Lumping or splitting? "Ophthalmoplegia-plus" or Kearns-Sayre syndrome?

A practical approach to the diagnosis and management of MELAS: case report and review

BACKGROUND

Mitochondrial encephalomyopathy, lactic acidosis with stroke-like episodes (MELAS) is a mitochondrial disorder and an important diagnostic consideration in the young patient with nonhemorrhagic stroke. Its presentation is varied and diagnosis is based on early recognition of the clinical features and correct interpretation of laboratory and radiologic studies.

SUMMARY

In this article, we report a patient with MELAS and review the clinical, laboratory, and neuroradiologic features of the condition. In the young patient with multiple stroke-like episodes in different vascular territories and neuroradiologic features of transient abnormalities in varying regions, laboratory testing for MELAS must be performed. The presence of ragged red fibers in skeletal muscle and biochemical demonstration of defects in mitochondrial respiratory enzymes strongly support the diagnosis. Molecular genetic testing for abnormalities in mitochondrial DNA will confirm the diagnosis. The importance of a thorough assessment of family history is also emphasized. The basic principles of mitochondrial genetics and the common point mutations and rearrangements of mitochondrial DNA associated with MELAS are reviewed. Although treatment options are limited, several therapeutic agents have been studied.

CONCLUSIONS

The diagnosis of MELAS should be considered in the young patient with stroke, especially when accompanied by other clinical features such as seizures, encephalopathy, and muscle weakness. Laboratory evaluation can provide an accurate diagnosis, especially when the appropriate mitochondrial DNA studies are performed. Genetic counseling should be provided to patients with MELAS associated with mitochondrial DNA point mutations. Better understanding of the molecular basis of the condition may result in the development of effective treatment strategies.

Cardiac abnormalities in patients with mitochondrial DNA mutation 3243A>G

BACKGROUND

Tissues that depend on aerobic energy metabolism suffer most in diseases caused by mutations in mitochondrial DNA (mtDNA). Cardiac abnormalities have been described in many cases, but their frequency and clinical spectrum among patients with mtDNA mutations is unknown.

METHODS

Thirty-nine patients with the 3243A>G mtDNA mutation were examined, methods used included clinical evaluation, electrocardiogram, Holter recording and echocardiography. Autopsy reports on 17 deceased subjects were also reviewed. The degree of 3243A>G mutation heteroplasmy was determined using an Apa I restriction fragment analysis. Better hearing level (BEHL0.5-4 kHz) was used as a measure of the clinical severity of disease.

RESULTS

Left ventricular hypertrophy (LVH) was diagnosed in 19 patients (56%) by echocardiography and in six controls (15%) giving an odds ratio of 7.5 (95% confidence interval; 1.74-67). The dimensions of the left ventricle suggested a concentric hypertrophy. Left ventricular systolic or diastolic dysfunction was observed in 11 patients. Holter recording revealed frequent ventricular extrasystoles (>10/h) in five patients. Patients with LVH differed significantly from those without LVH in BEHL0.5-4 kHz, whereas the contribution of age or the degree of the mutant heteroplasmy in skeletal muscle to the risk of LVH was less remarkable.

CONCLUSIONS

Structural and functional abnormalities of the heart were common in patients with 3243A>G. The risk of LVH was related to the clinical severity of the phenotype, and to a lesser degree to age, suggesting that patients presenting with any symptoms from the mutation should also be evaluated for cardiac abnormalities.

Cardiovascular Complications of Neuromuscular Disorders

In the past decade, advances in molecular genetics have shown that many familial neuromuscular and cardiovascular diseases share a common pathophysiology. They are caused by inherited mutations in the cellular cytoskeleton of cardiac and skeletal muscle cells. The clinical manifestation of cardiac disease in neuromuscular disorders is common and their management should include both periodic cardiac assessment and appropriate symptomatic and definitive therapy. Dilated cardiomyopathy is a common complication of neuromuscular diseases. Cardiac function may decline progressively as part of the natural history of the disease, but current medical therapy, including angiotensin-converting enzyme inhibitors, beta-blockers, and diuretics, can be used to alleviate symptoms of left ventricular dysfunction. Conduction disturbances may be an important cause of mortality, especially in patients with Emery Dreifuss muscular dystrophy, Kearns-Sayre syndrome, and myotonic dystrophy, and thus pacemaker implantation can be life-saving. Rhythm disturbances, such as atrial fibrillation and ventricular tachyarrhythmias, have been reported in patients with neuromuscular diseases. Treatment is based on preventing sudden death and embolic phenomena and cardioverting or controlling atrial fibrillation. In these patients, problems may arise with anticoagulation and antiarrhythmic therapy due to the inherent locomotor instability associated with the disease, and the presence of concomitant atrioventricular disease. Although uncommon, hypertrophic cardiomyopathy may be a feature of some neuromuscular disorders. Patients should undergo regular risk stratification for sudden cardiac death and symptoms such as heart failure can be treated with medical therapy.

Progressive sensorineural hearing loss in children with mitochondrial encephalomyopathies

OBJECTIVE

Mitochondrial disorders are responsible for a variety of neurological syndromes. Specific mitochondrial DNA mutations have been identified recently in some of these rare disorders. Clinical symptoms may occur in different organs to various extent; often they are associated with progressive hearing loss. The aims of this study were to determine incidence, onset, and characteristics of hearing loss in children with mitochondrial encephalomyopathies and to investigate a possible correlation between the degree of hearing loss and neurological symptoms. In addition, we investigated the prognostic value of hearing loss as a predictor of the disease.

STUDY DESIGN

From August 1992 to September 1998, 29 patients ranging in age from 5 to 23 years (mean years) were studied. These children were hospitalized for diagnostic purposes in the neuropediatric department.

METHODS

The mitochondrial disorder was diagnosed by clinical and laboratory testings, including analysis of the mtDNA. Audiological evaluation consisted of measurements of pure-tone and speech audiometry, tympanometry, and acoustic refle- threshold testing, auditory brainstem response, and evoked as well as distortion-product otoacoustic emissions.

RESULTS

A sensorineural hearing loss was identified in 12 children. Three of these were diagnosed as having classic Kearns-Sayre syndrome; five as having multisystem KSS; two as having the syndrome of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS); one as having KSS-MELAS overlap syndrome; and one as having Friedreich ataxia. Longitudinal testing was performed in seven children, and in all of them a progression of the hearing loss could be demonstrated. Audiological test results in all 12 children suggested cochlear as well as retrocochlear origin of the hearing loss presenting independently from the severity of hearing impairment. No correlation between the characteristics and degrees of hearing loss and the number and severity of clinical neurological symptoms could be found.

