A comparison of the homozygous states for G gamma and G gamma A gamma delta beta thalassaemia

Phenotypic heterogeneity of asian Indian inversion deletions gγ(aγδβ)0 breakpoint a and breakpoint B

Asian Indian inversion deletion Gγ (Aγδβ)0-thalassemia is a rare entities characterized by high HbF. Due to interaction with various genetic factors, patients with Gγ (Aγδβ)0-thalassemia showed clinical variability. Here we are presenting the phenotypic expression of Gγ(Aγδβ)0 thalassemia under influence of various co-inherited factors. Patient with α-globin gene deletion had mild phenotype than the patient with β-globin mutations. Patient with alpha gene deletion were presenting clinical character like thalassemia intermedia while Gγ (Aγδβ)0-thalassemia patients with co- presence of beta thalssemia mutation clinically behaved like thalassemia major.

Molecular characterization of delta beta-thalassemia and hereditary persistence of fetal hemoglobin in the Indian population

delta beta-Thalassemia (delta beta-thal) and hereditary persistence of fetal hemoglobin (HPFH) are heterogeneous disorders characterized by elevated levels of Hb F in adult life. The two disorders should not be considered as unambiguously separate entities but rather as a group of disorders with a variety of partially overlapping phenotypes. This study was undertaken to determine the hematological and molecular characteristics of high Hb F determinants among Indians. A gap-polymerase chain reaction (gap-PCR)-based approach was used for molecular characterization of high Hb F phenotypes. Fifty-five unrelated individuals were studied. The molecular findings were correlated with the hematological data. DNA analysis identified the deletion-inversion (G)gamma((A)gamma delta beta)(0)-thal in 15 cases (27%) and the HPFH-3 (Indian deletion) determinant in 26 cases (47.2%) and the Vietnamese/Chinese determinant (27 kb deletion) in five cases (9%), which is being reported for the first time from India; 16% (nine cases) of the samples remained uncharacterized. This study emphasizes that delta beta-thal and HPFH determinants are common in India. Molecular analysis will aid in understanding genotype-phenotype correlations and will facilitate prevention and control programs of thalassemia and hemoglobinopathies in this region.

Fetal hemoglobin levels in adults

The synthesis of fetal hemoglobin (HbF) is normally reduced to very low levels of less than 0.6% of the total hemoglobin in adults. The HbF is restricted to a sub-population of erythrocytes termed 'F-cells'; 85% of the normal adult population have 0.3% to 4.4% F-cells. The levels of HbF and F-cells vary by more than 10-fold in normal adults; family studies show that these levels are genetically controlled but the number and nature of these genetic factors are still poorly understood. HbF levels may be increased in adults in a number of inherited and acquired disorders, accompanied by an increase in both the number of F-cells and the amount of HbF per F-cell. The clinical significance of these conditions with raised HbF relates to their interaction in disorders such as sickle cell disease and beta thalassaemia in which raised levels of HbF can lead to considerable amelioration of disease severity. Study of the 'natural' mutants primarily associated with increased HbF has provided considerable insight into the understanding of the control of globin gene regulation and hemoglobin switching. Currently considerable effort is being channelled into clinical trials and the search for the 'ideal' therapeutic agents which could increase HbF in adult life with minimal drug toxicity.

Analysis of an inversion within the human beta globin gene cluster

We have cloned and sequenced the DNA from two regions of the defective beta-globin gene cluster from a patient with Indian A gamma delta beta thalassaemia, and confirmed the complex and unusual pattern of rearrangement involving two separate deletions (0.8 kb and 7.5 kb) the inversion of the 15.5 kb segment separating them, as previously proposed from gene mapping studies [1]. All four breakpoints occur within the transcribed region of the globin genes and at one junction are found six nucleotides of unknown origin. This unique rearrangement results in enhanced expression of the upstream fetal gene, and is therefore is pertinent to the localisation of any putative control region involved in the coordinate expression of fetal and adult genes.

