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Background and Purpose: Primary mitochondrial diseases (PMDs) are common inborn errors of energy metabolism, with an estimated prevalence of one in 4300. These disorders typically affect tissues with high energy requirements, including heart, muscle and brain. Epilepsy may be the presenting feature of PMD, can be difficult to treat and often represents a poor prognostic feature. The aim of this study was to develop guidelines and consensus recommendations on safe medication use and seizure management in mitochondrial epilepsy., Methods: A panel of 24 experts in mitochondrial medicine, pharmacology and epilepsy management of adults and/or children and two patient representatives from seven countries was established. Experts were members of five different European Reference Networks, known as the Mito InterERN Working Group. A Delphi technique was used to allow the panellists to consider draft recommendations on safe medication use and seizure management in mitochondrial epilepsy, using two rounds with predetermined levels of agreement., Results: A high level of consensus was reached regarding the safety of 14 out of all 25 drugs reviewed, resulting in endorsement of National Institute for Health and Care Excellence guidelines for seizure management, with some modifications. Exceptions including valproic acid in POLG disease, vigabatrin in patients with γ-aminobutyric acid transaminase deficiency and topiramate in patients at risk for renal tubular acidosis were highlighted., Conclusions: These consensus recommendations describe our intent to improve seizure control and reduce the risk of drug-related adverse events in individuals living with PMD-related epilepsy., (© 2024 The Authors. European Journal of Neurology published by John Wiley & Sons Ltd on behalf of European Academy of Neurology.)

Background and Purpose: Primary mitochondrial diseases (PMDs) are rare diseases for which diagnosis is challenging, and management and training programs are not well defined in Europe. To capture and assess care needs, five different European Reference Networks have conducted an exploratory survey., Methods: The survey covering multiple topics relating to PMDs was sent to all ERNs healthcare providers (HCPs) in Europe., Results: We have collected answers from 220 members based in 24/27 European member states and seven non-European member states. Even though most of the responders are aware of neurogenetic diseases, difficulties arise in the ability to deliver comprehensive genetic testing. While single gene analysis is widely available in Europe, whole exome and genome sequencing are not easily accessible, with considerable variation between countries and average waiting time for results frequently above 6 months. Only 12.7% of responders were happy with the ICD-10 codes for classifying patients with PMDs discharged from the hospital, and more than 70% of them consider that PMDs deserve specific ICD codes to improve clinical management, including tailored healthcare, and for reimbursement reasons. Finally, 90% of responders declared that there is a need for further education and training in these diseases., Conclusions: This survey provides information on the current difficulties in the care of PMDs in Europe. We believe that the results of this survey are important to help rare disease stakeholders in European countries identify key care and research priorities., (© 2023. The Author(s).)

Background and Purpose: Mitochondrial diseases (MDs) are heterogeneous disorders caused by mutations in nuclear DNA (nDNA) or mitochondrial DNA (mtDNA) associated with specific syndromes. However, especially in childhood, patients often display heterogeneity. Several reports on the biochemical and molecular profiles in children have been published, but studies tend not to differentiate between mtDNA- and nDNA-associated diseases, and focus is often on a specific phenotype. Thus, large cohort studies specifically focusing on mtDNA defects in the pediatric population are lacking., Methods: We reviewed the clinical, metabolic, biochemical, and neuroimaging data of 150 patients with MDs due to mtDNA alterations collected at our neurological institute over the past 20 years., Results: mtDNA impairment is less frequent than nDNA impairment in pediatric MDs. Ocular involvement is extremely frequent in our cohort, as is classical Leber hereditary optic neuropathy, especially with onset before 12 years of age. Extraneurological manifestations and isolated myopathy appear to be rare, unlike adult phenotypes. Deep gray matter involvement, early disease onset, and specific phenotypes, such as Pearson syndrome and Leigh syndrome, represent unfavorable prognostic factors. Phenotypes related to single large scale mtDNA deletions appear to be very frequent in the pediatric population. Furthermore, we report for the first time an mtDNA pathogenic variant associated with cavitating leukodystrophy., Conclusions: We report on a large cohort of pediatric patients with mtDNA defects, adding new data on the phenotypical characterization of mtDNA defects and suggestions for diagnostic workup and therapeutic approach., (© 2023 The Authors. European Journal of Neurology published by John Wiley & Sons Ltd on behalf of European Academy of Neurology.)

