Phenotype variability in 130 adult patients with respiratory chain disorders

Mitochondrial multiorgan disorder syndrome score generated from definite mitochondrial disorders

OBJECTIVES

Mitochondrial disorders (MIDs) frequently present as mitochondrial multiorgan disorder syndrome (MIMODS) at onset or evolve into MIMODS during the course. This study aimed to find which organs and/or tissues are most frequently affected by MIMODS, which are the most frequent abnormalities within an affected organ, whether there are typical MIMODS patterns, and to generate an MIMODS score to assess the diagnostic probability for an MID.

METHODS

This is a retrospective evaluation of clinical, biochemical, and genetic investigations of adult patients with definite MIDs. A total of 36 definite MID patients, 19 men and 17 women, aged 29-82 years were included in this study. The diagnosis was based on genetic testing (n=21), on biochemical investigations (n=17), or on both (n=2).

RESULTS

The number of organs most frequently affected was 4 ranging from 1 to 9. MIMODS was diagnosed in 97% of patients. The organs most frequently affected were the muscle (97%), central nervous system (CNS; 72%), endocrine glands (69%), heart (58%), intestines (55%), and peripheral nerves (50%). The most frequent CNS abnormalities were leukoencephalopathy, prolonged visually evoked potentials, and atrophy. The most frequent endocrine abnormalities included thyroid dysfunction, short stature, and diabetes. The most frequent cardiac abnormalities included arrhythmias, systolic dysfunction, and hypertrophic cardiomyopathy. The most frequent MIMODS patterns were encephalomyopathy, encephalo-myo-endocrinopathy, and encepalo-myo-endocrino-cardiopathy. The mean ± 2SD MIMODS score was 35.97±27.6 (range =11-71). An MIMODS score >10 was regarded as indicative of an MID.

CONCLUSION

Adult MIDs manifest as MIMODS in the vast majority of the cases. The organs most frequently affected in MIMODS are muscles, CNS, endocrine glands, and heart. An MIMODS score >10 suggests an MID.

A Metabolic Signature of Mitochondrial Dysfunction Revealed through a Monogenic Form of Leigh Syndrome

A decline in mitochondrial respiration represents the root cause of a large number of inborn errors of metabolism. It is also associated with common age-associated diseases and the aging process. To gain insight into the systemic, biochemical consequences of respiratory chain dysfunction, we performed a case-control, prospective metabolic profiling study in a genetically homogenous cohort of patients with Leigh syndrome French Canadian variant, a mitochondrial respiratory chain disease due to loss-of-function mutations in LRPPRC. We discovered 45 plasma and urinary analytes discriminating patients from controls, including classic markers of mitochondrial metabolic dysfunction (lactate and acylcarnitines), as well as unexpected markers of cardiometabolic risk (insulin and adiponectin), amino acid catabolism linked to NADH status (α-hydroxybutyrate), and NAD⁺ biosynthesis (kynurenine and 3-hydroxyanthranilic acid). Our study identifies systemic, metabolic pathway derangements that can lie downstream of primary mitochondrial lesions, with implications for understanding how the organelle contributes to rare and common diseases.

Mitochondrial Myopathy in Follow-up of a Patient With Chronic Fatigue Syndrome

Introduction. Symptoms of mitochondrial diseases and chronic fatigue syndrome (CFS) frequently overlap and can easily be mistaken. Methods. We report the case of a patient diagnosed with CFS and during follow-up was finally diagnosed with mitochondrial myopathy by histochemical study of muscle biopsy, spectrophotometric analysis of the complexes of the mitochondrial respiratory chain, and genetic studies. Results. The results revealed 3% fiber-ragged blue and a severe deficiency of complexes I and IV and several mtDNA variants. Mother, sisters, and nephews showed similar symptoms, which strongly suggests a possible maternal inheritance. The patient and his family responded to treatment with high doses of riboflavin and thiamine with a remarkable and sustained fatigue and muscle symptoms improvement. Conclusions. This case illustrates that initial symptoms of mitochondrial disease in adults can easily be mistaken with CFS, and in these patients a regular reassessment and monitoring of symptoms is recommended to reconfirm or change the diagnosis.

