Mitochondrial DNA deletions in inherited recurrent myoglobinuria

We describe two brothers with inherited recurrent exertional myoglobinuria and alcohol intolerance associated with distinct morphological abnormalities of muscle mitochondria and multiple deletions of muscle mitochondrial DNA. Patient 1 (26 years old) and Patient 2 (21 years old) had recurrent episodes of myoglobinuria provoked by strenuous exercise or alcohol intake, from the age of 18 years. Although their serum lactate and pyruvate levels were normal at rest, they were significantly elevated by aerobic exercise. Histochemistry of their biopsied limb muscles showed ragged-red fibers and cytochrome c oxidase-negative fibers as well as degenerating and regenerating fibers. Electron microscopy showed pronounced accumulation of abnormal mitochondria containing paracrystalline inclusions and moderate increases of glycogen particles. The enzyme activities of the electron-transfer complexes in the isolated muscle mitochondria of Patient 2 were within normal ranges. Southern blot analysis revealed multiple deletions of mitochondrial DNA, some of which were common between the patients. Polymerase chain reaction of their muscle mitochondrial DNA detected multiple abnormal fragments indicating mitochondrial DNA deletions. We propose that a defect of the mitochondrial energy-transducing system due to multiple mitochondrial DNA deletions is a novel genetic cause of inherited recurrent myoglobinuria.     

Mitochondrial DNA deletions in mitochondrial cytopathies: observations in 19 patients.

Among 56 patients with mitochondrial myopathies or cytopathies, 19 had large-scale deletions of mitochondrial DNA (mtDNA). Consistent with previous observations, all 19 had progressive external ophthalmoplegia and 12 had complete or partial Kearns-Sayre syndrome. One of two patients in whom mitochondrial rather than whole muscle DNA was analyzed had multiple populations of deleted mtDNA (dmtDNA). In all patients, the length of dmtDNA was inversely related to age of onset, but was not related to multiplicity of organ involvement. Patients with greater than 50% dmtDNA tended to have an earlier onset of symptoms and a higher proportion of ragged-red fibers and cytochrome c oxidase (CCO)-negative fibers than patients with less than 50% dmtDNA, but these differences did not reach statistical significance. In some patients, CCO-negative fibers were more abundant than ragged-red fibers, indicating that the distribution of abnormal mitochondria can be more widespread than suggested by the frequency of ragged-red fibers. In biochemical assays, citrate synthase activity was a better reference for detecting defects in the respiratory complexes than the wet weight of muscle. Using this reference, 10 of 14 patients had one or more respiratory complex defects, and 74% of the observed defects could be correlated with an appropriate mtDNA deletion.     

Ophthalmoplegia plus with morphological and chemical studies of cerebellar and muscle tissue

A case resembling the syndrome of “ophthalmoplegia plus” is reported. Chemical and morphological studies on biopsied tissue from the cerebellum, ocular, and somatic muscle revealed abnormal mitochondria in all three tissues. There were no abnormalities in cerebellar lipids. While this case is clinically similar to cases of ophthalmoplegia plus and has mitochondrial changes similar to oculocraniosomatic neuromuscular disease with “ragged-red” fibers, no “ragged-red” fibers or lipid accumulations were observed in any of the muscle tissue examined. Ophthalmoplegia plus may be a neurogenic rather than myopathic disorder with associated mitochondrial dysfunction.     

Severe mitochondrial cytopathy with complete A-V block,PEO, and mtDNA deletions

We describe a 17-year-old male with neurologic and cardiovascular disorders characterized by complete atrioventricular block and a mitochondrial cytopathy with clinical, structural, biochemical, and molecular features shared by chronic progressive external ophthalmoplegia and Kearns-Sayre syndrome. The patient's manifestations included progressive external ophthalmoplegia, bilateral ptosis, muscle weakness, delayed development, and progressive hearing loss with multiple mitochondrial DNA deletions, including an abundant 11-kb novel deletion and reduced specific activities of respiratory complexes I, III, and IV present in skeletal muscle. Ultrastructural analysis of biopsied muscle revealed a heterogenous mixture of normal and abnormal mitochondria with unusual cristae. This unique mitochondrial DNA deletion, which eliminates the origin of mitochondrial DNA replication for the light strand, may be responsible for generating an intermediate clinical phenotype.     

