Mitochondrial genome distribution in histochemically cytochrome c oxidase-negative muscle fibres in patients with a mixture of deleted and wild type mitochondrial DNA.

In situ hybridization studies were performed on a series of chronic progressive external ophthalmoplegia patients harbouring large mitochondrial DNA deletions, using intra- and extra-deletional probes. Clear differences in the distribution of wild type and deleted mitochondrial genomes were seen in both ragged-red and non-ragged red, cytochrome c oxidase-negative fibres, with an accumulation of deleted genomes in the subsarcolemmal zone. Wild type genome content was normal or decreased in the cytochrome c oxidase-negative regions of one case, but in two patients, wild type mtDNA content in cytochrome c oxidase-negative regions was either normal (most fibres) or increased (occasional fibres). The latter observation suggests there may be a stage in the natural history of ragged-red fibre evolution where wild type genomes are transiently increased. The significance of this finding is discussed.

Proximal motor neuropathy, dermato-endocrine syndrome, and IgG kappa paraproteinemia.

The association of monoclonal paraproteinemia, neuropathy, and dermato-endocrine disturbances is well recognized in Japan, and it also occurs in white patients. Neuropathy in such patients is classically distal and sensorimotor, and the paraprotein almost always contains lambda light chains. A 58-year-old white man presented with severe progressive proximal motor neuropathy, dermato-endocrine changes, and an IgG kappa paraprotein. Over a 2 1/2-year period, treatment with melphalan and prednisolone produced improvement in the neuropathy and resolution of dermato-endocrine features with a corresponding decline in the serum paraprotein concentration. Subsequent reappearance of the paraprotein, despite treatment, was associated with clinical relapse.

Mitochondrial theory of senescence: respiratory chain protein studies in human skeletal muscle.

In view of a previously demonstrated negative correlation between stage III respiratory activity in human mitochondria and increasing age, the relationship between human respiratory chain complex protein content and age was investigated. Quantitative immunoblot studies were carried out using holo complex I, III and IV antibody probes in human skeletal muscle mitochondrial homogenate from patients of varying ages. No significant negative correlation between increased age and respiratory complex chain protein content was seen for either total complex activity or for any of the subunits which could be reliably identified. As respiratory complex protein content is preserved with ageing, the decrease in respiratory efficiency is likely to follow aggregation of mutations in structural mitochondrial (mt) DNA genes which do not interfere with mt DNA transcription and protein translation rather than mutations in mt tRNA or ribosomal RNA genes. This is consistent with the fact that mt genes involved in protein translation only occupy a fairly small percentage of the mitochondrial genome.

Mitochondrial studies in Kearns-Sayre syndrome: normal respiratory chain function with absence of a mitochondrial translation product.

Intact mitochondria were isolated from skeletal muscle of two patients with Kearns-Sayre syndrome (retinitis pigmentosa, heart block, chronic external ophthalmoplegia), and mitochondrial protein translation was measured. Mitochondrial protein synthesis was up to 10 times greater than in control subjects and SDS-polyacrylamide gel electrophoresis revealed absence of a translation product with the mobility of a 5 KDa protein. State 3 respiration rates were normal with site 1 and site 2 substrates, suggesting that the absent protein was not a functional subunit of a respiratory chain complex.

Benign acute childhood myositis: laboratory and clinical features.

BACKGROUND: Benign acute myositis of childhood is a disorder of midchildhood, typically affecting boys. Symptoms include calf pain and difficulty walking after a viral illness. There is an epidemiologic association with influenza. OBJECTIVES: To describe the clinical and laboratory features of benign acute myositis. RESULTS: Thirty-eight children (32 boys, 6 girls) were seen with 41 episodes of myositis between 1978 and 1997. Two were siblings and three had recurrent episodes. Mean age at onset of symptoms was 8.1 years. Children remained ambulant during 33 of 41 episodes. Two characteristic gaits were noted: toe-walking in 13, with a wide-based stiff-legged gait in another 7. Muscle tenderness was isolated to the gastrocnemius-soleus muscles in 82% of episodes. Recovery occurred within 1 week. Creatine kinase levels were elevated during all episodes. Viral studies were positive in 10 of 24 episodes, 5 because of influenza B. CONCLUSION: Benign acute myositis is a syndrome of midchildhood that can be differentiated from more serious causes of walking difficulty by the presence of calf tenderness, normal power, intact tendon reflexes, and elevated creatine kinase. The gait patterns noted may minimize power generation of the calf muscles by splinting the ankles. Onset in childhood may reflect an age-related response to viral infection, and occurrence primarily in boys may reflect a genetic predisposition or an as-yet unknown metabolic defect.

