MELAS: a nationwide prospective cohort study of 96 patients in Japan

Modeling Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes Syndrome Using Patient-Derived Induced Neurons Generated by Direct Reprogramming

Mitochondrial diseases are a heterogeneous group of rare genetic disorders caused by mutations in nuclear or mitochondrial DNA (mtDNA). These diseases are frequently multisystemic, although mainly affect tissues that require large amounts of energy such as the brain. Mutations in mitochondrial transfer RNA (mt-tRNA) lead to defects in protein translation that may compromise some or all mtDNA-encoded proteins. Mitochondrial Encephalomyopathy, Lactic Acidosis and Stroke-like episodes (MELAS) syndrome is mainly caused by the m.3243A>G mutation in the mt-tRNA^Leu(UUR) (MT-TL1) gene. Owing to the lack of proper animal models, several cellular models have been developed to study the disease, providing insight in the pathophysiological mechanisms of MELAS. In this study, we show a successful direct conversion of MELAS patient-derived fibroblasts into induced neurons (iNs) for the first time, as well as an electrophysiological characterization of iNs cocultured with astrocytes. In addition, we performed bioenergetics analysis to study the consequences of m.3243A>G mutation in this neuronal model of MELAS syndrome.

Molecular and neurological features of MELAS syndrome in paediatric patients: A case series and review of the literature

BACKGROUND

Mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome is one of the most well-known mitochondrial diseases, with most cases attributed to m.3243A>G. MELAS syndrome patients typically present in the first two decades of life with a broad, multi-systemic phenotype that predominantly features neurological manifestations--stroke-like episodes. However, marked phenotypic variability has been observed among paediatric patients, creating a clinical challenge and delaying diagnoses.

METHODS

A literature review of paediatric MELAS syndrome patients and a retrospective analysis in a UK tertiary paediatric neurology centre were performed.

RESULTS

Three children were included in this case series. All patients presented with seizures and had MRI changes not confined to a single vascular territory. Blood heteroplasmy varied considerably, and one patient required a muscle biopsy. Based on a literature review of 114 patients, the mean age of presentation is 8.1 years and seizures are the most prevalent manifestation of stroke-like episodes. Heteroplasmy is higher in a tissue other than blood in most cases.

CONCLUSION

The threshold for investigating MELAS syndrome in children with suspicious neurological symptoms should be low. If blood m.3243A>G analysis is negative, yet clinical suspicion remains high, invasive testing or further interrogation of the mitochondrial genome should be considered.

[A case of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) complicated by chronic intestinal pseudo-obstruction]

A 42-year-old woman presented at our hospital with acute paraphasia and word finding difficulty. She was not paralyzed or ataxic. Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) was diagnosed based on brain MRI finding of edematous lesions in bilateral temporal lobe cortexes that did not match the vascular territory, elevated lactate and pyruvate levels in blood and cerebrospinal fluid, and the presence of a mtDNA 3243A>G mutation. From six months before her visit, she had persistent anorexia, bloating, nausea and vomiting, and weight loss to 25 kg. We diagnosed her condition as chronic intestinal pseudo-obstruction (CIPO) associated with MELAS, because a gastroenterologist had previously diagnosed her with megacolon associated with colonic dysfunction. Usually, CIPO is often associated with the chronic phase of MELAS. However, since CIPO complication from the early stage of the disease is occasionally encountered, it is necessary to include mitochondrial disease in differential diagnosis of CIPO of unknown cause.

Diagnosis of adult‑onset MELAS with suspected recurrent strokes: A case report

Mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) is caused by mutations in mitochondrial DNA and is one of the most common syndromes among the mitochondrial diseases. Clinical manifestations typically occur before the age of 40 years. The present study reports a case of MELAS with a mutation in the adenine to guanine conversion at mitochondrial genome 3243 in a 48-year-old woman who was suspected of suffering from recurrent strokes. Finally, the genomic analysis confirmed the diagnosis of MELAS. This case highlights the importance of considering MELAS as a potential cause of recurrent stroke-like events if imaging findings are atypical for cerebral infarction, even among middle-aged patients with vascular risk factors.

Wernicke Encephalopathy Mimicking MELAS

Objectives: a stroke-like lesion, the morphological equivalent of a stroke-like episode and the hallmark of mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, have not been reported as manifestations of thiamine deficiency. Case report: a 62-year-old man with a history of chronic alcoholism was admitted after a series of epileptic seizures. Upon waking up from the coma, he presented with disorientation, confusion, confabulation, psychomotor agitation, aggressiveness, right hemianopsia, aphasia, and right hemineglect over weeks. Electroencephalography showed a questionable focal status epilepticus over the left hemisphere, responsive to lorazepam and oxcarbazepine. Follow-up electroencephalographies no longer recorded epileptiform discharges. Cerebral magnetic resonance imaging (MRI) revealed T2-/diffusion weighted imaging (DWI) hyperintensity in the left occipito-temporal region that was not congruent to a vascular territory which persisted for at least nine weeks. Since a lactate-peak could be seen in this lesion by magnetic resonance-spectroscopy, this was interpreted as a stroke-like lesion. Since thiamine was reduced, the stroke-like lesion was attributed to thiamine deficiency after the exclusion of differential diseases, including MELAS and status epilepticus. The patient’s behavioural and cognitive dysfunctions largely resolved upon vitamin-B1 substitution. Conclusions: the case suggests that thiamine deficiency presumably causes mitochondrial dysfunction with cerebrospinal fluid lactic acidosis and a stroke-like lesion mimicking MELAS syndrome. It should be further studied whether nutritional deficits, such as thiamine deficiency, could give rise to secondary stroke-like lesions.

Visual memory failure presages conversion to MELAS phenotype

OBJECTIVE

To examine the correlation between verbal and visual memory function and correlation with brain metabolites (lactate and N-Acetylaspartate, NAA) in individuals with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS).

METHODS

Memory performance and brain metabolites (ventricular lactate, occipital lactate, and occipital NAA) were examined in 18 MELAS, 58 m.3243A > G carriers, and 20 familial controls. Measures included the Selective Reminding Test (verbal memory), Benton Visuospatial Retention Test (visual memory), and MR Spectroscopy (NAA, Lactate). ANOVA, chi-squared/Fisher's exact tests, paired t-tests, Pearson correlations, and Spearman correlations were used.

RESULTS

When compared to carriers and controls, MELAS patients had the: (1) most impaired memory functions (Visual: p = 0.0003; Verbal: p = 0.02), (2) greatest visual than verbal memory impairment, (3) highest brain lactate levels (p < 0.0001), and (4) lowest brain NAA levels (p = 0.0003). Occipital and ventricular lactate to NAA ratios correlated significantly with visual memory performance (p ≤ 0.001). Higher lactate levels (p ≤ 0.01) and lower NAA levels (p = 0.0009) correlated specifically with greater visual memory dysfunction in MELAS. There was little or no correlation with verbal memory.

