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Biomedical subjects

B G Forget

Publications and source records attributed to B G Forget.

At least 19 recordsLinked to original sources
PubMed1979

Restriction endonuclease mapping of the human gamma globin gene loci.

The restriction endonuclease sites in and around the human gamma globin gene loci have been mapped using the gel blotting technique of Southern, in both normal DNA and DNA from an individual with hereditary persistence of fetal hemoglobin (HPFH). In normal DNA, the gamma genes are linked to the delta (and beta) globin genes, and the orientation of these genes with respect to transcription is (5') G gamma leads to A gamma leads to delta leads to beta (3'). The distance between the G gamma and A gamma genes is 3.5 kb and that between the A gamma and delta genes is 16 kb. In both normal DNA and HPFH DNA, the gamma genes are interrupted by an intervening sequence, approximately 1 kb in length that is situated between codon positions 99 and 121 of the coding sequence. In different DNA samples, there is polymorphism for the presence or absence of a Hind III site in the intervening sequence of either gamma golbin gene. In HPFH DNA, a deletion of at least 16 kb of DNA has been detected. This deletion starts at a point approximately 12.5 kb from the 3'-end of A gamma gene and extends through the delta and beta globin genes to a point at least 3 kb beyond the 3'-end of beta globin gene.

Base Sequence↗
PubMed1979

Prenatal diagnosis of classic hemophilia.

Prenatal diagnosis of classic hemophilia (hemophilia A) in mid-trimester was achieved by means of immunoradiometric assays for factor VIII on fetal plasma and amniotic-fluid mixtures obtained by fetoscopy. Samples were analyzed from six male fetuses at risk for severe hemophilia and from nine control fetuses for which fetoscopy was carried out to attempt prenatal diagnosis of other genetic disorders. The factor VIII coagulant-antigen values for the control (non-hemophilic) samples were 17 to 94, and the factor VIII related-antigen concentrations were 50 to 155 U per deciliter. Three of the fetuses at risk for hemophilia had factor VIII values in the control range, and these infants were normal at birth. The other three fetuses had low concentrations of factor VIII coagulant antigen but normal concentrations of factor VIII related antigen. These values and the diagnoses of severe hemophilia were confirmed with blood from the abortuses.

Amniotic Fluid↗
PubMed1979

Prenatal diagnosis of homozygous alpha-thalassemia.

A Vietnamese couple were both carriers of alpha-thalessemia-1. The woman had a first pregnancy terminated in the delivery of a hydropic fetus due to homozygous alpha-thalassemia. The couple requested prenatal diagnosis for the second pregnancy. The DNA obtained from cultured amniotic fluid cells was studied pregnancy. The DNA obtained from cultured amniotic fluid cells was studied by hybridization with globin cDNA in solution and on filters (Southern technique). Both analyses demonstrated no alpha-globin structural genes were present. Following termination of the pregnancy, the diagnosis was established by the presence of only hemoglobins Barts (gamma 4) and Portland (zeta 2 gamma 2) in the fetal blood.

DNA↗
PubMed1979

RNA polymerase III transcriptional units are interspersed among human non-alpha-globin genes.

Cloned human DNA fragments containing globin genes are transcribed in vitro to form discrete RNA species. One transcription unit is located approximately 1500 base pairs upstream from the G-gamma-globin gene. This transcript is partially homologous to a polymerase III template located approximately 1000 base pairs upstream from the delta-globin gene and to DNA located a short distance downstream from the beta-globin gene.

Cloning, Molecular↗
PubMed1979

Hemoglobin Indianapolis (beta 112[G14] arginine). An unstable beta-chain variant producing the phenotype of severe beta-thalassemia.

