Experimental germanium myopathy

Summary The long-term administration of germanium dioxide (GeO₂) to rats produced Ge myopathy characterized by the formation of ragged-red fibers. The earliest pathological changes in experimental Ge myopathy were a decrease in cytochrome c oxidase activity and accumulation of high electron-dense materials in mitochondria. These findings suggest that a mitochondrial dysfunction may be most important in the genesis of experimental Ge myopathy, which could be a useful animal model for the investigation of and therapeutic trials for human mitochondrial myopathies.     

Association of myopathy with large-scale mitochondrial dna duplications and deletions: Which is pathogenic?

We identified large-scale heteroplasmic mitochondrial DNA (mtDNA) rearrangements in a 50–year-old woman with an adult-onset progressive myopathy. The predominant mtDNA abnormality was a 21.2–kb duplicated molecule. In addition, a small population of the corresponding partially deleted 4.6–kb molecule was detected. Skeletal muscle histology revealed fibers that were negative for cytochrome c oxidase (COX) activity and had reduced mtDNA-encoded COX subunits. By single-fiber polymerase chain reaction analysis, COX-negative fibers contained a low number of wild-type or duplicated mtDNA molecules (ie, nondeleted). In situ hybridization demonstrated that the abnormal fibers contained increased amounts of mtDNA compared with normal fibers and that most of the genomes were deleted. We concluded that deleted mtDNA molecules were primarily responsible for the phenotype in this patient.     

Germanium myopathy: clinical and experimental pathological studies

Summary Pathological examinations were carried out on the skeletal muscle of a patient with germanium intoxication. The prominent histochemical finding was vacuolar myopathy with lipid excess, increased acid phosphatase activity and decreased cytochrome c oxidase activity. Ultrastructural lesions revealed a mitochondrial abnormality, autophagic vacuoles and accumulation of high electron-dense materials in deformed mitochondria and at the periphery of lipid droplets. Furthermore, the toxic effect of germanium on skeletal muscle was confirmed by the experimentally induced germanium myopathy, which showed autophagic degeneration, decreased cytochrome c oxidase activity and a mitochondrial abnormality with high electron-dense materials.     

Cytochrome c oxidase deficiency in the muscle of patients with zidovudine myopathy is segmental and affects both mitochondrial DNA- and nuclear DNA-encoded subunits

Zidovudine (AZT) can induce a mitochondrial disorder associated with mitochondrial (mt) DNA depletion affecting skeletal muscle, heart, and liver. Zidovudine myopathy is characterized by ragged-red fibers and partial cytochrome c oxidase (COX) deficiency. We evaluated at a single fiber level the expression of COX II (mtDNA-encoded) and COX IV (nuclear DNA-encoded) subunits in 12 HIV-infected patients with zidovudine myopathy. We also evaluated COX activity on longitudinal muscle sections in one patient. In all patients, evaluation of the expression of COX II and COX IV subunits showed focal deficiency. All fibers negative for COX II or COX IV were negative by COX histochemistry; 32–92% (median 61%) of COX-negative fibers were negative for COX II antigens, and 7–58% (median 28%) were negative for COX IV antigens. One hundred and thirty-nine of 317 COX-negative fibers 139 (43.8%) were selectively negative for COX II; 28 of 317 (8.8%) COX-negative fibers were selectively negative for COX IV. A study of longitudinal distribution of COX activity demonstrated that COX deficiency was segmental with blurred borders, as previously observed in patients with myoclonus epilepsy with ragged-red fibers. We conclude that proteins encoded by mtDNA are predominantly, but not exclusively, involved in zidovudine myopathy. Our results confirm the value of single muscle fiber evaluation in the assessment of mitochondrial abnormalities related to zidovudine. Received: 8 July 1999 / Revised: 6 October 1999 / Accepted: 12 October 1999     

Cytochrome c oxidase reaction improves histopathological assessment of zidovudine myopathy

Zidovudine can induce a mitochondrial myopathy with ragged-red fibers and partial cytochrome c oxidase deficency. In an attempt to improve histological assessment of zidovudine myopathy, we evaluated cytochorme c oxidase histochemical reaction in the muscle of 10 patients with biopsy-proven zidovudine myopathy (Group 1), 10 myopathic immunodeficiency virus (HIV)-infected patients not treated by zidovudine who had an immunohistological profile of HIV-associated myopathy or other neuromuscular disorders (Group 3). Among zidovudine receivers, cytochrome c oxidase deficiency was found in 10 of 10 patients from Group 1 and 7 of 10 from Group 2. No cytochrome c oxidase deficiency was observed in patients not treated by zidovudine. When present, cytochrome c oxidase-negative fibers accounted for 2 to 28% of fibers, and there was no difference for the number of cytchrome c oxidase-negative fibers between Group 1 and Group 2. Most patients with cytochrome c oxidase deficiency that could be evaluated clinically after muscle biopsy improved after withdrawal of zidovudine (5 of 7 in Group 1,5 of 5 in Group 2). Patients who did not improve had an HIV-associated myopathy concurrently with zidovudine myopathy. We conclude that cytochrome c oxidase reaction may be used as a reliable marker of zidovudine mitochondrial toxicity in HIV-infected patients with muscular symptoms.     