INTERPRETATION

Individuals with MELAS are at increased risk for impaired memory. Although verbal and visual memory are both affected, visual memory is preferentially affected and more clearly associated with brain metabolite levels. Preferential involvement of posterior brain regions is a distinctive clinical signature of MELAS. We now report a distinctive cognitive phenotype that targets visual memory more prominently and earlier than verbal memory. We speculate that this finding in carriers presages a conversion to the MELAS phenotype.

Forecasting stroke-like episodes and outcomes in mitochondrial disease

In this retrospective, multicentre, observational cohort study, we sought to determine the clinical, radiological, EEG, genetics and neuropathological characteristics of mitochondrial stroke-like episodes and to identify associated risk predictors. Between January 1998 and June 2018, we identified 111 patients with genetically determined mitochondrial disease who developed stroke-like episodes. Post-mortem cases of mitochondrial disease (n = 26) were identified from Newcastle Brain Tissue Resource. The primary outcome was to interrogate the clinico-radiopathological correlates and prognostic indicators of stroke-like episode in patients with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes syndrome (MELAS). The secondary objective was to develop a multivariable prediction model to forecast stroke-like episode risk. The most common genetic cause of stroke-like episodes was the m.3243A>G variant in MT-TL1 (n = 66), followed by recessive pathogenic POLG variants (n = 22), and 11 other rarer pathogenic mitochondrial DNA variants (n = 23). The age of first stroke-like episode was available for 105 patients [mean (SD) age: 31.8 (16.1)]; a total of 35 patients (32%) presented with their first stroke-like episode ≥40 years of age. The median interval (interquartile range) between first and second stroke-like episodes was 1.33 (2.86) years; 43% of patients developed recurrent stroke-like episodes within 12 months. Clinico-radiological, electrophysiological and neuropathological findings of stroke-like episodes were consistent with the hallmarks of medically refractory epilepsy. Patients with POLG-related stroke-like episodes demonstrated more fulminant disease trajectories than cases of m.3243A>G and other mitochondrial DNA pathogenic variants, in terms of the frequency of refractory status epilepticus, rapidity of progression and overall mortality. In multivariate analysis, baseline factors of body mass index, age-adjusted blood m.3243A>G heteroplasmy, sensorineural hearing loss and serum lactate were significantly associated with risk of stroke-like episodes in patients with the m.3243A>G variant. These factors informed the development of a prediction model to assess the risk of developing stroke-like episodes that demonstrated good overall discrimination (area under the curve = 0.87, 95% CI 0.82-0.93; c-statistic = 0.89). Significant radiological and pathological features of neurodegeneration were more evident in patients harbouring pathogenic mtDNA variants compared with POLG: brain atrophy on cranial MRI (90% versus 44%, P < 0.001) and reduced mean brain weight (SD) [1044 g (148) versus 1304 g (142), P = 0.005]. Our findings highlight the often idiosyncratic clinical, radiological and EEG characteristics of mitochondrial stroke-like episodes. Early recognition of seizures and aggressive instigation of treatment may help circumvent or slow neuronal loss and abate increasing disease burden. The risk-prediction model for the m.3243A>G variant can help inform more tailored genetic counselling and prognostication in routine clinical practice.

MRI Features of Stroke-Like Episodes in Mitochondrial Encephalomyopathy With Lactic Acidosis and Stroke-Like Episodes

Mitochondrial myopathy encephalopathy lactic acidosis and stroke-like episodes (MELAS) is an important cause of stroke-mimicking diseases that predominantly affect patients before 40 years of age. MELAS results from gene mutations in either mitochondrial DNA (mtDNA) or nuclear DNA (nDNA) responsible for the wide spectrum of clinical symptoms and imaging findings. Neurological manifestations can present with stroke-like episodes (the cardinal features of MELAS), epilepsy, cognitive and mental disorders, or recurrent headaches. Magnetic resonance imaging (MRI) is an important tool for detecting stroke-like lesions, accurate recognition of imaging findings is important in guiding clinical decision making in MELAS patients. With the development of neuroimaging technologies, MRI plays an increasingly important role in course monitoring and efficacy assessment of the disease. In this article, we provide an overview of the neuroimaging features and the application of novel MRI techniques in MELAS syndrome.

Neuroimaging of primary mitochondrial disorders in children: A review

Mitochondrial disorders represent a diverse and complex group of entities typified by defective energy metabolism. The mitochondrial oxidative phosphorylation system is typically impaired, which is the predominant source of energy production. Because mitochondria are present in nearly all organs, multiple systems may be affected including the central nervous system, skeletal muscles, kidneys, and liver. In particular, those organs that are metabolically active with high energy demands are explicitly vulnerable. Initial diagnostic work up relies on a detailed evaluation of clinical symptoms including physical examination as well as a comprehensive review of the evolution of symptoms over time, relation to possible "triggering" events (eg, fever, infection), blood workup, and family history. High-end neuroimaging plays a pivotal role in establishing diagnosis, narrowing differential diagnosis, monitoring disease progression, and predicting prognosis. The pattern and characteristics of the neuroimaging findings are often highly suggestive of a mitochondrial disorder; unfortunately, in many cases the wide variability of involved metabolic processes prevents a more specific subclassification. Consequently, additional diagnostic steps including muscle biopsy, metabolic workup, and genetic tests are necessary. In the current manuscript, basic concepts of energy production, genetics, and inheritance patterns are reviewed. In addition, the imaging findings of several illustrative mitochondrial disorders are presented to familiarize the involved physicians with pediatric mitochondrial disorders. In addition, the significance of spinal cord imaging and the value of "reversed image-based discovery" for the recognition and correct (re-)classification of mitochondrial disorders is discussed.

MELAS with multiple stroke-like episodes due to the variant m.13513G>A in MT-ND5

Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is characterized by metabolic stroke, seizures, cognitive decline, lactic acidosis, ragged-red fibers, headache, and vomiting, and in 80% of cases due to the mtDNA variant m.3243A>G. We report the case of a MELAS patient carrying a variant in subunit-5 of the respiratory chain (MT-ND5), rarely reported in MELAS. The patient is a 33-year-old male, who experienced a series of stroke-like episodes (StLEs) since age 23 years, which manifested clinically as seizures transient sensory disturbances, weakness, and visual or cognitive impairment. Over 9 years, these StLEs were misinterpreted as ischemic strokes, respectively, as cerebral vasculitis. He presented with mild, recurrent elevations of the creatine kinase. Initially, anti-seizure drugs and steroids appeared to be beneficial. Despite good recovery of each single StLE, the patient experienced a progressive decline of cognitive functions and activities of daily living. Cerebral imaging showed corresponding stroke-like lesions in changing locations. At age 32y, genetic work-up revealed the variant m.13513G>A in MT-ND5. The patient profited significantly from a cocktail with anti-oxidants/cofactors. This case shows that the variant m.13513G>A in MT-ND5 can manifest as MELAS that StLEs recover spontaneously and that the course of MELAS is slowly progressive.