Hemoglobin (Hb) Indianapolis is an extremely labile beta-chain variant, present in such small amounts that it was undetectable by usual techniques. Clinically, it produces the phenotype of severe beta-thalassemia. Biosynthetic studies showed a beta:alpha ratio of 0.5 in reticulocytes and about 1.0 in marrow after a 1-h incubation. These results, similar to those seen in typical heterozygous beta-thalassemia, suggested that betaIndianapolis was destroyed so rapidly that its net synthesis was essentially zero. To examine the kinetics of globin synthesis, reticulocyte incubations of 1.25--20 min were performed with [3H]leucine. The betaIndianapolis:beta A ratio at 1.25 min was 0.80 suggesting that beta Indianapolis was synthesized at a near normal rate. At 20 min, this ratio was 0.46 reflecting rapid turnover of beta Indianapolis. The erythrocyte ghosts from these incubations contained only betaIndianapolis and alpha-chains, and the proportion of betaIndianapolis decreased with time, indicating loss of betaIndianapolis. Pulse-chase studies showed little change in beta A:alpha ratio and decreasing betaIndianapolis:alpha and betaIndianapolis:beta A with time. The half-life of betaIndianapolis in the soluble hemoglobin was approximately equal to 7 min. There was also rapid loss of beta Indianapolis from the erythrocyte membrane. From these results, it may be inferred that betaIndianapolis is rapidly precipitated from the soluble cell phase to the membrane, where it is catabolized. Heterozygotes for beta 0-thalassemia usually have minimal hematologic abnormalities, whereas heterozygotes with betaIndianapolis, having a similar net content of beta-chain, have severe disease. The extremely rapid precipitation and catabolism of betaIndianapolis and the resulting excess of alpha-chains, both causing membrane damage, may be responsible for the severe clinical manifestations associated with this variant. It seems likely that other, similar disturbances in the primary sequence of globin polypeptide chains may produce clinical findings similar to those seen with hemoglobin Indianapolis and thus produce the phenotype of severe beta-thalassemia.

Adolescent↗
PubMed1979

Molecular genetics of human hemoglobin synthesis.

Molecular analysis of normal and abnormal human globin genes and their gene products has recently provided information on the precise genetic events that result in hemoglobinopathies. In the case of structurally abnormal hemoglobins, the following mechanisms can be invoked: single nucleotide base substitutions leading to amino acid replacement or chain termination variants; nucleotide deletions (or additions) leading to deletion and frameshift variants; and nonhomologous crossing over leading to the production of fused globin chains. The molecular basis of the thalassemia syndromes, disorders characterized by absent or decreased synthesis of alpha- or beta-globin chains, is quite heterogeneous. In some cases globin gene deletions have been demonstrated; whereas in others there is probably either a defect in globin gene transcription or a defect in nuclear globin messenger RNA (mRNA) processing, mRNA transport or globin mRNA stability. In one form of beta(0)-thalassemia a nonsense mutation has recently been demonstrated, and other cases are also associated with some as yet undetermined functional abnormality of beta-globin mRNA.

Amino Acid Sequence↗
PubMed1979

Induction of erythropoietic colonies in a human chronic myelogenous leukemia cell line.

The ability of cells derived from the K562 cell line to generate erythropoietic colonies was studied. The K562 cell line was derived from a patient with chronic myelogenous leukemia 8 yr ago by Lozzio and Lozzio. Rare benzidine-positive colonies formed when these cells were cloned in plasma clots (3 +/- 1/10(4) cells), and their number was not substantially increased by the addition of erythropoietin (9.5 +/- 1/10(4) cells). Sodium butyrate was capable of markedly enhancing the number of benzidine-positive colonies (19.5 +/- 1/10(4) cells) formed, while the combination of sodium butyrate plus erythropoietin exerted a synergistic effect on erythropoietic colony formation (57 +/- 4/10(4) cells). The K562 cell line is a long-term culture system that contains human erythropoietic stem cells. This cell line should be useful in future studies on the cellular and molecular events associated with human erythroid cell differentiation.

Benzidines↗
PubMed1978

Idiopathic thrombocytopenic purpura occurring in a subject previously splenectomized for traumatic splenic rupture. Role of splenosis in the pathogenesis of thrombocytopenia.

