Maternally transmitted partial direct tandem duplication of mitochondrial DNA associated with diabetes mellitus

Mitochondrial DNA from a 38 year old male with diabetes mellitus and features of mitochondrial dysfunction was analysed and shown to include a population with a partial duplication. The partially duplicated mitochondrial DNA molecules were evident in both muscle and blood. The region of mitochondrial DNA duplicated includes the origin of heavy strand replication, but not the light strand origin. This patient has features in common with other cases of partial direct tandem duplications and with a family which was reported to harbour a 10.4 kb mtDNA deletion. Initial restriction enzyme analysis of our case produced results consistent with a partial deletion of mitochondrial DNA. This leads us to propose that the rarity of reports of partial mitochondrial DNA duplications may stem in part from the classification of such mutants as partial deletions.

Treatment of complex I deficiency with riboflavin

We have evaluated the effects of treatment with riboflavin in five patients with a mitochondrial myopathy, associated with a complex I (NADH dehydrogenase) deficiency. Two patients suffered from a clinically pure myopathy and the other patients presented with encephalomyopathic features. Treatment with riboflavin resulted in a clear clinical improvement in the two patients with the myopathic form of complex I deficiency. However, only one of the patients with the encephalomyopathic form improved during therapy. In three of the four patients in whom complex I activity in muscle tissue has been determined again during therapy, complex I activity appeared to be normalized. The clinical effects of treatment in this group of patients do not correlate well with normalization of complex I activity.

Human immunodeficiency virus type 1 infection and myopathy: clinical relevance of zidovudine therapy

Fifty consecutive patients infected with human immunodeficiency virus type 1 (HIV-1) were evaluated regarding the prevalence of HIV-related myopathies and the relevance of zidovudine-related mitochondrial myopathy. Disease stage, total lifetime intake of zidovudine, anthropometric and nutritional parameters, muscle strength, and histochemical and immunohistochemical findings in muscle specimens were recorded. The series was divided into two groups, patients with a total lifetime intake of zidovudine under 200 gm and those with a total lifetime intake over 200 gm. A control group included 50 healthy people matched for age and sex. HIV-related myopathy was defined by the presence of at least one of the classic pathological reactions in muscle, while zidovudine-related myopathy was defined by the presence of ragged red fibers in any percentage. Lower values of the nutritional parameters were detected in the HIV cohort, when compared with normal control values. HIV-related myopathy was detected in 13 (26%) of the 50 patients. There were no differences between groups except for the development of mitochondrial myopathy that occurred in 1 of the 26 patients in Group 1 and in 16 of the 24 in Group II. Six patients who had a total intake of more than 200 gm of zidovudine and demonstrated red ragged fibers in their muscle specimens were absolutely asymptomatic. There was a positive correlation between total intake of zidovudine and the percentage of red ragged fibers in muscle biopsy specimens.

Ventricular arrhythmia revealing mitochondrial myopathy in a 69-year-old woman

We report a case of mitochondrial myopathy (MM), assessed by histological and biochemical studies. This illness was diagnosed in a 69-year-old patient with myocardiopathy revealed by ventricular arrhythmias. The originality of this case lies in the patient's age, the mode of onset and the biochemical features (i.e. normal mitochondrial enzymatic complexes but very low respiration when using glutamate as a substrate).

Multiple respiratory chain abnormalities associated with hypertrophic cardiomyopathy and 3-methylglutaconic aciduria

In a 4.5-month-old boy presenting with marked muscular hypotonia in the neonatal period, hepatomegaly, cardiac hypertrophy, recurrent hypoglycemia, metabolic acidosis, and secondary carnitine deficiency, there was a considerable urinary excretion of 3-methylglutaconic and 3-methylglutaric acid. Estimation of 3-methylglutaconyl-CoA hydratase, 3-hydroxy-3-methylglutaryl-CoA lyase and initial enzymatic steps of cholesterol biosynthesis in cultured fibroblasts and in different tissues postmortem revealed no enzyme deficiency. Analyses of the respiratory chain in postmortem tissues demonstrated severe impairment of complex I (NADH ubiquinone oxidoreductase) and complex IV (cytochrome c oxidase) activities in skeletal muscle and reduced complex IV activity in heart.

Multiple deletions of mitochondrial DNA in a patient with periodic attacks of paralysis

In this study multiple deletions of mitochondrial genome were found in a patient presenting with periodic attacks of paralysis. Morphological studies revealed mitochondrial abnormalities along with typical histopathological features of periodic paralysis. Southern blot and PCR analysis revealed multiple mtDNA deletions. Our patient could be affected by two unrelated diseases, idiopathic periodic paralysis and presymptomatic mitochondrial myopathy. Alternatively, mtDNA alterations and oxidative deficiency might express themselves phenotypically as periodic paralytic attacks, although this correlation has never been reported.