Mitochondrial diseases are a heterogeneous group of multisystem disorders caused by impaired mitochondrial function. These disorders occur at any age and involve any tissue, typically affecting organs highly dependent on aerobic metabolism. Diagnosis and management are extremely difficult due to various underlying genetic defects and a wide range of clinical symptoms. Preventive care and active surveillance are strategies to try to reduce morbidity and mortality by timely treatment of organ-specific complications. More specific interventional therapies are in early phases of development and no effective treatment or cure currently exists. A variety of dietary supplements have been utilized based on biological logic. For several reasons, few randomized controlled trials have been completed to assess the efficacy of these supplements. The majority of the literature on supplement efficacy represents case reports, retrospective analyses and open-label studies. We briefly review selected supplements that have some degree of clinical research support. In mitochondrial diseases, potential triggers of metabolic decompensation or medications that are potentially toxic to mitochondrial function should be avoided. We shortly summarize current recommendations on safe medication in mitochondrial diseases. Finally, we focus on the frequent and debilitating symptoms of exercise intolerance and fatigue and their management including physical training strategies., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Leucine zipper-EF-hand containing transmembrane protein 1 (LETM1) encodes an inner mitochondrial membrane protein with an osmoregulatory function controlling mitochondrial volume and ion homeostasis. The putative association of LETM1 with a human disease was initially suggested in Wolf-Hirschhorn syndrome, a disorder that results from de novo monoallelic deletion of chromosome 4p16.3, a region encompassing LETM1. Utilizing exome sequencing and international gene-matching efforts, we have identified 18 affected individuals from 11 unrelated families harboring ultra-rare bi-allelic missense and loss-of-function LETM1 variants and clinical presentations highly suggestive of mitochondrial disease. These manifested as a spectrum of predominantly infantile-onset (14/18, 78%) and variably progressive neurological, metabolic, and dysmorphic symptoms, plus multiple organ dysfunction associated with neurodegeneration. The common features included respiratory chain complex deficiencies (100%), global developmental delay (94%), optic atrophy (83%), sensorineural hearing loss (78%), and cerebellar ataxia (78%) followed by epilepsy (67%), spasticity (53%), and myopathy (50%). Other features included bilateral cataracts (42%), cardiomyopathy (36%), and diabetes (27%). To better understand the pathogenic mechanism of the identified LETM1 variants, we performed biochemical and morphological studies on mitochondrial K + /H + exchange activity, proteins, and shape in proband-derived fibroblasts and muscles and in Saccharomyces cerevisiae, which is an important model organism for mitochondrial osmotic regulation. Our results demonstrate that bi-allelic LETM1 variants are associated with defective mitochondrial K + efflux, swollen mitochondrial matrix structures, and loss of important mitochondrial oxidative phosphorylation protein components, thus highlighting the implication of perturbed mitochondrial osmoregulation caused by LETM1 variants in neurological and mitochondrial pathologies., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Introduction: Both prevalence and clinical features of the various movement disorders in adults with primary mitochondrial diseases are unknown., Methods: Based on the database of the "Nation-wide Italian Collaborative Network of Mitochondrial Diseases", we reviewed the clinical, genetic, neuroimaging and neurophysiological data of adult patients with primary mitochondrial diseases (n = 764) where ataxia, myoclonus or other movement disorders were part of the clinical phenotype., Results: Ataxia, myoclonus and movement disorders were present in 105/764 adults (13.7%), with the onset coinciding or preceding the diagnosis of the mitochondrial disease in 49/105 (46.7%). Ataxia and parkinsonism were the most represented, with an overall prevalence at last follow-up of 59.1% and 30.5%, respectively. Hyperkinetic movement disorders were reported in 15.3% at last follow-up, being the less common reported movement disorders. The pathogenic m.8344A > G and POLG variants were always associated with a movement disorder, while LHON variants and mtDNA single deletions were more commonly found in the subjects who did not present a movement disorder. The most common neuroimaging features were cortical and/or cerebellar atrophy, white matter hyperintensities, basal ganglia abnormalities and nigro-striatal degeneration. Almost 70% of patients with parkinsonism responded to dopaminergic therapy, mainly levodopa, and 50% with myoclonus were successfully treated with levetiracetam., Conclusion: Movement disorders, mainly ataxia and parkinsonism, are important findings in adult primary mitochondrial diseases. This study underlies the importance of looking for a mitochondrial etiology in the diagnostic flowchart of a movement disorder and may help direct genetic screening in daily practice., (© 2021. The Author(s).)