Biochemical and genetic studies in a family with mitochondrial myopathy

We present a family with severe exercise intolerance, progressive proximal weakness, and lactic acidemia. Fifteen of 24 family members in five generations were affected. Since the affected males do not have offspring at this time, the family pedigree is consistent with either maternal or autosomal dominant inheritance. Muscle histochemistry showed ragged-red fibers and electron microscopy showed globular mitochondrial inclusions. Biochemical analysis showed reduced muscle activities of mitochondrial NADH-cytochrome c reductase (1 of 2 patients), succinate-cytochrome c reductase (2 patients), and cytochrome c oxidase (2 patients). For 1 patient, sequence analysis of 44% of the muscle mitochondrial DNA including all 22 transfer RNA regions showed no point mutation with pathogenic significance. Southern blot analysis showed no deletion. Six affected members of the family were treated with methylprednisolone (0.25 mg/kg) for 3 months. Muscle strength, serum lactate, and energy metabolism at rest (measured by ³¹P magnetic resonance spectroscopy) significantly improved with treatment. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20: 1219–1224, 1997     

核黄素反应性脂质沉积性肌病的临床和病理特征

目的 探讨核黄素反心性脂质沉积性肌病的临床和病理特征。方法 回顾性分析4例核黄素反应性脂质沉积性肌病患者的临床资料结果本组4例患者表现为亚急性起病的四肢近端和躯干肌无力,不能耐受疲劳,3例患者有颈肌和脊旁肌萎缩、无力,2例有明显的咀嚼肌无力。2例肌电图示肌源性损害,1例示双侧胫神经传导速度轻度减慢。肌肉活检发现肌纤维内大量脂肪沉积,未见肌纤维坏死和再生,改良Gomorii色染色、琥珀酸脱氢酶和细胞色素C氧化酶染色以及电镜观察未发现有线粒体酶活性缺失,以及线粒体结构和数量的异常改变。应用维小素B2单药治疗后2例明显好转,2例痊愈。2例患者分别在治愈后1年、5年复发,重新给予维生素B2治疗仍然有效。结论 本病多以颈肌、脊旁肌和咀嚼肌受累,病理特征为肌肉脂肪沉积,无线粒体异常改变。维生素B2单一治疗对本病有显著疗效,此亦可与其他肌病鉴别。     

Mitochondrial myopathy with dystrophic features due to a novel mutation in the MTTM gene

Introduction: A 61‐year‐old woman with a 5‐year history of progressive muscle weakness and atrophy had a muscle biopsy characterized by a combination of dystrophic features (necrotic fibers and endomysial fibrosis) and mitochondrial alterations [ragged‐red, cytochrome c oxidase (COX)‐negative fibers]. Methods: Sequencing of the whole mtDNA, assessment of the mutation load in muscle and accessible nonmuscle tissues, and single fiber polymerase chain reaction. Results: Muscle mitochondrial DNA (mtDNA) sequencing revealed a novel heteroplasmic mutation (m.4403G>A) in the gene (MTTM) that encodes tRNA^Met. The mutation was not present in accessible nonmuscle tissues from the patient or 2 asymptomatic sisters. Conclusions: The clinical features and muscle morphology in this patient are very similar to those described in a previous patient with a different mutation, also in MTTM, which suggests that mutations in this gene confer a distinctive “dystrophic” quality. This may be a diagnostic clue in patients with isolated mitochondrial myopathy. Muscle Nerve 50:292–295, 2014     

Inflammatory myopathy with cytochrome oxidase negative muscle fibers: Methotrexate treatment