Unusual presentations of patients with the mitochondrial MERRF mutation A8344G

MERRF is typically characterized by myoclonus, generalized seizures and ragged-red fibers in muscular biopsy. We report a family (harbouring the A8344G mutation) with a late onset of the disease and an uncommon clinical manifestation, including episodes of reversible respiratory failure, the presence of ophthalmoplegia, and the absence of seizures and myoclonus in most subjects. We conducted histochemical, biochemical and molecular genetic studies. Mutation analysis revealed that the level of mutated mitochondrial DNA (mtDNA) was above 80% in the skeletal muscle of all siblings. Nevertheless, one severely affected individual did neither present cytochrome c oxidase-negative fibers nor ragged-red fibers in the skeletal muscle biopsy. These data extend the phenotypic range associated with the MERRF syndrome. We suggest that the analysis of mtDNA could be of importance in many cases of unclear multisystem disorders in later life.     

Mitochondrial myopathy, parkinsonism, and multiple mtDNA deletions in a Sephardic Jewish family

The authors describe a family of Sephardic Jews with progressive external ophthalmoparesis, skeletal muscle weakness, and parkinsonism. Autosomal recessive inheritance was suggested by many consanguineous marriages, although a dominant disorder could not be excluded. No linkage to known progressive external ophthalmoparesis locus was found. The presence of cytochrome c oxidase-negative ragged-red fibers, biochemically reduced respiratory chain complexes, and multiple mitochondrial DNA deletions in muscle biopsies from four patients suggested a new mitochondrial disorder of intergenomic communication.     

Familial mitochondrial encephalomyopathy with deaf-mutism, ophthalmoplegia and leukodvstrophy.

We report two sisters (32 and 36 years old) with familial deaf-mutism, progressive external ophthalmoplegia, leukodystrophy and mitochondrial myopathy. T2-weighted brain MRI demonstrated diffuse symmetrical high intensity areas in the white matter. Their muscle biopsies showed ragged-red fibers and cytochrome c oxidase (CCO)-negative fibers. CCO activity in biopsied muscle decreased to about 20% of normal control. They had no deletions of the mitochondrial DNA and no point mutations in mitochondrial tRNA. Their brother was diagnosed as having Kugelberg-Welander disease, grand mal seizures and urinary dysfunction. Their parents and grandparents had consanguinity. Three relatives were found to have deaf-mutism without accompanying ophthalmoplegia. This rare combination of mitochondrial encephalomyopathy and familial deaf-mutism might be caused by a nuclear DNA mutation in these sisters.     

Residual muscle cytochrome c oxidase activity accounts for submaximal exercise lactate threshold in chronic progressive external ophthalmoplegia

The data from histological, biochemical, and mitochondrial DNA (mtDNA) studies of muscle biopsies from 10 patients affected with chronic progressive external ophthalmoplegia (CPEO) were related to dynamic and metabolic parameters of incremental submaximal exercise. Maximum power output was reduced in all patients as compared to controls. Analysis of the venous lactate curve during exercise revealed a lactate threshold at exercise levels ranging from 40 to 50% of the predicted maximal power output. An earlier significant increase in lactate could be detected by calculating the mean δ lactate. Lactate values were inversely correlated with the cytochrome c oxidase (COX) activity of isolated muscle mitochondria. No relationship was found between lactate values and the number of ragged red fibers, or cytochrome c oxidase-negative fibers or the proportion of deleted mtDNA measured in muscle biopsy specimens. The discussion underscores the value of lactate kinetics in assessing skeletal muscle function, as well as the use of muscle COX levels to predict the effectiveness of wild-type complementation of deleted skeletal muscle mtDNA in in vivo contractile performance of CPEO subjects. © 1996 John Wiley & Sons, Inc.     

Kearns-Sayre syndrome with a novel mitochondrial DNA deletion

We describe a 17-year-old boy with a clinical neurologic picture consistent with Kearns-Sayre syndrome. His manifestations included progressive external ophthalmoplegia, bilateral ptosis, retinitis pigmentosa, and muscle weakness. He was found to harbor an abundant novel deletion in skeletal muscle mitochondrial DNA. Biochemical analysis of the patient's biopsied skeletal muscle showed that the specific activities of all four respiratory complexes with mitochondrial DNA-encoded subunits were markedly reduced in contrast to normal activity levels of entirely nuclear DNA-encoded enzyme activities (eg, complex II and citrate synthase). Ultrastructural analysis also indicated the presence of strikingly abnormal mitochondria with both unusual cristae and frequent paracrystalline inclusions. The great amount of the deleted mitochondrial DNA in this patient's muscle, as well as the concomitant reduction in specific respiratory complex activity, suggests that the mitochondrial DNA deletion plays a role in the pathogenesis of this neurologic disease.     