Coenzyme Q (CoQ) is a key component of the respiratory chain of all eukaryotic cells. Its function is closely related to mitochondrial respiration, where it acts as an electron transporter. However, the cellular functions of coenzyme Q are multiple: it is present in all cell membranes, limiting the toxic effect of free radicals, it is a component of LDL, it is involved in the aging process, and its deficiency is linked to several diseases. Recently, it has been proposed that coenzyme Q contributes to suppressing ferroptosis, a type of iron-dependent programmed cell death characterized by lipid peroxidation. In this review, we report the latest hypotheses and theories analyzing the multiple functions of coenzyme Q. The complete knowledge of the various cellular CoQ functions is essential to provide a rational basis for its possible therapeutic use, not only in diseases characterized by primary CoQ deficiency, but also in large number of diseases in which its secondary deficiency has been found.

Background: Leigh syndrome (LS) is a progressive neurodegenerative disorder associated with primary or secondary dysfunction of mitochondrial oxidative phosphorylation and is the most common mitochondrial disease in childhood. Numerous reports on the biochemical and molecular profiles of LS have been published, but there are limited studies on genetically confirmed large series. We reviewed the clinical, imaging, biochemical and molecular data of 122 patients with a diagnosis of LS collected in the Italian Collaborative Network of Mitochondrial Diseases database., Results: Clinical picture was characterized by early onset of several neurological signs dominated by central nervous system involvement associated with both supra- and sub-tentorial grey matter at MRI in the majority of cases. Extraneurological organ involvement is less frequent in LS than expected for a mitochondrial disorder. Complex I and IV deficiencies were the most common biochemical diagnoses, mostly associated with mutations in SURF1 or mitochondrial-DNA genes encoding complex I subunits. Our data showed SURF1 as the genotype with the most unfavorable prognosis, differently from other cohorts reported to date., Conclusion: We report on a large genetically defined LS cohort, adding new data on phenotype-genotype correlation, prognostic factors and possible suggestions to diagnostic workup., (© 2021. The Author(s).)

Patients with mitochondrial diseases, who usually manifest a multisystem disease, are considered potentially at-risk for a severe coronavirus disease 2019 (COVID-19). The objective of this study is to analyze the clinical features, prognosis and outcomes of COVID-19 in patients with primary mitochondrial diseases in a cohort of patients followed in Italy. We searched for patients with primary mitochondrial diseases and COVID-19 followed by the Italian Collaborative Network of Mitochondrial Diseases. In a total of 1843 patients followed by the National Network, we have identified from March 1st to January 30th, 2021, 27 SARS-CoV-2 infection. Most of the patients were pauci or asymptomatic (85%) and treated at home. The most common signs of COVID-19 were fever (78,9%), fatigue (47,4%), myalgia (42,1%), cough and headache (36,8%), and dyspnea (31,6%). Those who required COVID-19 therapy were treated with low-molecular-weight heparin, glucocorticoids, and antibiotics (mainly azithromycin) without serious side effects related to the therapy. Five patients (18,5%) clinically deteriorated during the infection, and one of them died for pneumonia. Primary mitochondrial diseases infected individuals seemed to be similarly affected by SARS-CoV-2 compared with the general Italian population in terms of clinical presentation and outcome., (Copyright © 2021 Elsevier B.V. and Mitochondria Research Society. All rights reserved.)

Clinical guidance is often sought when prescribing drugs for patients with primary mitochondrial disease. Theoretical considerations concerning drug safety in patients with mitochondrial disease may lead to unnecessary withholding of a drug in a situation of clinical need. The aim of this study was to develop consensus on safe medication use in patients with a primary mitochondrial disease. A panel of 16 experts in mitochondrial medicine, pharmacology, and basic science from six different countries was established. A modified Delphi technique was used to allow the panellists to consider draft recommendations anonymously in two Delphi rounds with predetermined levels of agreement. This process was supported by a review of the available literature and a consensus conference that included the panellists and representatives of patient advocacy groups. A high level of consensus was reached regarding the safety of all 46 reviewed drugs, with the knowledge that the risk of adverse events is influenced both by individual patient risk factors and choice of drug or drug class. This paper details the consensus guidelines of an expert panel and provides an important update of previously established guidelines in safe medication use in patients with primary mitochondrial disease. Specific drugs, drug groups, and clinical or genetic conditions are described separately as they require special attention. It is important to emphasise that consensus-based information is useful to provide guidance, but that decisions related to drug prescribing should always be tailored to the specific needs and risks of each individual patient. We aim to present what is current knowledge and plan to update this regularly both to include new drugs and to review those currently included., (© 2020 The Authors. Journal of Inherited Metabolic Disease published by John Wiley & Sons Ltd on behalf of SSIEM.)

