Segregation of the G8993 mutant mitochondrial DNA through generations and embryonic tissues in a family at risk of Leigh syndrome.

We identified the T8993G mitochondrial mutation in a female infant who died of Leigh syndrome. The proportion of mutant mitochondrial DNA increased to near homoplasmy in three generations of the pedigree. A similarly high proportion of mutant mitochondrial DNA was found in the chorionic villi and in fetal tissues from a pregnancy interrupted because of the risk of Leigh syndrome. This study supports the concept that prenatal diagnosis can be used for Leigh syndrome with the T8993G mitochondrial DNA mutation.

Detection of mitochondrial DNA deletions by a screening procedure using the polymerase chain reaction.

We describe an accurate procedure for a rapid diagnosis of heteroplasmic mtDNA deletions based on the polymerase chain reaction (PCR). For a selective amplification of deleted mtDNA across the breakpoints of the deletion, we used seven combinations of primers surrounding the most common deleted region between the two origins of mtDNA replication. This procedure was performed on muscle biopsies of twenty patients harboring a single mtDNA deletion and one patient with multiple mtDNA deletions. The results were compared with Southern-blotting analysis. We conclude that this PCR procedure is a sensitive and convenient screening method for the detection of mtDNA deletions.

Expression of oxidative phosphorylation genes in muscle cell cultures from patients with mitochondrial myopathies.

The expression of several mitochondrial and nuclear genes involved in ATP production was examined in cells cultured from muscle biopsies of patients harboring mitochondrial pathologies. The transcript patterns in muscle cells from the patients affected by carnitine palmitoyl transferase II or 2-ketoglutarate dehydrogenase deficiencies were almost similar to control patterns. In the opposite, patterns were strikingly abnormal in all the other cell cultures from patients with defects in enzymatic complexes involved in oxidative phosphorylation: mitochondrial complex II and III deficiencies, two MELAS syndromes (myopathy, encephalopathy, lactic acidosis and stroke like episodes), a case of Kearns-Sayre syndrome and a case of chronic progressive external ophthalmoplegia. In cultured muscle cells from patients with mtDNA mutations, the percentage of mutated mtDNA was low as compared with those determined in the corresponding skeletal muscle biopsy. Moreover, the complex II defect resulting of a nuclear mutation was not expressed in the cell cultures. Thus, an undetermined transcriptional event, transmitted from muscle biopsies to cultured muscle cells, should be involved to account for such abnormal transcript patterns.

Accumulation of mitochondrial DNA deletions in myotubes cultured from muscles of patients with mitochondrial myopathies.

Myoblast cultures were established from muscle biopsies of two patients harboring heteroplasmic mitochondrial (mt) DNA deletions. The accumulation kinetics of the deleted mtDNA was followed during myoblast to myotube differentiation. The percentage of deleted mtDNA was determined by quantitative PCR in myoblasts, myotubes, and muscle biopsies. The deleted form accounted for 65% of the mtDNA present in a muscle biopsy from a patient harboring a 5.6-kb deletion. The percentage of deleted mtDNA was 1.2% in myoblasts and increased progressively after differentiation, up to 12% at 21 days after the commitment time. In a second patient harboring a 2.8-kb deletion, the percentage of deleted mtDNA increased much more slowly: from 0.07% in myoblasts to 0.21% after 22 days of differentiation, as compared with 45% in the muscle biopsy. Thus, a three- and ten-fold increase, respectively, in the fraction of deleted mtDNA occurred during the differentiation of myoblasts to myotubes from the two patients. The faster accumulation of deleted mtDNA int he first patient's cells was linked to an earlier myoblast to myotube differentiation, suggesting that the level of deleted mtDNA is inversely related to the rate of cell proliferation.

A novel gly290asp mitochondrial cytochrome b mutation linked to a complex III deficiency in progressive exercise intolerance.

We have identified a new mitochondrial (mt) cytochrome b mutation in a 29-year-old man with progressive exercise muscle intolerance associated with a marked deficiency of complex III activity and a decreased amount of mitochondrial-encoded cytochrome b. This G to A transition at mtDNA position 15615 leads to the substitution (G290D) of a very highly conserved amino acid of cytochrome b during evolution. The mutant mtDNA was heteroplasmic (80% mutant) in patient muscle but was undetectable in blood from the patient and his healthy mother and sisters. A maternally inherited cytochrome b polymorphism was also identified in this patient. Molecular screening of 150 individuals showed that the G290D mutation associated with the described phenotype. We suggest that this molecular defect is the primary cause of the muscle disease in this patient.