Elevated glutamate and decreased glutamine levels in the cerebrospinal fluid of patients with MELAS syndrome

Background

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is a genetically heterogeneous disorder caused by mitochondrial DNA (mtDNA) mutations in the MT-TL1 gene. The pathophysiology of neurological manifestations is still unclear, but neuronal hyperexcitability and neuron–astrocyte uncoupling have been suggested. Glutamatergic neurotransmission is linked to glucose oxidation and mitochondrial metabolism in astrocytes and neurons. Given the relevance of neuron–astrocyte metabolic coupling and astrocyte function regulating energetic metabolism, we aimed to assess glutamate and glutamine CSF levels in MELAS patients.

Methods

This prospective observational case–control study determined glutamate and glutamine CSF levels in patients with MELAS syndrome and compared them with controls. The plasma and CSF levels of the remaining amino acids and lactate were also determined.

Results

Nine adult patients with MELAS syndrome (66.7% females mean age 35.8 ± 3.2 years) and 19 controls (63.2% females mean age 42.7 ± 3.8 years) were included. The CSF glutamate levels were significantly higher in patients with MELAS than in controls (18.48 ± 1.34 vs. 5.31 ± 1.09 μmol/L, p < 0.001). Significantly lower glutamine concentrations in patients with MELAS than controls were shown in CSF (336.31 ± 12.92 vs. 407.06 ± 15.74 μmol/L, p = 0.017). Moreover, the CSF levels of alanine, the branched-chain amino acids (BCAAs) and lactate were significantly higher in patients with MELAS.

Conclusions

Our results suggest the glutamate–glutamine cycle is altered probably due to metabolic imbalance, and as a result, the lactate–alanine and BCAA–glutamate cycles are upregulated. These findings might have therapeutic implications in MELAS syndrome.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00415-021-10942-7.

Molecular Genetics Overview of Primary Mitochondrial Myopathies

Mitochondrial disorders are the most common inherited conditions, characterized by defects in oxidative phosphorylation and caused by mutations in nuclear or mitochondrial genes. Due to its high energy request, skeletal muscle is typically involved. According to the International Workshop of Experts in Mitochondrial Diseases held in Rome in 2016, the term Primary Mitochondrial Myopathy (PMM) should refer to those mitochondrial disorders affecting principally, but not exclusively, the skeletal muscle. The clinical presentation may include general isolated myopathy with muscle weakness, exercise intolerance, chronic ophthalmoplegia/ophthalmoparesis (cPEO) and eyelids ptosis, or multisystem conditions where there is a coexistence with extramuscular signs and symptoms. In recent years, new therapeutic targets have been identified leading to the launch of some promising clinical trials that have mainly focused on treating muscle symptoms and that require populations with defined genotype. Advantages in next-generation sequencing techniques have substantially improved diagnosis. So far, an increasing number of mutations have been identified as responsible for mitochondrial disorders. In this review, we focused on the principal molecular genetic alterations in PMM. Accordingly, we carried out a comprehensive review of the literature and briefly discussed the possible approaches which could guide the clinician to a genetic diagnosis.

Adult-Onset Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-Like Episodes (MELAS) in a Patient Without Significant Family History

This case reports a 53-year-old Caucasian female previously diagnosed with viral encephalitis and Fahr's Syndrome who presented with altered mental status. Shortly after arrival, she displayed severe lactic acidosis and was transferred to the intensive care unit (ICU), where she had a brief seizure. Neurological workup was performed including carotid ultrasound, magnetic resonance angiography (MRA) brain, and computed tomography (CT) angiogram of the neck, all of which were unremarkable. Initial magnetic resonance imaging (MRI) performed showed small, acute ischemic foci in the bilateral occipital lobes and medial left thalamus. Subsequent diffusion-weighted imaging (DWI) MRI of the bilateral occipital lobes showed vasogenic edema, a common finding in Mitochondrial Encephalopathy, Lactic Acid, and Stroke-like episodes (MELAS). The patient was given Levetiracetam and managed supportively. She was progressively extubated and her seizure symptoms and lactic acidosis resolved. Our case represents a unique case in which a patient with non-contributory family history is first diagnosed with MELAS after age 40 after her symptoms were initially attributed to other pathologies. 

Molecular biomarkers correlate with brain grey and white matter changes in patients with mitochondrial m.3243A > G mutation

INTRODUCTION

The mitochondrial DNA (mtDNA) m.3243A > G mutation in the MT-TL1 gene results in a multi-systemic disease, that is commonly associated with neurodegenerative changes in the brain.

METHODS

Seventeen patients harboring the m3243A > G mutation were enrolled (age 43.1 ± 11.4 years, 10 M/7F). A panel of plasma biomarkers including lactate acid, alanine, L-arginine, fibroblast growth factor 21 (FGF-21), growth/differentiation factor 15 (GDF-15) and circulating cell free -mtDNA (ccf-mtDNA), as well as blood, urine and muscle mtDNA heteroplasmy were evaluated. Patients also underwent a brain standardized MR protocol that included volumetric T1-weighted images and diffusion-weighted MRI. Twenty sex- and age-matched healthy controls were included. Voxel-wise analysis was performed on T1-weighted and diffusion imaging, respectively with VBM (voxel-based morphometry) and TBSS (Tract-based Spatial Statistics). Ventricular lactate was also evaluated by ¹H-MR spectroscopy.

RESULTS

A widespread cortical gray matter (GM) loss was observed, more severe (p < 0.001) in the bilateral calcarine, insular, frontal and parietal cortex, along with infratentorial cerebellar cortex. High urine mtDNA mutation load, high levels of plasma lactate and alanine, low levels of plasma arginine, high levels of serum FGF-21 and ventricular lactate accumulation significantly (p < 0.05) correlated with the reduced brain GM density. Widespread microstructural alterations were highlighted in the white matter, significantly (p < 0.05) correlated with plasma alanine and arginine levels, with mtDNA mutation load in urine, with high level of serum GDF-15 and with high content of plasma ccf-mtDNA.

CONCLUSIONS

Our results suggest that the synergy of two pathogenic mechanisms, mtDNA-related mitochondrial respiratory deficiency and defective nitric oxide metabolism, contributes to the brain neurodegeneration in m.3243A > G patients.

Neuropsychological Features of Children and Adolescents With Mitochondrial Disorders: A Descriptive Case Series

BACKGROUND

Mitochondrial disorders (MD) are metabolic diseases related to genetic mutations in mitochondrial DNA and nuclear DNA that cause dysfunction of the mitochondrial respiratory chain. Cognitive impairment and psychiatric symptoms are frequently associated with MD in the adult population. The aim of this study is to describe the neuropsychological profile in children and adolescents with MD.

METHODS

We prospectively recruited a sample of 12 children and adolescents between February 2019 and February 2020 in the Reference Center for Mitochondrial Disorders of Angers (France). Participants and their parents completed an anamnestic form describing socio-demographic data and completed the WISC-V (Wechsler Intelligence Scale for Children, 5th edition) and the Parent and Teacher forms of the BRIEF (Behavior Rating Inventory of Executive Function).

RESULTS

In our sample, the mean IQ (Intellectual Quotient) score was 87.3 ± 25.3. The score ranged from 52 to 120. Concerning executive functions, a significant global clinical complaint was found for parents (six times more than normal) and to a lesser extent, for teachers (among 3 to 4 times more). Levels of intelligence and executive functioning were globally linked in our cohort but dissociation remains a possibility.

