Leigh Syndrome Research Articles

Leigh syndrome global patient registry: uniting patients and researchers worldwide

BackgroundLeigh Syndrome (LS) is a rare genetic neurometabolic disorder, that leads to the degeneration of the central nervous system and subsequently, early death. LS can be caused by over 80 mutations in mitochondrial or nuclear DNA. Patient registries are important for many reasons, such as studying the natural history of the disease, improving the quality of care, and understanding the healthcare burden. For rare diseases, patient registries are significantly important as patient numbers are small, and funding is limited. Cure Mito Foundation started a global patient registry for LS in September 2021 to identify and learn about the LS patient population, facilitate clinical trial recruitment, and unite international patients and researchers. Priorities were to allow researchers and industry partners to access data at no cost through a clear and transparent process, active patient engagement, and sharing of results back to the community.ResultsPatient registry platform, survey design, data analysis process, and patient recruitment strategies are described. Reported results include demographics, diagnostic information, symptom history, loss of milestones, disease management, healthcare utilization, quality of life, and caregiver burden for 116 participants. Results show a high disease burden, but a relatively short time to diagnosis. Despite the challenges faced by families impacted by Leigh syndrome, participants, in general, are described as having a good quality of life and caregivers are overall resilient, while also reporting a significant amount of stress.ConclusionThis registry provides a straightforward, no-cost mechanism for data sharing and contacting patients for clinical trials or research participation, which is important given the recruitment challenges for clinical trials for rare diseases. This is the first publication to present results from a global patient registry for Leigh Syndrome, with details on a variety of patient-specific and caregiver outcomes reported for the first time. Additionally, this registry is the first for any mitochondrial disease with nearly 70% of participants residing outside of the United States. Future efforts include continued publication of results and further collaboration with patients, industry partners, and researchers.

Expert Panel Curation of 113 Primary Mitochondrial Disease Genes for the Leigh Syndrome Spectrum.

Primary mitochondrial diseases (PMDs) are heterogeneous disorders caused by inherited mitochondrial dysfunction. Classically defined neuropathologically as subacute necrotizing encephalomyelopathy, Leigh syndrome spectrum (LSS) is the most frequent manifestation of PMD in children, but may also present in adults. A major challenge for accurate diagnosis of LSS in the genomic medicine era is establishing gene-disease relationships (GDRs) for this syndrome with >100 monogenic causes across both nuclear and mitochondrial genomes. The Clinical Genome Resource (ClinGen) Mitochondrial Disease Gene Curation Expert Panel (GCEP), comprising 40 international PMD experts, met monthly for 4 years to review GDRs for LSS. The GCEP standardized gene curation for LSS by refining the phenotypic definition, modifying the ClinGen Gene-Disease Clinical Validity Curation Framework to improve interpretation for LSS, and establishing a scoring rubric for LSS. The GDR with LSS across the nuclear and mitochondrial genomes was classified as definitive for 31 of 114 GDRs curated (27%), moderate for 38 (33%), limited for 43 (38%), and disputed for 2 (2%). Ninety genes were associated with autosomal recessive inheritance, 16 were maternally inherited, 5 were autosomal dominant, and 3 were X-linked. GDRs for LSS were established for genes across both nuclear and mitochondrial genomes. Establishing these GDRs will allow accurate variant interpretation, expedite genetic diagnosis of LSS, and facilitate precision medicine, multisystem organ surveillance, recurrence risk counseling, reproductive choice, natural history studies, and determination of eligibility for interventional clinical trials. ANN NEUROL 2023;94:696-712.

Peripheral macrophages drive CNS disease in the Ndufs4(-/-) model of Leigh syndrome.

