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T Bourgeron

Publications and source records attributed to T Bourgeron.

36 records · Page 2Linked to original sources
PubMed1995

Phenotypic expression of mitochondrial genotypes in cultured skin fibroblasts and in Epstein-Barr virus-transformed lymphocytes in Pearson syndrome.

Pearson syndrome is a fatal disorder involving the hematopoietic system and exocrine pancreas. Mitochondrial respiratory chain deficiencies and/or rearrangements of the mitochondrial DNA were consistently observed in all patients. We report here on the variant phenotypic expression of mitochondrial genotypes in cultured cells from a patient with Pearson syndrome. Skin fibroblasts and lymphocytes harbored, respectively, 60% and 80% of deleted mtDNA molecules initially and displayed defective respiratory chain activities. In both cases, there was a progressive recovery of respiratory chain activities during in vitro cell proliferation due to the loss of deleted mtDNA molecules in cultured skin fibroblasts and to an increase in the mtRNA translation efficiency in Epstein-Barr virus-transformed lymphocytes. The present study suggests that various cellular responses to abnormal mitochondrial genotypes might contribute to the tissue-specific expression of mitochondrial disorders in vivo.

Anemia, Sideroblastic↗
PubMed1995

Mutation of a nuclear succinate dehydrogenase gene results in mitochondrial respiratory chain deficiency.

We now report a mutation in the nuclear-encoded flavoprotein (Fp) subunit gene of the succinate dehydrogenase (SDH) in two siblings with complex II deficiency presenting as Leigh syndrome. Both patients were homozygous for an Arg554Trp substitution in the Fp subunit. Their parents (first cousins) were heterozygous for the mutation that occurred in a conserved domain of the protein and was absent from 120 controls. The deleterious effect of the Arg to Trp substitution on the catalytic activity of SDH was observed in a SDH- yeast strain transformed with mutant Fp cDNA. The Fp subunit gene is duplicated in the human genome (3q29; 5p15), with only the gene on chromosome 5 expressed in human-hamster somatic cell hybrids. This is the first report of a nuclear gene mutation causing a mitochondrial respiratory chain deficiency in humans.

Amino Acid Sequence↗
PubMed1995

Spectrum of mitochondrial DNA rearrangements in the Pearson marrow-pancreas syndrome.

The Pearson marrow-pancreas syndrome (MIM 557000) is a disorder involving the hematopoietic system and the exocrine pancreas in early infancy. We have previously shown that this disease results from a defect of oxidative phosphorylation associated with deletions of the mitochondrial DNA. We present here a series of 21 cases (including 15 unreported patients) with Pearson syndrome and describe mitochondrial DNA deletions as consistent features in this syndrome. Nine patients presented the same 4.9 kb deletion, while other patients presented different deletions ranging in size from 9 to 14 kb between tRNACyst and the D-loop. Direct repeats (4-13 bp) were consistently present in the wild-type mtDNA at the boundaries of the deletions. Deletion-dimers, deletion-multimers or duplications were observed in association with deletions. Duplications were identified both in patients who died of their Pearson syndrome and in the ones who survived and developed Kearns-Sayre syndrome, suggesting that no correlation could be made between the clinical severity and the type, size or location of the rearrangements.

Base Sequence↗
PubMed1994

Biochemical and molecular investigations in respiratory chain deficiencies.

This paper describes our present strategy for the investigation of respiratory chain disorders in humans. Because very few of the underlying mutations causing mitochondrial disorders in humans are currently known, biochemical studies constitute a major tool in screening procedures for respiratory chain deficiencies. All biochemical and molecular methods described are scaled-down methods, allowing investigation in both adults and young children. Polarographic studies and/or spectrophotometric studies on whole cells (circulating lymphocytes), isolated mitochondria (skeletal muscle) and tissue homogenates are presented. Advantages and limitations of each approach, as well as useful parameters for the characterization of defects and comparison between various tissues are discussed.

Cells, Cultured↗
PubMed1994

Reference charts for respiratory chain activities in human tissues.

This paper presents a collection of quantitative values for respiratory chain activities in human tissues. These were measured in the most widely used tissues in screening procedures for respiratory chain deficiencies. Investigations were mainly carried out using the different standardized micro-methods previously detailed (Rustin et al., Clin Chim Acta, 1994). The potential effect of the age of the patients on both absolute and relative levels of respiratory chain activities in their skeletal muscle tissue was first considered. No evidence for any significant difference between the various age groups in the studied population (ranging from 0 to above 50 years of age) was observed. Moreover, a quite similar picture of the organization of the respiratory chain was suggested independent of the tissue or the cells investigated. In particular, it was found that roughly identical enzyme activity ratios could be measured in all tissues, which allowed study of the differential involvement of organs and tissues in patients potentially affected by a respiratory chain deficiency. Some tissue-specific features were, however, observed, including varying rates of glycerol-3-phosphate dehydrogenase activities and increased succinate dehydrogenase activity in liver. The technical limitations remaining in the investigations of respiratory chain disorders in man are discussed in the conclusion.

