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We identify and characterize a novel β0-thalassemia mutation that is associated with an unusually high level of hemoglobin (Hb) A2in the heterozygote. This newly discovered mutation is caused by a 532-basepair deletion that extends from positions –454 to +78 relative to the mRNA cap site of the β-globin gene. The propositi are 9-month-old fraternal twins. One of the twins is a compound heterozygote for the deletion and Hb S, the other is a compound heterozygote for the deletion and Hb C.

The characteristic clinical heterogeneity of sickle cell anemia (HbSS) may be, in part, a result of its interactions with α-thalassemia. Although α-thalassemia clearly affects some hematologic features of HbSS, its role in modulating the vasoocclusive severity of disease is not clear. To further explore this relationship, we examined the incidence of painful episodes, acute chest syndrome, aseptic bone necrosis, and leg ulcers in 3 patient groups with sickle cell disease: (1) 2,147 patients over age 2 yr, stratified according to mean corpuscular volume (MCV); (2) 183 patients selected on the basis of microcytosis and elevated HbA2, on whom globin biosynthesis studies were done; and (3) 125 patients who had α-globin genotype assigned by restriction endonuclease gene mapping. When patients were stratified by MCV, there was a reciprocal relationship between HbA2levels and MCV, reflecting the presence of patients with β0and α-thalassemia in the low MCV groups. The erythrocyte indices and HbA2levels in patients classified as HbSS-α-thalassemia, by either globin synthesis studies or gene mapping, were very similar to those previously reported by others. Neither microcytosis, β0, or α-thalassemia appeared to provide any clear protection from the vasoocclusive complication evaluated, and the prevalence of aseptic necrosis was increased in patients with microcytosis over age 20 yr and in groups with α-thalassemia. The effects of a reduced MCV and mean corpuscular hemoglobin concentration (MCHC), of possible benefit by themselves, when accompanied by a reduction in hemolysis and rise in hemoglobin concentration, as in HbSS-α-thalassemia, may cause sufficient rise in blood viscosity in critical vascular beds to impair blood flow and negate any amelioration of vasoocclusive complications in HbSS.

A novel deletion of at least 26 kilobase of DNA, including both a-globin genes, the Ψα-and -globin genes, but sparing the functional ς-gene was found in a 10-year-old black boy with HbH disease and sickle cell trait. This particular deletion has not previously been described in blacks. Its existence makes it likely that the absence of Hb Barts hydrops fetalis in blacks is due to the rarity of the chromosome lacking two a-globin genes rather than a result of early embryonic death due to the failure to synthesize embryonic hemoglobins because of deletion of functional ς-globin genes. © 1986 by Grune & Stratton, Inc.

Hemoglobin (Hb) Suan-Dok (α109Arg) is a rare α-globin structural mutation that is linked to an α-thalassemia (α-thal) determinant. When inherited in trans to an α-thal-1 mutation (– –), it results in Hb H disease associated with low levels (9%) of the Suan-Dok Hb. The nature of the thalassemic defect associated with the αSDmutation has been investigated by structural and functional studies. Sequence analysis of the cloned Suan-Dok allele showed a missense mutation (T → G) at codon 109 in an otherwise normal α2-globin gene. When the α2SD-globin gene was introduced into mouse erythroleukemia cells, the steady state α-globin messenger RNA (mRNA) level was equivalent to the αA-globin gene control. Although in vitro translation of a synthetic α2SD-globin mRNA generated levels of αglobin equivalent to α2A-globin mRNA at early time points, the ratio of αSDto αAglobin decreased markedly at later time points. These data suggest that the thalassemic defect associated with the Suan-Dok mutation results from a significant instability of the αSDglobin.

Mutations producing β-thalassemia reach individual gene frequencies greater than .01 in malarial-endemic regions because β-thalassemia trait individuals have increased genetic fitness over that of normal individuals. Exon 3 of the β-globin gene has been relatively spared as a site of common β-thalassemia mutations. Frameshifts caused by the loss of a single nucleotide and nonsense mutations produce β-thalas-semia trait when they occur in exons 1 and 2. In contrast, they usually produce chronic hemolytic anemia when present in exon 3. Certain missense mutations in exon 3 produce unstable globins and thalassemia intermedia with hemolysis in heterozygotes. Here we report two new mutations in exon 3 of the p-globin gene. One is a single nucleotide deletion in codon 109 in a 78-year-old Lithuanian with chronic hemolytic anemia and features of thalassemia, It leads to an abnormal globin (βManhattan) that is elongated to 156 amino acids. The second is a CAG-CGG missense mutation at codon 127 that causes a Gin Pro substitution (βHouston) and a thalassemia intermedia with hemolysis in three generations of a British-American family. Although the clinical phenotypes of these two patients differed little, differences in globin-synthetic ratios were significant, presumably reflecting differences in the ability of each abnormal p-globin to form ap dimers. The paucity of high-frequency exon 3 mutations and their worldwide distribution is likely attributable to their phenotypic severity and loss of increased genetic fitness vis-a-vis malaria.

An electrophoretically fast-moving hemoglobin variant was found in a 2-yr-old boy who was referred for evaluation with findings of iron deficiency anemia. The anemia was corrected, and no hematologic abnormality remained after treatment with iron. Oxygen affinity of the blood was normal, and no evidence was found of instability of the variant hemoglobin. Structural studies demonstrated a substitution of aspartic acid for alanine at β76 (E20). This change did not appear to cause any functional disruption of the hemoglobin in this patient, as would be predicted by the position of the affected amino acid residue on the surface of the molecule.

Hemoglobin (Hb) North Shore (β134val → glu) is a mutant hemoglobin that is associated with the phenotype of mild heterozygous β-thalassemia. Heterozygotes are characterized low normal hemoglobin levels or mild anemia, microcytosis, increased HbA2, and 34%–38% Hb North Shore. The mechanism of the anemia and microcytosis associated with Hb North Shore was explored by studies of hemolysate thermal instability, peripheral blood globin biosynthesis, and whole blood oxygen affinity. Hb North Shore was mildly heat unstable in comparison to normal adult hemolysate. Pulse labeling of reticulocytes with 3H-leucine showed an α/β ratio of 1.35 (normal 1.0). The βNorthShwore/α ratio was 0.22–0.27, which was less than expected on the basis of gene dosage and less than that seen for most β-chain variants. The βA/α ratio was 0.50, as would be expected. The βNorth Shoe/α ratio was 0.26 after a 15-min pulse and did not decrease during 120 min of chase. These findings suggest that suboptimal synthesis rather than posttranslational degradation is responsible for the thalassemic phenotype associated with this variant hemoglobin. These observations parallel the findings in heterozygous HbE. It is not presently known whether the thalassemia phenotype is conferred by the structural mutation itself or by another mutation cis to the βNorthShoregene.

Baboons exposed to acute hemolytic stres increase their production of fetal hemoglobin (HbF). Although the maximal in vivo HbF levels attained in 5 treated animals varied from 6.4% to 34.8%, their cultured bone marrow erythroid cells reverted to the fetal pattern of hemoglobin synthesis. These data suggest that HbF synthesis is modulated by the interaction of inhibiting and promoting factors, which is different among animals in vivo but equal in the cultures of their bone marrow erythroid cells.