Subacute necrotizing encephalopathy, or Leigh syndrome (LS), is the most common pediatric presentation of genetic mitochondrial disease. LS is a multi-system disorder with severe neurologic, metabolic, and musculoskeletal symptoms. The presence of progressive, symmetric, and necrotizing lesions in the brainstem are a defining feature of the disease, and the major cause of morbidity and mortality, but the mechanisms underlying their pathogenesis have been elusive. Recently, we demonstrated that high-dose pexidartinib, a CSF1R inhibitor, prevents LS CNS lesions and systemic disease in the Ndufs4(-/-) mouse model of LS. While the dose-response in this study implicated peripheral immune cells, the immune populations involved have not yet been elucidated. Here, we used a targeted genetic tool, deletion of the colony-stimulating Factor 1 receptor (CSF1R) macrophage super-enhancer FIRE (Csf1rΔFIRE), to specifically deplete microglia and define the role of microglia in the pathogenesis of LS. Homozygosity for the Csf1rΔFIRE allele ablates microglia in both control and Ndufs4(-/-) animals, but onset of CNS lesions and sequalae in the Ndufs4(-/-), including mortality, are only marginally impacted by microglia depletion. The overall development of necrotizing CNS lesions is not altered, though microglia remain absent. Finally, histologic analysis of brainstem lesions provides direct evidence of a causal role for peripheral macrophages in the characteristic CNS lesions. These data demonstrate that peripheral macrophages play a key role in the pathogenesis of disease in the Ndufs4(-/-) model.

Deep brain stimulation in a pediatric dystonia patient with cochlear implants and mitochondrial disorder: novel application of a frameless stereotactic system and navigating the anesthesia choice and neurosurgical complexities. Illustrative case.

This report presents a case of medically refractory dystonia in a pediatric patient successfully treated with bilateral subthalamic nucleus (STN) deep brain stimulation (DBS) while under general anesthesia by using microelectrode recordings (MERs) with intraoperative computed tomography (CT). The patient was an 18-year-old female with primary dystonia secondary to mitochondrial Leigh syndrome. Her past medical history was significant for complex partial epilepsy and hearing loss treated with cochlear implants. Her cochlear implants precluded anatomical targeting via magnetic resonance imaging. Additionally, the patient could not tolerate awake surgery with MER. The decision was made to proceed with bilateral STN DBS with intraoperative CT with the patient under general anesthesia. The patient's cochlear implants made standard frame placement difficult, so navigation was performed with the Nexframe system. Recordings were obtained with the patient under general anesthesia with ketamine, dexmedetomidine, and remifentanil. At the 3- and 6-month follow-ups, the patient demonstrated marked improvement in dystonia without neurological complications. This is the first case of dystonia secondary to Leigh syndrome treated with DBS. Additionally, the authors describe the novel use of the Nexframe for DBS lead placement in a pediatric patient. This demonstrates that STN DBS with the use of MER and intraoperative CT can be a safe and effective method of treating dystonia in certain pediatric patients.

Abstract P1032: Substrate Optimization For Patients With Melas And Leigh Syndrome Using Induced Pluripotent Stem Cells-derived Cardiomyocytes

Mitochondrial DNA (mtDNA) mutations increase the risk of health issues with overlapping clinical phenotypes. We propose that patient-derived induced pluripotent stem cells (iPSCs) can serve as surrogates for studying mitochondrial diseases, provided a standardized protocol is used to mitigate effects of mtDNA heteroplasmy. Accordingly, we reprogrammed peripheral blood mononuclear cells (CytoTune Kit) from mtDNA disease patients with epilepsy enrolled in clinical trials. After culturing the reprogrammed cells, six iPSC cell colonies were selected (Alkaline Phosphatase Live Stain) from each donor, pooled, and sorted by SSEA4+ marker at passage 6. Pluripotency was confirmed using OCT4 immuno-staining and RT-PCR for OCT4, NANOG, and SOX2 at passage 10. Because two of the patients (m.3243A>G MT-TL1, MELAS, and m.T8993G MT-ATP6, Leigh Syndrome) showed signs of improvement on drug therapy, we differentiated their iPSCs into cardiomyocytes (iCMs) and characterized them using immuno-staining (cTnT). We then screened the substrate utilization preferences of the iCMs using Phenotype MicroArray Mammalian assays (Biolog). The MELAS-iCMs failed to metabolize lactic acid, L-ornithine, and branched-chain amino acids, but performed better than control iCMs in the presence of arginine and glycerol phosphate. In contrast, LS-iCMs exhibited distinctly different substrate preferences and thrived in the presence of acetoacetic acid and α-keto-butyric acid with reduced oxidative stress (AmplexRed). The failure of MELAS-iCMs to survive in the presence of only lactic acid recapitulates a characteristic feature of MELAS, underscoring the potential of iPSCs for disease modeling. Our findings suggest that diverse outcomes to nutritional and pharmaceutical interventions must be tailored to each patient. To validate the pharmacological efficacy of iCMs, we will continuously evaluate their response in patients who are refractory to treatment.

