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T M Cox

Publications and source records attributed to T M Cox.

At least 91 records · Page 5Linked to original sources
PubMed1993

DNA diagnosis of fatal fructose intolerance from archival tissue.

Hereditary fructose intolerance is a recessively-transmitted disorder of metabolism caused by deficiency of aldolase B in the liver, intestine and kidney, that responds favourably to an exclusion diet. The occurrence of fatal hepatorenal failure in a 16-year-old girl, who had received infusions of fructose and sorbitol during minor surgery, led us to suspect that she had suffered from hereditary fructose intolerance. Molecular analysis of leucocyte DNA obtained from her brother who had had a long-standing aversion to fruit and sugar, showed two previously unknown mutations in the aldolase B gene. An initiation codon mutation, M-1T, was inherited from the father, whereas Y203X, inherited from the mother, is a nonsense mutation that replaces a tyrosine codon by the ochre termination signal. The only source of genomic DNA from the index case was a fixed fragment of necrotic liver that had been obtained by needle aspiration postmortem and was embedded in paraffin wax. Analysis of aldolase B genes in this sample by procedures based on the polymerase chain reaction (PCR) confirmed the presence of both mutations in the proposita, the diagnosis of hereditary fructose intolerance, and the cause of death.

Adolescent↗
PubMed1993

The MB PhD programme. Training to be a clinician-scientist in the UK.

Rapid changes in the universities and in the organisation of the National Health Service are altering the perception of opportunity for clinical scientists in training. Cambridge University has established an integrated programme that combines training in scientific research and clinical medicine leading to the MB, BChir, and PhD degrees. The need for this and other options in the development of careers for aspiring medical researchers is reviewed here.

Education, Medical↗
PubMed1992

Genetic diagnosis of Gaucher's disease.

The inherited disorder Gaucher's disease can be caused by various mutations in the glucocerebrosidase gene. Some mutations may be associated with greater severity, and there is a need for methods of gene analysis that would facilitate screening and diagnosis. We have studied the molecular basis of Gaucher's disease in twelve unrelated patients of diverse ethnic origin by means of the amplification refractory mutation system (ARMS). Primers for the polymerase chain reaction were designed to discriminate between mutant and wild-type alleles of glucocerebrosidase and to allow separation from products of the related pseudogene. The nucleotide 1226 mutation (asparagine 370----serine) and 84GG (an insertional frameshift mutation) were found exclusively in five patients of Ashkenazi Jewish descent (7 and 2 of the 10 disease alleles, respectively). Two point mutations, at nucleotides 1448 (leucine 444----proline) and 1504 (arginine 463----cysteine), were found in 4 and 3 alleles, respectively; they were associated with rapidly progressive disease and neurological involvement in non-Jewish patients. The ARMS procedure for direct detection of common mutations in glucocerebrosidase will facilitate genetic counselling and screening programmes for individuals at risk of Gaucher's disease.

Adolescent↗
PubMed1992

Basis of unique red cell membrane properties in hereditary ovalocytosis.

Hereditary ovalocytes from a Mauritian subject are extremely rigid, with a shear elastic modulus about three times that of normal cells, and have increased resistance to invasion by the malaria parasite Plasmodium falciparum in vitro. The genetic anomaly resides in band 3; the protein gives rise to chymotryptic fragments with reduced mobility in SDS/polyacrylamide gel electrophoresis, but this is a result of anomalous binding of SDS and not a higher molecular weight. Analysis of the band 3 gene reveals (1) a point mutation (Lys56----Glu), which also occurs in a common asymptomatic band 3 (Memphis) variant and governs the electrophoretic properties, and (2) a deletion of nine amino acid residues, including a proline residue, encompassing the interface between the membrane-associated and the N-terminal cytoplasmic domains. The interaction of the mutant band 3 with ankyrin appears unperturbed. The fraction of band 3 capable of undergoing translation diffusion in the membrane is greatly reduced in the ovalocytes. Cells containing the asymptomatic band 3 variant were normal with respect to all the properties that we have studied. Possible mechanisms by which a structural change in band 3 at the membrane interface could regulate rigidity are examined.