Inflammatory myopathy with cytochrome oxidase negative muscle fibers (IM/COX−) is characterized by slowly progressive weakness, most prominent in the quadriceps, muscle fibers with reduced COX staining and mitochondrial DNA mutations, and a poor response to corticosteroid treatment. We reviewed records of quantitative measurements of muscle strength in 7 IM/COX− patients to evaluate the outcomes after treatment with oral, once weekly, methotrexate for an average of 15 months. We compared the results to 6 patients with IM/COX− who received no long-term immunosuppression, and to 4 with inclusion body myositis (IBM) who received methotrexate during the same period. Methotrexate treatment of IM/COX− was followed by improved muscle strength in 5 of 7 patients, averaging 17 ± 5%. In contrast, there was no improvement in the strength of 6 untreated IM/COX− patients (−6 ± 4%; P = 0.003), or 4 methotrexate-treated IBM patients (1 ± 2%; P = 0.03). We conclude that, despite clinical similarities to inclusion body myositis, which is usually refractory to immunosuppressive therapy, strength in IM/COX− appears to improve with methotrexate treatment. Biopsy studies of inflammatory myopathies with evaluation of muscle for mitochondrial changes and vacuoles can help to direct the choice of appropriate immunomodulating treatments. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21: 1724–1728, 1998     

Mosaicism of mitochondria in mitochondrial myopathy: an electronmicroscopic analysis of cytochrome c oxidase

Summary Electron microscopic histochemistry was applied to the study of cytochrome c oxidase activity in each mitochondrion of biopsied muscles from four patients with mitochondrial myopathy [one case of fatal infantile mitochondrial myopathy, one case of myoclonus epilepsy associated with ragged-red fibers (MERRF), and two cases of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS)]. In the patient with fatal infantile mitochondrial myopathy, intercellular heterogeneity of mitochondria was recognized. In the three patients with either MERRF or MELAS, cytochrome c oxidase activity was segmentally changed from positive to negative within single muscle fibers. In the two patients with MELAS, small groups of positive-stained mitochondria were located among negative-stained mitochondria in the negative segment of a few muscle fibers. These findings revealed that there were heterogeneous populations of normal and abnormal mitochondria intracellularly or intercellularly within the muscles of these patients.Supported in part by Grant-in-Aid for Scientific Research 63570422 from the Ministry of Education, Science and Culture, and Grant 62A-5-08 from the National Center of Neurology and Psychiatry (NCNP) of the Ministry of Health and Welfare, Japan     

Single muscle fiber analysis of mitochondrial myopathy,encephalopathy, lactic acidosis,and stroke-like episodes (MELAS)

We examined muscle sections from 3 patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), using single-fiber polymerase chain reaction, histochemistry, and in situ hybridization. Most type 1 ragged-red fibers showed positive cytochrome c oxidase activity at the subsarcolemmal region, while type 2 ragged-red fibers had little cytochrome c oxidase activity. However, there was no difference in the amount of total (mutant and wild-type) mitochondrial DNAs (mtDNAs) and the proportion of mutant mtDNA between type 1 and type 2 ragged-red fibers. These observations suggest that mitochondrial proliferation and nuclear factors affect muscle pathology, including cytochrome c oxidase activity, in MELAS. Total mtDNAs were greatly increased in ragged-red fibers (about 5–17 times over those in non–ragged-red fibers). The proportion of mutant mtDNA was significantly higher in ragged-red fibers (88.1 ± 5.5%) than in non–ragged-red fibers (63.2 ± 21.6%). Thus, the amount of wild-type mtDNA as well as mutant mtDNA was increased in ragged-red fibers in MELAS, failing to support the contention of a replicative advantage of mutant mtDNA. The proportion of mutant mtDNA was significantly higher in the strongly succinate dehydrogenase–reactive blood vessels (83.2 + 4.2%) than in non–succinate dehydrogenase–reactive blood vessels (38.8 ± 16.2%). It seems likely that systemic vascular abnormalities involving cerebral vessels lead to the evolution of stroke-like episodes in MELAS.     

Quantitative evaluation of electron transport system proteins in mitochondrial encephalomyopathy

Summary The levels of mitochondrial electron transport system proteins cytochrome c oxidase (COX) and complex III were measured in muscle fibers of patients with mitochondrial encephalomyopathy using quantitative immunoelectron microscopy. In a patient with Leigh's encephalopathy, immunoreactive COX protein was decreased to 20% of the normal mean value in all muscle fibers examined, while the amount of complex III was within the normal range. In a patient with fatal infantile COX deficiency, the level of COX protein was found to be decreased to 27–40% of the normal value in all muscle fibers examined. In patients with mitochondrial myopathy, encephalopathy, lactic acidosis associated with stroke-like episodes (MELAS) and chronic progressive external ophthalmoplegia (CPEO), COX protein levels were decreased to 20% of normal in muscle fibers lacking COX activity. In normal fibers, however, COX protein levels were also normal. The amount of complex III protein was normal in COX-deficient muscle fibers. In two patients, in situ hybridization was performed for detection of mitochondrial mRNA. Mitochondrial mRNAs were found to be abundant in muscle fibers with decreased COX protein, suggesting a defect at the mitochondrial protein-synthesis level in a COX-deficient muscle fiber.Supported in part by a Grant-in-Aid for Scientic Research No. 63570422 from the Ministry of Education, Science and Culture, and Grant No. 32A-5-08 from the National Center of Neurology and Psychiatry of the Ministry of Health and Welfare, Japan     