Advanced Practice Nursing Experience of a Female Adolescent With Leigh Syndrome and Her Family: A Family Strengths-Oriented Therapeutic Conversations Approach

This article applied a family strengths-oriented therapeutic conversations approach to explore the advanced practice nursing experience of a female adolescent with Leigh Syndrome and her family. During the nursing care period from September 20 to November 19, 2022, the author collected data through direct care, observation, interview, telecare, home visits, and medical record reviews and confirmed the nursing problems to be the inadequate coping capability of the family. The author leveraged her advanced nurse practitioner role and used family strength-oriented therapeutic conversations to enable the parents of the patient to reflect on their experiences with this disease and to improve their quality of life and satisfaction with healthcare services. Three modes of care, including accessibility, coordination, and comprehensiveness, were offered to the female adolescent patient and her family to achieve the goal of family-centered, community-based, and medical-system-centered care. It is suggested that before making healthcare decisions, patients and their families should be given the opportunity to participate in the healthcare process and reach consensus on healthcare decisions based on existing evidence and their values and preferences. The medical decisions made by patients and their families after carefully considering their current situation and needs should be supported and assisted.

Mitochondrial defects caused by PARL deficiency lead to arrested spermatogenesis and ferroptosis.

Impaired spermatogenesis and male infertility are common manifestations associated with mitochondrial diseases, yet the underlying mechanisms linking these conditions remain elusive. In this study, we demonstrate that mice deficient for the mitochondrial intra-membrane rhomboid protease PARL, a recently reported model of the mitochondrial encephalopathy Leigh syndrome, develop early testicular atrophy caused by a complete arrest of spermatogenesis during meiotic prophase I, followed by degeneration and death of arrested spermatocytes. This process is independent of neurodegeneration. Interestingly, genetic modifications of PINK1, PGAM5, and TTC19 - three major substrates of PARL with important roles in mitochondrial homeostasis - fail to reproduce or modify this severe phenotype, indicating that the spermatogenic arrest arises from distinct molecular pathways. We further observed severe abnormalities in mitochondrial ultrastructure in PARL-deficient spermatocytes, along with prominent electron transfer chain defects, disrupted coenzyme Q (CoQ) biosynthesis, and metabolic rewiring. These mitochondrial defects are associated with a germ cell-specific decrease in GPX4 expression leading arrested spermatocytes to ferroptosis - a regulated cell death modality characterized by uncontrolled lipid peroxidation. Our results suggest that mitochondrial defects induced by PARL depletion act as an initiating trigger for ferroptosis in primary spermatocytes through simultaneous effects on GPX4 and CoQ - two major inhibitors of ferroptosis. These findings shed new light on the potential role of ferroptosis in the pathogenesis of mitochondrial diseases and male infertility warranting further investigation.

Leigh Syndrome Spectrum: A Portuguese Population Cohort in an Evolutionary Genetic Era.

Mitochondrial diseases are the most common inherited inborn error of metabolism resulting in deficient ATP generation, due to failure in homeostasis and proper bioenergetics. The most frequent mitochondrial disease manifestation in children is Leigh syndrome (LS), encompassing clinical, neuroradiological, biochemical, and molecular features. It typically affects infants but occurs anytime in life. Considering recent updates, LS clinical presentation has been stretched, and is now named LS spectrum (LSS), including classical LS and Leigh-like presentations. Apart from clinical diagnosis challenges, the molecular characterization also progressed from Sanger techniques to NGS (next-generation sequencing), encompassing analysis of nuclear (nDNA) and mitochondrial DNA (mtDNA). This upgrade resumed steps and favored diagnosis. Hereby, our paper presents molecular and clinical data on a Portuguese cohort of 40 positive cases of LSS. A total of 28 patients presented mutation in mtDNA and 12 in nDNA, with novel mutations identified in a heterogeneous group of genes. The present results contribute to the better knowledge of the molecular basis of LS and expand the clinical spectrum associated with this syndrome.