Diagnostic criteria for respiratory chain disorders in adults and children.

BACKGROUND: Respiratory chain (RC) disorders are clinically, biochemically, and molecularly heterogeneous. The lack of standardized diagnostic criteria poses difficulties in evaluating diagnostic methodologies. OBJECTIVE: To assess proposed adult RC diagnostic criteria that classify patients into "definite," "probable," or "possible" categories. METHODS: The authors applied the adult RC diagnostic criteria retrospectively to 146 consecutive children referred for investigation of a suspected RC disorder. Data were collected from hospital, genetics, and laboratory records, and the diagnoses predicted by the adult criteria were compared with the previously assigned assessments. RESULTS: The authors identified three major difficulties in applying the adult criteria:lack of pediatric-specific criteria; difficulty in segregating continuous data into circumscribed major and minor criteria; and lack of additivity of clinical features or enzyme tests. They therefore modified the adult criteria to allow for pediatric clinical and histologic features and for more sensitive coding of RC enzyme and functional studies. Reanalysis of the patients' data resulted in congruence between the diagnostic certainty previously assigned by the authors' center and that defined by the new general RC diagnostic criteria in 99% of patients. CONCLUSIONS: These general diagnostic criteria appear to improve the sensitivity of the adult criteria. They need further assessment in prospective clinical and epidemiologic studies.

Respiratory chain complex I deficiency: an underdiagnosed energy generation disorder.

OBJECTIVE: To define the spectrum of clinical and biochemical features in 51 children with isolated complex I deficiency. BACKGROUND: Mitochondrial respiratory chain defects are one of the most commonly diagnosed inborn errors of metabolism. Until recently there have been technical problems with the diagnosis of respiratory chain complex I defects, and there is a lack of information about this underreported cause of respiratory chain dysfunction. METHODS: A retrospective review of clinical features and laboratory findings was undertaken in all diagnosed patients who had samples referred over a 22-year period. RESULTS: Presentations were heterogeneous, ranging from severe multisystem disease with neonatal death to isolated myopathy. Classic indicators of respiratory chain disease were not present in 16 of 42 patients in whom blood lactate levels were normal on at least one occasion, and in 23 of 37 patients in whom muscle morphology was normal or nonspecific. Ragged red fibers were present in only five patients. Tissue specificity was observed in 19 of 41 patients in whom multiple tissues were examined, thus the diagnosis may be missed if the affected tissue is not analyzed. Nine patients had only skin fibroblasts available, the diagnosis being based on enzyme assay and functional tests. Modes of inheritance include autosomal recessive (suggested in five consanguineous families), maternal (mitochondrial DNA point mutations in eight patients), and possibly X-linked (slight male predominance of 30:21). Recurrence risk was estimated as 20 to 25%. CONCLUSION: Heterogeneous clinical features, tissue specificity, and absence of lactic acidosis or abnormal mitochondrial morphology in many patients have resulted in underdiagnosis of respiratory chain complex I deficiency.

Partial cytochrome oxidase (aa3) deficiency in chronic progressive external ophthalmoplegia. Histochemical and biochemical studies.

Biochemical and histochemical studies were carried out on 2 patients with chronic progressive external ophthalmoplegia (CPEO). Histological examination revealed prominent ragged-red fibres in the Gomori trichrome stain and cytochrome oxidase staining revealed partial depletion of cytochrome oxidase with negative staining in some fibres with prominent subsarcolemmal mitochondrial aggregations. Polarographic studies with isolated intact skeletal muscle mitochondria revealed low State III respiration rates with NAD- and FAD-linked substrates. Cytochrome aa3 levels were depressed in the one case where a cytochrome difference spectra was recorded. Cytochrome oxidase levels were greatly depressed in muscle homogenate, whereas monoamine oxidase levels were in the normal range, indicating a selective depletion of the former enzyme complex. It is possible that deficiency of cytochrome oxidase may arise as an epiphenomenon in degenerating mitochondria rather than a primary deficiency.

Mitochondrial myoneuropathy with respiratory failure and myoclonic epilepsy. A case report with biochemical studies.