(A gamma delta beta) thalassaemia: similarity of phenotype in four different molecular defects, including one newly described

Globin gene mapping of DNA from families with (A gamma delta beta) thalassaemia has revealed a previously unreported gene deletion responsible for this condition. The deletion removes the A gamma, delta and beta genes and while its 5' end is in a similar position to that described in a previous deletion of this type, the 3' ends of the two deletions are quite different. In addition we have observed further examples of two other previously described deletions which result in this disorder. Phenotypic comparisons of families with (A gamma delta beta) thalassaemia, in which the molecular basis has been defined, show a remarkable similarity among the four different deletion defects, with important implications with regard to the mechanism by which deletions allow the continued expression of gamma genes.

delta beta-Thalassaemia in Sicily: report of a case of double heterozygosity for A gamma delta beta-thalassaemia and A gamma G gamma delta beta-thalassaemia

A case of double heterozygosity for A gamma delta beta-thalassaemia and A gamma G gamma delta beta-thalassaemia was found during a screening programme in Sicily. The proband, a 4-year-old girl, showed a clinical picture of thalassaemia intermedia. Hb F (85.12% by the Singer method) was G gamma A gamma type. The parents and the brother were delta beta-thalassaemia carriers. Structural analysis of Hb F showed both G gamma and A gamma chains in the father, but only A gamma chains in the mother.

Restriction mapping of a new deletion responsible for G gamma (delta beta)o thalassemia

DNA from individuals heterozygous for (G)gamma(deltabeta)(o) thalassaemia has been studied by restriction endonuclease analysis. The results reveal a new molecular defect associated with this condition. A total of three defects is now responsible for the one single phenotype, thereby emphasising the complex relationship between genotype and phenotype among the disorders of beta-like globin synthesis in man.

Homozygous G gamma delta beta thalassaemia

This report describes the clinical and haematological findings in three siblings homozygous for G gamma delta beta thalassaemia in an Indian family. There was a mild to moderate anaemia and markedly abnormal red cell morphology. Haemoglobin analysis showed 100% Hb F, solely of the G gamma type, with a pancellular but uneven distribution. Considerable chain imbalance was detectable in globin synthesis studies. In contrast to five previously reported cases, these children were essentially asymptomatic and have never required transfusions.

Interaction of alpha- and delta beta o- thalassaemia: haematological features and globin chain synthesis analysis

An observation of suspected interaction of δβ⁰- and α-thalassaemia, identified through careful examination of the family, is reported. The δβ⁰-thalassaemia was of the usual type found in Sardinia, characterised by high Hb F levels and very low levels of glycine in the isolated γCB₃ peptide. The haematological findings in the double δβ⁰-/α-thalassaemia heterozygotes were: normal MCV and Hb A₂ levels, increased Hb F (11·3 to 16·8%) heterogeneously distributed in red cells, and almost balanced α/β globin chain synthesis ratios.

Occurrence of G gamma Hb F in Greek HPFH: analysis of heterozygotes and compound heterozygotes with beta thalassaemia

Haemoglobin F has been isolated from the red cells of individuals with the Greek form of hereditary persistence of fetal haemoglobin (HPFH), and the glycine/alanine composition of the gamma CB3 peptides determined. In contrast to previous reports we have shown that the Hb F of the Greek HPFH heterozygotes contains significant amounts of G gamma chains and circumstantial evidence indicates that these are the products of the same chromosome that carries the Greek HPFH determinant. Hence this chromosome must be directing the synthesis of G gamma, A gamma and (probably) beta and delta chains, thus implying that the Greek form of HPFH does not result from a deletion involving the globin chain structural genes. Analysis of the levels and structure of Hb F from the Greek HPFH heterozygotes and from separated cell populations from the Greek HPFH/beta thalassaemia compound heterozygotes indicate that the Greek HPFH determinant, while allowing an overall increase in gamma chain synthesis, is not the sole factor determining the absolute amount of Hb F production on a cellular basis.