Many aspects of epilepsy in mitochondrial disorders (MDs) need to be further clarified. To this aim, we explored retrospectively a cohort of individuals with MDs querying the "Nationwide Italian Collaborative Network of Mitochondrial Diseases" (NICNMD) database (1467 patients included since 2010 to December 2016). We collected information on age at epilepsy onset, seizure type and frequency, genetic findings, and antiepileptic drugs (AEDs). At the time of our survey, 147/1467 (10%) patients in the NICNMD database had epilepsy. Complete information was available only for 98 patients, 52 males and 46 females, aged 5-92 years (mean age 40.4 ± 18.4; 14/98 children/teenagers and 84 adults). Epilepsy was the presenting feature of MD in 46/98 (47%) individuals, with onset at a median age of 19 years (range, 0.2-68; < 3 years in 14/97 (14%), 3-19 years in 36/97 (37%), > 19 years in 47/97 (49%)). Moreover, 91/98 patients (93%) displayed multiple seizures, with daily or weekly frequency in 25/91 (28%). Interictal EEG was abnormal in 70/78 (90%) patients, displaying abnormal background (47/70; 67%) and/or interictal paroxysms (53/70; 76%). Eighty of 90 patients (89%) displayed a 50-100% reduction of seizures on AEDs; levetiracetam was the most commonly used. Forty-one patients (42%) carried the m.3243A>G mutation, 16 (16%) the m.8344A>G, and 9 (9%) nuclear DNA (nDNA) mutations. Individuals with early-onset seizures mainly carried nDNA mutations and had a more severe epilepsy phenotype, higher seizure frequency, and disorganized background EEG activity. A better definition of epilepsy in MDs may foster the diagnostic workup, management, and treatment of affected patients, and allow more homogeneous patient stratification.

Muscle pain may be part of many neuromuscular disorders including myopathies, peripheral neuropathies and lower motor neuron diseases. Although it has been reported also in mitochondrial diseases (MD), no extensive studies in this group of diseases have been performed so far. We reviewed clinical data from 1398 patients affected with mitochondrial diseases listed in the database of the "Nation-wide Italian Collaborative Network of Mitochondrial Diseases", to assess muscle pain and its features. Muscle pain was present in 164 patients (11.7%). It was commonly observed in subjects with chronic progressive external ophthalmoplegia (cPEO) and with primary myopathy without cPEO, but also-although less frequently-in multisystem phenotypes such as MELAS, MERFF, Kearns Sayre syndrome, NARP, MNGIE and Leigh syndrome. Patients mainly complain of diffuse exercise-related muscle pain, but focal/multifocal and at rest myalgia were often also reported. Muscle pain was more commonly detected in patients with mitochondrial DNA mutations (67.8%) than with nuclear DNA changes (32.2%). Only 34% of the patients showed a good response to drug therapy. Interestingly, patients with nuclear DNA mutations tend to have a better therapeutic response than patients with mtDNA mutations. Muscle pain is present in a significant number of patients with MD, being one of the most common symptoms. Although patients with a myopathic phenotype are more prone to develop muscle pain, this is also observed in patients with a multi system involvement, representing an important and disabling symptom having poor response to current therapy.

Next Generation Sequencing (NGS) technologies are revolutionizing the diagnostic screening for rare disease entities, including primary mitochondrial disorders, particularly those caused by nuclear gene defects. NGS approaches are able to identify the causative gene defects in small families and even single individuals, unsuitable for investigation by traditional linkage analysis. These technologies are contributing to fill the gap between mitochondrial disease cases defined on the basis of clinical, neuroimaging and biochemical readouts, which still outnumber by approximately 50% the cases for which a molecular-genetic diagnosis is attained. We have been using a combined, two-step strategy, based on targeted genes panel as a first NGS screening, followed by whole exome sequencing (WES) in still unsolved cases, to analyze a large cohort of subjects, that failed to show mutations in mtDNA and in ad hoc sets of specific nuclear genes, sequenced by the Sanger's method. Not only this approach has allowed us to reach molecular diagnosis in a significant fraction (20%) of these difficult cases, but it has also revealed unexpected and conceptually new findings. These include the possibility of marked variable penetrance of recessive mutations, the identification of large-scale DNA rearrangements, which explain spuriously heterozygous cases, and the association of mutations in known genes with unusual, previously unreported clinical phenotypes. Importantly, WES on selected cases has unraveled the presence of pathogenic mutations in genes encoding non-mitochondrial proteins (e.g. the transcription factor E4F1), an observation that further expands the intricate genetics of mitochondrial disease and suggests a new area of investigation in mitochondrial medicine. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi., (Copyright © 2016. Published by Elsevier B.V.)