Central Nervous System Imaging in Mitochondrial Disorders

Imaging of central-nervous-system (CNS) abnormalities is important in patients with mitochondrial disorders (MCDs) since the CNS is the organ second most frequently affected in MCDs and some of them are potentially treatable. Clinically relevant imaging techniques for visualization of CNS abnormalities in MCDs are computed tomography, magnetic resonance imaging, and MR-spectroscopy. The CNS abnormalities in MCDs visualized by imaging techniques include stroke-like lesions with cytotoxic or vasogenic edema, laminar cortical necrosis, basal ganglia necrosis, focal or diffuse white matter lesions, focal or diffuse atrophy, intra-cerebral calcifications, cysts, lacunas, hypometabolisation, lactacidosis, hemorrhages, cerebral hypo- or hyperperfusion, intra-cerebral artery stenoses, or moyamoya syndrome. The CNS lesions may proceed with or without clinical manifestations, why neuroimaging should be routinely carried out in all MCDs to assess the degree of CNS involvement. Some of these lesions may remain unchanged for years, some may show contiguous spread and progression, but some may even disappear, spontaneously or in response to medication. Dynamics of Stroke-like lesions may be positively influenced by L-arginine, dichloracetate, steroids, edavarone, or antiepileptics. Symptomatic treatment of CNS abnormalities in MCD patients may positively influence their outcome.

Cardiac manifestations of primary mitochondrial disorders

OBJECTIVES

One of the most frequently affected organs in mitochondrial disorders (MIDs), defined as hereditary diseases due to affection of the mitochondrial energy metabolism, is the heart. Cardiac involvement (CI) in MIDs has therapeutic and prognostic implications. This review aims at summarizing and discussing the various cardiac manifestations in MIDs.

METHODS

Data for this review were identified by searches of MEDLINE, Current Contents, and PubMed using appropriate search terms.

RESULTS

CI in MIDs may be classified according to various different criteria. In the present review cardiac abnormalities in MIDs are discussed according to their frequency with which they occur. CI in MIDs includes cardiomyopathy, arrhythmias, heart failure, pulmonary hypertension, dilation of the aortic root, pericardial effusion, coronary heart disease, autonomous nervous system dysfunction, congenital heart defects, or sudden cardiac death. The most frequent among the cardiomyopathies is hypertrophic cardiomyopathy, followed by dilated cardiomyopathy, and noncompaction.

CONCLUSIONS

CI in MID is more variable and prevalent than previously thought. All tissues of the heart may be variably affected. The most frequently affected tissue is the myocardium. MIDs should be included in the differential diagnoses of cardiac disease.

Imaging manifestations of the leukodystrophies, inherited disorders of white matter

The leukodystrophies are a diverse set of inherited white matter disorders and are uncommonly encountered by radiologists in everyday practice. As a result, it is challenging to recognize these disorders and to provide a useful differential for the referring physician. In this article, leukodystrophies are reviewed from the perspective of 4 imaging patterns: global myelination delay, periventricular/deep white matter predominant, subcortical white matter predominant, and mixed white/gray matter involvement patterns. Special emphasis is placed on pattern recognition and unusual combinations of findings that may suggest a specific diagnosis.

Adult-onset leukodystrophies from respiratory chain disorders: do they exist?

Respiratory chain disorders (RCDs) have been included in the differential diagnosis of adult-onset leukodystrophies. Here, we first report a 32-year-old female with an atypical, adult-onset, non-syndromic RCD due to a mitochondrial DNA deletion and manifesting as complicated ataxia. A 'leukodystrophic' pattern was found on brain MRI, but it was neither isolated nor predominant because of the presence of overt basal ganglia and infratentorial lesions, which led us to the proper diagnosis. Subsequently, we evaluated our series of patients with RCDs in order to verify whether a 'leukodystrophic' pattern with little or no involvement of deep grey structures and brainstem may be found in adult-onset RCDs, as reported in children. Among 52 patients with adult-onset RCDs, no case with a 'leukodystrophic' pattern was found, apart from three cases with a classical phenotype of mitochondrial neurogastrointestinal encephalopathy. In addition, no case of RCDs was found among six cases of adult-onset leukodystrophy of unknown origin and at least one feature suggestive of mitochondrial disease. The review of the literature was in agreement with these findings. Thus, we provide evidence that, unlike in children, RCDs should not be included in the differential diagnosis of adult-onset leukodystrophies, except when there are additional MRI findings or clinical features which unequivocally point towards a mitochondrial disorder.