CONCLUSION

The results of this study show that MD can be associated to neuropsychological disorders in children and adolescents, especially regarding the intelligence quotient and the executive function. Our study also highlights the need for regular neuropsychological assessments in individuals with MD and developing brains, such as children and adolescents.

Clinical features, pathogenesis, and management of stroke-like episodes due to MELAS

Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) is a disease that should be considered as a differential diagnosis to acute ischemic stroke taking into account its onset pattern and neurological symptoms, which are similar to those of an ischemic stroke. Technological advancements in neuroimaging modalities have greatly facilitated differential diagnosis between stroke and MELAS on diagnostic imaging. Stroke-like episodes in MELAS have the following features: (1) symptoms are neurolocalized according to lesion site; (2) epileptic seizures are often present; (3) lesion distribution is inconsistent with vascular territory; (4) lesions are common in the posterior brain regions; (5) lesions continuously develop in adjacent sites over several weeks or months; (6) neurological symptoms and stroke-like lesions tend to be reversible, as presented on magnetic resonance imaging; (7) the rate of recurrence is high; and; (8) brain dysfunction and atrophy are slowly progressive. The m.3243ANG mutation in the MT-TL1 gene encoding the mitochondrial tRNA^Leu(UUR) is most commonly associated with MELAS. Although the precise pathophysiology is still unclear, one possible hypothesis for these episodes is a neuronal hyperexcitability theory, including neuron-astrocyte uncoupling. Supplementation, such as with L-arginine or taurine, has been proposed as preventive treatments for stroke-like episodes. As this disease is still untreatable and devastating, numerous drugs are being tested, and new gene therapies hold great promise for the future. This article contributes to the understanding of MELAS and its implications for clinical practice, by deepening their insight into the latest pathophysiological hypotheses and therapeutic developments.

Mutational Analysis and mtDNA Haplogroup Characterization in Three Serbian Cases of Mitochondrial Encephalomyopathies and Literature Review

Mitochondrial encephalomyopathies (MEMP) are heterogeneous multisystem disorders frequently associated with mitochondrial DNA (mtDNA) mutations. Clinical presentation varies considerably in age of onset, course, and severity up to death in early childhood. In this study, we performed molecular genetic analysis for mtDNA pathogenic mutation detection in Serbian children, preliminary diagnosed clinically, biochemically and by brain imaging for mitochondrial encephalomyopathies disorders. Sanger sequencing analysis in three Serbian probands revealed two known pathogenic mutations. Two probands had a heteroplasmic point mutation m.3243A>G in the MT-TL1 gene, which confirmed mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode syndrome (MELAS), while a single case clinically manifested for Leigh syndrome had an almost homoplasmic (close to 100%) m.8993T>G mutation in the MT-ATP6 gene. After full mtDNA MITOMASTER analysis and PhyloTree build 17, we report MELAS' association with haplogroups U and H (U2e and H15 subclades); likewise, the mtDNA-associated Leigh syndrome proband shows a preference for haplogroup H (H34 subclade). Based on clinical-genetic correlation, we suggest that haplogroup H may contribute to the mitochondrial encephalomyopathies' phenotypic variability of the patients in our study. We conclude that genetic studies for the distinctive mitochondrial encephalomyopathies should be well-considered for realizing clinical severity and possible outcomes.

Clinical Characteristics of Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, a maternally inherited mitochondrial disorder, is characterized by its genetic, biochemical and clinical complexity. The most common mutation associated with MELAS syndrome is the mtDNA A3243G mutation in the MT-TL1 gene encoding the mitochondrial tRNA-leu(UUR), which results in impaired mitochondrial translation and protein synthesis involving the mitochondrial electron transport chain complex subunits, leading to impaired mitochondrial energy production. Angiopathy, either alone or in combination with nitric oxide (NO) deficiency, further contributes to multi-organ involvement in MELAS syndrome. Management for MELAS syndrome is amostly symptomatic multidisciplinary approach. In this article, we review the clinical presentations, pathogenic mechanisms and options for management of MELAS syndrome.

Mitochondrial Strokes: Diagnostic Challenges and Chameleons

Mitochondrial stroke-like episodes (SLEs) are a hallmark of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). They should be suspected in anyone with an acute/subacute onset of focal neurological symptoms at any age and are usually driven by seizures. Suggestive features of an underlying mitochondrial pathology include evolving MRI lesions, often originating within the posterior brain regions, the presence of multisystemic involvement, including diabetes, deafness, or cardiomyopathy, and a positive family history. The diagnosis of MELAS has important implications for those affected and their relatives, given it enables early initiation of appropriate treatment and genetic counselling. However, the diagnosis is frequently challenging, particularly during the acute phase of an event. We describe four cases of mitochondrial strokes to highlight the considerable overlap that exists with other neurological disorders, including viral and autoimmune encephalitis, ischemic stroke, and central nervous system (CNS) vasculitis, and discuss the clinical, laboratory, and imaging features that can help distinguish MELAS from these differential diagnoses.

The Genetic Landscape of Mitochondrial Diseases in Spain: A Nationwide Call

The frequency of mitochondrial diseases (MD) has been scarcely documented, and only a few studies have reported data in certain specific geographical areas. In this study, we arranged a nationwide call in Spain to obtain a global estimate of the number of cases. A total of 3274 cases from 49 Spanish provinces were reported by 39 centres. Excluding duplicated and unsolved cases, 2761 patients harbouring pathogenic mutations in 140 genes were recruited between 1990 and 2020. A total of 508 patients exhibited mutations in nuclear DNA genes (75% paediatric patients) and 1105 in mitochondrial DNA genes (33% paediatric patients). A further 1148 cases harboured mutations in the MT-RNR1 gene (56% paediatric patients). The number of reported cases secondary to nuclear DNA mutations increased in 2014, owing to the implementation of next-generation sequencing technologies. Between 2014 and 2020, excepting MT-RNR1 cases, the incidence was 6.34 (95% CI: 5.71–6.97) cases per million inhabitants at the paediatric age and 1.36 (95% CI: 1.22–1.50) for adults. In conclusion, this is the first study to report nationwide epidemiological data for MD in Spain. The lack of identification of a remarkable number of mitochondrial genes necessitates the systematic application of high-throughput technologies in the routine diagnosis of MD.

Circulating markers of NADH-reductive stress correlate with mitochondrial disease severity

Mitochondrial disorders represent a large collection of rare syndromes that are difficult to manage both because we do not fully understand biochemical pathogenesis and because we currently lack facile markers of severity. The m.3243A>G variant is the most common heteroplasmic mitochondrial DNA mutation and underlies a spectrum of diseases, notably mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes (MELAS). To identify robust circulating markers of m.3243A>G disease, we first performed discovery proteomics, targeted metabolomics, and untargeted metabolomics on plasma from a deeply phenotyped cohort (102 patients, 32 controls). In a validation phase, we measured concentrations of prioritized metabolites in an independent cohort using distinct methods. We validated 20 analytes (1 protein, 19 metabolites) that distinguish patients with MELAS from controls. The collection includes classic (lactate, alanine) and more recently identified (GDF-15, α-hydroxybutyrate) mitochondrial markers. By mining untargeted mass-spectra we uncovered 3 less well-studied metabolite families: N-lactoyl-amino acids, β-hydroxy acylcarnitines, and β-hydroxy fatty acids. Many of these 20 analytes correlate strongly with established measures of severity, including Karnofsky status, and mechanistically, nearly all markers are attributable to an elevated NADH/NAD+ ratio, or NADH-reductive stress. Our work defines a panel of organelle function tests related to NADH-reductive stress that should enable classification and monitoring of mitochondrial disease.