Adolescent↗
PubMed1994

Endomyocardial biopsies for early detection of mitochondrial disorders in hypertrophic cardiomyopathies.

Considering the high proportion of unexplained hypertrophic cardiomyopathies on the one hand and the occurrence of cardiomyopathies in several mitochondrial disorders on the other, we hypothesized that isolated hypertrophic cardiomyopathies in infancy could occasionally be the result of defects of oxidative phosphorylation. By means of a scaled-down technique, we were able to investigate oxidative phosphorylation on minute amounts of endomyocardial tissue (1 mg) in three patients with concentric hypertrophic cardiomyopathy (shortening fraction in diameter, 18% to 27%; normal mean +/- 1 SD, 33 +/- 3%) and in control subjects. Although the absolute respiratory chain enzyme activities in the endomyocardial biopsy specimens of the patients were within the low normal range, the determination of the activity ratios allowed us to ascribe hypertrophic cardiomyopathies to respiratory chain enzyme abnormalities in all three cases (complex I, two cases; multiple enzyme deficiency, one case). The respiratory chain enzyme activity ratios, which are normally constant irrespective of the tissue tested, were markedly abnormal in all three patients (cytochrome c oxidase/reduced nicotinamide-adenine dinucleotide cytochrome c reductase, 4.6 to 10.4; normal mean +/- 1 SD, 2.9 +/- 0.5). We conclude that mitochondrial disorders should be regarded as potential causes of hypertrophic cardiomyopathy in early infancy. Because cardiac catheterization is routinely performed for hemodynamic investigation of cardiomyopathies, we suggest that endomyocardial biopsies be considered as a tool for early detection of mitochondrial cardiomyopathies, especially in hypertrophic forms of the disease.

Biopsy↗
PubMed1994

Mutation of the fumarase gene in two siblings with progressive encephalopathy and fumarase deficiency.

We report an inborn error of the tricarboxylic acid cycle, fumarase deficiency, in two siblings born to first cousin parents. They presented with progressive encephalopathy, dystonia, leucopenia, and neutropenia. Elevation of lactate in the cerebrospinal fluid and high fumarate excretion in the urine led us to investigate the activities of the respiratory chain and of the Krebs cycle, and to finally identify fumarase deficiency in these two children. The deficiency was profound and present in all tissues investigated, affecting the cytosolic and the mitochondrial fumarase isoenzymes to the same degree. Analysis of fumarase cDNA demonstrated that both patients were homozygous for a missense mutation, a G-955-->C transversion, predicting a Glu-319-->Gln substitution. This substitution occurred in a highly conserved region of the fumarase cDNA. Both parents exhibited half the expected fumarase activity in their lymphocytes and were found to be heterozygous for this substitution. The present study is to our knowledge the first molecular characterization of tricarboxylic acid deficiency, a rare inherited inborn error of metabolism in childhood.

Amino Acid Sequence↗
PubMed1993

Fate and expression of the deleted mitochondrial DNA differ between human heteroplasmic skin fibroblast and Epstein-Barr virus-transformed lymphocyte cultures.

We report on the variant phenotypic expression of mitochondrial genotypes in cultured skin fibroblasts and Epstein-Barr virus-transformed lymphocyte cultures from a patient with Pearson syndrome (McKusick no. 260560). Both cell types harbored a heteroplasmic population of normal and deleted mtDNA molecules. The deletion encompassed five tRNA genes and seven genes encoding subunits of cytochrome c oxidase, complex I, and ATPase. Patient skin fibroblasts and lymphocytes harbored 60 and 80% of deleted mtDNA molecules, respectively, and initially displayed defective respiratory chain activities. In both cases, there was a progressive recovery of respiratory chain activities during in vitro cell proliferation. In cultured skin fibroblasts, the loss of the deleted mtDNA molecules accounted for the recovery of normal respiratory chain activities. These features were prevented by allowing respiratory chain-deficient cells to grow in the presence of uridine (200 microM). In Epstein-Barr virus-transformed lymphocytes containing 60% of deleted mtDNA, the recovery of respiratory chain activities was attributable to an increase in the mtRNA translation efficiency rather than to an increased content in mtDNA or mtRNA. The present study suggests that the variant cellular responses to abnormal mitochondrial genotypes might contribute to the tissue-specific expression of mitochondrial disorders in vivo.

Cell Line, Transformed↗
PubMed1993

Investigation of respiratory chain activity in human heart.