Contrasting histochemical features of various mitochondrial syndromes

A comparative histochemical analysis of the prevalence and cytochrome oxidase staining characteristics of ragged-red fibres in limb skeletal muscles was performed in 19 patients spanning four distinct mitochondrial syndromes: chronic progressive external ophthalmoplegia; myoclonus epilepsy with ragged-red fibres; mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes; and pure limb myopathy. The percentage occurrence of non-ragged red but cytochrome oxidase negative fibres was additionally noted. Ragged-red fibres and cytochrome oxidase-negative fibres were generally more prevalent in the chronic progressive external ophthalmoplegia syndrome than in myoclonus epilepsy ragged-red fibres syndrome or mitochondrial myopathy encephalopathy lactic acidosis and stroke-like episodes syndrome. Isolated cytochrome oxidase-negative fibres were a common finding in each phenotypic syndrome except pure limb myopathy and could involve any of the major fibre types non-specifically. Ragged-red fibres were devoid of cytochrome oxidase activity in chronic progressive external ophthalmoplegia, but commonly displayed activity in the other three syndromes providing a clue to syndromal differentiation on a histochemical basis.     

Immunocytological and histochemical correlation in Kearns-Sayre syndrome with mtDNA deletion and partial cytochrome c oxidase deficiency in skeletal muscle

We report histochemical, immunocytochemical, biochemical and molecular studies of skeletal muscle from a 23-year-old man with Kearns-Sayre syndrome. Southern blot analysis revealed a 4.7 kb heteroplasmic deletion of the mitochondrial DNA mapping within genes coding for subunits of complexes I, IV and V of the respiratory chain and for tRNA. Cytochrome c oxidase activity was decreased by 30% in isolated muscle mitochondria, without alteration of the Km. Histochemical and immunocytochemical correlation studies for cytochrome c oxidase revealed a lack of activity in 34% of individual muscle fibers including all the typical ragged-red fibers and a low percentage of immunodeficient fibers.     

Vascular pathology in chronic progressive external ophthalmoplegia with ragged-red fibers]

Vascular involvement in biopsied muscle specimens from 11 patients with chronic progressive external ophthalmoplegia (CPEO) with ragged-red fibers (RRF) was studied. Almost none of 69 intramuscular arteries examined were strongly stained with succinate dehydrogenase (SDH) except one patient who had 2 SSV (strongly SDH-reactive blood vessels) in his muscle biopsy. Although RRF and focal cytochrome c oxidase (CCO) deficiency in muscle fibers were the common histochemical changes in muscle biopsy specimens from CPEO patients, all mitochondria in both endothelial and smooth muscle cells of the arteries had normal morphology except for the two SSV and all mitochondria in the blood vessels had normal CCO activity by electron cytochemistry. The findings obtained from the present study were quite different from those in mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), and myoclonus epilepsy associated with ragged-red fibers (MERRF) in which the striking vascular involvement with SSV is the most common and major abnormality in muscle biopsy specimens. To study vascular involvement in mitochondrial encephalomyopathies is the one of very important clues to understand the pathophysiology of phenotypic expressions in mitochondrial encephalomyopathies.     

Clonal expansion of mitochondrial DNA with multiple deletions in autosomal dominant progressive external ophthalmoplegia

Sporadic progressive external ophthalmoplegia and Kearns-Sayre syndrome are usually associated with single large-scale mitochondrial DNA deletions in muscle. In progressive external ophthalmoplegia with autosomal dominant inheritance, multiple mitochondrial DNA deletions have been reported. We studied several members of a Swedish family with autosomal dominant progressive external ophthalmoplegia and multiple mitochondrial DNA deletions by polymerase chain reaction analysis of singl emuscle fibers and by in sit hybridization, combined with enzyme histochemical analysis. Muscle fiber segments with deficiency of cytochrome c oxidase, which is partially encoded by mitochondrial DNA, had accumulated mitochondrial DNA with deletions and showed reduced levels of wild-type mitochondrial DNA. The deletions varied between individual muscle fibers. There was one predominant deletion in each cytochrome c oxidase-deficient muscle fiber segment. Sequencing of the deletion breakpoints showed that most but not all of the deletions were flanked by direct repeats. Young, clinically affected individuals of this family without limb muscle symptoms did not show mitochondral DNA deletions or cytochorme c oxidase-deficient muscle fibers. Our result indicate that a nuclear factor predisposes to the developement of somatic multiple mitochondrial DNA deletions. Mitochondrial DNA with multiple different deletions shows clonal expansion, which leads to mitochondrial myopathy with ragged-red fibers and muscle weakness.     