Hearing loss in inherited metabolic disorders: A systematic review

Inherited metabolic disorders (IMDs) have been observed in individuals with hearing loss (HL), but IMDs are rarely the cause of syndromic HL. With early diagnosis, management of HL is more effective and cortical reorganization is possible with hearing aids or cochlear implants. This review describes relationships between IMDs and HL in terms of incidence, etiology of HL, pathophysiology, and treatment. Forty types of IMDs are described in the literature, mainly in case reports. Management and prognosis are noted where existing. We also describe IMDs with HL given age of occurrence of HL. Reviewing the main IMDs that are associated with HL may provide an additional clinical tool with which to better diagnose syndromic HL.

Cardiovascular Outcomes in Patients With Mitochondrial Disease in the United States: A Propensity Score Analysis

Mitochondrial disease comprises a wide range of genetic disorders caused by mitochondrial dysfunction. Its rarity, however, has limited the ability to assess its effects on clinical outcomes. To evaluate this relationship, we collected data from the 2016 National Inpatient Sample, which includes data from >7 million hospital stays. We identified 705 patients (mean age, 22 ± 20.7 yr; 54.2% female; 67.4% white) whose records included the ICD-10-CM code E88.4. We also identified a propensity-matched cohort of 705 patients without mitochondrial disease to examine the effect of mitochondrial disease on major adverse cardiovascular events, including all-cause in-hospital death, cardiac arrest, and acute congestive heart failure. Patients with mitochondrial disease were at significantly greater risk of major adverse cardiovascular events (odds ratio [OR]=2.42; 95% CI, 1.29-4.57; P=0.005), systolic heart failure (OR=2.37; 95% CI, 1.08-5.22; P=0.027), and all-cause in-hospital death (OR=14.22; 95% CI, 1.87-108.45; P<0.001). These findings suggest that mitochondrial disease significantly increases the risk of inpatient major adverse cardiovascular events.

Leukoaraiosis and acute ischemic stroke

Ischaemic stroke is characterized by high morbidity, high disability rate, high mortality and high recurrence rate, which can have a grave impact on the quality of life of the patients and consequently becomes an economic burden on their families and society. With the developments in imaging technology in recent years, patients with acute cerebral infarction are predominantly more likely to be diagnosed with leukoaraiosis (LA). LA is a common degenerative disease of the nervous system, which is related to cognitive decline, depression, abnormal gait, ischaemic stroke and atherosclerosis. The aetiology of LA is not clear and there is no gold standard for imaging assessment. Related studies have shown that LA has an adverse effect on the prognosis of cerebral infarction, but some experts have contrary beliefs. Hence, we undertook the present review of the literature on the mechanism and the effect of LA on the prognosis of patients with acute ischaemic stroke.

Psychiatric Symptoms of Children and Adolescents With Mitochondrial Disorders: A Descriptive Case Series

Background: Mitochondrial disorders (MD) are a group of clinically heterogeneous genetic disorders resulting from dysfunction of the mitochondrial respiratory chain. Cognitive impairment is a common feature in adults with MD and psychiatric symptoms are associated with MD in up to 70% of the adult population. The aim of this study is to describe the psychiatric profile in children and adolescents with MD by focusing on the description of psychiatric symptoms. Methods: A cohort of 12 children and adolescents was prospectively recruited between February 2019 and February 2020 in the Reference Center for Mitochondrial Disorders of Angers (France). Participants and their parents completed an anamnestic form to provide socio-demographic data and completed the Global Assessment of Functioning scale, the Brief Psychiatric Rating Scale, the Child Depression Inventory, the Revised Children's Manifest Anxiety Scale, and the Conner's Rating Scale to evaluate the inattention/hyperactivity symptoms as well as the Quality of Life scale. Results: Four children (33.3%) were diagnosed with depressive symptoms. With regarding to anxiety, 6 children (50%) reported anxiety issues during the psychiatric interview and 3 children (25%) were suffering from anxiety according to the RCMAS scale. Compared to other children with chronic illnesses, the individuals in our cohort reported a lower overall quality of life score and lower scores in physical and social subscales. Conclusion: Our study shows that MD can lead to psychiatric disorders in children and adolescents, in particular anxiety and depression, as well as poor quality of life. This highlights the need for regular psychiatric assessments in individuals with developing brains, such as children and adolescents. We do not, however, have data regarding the neuropsychological profile of this population.

Primary Mitochondrial Disorders of the Pediatric Central Nervous System: Neuroimaging Findings

Primary mitochondrial disorders (PMDs) constitute the most common cause of inborn errors of metabolism in children, and they frequently affect the central nervous system. Neuroimaging findings of PMDs are variable, ranging from unremarkable and nonspecific to florid and highly suggestive. An overview of PMDs, including a synopsis of the basic genetic concepts, main clinical symptoms, and neuropathologic features, is presented. In addition, eight of the most common PMDs that have a characteristic imaging phenotype in children are reviewed in detail. Online supplemental material is available for this article. ^©RSNA, 2020.

Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like Episodes (MELAS) Syndrome: Frequency, Clinical Features, Imaging, Histopathologic, and Molecular Genetic Findings in a Third-level Health Care Center in Mexico

INTRODUCTION

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, is a multisystemic entity of mitochondrial inheritance. To date, there is no epidemiological information on MELAS syndrome in Mexico.

CASE SERIES

A retrospective, cross-sectional design was employed to collect and analyze the data. The clinical records of patients with mitochondrial cytopathies in the period ranging from January 2018 to March 2020 were reviewed. Patients who met definitive Yatsuga diagnostic criteria for MELAS syndrome were included to describe frequency, clinical, imaging, histopathologic, and molecular studies. Of 56 patients diagnosed with mitochondrial cytopathy, 6 patients met definitive Yatsuga criterion for MELAS (10.7%). The median age at diagnosis was 34 years (30 to 34 y), 2 females and the median time from onset of symptoms at diagnosis 3.5 years (1 to 10 y). The median of the number of stroke-like episodes before the diagnosis was 3 (range, 2 to 3). The main findings in computed tomography were basal ganglia calcifications (33%), whereas in magnetic resonance imaging were a lactate peak in the spectroscopy sequence in 2 patients. Five patients (84%) had red-ragged fibers and phantom fibers in the Cox stain in the muscle biopsy. Four patients (67%) had presence of 3243A>G mutation in the mitochondrial MT-TL1 gene. One patient died because of status epilepticus.