Involvement of the peripheral nervous system in mitochondrial disorders has been previously reported. However, the prevalence of peripheral neuropathy in mitochondrial disorders is still unclear. Based on the large database of the "Nation-wide Italian Collaborative Network of Mitochondrial Diseases", we reviewed the clinical data of 1200 patients, with special regard to peripheral neuropathy (mean age at onset 24.3 ± 20.1 years; age at last evaluation 39.8 ± 22.3 years; females 52.7%; childhood onset [before age 16 years] 43.1%). Peripheral neuropathy was present in 143/1156 patients (12.4%), being one of the ten most common signs and symptoms. POLG mutations cause a potentially painful, axonal/mixed, mainly sensory polyneuropathy; TYMP mutations lead to a demyelinating sensory-motor polyneuropathy; SURF1 mutations are associated with a demyelinating/mixed sensory-motor polyneuropathy. The only mtDNA mutation consistently associated with peripheral neuropathy (although less severely than in the above-considered nuclear genes) was the m.8993T > G (or the rarer T > C) changes, which lead to an axonal, mainly sensory polyneuropathy. In conclusion, peripheral neuropathy is one of the most common features of a mitochondrial disorder, and may negatively impact on the quality of life of these patients. Furthermore, the presence or absence of peripheral neuropathy, as well as its specific forms and the association with neuropathic pain (indicative of a POLG-associated disease) can guide the molecular analysis., (Copyright © 2016 Elsevier B.V. All rights reserved.)

With a combined carrier frequency of 1:200, heteroplasmic mitochondrial DNA (mtDNA) mutations cause human disease in ∼1:5000 of the population. Rapid shifts in the level of heteroplasmy seen within a single generation contribute to the wide range in the severity of clinical phenotypes seen in families transmitting mtDNA disease, consistent with a genetic bottleneck during transmission. Although preliminary evidence from human pedigrees points towards a random drift process underlying the shifting heteroplasmy, some reports describe differences in segregation pattern between different mtDNA mutations. However, based on limited observations and with no direct comparisons, it is not clear whether these observations simply reflect pedigree ascertainment and publication bias. To address this issue, we studied 577 mother-child pairs transmitting the m.11778G>A, m.3460G>A, m.8344A>G, m.8993T>G/C and m.3243A>G mtDNA mutations. Our analysis controlled for inter-assay differences, inter-laboratory variation and ascertainment bias. We found no evidence of selection during transmission but show that different mtDNA mutations segregate at different rates in human pedigrees. m.8993T>G/C segregated significantly faster than m.11778G>A, m.8344A>G and m.3243A>G, consistent with a tighter mtDNA genetic bottleneck in m.8993T>G/C pedigrees. Our observations support the existence of different genetic bottlenecks primarily determined by the underlying mtDNA mutation, explaining the different inheritance patterns observed in human pedigrees transmitting pathogenic mtDNA mutations., (© The Author 2016. Published by Oxford University Press.)

Mitochondrial disorders are a group of highly invalidating human conditions for which effective treatment is currently unavailable and characterized by faulty energy supply due to defective oxidative phosphorylation (OXPHOS). Given the complexity of mitochondrial genetics and biochemistry, mitochondrial inherited diseases may present with a vast range of symptoms, organ involvement, severity, age of onset, and outcome. Despite the wide spectrum of clinical signs and biochemical underpinnings of this group of dis-orders, some common traits can be identified, based on both pathogenic mechanisms and potential therapeutic approaches. Here, we will review two peculiar mitochondrial disorders, ethylmalonic encephalopathy (EE) and mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), caused by mutations in the ETHE1 and TYMP nuclear genes, respectively. ETHE1 encodes for a mitochondrial enzyme involved in sulfide detoxification and TYMP for a cytosolic enzyme involved in the thymidine/deoxyuridine catabolic pathway. We will discuss these two clinical entities as a paradigm of mitochondrial diseases caused by the accumulation of compounds normally present in traces, which exerts a toxic and inhibitory effect on the OXPHOS system., (© 2015 The Authors. Published under the terms of the CC BY 4.0 license.)

