analysis of globin mRNA by cell-free translation and molecular hybridization confirmed that the unexpectedly low levels of betaE-globin synthesis were associated with comparable reduction in the levels of beta-globin mRNA. In Hb E-beta-thalassemia the betaA + betaE (alpha globin nRNA ratio observed were substantially lower than those obtained from reticulocytes of patients with heterozygous beta-thalassemia, or Hb S-betaO-thalassemia, while in Hb E trait, the betaA + betaE/alpha mRNA ratio was in the ranged observed for beta-thalassemia trait. The betaE-globin gene specifies reduced accumulation of betaE-globin mRNA, a property characteristic of other forms of beta-thalassemia. The beta-thalassemia phenotype associated with inheritance of Hb E is thus determined at the level of beta-globin mRNA metabolism.

Inclusions in red blood cells containing Hb S or Hb C

To demonstrate and characterize red cell inclusions in 101 persons with Hb S or Hb C disorders three methods were used: (1) examination of unstained blood smears by dark field microscopy (DFM), (2) examination of blood smears after acid elution and staining (AE), and (3) measurement of membrane-associated denatured haemoglobin (MADH) in ghosts. The control group had inclusions in less than 5% of red cells by DFM and AE and the mean percentage of MADH per total cellular Hb was 0.030+/-0.016%. The highest percentages of red cells with inclusions and of MADH were present in clinically severe haemoglobin disorders, e.g. homozygous sickle cell disease (Hb SS) with less than 10% Hb F and Hb SOArab, with successively lower percentages in moderate to severe disorders, e.g. Hb SS-alpha thalassaemia, Hb-S-beta0 thalassaemia, Hb SC disease, and Hb SS with more than 10% Hb F, indicating agreement in results by three methods. In asymptomatic or mild disorders, e.g. Hb-S-beta+ thalassaemia, Hb CC, Hb AC and Hb AS, the results by AE and measurements of MADH were the same or similar to those in controls, while those by DFM were different. Of 56 patients with Hb SS or Hb SC, the group with functional asplenia had higher percentages of MADH and of red cells with inclusions than those with functioning spleens. Our study suggests that inclusions in sickling disorders may be due to denatured Hb S, with AE being the more accurate method for visualizing these inclusions, as results by this method correlate better with the amount of MADH than those by DFM.