AZT-induced mitochondrial myopathy

Histochemical, electron microscopy and biochemical studies were performed on muscle biopsy specimens from 11 AIDS patients treated with zidovudine. A peculiar association of structural abnormalities and mitochondrial dysfunction was found. Focal cytochrome c oxidase (COX) deficiency was evident in muscle sections from 9 patients, 8 of whom had received long-term treatment while one had been treated for 1 month only. Electron microscopy showed changes in number, size and structure of mitochondria. Biochemical studies proved partial COX and succinate cytochrome c reductase (SCR) deficiency in 4 patients; one patient had only reduced SCR activity. Our data confirm that AZT therapy can cause toxic myopathy with mitochondrial dysfunction.Paper presented at the National Congress at Sorrento in 1991 and selected by the Editorial Board of the Journal     

Multiple mitochondrial DNA deletions in hereditary inclusion body myopathy

We have recently described an autosomal dominant hereditary inclusion body myopathy (h-IBM). Clinically it is is characterized by congenital joint contractures and slowly progressive, proximal muscle weakness and ophthalmoplegia. There is deterioration of muscle function between 30 and 50 years of age. While young patients show minor pathological changes in muscle, the middle-aged and old patients show rimmed vacuoles and inclusions of filaments measuring 15–18 nm in diameter. Except for the absence of significant inflammation the histopathology is similar to that found in sporadic inclusion body myositis (s-IBM). In s-IBM mitochondrial alterations including cytochrome c oxidase (COX) -deficient muscle fibers are common. These are due to multiple mitochondrial DNA (mtDNA) deletions. In this study we investigated the occurrence of mitochondrial alterations in autosomal dominant h-IBM. Young affected individuals showed no mitochondrial changes but three patients aged 38, 51 and 59 years, respectively, showed ragged red fibers and COX-deficient muscle fibers. Polymerase chain reaction analysis showed multiple mtDNA deletions. By in situ hybridization clonal expansions of mtDNA with deletions were demonstrated in COX-deficient muscle fibers. Most of the analyzed deletion breakpoints showed nucleotide repeats flanking the deletions. The results show that COX-deficient muscle fibers and somatic mtDNA deletions are present in this family with h-IBM. The same factors may be involved in the development of mtDNA deletions in s-IBM and this family with h-IBM. Received: 13 July 1999 / Revised: 6 October 1999 · Accepted: 12 October 1999     

Study of mitochondrial DNA depletion in muscle by single-fiber polymerase chain reaction

We studied muscle biopsies from 3 children with a mitochondrial myopathy characterized histochemically by the presence of ragged-red fibers (RRF) and various numbers of cytochrome c oxidase (COX)-negative fibers. We quantitated the absolute amounts of total mitochondrial DNA (mtDNA) in isolated normal COX-positive muscle fibers and in COX-negative RRF. There was severe mtDNA depletion in all fibers from the two most severe cases. In the third case mtDNA depletion could not be established with conventional diagnostic tools, but it was documented in single COX-negative fibers; COX-positive fibers showed the same amounts of mtDNA as fibers from aged-matched controls. Our observations indicate that mtDNA single-fiber PCR quantitation is a highly sensitive and specific method for diagnosing cases with focal mtDNA depletion. This method also allows one to correlate amounts of mtDNA with histochemical phenotypes in individual fibers from patients and age-matched controls, thereby providing important information about the functional role of residual mtDNA. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21: 1374–1381, 1998     

Mitochondrial myopathy with exercise intolerance and retinal dystrophy in a sporadic patient with a G583A mutation in the mt tRNA(phe) gene

We describe a second patient with the 583G>A mutation in the tRNA(phe) gene of mitochondrial DNA (mtDNA). This 17-year-old girl had a mitochondrial myopathy with exercise intolerance and an asymptomatic retinopathy. Muscle investigations showed occasional ragged red fibers, 30% cytochrome c oxidase (COX)-negative fibers, and reduced activities of complex I+IV in the respiratory chain. The mutation was heteroplasmic (79%) in muscle but undetectable in other tissues. Analysis of single muscle fibers revealed a significantly higher level of mutated mtDNA in COX-negative fibers. Our study indicates that the 583G>A mutation is pathogenic and expands the clinical spectrum of this mutation.     