Auditory Brainstem Response in a Child with Mitochondrial Disorder-Leigh Syndrome.

The mitochondrial disorder-Leigh syndrome is a neurodegenerative disorder often manifested with brainstem abnormalities. The case report highlights the auditory brainstem response in a child with medical findings suggestive of Leigh syndrome. The case report also emphasizes the importance of ruling out any underlying neural pathology before making a clinical impression in children with developmental delays.

Compound heterozygous mutation of the IARS2 gene: a rare cause of Leigh Syndrome

Described in 2005 by Bonnefond, L. et al, IARS2 (OMIM 612801) is a mitochondrial isoleucyl-tRNA synthetase encoded in the nucleus. Phenotypically, the mutation in the IARS2 is expressed in a broad clinical spectrum, which includes Leigh Syndrome (LS) as well as extra-neurological effects. We described a 7-year-old boy who presented global developmental delay, hypotonia and epilepsy, evolving with epileptic encephalopathy. An MRI showed diffuse brain atrophy and areas of capsular changes bilaterally, while the exome showed compound heterozygous mutation in the IARS2 gene, a probable pathogenic variant inherited from the mother - p.[(Arg201His)], and a pathogenic variant inherited from the father - p.[(Trp520*)]. In the literature, we found 11 cases of patients who presented phenotypically as LS with mutation of the IARS2 gene. This report shows a patient with pathogenic variants never described in IARS2 compound heterozygosity, reinforcing the hypothesis of association of the IARS2 gene with this syndrome.

Reply to the Letter "Reversible Vasoconstriction Syndrome Is a Complication of SARS-CoV-2 Infection/Vaccination Rather than That of Leigh Syndrome".

Reply to the Letter "Reversible Vasoconstriction Syndrome Is a Complication of SARS-CoV-2 Infection/Vaccination Rather than That of Leigh Syndrome".

Adult-onset Leigh Syndrome with a m.9176 T>C Mutation Manifested as Reversible Cerebral Vasoconstriction Syndrome.

A 26-year-old woman developed a sudden headache, ptosis, and diplopia. Magnetic resonance imaging and angiography demonstrated a symmetrical lesion from the midbrain to the brainstem, involving the solitary nucleus and multifocal cerebral artery narrowing. Reversible cerebral vasospasm syndrome (RCVS) was suspected, and the patient improved after vasodilatation. Leigh syndrome was suspected due to the elevated serum lactate levels, so mitochondrial DNA was analyzed, and an m.9176 T>C mutation was detected. The final diagnosis was adult-onset Leigh syndrome manifesting as RCVS. An uncontrolled baroreflex due to a solitary nuclear lesion or endothelial dysfunction may have contributed to her unique presentation.

Acarbose suppresses symptoms of mitochondrial disease in a mouse model of Leigh syndrome.

Mitochondrial diseases represent a spectrum of disorders caused by impaired mitochondrial function, ranging in severity from mortality during infancy to progressive adult-onset disease. Mitochondrial dysfunction is also recognized as a molecular hallmark of the biological ageing process. Rapamycin, a drug that increases lifespan and health during normative ageing, also increases survival and reduces neurological symptoms in a mouse model of the severe mitochondrial disease Leigh syndrome. The Ndufs4 knockout (Ndufs4-/-) mouse lacks the complex I subunit NDUFS4 and shows rapid onset and progression of neurodegeneration mimicking patients with Leigh syndrome. Here we show that another drug that extends lifespan and delays normative ageing in mice, acarbose, also suppresses symptoms of disease and improves survival of Ndufs4-/- mice. Unlike rapamycin, acarbose rescues disease phenotypes independently of inhibition of the mechanistic target of rapamycin. Furthermore, rapamycin and acarbose have additive effects in delaying neurological symptoms and increasing maximum lifespan in Ndufs4-/- mice. We find that acarbose remodels the intestinal microbiome and alters the production of short-chain fatty acids. Supplementation with tributyrin, a source of butyric acid, recapitulates some effects of acarbose on lifespan and disease progression, while depletion of the endogenous microbiome in Ndufs4-/- mice appears to fully recapitulate the effects of acarbose on healthspan and lifespan in these animals. To our knowledge, this study provides the first evidence that alteration of the gut microbiome plays a significant role in severe mitochondrial disease and provides further support for the model that biological ageing and severe mitochondrial disorders share underlying common mechanisms.