A 25 year old woman presented with idiopathic thrombocytopenic purpura. She had undergon splenectomy 12 years previously for traumatic splenic rupture. Thrombocytopenia was ultimately resistant to steroid therapy. Howell-Jolly bodies were absent from the peripheral smear and 99mTC-spleen scan demonstrated foci of increased uptake thought consistent with accessory spleens. However, splenosis alone was demonstrated at laparotomy, and all visible splenotic tissue was surgically removed. The patient responded and adequate platelet counts were maintained after discontinuation of steroid therapy. The functional capacity of splenic implants has been previously demonstrated both in animal and man. However, reports linking splenosis to hematologic disease are rare. In the present case, characteristic splenic function was demonstrated by both the the -9mTc-spleen scan and the absence of the typical peripheral blood findings of asplenia. The hematologic response to the removal of the splenotic tissue attests to its importance in maintaining the thrombocytopenic state. In the setting of prior splenectomy for splenic trauma, splenosis may contribute to hematologic disease. Removal of this splenotic tissue may result in hematologic remission.

Adult↗
PubMed1978

Variability in the amount of beta-globin mRNA in beta0 thalassemia.

Globin mRNA isolated from a number of beta0 thalassemia patients of different ethnic origins was analyzed by RNA-cDNA hybridization and, in two cases, by fingerprint analysis of 125I-labeled mRNA. Quantitation of the relative amounts of alpha- and beta-mRNA by hybridization to purified alpha-and beta-cDNA revealed that in approximately half the cases, there was less than 1% as much beta-mRNA as alpha-mRNA. In the rest of the cases, low levels of beta-like mRNA were detected in amounts 4-12% as abundant as alpha-mRNA. There was variability in the yield of beta-like mRNA in patients of the same racial group, in the same patient at different times and in similarly affected siblings: beta-mRNA was virtually absent in some samples, whereas low but significant levels were found in other samples. In one patient, beta-like mRNA was not detected in peripheral blood RNA, but was present in the RNA of bone marrow cells. In one case, the thermal stability of the beta0 thalassemia mRNA-beta-cDNA hybrid was measured and found to be slightly lower than that of the authentic beta-mRNA-beta-cDNA hybrid. In none of the cases tested was there synthesis of beta-globin chains directed by beta0 thalassemia mRNA in a cell-free protein-synthesizing system, even when beta-like mRNA was detected in the sample by hybridization assays. mRNA from two patients was labeled in vitro with 125I, digested with T1 RNAase and fractionated in two dimensions. Analysis of the resulting fingerprints revealed the presence of prominent alpha chain-specific oligonucleotides without detectable beta chain-specific oligonucleotides, and thereby confirmed the results of hybridization assays showing absent or very low levels of beta-mRNA in the same RNA samples. Our results support the concept that beta0 thalassemia is heterogeneous in its molecular basis even within the same racial group: in some patients, it is associated with absent beta globin mRNA, whereas in other patients, it is associated with low but significant levels of nonfunctional beta or beta-like globin mRNA. The variable amounts of beta-like mRNA detected in different samples from the same patient, and in patients with the same genotype, indicate that as yet undefined factors can influence the yield of beta-like mRNA observed in beta0 thalassemia.

Blood Cells↗
PubMed1978

Insertion of synthetic copies of human globin genes into bacterial plasmids.

Double stranded human globin cDNA was synthesized by use of viral reverse transcriptase from globin mRNA of cord blood of premature infants requiring exchange transfusions. The cDNA was introduced into plasmids and the recombinant DNA plasmids used to transform E. coli X1776. A number of transformants were obtained. Plasmid DNA from selected colonies was isolated and characterized for the type of globin cDNA it contained by three types of procedures: 1) hybridization to previously characterized 3H-labeled alpha,beta and gamma cDNA; 2) analysis of the size and nature of fragments produced by digestion of the plasma DNA by different restriction endonucleases; and 3) by rapid DNA sequence analysis of selected DNA fragments produced by restriction endonuclease digestion. Analysis by these techniques of plasmid DNA from different colonies has definitively identified the presence of human alpha, beta or gamma cDNA sequences in different plasmids.