CONCLUSIONS

The present study demonstrated a high incidence (42%) of sensorineural hearing loss in children with mitochondrial encephalomyopathies. The progressive nature of the hearing impairment was confirmed by a significant correlation between the duration in years and severity of hearing loss in the children. The hearing loss does not have a prognostic value for the progression of the disorder. Based on our findings, we recommend regular audiometric examinations in patients with mitochondrial disorders.

Kearns-sayre syndrome: oncocytic transformation of choroid plexus epithelium

Kearns-Sayre syndrome (KSS) is a sporadic multisystem disorder due to a defect of oxidative phosphorylation and associated with clonally-expanded rearrangements of mitochondrial DNA (mtDNA) deletions (Delta-mtDNAs) and/or duplications (dup-mtDNAs). To gain further insight into the pathogenesis of CNS dysfunction in KSS, we studied the choroid plexus from two autoptic cases using in situ hybridization (ISH) of mtDNA, and immunohistochemistry to detect mtDNA and nuclear DNA-encoded subunits of the respiratory chain. Neuropathological examination of both cases showed oncocytic transformation of choroid plexus epithelial cells. In the same cells, ISH demonstrated that the predominant species of mtDNA were Delta-mtDNAs, and immunohistochemistry showed a decreased expression of mtDNA-encoded proteins. We suggest that mitochondrial abnormalities due to the presence of abundant Delta-mtDNAs in the choroid plexus play an important role in causing the increased cerebrospinal fluid (CSF) protein and reduced folic-acid levels that are characteristic of KSS.

Rearrangements of human mitochondrial DNA (mtDNA): new insights into the regulation of mtDNA copy number and gene expression

Mitochondria from patients with Kearns-Sayre syndrome harboring large-scale rearrangements of human mitochondrial DNA (mtDNA; both partial deletions and a partial duplication) were introduced into human cells lacking endogenous mtDNA. Cytoplasmic hybrids containing 100% wild-type mtDNA, 100% mtDNA with partial duplications, and 100% mtDNA with partial deletions were isolated and characterized. The cell lines with 100% deleted mtDNAs exhibited a complete impairment of respiratory chain function and oxidative phosphorylation. In contrast, there were no detectable respiratory chain or protein synthesis defects in the cell lines with 100% duplicated mtDNAs. Unexpectedly, the mass of mtDNA was identical in all cell lines, despite the fact that different lines contained mtDNAs of vastly different sizes and with different numbers of replication origins, suggesting that mtDNA copy number may be regulated by tightly controlled mitochondrial dNTP pools. In addition, quantitation of mtDNA-encoded RNAs and polypeptides in these lines provided evidence that mtDNA gene copy number affects gene expression, which, in turn, is regulated at both the post-transcriptional and translational levels.

Oxidative phosphorylation disease diagnosis

Although the mtDNA encodes only 13 polypeptide subunits of the OXPHOS enzymes, approximately 1,000 proteins are estimated to be necessary for proper OXPHOS function. Over the past 10 years a wide variety of adult and pediatric OXPHOS diseases were found to be caused by or associated with mitochondrial DNA (mtDNA) mutations and nuclear DNA mutations. These advances enhanced the ability to definitively diagnose patients, develop management plans, and provide genetic counseling. Recently described nuclear DNA and mtDNA mutations are enhancing our understanding of this complex group of diseases. The impact of these advances on our understanding of OXPHOS disease pathogenesis will be reviewed.

Mitochondrial myopathy diagnosis

Oxidative phosphorylation (OXPHOS) accounts for approximately 95% of the adenosine triphosphate (ATP) produced by the cell. The central nervous system, peripheral nervous system, cardiac muscle, skeletal muscle, and smooth muscle are highly susceptible to dysfunction of this complex enzyme system. Although most OXPHOS diseases are multisystem disorders, the neuromuscular manifestations are often prominent and play an important role in patient diagnosis. To assist the neurologist in evaluating these complex patients, this article focuses on selected samples of OXPHOS diseases with identifiable neuromuscular abnormalities and presents an evaluation algorithm to facilitate patient diagnosis.

Kearns-Sayre syndrome "plus". Classical clinical findings and dystonia

We present a boy of eight years of age with symptoms of Kearns-Sayre syndrome (KSS) characterised by ophthalmoparesis, palpebral ptosis, mitochondrial myopathy, pigmentous retinitis, associated to short stature, cerebellar signs, cardiac blockade, diabetes mellitus, elevated cerebrospinal fluid protein concentration, and focal hand and foot dystonia. The skeletal muscle biopsy demonstrated ragged red fibers, cytochrome C oxidase-negative and succinate dehydrogenase-positive fibers. The magnetic resonance imaging showed symmetrical signal alteration in tegmentum of brain stem, pallidum and thalamus. Mitochondrial DNA analysis from skeletal muscle showed a deletion in heteroplasmic condition. The association of dystonia to KSS, confirmed by molecular analysis, is first described in this case, and the importance of oxidative phosphorylation defects in the physiopathogenesis of this type of movement disorder is stressed.

Audiological assessment in patients with mitochondrial myopathy

Mitochondrial myopathies comprise a heterogeneous group of disorders characterized by the presence of ragged red fibres in muscle biopsy. The present study investigates the audiological features in a group of 14 patients in whom diagnosis was histologically confirmed. A complete ENT, neurological and audiological work-up was performed for every patient, including measurement of brainstem auditory evoked potentials (BAEPs). Most patients presented with a varying degree of hearing loss and occasional abnormalities of the latencies and interpeak latencies of the BAEPs, but only the increased latencies of waves I and V have been statistically confirmed. Audiological data suggest non-specific involvement at one or more sites along the auditory pathway.

Age and cause of death in mitochondrial diseases

We report on the age and the causes of death in 16 patients with mitochondrial diseases. Nine patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) died at a mean age of 34 years and three patients with chronic progressive external ophthalmoplegia at a mean age of 56 years. The causes of death were cardiopulmonary failure (n = 5), status epilepticus (n = 4), aspiration pneumonia (n = 2), pulmonary embolism (n = 2), renal failure (n = 1), metabolic disturbance (n = 1), and unknown causes (n = 1). Thus, many patients in this series died of medical complications, some of which may be prevented.