Superoxide dismutases of muscle in mitochondrial encephalomyopathies

Lmmunohistochemical analyses were made of the superoxide dismutases (Mn-SOD and CuiZn-SOD) in biopsied muscles from 7 patients with mitochondrial encephalomyopathies that included mitochondrial encephalomyopathy, lactic acidosis and strokelike episodes (MELAS), and chronic progressive external ophthalmoplegia (CPEO). Mn-SOD mainly was present in the subsarcolemmal region, but it also was found in a coarsely granular, reticular, or diffuse pattern of staining within the muscle fibers. These Mn-SOD-positive fibers corresponded almost completely to the ragged-red fibers. The immunoreaction for CuiZn-SOD was weakly positive in some of the muscle fibers positive for Mn-SOD. In CPEO, Mn-SOD-positive fibers predominantly showed decreased cytochrome c oxidase (COX) activity. In MELAS, Mn-SOD-positive fibers tended to be stained deeply for COX although a few were COX-negative. These findings suggest that Mn-SOD-positive fibers can be used to make a differential diagnosis between CPEO and MELAS and that in mitochondrial encephalomyopathies Mn-SOD in the raggedred fibers may protect against oxidative stress. © John Wiley & Sons, Inc.     

Mitochondrial damage in patients with long-term corticosteroid therapy: development of oculoskeletal symptoms similar to mitochondrial disease

Two patients with long-term corticosteroid administration sporadically developed limb muscle wasting followed by ophthalmoplegia, and the skeletal muscle pathology revealed ragged-red fibers (RRFs) with abnormal mitochondria, in addition to the findings of corticosteroid myopathy. The oculoskeletal symptoms of the present cases resemble those of chronic progressive external ophthalmoplegia, a type of mitochondrial disease. The ocular muscles have more RRFs than limb muscles, and large multiple deletions of mitochondrial DNA was detected in ocular and limb muscles of the two patients by PCR but not by Southern blotting. Immunohistochemistry demonstrated that 8-hydroxy-deoxyguanosine (8-OH-dG) and 4-hydroxy-2-nonenal were intensely stained in skeletal muscles of these patients particularly in RRFs. High-performance liquid chromatography with electrochemical detection analysis revealed an increase in 8-OH-dG from mitochondrial DNA. These findings may suggest that long-term corticosteroid administration potentially induces oxidative stress-mediated mitochondrial damage, resulting in the development of the oculoskeletal symptoms in some patients.     

A case of chronic progressive external ophthalmoplegia associated with familial hypercholesterolemia]

A 52-year-old woman with chronic progressive external ophthalmoplegia (CPEO) with familial hypercholesterolemia (FH) was reported. Her mother died from heart disease, and her elder sister has hypercholesterolemia with swelling of Achilles tendons. She had slowly progressive external ophthalmoplegia, bilateral ptosis, swelling of Achilles tendons since twenties. At 40 years of age, she was pointed out hypercholesterolemia. Physical examination was within normal limits except for bilateral swelling of Achilles tendons. Neurological findings showed bilateral ptosis, disturbance of eye movements, mild proximal muscle weakness and dysesthesia in bilateral hands. Routine laboratory findings were within normal limits except for high serum cholesterol level (512 mg/dl). In the biopsied muscle, there was mild variation in fiber size with several ragged-red fibers and focal cytochrome c oxidase defective fibers. Biochemical analysis of the biopsied muscle revealed normal values in the mitochondrial fraction. Southern blot analysis of the mitochondrial DNA (mtDNA) of the muscle disclosed mixed population of mtDNA, consisting of the normal one and partially deleted (4.9-kilobase). Southern blot analysis of the leukocytes from the patient against the cDNA of LDL receptor was normal at least using the restriction enzyme of BglII, XbaI, EcoRI, PvuII and BamHI. This case has CPEO with deleted mtDNA associated with familial hypercholesterolemia, which is caused to nuclear DNA abnormalities, and is thought to be an important case for us to study the relationship between deleted mtDNA and abnormal nuclear DNA in CPEO.     

Muscle histopathology in myoclonus epilepsy with ragged-red fibers (MERRF).

Histopathologic findings were examined in skeletal muscle biopsies from 6 patients with myoclonus epilepsy with ragged-red fibers (MERRF) who had an A to G base substitution at mitochondrial DNA (mtDNA) nucleotide pair 8344. In addition to variation in fiber size and ragged-red fibers, all specimens in cross sections showed focal cytochrome c oxidase (CCO) deficiency, suggesting that this finding is crucial in elucidating the role of the mutant mtDNA in the pathogenesis of this disorder. Along the length of single muscle fibers, defects in CCO activity were distributed segmentally with blurred borders in 5 patients which were in contrast with segmental defects with sharply delineated borders seen in chronic progressive external ophthalmoplegia with deleted mtDNA. These morphologically heterogeneous defects in CCO activity may in part be due to differing populations of and distributions of wild and mutants mtDNAs.     