Targeted exome sequencing of suspected mitochondrial disorders

OBJECTIVE

To evaluate the utility of targeted exome sequencing for the molecular diagnosis of mitochondrial disorders, which exhibit marked phenotypic and genetic heterogeneity.

METHODS

We considered a diverse set of 102 patients with suspected mitochondrial disorders based on clinical, biochemical, and/or molecular findings, and whose disease ranged from mild to severe, with varying age at onset. We sequenced the mitochondrial genome (mtDNA) and the exons of 1,598 nuclear-encoded genes implicated in mitochondrial biology, mitochondrial disease, or monogenic disorders with phenotypic overlap. We prioritized variants likely to underlie disease and established molecular diagnoses in accordance with current clinical genetic guidelines.

RESULTS

Targeted exome sequencing yielded molecular diagnoses in established disease loci in 22% of cases, including 17 of 18 (94%) with prior molecular diagnoses and 5 of 84 (6%) without. The 5 new diagnoses implicated 2 genes associated with canonical mitochondrial disorders (NDUFV1, POLG2), and 3 genes known to underlie other neurologic disorders (DPYD, KARS, WFS1), underscoring the phenotypic and biochemical overlap with other inborn errors. We prioritized variants in an additional 26 patients, including recessive, X-linked, and mtDNA variants that were enriched 2-fold over background and await further support of pathogenicity. In one case, we modeled patient mutations in yeast to provide evidence that recessive mutations in ATP5A1 can underlie combined respiratory chain deficiency.

CONCLUSION

The results demonstrate that targeted exome sequencing is an effective alternative to the sequential testing of mtDNA and individual nuclear genes as part of the investigation of mitochondrial disease. Our study underscores the ongoing challenge of variant interpretation in the clinical setting.

Neuromuscular and systemic presentations in adults: diagnoses beyond MERRF and MELAS

Mitochondrial diseases are a diverse group of inherited and acquired disorders that result in inadequate energy production. They can be caused by inheritable genetic mutations, acquired somatic mutations, and exposure to toxins (including some prescription medications). Normal mitochondrial physiology is responsible, in part, for the aging process itself, as free radical production within the mitochondria results in a lifetime burden of oxidative damage to DNA, especially the mitochondrial DNA that, in turn, replicate the mutational burden in future copies of itself, and lipid membranes. Primary mitochondrial diseases are those caused by mutations in genes that encode for mitochondrial structural and enzymatic proteins, and those proteins required for mitochondrial assembly and maintenance. A number of common adult maladies are associated with defective mitochondrial energy production and function, including diabetes, obesity, hyperthyroidism, hypothyroidism, and hyperlipidemia. Mitochondrial dysfunction has been demonstrated in many neurodegenerative disorders, including Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis, and some cancers. Polymorphisms in mitochondrial DNA have been linked to disease susceptibility, including death from sepsis and survival after head injury. There is considerable overlap in symptoms caused by primary mitochondrial diseases and those illnesses that affect mitochondrial function, but are not caused by primary mutations, as well as disorders that mimic mitochondrial diseases, but are caused by other identified mutations. Evaluation of these disorders is complex, expensive, and not without false-negative and false-positive results that can mislead the physician. Most of the common heritable mitochondrial disorders have been well-described in the literature, but can be overlooked by many clinicians if they are uneducated about these disorders. In general, the evaluation of the classic mitochondrial disorders has become straightforward if the clinician recognized the phenotype and orders appropriate confirmatory testing. However, the majority of patients referred for a mitochondrial evaluation do not have a clear presentation that allows for rapid identification and testing. This article provides introductory comments on mitochondrial structure, physiology, and genetics, but will focus on the presentation and evaluation of adults with mitochondrial symptoms, but who may not have a primary mitochondrial disease.