Dilated cardiomyopathy and atrioventricular conduction blocks induced by heart-specific inactivation of mitochondrial DNA gene expression

Mutations of mitochondrial DNA (mtDNA) cause several well-recognized human genetic syndromes with deficient oxidative phosphorylation and may also have a role in ageing and acquired diseases of old age. We report here that hallmarks of mtDNA mutation disorders can be reproduced in the mouse using a conditional mutation strategy to manipulate the expression of the gene encoding mitochondrial transcription factor A (Tfam, previously named mtTFA), which regulates transcription and replication of mtDNA. Using a loxP-flanked Tfam allele (TfamloxP) in combination with a cre-recombinase transgene under control of the muscle creatinine kinase promoter, we have disrupted Tfam in heart and muscle. Mutant animals develop a mosaic cardiac-specific progressive respiratory chain deficiency, dilated cardiomyopathy, atrioventricular heart conduction blocks and die at 2-4 weeks of age. This animal model reproduces biochemical, morphological and physiological features of the dilated cardiomyopathy of Kearns-Sayre syndrome. Furthermore, our findings provide genetic evidence that the respiratory chain is critical for normal heart function.

Mitochondrial neurogastrointestinal encephalomyopathy: diagnosis by rectal biopsy

A 14-year-old girl with the mitochondrial neurogastrointestinal encephalopathy syndrome had an 8-year history of intestinal pseudoobstruction with abdominal pain, persistent vomiting, gastric and duodenal dilatation, and duodenal diverticulosis. The child appeared chronically malnourished and had severe growth failure. Multisystem involvement was evident with the presence of ptosis, external ophthalmoplegia, muscle wasting, peripheral neuropathy, and diffuse white matter disease seen on magnetic resonance imaging. Lactic acidosis and increased cerebrospinal fluid protein were observed. Mitochondrial enzyme analysis of fresh-frozen skeletal muscle revealed a respiratory chain defect. Molecular genetic studies showed multiple mitochondrial DNA deletions. Pathologic findings in the intestine included atrophy of the external layer of the muscularis propria and an increased number of abnormal-appearing mitochondria in ganglion and smooth-muscle cells. Microvesicular steatosis was observed in liver, skeletal, and gastrointestinal smooth muscle, and Schwann cells of peripheral nerve. Brightly eosinophilic inclusions in the cytoplasm of gastrointestinal ganglion cells were visible by light microscopy, which were confirmed to be megamitochondria by ultrastructural studies. This is the first report of abnormal mitochondria observed in intestinal ganglion and smooth-muscle cells in this syndrome.

Mitochondrial encephalomyopathy (Kearns-Sayre syndrome) with complete atrioventricular block: a case report

A pacemaker was implanted into a 17-year-old man with cardiac failure due to complete atrioventricular block complicated by mitochondrial encephalomyopathy (Kearns-Sayre syndrome). Due to the possible complication of latent myocardial dysfunction, it was decided to implant the dual chamber pacemaker (DDD) and the operation mode was set to DDD 70 ppm 1 year after implantation; this alleviated the cardiac failure. In this case, the necessity of preventive pacemaker implantation in the early stage of cardiac failure was recognized.

Clinical and laboratory findings in referrals for mitochondrial DNA analysis

BACKGROUND

Increasingly, mutations of mitochondrial DNA (mtDNA) are being considered when investigating the aetiology of neurological diseases in childhood. However, they are often difficult to predict clinically.

METHOD

Mitochondrial DNA analysis was carried out on 190 children from 1992 to 1996. Most patients were screened for large scale rearrangements and point mutations at nucleotide positions 3243, 3271, 8344, and 8993.

RESULTS

Mutations were found in only 15 patients (7.9%) and were either large scale rearrangements (seven patients) or point mutations at nucleotide position 3243 (eight patients). Other point mutations were screened for depending on the clinical picture. The age of symptom onset was significantly older in children with an mtDNA mutation (mean 7.0 years) compared with children without a mutation (mean 2.8 years). Neither Leigh's syndrome (28 cases) nor severe infantile lactic acidosis (12 cases) was associated with mtDNA mutation. Only three clinical features were significantly associated with an mtDNA mutation: progressive external ophthalmoplegia, myopathy, and pigmentary retinopathy. Family history was valuable: the point mutation at nucleotide 3243 (but not the large scale rearrangements) was associated with maternal inheritance; and consanguinity was not associated with mtDNA mutations. The only investigation that provided specific evidence of an underlying mtDNA mutation was histochemical staining of muscle biopsy specimens. The large scale mutations associated with Kearns-Sayre syndrome and progressive external ophthalmoplegia were found in DNA from muscle only, not leucocyte DNA; whereas point mutations were found in leucocyte DNA.

CONCLUSIONS

Even among children seen at a neurogenetic referral centre, mtDNA mutations were very uncommon. Muscle biopsy was the only investigation to provide evidence of mtDNA abnormality.

Pyruvate dehydrogenase complex deficiency and altered respiratory chain function in a patient with Kearns-Sayre/MELAS overlap syndrome and A3243G mtDNA mutation

Combined alteration of the pyruvate dehydrogenase complex and respiratory chain function is described in a 21 year-old male patient with overlapping MELAS (mitochondrial encephalomyopathy, lactic acidosis, and 'stroke-like' episodes) and Kearns-Sayre syndrome. Progressive external ophthalmoplegia, pigmentary retinopathy and right bundle branch block were present when he experienced the first 'stroke-like' episode at 18 years old. The A>G tRNALeu(UUR) point mutation at nucleotide 3243 of the mitochondrial DNA was predominant in muscle tissue (79%) and present, but at lower levels in fibroblasts (49%) and blood cells (37%). Biochemical analysis revealed diminished activities of pyruvate dehydrogenase (23%) and respiratory chain complexes I and IV (57%, respectively) in muscle, but normal activities in the fibroblasts. Immunochemical studies of the muscular pyruvate dehydrogenase components showed normal content of E1alpha, E1beta and E2 protein. Molecular screening of the E1alpha gene did not indicate a nuclear mutation. These observations suggest that mitochondrial DNA defects may be associated with altered nuclear encoded enzymes which are actively imported into mitochondria and constitute components of the mitochondrial matrix. Biochemical workup of mitochondrial disorders should not be restricted to the respiratory chain even if mitochondrial DNA mutations are present.

