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S L Thein

Publications and source records attributed to S L Thein.

At least 19 recordsLinked to original sources
PubMed1997

Erythroblastic inclusions in dominantly inherited beta thalassemias.

While the precipitation of unstable variant beta-globin chains has been implicated as a major pathogenic mechanism in dominantly inherited beta thalassemia, their instability and presence in intra-erythroblastic inclusions have not been conclusively shown. We report the investigation of two cases of dominantly inherited beta thalassemia due to heterozygosity for the beta-codon 121 G-T mutation. In one case, we were able to demonstrate the presence of an abnormal beta-globin chain in both peripheral blood reticulocytes and bone marrow erythroblasts, and to assess its stability in relation to the substantial amounts of mutant beta mRNA transcript. The serum transferrin receptor (TfR) level was markedly increased, an indication of increased erythropoietic activity. In both cases, we could show by immunoelectron microscopy that the intra-erythroblastic inclusion bodies, a prominent feature of diseases in this category, contained not only precipitated alpha-globin chains, but also beta chains. The data confirm previous suggestions that the cellular pathology underlying this group of beta thalassemias is related to the synthesis of highly unstable beta-globin chain variants, which fail to form functional tetramers and precipitate intracellularly with the concomitant excess alpha chains, leading to increased ineffective erythropoiesis.

Adult↗
PubMed1997

Beta-thalassemia and beta[A] globin gene haplotypes in Mexican mestizos.

B-globin haplotypes of 20 beta-thalassemia (beta-thal) and 87 beta(A) Mexican mestizo chromosomes were analyzed to ascertain the origin of the beta-thal alleles and the frequencies and distribution of the beta(A) haplotypes among northwestern Mexican mestizos. Sixteen beta-thal chromosomes carried six Mediterranean alleles [five codon 39 C-->T; two IVS1:1 G-->A; two IVS1:5 G-->A; three IVS1:110 G(A; one codon 11 (-T) and three (deltabeta)zero-thal]; the remaining four were linked to three rare alleles (two -28 A-->C and one each: -87 C-->T and initiation codon ATG-->GTG). Among the 87 beta(A) chromosomes, 17 different 5' haplotypes with frequencies for 1, 3, 2 and 5 of 39.0%, 17. 2%, 9.2% and 6.9%, respectively, were observed. The beta-haplotype analysis showed that 13 out of 16 Mediterranean chromosomes could easily be explained by gene migration; however, one codon 39 associated with haplotype 4 (----+ +-), one IVS1:1 with haplotype 1(+----++) and one IVS1:5 G-->A, may represent separate mutational events. Analysis of the rare alleles showed that the -28 A-->C mutation was associated with the commonest beta(A) haplotype in Mexican mestizos, Mediterraneans and the total world population; therefore an independent origin cannot be ruled out. The -87 C-->T and initiation codon ATG-->GTG were found with beta-haplotypes different from the reported ones, suggesting an indigenous origin.

Alleles↗
PubMed1996

Interaction of hemoglobin E and pyrimidine 5' nucleotidase deficiency.

A Bangladeshi family is described in which the genes for both hemoglobin E (Hb E) and pyrimidine 5' nucleotidase deficiency are segregating. An individual homozygous for both these conditions has a severe hemolytic anemia, whereas family members who are homozygous for Hb E are asymptomatic and those homozygous for pyrimidine 5' nucleotidase deficiency have the mild hemolytic anemia that is characteristic of this disorder. Globin-chain synthesis experiments have shown that the mechanism underlying the interaction between these two genotypes is a marked decrease in the stability of Hb E in pyrimidine 5' nucleotidase-deficient red blood cells (RBCs). It has also been found that in the enzyme-deficient RBCs in which Hb E is highly unstable, free alpha-chains, though not beta E-chains, acoumulate on the membrane. In view of the increasing evidence that the hemolysis associated with pyrimidine 5' nucleotidase deficiency results not only from an increase in the level of erythrocyte pyrimidines, but also from inhibition of the hexose monophosphate shunt activity in young erythrocytes, it is likely that the marked instability of Hb E in the enzyme-deficient cells results from oxidant damage acting on a mildly unstable Hb variant. These observations may have important implications for the better understanding of the pathophysiology of Hb E/beta-thalassemia, globally the commonest important form of thalassemia.

