Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0039730 (thalassemia)
 10,305 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The common form of beta thalassaemia associated with elevated haemoglobin A2 levels can be broadly classified as beta + or beta 0 type according to the presence or absence of beta-globin chain synthesis in the homozygous state. The molecular pathology of each type is heterogeneous. Apart from a subgroup of Indo-Pakistani patients, the beta-globin structural gene is intact in the majority of patients with beta 0 thalassaemia. The amount of beta-globin mRNA present in the reticulocytes of these patients varies: in some it is absent or barely detectable; in others, a substantial amount is present, but it is nonfunctional. We recently demonstrated that the molecular lesion in a Chinese patient with nonfunctional beta-globin mRNA was due to the mutation of the normal lysine codon AAG at amino acid 17 to the amber terminator codon UAG, which prematurely terminates the beta-globin chain. In the present study we demonstrate the first example of a nonsense mutation in humans which can be suppressed in vitro by the suppressor tRNA, as has been found in other eukaryotic cells and viruses.
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PMID:Suppression of the nonsense mutation in homozygous beta 0 thalassaemia. 49 26

We have identified a novel repetitive family in human DNA. One member of this family is found downstream of the beta-globin gene cluster between the 3' breakpoints of the deletions associated with Chinese G gamma + (A gamma delta beta)O thalassemia and HPFH-2. This repetitive element is approximately 6 kbp in length and includes terminal direct repeats of 415 bp. Numerous DNA sequence features of the direct repeats (LTRs) and their flanking regions indicate that the element is a retrovirus-like structure. The most striking of these features is the presence of a histidine tRNA binding site just 3' to the 5' LTR. Accordingly the element is named RTVL-H (retrovirus-like element-histidine). The LTRs of the RTVL-H element are not strongly homologous to the LTRs of any previously described mammalian retrovirus or retrovirus-like element. Copy number estimates suggest that there are approximately 1000 RTVL-H elements in the human genome. The element found 3' (greater than 60 kbp) to the beta-globin gene appears to be a stable part of the normal genome. This retrovirus-like element is brought close to the fetal gamma-globin locus by the Chinese thalassemia deletion but is deleted in HPFH-1 and HPFH-2.
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PMID:A retrovirus-like element occurs between the 3' breakpoints of two large deletions in the human beta-globin gene cluster. 241 85

We have analyzed a cloned beta O-thalassemia (beta O-thal) gene from a patient doubly heterozygous for hemoglobin Lepore and beta O-thalassemia. Studies of 3H-uridine incorporation into beta-globin mRNA in this patient's erythroblasts suggested an intranuclear defect in both beta and Lepore (delta beta) mRNA synthesis, as did S1 nuclease analysis of nuclear RNA. However, the nucleotide sequence of the beta O-thal gene revealed only a single base change in codon 39 (CAG----UAG), which created a premature translation termination codon. The 5' flanking sequence, including transcription promotor boxes and the mRNA initiation (CAP) site, were normal. The unexpected effect of this mutation on intranuclear beta-mRNA synthesis in vivo was studied by insertion of the cloned gene into a plasmid expression vector and transfection into tissue culture (COS-1) cells. beta-Globin mRNA produced by the transfected cells was assessed by S1 nuclease analysis. The beta O-39 thalassemia gene generated five- to tenfold less beta-mRNA than a normal beta-gene in both nuclear and cytoplasmic RNA, simulating the results observed in vivo. Moreover, the small amount of beta O-39 mRNA produced was as stable as normal beta-mRNA during an actinomycin D chase, ruling out rapid cytoplasmic turnover as a cause of the reduced accumulation. Cotransfection of the beta O-39 thalassemia gene with a mutant tyrosine suppressor tRNA gene resulted in restoration of the beta O-39 mRNA accumulation to near-normal levels. On the basis of these results, we suggest that the low levels of beta-mRNA known to exist in the common form of beta O-thalassemia, beta O-39 thalassemia, result from a lesion in transcription, or early posttranscriptional processes; the defect appears to be corrected by restoration of proper translational potential to the mutant mRNA, at least in a gene transfer-expression system in tissue-culture cells.
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PMID:Intranuclear defect in beta-globin mRNA accumulation due to a premature translation termination codon. 673 65

A human tRNALys gene was converted to an amber suppressor by site-specific mutagenesis of the anticodon. The mutated tRNALys gene directed synthesis of a tRNA that suppressed the UAG amber nonsense mutation in beta O thalassemia mRNA. Such genes may be used to detect other nonsense mutations in mammalian cells and may provide an approach to gene therapy for beta O thalassaemia due to nonsense mutations.
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PMID:Construction of a functional human suppressor tRNA gene: an approach to gene therapy for beta-thalassaemia. 680 69