Spectrum of Magnetic Resonance Spectroscopy (MRS) in Differentiating Paediatric Leukodystrophies in Pakistani Population

Aim: To determine the frequency of findings of MRS in differentiating paediatric leukodystrophies in Pakistani population. Study design: Cross sectional descriptive study. Place and duration of study: Armed Forces Institute of Radiology and Imaging, Military Hospital Rawalpindi from 25thAugust 2018 to 24th February 2019. Methodology: A total of 110 individuals who were coming in for an MRI test and were either male or female, older than one month of age, and younger than 12 years of age, were chosen. A 3.0T MRI scanner equipped with MRS techniques was used for each scan. Axial T1 and T2 Weighted spin-echo, FLAIR, coronal, and sagittal T2 Weighted spin-echo images were all part of the MRI imaging protocol. During the same session, a single section multivoxel 2D chemical shift spectroscopy sequence was also carried out. In MRS, the metabolites that were detected in each of our patients were choline, creatine, lactate, N-acetyl aspartate, and myo-inositol. Data were examined utilizing SPSS 21. Results: The average age was 5.24±1.89 year. 56 (50.91%) of the 110 patients were male children, compared to 54 (49.09%) female children, for a male to female ratio of 1.1:1. The following paediatric leukodystrophies were more often found with MRS in this study: Krabbes disease in 13 (11.82%), Canavan's disease in 19 (17.27%), Adrenoleukodystrophy in 41 (37.27%), Leigh disease in 25 (22.73%), and Metachromatic leukodystrophy in 12 (10.91%). Practical Implication: The underlying issue has recently been linked to mutations in the DARS2 gene, which codes for mitochondrial aspartyl-tRNA synthetase. Conclusion: MRS, which is more affordable than other existing tests, should be utilized in every patient with clinical leukodystrophies. Keywords: Leukodystrophies, Magnetic resonance spectroscopy, MRS

Walking Difficulties and Brainstem Dysfunction: a Case Report of Adult Onset Leigh Syndrome

Leigh syndrome (LS) or subacute necrotizing encephalomyelopathy is a progressive, lethal, mitochondrial disease mostly presenting in childhood. We report a 36-year-old African male presenting to the Emergency Department with a 6-month history of progressive dysarthria. Examination also showed oculomotor limitations for downgaze and convergence, mild right hemiparesis with Babinski sign, and absent lower limb tendon reflexes. He revealed he was presenting mild walking difficulties since the age of 25. Family history was unremarkable. A brain magnetic resonance showed diffuse white matter lesions without enhancing around the third ventricle, in the medulla oblongata, and bilaterally to the caudate and the putamen. Polymerase-chain-reaction amplification of the mitochondrial genes, followed by direct sequencing, found a 10191T>C variant related to LS. To now, only 8 late-onset patients share the same pathogenic variant.

Low Plasma Citrulline Guiding the Diagnosis of a Mitochondrial Disorder.