CONCLUSIONS

MELAS syndrome represents a common diagnostic challenge for clinicians, often delaying definitive diagnosis. It should be suspected in young patients with stroke of undetermined etiology associated with other systemic and neurological features.

Mitochondrial DNA Copy Number and Developmental Origins of Health and Disease (DOHaD)

Mitochondrial dysfunction is known to contribute to mitochondrial diseases, as well as to a variety of aging-based pathologies. Mitochondria have their own genomes (mitochondrial DNA (mtDNA)) and the abnormalities, such as point mutations, deletions, and copy number variations, are involved in mitochondrial dysfunction. In recent years, several epidemiological studies and animal experiments have supported the Developmental Origin of Health and Disease (DOHaD) theory, which states that the environment during fetal life influences the predisposition to disease and the risk of morbidity in adulthood. Mitochondria play a central role in energy production, as well as in various cellular functions, such as apoptosis, lipid metabolism, and calcium metabolism. In terms of the DOHaD theory, mtDNA copy number may be a mediator of health and disease. This paper summarizes the results of recent epidemiological studies on the relationship between environmental factors and mtDNA copy number during pregnancy from the perspective of DOHaD theory. The results of these studies suggest a hypothesis that mtDNA copy number may reflect environmental influences during fetal life and possibly serve as a surrogate marker of health risks in adulthood.

Epilepsy Associated With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes

Objectives: The present study explored the clinical characteristics and prognostic factors of epilepsy in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS).

Methods: Thirty-four MELAS patients were included in the present study. They were diagnosed by clinical characteristics, genetic testing, muscle biopsy, and retrospective analysis of other clinical data. The patients were divided into three groups according to the effects of treatment after at least 2 years of follow-up.

Results: Epilepsy was more common in male MELAS patients than in females (20/14). The age of onset ranged from 0.5 to 57 years, with an average of 22.6 years. Patients with epilepsy and MELAS had various forms of seizures. Focal seizures were the most common type affecting 58.82% of patients, and some patients had multiple types of seizures. The abnormal EEG waves were mainly concentrated in the occipital (69.57%), frontal (65.22%) and temporal lobes (47.83%). Overall, the prognosis of patients with epilepsy and MELAS was poor. Poor prognosis was associated with brain atrophy (P = 0.026), status epilepticus (P < 0.001), and use of anti-seizure medications with high mitochondrial toxicity (P = 0.015).

Interpretation: Avoiding the application of anti-seizure medications with high mitochondrial toxicity, controlling seizures more actively and effectively, and delaying the occurrence and progression of brain atrophy as much as possible are particularly important to improve the prognosis of patients with MELAS and epilepsy.

Identification of a Novel Variant in MT-CO3 Causing MELAS

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is a maternally inherited mitochondrial disease. Most cases of MELAS are caused by the m.3243A > G variant in the MT-TL1 gene encoding tRNALeu^(UUR). However, the genetic cause in 10% of patients with MELAS is unknown. We investigated the pathogenicity of the novel mtDNA variant m.9396G > A/MT-CO3 (p.E64K), which affects an extremely conserved amino acid in the CO3 subunit of mitochondrial respiratory chain (MRC) complex IV (CIV) in a patient with MELAS. Biochemical assays of a muscle biopsy confirmed remarkable CIV deficiency, and pathological examination showed ragged red fibers and generalized COX non-reactive muscle fibers. Transfer of the mutant mtDNA into cybrids impaired CIV assembly, followed by remarkable mitochondrial dysfunction and ROS production. Our findings highlight the pathogenicity of a novel m.9396G > A variant and extend the spectrum of pathogenic mtDNA variants.

MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies

Introduction: Mitochondrial diseases are characterized by considerable clinical and genetic heterogeneity. Mitochondrial encephalomyopathy with lactate acidosis and stroke-like episodes (MELAS) and Leigh syndrome (LS) are both established mitochondrial syndromes; sometimes they can overlap.

Methods: A retrospective observational cohort study was done to analyze the clinical manifestations, biochemical findings, neuroimaging and genetic data, and disease outcomes of 14 patients with identified MELAS/LS overlap syndrome.

Results: A total of 14 patients, 9 males and 5 females, were enrolled. The median age at onset was 14 years, while the average age was 12.6 years. As for clinical features in concordance with MELAS, the top three most common symptoms were seizures, cognitive impairment, and stroke-like episodes (SLE). Brain atrophy was present in seven patients. As for the clinical hallmarks of LS, the top three most common symptoms were ataxia, spastic paraplegia, and bulbar palsy. Patients presented with individual syndrome or overlap syndromes with similar frequency, and the prognosis did not seem to be related to the initial presentation. Thirteen patients were identified with MTND mutations, among which m.13513G>A mutation in the MT-ND5 gene was the most common. Only one patient with m.8344A>G mutation of MTTK gene was found.

Discussion: Our study demonstrated that MTND genes are important mutation hot spots in MELAS/LS overlap syndrome. The follow-up is very important for the final diagnosis of overlap syndrome.

Brain MRS correlates with mitochondrial dysfunction biomarkers in MELAS-associated mtDNA mutations

Objective

The purpose of this study was to investigate correlations between brain proton magnetic resonance spectroscopy (¹H‐MRS) findings with serum biomarkers and heteroplasmy of mitochondrial DNA (mtDNA) mutations. This study enrolled patients carrying mtDNA mutations associated with Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke‐like episodes (MELAS), and MELAS‐Spectrum Syndrome (MSS).

Methods

Consecutive patients carrying mtDNA mutations associated with MELAS and MSS were recruited and their serum concentrations of lactate, alanine, and heteroplasmic mtDNA mutant load were evaluated. The brain protocol included single‐voxel ¹H‐MRS (1.5T) in the medial parieto‐occipital cortex (MPOC), left cerebellar hemisphere, parieto‐occipital white matter (POWM), and lateral ventricles. Relative metabolite concentrations of N‐acetyl‐aspartate (NAA), choline (Cho), and myo‐inositol (mI) were estimated relative to creatine (Cr), using LCModel 6.3.

Results

Six patients with MELAS (age 28 ± 13 years, 3 [50%] female) and 17 with MSS (age 45 ± 11 years, 7 [41%] female) and 39 sex‐ and age‐matched healthy controls (HC) were enrolled. These patients demonstrated a lower NAA/Cr ratio in MPOC compared to HC (p = 0.006), which inversely correlated with serum lactate (p = 0.021, rho = −0.68) and muscle mtDNA heteroplasmy (p < 0.001, rho = −0.80). Similarly, in the cerebellum patients had lower NAA/Cr (p < 0.001), Cho/Cr (p = 0.002), and NAA/mI (p = 0.001) ratios, which negatively correlated with mtDNA blood heteroplasmy (p = 0.001, rho = −0.81) and with alanine (p = 0.050, rho = −0.67). Ventricular lactate was present in 78.3% (18/23) of patients, correlating with serum lactate (p = 0.024, rho = 0.58).

Conclusion

Correlations were found between the peripheral and biochemical markers of mitochondrial dysfunction and brain in vivo markers of neurodegeneration, supporting the use of both biomarkers as signatures of MELAS and MSS disease, to evaluate the efficacy of potential treatments.