Cochlear origin of hearing loss in MELAS syndrome

There have been few studies investigating the mechanism and nature of the hearing loss that occurs in the mitochondrial disorders. We studied 18 patients with the MELAS A3243G point mutation from four different kindreds. Pure tone audiometry, speech discrimination testing, acoustic reflexes, tympanometry, and brain stem auditory evoked responses were performed to localize the site of pathology in the auditory pathways. In 12 patients, we performed electrocochleography and otoacoustic emissions to assess cochlear involvement. Neuroimaging and promontory nerve stimulation were performed to exclude retrocochlear pathology. Audiological testing confirmed sensorineural hearing loss in 14 of the 18 patients studied; hearing loss was usually gradual in onset, was symmetrical, and initially affected the higher frequencies. In some patients, there were features that distinguished the hearing loss from presbyacusis, including a young age at onset, asymmetrical involvement, stepwise progression, and partial recovery. We treated one patient who had profound bilateral hearing loss with cochlear implantation; this restored good functional hearing. Hearing loss in MELAS syndrome appears to be due to dysfunction of the cochlea, probably resulting from metabolic failure of the stria vascularis and outer hair cells. Cochlear implantation is a therapeutic option worth considering in those patients who become deaf.

Recent developments in the molecular genetics of mitochondrial disorders

Rapid progress has been made in the identification of mitochondrial DNA mutations which are typically associated with diseases of the nervous system and muscle. The well established mitochondrial disorders are maternally inherited and males and females are equally affected. An exception is Leber's hereditary optic atrophy (LHON) which is observed much more frequently in males than in females. There are three common point mutations in LHON which can be homoplasmic or heteroplasmic. In mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) most mutations are single base changes and lie within the tRNA-Leu gene. Point mutations in myoclonic epilepsy with ragged red fibres (MERRF) usually occur within the tRNA-Lys gene but mutations of the tRNA-Leu gene are also observed. MELAS and MERRF mutations are heteroplasmic and there is considerable clinical overlap between these diseases. Point mutations within the ATPase6 gene result in either neuropathy, ataxia and retinitis pigmentosa (NARP) or in Leigh's syndrome. The latter occurs if the mutation is present in the majority of mitochondria (extreme heteroplasmy). Finally, mitochondrial DNA deletions are the cause underlying Kearns-Sayre syndrome (KSS). Apart from the well-established mitochondrial diseases, there is increasing evidence that mitochondrial mutations may also play a role in the neurodegenerative disorders Parkinson, Alzheimer and Huntington disease. The complex I defect found in Parkinson disease is especially interesting in this respect. However, no causative mitochondrial mutation has as yet been established in any of these three common disorders.

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.

Hypoparathyroidism and deafness associated with pleioplasmic large scale rearrangements of the mitochondrial DNA: a clinical and molecular genetic study of four children with Kearns-Sayre syndrome

In four children with hypoparathyroidism and deafness as initial major manifestations of Kearns-Sayre syndrome, a unique pattern of mitochondrial DNA rearrangements was observed. Hypocalcemic tetany caused by PTH deficiency started between age of 6-13 y and was well controlled by small amounts of 1.25-(OH)2-cholecalciferol. Rearranged mitochondrial genomes were present in blood cells of all patients and consisted of partially duplicated and deleted molecules, created by the loss of 7813, 8348, 8587, and 9485 bp, respectively. The deletions were localized between the origins of replication of heavy and light strands and encompassed at least eight polypeptide-encoding genes and six tRNA genes. Sequence analysis revealed imperfect direct repeats present in all rearrangements flanking the break-points. The duplicated population accounted for 25-53% of the mitochondrial genome and was predominant to the deleted DNA (5-30%) in all cases. The proportions of the mutant populations (30-75%) correlated with the age at onset of the disease. We conclude that, unlike heteroplasmic deletions, pleioplasmic rearrangements may escape selection in rapid-dividing cells, distribute widely over many tissues, and thus cause multisystem involvement. Hypoparathyroidism and deafness might be the result of altered signaling pathway caused by selective ATP deficiency.

Strabismus and mitochondrial defects in chronic progressive external ophthalmoplegia

PURPOSE

To describe the results of strabismus surgery on three patients with chronic progressive external ophthalmoplegia, a group of rare disorders characterized by ptosis and slowly progressive ophthalmoparesis that has been shown to result from defects in mitochondrial DNA.

METHODS

Strabismus surgery using the adjustable suture technique was performed in three patients with strabismus and chronic progressive external ophthalmoplegia confirmed by clinical, biochemical, histopathologic, and genetic criteria. All three patients had mitochondrial DNA deletions. Two patients were exotropic; one patient was esotropic.

RESULTS

Rectus muscle recessions were initially unsuccessful in correcting strabismus in one patient, although a subsequent procedure employing rectus muscle resections was successful in alleviating a significant head turn and improved ocular alignment. In the two other patients, a single procedure consisting of rectus muscle recessions combined with large rectus muscle resections successfully achieved good postoperative alignment. The amount of surgery performed in these three patients exceeded that predicted in standard strabismus tables.

CONCLUSIONS

The myopathic process that results in chronic progressive external ophthalmoplegia renders rectus muscle recessions less effective compared with resections for correcting the associated strabismus seen in these patients. Rectus muscle resections therefore should be an integral procedure in the surgical management of the strabismus associated with chronic progressive external ophthalmoplegia.

Mitochondrial encephalomyopathies presenting with features of autonomic and visceral dysfunction

Three children are reported with mitochondrial encephalomyopathy who presented with autonomic dysfunction. Autonomic dysfunction included gastrointestinal dysmotility, apnea, cardiac arrhythmias, decreased lacrimation, supersensitivity to metacholine, altered sweating, and postural hypotension. These patients illustrate that in some mitochondrial encephalomyopathies autonomic features may be prominent and can mimic the clinical features associated with hereditary sensory and autonomic neuropathies.