Molecular histology of mitochondrial and nuclear transcripts in the muscle of patients harbouring a single mitochondrial DNA deletion.

The distribution of transcripts of mitochondrial and nuclear genes involved in oxidative phosphorylation and of the mitochondrial creatine kinase nuclear gene was examined, using in situ hybridisation, in the skeletal muscle of 11 patients harbouring a heteroplasmic mitochondrial DNA (mtDNA) single deletion. Levels of mRNAs transcribed from genes located within the deletions were not decreased, suggesting that the remaining wild-type mtDNA was still transcribed. Those muscle fibres with characteristic abnormal mitochondrial proliferation always showed overexpression of mRNAs and rRNAs transcribed from mitochondrial genes located outside the deletions. Interestingly, they also showed overexpression of the nuclear-encoded ATP synthase beta subunit mRNA, but not of mitochondrial creatine kinase mRNA. These observations lead to three proposals: (1) overexpression of mitochondrial transcripts within fibres harbouring mitochondrial proliferation, together with the apparently normal expression of the remaining wild-type mtDNA, is not related to decreased mitochondrial translation; (2) it is more probably related to an up-regulation mechanism which co-ordinates both mitochondrial and nuclear expression; and (3) this mechanism is restricted to transcripts directly involved in oxidative phosphorylation and to fibres with mitochondrial accumulation.

Fine mapping of randomly distributed multiple deletions of mitochondrial DNA in a case of chronic progressive external ophthalmoplegia.

Multiple deletions of mitochondrial DNA have been detected by Southern blotting in the skeletal muscle of a 42-year-old woman with chronic progressive external ophthalmoplegia. A PCR method, using several combinations of primers covering the whole mtDNA as well as sequence analysis, disclosed the wide spectrum of these multiple deletions differing in size, location and sequence at the breakpoint junction. Most involved the major region between the two replication origins. However, three deletions affected the minor region and lacked either the light strand origin of replication or the heavy strand promoter. These data suggest an impairment of mtDNA replication leading to illegitimate recombination and extensive damage of mtDNA.

An abnormal exercise test response revealing a respiratory chain complex III deficiency.

A 29-year-old man with a progressive exertional muscle intolerance since childhood was referred for incremental exercise test on a bicycle ergometer. The response pattern suggested a mitochondrial myopathy: that is, a greatly reduced maximum oxygen consumption with appropriate heart rate increase and an anaerobic threshold point reached early. The metabolic investigation in plasma revealed an abnormal oxidoreduction status (hyperlactataemia and high lactate/pyruvate ratio) at rest and after a carbohydrate rich meal. The histochemical examination of a muscle biopsy revealed red granular deposits under the sarcolemma for all type 1 fibers. Oxypolarographic and enzymological studies of the mitochondrial respiratory chain in both isolated mitochondria and muscle homogenate demonstrated a marked deficiency of ubiquinol cytochrome c reductase (complex III) activity.

Cardiac transplantation in an incomplete Kearns-Sayre syndrome with mitochondrial DNA deletion.

A 38-yr-old man with external ophthalmoplegia, cardiac conduction abnormalities, hearing loss, and ragged-red fibres in skeletal muscle biopsy, developed severe signs of cardiac failure within a few months. Echocardiography and angiography demonstrated a dilated cardiomyopathy. Ubiquinone 140 mg day-1 did not stop the worsening of the cardiac status and cardiac transplantation was performed. Molecular analysis showed a heteroplasmic 4.5 kb mitochondrial DNA deletion in endomyocardial tissue. Eighteen months later, cardiac evolution is good and neurological status is stable.

Carnitine palmitoyl transferase I deficiency presenting as a Reye-like syndrome without hypoglycaemia.

An apparently healthy girl aged 2 years 9 months developed a coma with hepatomegaly within 24 h after an influenza-like infection. Plasma glucose and urinary organic acid profile were normal but plasma and urinary carnitine concentrations were increased. Despite symptomatic therapy, she died 11 days later. Oxidation of [1-14C] palmitic acid in the patient's fibroblasts was severely decreased (13% of controls). Further investigations revealed a deficiency of carnitine palmitoyl transferase I (CPT I) in the patient's fibroblasts (15% of controls) whereas CPT II activity was normal. Only four patients with CPT I deficiency have been reported so far. The subtle clinical and biochemical presentation of this disorder, which may account for the small number of cases diagnosed, is discussed.