A 55-year-old man is presented who developed severe multifocal myoclonus and tonic clonic seizures in his early thirties, and progressive limb weakness in his mid forties, when a ragged red fibre myopathy was diagnosed. He went on to develop a distal motor neuropathy and respiratory failure. Respiratory function tests indicated respiratory failure secondary to respiratory muscle weakness and a central hypoventilation syndrome. CT scan revealed brain stem atrophy and brain stem evoked responses were abnormal. A sural nerve biopsy showed severe axonal degeneration. Cytochrome difference spectra and polarographic studies on isolated intact muscle mitochondria were normal. This study reports the association of respiratory failure and sleep apnoea with Fukuhara's syndrome and presents biochemical data suggesting that the mitochondrial respiratory chain may be intact in some patients with this syndrome.

Progression from MERRF to MELAS phenotype in a patient with combined respiratory complex I and IV deficiencies.

Identical twins developed myoclonic epilepsy in their teens. One twin remained mildly affected but the other went on to develop sensorineural deafness and ataxia with lactic acidosis and ragged red fibres leading to a diagnosis of mitochondrial encephalopathy. Multiple stroke-like episodes with hemiparesis followed, indicating progression from a MERRF to a MELAS phenotype. Biochemical studies revealed a severe deficiency of mitochondrial NADH-ubiquinone reductase and a moderate deficiency of cytochrome aa3. Western immunoblotting experiments using polyclonal antibodies raised against human placental cytochrome oxidase identified a similar profile of bands to those seen in controls, supporting the view that cytochrome aa3 deficiency in this case may be a secondary consequence of a failure of assembly related to a severe proximal respiratory chain defect.

Functional respiratory chain studies in subjects with chronic progressive external ophthalmoplegia and large heteroplasmic mitochondrial DNA deletions.

The functional consequences of large heteroplasmic mtDNA deletions were investigated in a group of 6 patients with chronic progressive external ophthalmoplegia (CPEO) syndromes. State III respiration rates corrected for age were low with site I and II substrates in all cases and cytochrome oxidase activity was depressed. The severity of impairment varied and is consistent with inclusion of a variable percentage of non-functioning mitochondria (with deleted mtDNA) in the pellet. Western blot studies with a holocomplex antibody battery revealed no abnormalities in subunit content of complexes III and IV. A deficiency of several complex I subunits in 3 cases suggests that abnormal nuclear-mitochondrial regulation of complex I assembly may follow large mtDNA deletions.

Haemochromatosis presenting as severe cardiac failure in a young adolescent.

A 13-year-old girl, who presented almost moribund in severe heart failure, was shown to have haemochromatosis. Repeated venesection has led to return of normal cardiac function. This adolescent would appear to be the youngest patient described with haemochromatosis whose initial presentation was that of congestive cardiac failure.

Respiratory chain failure in adult muscle fibres: relationship with ageing and possible implications for the neuronal pool.

A histochemical analysis of mitochondrial enzyme activity was carried out in 103 human diaphragmatic skeletal muscles from 49 subjects of different ages, obtained either at the time of abdominal surgery or at necropsy. Evidence of respiratory failure (cytochrome oxidase negativity) was seen in occasional fibres from the fourth decade on with an approximate 10-fold increase between the fourth and ninth decade (0.16% to 2.85%). A similar incidence of mitochondrial failure in CNS neurones to that documented in skeletal muscle could easily account for attrition of 25% of neurones over a 50-year period as reported in the literature. Possible theoretical relationships between morphological markers of mitochondrial failure and cell attrition are explored. While the projections from muscle to neurone are somewhat speculative, it is clear that if a similar extent of mitochondrial pathology exists in the brain to that documented in skeletal muscle, this could easily account for neuronal loss in the ageing brain.

Congenital muscular dystrophy, white-matter abnormalities, and neuronal migration disorders: the expanding concept.

The congenital muscular dystrophies are a heterogeneous, recessively inherited group of disorders that have been subclassified on the basis of clinical central nervous system involvement. We report two children with "pure" congenital muscular dystrophy, one merosin negative and one merosin positive with extensive white matter and occipital cortical neuromigration abnormalities on magnetic resonance imaging (MRI). The first patient (merosin-negative congenital muscular dystrophy) presented with hypotonia and weakness in the neonatal period and subsequently was found to have a leukoencephalopathy and occipital cortical dysplasia on magnetic resonance imaging. The second patient presented with developmental delay without definite weakness. Initial investigations revealed a leukoencephalopathy and cortical dysplasia, but the patient subsequently was shown to have merosin-positive congenital muscular dystrophy. These patients illustrate that white-matter changes are not specific for merosin-negative congenital muscular dystrophy alone and that extensive cortical abnormality can be found in both groups of patients. In addition, our second patient illustrates a nonmuscular mode of congenital muscular dystrophy presentation that should be considered in patients with a "nonprogressive leukodystrophy."

Endomyocardial biopsy in infants and children with cardiomyopathy.