CPEO and carnitine deficiency overlapping in MELAS syndrome

Mitochondrial myopathy, encephalopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome is one of the mitochondrial encephalomyopathies that has distinct clinical features including stroke-like episodes with migraine-like headache, nausea, vomiting, encephalopathy and lactic acidosis. We report a 27-year-old woman who presented with partial seizure, stroke-like episodes including hemiparesis, hemianopia and hemihypethesia, sensorineural hearing loss, migraine-like headache, and lactic acidosis. Brain computed tomographic scan showed encephalomalacia in the right parieto-occipital area and recent hypodensity in the left temporoparieto-occipital area with cortical atrophy. Muscle biopsy revealed ragged-red fibers and paracrystaline inclusions in the mitochondria. Genetic study revealed an A to G point mutation at nucleotide position (np) 3243 of mitochondrial DNA. External ophthalmoplegia and ptosis were also found during two exaggerated episodes in this patient. Therefore, the overlapping syndrome of chronic progressive external ophthalmoplegia in the MELAS syndrome is considered in this case. Furthermore, we also found carnitine deficiency in this patient and she was responsive well to steroid therapy. Muscle biopsy also revealed excessive lipid droplets deposits. Therefore, the carnitine deficiency may occur in MELAS syndrome with the A to G point mutation at np 3243. We recommend the steroid or carnitine supplement therapy be applied to the MELAS syndrome with carnitine deficiency.

Chronic progressive external ophthalmoplegia with ragged-red fibers: clinical, morphological and genetic investigations in 43 patients

The evaluation of the severity of progressive external ophthalmoplegia (PEO) with ragged-red fibers in muscle, at the onset of the disease, when PEO is most often the only presenting symptom, is a difficult problem in neurological practice. In order to address that issue, we have performed a comparative analysis of the clinical, morphological and molecular characteristics of 43 patients affected with that form of ocular myopathy. Quantification of mitochondrial accumulation was performed with an image analysis application on muscle sections stained with succinate dehydrogenase histochemical reaction. The proportion of muscle fibres appearing as cytochrome c oxidase deficient was used as an index of the muscle-energy defect. Muscle mitochondrial DNA deletions were detected, localized and quantitated by Southern blot analysis. Point mutations were screened in five transfer RNA genes in the mtDNA (tRNA(Leucine (UUR)), tRNA(Lysine), tRNA(Glutamine), tRNA(Isoleucine) and tRNA(Formylmethionine)) by a denaturing gradient gel electrophoresis technique. This investigation confirmed the high frequency of mtDNA deletions or point mutations in PEO. At the onset of the disease, no clinical, morphological or molecular features could predict whether PEO would remain isolated or become part of a more severe multisystem disease. However, patients with mtDNA deletions were characterized by more severe ophthalmoplegia of earlier onset. Their muscle alterations were roughly parallel in severity to the proportion of deleted mtDNA molecules in muscle. Patients with a multitissular disease and mtDNA deletions were always sporadic cases and their clinical presentation was, most often, closely related to Kearns Sayre syndrome.

Kearns-Sayre syndrome associated with mitochondrial DNA deletion or duplication: a molecular genetic and pathological study

The neuropathological findings in 2 patients with Kearns-Sayre syndrome and mitochondrial DNA (mtDNA) rearrangements, one a predominant deletion and the other a predominant duplication, were remarkably similar, showing diffuse vacuolation of white matter. There were some of the pathological features of Leigh's syndrome in the spinal cord of the patient with a duplication. In the patient with a predominant deletion, rearranged mtDNA was undetectable in blood, spleen, and testis, and present in highest amounts in muscle and the brain, but relatively low in cerebellum, reflecting the ratio seen, albeit in much smaller amounts, in normal aged brains. MtDNA rearrangements in this patient were largely deletions or deletion dimers; duplicated mtDNA was present in only trace amounts in some tissues and there was none in skeletal muscle. The patient with a predominant duplication of mtDNA had higher amounts of rearranged mtDNA in blood (mainly duplicated) than muscle (mainly deleted). Correlation of these data with tissue dysfunction is probably complicated by the replicative behaviour of deleted, duplicated and normal mtDNA.

Mitochondrial DNA (mtDNA) diseases: correlation of genotype to phenotype

This study examines the relationship of genotype to phenotype in 14 unselected patients who were found to harbour the A3243G transition in the mitochondrial transfer RNALeu(UUR) gene commonly associated with the syndrome of mitochondrial encephalopathy, lactic acidosis and strokes (MELAS). Only 6 of the 14 cases (43%) had seizures and recurrent strokes, the core clinical features of the MELAS phenotype. Of the remaining cases, four had an encephalomyopathy with deafness, ataxia and dementia, two had syndromes with progressive external ophthalmoplegia and two had limb weakness alone. Even within the MELAS subgroup, the majority of patients had one or more clinical manifestations considered to be atypical of the MELAS syndrome. They included developmental delay, ophthalmoparesis, pigmentary retinopathy and intestinal pseudo-obstruction. The proportion of mutant mitochondrial DNA (mtDNA) in muscle was generally higher in patients with recurrent strokes than in those without strokes, the highest levels being observed in MELAS cases with early onset disease. Studies of isolated muscle mitochondria identified a range of respiratory chain abnormalities mostly involving Complex I; immunoblots of Complex I in 3 of 10 cases showed selective loss of specific subunits encoded by nuclear genes. In the group as a whole, however, no clear correlations were observed between the severity or extent of the respiratory chain abnormality and clinical phenotype or the proportion of mutant mtDNA in biopsied skeletal muscle. These discrepancies suggest that, in patients harbouring the common MELAS3243 mutation, differences in heteroplasmy and the proportions of mutant mtDNA may not be the sole determinants of disease expression and that additional genetic mechanisms are involved in defining the range of clinical and biochemical phenotypes associated with this aberrant mitochondrial genome.

123I-IMP SPECT findings in mitochondrial encephalomyopathies

We performed N-isopropyl-[123I]p-iodoamphetamine (IMP) single photon emission computed tomography (SPECT) in three patients with Leigh syndrome, two patients with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), and two siblings with progressive external ophthalmoplegia (PEO). The SPECT images were compared with the findings on magnetic resonance imaging (MRI) and computed tomography (CT). All Leigh syndrome patients showed low accumulation areas (LAA) bilaterally in the frontal lobes and the basal ganglia. The frontal lobe LAA was seen even in an area without abnormalities on CT/MRI. Each MELAS patient showed a focal LAA. SPECT could also detect an old stroke-like lesion that was no longer shown by CT/MRI. However, SPECT did not show LAA in the basal ganglia, which showed calcification on CT or abnormal signal intensity on MRI. MRI in the 2 PEO patients showed lesions bilaterally in the basal ganglia in one, and in the internal capsules in the other. SPECT showed LAA not only in corresponding areas, but also in the occipital lobes, where no lesions were revealed by MRI. Thus, 123I-IMP SPECT was more sensitive than CT/MRI for detecting stroke-like lesions in MELAS patients, although it did not detect small lesions in the basal ganglia. LAA in the frontal lobes and occipital lobes may be SPECT findings characteristic of Leigh syndrome and PEO, respectively.