A 3-month-old male presented with generalized seizures in the setting of a viral upper respiratory tract infection. The newborn screen (NBS) collected at 27 hours of life was normal. Initial evaluation was notable for lactic acidosis (lactate 4.1 mmol/L, reference interval [RI] 0.5–2.2 mmol/L; bicarbonate 12 mmol/L, RI 18–28 mmol/L). Cerebrospinal fluid analysis was normal. Brain magnetic resonance imaging (MRI) revealed T2 hyperintensities involving bilateral deep gray nuclei and upper brainstem regions suggestive of genetic or metabolic etiologies. Diffuse lactate elevation was also observed by magnetic resonance spectroscopy, consistent with a diagnosis of Leigh syndrome (LS, OMIM# 256000). Due to concerns for LS, a metabolic evaluation was obtained. The plasma amino acid (PAA) profile was notable for reduced citrulline (3 µmol/L, RI 7–47 µmol/L) in the context of normal glutamine (444 µmol/L, RI 285–832 µmol/L), leading to an abnormal plasma glutamine/citrulline ratio (148, RI <25). Given normal plasma ammonia and glutamine, a proximal urea cycle defect was unlikely. Low citrulline is also observed with short intestinal length and impaired intestinal absorption; however, the patient did not exhibit abnormal bowel function. Urine organic acid (UOA) analysis revealed elevated propionate metabolites (i.e., propionylglycine and methylcitrate) along with lactate, ketones, and tricarboxylic acid cycle metabolites (Fig.1). 3-Hydroxyisovaleric acid was normal, while 3-hydroxypropionic acid and 3-methylcrotonylglycine were not detected. The plasma acylcarnitine (PAC) profile was notably normal. Given the clinical and biochemical presentation, mitochondrial complex V deficiency mitochondrial type 1 (MC5DM1) caused by variants in MT-ATP6 (OMIM# 500015) was highly suspected (1, 2). Subsequent mitochondrial genome analysis of the proband’s blood revealed a pathogenic variant (m.8993T>G) in MT-ATP6 at 96% heteroplasmy, confirming a diagnosis of MC5DM1.

A CASE SERIES ON VARIED CLINICAL PRESENTATION IN LEIGHS SYNDROME IN A TERTIARY CARE HOSPITAL

Background:Leigh syndrome (LS) is a hereditary neurometabolic disease, also known as subacute necrotizing encephalomyelopathy, and was described by the British neuropathologist and psychiatrist Denis Leigh in 1951. It is a neurodegenerative disease with variable symptoms that occurs due to a mitochondrial dysfunction caused by a hereditary genetic defect, associated with bilateral central nervous system lesions. Although it is a rare disease, with an approximate incidence of 1: 40,000 live births, it is the most frequent mitochondrial disease in the first year of life. Clinical Scenario: Case 1 Baby Nikshitha, a 6-and-a-half-month old female child born to a multigravida mother in a non-consanguineous marriage with previous 2 abortions and 1 intrauterine death. The baby was born through LSCS (oligohydramnios) and cried immediately at birth with a weight of 2.5kgs with uneventful antenatal periods.Excessive Vomiting x 1 month, increased over 5 days, Inability to gain weight over the past 3 months, Abnormal Posturing - 2 days prior to admission Mri Brain: Symmetric areas of altered intensity in bilateral caudate nucleus relatively sparing Globus pallidi showing diffusion restriction. Clinical Scenario: Case 2 Baby of suhasini, a 3 months old female child born to a primi mother in a non-consanguineous marriage with previous 1 sibling death. The baby was born through NVD and cried immediately at birth with a weight of 2.5kgs with uneventful antenatal periods.Child presented to the hospital at 3months of life with the chief complaints of - FEVER x 4 days, Noisy breathing since 4 days, Abnormal Posturing – since yesterday nightInitial Septic workup to rule out meningitis – NORMAL. ABG done in view of failure to thrive with recurrent vomiting – Metabolic Acidosis.Mri Brain: Symmetric areas of altered intensity in bilateral caudate nucleus relatively sparing Globus pallidi showing diffusion restriction. No blooming to suggest haemorrhage or calcification. Myelination is consistent with age Clinical Scenario: Case 3 Shobhakumari, 2Y old female child born to a multigravida mother in a non-consanguineous marriage with h/o sibling death at 5 years of age (leighs disease). The baby was born through NVD and cried immediately at birth with a weight of 2.5kgs with uneventful antenatal periods.Child presented to the hospital at 2 years with the chief complaints of - Excessive Vomiting since 6daysInability to gain weight over the past 3 months MRI brain :T2/Flair hyperintense signal with restricted diffusion in deep grey matter of b/l cerebellar hemisphere and periaqueductal grey matter of midbrain caudate nucleus and putamen Clinical Scenario: Case 4 B/o Afreen 4 year male born to a primi mother through normal vaginal delivery in a non-consanguineousmarriage with birth weight of 2.7 kg . Child presented to a hospital with History of regression of milestones and rhythmic repetitive movement of upper limb since 15 months of age. Serum lactate was high and MRI brain showed symmetrical B/l T2/FLAIR caudate and putamen nucleus hyperintensity with restriction on DW1 images Discussion:Several studies showed significant heterogeneity in the clinical findings of Leigh syndrome. Sofou K et al., revealed in a study that 69% of the cases presented before 2 years of age, while three patients presented with ataxia or seizures at 8,10 and 21 years of age. Conclusion:The diagnosis of Leighs disease should be considered in appropriate clinical and laboratory settings whenever symmetrical hypo densities are encountered in the putamen and midbrain on.