Lifestyle Changes Normalize Serum Lactate Levels in an m.3243A>G Carrier

BACKGROUND The normalization of serum lactate levels in a patient with non-syndromic mitochondrial disorder due to the m.3243A>G mitochondrial DNA (mtDNA) variant has not been previously reported. CASE REPORT A 57-year-old woman was diagnosed with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) due to the m.3243A>G variant, with low heteroplasmy rates (31%), at age 50. The initial manifestations were short stature, migraine, and diabetes. With progression of the disease, multisystem involvement developed, affecting the brain (stroke-like episode, mild cognitive impairment), eyes (pigmentary retinopathy), ears and the vestibular system (impaired hearing, tinnitus, imbalance, drop attacks, vertigo), intestines (constipation, distended abdomen, gastro-esophageal reflux, gastroparesis), and the muscles (muscle weakness). The gastrointestinal involvement was most prominent and most significantly lowered the patient's quality of life. The diabetes was well controlled with an insulin pump. Recurrent, acute deteriorations responded favorably to L-arginine. Owing to lifestyle and diet changes 2 years after diagnosis (start of art classes, increase in spin biking to 22.5 km 3 times per week, travel to Hawaii, adherence to low-carbohydrate high-protein diet), the patient managed to lower elevated serum lactate levels to largely normal values. CONCLUSIONS Gastrointestinal compromise may be the prominent manifestation of the m.3243A>G variant, lifestyle and diet changes may lower serum lactate in m.3243A>G carriers, and low heteroplasmy rates of the m.3243A>G variant in scarcely affected tissues do not exclude pathogenicity.

The molecular pathology of pathogenic mitochondrial tRNA variants

Mitochondrial diseases are clinically and genetically heterogeneous disorders, caused by pathogenic variants in either the nuclear or mitochondrial genome. This heterogeneity is particularly striking for disease caused by variants in mitochondrial DNA-encoded tRNA (mt-tRNA) genes, posing challenges for both the treatment of patients and understanding the molecular pathology. In this review, we consider disease caused by the two most common pathogenic mt-tRNA variants: m.3243A>G (within MT-TL1, encoding mt-tRNALeu(UUR) ) and m.8344A>G (within MT-TK, encoding mt-tRNALys ), which together account for the vast majority of all mt-tRNA-related disease. We compare and contrast the clinical disease they are associated with, as well as their molecular pathologies, and consider what is known about the likely molecular mechanisms of disease. Finally, we discuss the role of mitochondrial-nuclear crosstalk in the manifestation of mt-tRNA-associated disease and how research in this area not only has the potential to uncover molecular mechanisms responsible for the vast clinical heterogeneity associated with these variants but also pave the way to develop treatment options for these devastating diseases.

Seeking impact: Global perspectives on outcome measure selection for translational and clinical research for primary mitochondrial disorders

Primary mitochondrial disorders (PMDs) are challenging due to overall poor outcomes, no proven treatments, and a history of failed clinical trials, leading to a critical need to design future trials that can prove efficacy of an intervention. Selection of outcome measures for PMDs is complicated by extreme clinical, biochemical and genetic heterogeneity; PMDs are effectively a collection of nearly 400 individually ultrarare diseases. In clinical trials, outcome measures aim to evaluate, and ideally quantitate, the efficacy of an intervention in ameliorating clinical phenotype(s). The heterogeneity and multisystemic nature of PMDs makes it unlikely that a universal outcome measure will be applicable to all PMDs. Instead, a composite score of the individual's most worrisome symptoms may be a preferable endpoint. A further challenge arises from the tension between finding outcomes suitable for use in clinical trials (able to produce a measurable change in a relatively short period of time, namely the duration of a clinical trial) vs measures that are clinically meaningful to individual patients. A number of clinical rating scales and proposed biomarkers have emerged to capture the features of PMDs for natural history and interventional trials. Here we review our collective experiences with clinical rating scales, patient-reported outcome measures, and physiological, imaging, biochemical and muscle phenotypes as outcome measures in paediatric and adult PMDs in natural history studies and recent clinical trials. There is a pressing need to agree on a set of validated, robust, clinically meaningful outcome measures internationally, to facilitate the multicentre international clinical trials needed for optimal evaluation of novel therapies for these ultrarare diseases.

Neurofilament light is a novel biomarker for mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is a complicated maternally inherited disorder lacking of sensitive and specific biomarkers. The objective of this study was to investigate the serum neurofilament light chain (NfL) as a novel biomarker of neurological dysfunction in MELAS. Patients with different status of MELAS were enrolled in this study. The Mini-Mental State Examination (MMSE) was given to the participants to evaluate cognition status. Multiple functional MRI was performed on the participants. Blood samples were collected and the serum NfL concentrations were determined by the single-molecule array technology (Simoa). This study enrolled 23 patients with MELAS, 15 people in the acute attack phase of MELAS and 10 people in the remission phase, including 2 patients in both acute attack and remission phase. Sixteen healthy controls (HCs) were also enrolled. Serum NfL level increased significantly in patients with MELAS. Serum NfL level in the acute attack group (146.73 [120.91–411.31] pg/ml, median [IQR]) was higher than in the remission group (40.31 [19.54–151.05] pg/ml, median [IQR]) and HCs group (7.70 [6.13–9.78] pg/ml, median [IQR]) (p < 0.05). The level of NfL in the remission phase group was higher than in HCs group (p < 0.05). A negative correlation was found between the serum NfL level and MMSE (p = 0.006, r = -0.650). The NfL concentration correlated positively with stroke-like lesion volume in the brain (r = 0.740, p < 0.001). Serum NfL may serve as a novel biomarker for the neurological dysfunction in MELAS patients.

Mitochondrial Medicine: Genetic Underpinnings and Disease Modeling Using Induced Pluripotent Stem Cell Technology

Mitochondrial medicine is an exciting and rapidly evolving field. While the mitochondrial genome is small and differs from the nuclear genome in that it is circular and free of histones, it has been implicated in neurodegenerative diseases, type 2 diabetes, aging and cardiovascular disorders. Currently, there is a lack of efficient treatments for mitochondrial diseases. This has promoted the need for developing an appropriate platform to investigate and target the mitochondrial genome. However, developing these therapeutics requires a model system that enables rapid and effective studying of potential candidate therapeutics. In the past decade, induced pluripotent stem cells (iPSCs) have become a promising technology for applications in basic science and clinical trials, and have the potential to be transformative for mitochondrial drug development. Engineered iPSC-derived cardiomyocytes (iPSC-CM) offer a unique tool to model mitochondrial disorders. Additionally, these cellular models enable the discovery and testing of novel therapeutics and their impact on pathogenic mtDNA variants and dysfunctional mitochondria. Herein, we review recent advances in iPSC-CM models focused on mitochondrial dysfunction often causing cardiovascular diseases. The importance of mitochondrial disease systems biology coupled with genetically encoded NAD⁺/NADH sensors is addressed toward developing an in vitro translational approach to establish effective therapies.