5'-Nucleotidase↗
PubMed1996

Moderate reduction of beta-globin gene transcript by a novel mutation in the 5' untranslated region: a study of its interaction with other genotypes in two families.

We have identified two individuals of Greek Cypriot origin with thalassemia intermedia. Molecular analysis has shown that each individual is a compound heterozygote for a previously described beta zero thalassemia allele and a novel mutation, C-->G in position +33, in the 5' untranslated region of the beta globin gene. In both families the beta +33 allele is associated with the same beta haplotype (-++- ) suggesting that it is likely to be of a single origin, beta-cDNAs from normal and mutant beta alleles were isolated from peripheral blood reticulocytes using the technique of reverse transcription-polymerase chain reaction. Because the beta +33 (C-->G) mutation creates a cutting site for the restriction enzyme NlalV, we could demonstrate by differential restriction analysis that the beta gene with +33 mutation showed 25% to 35% residual activity compared with normal. The additive effect of this moderate deficit in beta globin production with the beta zero thalassemia mutation would explain the clinical phenotypes observed in the two probands. In contrast, two siblings of one proband who were also compound heterozygotes for the same beta thalassemia mutations, as well as heterozygotes for a nondeletional alpha thalassemia variant, and two other compound heterozygotes for the beta +33 and a beta+ thalassemia allele were completely asymptomatic. Individuals heterozygous for the beta +33 C-G mutation alone are clinically and hematologically silent, with normal red blood cell indices and normal levels of hemoglobin (Hb) A2. A direct relationship between genotypic and phenotypic severity is clearly demonstrated in these cases with obvious implications for prenatal diagnosis.

Alleles↗
PubMed1996

Molecular genetics of antithrombin deficiency.

Antithrombin is the major proteinase inhibitor of thrombin and other blood coagulation proteinases. Antithrombin has two functional domains, a heparin binding site and a reactive centre (that complexes and inactivates the proteinase). Its deficiency results in an increased risk of venous thromboembolism. Appreciable progress has been made in recent years in understanding the structure and function of this protein, the genetic cause of inherited deficiency and its clinical consequence. The structure of antithrombin is now considered in terms of the models derived from X-ray crystallography, which have provided explanations for the function of its heparin interaction site and of its reactive loop. The structural organization of the antithrombin gene has been defined and numerous mutations have been identified that are responsible for antithrombin deficiency: these may reduce the level of the protein (Type I deficiency), alter the function of the protein (Type II deficiency, altering heparin binding or reactive sites), or even have multiple or 'pleiotropic effects' (Type II deficiency, altering both functional domains and the level of protein).

Antithrombin III↗
PubMed1996

Prenatal diagnosis in combined antithrombin and factor V gene mutation.

We report prenatal diagnosis in a family with combined antithrombin deficiency (type II heparin binding site) and factor V 506 Arg to Gln mutation. Both clinically unaffected parents are heterozygous for the antithrombin mutation, which results in a 99 Leu to Phe substitution, and the father is also heterozygous for the factor V gene defect. There is one daughter, homozygous for the antithrombin and heterozygous for the factor V mutations, who suffered a right-sided hemiparesis at the age of 4 months due to occlusion of the left middle cerebral artery and a large left sided infarct followed by further thromboembolic events. The family requested prenatal diagnosis and chorionic villi was sampled at 12 weeks gestation. The fetus was shown to be heterozygous for the antithrombin and factor V gene mutations, the same genotype as the unaffected father. No further intervention was considered necessary. To our knowledge this is the first report of prenatal diagnosis in antithrombin deficiency.

Antithrombins↗
PubMed1996

Hb Sun Prairie: diagnostic pitfalls in thalassemic hemoglobinopathies.