Consider Non-Syndromic Mitochondrial Disorders as Part of the Pediatric Phenotypic Spectrum

With interest we read the article by Ardissone et al. about a retrospective, singlecenter study of 150 pediatric patients with a genetically confirmed mitochondrial disorder (MID) due to a pathogenic mtDNA variant (mtDNA point mutation or single mtDNA deletion) [1]. The study is excellent but has limitations that are cause of concerns and should be discussed. A limitation of the study is that only syndromic MIDs were included [1]. Since MIDs often do not fit into any of the syndromic phenotypes, we should know whether these patients were deliberately excluded or did not appear at the study center at all. We should know whether the entire group of 902 patients also included patients with nonsyndromic MIDs. Another limitation is that heteroplasmy rates were only determined by estimating the densitometric ratio between wild-type and mutant mtDNA [1]. Heteroplasmy is usually determined by a number of quantitative methods, such as Sanger sequencing, high performance liquid chromatography, pyrosequencing, Snapshot, high resolution melt profiling (HRM), temporal temperature gradient gel electrophoresis (TTGE), invader assay, amplification refractory mutation system (ARMS), endonuclease method using Surveyor nuclease, and next generation sequencing (NGS) [2]. These techniques usually provide more accurate results than semi-quantitative estimation. There is a discrepancy between the statement in the method section ("only few data were not available from all patients”) and the results section (“CSF data were available from only 17 %, follow-up data only from 47%, and biochemical data only from 58 % of patients”) [1]. This discrepancy should be clarified. Another limitation is that the total observation time up to the last follow-up was not given [1]. Knowing this latency is important to assess the speed of disease progression and estimate the outcome. There is also a discrepancy between the statement in the result section that “outcome data were evaluated from 70 patients” and the detailed description in the results section, which included 71 patients. Which number is correct? Surprisingly, the biochemical examination was normal in almost a quarter of the patients with Leigh syndrome. We should know if these results are from studies of just muscle or fibroblasts, or if other tissues have been studied as well If only muscle or fibroblasts were examined, we should know whether or not these tissues were clinically affected in the one quarter of the Leigh patients. Surprisingly, only two thirds of the MELAS patients presented with stroke-like episodes (SLEs), which are pathognomonic for MELAS. We should know if this was due to the short observation or follow-up time in these patients. According to what criteria were these patients without SLE classified as MELAS? Were the Hirano or Japanese criteria applied? We should also know how “MELAS-like” was defined. There is no mention of the underlying mutations in the PEO patients. It would be interesting to know if these patients all carried a single mtDNA deletion, a nuclear DNA-located variant, or an mtDNA point mutation. Overall, the interesting study has limitations that call the results and their interpretation into question. With a prospective design and extensive and long-term follow-up, the study goals could be better achieved.

Reply to Letter: "MTFMT-Related Leigh Syndrome Phenotypically Manifesting with Mobile Dystonia and Hypoacusis".