Adult↗
PubMed1992

Successful treatment of bone marrow failure in Gaucher's disease with low-dose modified glucocerebrosidase.

We report the beneficial effects of enzyme replacement therapy with mannose-terminated human glucocerebrosidase ('Ceredase') in a patient suffering from transfusion-dependent bone marrow failure due to Gaucher's disease. Treatment with low-dose enzyme infusions, given twice weekly, rapidly reversed the haematopoietic failure and incapacitating skeletal disease. It appears likely that prior splenectomy favourably influenced the response to this therapy.

Bone Marrow Diseases↗
PubMed1991

Biosynthesis of delta-aminolevulinic acid and the regulation of heme formation by immature erythroid cells in man.

Heme formation in the erythron is subject to end product regulation by negative feedback, but the exact point of metabolic control in human erythroid cells is unknown. To investigate the mode of action of heme on its own formation, the effects of micromolar concentrations of hemin on de novo synthesis of protoporphyrin IX and delta-aminolevulinate (delta-ALA) by intact human reticulocytes were examined in the presence of 1 mM alpha,alpha'-bipyridyl and 200 microM 4,6-dioxoheptanoate to block their further conversion by ferrochelatase or delta-ALA dehydrase, respectively. At final concentrations (25-40 microM), hemin, which is known to reduce incorporation of [2-14C]glycine into cellular heme, significantly inhibited formation of protoporphyrin IX and total delta-aminolevulinate in situ by these cells. Since synthesis of the first committed precursor, delta-aminolevulinate, as well as protoporphyrin (which is derived from it) were diminished, the effects of hemin on delta-aminolevulinate synthase (EC 2.3.1.37) were studied. Hemin, at concentrations up to 40 microM, had no direct effect on enzymatic activity, as measured with [5-14C] alpha-ketoglutarate (in hypotonically lysed cells) or [1,4-14C]succinyl coenzyme A (in deoxycholate lysates), even after preincubation. However, when intact human reticulocytes were incubated with hemin before assay for delta-ALA synthase, there was a rapid, concentration-dependent reduction in enzymatic activity (mean 42 and 23% inhibition after 60 min for these two substrates, respectively). Hemin had no effect on steady-state levels of delta-ALA synthase mRNA, as determined by Northern blot hybridization using an erythroid-specific human cDNA probe. Thus, a mechanism for inducing feedback inhibition of the tetrapyrrole pathway exists in human erythroid cells. It controls formation of the first committed precursor of protoporphyrin IX, delta-aminolevulinate, and hence regulates heme biosynthesis by limiting the availability of the porphyrin, rather than the metal substrate for the ferrochelatase reaction. Hemin interacts with constituents of the intact reticulocyte significantly to reduce delta-aminolevulinic acid synthase activity by an indirect cellular process that does not influence the abundance of erythroid-specific synthase mRNA but may either inhibit its ribosomal translation in an unknown manner or promote degradation of the enzyme itself by specific proteolysis.

5-Aminolevulinate Synthetase↗
PubMed1991

Assignment of the human ferrochelatase gene (FECH) and a locus for protoporphyria to chromosome 18q22.

We have mapped the human gene for ferrochelatase (FECH; ferroheme-protolyase, EC 4.99.1.1) to chromosome 18 by hybridization of cDNA to sorted chromosomes. The probe was obtained by PCR-directed amplification of a human marrow cDNA library in lambda gt 10. Subchromosomal localization of ferrochelatase to 18q22 was determined by chromosomal hybridization in situ using a human ferrochelatase genomic clone in lambda EMBL 3 that contained a 20-kb insert. Since ferrochelatase activity is deficient in patients with the inherited disease erythropoietic protoporphyria, a locus for this disease may be assigned to 18q22, one of few monogenic defects that have been mapped to this chromosome.

Chromosome Mapping↗
PubMed1991

Aldolase B mutations in Italian families affected by hereditary fructose intolerance.