Cognitive dysfunction in mitochondrial disorders

Among the various central nervous system (CNS) manifestations of mitochondrial disorders (MIDs), cognitive impairment is increasingly recognized and diagnosed (mitochondrial cognitive dysfunction). Aim of the review was to summarize recent findings concerning the aetiology, pathogenesis, diagnosis and treatment of cognitive decline in MIDs. Among syndromic MIDs due to mitochondrial DNA (mtDNA) mutations, cognitive impairment occurs in patients with mitochondrial encephalopathy, lactic acidosis and stroke-like episodes syndrome, myoclonus epilepsy with ragged-red fibres syndrome, mitochondrial chronic progressive external ophthalmoplegia, Kearns-Sayre syndrome, neuropathy, ataxia and retinitis pigmentosa syndrome and maternally inherited diabetes and deafness. Among syndromic MIDs due to nuclear DNA (nDNA) mutations, cognitive decline has been reported in myo-neuro-gastro-intestinal encephalopathy, mitochondrial recessive ataxia syndrome, spinocerebellar ataxia with encephalopathy, Mohr-Tranebjaerg syndrome, leuko-encephalopathy; brain and spinal cord involvement and lactic acidosis, CMT2, Wolfram syndrome, Wolf-Hirschhorn syndrome and Leigh syndrome. In addition to syndromic MIDs, a large number of non-syndromic MIDs due to mtDNA as well as nDNA mutations have been reported, which present with cognitive impairment as the sole or one among several other CNS manifestations of a MID. Delineation of mitochondrial cognitive impairment from other types of cognitive impairment is essential to guide the optimal management of these patients. Treatment of mitochondrial cognitive impairment is largely limited to symptomatic and supportive measures. Cognitive impairment may be a CNS manifestation of syndromic as well as non-syndromic MIDs. Correct diagnosis of mitochondrial cognitive impairment is a prerequisite for the optimal management of these patients.

Value of brain magnetic resonance imaging in mitochondrial respiratory chain disorders

Mitochondrial respiratory chain (MRC) disorders have variable clinical manifestations which are mainly neurologic. Diagnosis in children is more complex than in adults because the classic phenotype, ragged red fibers, and mtDNA mutations are rarely seen in children. Moreover, clinical manifestations of disease in developing brains are less explicit. Although not specific, neuroimaging may be contributory to the diagnosis of these disorders in pediatric patients. Brain magnetic resonance images were reviewed for 133 pediatric patients investigated for a MRC disorder at a single center over a period of 10 years (1997-2006), in an attempt to identify distinctive neuroimaging features of MRC defects. Patients fit into four groups, according to the Bernier criteria: definite (63 cases), probable (53 cases), possible (7 cases) and unlikely diagnosis (10 cases). Brain atrophy (41 cases), supratentorial white matter lesions (14 cases), basal ganglia involvement (9 cases), and delayed myelination (9 cases) were the most frequent anomalies in the definite group, and 8 patients presented Leigh syndrome. Neuroimaging findings of the 63 children in the definite group were compared with the remainder and with those in the possible and unlikely groups. There were no significant differences in brain images between the groups analyzed, and therefore no distinctive brain imaging features were identified specific for MRC disorders.

Treatment of mitochondrial disorders

Treatment of mitochondrial disorders (MIDs) is a challenge since there is only symptomatic therapy available and since only few randomized and controlled studies have been carried out, which demonstrate an effect of some of the symptomatic or supportive measures available. Symptomatic treatment of MIDs is based on mainstay drugs, blood transfusions, hemodialysis, invasive measures, surgery, dietary measures, and physiotherapy. Drug treatment may be classified as specific (treatment of epilepsy, headache, dementia, dystonia, extrapyramidal symptoms, Parkinson syndrome, stroke-like episodes, or non-neurological manifestations), non-specific (antioxidants, electron donors/acceptors, alternative energy sources, cofactors), or restrictive (avoidance of drugs known to be toxic for mitochondrial functions). Drugs which more frequently than in the general population cause side effects in MID patients include steroids, propofol, statins, fibrates, neuroleptics, and anti-retroviral agents. Invasive measures include implantation of a pacemaker, biventricular pacemaker, or implantable cardioverter defibrillator, or stent therapy. Dietary measures can be offered for diabetes, hyperlipidemia, or epilepsy (ketogenic diet, anaplerotic diet). Treatment should be individualized because of the peculiarities of mitochondrial genetics. Despite limited possibilities, symptomatic treatment should be offered to MID patients, since it can have a significant impact on the course and outcome.

