Mary B. Coleman

BETA-THALASSEMIA IN SOUTHWESTERN IRAN

Seventeen unrelated beta-thalassemia patients or carriers from Southwestern Iran were examined for the beta-globin gene mutations by polymerase chain reaction amplification of the beta-globin gene and direct genomic sequencing, or by the method of allele-specific oligonucleotide hybridization. Their clinical and hematological characteristics were also recorded. Of 26 potential thalassemia-causing chromosomes examined, 10 different mutations were found. The IVS-II-1 (G-->A) mutation was the most frequent (31%) followed by the IVS-I-6 (T-->C) mutation (15%). Eight mutations were initially described in Mediterranean populations and two were of Kurdish origin. Four of these mutations, both initially described in the Mediterranean region, are reported here for the first time in Iranians. The unexpectedly high number of different mutations that account for beta-thalassemia in this region of Iran suggest migration of chromosomes from distant places and genetic admixture.

Erythrocyte calcium abnormalities and the clinical severity of sickling disorders.

Summary. We studied erythrocyte calcium levels and uptake in a group of patients with sickle haemoglobinopathies of different clinical severity in an attempt to relate these measurements to the production of irreversibly sickled cells and disease severity. Erythrocyte calcium levels were measured by atomic absorption spectroscopy and calcium uptake by isotopic means. In sickle cell anaemia, erythrocyte calcium content was elevated and the uptake of isotopic calcium increased under both oxygenated and deoxygenated conditions. There was a direct correlation between the numbers of irreversibly sickled cells and calcium uptake and an inverse relationship between calcium uptake and red cell potassium level. The clinical course of disease was milder in patients with high fetal haemoglobin levels, but there was no relationship between clinical course and calcium levels, calcium flux or irreversibly sickled cells. Our observations suggest that calcium accumulation and irreversibly sickled cell formation are related processes. The absence of good correlation between various biochemical and clinical parameters emphasizes the complexity of factors which modify the clinical course of this disorder.

The effects of alpha-thalassaemia in HbSC disease

Summary. In HbSC disease, as in sickle cell anaemia, there is a spectrum of clinical severity. A reduced mean corpuscular volume and haemoglobin concentration, traits typical of thalassaemia, might retard sickling. We therefore ascertained the prevalence of α‐thalassaemia in 53 adults with HbSC disease and related α‐globin gene deletion to the haematologic and clinical findings. Alpha‐globin genotype was identified by restriction endonuclease gene mapping. Indirect ophthalmoscopy and fluorescein angiography were used to document the presence of proliferative retinopathy. Bone necrosis and infarction were determined roentgenographically or by radionuclide scanning. Either heterozygous or homozygous alpha‐thalassaemia‐2 was present in 26% of patients. There was no relationship between α‐globin genotype and haematocrit, pain crises, bone lesions, proliferation retinopathy or clinical severity score.

Interaction Between HBS-β°-Tha lassemia and α-Thalassemia

We have defined the clinical and laboratory characteristics of a group of patients with HbS-βo+α-thalassemia plus α-thalassemia, by analysis of erythrocyte indices, hemoglobin A2 and F levels, globin biosynthesis studies and α-globin gene mapping. Patients with HbS-βo + α-thalassemia closely resembled individuals with HbS-βo-thalassemia except for balanced globin synthesis ratios and a lower HbF level. The frequency of painful crises, leg ulceration, aseptic necrosis of bone and acute chest syndrome was similar in HbS-βo + α-thalassemia patients and controls with sickle cell anemia (HbSS), HbSS-α-thalassemia and HbS-βo-thalassemia. These findings are consistent with previous work which failed to show a reduction in the vaso-occlusive severity of sickle cell disease by the coexistence of α-thalassemia.

β-Thalassemia Intermedia with Exceptionally High Hemoglobin A2: Relationship to Mutations in the β-Gene Promoter

Small deletions of the 5′ portion of the β-globin gene that remove the promoters but stop 3′ to the δ-globin gene are recognized as the sole cause of β-thalassemia with exceptionally high hemoglobin A2 (HbA2) levels. Two patients with β-thalassemia intermedia and exceptionally high levels of HbA2 (10.4 and 12.0%) were examined. One patient was a combined heterozygote for the − 88 C→T and a novel − 87 C→A mutation, while the other was homozygous for the − 29 A→G β+-thalassemia mutation. The remainder of the β genes were normal. There was no evidence for deletions involving the 5′ portion of the β gene or the region between the β and δ genes. Gene mapping studies excluded the possibility of a βδ-anti-Lepore hemoglobin gene with β promoters and δ coding sequences. There were no mutations in the promoters of the Gγ or Aγ- globin genes that have been associated with the hereditary persistence of HbF phenotype. The δ-globin gene promoters were normal from codon 17 to position − 145 relative to the mRNA capping site. There appears to be considerable heterogeneity of HbA2 and HbF levels in patients who are homozygous or mixed heterozygotes for mutations in the TATA box and other promoter elements of the β-globin gene. The capacity for proteolysis within the erythrocyte may vary among individuals. The authors hypothesize that in the exceptionally high HbA2 β-thalassemia intermedia phenotype, proteolysis of superfluous α-globin chains is less efficient than in patients with customary levels of HbA2. The relative surfeit of α-chains may combine with δ-globin and account for the unusually high HbA2 levels.

Globin Biosynthesis in Erythroid Bursts of Heterozygous α or β Thalassaemia

Summary. We examined globin chain synthesis in erythroid bursts (BFU‐E) of patients with heterozygous α or β thalassaemia. BFU‐E were cloned from circulating mononuclear cells, labelled with [H]leucine and globin chains purified by gel filtration and column chromatography. In six patients heterozygous for β thalassaemia, globin synthesis in BFU‐E was nearly balanced, with an α/non α ratio of 1.05 0α12. These BFU‐E produced 33.8 12.7%γ globin chain, an amount similar (P >1 0.05) to that found in 10 controls with sickle cell anaemia (25.6 6.7) but greater (P <0.05) than that of five normal controls (17.2 2.2). The balanced globin synthesis appeared due to the large amounts of γ chain made by BFU‐E. In two α thalassaemia carriers, who also had sickle cell trait, the BFU‐E α/non‐α ratio was 0.67 and 0.79. These BFU‐E produced 15% and 20%γ chain and 39% and 45%βS globin. The synthesis of βS globin in BFU‐E exceeded the erythrocyte levels of 20% and 29% HbS and indicated nearly equal expression of βA and βB globin genes in these proliferating erythroid precursors. This provides further evidence that the low levels of HbS in sickle cell carriers with α thalassaemia are due to post‐translational events resulting from the differing affinity of βS and βA globin for α chain and the destruction of excessive βS chain.