Hyperglycemic Crisis in Patients With Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes (MELAS)

BACKGROUND

Diabetes mellitus is the most commonly encountered endocrinopathy in patients with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), which manifests as multisystemic organ failure. Whether the management of diabetes mellitus in MELAS requires special consideration is not fully clarified.

METHODS

In this single-center study, we retrospectively reviewed the medical records of patients with MELAS to elucidate the clinical characteristics of MELAS-associated diabetes mellitus.

RESULTS

Four patients among a total of 25 individuals with MELAS who were treated in the study institution developed diabetes mellitus. One patient had well-controlled diabetes mellitus, whereas the remaining three patients experienced hyperglycemic crisis as the first manifestation of diabetes mellitus. Two of the three patients were children aged four and six years. The hyperglycemic events occurred after surgery, infection, and status epilepticus, respectively. None of the three patients had diabetes mellitus previously based on randomly measured serum glucose levels that were within the normal range before the hyperglycemic crisis. Glycated hemoglobin levels measured during the hyperglycemic crisis indicated prediabetes in two patients and diabetes mellitus in one patient. Two patients recovered, whereas one patient died after developing multiorgan failure.

CONCLUSIONS

Fulminant-onset diabetes mellitus occurring in patients with MELAS underscore the importance of routine measurement for glycated hemoglobin and more intense evaluation of glucose intolerance regardless of the patient age and lack of symptoms. Clinicians should be aware of the potential acute onset of hyperglycemic crisis in patients with MELAS, especially in individuals with aggravating factors.

Point Prevalence and Associated Factors of Hip Displacement in Pediatric Patients With Mitochondrial Disease

Objective: Mitochondrial disease is a multisystem disorder resulting from mitochondrial dysfunction. Although musculoskeletal system is vulnerable to mitochondrial dysfunction, little information is available on orthopedic issues such as hip displacement and scoliosis in patients with mitochondrial disease. We aimed to examine the point prevalence of hip displacement and investigate the associated factors in patients with mitochondrial disease. Methods: We retrospectively reviewed the medical records and plain radiographs of patients diagnosed with mitochondrial disease between January 2006 and January 2019 at a single institution. Data, including patient age, sex, follow-up duration, syndromic diagnosis, and gross motor function were collected. Migration percentage was measured on the radiographs. The clinical and radiologic variables were compared between patients classified according to the presence of hip displacement and motor function level. Results: We included 225 patients (135 men, 90 women). The mean age at the latest follow-up was 11.1 years, and the mean follow-up duration was 7.0 years. Hip displacement was noted in 70 (31.1%) patients. The proportion of patients with Leigh disease (p = 0.007) and the ratio of non-ambulators (p < 0.001) were higher among patients with hip displacement. The proportion of patients with Leigh disease was higher in the non-ambulators than the ambulators. Conclusion: One-third of patients with mitochondrial disease developed hip displacement. Hip displacement was more common in non-ambulators or patients with hypertonia. Careful and serial monitoring for hip problems is required for non-ambulatory patients with mitochondrial disease who have increased muscle tone.

Phenotypic Heterogeneity in 5 Family Members with the Mitochondrial Variant m.3243A>G

Case series

Patients:—

Final Diagnosis: Metabolic acidosis

Symptoms: Deafness

Medication: —

Clinical Procedure: —

Specialty: Neurology

Chronic intestinal pseudo-obstruction in MELAS

MELAS syndrome with chronic intestinal pseudo-obstruction and neurological symptoms in a patient with a fatal evolution despite medical and surgical treatment.

Optical coherence tomography as a possible tool to monitor and predict disease progression in mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes

Optical coherence tomography (OCT) is an imaging technique used to obtain three-dimensional information on the retina. In this article, we evaluated the structural neuro-retinal abnormalities, especially the thickness in the ganglion cell complex (GCC), in patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). The GCC thickness in MELAS patients was significantly thinner than that in normal controls even when they had no history of transient homonymous hemianopia. There was a negative correlation between GCC thickness and disease duration. In conclusion, OCT may be an effective tool to monitor and predict disease progression in MELAS patients.

Topological reorganization of brain functional networks in patients with mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes

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MELAS patients showed topological reorganization of brain functional network.

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Network abnormalities in MELAS patients may be affected by stroke-like lesions.

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Graph theory based on rs-fMRI may be used for monitoring the status of MELAS.

Mitochondrial encephalomyopathy with lactic acidosis and stroke‐like episodes (MELAS) is a rare maternally inherited genetic disease; however, little is known about its underlying brain basis. Furthermore, the topological organization of brain functional network in MELAS has not been explored. Here, 45 patients with MELAS (22 at acute stage, 23 at chronic stage) and 22 normal controls were studied using resting- state functional magnetic resonance imaging and graph theory analysis approaches. Topological properties of brain functional networks including global and nodal metrics, rich club organization and modularity were analyzed. At the global level, MELAS patients exhibited reduced clustering coefficient, normalized clustering coefficient, normalized characteristic path length and local network efficiency compared with the controls. At the nodal level, several nodes with abnormal degree centrality and nodal efficiency were detected in MELAS patients, and the distribution of these nodes was partly consistent with the stroke-like lesions. For rich club organization, rich club nodes were reorganized and the connections among them were decreased in MELAS patients. Modularity analysis revealed that MELAS patents had altered intra- or inter-modular connections in default mode network, fronto-parietal network, sensorimotor network, occipital network and cerebellum network. Notably, the patients at acute stage showed more obvious changes in these topological properties than the patients at chronic stage. These findings indicated that MELAS patients, particularly those at acute stage, exhibited topological reorganization of the whole-brain functional network. This study may help us to understand the neuropathological mechanisms of MELAS.

PET Imaging for Oxidative Stress in Neurodegenerative Disorders Associated with Mitochondrial Dysfunction

Oxidative stress based on mitochondrial dysfunction is assumed to be the principal molecular mechanism for the pathogenesis of many neurodegenerative disorders. However, the effects of oxidative stress on the neurodegeneration process in living patients remain to be elucidated. Molecular imaging with positron emission tomography (PET) can directly evaluate subtle biological changes, including the redox status. The present review focuses on recent advances in PET imaging for oxidative stress, in particular the use of the Cu-ATSM radioligand, in neurodegenerative disorders associated with mitochondrial dysfunction. Since reactive oxygen species are mostly generated by leakage of excess electrons from an over-reductive state due to mitochondrial respiratory chain impairment, PET with ⁶²Cu-ATSM, the accumulation of which depends on an over-reductive state, is able to image oxidative stress. ⁶²Cu-ATSM PET studies demonstrated enhanced oxidative stress in the disease-related brain regions of patients with mitochondrial disease, Parkinson’s disease, and amyotrophic lateral sclerosis. Furthermore, the magnitude of oxidative stress increased with disease severity, indicating that oxidative stress based on mitochondrial dysfunction contributes to promoting neurodegeneration in these diseases. Oxidative stress imaging has improved our insights into the pathological mechanisms of neurodegenerative disorders, and is a promising tool for monitoring further antioxidant therapies.