Movement Disorders Clinical PracticeAccepted Articles LETTERS: PUBLISHED ARTICLES Reply to Letter: “MTMFT-related Leigh syndrome phenotypically manifesting with mobile dystonia and hypoacusis.” Kallol Kumar Set MD, Corresponding Author Kallol Kumar Set MD [email protected] orcid.org/0000-0002-5911-8105 Pediatric Neurologist at Dayton Children's Hospital. Clinical Assistant Professor, Boonshoft School of Medicine, Wright State University, Ohio, USA Correspondence to: Address: One Children's Plaza. Dayton, Ohio, USA 45404-1815, E-mail: [email protected], Phone : 937 641 3080 Fax 937 641 4350Search for more papers by this authorKarl De Dios MD, Karl De Dios MD [email protected] Medical Genetics, Dayton Children's Hospital, One Children's Plaza., Dayton, Ohio, USA, 45404-1815Search for more papers by this author Kallol Kumar Set MD, Corresponding Author Kallol Kumar Set MD [email protected] orcid.org/0000-0002-5911-8105 Pediatric Neurologist at Dayton Children's Hospital. Clinical Assistant Professor, Boonshoft School of Medicine, Wright State University, Ohio, USA Correspondence to: Address: One Children's Plaza. Dayton, Ohio, USA 45404-1815, E-mail: [email protected], Phone : 937 641 3080 Fax 937 641 4350Search for more papers by this authorKarl De Dios MD, Karl De Dios MD [email protected] Medical Genetics, Dayton Children's Hospital, One Children's Plaza., Dayton, Ohio, USA, 45404-1815Search for more papers by this author First published: 28 April 2023 https://doi.org/10.1002/mdc3.13760 This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/mdc3.13760. AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Accepted ArticlesAccepted, unedited articles published online and citable. The final edited and typeset version of record will appear in the future. RelatedInformation

MTFMT-Related Leigh Syndrome Phenotypically Manifesting with Mobile Dystonia and Hypoacusis.

Movement Disorders Clinical PracticeAccepted Articles LETTERS: PUBLISHED ARTICLES MTMFT-related Leigh syndrome phenotypically manifesting with mobile dystonia and hypoacusis Josef Finsterer MD, PhD, Corresponding Author Josef Finsterer MD, PhD [email protected] orcid.org/0000-0003-2839-7305 Neurology & Neurophysiology Center, Vienna, Austria Correspondence to: Josef Finsterer, MD, PhD, Postfach 20, 1180 Vienna, Austria, Tel. +43-1-5861075, Fax. +43-1-5861075, E-mail: [email protected]Search for more papers by this authorFulvio Alexandre Scorza MD, Fulvio Alexandre Scorza MD orcid.org/0000-0002-0694-8674 Disciplina de Neurociência. Universidade Federal de São Paulo/Escola Paulista de Medicina (UNIFESP/EPM), São Paulo, BrasilSearch for more papers by this authorCarla Alexandra Scorza MD, Carla Alexandra Scorza MD Disciplina de Neurociência. Universidade Federal de São Paulo/Escola Paulista de Medicina (UNIFESP/EPM), São Paulo, BrasilSearch for more papers by this authorAntonio-Carlos G. de Almeida MD, Antonio-Carlos G. de Almeida MD Centro de Neurociências e Saúde da Mulher “Professor Geraldo Rodrigues de Lima.” Escola Paulista de Medicina/Universidade Federal de São Paulo (EPM/UNIFESP), São Paulo, BrasilSearch for more papers by this author Josef Finsterer MD, PhD, Corresponding Author Josef Finsterer MD, PhD [email protected] orcid.org/0000-0003-2839-7305 Neurology & Neurophysiology Center, Vienna, Austria Correspondence to: Josef Finsterer, MD, PhD, Postfach 20, 1180 Vienna, Austria, Tel. +43-1-5861075, Fax. +43-1-5861075, E-mail: [email protected]Search for more papers by this authorFulvio Alexandre Scorza MD, Fulvio Alexandre Scorza MD orcid.org/0000-0002-0694-8674 Disciplina de Neurociência. Universidade Federal de São Paulo/Escola Paulista de Medicina (UNIFESP/EPM), São Paulo, BrasilSearch for more papers by this authorCarla Alexandra Scorza MD, Carla Alexandra Scorza MD Disciplina de Neurociência. Universidade Federal de São Paulo/Escola Paulista de Medicina (UNIFESP/EPM), São Paulo, BrasilSearch for more papers by this authorAntonio-Carlos G. de Almeida MD, Antonio-Carlos G. de Almeida MD Centro de Neurociências e Saúde da Mulher “Professor Geraldo Rodrigues de Lima.” Escola Paulista de Medicina/Universidade Federal de São Paulo (EPM/UNIFESP), São Paulo, BrasilSearch for more papers by this author First published: 28 April 2023 https://doi.org/10.1002/mdc3.13761 This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/mdc3.13761. AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Accepted ArticlesAccepted, unedited articles published online and citable. The final edited and typeset version of record will appear in the future. RelatedInformation