Cardiac involvement in mitochondrial diseases. A study on 17 patients with documented mitochondrial DNA defects

BACKGROUND

Mutations of mitochondrial DNA have been demonstrated as causes of human mitochondrial diseases. While these disorders typically involve multiple organs, the effect of mitochondrial mutations on the heart has not been systematically studied.

METHODS AND RESULTS

We studied mitochondrial mutations and cardiac changes in 17 patients with Kearns-Sayre syndrome; ocular myopathy; myoclonus epilepsy with ragged red fibers (MERRF); and mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS). Cardiac involvement was evaluated by chest radiograph, ECG, His-bundle electrogram, and echocardiogram. All 3 patients with Kearns-Sayre syndrome had large deletions of mitochondrial DNA and disturbances in cardiac conduction. ECG abnormalities were found in 2 of 6 patients with ocular myopathy who showed large deletions of mitochondrial DNA. All 3 patients with MERRF had an A-to-G mutation at nucleotide position 8344; 2 had cardiomegaly, asymmetrical septal hypertrophy, and diffuse hypokinesis of the left ventricle. One patient with asymmetrical septal hypertrophy developed dilated cardiomyopathy 2 years later. All 5 patients with MELAS had an A-to-G mutation at nucleotide position 3243, and 2 had symmetrical left ventricular hypertrophy with or without abnormal wall motion.

CONCLUSIONS

The clinical features of cardiac involvement in mitochondrial diseases vary in the different subgroups of these disorders. Particular mitochondrial mutations can cause characteristic cardiac abnormalities.

Inhalation anaesthesia and the Kearns-Sayre syndrome

Kearns-Sayre syndrome is an extremely rare mitochondrial myopathy, characterised by retinitis pigmentosa associated with progressive external ophthalmoplegia. Cardiac conduction abnormalities are common and range from bundle branch block to third degree atrioventricular block. Generalised degeneration of the central nervous system has also been reported. We describe the anaesthetic management of a child afflicted by this syndrome. The major anaesthetic complication in this disease is sudden third degree atrioventricular block which may lead to death in the absence of an artificial cardiac pacemaker.

Non-Mendelian mitochondrial inheritance as a cause of progressive genetic sensorineural hearing loss

Awareness of non-Mendelian mitochondrial inheritance and of its role as an agent of genetic sensorineural hearing loss (SNHL) is recent. Mitochondria are passed on exclusively from the ovum to all the offspring of both sexes, a novel pattern of inheritance. Owing to the critical role of mitochondria in cellular energy metabolism, deletions or point mutations of the mitochondrial DNA often cause progressive SNHL and a variety of disorders in other organ systems (mitochondrial cytopathies). The clinical expression of mitochondrial diseases varies and depends on the proportion of mutated mitochondria in various body tissues, as well as the nature of the mutation or deletion. In order to determine how often SNHL occurs in mitochondrial diseases and what is its presenting symptom, and also whether SNHL is a marker for particular phenotypes, we carried out a review of published case reports of patients with an established diagnosis of mitochondrial disease. The review indicates that SNHL occurs at all ages and in virtually all variants of mitochondrial diseases. It is not clear whether SNHL is a marker for a more severe and more rapid course of disease; the lower prevalence of SNHL in descriptions of live patients than of those who had died may be an artifact of case selection reported in the literature. Mitochondrial disease needs to be considered in progressive hearing loss and better longitudinal audiometric study of established cases will be required to answer these questions.

Sinus dysrhythmia in Kearns-Sayre syndrome

Kearns-Sayre syndrome is the triad of progressive external ophthalmoplegia, pigmentary retinopathy, and complete AV block. The etiology is unknown, but is thought to be due to a mitochondrial DNA deletion. Reported electrocardiographic abnormalities include first-degree AV block, fascicular blocks, and complete heart block, as well as non-specific S-T segment changes and T wave abnormalities, but has not included sinus node dysfunction. We report a case with episodes of sinus arrest in an asymptomatic patient with Kearns-Sayre syndrome resulting in pauses lasting up to 6 seconds.

Central and peripheral nervous system conduction in mitochondrial myopathy with chronic progressive external ophthalmoplegia

Involvement of the peripheral and central nervous systems in mitochondrial myopathy with chronic progressive external ophthalmoplegia (CPEO) has been demonstrated clinically and electrophysiologically. Systematic electrophysiological investigations of the peripheral and central nervous systems, particularly of cortico-spinal tract function, however, are not available. We studied peripheral and central nervous system involvement in 28 patients with histologically and biochemically proven mitochondrial CPEO by motor and sensory nerve conduction tests, by somatosensory, auditory and visual evoked potentials and, for the first time, by transcranial magnetic stimulation. Nervous system involvement could be demonstrated in 24 patients, affecting the peripheral and central nervous systems in 18 and 10 patients, respectively. Evidence of cortico-spinal tract involvement was found in 4 patients, which was clinically expected in only 2. Therefore, dysfunction of the cortico-spinal tract in mitochondrial CPEO may occur more frequently than so far assumed. Generally, electrophysiological tests serve as valuable supplements to clinical examination in patients with mitochondrial CPEO and may be especially helpful in therapeutic studies, i.e., coenzyme Q administration.

Mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS): current concepts

Mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) syndrome is one of many mitochondrially inherited multisystem diseases. The features of 110 reported mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes patients are reviewed to define the clinical spectrum of this disease. The clinical disorder, in addition to emerging concepts of genetic etiology, is promoting our understanding of mitochondrial functions. New knowledge may lead to more rational therapies. Finally, the recent revolution in the study of mitochondrial diseases may further our understanding of other degenerative disorders and even aging.