Increased levels of the mitochondria-shaping protein Opa1 improve respiratory chain efficiency and protect from tissue damage, suggesting that it could be an attractive target to counteract mitochondrial dysfunction. Here we show that Opa1 overexpression ameliorates two mouse models of defective mitochondrial bioenergetics. The offspring from crosses of a constitutive knockout for the structural complex I component Ndufs4 (Ndufs4(-/-)), and of a muscle-specific conditional knockout for the complex IV assembly factor Cox15 (Cox15(sm/sm)), with Opa1 transgenic (Opa1(tg)) mice showed improved motor skills and respiratory chain activities compared to the naive, non-Opa1-overexpressing, models. While the amelioration was modest in Ndufs4(-/-)::Opa1(tg) mice, correction of cristae ultrastructure and mitochondrial respiration, improvement of motor performance and prolongation of lifespan were remarkable in Cox15(sm/sm)::Opa1(tg) mice. Mechanistically, respiratory chain supercomplexes were increased in Cox15(sm/sm)::Opa1(tg) mice, and residual monomeric complex IV was stabilized. In conclusion, cristae shape amelioration by controlled Opa1 overexpression improves two mouse models of mitochondrial disease., (Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.)

Progressive external ophthalmoplegia (PEO), Kearns-Sayre syndrome (KSS) and Pearson syndrome are the three sporadic clinical syndromes classically associated with single large-scale deletions of mitochondrial DNA (mtDNA). PEO plus is a term frequently utilized in the clinical setting to identify patients with PEO and some degree of multisystem involvement, but a precise definition is not available. The purpose of the present study is to better define the clinical phenotypes associated with a single mtDNA deletion, by a retrospective study on a large cohort of 228 patients from the database of the "Nation-wide Italian Collaborative Network of Mitochondrial Diseases". In our database, single deletions account for about a third of all patients with mtDNA-related disease, more than previously recognized. We elaborated new criteria for the definition of PEO and "KSS spectrum" (a category of which classic KSS represents the most severe extreme). The criteria for "KSS spectrum" include the resulting multisystem clinical features associated with the KSS features, and which therefore can predict their presence or subsequent development. With the new criteria, we were able to classify nearly all our single-deletion patients: 64.5% PEO, 31.6% KSS spectrum (including classic KSS 6.6%) and 2.6% Pearson syndrome. The deletion length was greater in KSS spectrum than in PEO, whereas heteroplasmy was inversely related with age at onset. We believe that the new phenotype definitions implemented here may contribute to a more homogeneous patient categorization, which will be useful in future cohort studies of natural history and clinical trials.

Primary coenzyme Q10 (CoQ10) deficiencies are rare, clinically heterogeneous disorders caused by mutations in several genes encoding proteins involved in CoQ10 biosynthesis. CoQ10 is an essential component of the electron transport chain (ETC), where it shuttles electrons from complex I or II to complex III. By whole-exome sequencing, we identified five individuals carrying biallelic mutations in COQ4. The precise function of human COQ4 is not known, but it seems to play a structural role in stabilizing a multiheteromeric complex that contains most of the CoQ10 biosynthetic enzymes. The clinical phenotypes of the five subjects varied widely, but four had a prenatal or perinatal onset with early fatal outcome. Two unrelated individuals presented with severe hypotonia, bradycardia, respiratory insufficiency, and heart failure; two sisters showed antenatal cerebellar hypoplasia, neonatal respiratory-distress syndrome, and epileptic encephalopathy. The fifth subject had an early-onset but slowly progressive clinical course dominated by neurological deterioration with hardly any involvement of other organs. All available specimens from affected subjects showed reduced amounts of CoQ10 and often displayed a decrease in CoQ10-dependent ETC complex activities. The pathogenic role of all identified mutations was experimentally validated in a recombinant yeast model; oxidative growth, strongly impaired in strains lacking COQ4, was corrected by expression of human wild-type COQ4 cDNA but failed to be corrected by expression of COQ4 cDNAs with any of the mutations identified in affected subjects. COQ4 mutations are responsible for early-onset mitochondrial diseases with heterogeneous clinical presentations and associated with CoQ10 deficiency., (Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.)

Myoclonus is a possible manifestation of mitochondrial disorders, and its presence is considered, in association with epilepsy and the ragged red fibers, pivotal for the syndromic diagnosis of MERRF (myoclonic epilepsy with ragged red fibers). However, its prevalence in mitochondrial diseases is not known. The aims of this study are the evaluation of the prevalence of myoclonus in a big cohort of mitochondrial patients and the clinical characterization of these subjects. Based on the database of the "Nation-wide Italian Collaborative Network of Mitochondrial Diseases," we reviewed the clinical and molecular data of mitochondrial patients with myoclonus among their clinical features. Myoclonus is a rather uncommon clinical feature of mitochondrial diseases (3.6% of 1,086 patients registered in our database). It is not strictly linked to a specific genotype or phenotype, and only 1 of 3 patients with MERRF harbors the 8344A>G mutation (frequently labeled as "the MERRF mutation"). Finally, myoclonus is not inextricably linked to epilepsy in MERRF patients, but more to cerebellar ataxia. In a myoclonic patient, evidences of mitochondrial dysfunction must be investigated, even though myoclonus is not a common sign of mitochondriopathy. Clinical, histological, and biochemical data may predict the finding of a mitochondrial or nuclear DNA mutation. Finally, this study reinforces the notion that myoclonus is not inextricably linked to epilepsy in MERRF patients, and therefore the term "myoclonic epilepsy" seems inadequate and potentially misleading., (© 2014 International Parkinson and Movement Disorder Society.)