Although disorders of oxidative phosphorylation have long been regarded as neuromuscular diseases only, they can actually give rise to any symptom specifically affecting any organ or tissue, particularly in childhood. The early diagnosis of such a condition may thus require the specific assessment of the mitochondrial function in the organ or tissue shown to be clinically involved. A method is presented allowing such an early detection of respiratory chain defects in human heart. Respiratory chain enzyme studies were carried out using endomyocardial biopsies, less than 2 mg fresh weight. Enzyme activities measured in the endomyocardial biopsies were compared with those obtained using other sampling methods (surgical and postmortem microsamples). A comparison of the respiratory chain enzyme activities in heart and other human tissues is also presented. It was found that (i) the activities of respiratory chain complexes in human heart were similar with any sampling method; (ii) these activities were high compared to other human tissues, allowing the use of heart microsamples for enzyme measurements; (iii) the activity ratios between complexes of the respiratory chain were similar in heart and other human tissues or cells as well, allowing us to confidently characterize potential mitochondrial defects and to compare their expression in different tissues or cells. The value of such investigations on endomyocardial biopsies is illustrated in the case of two patients affected with mitochondrial cardiomyopathy and is discussed in regard to the tissue-specific nature of mitochondrial diseases.

Adolescent↗
PubMed1992

Isolation and characterization of mitochondria from human B lymphoblastoid cell lines.

Mitochondria were isolated from detergent-treated Epstein-Barr virus-transformed human lymphocytes to examine their potential use in the study of the functional expression of genetic disorders of the respiratory chain. The increase of cytochrome c oxidase activity in the mitochondrial fraction indicated a 6-fold purification of intact mitochondria. Polarographic and spectrophotometric studies revealed that the isolated mitochondria were functionally well preserved. Furthermore, the isolated mitochondria supported an active in organello protein synthesis, which was dependent on the presence of a respiratory substrate generating ATP and was essentially abolished by chloramphenicol or by a specific respiratory chain inhibitor, such as antimycin. Thus, B lymphoblastoid cell lines constitute a valuable source of mitochondria to investigate mitochondrial functions in patients affected by respiratory chain disorders.

Antimycin A↗
PubMed1990

The measurement of the rotenone-sensitive NADH cytochrome c reductase activity in mitochondria isolated from minute amount of human skeletal muscle.

Mitochondria isolated from minute amounts (100-500 mg) of human skeletal muscle displayed a very high rotenone-resistant NADH cytochrome c reductase activity. Moreover, compared to succinate cytochrome c reductase activity, a low rate of rotenone-sensitive NADH cytochrome c reductase activity was measured when using standard procedures to disrupt mitochondrial membranes. Only a drastic osmotic shock in distillated water as a mean to disrupt mitochondrial membrane was found to strongly increase the actual rate of the rotenone-sensitive activity. This was accompanied by a decrease in the rotenone-insensitive activity. Using such a simple procedure, the NADH cytochrome c reductase was found 70-80% inhibited by rotenone and roughly equivalent to 70-85% of the activity of the succinate cytochrome c reductase.

Cell Fractionation↗
PubMedDate not supplied

Expression of respiratory chain deficiencies in human cultured cells.

The expression of respiratory chain deficiencies was studied in cultured skin fibroblasts and B lymphoblastoid cell lines from patients with mitochondrial disorders. The genotype and phenotype of the cells were found to be dramatically different depending on the cell type and metabolic environment. In all cases, respiratory chain deficiencies gradually disappeared during the cell proliferation. However, in the presence of uridine, deficiencies were maintained in cultured skin fibroblasts. Accordingly, in cells harbouring a population of deleted mtDNA, the addition of uridine in the culture medium maintained the proportion of deleted mtDNA. In Epstein-Barr virus transformed lymphocytes, while a normal respiratory chain activity could be measured, deleted mtDNA was still present in high proportions (> 60% of the total mtDNA). The persistence of the deleted mtDNA was observed under all metabolic conditions tested, even when energy production from glycolysis was restricted. Finally, prenatal diagnosis of such a respiratory chain deficiency (cytochrome c oxidase deficiency) was performed in three cases. In all of them, a normal cytochrome c oxidase activity was measured in the cultured amniocytes. The children were born and are presenting no sign of an eventual affection.

B-Lymphocytes↗
PubMedDate not supplied

[Y chromosome and spermatogenesis].

World wide about 2% of men have a primary deficiency in sperm production. Familial cases of male infertility and chromosomal anomalies associated with this phenotype indicate that there is, at least in some cases, a genetic cause. In particular, deletions of the non-recombining portion of the Y chromosome are associated with a failure of sperm production. Deletion screening, using Y-specific markers has defined three regions (AZFa, b, c) that are associated with azoospermia. Each region contains one or more candidate genes that may be responsible for the phenotype. However, mutations have not yet been identified in any of these genes. This review discusses the structural organisation of the human Y chromosome and genes that are candidates for male infertility.

Genetic Testing↗