A new mitochondrial point mutation in the transfer RNA(Leu) gene in a patient with a clinical phenotype resembling Kearns-Sayre syndrome.

OBJECTIVE: To report on the molecular identification of a novel heteroplasmic G-to-A transition at mitochondrial DNA position 3249 in transfer RNA(Leu) gene in a patient with a clinical phenotype resembling Kearns-Sayre syndrome. PATIENT AND METHODS: A 34-year-old patient had been suffering for more than 10 years from progressive visual failure, neurosensorial hearing loss, exercise intolerance, muscle weakness, paresthesia in the lower limbs, and difficulties swallowing. Clinical examination revealed generalized muscle wasting, ptosis, external ophthalmoplegia, and ataxia. Ophthalmologic examination showed dystrophic features in the cornea and retina. In skeletal muscle, morphologic and biochemical studies of the respiratory chain complexes were performed. Polymerase chain reaction, single-strand conformation polymorphism, and direct sequencing were used to screen for mutations in the 22 mitochondrial transfer RNA genes. RESULTS: In skeletal muscle, a significantly decreased catalytic activity of complex I was detected by spectrophotometric analysis and numerous cytochrome c oxidase-negative ragged-red fibers were seen on morphologic examination. A G-to-A substitution 3249 (G3249A) mutation was found in the transfer RNA(Leu) gene of the patient and mutant mitochondrial DNA represented 85% of the total in skeletal muscle but only 45% in leukocytes. The mutation was shown to be present in a small fraction in leukocytes from the unaffected mother and to be absent in leukocytes from the healthy sister. CONCLUSIONS: A causal relationship between a heteroplasmic G3249A transfer RNA(Leu) mutation in a patient suffering from progressive external ophthalmoplegia, retinal dystrophy, ataxia, neurosensorial hearing loss, and muscle wasting is postulated. To our knowledge, the G3249A mutation has never previously been described and was not detected in control subjects.     

Myoclonic epilepsy and ragged-red fibers with cytochrome oxidase deficiency: neuropathology, biochemistry, and molecular genetics

A 36-year-old man with myoclonic epilepsy and ragged-red fibers (MERRF) died after more than 18 years of follow-up study. He was 1 of 3 affected siblings and the offspring of an affected mother, suggesting maternal transmission. At autopsy, there was neuronal loss and gliosis in the dentate nucleus of the cerebellum and in the inferior olivary nucleus. Skeletal muscle showed ragged-red fibers, and paracrystalline inclusions in mitochondria by electron microscopy. Biochemical analysis showed a generalized partial defect of cytochrome c oxidase (COX) in mitochondria isolated from all tissues, including brain, heart, skeletal muscle, kidney, and liver. The Michaelis constant (Km) for cytochrome c was abnormally low, suggesting a defect of the mitochondrially encoded subunit II of COX. Immunological studies (enzyme-linked immunosorbent assay, dot-blot, Western blot, and immunohistochemistry) showed that the holoenzyme was decreased but subunit II was decreased more than the holocomplex or the nuclearly encoded subunit IV. However, Northern and Southern blots showed that the gene for subunit II, as well as the genes for subunits I, III, IV, and VIII, were of normal size and were normally transcribed. A point mutation or a small deletion of mitochondrial DNA, probably affecting the COX-II gene, may be responsible for the COX deficiency in this case of MERRF.     

Dominantly inherited mitochondrial myopathy with multiple deletions of mitochondrial DNA: clinical, morphologic, and biochemical studies

We studied a large family with a dominantly inherited mitochondrial myopathy characterized by progressive external ophthalmoplegia, dysphagia, cataract, lactic acidosis, exercise intolerance, and early death. Morphologic studies of muscle biopsies suggested mitochondrial heteroplasmy and revealed ragged-red fibers and decreased histochemical reactions for cytochrome c oxidase and succinate dehydrogenase. Biochemistry showed a partial defect of cytochrome c oxidase and a mild generalized reduction of other mitochondrial enzymes requiring mitochondrial DNA-encoded subunits. Southern blot analysis and PCR amplification showed mitochondrial DNA deletions in muscle of all affected members, but not in lymphocytes or fibroblasts, suggesting a tissue-specific distribution. Deletions were multiple and seemed to increase with time and to correlate with the severity of the disease.