Pearson's marrow/pancreas syndrome: a histological and genetic study

A patient with features of Pearson's syndrome who presented with transfusion-dependent severe macrocytic anaemia, neutropenia, thrombocytopenia, and insulin-dependent diabetes mellitus in the neonatal period is described. His bone marrow was characterized by marked vacuolization of myeloid precursors and ringed sideroblasts. Autopsy examination revealed fibrosis and steatosis of the liver, reduction in the size and number of the islets, fibrosis and acinar atrophy of the pancreas, vacuolation of renal tubules, glomerulosclerosis, and "ragged red" fibres of skeletal muscles. Analysis of mitochondrial DNA (mtDNA) from the autopsied liver and skeletal muscle showed mtDNA heteroplasmy in both tissues, with one population of mtDNA deleted by 7374 bp. The deleted region was bridged by a single nucleotide, C, in normal mtDNA.

Alpha B-crystallin in oxidative muscle fibers and its accumulation in ragged-red fibers: a comparative immunohistochemical and histochemical study in human skeletal muscle

The alpha B-crystallin gene is abundantly expressed in the vertebrate lens and at lower levels in various non-lenticular tissues. Among the non-lenticular tissues, alpha B-crystallin is present at high levels in the heart and skeletal muscle. Using a specific antibody against alpha B-crystallin, the cellular localization of alpha B-crystallin was studied in biopsies of human skeletal muscles. Expression of alpha B-crystallin was observed in normal oxidative muscle fibers that show positive reactions for NADH-tetrazolium reductase and cytochrome c oxidase. In muscle diseases increased immunoreactivity for alpha B-crystallin was found in ragged-red fibers, which stained darkly with histochemistry for succinate dehydrogenase. Since alpha B-crystallin is related to small heat-shock proteins and can be induced by various stress conditions, the increased alpha B-crystallin immunoreactivity of ragged-red fibers could result from profound oxidative stress produced by the abnormal mitochondrial metabolism.

[Mitochondrial diseases]

Mitochondrial diseases are very complex. Their description, recent but still in progress, makes all classifications risky. In the first part of this article we present the original character of mitochondria, which is due to their functional structure aimed to produce energy, the respiratory chain being fundamental for the phosphorylation/oxidation and ATP production processes. Beside Mendelian transmission, mitochondria have their own DNA which codes for proteins that are few but play an essential role; the nuclear DNA probably has a regulatory effect. For these reasons, explorations of mitochondrial functioning, mainly by morphological, biochemical and genetic techniques, are specific. In the second, clinical part, we analyse the whole range of symptoms and syndromes which includes purely muscular lesions, predominantly nervous lesions and multisystemic lesions. Some syndromes can be individualized on a biochemical basis, whereas other are individualized on a genetic basis involving mainly mutations of mitochondrial DNA. Finally, we merely list lesions the origin of which might be mitochondrial but remains unknown.

Possible X linked congenital mitochondrial cardiomyopathy in three families

Familial cases of childhood congestive cardiomyopathy with X linked recessive inheritance and abnormalities of heart muscle mitochondria have been previously reported. We report here three families with possible X linked congestive cardiomyopathy and specific mitochondrial abnormalities. The heart disorder presented as endocardial fibroelastosis with neonatal death in two brothers in one family, and as heart failure and death in infancy in two brothers in the other two families. In one family a maternal uncle may also have been affected. Pyodermia and neutropenia was reported in one of the boys. Electron microscopy of heart muscle after necropsy showed increased numbers of mitochondria and abnormal mitochondrial crystal condensations and paracrystalline inclusions in all sibships. Barth's syndrome has been mapped to Xq28 and includes cardiomyopathy, skeletal muscle myopathy, neutropenia, and mitochondrial abnormalities similar to those found in the three families reported here. Since the clinical picture differed in the three families, they may represent more than one entity.

Familial visceral myopathy associated with a mitochondrial myopathy

A 27 year old man with intestinal pseudo-obstruction who developed parenteral nutrition induced hyperlipidaemia and who also had ophthalmoplegia and an undifferentiated myopathy is described. Histological examination of biopsy specimens and molecular analysis show that this patient had both familial visceral myopathy and a mitochondrial myopathy, suggesting that a mitochondrial DNA mutation is the molecular lesion in familial visceral myopathy.

Mitochondrial myopathy associated with chronic zidovudine therapy in AIDS

One hundred and eighteen consecutively identified AIDS patients, 88 of whom received zidovudine (1000-1200 mg/day), were followed for 1 year to investigate prospectively the relationship between zidovudine and myopathy. Clinical and biochemical evidence of proximal myopathy was seen in 7 of 41 patients (17%) who had been receiving zidovudine for more than 270 days, but in none of those on short-term therapy and in none of the controls. Serum creatine kinase levels rose a mean of 76 days (range 34-187) before the onset of clinical signs. Creatine kinase returned to normal within 4 weeks of cessation of zidovudine and strength returned within 8 weeks, though loss of muscle bulk persisted. Chronic malaise, anorexia and nausea accompanied the myopathy and remitted within 8 weeks of stopping zidovudine. Muscle histology in four patients with myopathy showed fibre size variation with atrophic, necrotic and degenerating fibres and an absence of inflammation. Ultrastructural studies showed glycogen-packed sarcoplasm, lipid droplets and grossly giant mitochondria. These abnormalities improved substantially after stopping zidovudine. Similar but less marked changes were seen in a zidovudine treated patient without myopathy, but were absent in one AIDS patient not taking the drug. Long-term zidovudine therapy is associated with a mitochondrial myopathy and the constitutional features suggest that it is part of a wider disorder affecting cellular function in other tissues.