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.

Background: Amyotrophic lateral sclerosis (ALS) is a major cause of neurological disability and its pathogenesis remains elusive despite a multitude of studies. Although defects of the mitochondrial respiratory chain have been described in several ALS patients, their pathogenic significance is unclear., Objective: To review systematically the muscle biopsy specimens from patients with typical sporadic ALS to search for possible mitochondrial oxidative impairment., Design: Retrospective histochemical, biochemical, and molecular studies of muscle specimens., Setting: Tertiary care university. Subjects Fifty patients with typical sporadic ALS (mean age, 55 years). Main Outcome Measure Number of patients showing a clear muscle mitochondrial dysfunction assessed through histochemical and biochemical muscle analysis., Results: Histochemical data showed cytochrome c oxidase (COX)-negative fibers in 46% patients. Based on COX histochemical activity, patients fell into 4 groups: 27 had normal COX activity; and 8 had mild (2-4 COX-negative fibers of 100 fibers), 8 had moderate (5-10 COX-negative fibers of 100), and 7 had severe (>10 COX-negative fibers of 100) COX deficiency. Spectrophotometric measurement of respiratory chain activities showed that 3 patients with severe histochemical COX deficiency also showed combined enzyme defects. In 1 patient, COX deficiency worsened in a second biopsy taken 9 months after the first. Among the patients with severe COX deficiency, one had a new mutation in the SOD1 gene, another a mutation in the TARDBP gene, and a third patient with biochemically confirmed COX deficiency had multiple mitochondrial DNA deletions detectable by Southern blot analysis., Conclusions: Our data confirm that the histochemical finding of COX-negative fibers is common in skeletal muscle from patients with sporadic ALS. We did not find a correlation between severity of the oxidative defect and age of the patients or duration of the disease. However, the only patient who underwent a second muscle biopsy did show a correlation between severity of symptoms and worsening of the respiratory chain defect. In 7 patients, the oxidative defect was severe enough to support the hypothesis that mitochondrial dysfunction must play a role in the pathogenesis of the disease.

A disulfide relay system (DRS) was recently identified in the yeast mitochondrial intermembrane space (IMS) that consists of two essential components: the sulfhydryl oxidase Erv1 and the redox-regulated import receptor Mia40. The DRS drives the import of cysteine-rich proteins into the IMS via an oxidative folding mechanism. Erv1p is reoxidized within this system, transferring its electrons to molecular oxygen through interactions with cytochrome c and cytochrome c oxidase (COX), thereby linking the DRS to the respiratory chain. The role of the human Erv1 ortholog, GFER, in the DRS has been poorly explored. Using homozygosity mapping, we discovered that a mutation in the GFER gene causes an infantile mitochondrial disorder. Three children born to healthy consanguineous parents presented with progressive myopathy and partial combined respiratory-chain deficiency, congenital cataract, sensorineural hearing loss, and developmental delay. The consequences of the mutation at the level of the patient's muscle tissue and fibroblasts were 1) a reduction in complex I, II, and IV activity; 2) a lower cysteine-rich protein content; 3) abnormal ultrastructural morphology of the mitochondria, with enlargement of the IMS space; and 4) accelerated time-dependent accumulation of multiple mtDNA deletions. Moreover, the Saccharomyces cerevisiae erv1(R182H) mutant strain reproduced the complex IV activity defect and exhibited genetic instability of the mtDNA and mitochondrial morphological defects. These findings shed light on the mechanisms of mitochondrial biogenesis, establish the role of GFER in the human DRS, and promote an understanding of the pathogenesis of a new mitochondrial disease.