Hereditary fructose intolerance (HFI) is an inborn error of metabolism caused by aldolase B deficiency. The aldolase B gene has been cloned and the following mutations causing HFI have been identified: A149P (a G----C transversion in exon 5), A174D (a C----A transversion in exon 5), L288 delta C (a base pair deletion in exon 8), and N334K (a G----C transversion in exon 9). We have investigated the occurrence of these mutations in 11 Italian patients affected by HFI using PCR and hybridisation to specific oligomers. We found that four patients were homozygous for the A149P mutation, two patients were homozygous for the A174D mutation, three patients were compound heterozygotes for both the A149P and A174D mutations, one patient was homozygous for the N334K mutation, and one patient did not show any of the reported mutations (HFI diagnosis carried out by aldolase B assay). The L288 delta C mutation has not been found in this survey.

Base Sequence↗
PubMed1991

Regulation and expression of type V (tartrate-resistant) acid phosphatase in human mononuclear phagocytes.

Human type V (tartrate-resistant) acid phosphatase belongs to a unique group of iron-binding proteins that includes uteroferrin and other purple phosphatases. The enzyme is normally restricted to osteoclasts and certain phagocytic cells but its rôle is unknown. We show that phosphatase mRNA is abundant in cells of monohistiocytic phenotype and that enzyme expression in cultured human monocyte-derived macrophages is depressed by gamma-interferon and bacterial lipopolysaccharide, agents that promote functional differentiation in these cells. In contrast, phorbol ester, which stimulates intracellular calcium-mediated events, greatly enhances type V phosphatase expression and mRNA abundance. Lymphokine and phorbol ester-modulated expression of type V acid phosphatase expression thus represents a model system for investigating proliferative responses that are specific to cells of the mononuclear macrophage system.

Acid Phosphatase↗
PubMed1990

Type 5 acid phosphatase. Sequence, expression and chromosomal localization of a differentiation-associated protein of the human macrophage.

The purple acid phosphatases and uteroferrin belong to a diverse multifunctional class of binuclear iron-containing proteins that includes haemerythrin and ribonucleotide reductase. In the pig, uteroferrin has been implicated in the delivery of iron to the foetus, but the role of the related human type 5 acid phosphatase that is principally found in resident tissue macrophages is not yet clear. To define further the function of this metalloenzyme, we have isolated and sequenced a cDNA clone for type 5 acid phosphatase and investigated expression of its gene in human tissues. The phosphatase clone contains an open reading frame of 975 bp and encodes a protein of 325 amino acids, including a signal peptide of 19 residues and two potential sites for N-glycosylation. The type 5 acid phosphatase gene mapped to the short arm of human chromosome 19 and was found to have a restriction fragment length polymorphism on digestion with XbaI. Expression of phosphatase mRNA was restricted to mononuclear phagocytes and the enzyme was induced greater than 20-fold on transformation of normal human monocytes to macrophages by culture in serum-supplemented medium. Type 5 acid phosphatase thus represents a tightly regulated system for the study of molecular events in the differentiation programme of the normal macrophage.

Acid Phosphatase↗
PubMed1990

Molecular analysis of the human MHC class I region in hereditary haemochromatosis. A study by pulsed-field gel electrophoresis.

The unknown allele that predisposes to the development of haemochromatosis in man has been localized to the HLA class I region on the short arm of chromosome 6. We have utilized pulsed-field gel electrophoresis in conjunction with probes that map within, or in the vicinity of, this region to search for structural lesions that may further define the disease locus. Using the enzyme Mlu I, fragments that associated specifically with the HLA-A23, A31 and B8 alleles were identified. However, in members of three pedigrees affected by haemochromatosis, and in six unrelated patients with the disorder, no disease-specific differences were detected in the DNA fragments with four restriction enzymes and eight probes when compared with healthy individuals. These data suggest that the lesion responsible for hereditary haemochromatosis lies beyond the resolution of this technique and does not involve large structural deletions or extensive re-arrangements in this highly polymorphic region of the genome.

Alleles↗
PubMed1990

Haemochromatosis.

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Bloodletting↗