Base Sequence↗
PubMed1978

Studies of globin chain synthesis and globin mRNA content in a patient homozygous for hemoglobin Lepore.

Globin chain synthesis and globin mRNA content were studied in blood cells of a patient homozygous for Hb Lepore. Peripheral blood cells incubated with tritiated leucine synthesized approximately 1.5 to 3% as many Lepore globin chains as alpha chains. Globin mRNA in peripheral blood cell RNA was assayed by molecular hybridization assays using human alpha and beta cDNA, and the results indicated the presence of approximately 1% to 2% as much beta-like mRNA (presumably deltabeta Lepore mRNA) as alpha mRNA. The amount of Lepore deltabeta chain mRNA in peripheral blood cells is therefore proportional to the amount of Lepore globin chain synthesis in the same cells. An incidental observation was the finding that peripheral blood cell RNA of this patient, at a time when she was being heavily transfused, contained substantially higher levels of beta-like mRNA (relative to alpha mRNA) than in subsequent studies. Cell-free translation of this mRNA however revealed that it contained authentic beta chain mRNA which must have been derived in some way from the transfused blood cells.

Child↗
PubMed1977

Human beta-globin messenger RNA. III. Nucleotide sequences derived from complementary DNA.

Sequences of human beta-globin mRNA were determined by analysis of complementary DNA. beta-mRNA was transcribed into double-stranded cDNA by RNA-dependent DNA polymerase. cDNA was cut by restriction endonucleases and the fragments were terminally labeled by means of polynucleotide kinase and [gamma-32P]ATP. After purification, fragments were degraded by snake venom phosphodiesterase. Alternatively single-stranded [32P]cDNA was prepared by transcription in the presence of [alpha-32P]dCTP and actinomycin D; the product was digested by endonuclease IV and degraded by snake venom phosphodiesterase. cDNA tracts obtained by both labeling methods enabled us to construct a sequence for the translated and 3'-terminal untranslated regions of human beta-mRNA.

Anemia, Sickle Cell↗
PubMed1977

Human beta-globin messenger RNA. I. Nucleotide sequences derived from complementary RNA.

Sequence analysis studies were carried out on human beta-globin mRNA (beta-mRNA) prepared from alpha-thalassemic, sickle cell, and Hb A reticulocytes. Highly purified beta-mRNA served as substrate for the preparation of cDNA by RNA-dependent DNA polymerase. The cDNA was transcribed by Escherichia coli RNA polymerase and the resulting cRNA was analyzed. Over 300 nucleotides were assigned to the beta-mRNA coding region and 37 nucleotides were assigned to the 3'-terminal noncoding region. The normal termination codon is UAA which is separated by 28 nucleotides from an out of phase UAA triplet. The origin of each of the abnormally long beta-globin variants Tak and Cranston is consistent with reduplication of dinucleotides prior to the normal termination codon, and both globin variants can terminate at the out of phase UAA.

Anemia, Sickle Cell↗
PubMed1977

Human globin messenger RNA: importance of cloning for structural analysis.

The sequence of most of the human beta globin messenger RNA and large sections of the alpha globin messenger RNA has been determined. Partly because of genetic polymorphism, it was necessary to clone globin complementary DNA in order to extend the analysis. Purified human fetal globin messenger RNA was isolated and used as a template by reverse transcriptase to produce duplex complementary DNA molecules. These molecules were linked in vitro to plasmid DNA by use of T4 ligase in the presence of Escherichia coli Pol 1. Several colonies transformed by these molecules have been shown to hybridize with labeled human globin complementary RNA.

Base Sequence↗