We report an Asian Indian family in which two daughters have Hb Sun Prairie, a known unstable alpha 2-globin variant [codon 130, GCT-->CCT; alpha 2 130(H13)Ala-->Pro beta 2]. While the homozygous probands have chronic hemolysis-the same phenotype as previously reported, the heterozygous parents are asymptomatic with a thalassemia carrier phenotype, distinct from the chronic hemolytic state previously described in a heterozygote. Unlike the earlier cases in which family studies were not available, this family clearly exhibits autosomal recessive inheritance, unusual amongst variants within the same region of helix H. Globin chain biosynthesis ratios initially suggested a beta-thalassemic hemoglobinopathy-this was excluded by normal sequence analysis of both beta-globin genes. This case report further illustrates the complexity of phenotypes in the thalassemic hemoglobinopathies. It also demonstrates inversion of the alpha/beta-globin chain biosynthesis ratio, a phenomenon which had been noted in other alpha-globin variants and can be a confounding factor in the investigation of thalassemic hemoglobinopathies.

Adolescent↗
PubMed1995

Somatic mutations detected by mini- and microsatellite DNA markers reveal clonal intratumor heterogeneity in gastrointestinal cancers.

We investigated clonal intratumor heterogeneity by comparing different areas of each tumor in 20 gastrointestinal cancers from female patients (1 esophageal cancer, 5 stomach cancers, and 14 colorectal cancers). In all 19 cases informative for X-inactivation analysis with the M27 beta and/or the phosphoglycerate kinase probes, the tumors were clonal. Separate areas from a given tumor showed identical X-inactivation patterns, providing evidence for its single-cell origin. Of 20 cancers, 11 showed p53 gene mutations (base pair insertions, point mutations, and one case of a base pair deletion) in exons 5-8. A particular p53 gene mutation was identical in all tumor areas investigated per case. The minisatellite probes detected loss of heterozygosity or new mutant alleles at 1p33, 1q21, 5q35, 17p13, or 18q21. In seven cases mutations at particular loci were restricted to one or two areas per tumor, while in another seven cases they were common to all tumor areas. Loss of heterozygosity or new alleles detected at the microsatellite loci D2S123, D3S1611, D5S107, D17S261, or D18S34 [(CA)n repeats] were common to all tumor areas in 7 of 19 cases. In another seven cases, however, microsatellite mutations at these loci were restricted to one to three areas per tumor. Tracing clonal intratumor heterogeneity would permit one to study the hierarchy of mutational events in cancers where no premalignant lesions can be harvested. Most important, our study indicates that clonal intratumor heterogeneity might lead to sampling errors in the molecular diagnosis of cancer biopsy specimens when using mini- or microsatellite markers.

Alleles↗
PubMed1995

Antithrombins Southport (Leu 99 to Val) and Vienna (Gln 118 to Pro): two novel antithrombin variants with abnormal heparin binding.

We report the characterization of three variant antithrombins with reduced heparin binding as the primary abnormality. Two of these variants, antithrombin Southport (Leu 99 to Val, 2759 C to G) and antithrombin Vienna (Gln 118 to Pro, 5349 A to C) were novel, whereas the third, Pro 41 to Leu, has been previously described as antithrombin Basel. All three variants exhibited reduced binding for heparin on crossed immunoelectrophoresis and in a quantitative monoclonal antibody-based assay. The mutations were characterized by direct sequence analysis of enzymatically amplified genomic DNA and all affected individuals were heterozygous for the mutations. These three mutations do not occur at the sites of the basic amino acids directly involved in heparin binding nor do they result in a change in charge of the affected residue. It seems probable that they reduce heparin affinity either by perturbing the initial contact site involved in the heparin-binding domain (Arg 47, Arg 129 and possibly Arg 24), or by preventing the subsequent heparin-induced conformational change.

Adult↗
PubMed1994

Hereditary antithrombin deficiency: heterogeneity of the molecular basis and mortality in Dutch families.

We studied the molecular basis and genetic heterogeneity of hereditary antithrombin (III) deficiency in nine Dutch families. Polymerase chain reaction (PCR) amplification and direct sequencing of all antithrombin gene exons and flanking intronic regions identified mutations in eight families. Given the opportunity to correlate the molecular basis with survival, we addressed the relevance of molecular defects to mortality in inherited antithrombin deficiency. The defects included single nucleotide deletions (7671 del G, 7768-69 del G) and insertions (5501 ins A, 2463 G-->TC) that lead to frameshifts, a single base substitution [5381 C-->T (129Arg-->stop)] leading to a premature termination codon, and single base substitutions resulting in amino acid substitutions [2652 A-->C (63Tyr-->Ser), 13380 T-->C (421Ile-->Thr), and 13407 G-->T (430Cys-->Phe)]. All affected individuals were heterozygous for the defects. Previously we found in Dutch families that antithrombin deficiency did not lead to higher mortality compared with the general population. In accordance with these findings, we observed no excess mortality in the nine families [Observed:Expected, 52:52.6; standardised mortality ratio (SMR) 1.0, 95% confidence interval (CI), 0.7-1.3]. Our findings confirmed a considerable genetic heterogeneity underlying antithrombin deficiency. We therefore concluded that the lack of excess mortality in these families is not caused by a Dutch mild defect. We suggest that the longevity is not affected by molecular defects in the antithrombin gene and hypothesize that differences in mortality or natural history between families most likely result from other (genetic) risk factors.