2-Ketoglutarate dehydrogenase deficiency, a rare cause of primary hyperlactataemia: report of a new case.

Two new familial cases of 2-ketoglutarate dehydrogenase (2-KGD) deficiency are reported: a girl who died at 10 years and a boy, still alive at 4 years, born to consanguineous parents. The cases developed progressively severe encephalopathy with axial hypotonia, psychotic behaviour, pyramidal symptoms and failure to thrive. Both children exhibited permanent lactic acidosis with acute episodes during emotional stress and various infections, associated with elevated lactate/pyruvate (L/P) ratio and slightly decreased ketone body ratio in plasma. In fibroblasts, the L/P ratio was greatly increased in the boy. No respiratory chain complex deficiency could be demonstrated in cultured fibroblasts or in mitochondria isolated from a muscle biopsy performed on the boy. In muscle isolated mitochondria, a progressive decrease of the rate of glutamate oxidation was observed after ADP addition; the rate of 2-ketoglutarate oxidation was low in the absence of ADP and did not increase after ADP addition. 2-KGD deficiency was demonstrated in fibroblasts from both children and in the boy's muscle and myoblasts. The 2-KGD complex is composed of three separate enzymes: E1, E2 and E3. We could demonstrate in our patient that the E1 and E3 subunits were normal, suggesting that the E2 component could be responsible for the defect.

[Value of skin fibroblasts in culture for the diagnosis of mitochondrial cell dysfunction. Apropos of 5 cases with cytochrome c oxidase deficiency]. / Intérêt des fibroblastes cutanés en culture pour le diagnostic des cytopathies mitochondriales. A propos de cinq observations de déficit en cytochrome c oxydase.

Mitochondrial respiratory chain dysfunction has been studied by two complementary methods using cultured skin fibroblasts from five patients with muscular cytochrome c oxidase (complex IV) deficiency: first, a screening test measuring lactate to pyruvate ratio (L/P) after supplementation of cultured cells; secondly, measurement of complex IV activity in whole cells. Respiratory chain defect (increased L/P ratio with decreased complex IV activity) was expressed in fibroblasts of four of the five patients. Our results show that skin fibroblasts can be helpful for biochemical diagnosis of mitochondrial respiratory chain defects.

Purification of electron transfer flavoprotein from pig liver mitochondria and its application to the diagnosis of deficiencies of acyl-CoA dehydrogenases in human fibroblasts.

Medium chain acyl-CoA dehydrogenase (MCAD) and long chain acyl-CoA dehydrogenase (LCAD) deficiency are defects of mitochondrial beta-oxidation. The method of choice to measure specifically acyl-CoA dehydrogenase activity in human tissues uses purified electron transfer flavoprotein (ETF). We describe a simple and optimized method of purification allowing isolation of ETF with a degree of purity never reported so far. An assay for acyl-CoA dehydrogenase activity in cultured skin fibroblasts was developed using microquantities of electron transfer flavoprotein and substrate. MCAD deficiency was demonstrated in fibroblasts from nine patients and LCAD deficiency in fibroblasts from two patients.

[Cysteamine in the treatment of cystinosis in children. In vitro and in vivo studies]. / La cystéamine dans le traitement de la cystinose infantile. Etudes in vitro et in vivo.

The effect of cysteamine was studied in 6 children with nephropathic cystinosis. In 3 of them an in vitro study on fibroblasts was performed. The cystine content of fibroblasts was immediately diminished (about 90% of total cystine content) as soon as the concentration of cysteamine in the medium was greater than or equal to 0,1 mmole/l. In vivo, 50 to 89 mg/kg/day of cysteamine was administered for 9 to 37 months (mean 21,3). There was no adverse reaction. In all cases a dramatic decline in leukocyte cystine level was observed (in 5 cases the level was within the range seen in clinically unaffected heterozygotes). Growth was not improved. The renal function was stabilised in 3 cases. Photophobia which was present in 4 children decreased in 2 cases or disappeared in 2 cases.