Mitochondrial myopathy with progressive decrease in mitochondrial tRNALeu(UUR) mutant genomes

A female patient with mitochondrial myopathy had a mitochondrial DNA mutation at nucleotide pair 3243, commonly seen in patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS), but unlike MELAS patients, she had no central nervous system symptoms. Muscle weakness, which was most severe when she was 7 years old, improved gradually with age. Comparison of two muscle biopsies obtained at an interval of 12.5 years (7 and 20 years of age, respectively), revealed that the number of ragged-red fibers was markedly decreased and histochemical cytochrome c oxidase activity increased in parallel with the decrease in population of mutant genomes.     

Congenital or late-onset myopathy in patients with the T14709C mtDNA mutation

Three patients with different clinical phenotypes harbored the same point mutation at nucleotide 14709 (T14709C) in the tRNAGlu gene of mitochondrial DNA (mtDNA). The first patient was a 21-month-old child with severe congenital myopathy, respiratory distress and mild mental retardation. Muscle biopsy showed about 12% cytochrome c oxidase (COX)-negative ragged-red fibers (RRFs), and markedly decreased activities of mitochondrial respiratory chain complexes I, III and IV. The other two patients were 51- and 55-year-old siblings with slowly progressive myopathy and diabetes mellitus. Muscle biopsy showed focal COX-negative RRFs and decreased activities of complexes I, III and IV. In all three patients, the T14709C mutation was abundant in muscle but present at lower levels in accessible tissues. Previously described patients with the same mutation also showed congenital or late-onset myopathy. Diabetes is frequently associated with both phenotypes and is a clinical clue to the molecular diagnosis.     

The composition of cellular infiltrates in anti‐HMG‐CoA reductase‐associated myopathy

Introduction: To characterize cellular infiltrates in muscle biopsies from patients with anti‐3‐hydroxy‐3‐methyl‐gulatryl‐CoA reductase (HMGCR)‐associated myopathy. Methods: Biopsies from 18 anti‐HMGCR myopathy and 7 control dermatomyositis patients were analyzed. Results: CD4+ and CD8+ T‐cells were scattered within the endomysium in 50% of anti‐HMGCR biopsies. All anti‐HMGCR biopsies included increased endomysial and/or perivascular CD163+ M2 macrophages; CD11c+ M1 macrophages were present in 18.8%. CD123+ plasmacytoid dendritic (PD) cells were observed within the endomysium and perivascular spaces in 62.5% of anti‐HMGCR biopsies. Membrane attack complex was deposited on endothelial cells in 50% and on the sarcolemma of nonnecrotic muscle fibers in 85.7% of anti‐HMGCR cases. Major histocompatibility complex class I antigen was up‐regulated in 87.5% of the anti‐HMGCR cases. Conclusions: In addition to necrosis, scattered CD4+, CD8+, and PD cells are characteristic of anti‐HMGCR myopathy. Predominant M2 polarization suggests infiltrating macrophages are more likely to be involved with tissue repair than destruction. Muscle Nerve, 2015. Muscle Nerve 52 : 189–195, 2015     

Increase in oxidative key enzymes in a case of muscle ubiquinol-cytochrome c reductase deficiency

In a 29-year-old patient suffering from exertional muscle intolerance with a ubiquinol-cytochrome c reductase deficiency related to a cytochrome b gene point mutation of the mitochondrial DNA, we conducted a study the aims of which were: (1) to test whether changes in the maximum activities of muscle key enzymes of the main energy-producing pathways occur, (2) to address the issue of whether fibers of different types are equally affected in their enzymatic machinery involved in energy production, and (3) to correlate the results obtained with histochemical and ³¹P NMR spectroscopy data. When compared to results obtained in six normal subjects, our study clearly shows that the type I fibers of the patient virtually all contained subsarcolemmal mitochondrial aggregates and increased activities of succinate dehydrogenase and cytochrome c oxidase; microdissected type I fibers also displayed a significant increase in both citrate synthase and β-hydroxyacyl-CoA dehydrogenase, two key enzymes of mitochondrial oxidative metabolism. Despite these changes in the patient’s muscle, its whole energy-producing machinery remained impaired as revealed by a slowed post-exercise recovery of phosphocreatine. Received: 11 June 1996 / Revised: 25 September 1996 / Accepted: 18 November 1996