RECONSIDERING IDIOPATHIC CK-ELEVATION

This study investigated the frequency of persisting, idiopathic creatine-kinase (CK)-elevation, how often the cause of idiopathic CK-elevation could be clarified, and the most frequent causes of idiopathic CK-elevation. Among 28 patients with previously idiopathic CK-elevation, CK remained elevated in 32%. The cause of idiopathic CK-elevation could be determined in 46%. Causes were mitochondriopathy (n = 5), seizure (n = 2), stroke (n = 2), myositis (n = 1), intramuscular-injection (n = 1), alcohol myopathy (n = 1), and pravastátin myopathy (n = 1). In 10 of these patients CK was normal at follow-up. CK-elevation remained idiopathic in 54%. Idiopathic CK-elevation should be comprehensively re-evaluated, even if CK is only slightly elevated or normal at follow-up.

Apical hypertrophic cardiomyopathy in encephalomyopathy

Apical hypertrophic cardiomyopathy (AHC) is associated with neurological abnormalities such as transient ischemic attack, stroke, limb-girdle muscular dystrophy, or eosinophilic myositis in single cases. The association of AHC and metabolic myopathy has not been reported. In an 84-year-old woman with long-standing gait disturbance, dementia, Parkinson syndrome, ptosis, ophthalmoparesis, tetraparesis, polyneuropathy, lactacidosis, polyarthralgia, dorsalgia, and osteoporosis, cardiac examination for long-standing anginal chest pain and palpitations, revealed supraventricular and monomorphic ventricular ectopic beats, hypertrophic signs, ST-depression and negative T waves on electrocardiogram (ECG), diastolic dysfunction with impaired relaxation, and AHC on transthoracic echocardiography. AHC was confirmed by cardiac magnetic resonance imaging, which additionally showed a small left ventricular apical aneurysm with a wall-thickness of only 3 mm. The patient was suspected to additionally have a multisystem disease, most likely due to impaired oxidative metabolism. This case shows that AHC may take a mild course and be associated with a number of extracardiac abnormalities.

Epilepsy and inborn errors of metabolism in adults: a diagnostic approach

Inborn errors of metabolism (IEMs) represent poorly known causes of epilepsy in adulthood. Although rare, these are important to recognize for several reasons: some IEMs respond to specific treatments, some antiepileptic drugs interfering with metabolic pathways may worsen the clinical condition, and specific genetic counselling can be provided. We review IEMs potentially revealed by epilepsy that can be encountered in an adult neurology department. We distinguished progressive myoclonic epilepsies (observed in some lysosomal storage diseases, respiratory chain disorders and Lafora disease), from other forms of epilepsies (observed in disorders of intermediary metabolism, including porphyrias, creatine metabolism defects, glucose transporter (GLUT-1) deficiency, Wilson disease or succinic semialdehyde dehydrogenase deficiency). We propose a diagnostic approach and point out clinical, radiological and electrophysiological features that suggest an IEM in an epileptic patient.

Genotype-phenotype correlation of maternally inherited disorders due to mutations in mitochondrial DNA

Mitochondrial disorders are heterogeneous systemic ailments that are most often caused by maternal inheritance of a variety of mutations of the mitochondrial (mt) DNA. Paternal inheritance and somatic mutation are rare. The disorders are well recognized not only for the genotypic heterogeneity, but also the phenotypic variation among the affected members of a single family. The genotype-phenotype correlation of the diversity of the syndromic and non-syndromic features of mitochondrial disorders are discussed. Some aspects of the molecular mechanisms of this heterogeneity, and the histopathologic findings are highlighted.