Juvenile Kearns-Sayre syndrome initially misdiagnosed as a psychosomatic disorder

We have investigated a 15 year old girl with progressive external ophthalmoplegia, including bilateral ptosis and retinal rod and cone cell dysfunction with atypical retinal pigmentation, complicated by cerebellar ataxia, partial cardiac conduction block, and diabetes mellitus. In infancy she had a severe crisis of bone marrow depression, and as a child she suffered from hypersensitivity to light, increasing fatigue, and vertigo, signs that were initially though to be psychosomatic. Histological examination showed mitochondrial myopathy, and subsequent mitochondrial DNA (mtDNA) analysis showed a deletion of approximately 5500 base pairs in 35 to 40% of her muscle mtDNA. We therefore conclude that this patient has developed the Kearns-Sayre syndrome after a Pearson syndrome-like crisis in her first year of life.

Defective brain energy metabolism shown by in vivo 31P MR spectroscopy in 28 patients with mitochondrial cytopathies

We studied brain energy metabolism by phosphorus magnetic resonance spectroscopy (31P MRS) in 28 patients with mitochondrial cytopathies, and 20 normal control subjects. Fourteen patients had myopathy alone, six had only mild brain symptoms, and eight showed different degrees of brain involvement. Brain 31P MRS showed a low phosphocreatine content in all patients, accompanied by a high inorganic phosphate in 14 of 28 patients. The average value of the Pi concentration in the patient group was significantly (p = 0.009) different from the control group. The cytosolic pH was normal. From these data were derived a high concentration of ADP (calculated from the creatine kinase equilibrium), a high percent value of V/Vmax for ATP biosynthesis, and a low phosphorylation potential, all features showing a derangement of brain energy metabolism, in all patients with mitochondrial cytopathies. 31P MRS proved to be sensitive enough to disclose a deficit of mitochondrial functionality not only in the affected patients, but also in those without clinically evident brain symptoms.

Neuropathy associated with mitochondrial disorders

Altered mitochondria within peripheral nerves were found in most cases of mitochondrial myopathy, in all cases of hereditary motor and sensory neuropathy with optic atrophy (HMSN VI) and in 25 cases out of a larger series of 280 unselected neuropathies studied by electron microscopy for diagnostic purposes. The mitochondrial changes differed from those seen in the corresponding skeletal muscle fibres. They comprised enlargements with an amorphous matrix and distorted cristae, hexagonal paracrystalline inclusions, sometimes longitudinally arranged in a zig-zag pattern, prominent cristae containing oblique striations and a variety of rare changes. Most mitochondrial abnormalities were found in Schwann cells. An occasional perineurial cell was also involved showing a unique paracrystalline inclusion. An increase of the number of mitochondria was noted in smooth muscle and endothelial cells of epineurial arterioles in three cases of mitochondrial encephalomyopathy (two cases with Kearns Sayre syndrome, and one with mitochondrial encephalomyopathy, lactic acidosis and stroke like episodes, i.e., "MELAS"). Neuropathy was present in all cases of mitochondrial myopathy as judged by morphometric analysis. Whether neuropathy is caused directly by mitochondrial dysfunction or by other pathogenetic mechanisms remains to be determined. Yet peripheral motor and sensory neurons with their peripheral axons are postmitotic, terminally differentiated cells which should be similarly prone to deleterious deletions of mitochondrial DNA as has been suggested as an etiologic factor for the predilection of mitochondrial diseases in muscle and brain.

Kinematic pharyngeal transit times in myopathy: evaluation for dysphagia

Measurement of kinematic pharyngeal transit times, a new videofluoroscopy technique, provides useful quantitative data to supplement the qualitative data previously available from videofluoroscopy swallowing studies. Kinematic pharyngeal transit times have not previously been reported for subjects with myopathy. This study demonstrates the use of quantitative kinematic pharyngeal transit times for dysphagia evaluation in 15 patients with myopathy. The successful treatment of dysphagia by cricopharyngeal myotomy is reported in two patients with limb-girdle syndrome.

The expanding clinical spectrum of mitochondrial diseases

The mitochondrion is the only extranuclear organelle containing DNA (mtDNA). As such, genetically determined mitochondrial diseases may result from a molecular defect involving the mitochondrial or the nuclear genome. The first is characterized by maternal inheritance and the second by Mendelian inheritance. Ragged-red fibers (RRF) are commonly seen with primary lesions of mtDNA, but this association is not invariant. Conversely, RRF are seldom associated with primary lesions of nuclear DNA. Large-scale rearrangements (deletions and insertions) and point mutations of mtDNA are commonly associated with RRF and lactic acidosis, e.g. Kearns-Sayre syndrome (KSS) (major large-scale rearrangements), Pearson syndrome (large-scale rearrangements), myoclonus epilepsy with RRF (MERRF) (point mutation affecting tRNA(lys) gene), mitochondrial myopathy, lactic acidosis, and stroke-like episodes (MELAS) (two point mutations affecting tRNA(leu)(UUR) gene) and a maternally-inherited myopathy with cardiac involvement (MIMyCa) (point mutation affecting tRNA(leu)(UUR) gene). However, RRF and lactic acidosis are absent in Leber hereditary optic neuropathy (LHON) (one point mutation affecting ND4 gene, two point mutations affecting ND1 gene, and one point mutation affecting the apocytochrome b subunit of complex III), and the condition associated with maternally inherited sensory neuropathy (N), ataxia (A), retinitis pigmentosa (RP), developmental delay, dementia, seizures, and limb weakness (NARP) (point mutation affecting ATPase subunit 6 gene). The point mutations in MELAS, MIMyCa, and MERRF, and the large-scale mtDNA rearrangements in KSS and Pearson syndrome have a broader biochemical impact since these molecular defects involve the translational sequence of mitochondrial protein synthesis. The nuclear defects involving mitochondrial function generally are not associated with RRF. The biochemical classification of mitochondrial diseases principally catalogues these nuclear defects. This classification divides mitochondrial diseases into five categories. Primary and secondary deficiencies of carnitine are examples of a substrate transport defect. A lipid storage myopathy is often present. Disturbances of pyruvate or fatty acid metabolism are examples of substrate utilization defects. Only four defects of the Krebs cycle are known: fumarase deficiency, dihydrolipoyl dehydrogenase deficiency, alpha-ketoglutarate dehydrogenase deficiency, and combined defects of muscle succinate dehydrogenase and aconitase. Luft disease is the singular example of a defect in oxidation-phosphorylation coupling. Defects of respiratory chain function are manifold. Two clinical syndromes predominate, one involving limb weakness, and the other primarily affecting brain function. Leigh syndrome may result from different enzyme defects, most notably pyruvate dehydrogenase complex deficiency, cytochrome c oxidase deficiency, complex I deficiency, and complex V deficiency associated with the recently described NARP point mutation. A new group of mitochondrial diseases has emerged.(ABSTRACT TRUNCATED AT 400 WORDS)

A case of Kearns-Sayre syndrome with metaphyseal dysplasia

A case of mitochondrial encephalomyopathy (Kearns-Sayre syndrome) demonstrating bilateral symmetric metaphyseal dysplasia is reported. This represents a new association with the syndrome.