Antithrombin III↗
PubMed1994

Rapid detection of deletions causing delta beta thalassemia and hereditary persistence of fetal hemoglobin by enzymatic amplification.

A considerable number of deletions of variable size and position that involve the beta-globin gene complex on chromosome 11 are associated with the clinical entities of hereditary persistence of fetal hemoglobin (HPFH) and delta beta thalassemia. Specific deletions appear to be associated with consistent phenotypes and some are known to be recurrent. To facilitate the molecular diagnosis of uncharacterized patients with HPFH and delta beta thalassemia, oligonucleotide primers have been designed to enzymatically amplify deletion-specific products for nine known deletions, which include those responsible for HPFH-1, HPFH-2, HPFH-3, Spanish (delta beta)zero thalassemia, hemoglobin (Hb) Lepore, Sicilian (delta beta)zero thalassemia, Chinese G gamma(A gamma delta beta)zero thalassemia, Asian-Indian inversion-deletion G gamma(A gamma delta beta)zero thalassemia, and Turkish inversion-deletion (delta beta)zero thalassemia. Using this approach, we have successfully characterized the molecular basis for delta beta thalassemia in 23 individuals from 16 families of diverse ethnic origins. Thirteen individuals from this group were shown to be heterozygous for the 13.4-kb Sicilian deletion, two were heterozygous for the 100-kb Chinese G gamma(A gamma delta beta)zero deletion, four were heterozygous for the Turkish form of inversion-deletion delta beta thalassemia, and three were heterozygous for the Asian-Indian form of inversion-deletion G gamma(A gamma delta beta)zero thalassemia. One Vietnamese subject was heterozygous for a 12.6-kb deletion, which we have fully characterized at the molecular level. Sequence analysis of the breakpoint regions of the Chinese deletion and the Turkish rearrangement indicates that, in each case, the mutation is likely to have arisen from a single origin. This hypothesis is supported by the evident geographical clustering of the various deletions described here.

Adult↗
PubMed1994

(ATT) trinucleotide repeats in the antithrombin gene and their use in determining the origin of repeated mutations.

Two (ATT) trinucleotide repeat polymorphisms have been identified in the tails of Alu repeat elements in intron 5 of the antithrombin gene. The frequency and distribution of allele sizes for the Alu 5 and Alu 8 tail polymorphisms have been defined in a sample Caucasian population. The Alu 5 polymorphism has two alleles while that of Alu 8 has 10 alleles with a heterozygosity of 0.83. These polymorphisms have been used in combination with four previously described polymorphisms within the antithrombin gene to construct antithrombin gene haplotypes in the sample Caucasian population. Twenty-two different haplotypes were observed, with the Alu 8 polymorphism being particularly useful in subdividing the core haplotype based on the previously identified polymorphisms. The haplotype data were used to investigate the origin of repeat mutations within the antithrombin locus. We compared the haplotypes associated the mutant antithrombin genes in five families with the mutation 2759C-->T (L99F) and five families with the mutation 5381C-->T (R129Stop). The mutation 2759C-->T (L99F), which occurs within a non-CpG dinucleotide, was carried on a gene associated with an identical haplotype in each of the five families. The mutation 5381C-->T (R129Stop), a single base substitution within a CpG dinucleotide, was associated with at least two different haplotypes. The findings suggest a founder effect in the five families sharing the 2759C-->T (L99F) and at least two independent origins for the CpG dinucleotide mutation 5381C-->T (R129Stop).

Antithrombins↗
PubMed1994

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.

Adult↗