Central nervous system manifestations of mitochondrial disorders

The central nervous system (CNS) is, after the peripheral nervous system, the second most frequently affected organ in mitochondrial disorders (MCDs). CNS involvement in MCDs is clinically heterogeneous, manifesting as epilepsy, stroke-like episodes, migraine, ataxia, spasticity, extrapyramidal abnormalities, bulbar dysfunction, psychiatric abnormalities, neuropsychological deficits, or hypophysial abnormalities. CNS involvement is found in syndromic and non-syndromic MCDs. Syndromic MCDs with CNS involvement include mitochondrial encephalomyopathy, lactacidosis, stroke-like episodes syndrome, myoclonic epilepsy and ragged red fibers syndrome, mitochondrial neuro-gastrointestinal encephalomyopathy syndrome, neurogenic muscle weakness, ataxia, and retinitis pigmentosa syndrome, mitochondrial depletion syndrome, Kearns-Sayre syndrome, and Leigh syndrome, Leber's hereditary optic neuropathy, Friedreich's ataxia, and multiple systemic lipomatosis. As CNS involvement is often subclinical, the CNS including the spinal cord should be investigated even in the absence of overt clinical CNS manifestations. CNS investigations comprise the history, clinical neurological examination, neuropsychological tests, electroencephalogram, cerebral computed tomography scan, and magnetic resonance imaging. A spinal tap is indicated if there is episodic or permanent impaired consciousness or in case of cognitive decline. More sophisticated methods are required if the CNS is solely affected. Treatment of CNS manifestations in MCDs is symptomatic and focused on epilepsy, headache, lactacidosis, impaired consciousness, confusion, spasticity, extrapyramidal abnormalities, or depression. Valproate, carbamazepine, corticosteroids, acetyl salicylic acid, local and volatile anesthetics should be applied with caution. Avoiding certain drugs is often more beneficial than application of established, apparently indicated drugs.

Adult unilateral periventricular pseudocysts with ipsilateral headache

OBJECTIVES

Unilateral periventricular pseudocysts (PVPC), manifesting as ipsilateral headache have been only rarely reported in adults.

CASE REPORT

In a 48-year-old woman, right-sided, pulsating headache occurred in 1999. Headache exclusively extended over the right head and periorbitally; it was frequently associated with a feeling of cold, lasted maximally for 1 day, and occasionally went along with nausea and right-sided lacrimation. Since January 2003, headache occurred daily with varying intensity. For headache, she was regularly taking doxepin (25 mg). Ordinary analgesics and tryptanes were only of minimal effect. Since 2001, left-sided hemi-hypesthesia occurred. CT and MRI scans of the brain disclosed right-sided cysts in the white matter with a maximal diameter of 1cm, partially grouped and partially disseminated and bilateral calcifications of the basal ganglia. Since hypoxemia/ischemia, subependymal hemorrhage, CNS infection, developmental defect of the mantle layer, chromosomal disorder, Zellweger syndrome, carbon monoxide intoxication, trauma, or mitochondriopathy were not causative, the etiology of PVPC remained questionable.

CONCLUSIONS

Rarely, unilateral PVPC become symptomatic in adulthood, manifesting as ipsilateral headache, contralateral hemi-hypesthesia, depression, collapses, and slight cognitive decline. Clinical progression of the disease is not necessarily related to the progression of the imaging findings. PVPC should be included in the differential diagnosis of unilateral headache.

Basal Ganglia calcification in mitochondrial disorders

Though basal ganglia calcification (BGC) has been recognized as a feature of mitochondriopathy, little is known about its frequency in a larger cohort. The aim of this work was to assess the frequency of BGC, type and frequency of clinical and additional imaging central-nervous-system (CNS) abnormalities and of non-CNS abnormalities in mitochondriopathy patients with BGC. Retrospectively reviewed were the records of all mitochondriopathy patients in whom BGC was found on cerebral CT during 10 years. Among those who underwent cerebral CT, thirty-six, 24 women, 12 men, aged 33-93 years, showed BGC. The most frequent clinical CNS manifestations in these patients were epilepsy (n = 9), Parkinson syndrome (n = 9), dementia (n = 7), dysarthria (n = 5), spasticity (n = 4), tremor (n = 4), or stroke (n = 4). Additional cerebral CT-findings were atrophy (n = 10), lacunas (n = 6), leucaraiosis (n = 6), focal gliosis (n = 4), or stroke (n = 1). MR imaging, carried out in 12 patients, confirmed BGC in one. The 36 patients presented with involvement of the CNS (n = 32), endocrine system (n = 29), peripheral nervous system (n = 28), heart (n = 23), inner ear (n = 16), eyes (n = 15), guts (n = 11), blood (n = 9), kidney (n = 2), or dermis (n = 2). BGC occurs in one sixth of non-selected patients with mitochondriopathy and is associated with clinical and imaging CNS abnormalities and multisystem disease in the majority of them.

