Showing papers by "Swee Lay Thein published in 1998"

Beta-thalassaemia intermedia: is it possible consistently to predict phenotype from genotype?

Abstract: Eighty-seven patients with beta thalassaemia of intermediate severity were investigated in our Unit to determine whether it is possible to consistently predict phenotypic severity from genotypic factors. The subjects were from the following ethnic backgrounds: Asian Indian (35.1%), Middle Eastern (24.3%), Mediterranean (21.6%), Northern European (14.9%) and South-East Asian/Chinese (4.1%). There was a wide spectrum of phenotypic severity; 49 had mild disease, 22 moderate and 16 severe disease. 22/87 patients had inherited only a single copy of a beta-thalassaemia allele, of whom 11 had also co-inherited triplicated alpha genes (alpha alpha alpha/alpha alpha or alpha alpha alpha/alpha alpha alpha) and seven had dominantly inherited beta thalassaemia. In four of the heterozygotes no explanation was found for the thalassaemia-intermedia phenotype. 65/87 patients were homozygous or compound heterozygous for 26 mutations (40 genotypes) which ranged from very mild beta+ to beta0 thalassaemia alleles. All patients with two mild or very mild beta+ thalassaemia alleles had mild to moderate disease. Although concurrent inheritance of extra alpha genes with heterozygous beta thalassaemia results in thalassaemia intermedia, the disease is mild. Co-inheritance of alpha thalassaemia as a modulating factor was not evident in this cohort of patients. Presence of the in-cis Xmn I-Ggamma site was a modulating factor but insufficient to explain the high fetal haemoglobin levels encountered. In conclusion, apart from the two categories of triplicated alpha genes with heterozygous beta thalassaemia and inheritance of mild beta+ thalassaemia alleles, it was not possible to consistently predict phenotype from alpha and beta genotypes alone, due to the influence of modulating factors, some implicated (such as inheritance of HPFH determinants) and others as yet unidentified.

Genetics of Hb F/F Cell Variance in Adults and Heterocellular Hereditary Persistence of Fetal Hemoglobin

Abstract: Hb F and F cell values in normal adults vary considerably with a continuous distribution that is substantially skewed to the right implicating a polygenic influence. The high values of Hb F and F cells are transmitted in the condition referred to as heterocellular hereditary persistence fetal hemoglobin which should be regarded as a multifactorial quantitative trait, quite distinct from the classical pancellular hereditary persistence of fetal hemoglobins. Several factors have been shown to influence F cell/Hb F levels in normal adults including age, gender, genetic determinants linked and unlinked to the β-globin locus on chromosome 11p. Two trans-acting quantitative trait loci for F cell variance have been mapped, one on 6q and the other on Xp, with at least one other implicated. As an initial step towards hunting for the other quantitative trait loci we have carried out a preliminary analysis of F cell variance in 182 pairs of monozygotic and 373 pairs of dizygotic twins. The correlation coefficient of...

3 β-Thalassaemia

Abstract: A complete spectrum of genetic lesions affecting the β-globin gene giving rise to a complete spectrum of phenotypic severity is described. Although most of the molecular lesions involve the structural β gene directly, some down regulate the gene through in-cis effects at a distance while trans-acting factors are implicated in a few cases. The remarkable phenotypic diversity can be related ultimately to the degree of α-globin-β-globin chain imbalance and arises from variability of mutations affecting the β gene itself and from interactions with other genetic loci, such as the α- and γ-globin genes. The presence of other interacting loci is implicated by their interactions in increasing γ gene expression or by an increased proteolytic capacity of the erythroid precursors. It is hoped that observations from the genotype-phenotype relationship might form the basis for a comprehensive diagnostic database that will be useful not only for genetic counselling and prenatal diagnosis but also for providing prognostic information for decision making in bone marrow transplantation and gene therapy programmes in the future. However, it is clear from recent analyses that, apart from the two categories of triplicated α genes with heterozygous β-thalassaemia and inheritance of mild β+-thalassaemia alleles, it is still not possible to predict consistently phenotype from α and β genotypes alone owing to the influence of the other modulating factors, some implicated (such as inheritance of hereditary persistence of fetal haemoglobin) and others as yet unidentified.

Elimination of Transfusions Through Induction of Fetal Hemoglobin Synthesis in Cooley's Anemiaa

Abstract: Pharmacological stimulation of fetal hemoglobin production is of considerable interest as an alternative approach to therapy for Cooley's anemia. While intravenous compounds have been effective in inducing short-term increases in fetal hemoglobin in a few patients, long-term elimination of transfusion requirement has not been reported. In patients with Cooley's anemia, treatment with oral sodium phenylbutyrate alone, sodium phenylbytyrate combined with hydroxyurea, and hydroxyurea alone, has augmented fetal hemoglobin production and increased total hemoglobin concentration as much as 5 g/dl over baseline eliminating transfusion requirement in two patients. Parallel declines in circulating nucleated red cell count, and concentrations of serum transform receptor and erythropoietin, are consistent with more effective erythropoiesis. Over extended periods of treatment, no induction of other fetal proteins and no adverse effects were observed. Particular disease mutations and other genetic factors may be of prime importance in determining the response to agents that induce production of fetal hemoglobin.

Disorders of Hemoglobin Structure and Synthesis

Abstract: All human hemoglobins have a tetrameric structure, consisting of two identical α-like (α or ζ) and two β-like (e, γ, δ, or β) globin chains, each linked to a heme group.

Cross Evaluation of Three Flow Cytometric F Cell Counting Methods Performed by Different Laboratories

Abstract: Three flow cytometric methods of counting F cells were evaluated in the settings of an external laboratory assessment scheme. The laboratories to participate with a different method were located in Oxford (method O), Athens (method A) and Jerusalem, (method J). Two monoclonal anti-γ chain antibodies were used: monoclonal antibody produced by P. Beverley (Oxford) (BEV) and an antibody provided by Bioatlantic S.A.R.L. (France) (BIO). The specimens tested were mixtures in five predefined ratios of a sample with homozygous δβ-thalassemia with 100% F cells with a sample with no F cells. A central independent laboratory prepared and distributed the aliquots (at room temperature) to the participating centers within 2 (O), 3 (A), and 6 (J) days. The performance of the three methods was evaluated by: 1) deviation indices, 2) relative accuracy, as percent difference of the counts from the target values, and 3) bias and linearity by linear regression of the counts versus the target values [parameters: slope (s), y-i...

Sequencing of PCR products.

Abstract: It is often necessary to obtain DNA sequence information following successful amplification. Although polymerase chain reaction (PCR) products may be cloned into a vector and sequenced at a later stage, it is often preferable to sequence PCR products directly, without subcloning, and it is this approach that is addressed in this chapter.