We reviewed our experience of endomyocardial biopsy performed on 21 symptomatic infants and children with cardiomyopathy. Clinical congestive cardiomyopathy was noted in 18 patients, 2 had hypertrophic cardiomyopathy, and 1 a restrictive cardiomyopathy. The biopsy findings led to a diagnosis of hemochromatosis in one patient, Adriamycin cardiomyopathy in another, and lymphocytic myocarditis in a third. Five patients had features of endocardial fibroelastosis, one endomyocardial fibrosis, and a further one, a mitochrondrial abnormality. In 11 patients normal or nonspecific features were seen. There were 2 myocardial perforations, both patients being successfully resuscitated. Endomyocardial biopsy, although occasionally hazardous, may sometimes provide valuable information which may lead to a diagnosis, facilitate treatment, and be of prognostic value. Despite the low positive yield, it may still be indicated in selected patients, in view of the seriousness and often poor prognosis of this disorder: 5 of our study group subsequently died.

Proximal myotonic myopathy: a report of a kindred.

We describe a family with an autosomal dominant myotonic myopathy with absence of the abnormal CTG expansion characteristic of myotonic dystrophy. We believe that the findings in this family concur with those of recent case reports which have postulated the existence of a new adult onset myotonic disorder, distinct from myotonic dystrophy: 'proximal myotonic myopathy'.

Intermittent claudication -- atypical presentation, diagnosis and treatment.

A unique case of a man with Fabry's disease and associated small vessel vasculopathy manifesting as recurrent episodes of intermittent claudication is described. The case highlights the concept that microvascular involvement due to local accumulation of glycosphingolipid in the smooth muscle fibres of vessel walls may be responsible for claudicant symptoms in such patients rather than the more classical macrovascular insufficiency.

Idiopathic granulomatous myositis: does the clinical spectrum include polymyalgia rheumatica?

Granulomatous inflammation restricted to muscle is an uncommon cause of myopathic syndromes. Two patients were diagnosed with idiopathic granulomatous polymyositis after appropriate investigations failed to reveal a systemic or alternative explanation for the granulomas seen in their muscle biopsy. One patient presented with a syndrome indistinguishable from polymyalgia rheumatica but both patients manifested disabling myalgias which were strikingly corticosteroid responsive. The two cases underscore the potential importance of muscle biopsy in polymyalgic states, the non-specificity of polymyalgia rheumatica as a syndrome which can be simulated by other disorders including granulomatous myositis, and the potential corticosteroid responsiveness of prominent, functionally limiting myalgias which can be seen in this disorder. Some controversy continues regarding the correct nosology of this disease, largely perpetuated by an awareness of the inherent limitations of current non-invasive evaluation techniques to confirm occult granulomatous involvement of non-myogenous organs.

McArdle's disease resembling an inflammatory myopathy.

Previous reports have shown that McArdle's disease may occasionally present in older patients (i.e. greater than 40 years of age) as a progressive myopathy that is clinically and sometimes electrophysiologically indistinguishable from idiopathic polymyositis. We report two such patients who in addition had muscle biopsies showing inflammatory infiltrates compatible with polymyositis. However, subsequent enzyme histochemistry demonstrated complete myophosphorylase deficiency and, in the absence of an alternative explanation, may be the reason for the inflammatory changes seen. These cases highlight the importance of a thorough evaluation of patients with an 'inflammatory myopathy' and the occasional diagnostic confusion that may arise in differentiating metabolic myopathies from idiopathic polymyositis. Diagnostic clarification is important to avoid the use of incorrect and potentially toxic treatment.

Are mitochondrial DNA deletions causative in chronic progressive external ophthalmoplegia patients?

Twenty-one patients with long standing unexplained ptosis (3), chronic progressive external ophthalmoplegia (CPEO, 16) or Kearns-Sayre syndrome (KSS, 2) were studied for the presence of mitochondrial DNA (mtDNA) deletions and the major disease-associated mtDNA point mutations with the aim of correlating mitochondrial genetic abnormalities with pathogenesis in these patients. Only 52% were found to have a deletion; of these, 82% harboured the 'common deletion'. Two of 2 KSS patients and 9 of 16 CPEO patients were deletion positive. None of the 3 patients with bilateral ptosis only had a deletion. Of those patients with ragged red fibres (RRF) on histology, 69% had a deletion. No disease associated mtDNA point mutation was observed with the exception of the nucleotide (nt) 11084 A-G mutation associated with mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS) in a patient also harbouring the common deletion. The role of deletions in CPEO patients is discussed.