[Isolated ptosis in a 58-year-old woman]

A 60-year-old woman who had experienced isolated ptosis for two years was seen when it had been fixed for one year. She had a personal and familial history of stromal corneal dystrophy. The diagnosis of mitochondrial cytopathy was made on the basis of clinical, electrophysiological, biological and histological findings. Surgical repair of the ptosis allowed visual recovery. The relationship between ptosis, corneal dystrophy and mitochondrial cytopathy is discussed.

Mitochondrial neuropathy

Polyneuropathy is a frequent feature of mitochondriopathy (MCP). If and how often polyneuropathy in MCP is primarily due to the underlying disorder (mitochondrial neuropathy, MN) or due to other well-known causes is unknown. Retrospectively investigated were 108 MCP-patients with polyneuropathy. According to established diagnostic criteria 37 patients were classified as definite MCP, 56 as probable MCP and 15 as possible MCP. In 38 of the 108 MCP-patients with polyneuropathy (35%), no plausible cause for polyneuropathy other than MCP could be found. MN was characterized by weakness, muscle cramps, wasting, reduced tendon reflexes, muscle pain, ataxia, restless legs, hypesthesia, paresthesia, dysesthesia, and vegetative impairment. In 21 cases predominantly motor fibers, in 14 cases both motor and sensory fibers and in 3 cases predominantly sensory fibers were affected. Axonal degeneration was found in 19 cases, demyelination in 4 and mixed-type polyneuropathy in 15. On sural nerve biopsy axonal loss was the predominant finding. In a single case tomaculae and abnormally shaped and structured mitochondria were found. MN exists, occurs in one third of the MCP-patients with polyneuropathy, and is characterized by predominant affection of the motor and sensory fibers with diffuse, symmetric and equal distribution between upper and lower limbs and by axonal degeneration.

Mitochondriopathies

Mitochondriopathies (MCPs) are either due to sporadic or inherited mutations in nuclear or mitochondrial DNA located genes (primary MCPs), or due to exogenous factors (secondary MCPs). MCPs usually show a chronic, slowly progressive course and present with multiorgan involvement with varying onset between birth and late adulthood. Although several proteins with signalling, assembling, transport, enzymatic function can be impaired in MCP, most frequently the activity of the respiratory chain (RC) protein complexes is primarily or secondarily affected, leading to impaired oxygen utilization and reduced energy production. MCPs represent a diagnostic challenge because of their wide variation in presentation and course. Systems frequently affected in MCP are the peripheral nervous system (myopathy, polyneuropathy, lactacidosis), brain (leucencephalopathy, calcifications, stroke-like episodes, atrophy with dementia, epilepsy, upper motor neuron signs, ataxia, extrapyramidal manifestations, fatigue), endocrinium (short stature, hyperhidrosis, diabetes, hyperlipidaemia, hypogonadism, amenorrhoea, delayed puberty), heart (impulse generation or conduction defects, cardiomyopathy, left ventricular non-compaction heart failure), eyes (cataract, glaucoma, pigmentary retinopathy, optic atrophy), ears (deafness, tinnitus, peripheral vertigo), guts (dysphagia, vomiting, diarrhoea, hepatopathy, pseudo-obstruction, pancreatitis, pancreas insufficiency), kidney (renal failure, cysts) and bone marrow (sideroblastic anaemia). Apart from well-recognized syndromes, MCP should be considered in any patient with unexplained progressive multisystem disorder. Although there is actually no specific therapy and cure for MCP, many secondary problems require specific treatment. The rapidly increasing understanding of the pathophysiological background of MCPs may further facilitate the diagnostic approach and open perspectives to future, possibly causative therapies.