Oral glucose lactate stimulation test in mitochondrial disease

We selected 23 patients with neurologic diseases, including 15 boys and 8 girls from 1 month to 10 years of age, who were divided into mitochondrial and nonmitochondrial disease groups. All patients were required to fast and rest for at least 4-10 hours before the test. Glucose was administered orally using a 50% glucose:water solution at a dose of 1.75 mg/kg. Blood samples then were drawn from a retained heparinized venous line at 0, 30, 60, 120, and 180 min and tested for lactate and glucose levels. Of the mitochondrial disease group, 10 of 11 patients had an upward sloping curve of lactate metabolism; the one who had a flat line response was a patient who suffered from a free-fatty-acid metabolic defect presenting with a recurrent Reye-like syndrome. There was a relatively flat line response in the nonmitochondrial disease group except in a patient with alternating hemiplegia whose symptoms responded well to flunarizine therapy. A significant increase in blood lactate content at 60 min after glucose loading occurred in the mitochondrial disease group, in contrast to that of the nonmitochondrial group. Sensitivity and specificity of a 5 mg/dl increase in blood lactate concentration at 60 min was 72.7% vs. 91.7% Moreover, all 4 patients whose blood lactate increased by 13 mg/dl at 60 min were in the mitochondrial disease group.

[Mitochondrial myopathy with peripheral neuropathy]

This paper reported mitochondrial myopathy with peripheral neuropathy of 2 cases. Both patients were males. Age: 22, 32.

DURATION

11, 14 years respectively. They showed recurrent paralysis and asthenia of limbs. Case 1 was motor sensory neuropathy, whose EMG revealed neurogenic injury. Case 2 involved only the lower limbs, whose lactic acid level was increased. In both patients, muscle biopsy showed Ragged Red fibers and abnormal mitochondria. Sural nerve biopsy revealed moderate reduction in the number of mylinated fibers and chronic axonal degeneration without regeneration cluster and hypertrophic neuropathy. Electron microscopic examination showed the increase of Schwann cells and mitochondria, and abnormal mitochondria being less marded in Case 2. Mitochondrial myopathy with peripheral neuropathy and its pathogenesis were discussed.

[Ptosis and asthenia manifesting a mitochondrial myopathy]

We report a case of mitochondrial myopathy discovered in a 55-year old woman who was being investigated for the cause of her asthenia. Physical examination showed ptosis of the upper eyelid and proximal muscle deficit. Histological examination of a muscle biopsy disclosed rare fibres with mitochondrial aggregates. Biochemical exploration of muscle tissue revealed a double enzyme deficit involving complexes I and IV of the respiratory chain. Clinical improvement was obtained after the patient was put on coenzyme Q10. We conclude that a diagnosis of mitochondrial myopathy must be considered in patients, including middle-aged adults, presenting with muscular asthenia.

Molecular analysis of the muscle pathology associated with mitochondrial DNA deletions

Large-scale deletions of mitochondrial DNA (mtDNA) are associated with a subgroup of mitochondrial encephalomyopathies. We studied seven patients with Kearns-Sayre syndrome or isolated ocular myopathy who harboured a sub-population of partially-deleted mitochondrial genomes in skeletal muscle. Variable cytochrome c oxidase (COX) deficiencies and reduction of mitochondrially-encoded polypeptides were found in affected muscle fibres, but while many COX-deficient fibres had increased levels of mutant mtDNA, they almost invariably had reduced levels of normal mtDNA. Our results suggest that a specific ratio between mutant and wild-type mitochondrial genomes is the most important determinant of a focal respiratory chain deficiency, even though absolute copy numbers may vary widely.

Variability of the expression of muscle mitochondrial damage in ocular mitochondrial myopathy

In this study we comparatively analysed deltoid histochemistry, biochemistry and mitochondrial DNA (mtDNA) in two groups of ten sporadic ocular mitochondrial myopathies (OMM), respectively with and without ragged red fibres (RRF). (1) All but one RRF--patients presented the mild form of OMM with blepharoptosis but without ophthalmoplegia; (2) the occurrence of cytochrome c oxidase deficient (COX-) fibres was significantly higher in the RRF+ group, but four RRF- cases also showed COX- fibres; (3) no difference was observed in biochemical findings between the groups; (4) two RRF- patients without COX- fibres showed mtDNA heteroplasmy; (5) in two RRF- patients without deltoid mtDNA deletion, biopsy of an eyelid muscle showed significant mitochondrial alterations. These results suggest that the expression of a mitochondrial defect can vary and that the absence of RRF in a skeletal muscle biopsy does not necessarily rule out the diagnosis of OMM, if other data support that.