Background: The axonal forms of Charcot-Marie-Tooth (CMT2) disease are a clinically and genetically heterogeneous group of disorders. Mitofusin 2 gene (MFN2) mutations are the most common cause of CMT2. Complex phenotypes have been described in association with MFN2 gene mutations, including CMT2 with pyramidal features (hereditary motor and sensory neuropathy [HSMN V]) and CMT2 with optic atrophy (HMSN VI)., Objective: To report on the clinical, neurophysiologic, and neuropathologic features of an Italian family with a novel MFN2 gene mutation and investigate brain functional parameters using magnetic resonance spectroscopy (MRS)., Methods: Three family members, a father and his two sons, were affected by peripheral neuropathy, cognitive impairment, and poor nocturnal vision (also optic neuropathy in one case). A member of this family also showed spastic paraparesis. The MFN2 gene sequence was analyzed. A sural nerve biopsy as well as brain (1)H-MRS and (31)P-MRS were evaluated in two patients., Results: Affected family members carried a novel MFN2 missense mutation, namely R104W, located within the critical GTPase domain of the protein which affects a highly conserved amino acid position. Sural nerve biopsies showed a normal mitochondrial network, particularly at the nodes of Ranvier, upon electron microscopy examination. A significant defect of high energy phosphates (HEPs) in the visual cortex was observed at rest by (31)P-MRS in the adult proband, while his son showed a defective recovery of HEPs after stimulation of the visual cortex., Conclusion: Cognitive impairment may be another feature of the MFN2-related phenotype. The widespread peripheral and CNS involvement, as well as the neurosensorial defects, underline the similarities among MFN2-related and primary mitochondrial disorders.

A 45-year-old male patient had an episode of acute renal failure with myoglobinuria, myalgias, weakness, and markedly increased serum CK levels. Similar episodes had occurred in the past. Carnitine palmitoyl-transferase II (CPT II) deficiency was documented both biochemically and genetically. Interestingly, muscle biopsy also showed some ragged red fibers (RRF) and complete mitochondrial DNA (mtDNA) sequence disclosed a homoplasmic T3394C point mutation. This mutation is described in Leber's hereditary optic neuropathy (LHON) or in patients with diabetes mellitus.

Objectives: To document 2 apparently incongruous clinical disorders occurring in the same infant: congenital myopathy with myophosphorylase deficiency (McArdle disease) and mitochondrial hepatopathy with liver failure and mitochondrial DNA depletion., Methods: An infant girl born to consanguineous Moroccan parents had severe congenital hypotonia and hepatomegaly, developed liver failure, and died at 5 months of age. We studied muscle and liver biopsy specimens histochemically and biochemically, and we sequenced the whole coding regions of the deoxyguanosine kinase (dGK) and myophosphorylase (PYGM) genes., Results: Muscle biopsy specimens showed subsarcolemmal glycogen accumulation and negative histochemical reaction for phosphorylase. Liver biopsy specimens showed micronodular cirrhosis and massive mitochondrial proliferation. Biochemical analysis showed phosphorylase deficiency in muscle and cytochrome c oxidase deficiency in liver. We identified a novel homozygous missense G-to-A mutation at codon 456 in exon 11 of PYGM, as well as a homozygous 4-base pair GATT duplication (nucleotides 763-766) in exon 6 of dGK, which produces a frame shift and a premature TGA stop codon at nucleotides 766 to 768, resulting in a truncated 255-amino acid protein. Both mutations were absent in 100 healthy individuals., Conclusions: Our data further expand the genetic heterogeneity in patients with McArdle disease; confirm the strong relationship between mitochondrial DNA depletion syndrome, liver involvement, and dGK mutations; and suggest that genetic "double trouble" should be considered in patients with unusual severe phenotypes.

Mitochondrial disorders are human genetic diseases with extremely variable clinical and genetic features. To better define them, we made a genotype-phenotype correlation in a series of 207 affected patients, and we examined most of them with six laboratory examinations (serum CK and basal lactate levels, EMG, cardiac and EEG studies, neuroradiology). We found that, depending on the genetic abnormality, hyperckemia occurs most often with either chronic progressive external ophthalmoplegia (CPEO) and ptosis or with limb weakness. Myopathic EMGs are more common than limb weakness, except in patients with A8344G mutations. Peripheral neuropathy, when present, is always axonal. About 80% of patients with A3243G and A8344G mutations have high basal lactate levels, whereas pure CPEO is never associated with increased lactate levels. Cardiac abnormalities mostly consist of conduction defects. Abnormalities on CT or MRI of the brain are relatively common in A3243G mutations independently of the clinical phenotype. Patients with multiple mtDNA deletions are somehow "protected" against the development of abnormalities with any of the tests. We conclude that, despite the phenotypic heterogeneity of mitochondrial disorders, correlation of clinical features and laboratory findings may give the clinician important clues to the genetic defect, allowing earlier diagnosis and counselling.