Reproducibility of the lactate stress test

Although the lactate stress test has been shown to be a powerful tool to screen for respiratory chain disorders, little is known about the reproducibility of this test. The aim of the present study was thus to look for the reliability of the lactate stress test in disease controls and patients with primary respiratory chain disorders. In 23 patients with respiratory chain disorder, 16 women and 7 men, aged 36-81 years, and 18 disease controls, 5 women and 18 men, aged 37-70 years, the lactate stress test was carried out when respiratory chain disorder was suspected for the first time and at the first follow-up. The sensitivity of the first lactate stress test was 81% and the specificity 72%. The sensitivity of the second lactate stress test was 74% and the specificity 61%. The reproducibility of the lactate stress test was 65% in patients with respiratory chain disorders and 78% in disease controls. In conclusion, this study shows that the sensitivity, specificity, and reproducibility of the lactate stress test is high enough to warrant its application as a reliable, supplementary method to search for respiratory chain disorders.

Mitochondriopathy mimicking amyotrophic lateral sclerosis

BACKGROUND

Mitochondriopathy has been rarely reported to imitate motor neuron disease.

REVIEW SUMMARY

A 57-year-old, 157-cm-tall woman with clinical and electrophysiological features of motor neuron disease since 1993 is reported. She also had increased liver function parameters, hypothyroidism, and sinus tachycardia. Because her mother and sister had both died from assumed amyotrophic lateral sclerosis, familial ALS was diagnosed. On reevaluation, screening for superoxide-dismutase gene mutations was negative, but lactate stress testing was abnormal and muscle biopsy revealed patchy COX deficiency and abnormal mitochondria. Analysis of the muscle mtDNA revealed substitutions in the isoleucine tRNA, in the ATPase-6, and in the cytochrome-b gene, respectively. Based on these data, the diagnosis of ALS was changed to mitochondriopathy.

CONCLUSIONS

Mitochondriopathy may mimic ALS, phenotypically and electrophysiologically. In patients with an ALS phenotype, slow progression, and multisystem involvement, mitochondriopathy should be considered a diagnostic possibility.

Mitochondriopathy as a differential diagnosis of amyotrophic lateral sclerosis

OBJECTIVES

To assess how often mitochondrial myopathy (MMP) mimics amyotrophic lateral sclerosis (ALS) and the phenotypic similarities and differences between these two disorders.

METHODS

Records of 123 MMP patients and 59 ALS patients, diagnosed during five years (1996-2000), were retrospectively evaluated.

RESULTS

Re-evaluation revealed that 8 patients, initially diagnosed as ALS had actually MMP (13.6%). Among the MMP patients, 6.5% were initially misdiagnosed as ALS. None of the MMP patients actually had ALS. Common features of ALS and MMP were weakness, wasting, upper motor neurone signs, bulbar abnormalities, and a neurogenic EMG. Features differentiating MMP from ALS were ptosis, sensory disturbances, multi-system involvement, slowly progressive disease course, abnormal lactate stress test, histological and biochemical abnormalities, and mtDNA analysis.

CONCLUSIONS

In a small number of cases MMP may clinically and electrophysiologically mimic ALS, particularly in the early stages of the disease. Patients with suspected ALS, but slow progression and multi-organ involvement, should undergo lactate stress testing and muscle biopsy. ALS should be diagnosed only if MMP has been excluded.

Parkinson syndrome as a manifestation of mitochondriopathy

OBJECTIVES

Although there is growing evidence for a relation between Parkinson syndrome (PS) and mitochondriopathy (MCP), little is known about the frequency of PS in MCP.

MATERIAL AND METHODS

This study assessed the frequency of PS in patients with MCP, the phenotype of these patients, and their response to anti-Parkinson medication, during a 1-year period.

RESULTS

Between April 1999 and March 2000 PS was diagnosed in nine of 76 patients with MCP (12%). The frequency of MCP among 144 patients with PS attending the department during the investigational period was 6.3%. Systems most frequently affected by the MCP in the nine patients were the peripheral nervous system, central nervous system, endocrinium, heart, intestines, eyes, ears and kidneys. PS in MCPs responded well to amantadine, L-DOPA, dopamine agonists and catechole-o-methyl-transferase inhibitors.

CONCLUSION

Twelve per cent of the patients with MCP have phenotypic features of PS and 6% of the patients with PS have features of MCP. MCP patients with PS frequently show multisystem involvement. PS in MCP responds well to anti-Parkinson medication.