In situ hybridization of mitochondrial DNA in the heart of a patient with Kearns-Sayre syndrome and dilatative cardiomyopathy

Previous studies have revealed cytochrome-c-oxidase-deficient cardiomyocytes and the 4,977 base pair deletion ("common deletion") of mitochondrial DNA (position 8,482-13,459) in the heart of a patient with dilatative cardiomyopathy and Kearns-Sayre syndrome. In the present investigation the co-localization of the enzymatic and genomic defects was studied. In situ hybridization of mitochondrial DNA (mtDNA) revealed different hybridization patterns in the cytochrome-c-oxidase-deficient cells: (1) a selective reduction of the hybridization signal with an mtDNA probe recognizing the common deletion, indicating predominance of the deleted over the nondeleted mtDNA molecules in the cytochrome-c-oxidase-deficient cells; (2) a reduced hybridization signal with different mtDNA probes, indicating depletion of mtDNA; and (3) normal hybridization signals with different probes in single cytochrome-c-oxidase-deficient cardiomyocytes. These results indicate that different mechanisms may co-exist in Kearns-Sayre syndrome and may lead to defective respiratory chain function. The question of the pathogenetic interrelationship is discussed.

Manometric characteristics of cervical dysphagia in a patient with the Kearns-Sayre syndrome

The manometric findings of deglutitive pharyngoesophageal function in a patient with the Kearns-Sayre syndrome and cervical dysphagia are described. These findings indicate that striated muscles of the pharynx, upper esophageal sphincter (UES), and proximal esophagus are involved. Near absence of pharyngeal peristalsis, abnormally low UES resting pressure, and absence of proximal esophageal peristalsis characterize the manometric findings in this patient. It is conceivable that in mild cases, a combination of various degrees of severity of the above findings may exist.

Progressive loss of cytochrome c oxidase in the human extraocular muscles in ageing--a cytochemical-immunohistochemical study

Cytochrome c oxidase (complex IV of the respiratory chain) was studied histochemically in autoptic human extraocular muscles (n = 135), revealing randomly distributed single fibers without enzyme activity. The enzyme defect was expressed in all the mitochondria of an involved fiber as evidenced by ultracytochemistry. Succinate dehydrogenase showed normal histochemical reactivity. The defects occurred already in the second decade and were regularly seen from the third decade on. The defect density (defects/mm2) increased from approx. 1/mm2 below the fifth decade to about 4/mm2 in advanced age (P = 0.000). The highest defect density was observed in the levator palpebrae muscle. On the whole, the defect density was about 5-6 times higher in the extraocular muscles than in the limb muscle, diaphragm and heart (Müller-Höcker, 1989, 1990). Immunocytochemical detection of cytochrome c oxidase showed that loss of cytochrome c oxidase activity was due to an almost complete absence of both nuclear and mitochondria subunits of the enzyme. The results document different organ and heterogenic cellular sensitivity to the age-related loss of cytochrome c oxidase. The loss of both mitochondrial and nuclear subunits indicates that nuclear factors are most probably involved in the decline of the respiratory chain function in senescence.

Mitochondrial DNA deletions and cytochrome c oxidase deficiency in muscle fibres

We have studied cytochrome c oxidase (COX) deficient muscle fibre segments in 6 patients with mitochondrial myopathy and deletions of mitochondrial DNA (mtDNA). The distribution of transcripts of normal and mutated mtDNA in skeletal muscle sections was studied by in situ hybridization. The results were compared with the enzyme histochemical activity of COX and the immunohistochemical distribution of mtDNA encoded and nuclear DNA encoded subunits of COX. In all cases a proportion of the muscle fibres (less than 1-30% of the fibres in cross-sections) had low COX activity and high activity of succinate dehydrogenase (COX deficient muscle fibres). Transcripts of normal and deleted mtDNA showed the same distribution within the tissue as the corresponding mtDNA, indicating that the deleted mtDNA is transcribed. The COX deficient muscle fibres showed accumulation of transcripts of deleted mtDNA, which had a similar distribution as the accumulated mitochondria within these fibres. With few exceptions, there was a low level of transcripts of normal mtDNA in these COX deficient fibres. Immunohistochemical analysis revealed low levels of immunoreactive material using antiserum to the mtDNA encoded subunits II/III as well as the nuclear DNA encoded subunit IV of COX in all COX deficient muscle fibres. The fraction of deleted mtDNA in muscle ranged from 43 to 87%. There was no correlation between the proportion of COX deficient muscle fibres and the fraction of deleted mtDNA. In 2 cases the deletion did not involve any COX gene. One of these cases had 87% deleted mtDNA but less than 1% COX deficient muscle fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

Endocrine dysfunction in Kearns-Sayre syndrome

Kearns-Sayre syndrome (KSS) is a form of mitochondrial myopathy in which specific clinical features, namely progressive external ophthalmoplegia, pigmentary retinal degeneration and cardiac conduction defects, occur. KSS has also been associated with a variety of endocrine and metabolic disorders, in particular short stature, gonadal failure, diabetes mellitus, thyroid disease, hyperaldosteronism, hypomagnesaemia, and bone, tooth and calcification abnormalities. A case is described exhibiting all of these features. A survey of the literature was conducted to determine the prevalence of these conditions among reported cases. Cases with hypoparathyroidism were considered separately to see if they constituted a distinct subgroup with multiple endocrine dysfunction. Short stature was common, being documented in 38% of cases. Gonadal dysfunction before or after puberty was also common (20% of cases) and affected both sexes equally. Diabetes mellitus was recorded in 13% of cases, half of which required insulin. Thyroid disease, hyperaldosteronism and hypomagnesaemia were uncommon but were probably not looked for in many cases. Bone or tooth abnormalities and calcification of the basal ganglia were found both in those with and without hypoparathyroidism. While endocrine and metabolic dysfunction was found more commonly in those with hypoparathyroidism this is likely to be due to increased recognition rather than increased prevalence. No evidence of an autoimmune polyendocrine syndrome including hypoparathyroidism was found.