Leigh syndrome: neuropathology and pathogenesis. J Neuropathol Exp Neurol. 2015;74:482-492. [PMID: 25978847 DOI: 10.1097/nen.0000000000000195]

Engineered mitochondria in diseases: mechanisms, strategies, and applications

Mitochondrial diseases represent one of the most prevalent and debilitating categories of hereditary disorders, characterized by significant genetic, biological, and clinical heterogeneity, which has driven the development of the field of engineered mitochondria. With the growing recognition of the pathogenic role of damaged mitochondria in aging, oxidative disorders, inflammatory diseases, and cancer, the application of engineered mitochondria has expanded to those non-hereditary contexts (sometimes referred to as mitochondria-related diseases). Due to their unique non-eukaryotic origins and endosymbiotic relationship, mitochondria are considered highly suitable for gene editing and intercellular transplantation, and remarkable progress has been achieved in two promising therapeutic strategies-mitochondrial gene editing and artificial mitochondrial transfer (collectively referred to as engineered mitochondria in this review) over the past two decades. Here, we provide a comprehensive review of the mechanisms and recent advancements in the development of engineered mitochondria for therapeutic applications, alongside a concise summary of potential clinical implications and supporting evidence from preclinical and clinical studies. Additionally, an emerging and potentially feasible approach involves ex vivo mitochondrial editing, followed by selection and transplantation, which holds the potential to overcome limitations such as reduced in vivo operability and the introduction of allogeneic mitochondrial heterogeneity, thereby broadening the applicability of engineered mitochondria.

Adult Leigh Syndrome Associated with the m.15635T>C Mitochondrial DNA Variant Affecting the Cytochrome b (MT-CYB) Gene

We report on a sporadic patient suffering Leigh syndrome characterized by bilateral lesions in the lenticular nuclei and spastic dystonia, intellectual disability, sensorineural deafness, hypertrophic cardiomyopathy, exercise intolerance, and retinitis pigmentosa. Complete sequencing of mitochondrial DNA revealed the heteroplasmic nucleotide change m.15635T>C affecting a highly conserved amino acid position (p.Ser297Pro) in the cytochrome b (MT-CYB) gene on a haplogroup K1c1a background, which includes a set of four non-synonymous polymorphisms also present in the same gene. Biochemical studies documented respiratory chain impairment due to complex III defect. This variant fulfils the criteria for being pathogenic and was previously reported in a sporadic case of fatal neonatal polyvisceral failure.

A Comprehensive Approach to the Diagnosis of Leigh Syndrome Spectrum

BACKGROUND

Leigh syndrome spectrum (LSS) is a novel nomenclature that encompasses both classical Leigh syndrome and Leigh-like phenotypes. Given the heterogeneity of disease presentation, a new consensus published recently addressed the main issues and proposed general guidelines towards diagnosis. Based on these recommendations, we developed a simple pipeline that can be useful in the diagnosis of LSS.

METHODS

We combined previously published criteria with our own experience to achieve a diagnostic framework that can provide faster satisfactory results with fewer resources.

RESULTS

We suggest adding basic biochemical tests for amino acids, acylcarnitine, and urinary organic acids as parallel investigations, as these results can be obtained in a short time. This approach characterized 80% of our cohort and promoted specific intervention in 10% of confirmed cases.

CONCLUSIONS

Genetic studies are crucial in the diagnosis of LSS, but they are time-consuming and might delay tailored interventions. Therefore, we suggest adding more affordable and less complex biochemical studies as primary tests when investigating treatable causes of LSS.

Primary cilia formation requires the Leigh syndrome-associated mitochondrial protein NDUFAF2

Mitochondria-related neurodegenerative diseases have been implicated in the disruption of primary cilia function. Mutation in an intrinsic mitochondrial complex I component NDUFAF2 has been identified in Leigh syndrome, a severe inherited mitochondriopathy. Mutations in ARMC9, which encodes a basal body protein, cause Joubert syndrome, a ciliopathy with defects in the brain, kidney, and eye. Here, we report a mechanistic link between mitochondria metabolism and primary cilia signaling. We discovered that loss of NDUFAF2 caused both mitochondrial and ciliary defects in vitro and in vivo and identified NDUFAF2 as a binding partner for ARMC9. We also found that NDUFAF2 was both necessary and sufficient for cilia formation and that exogenous expression of NDUFAF2 rescued the ciliary and mitochondrial defects observed in cells from patients with known ARMC9 deficiency. NAD+ supplementation restored mitochondrial and ciliary dysfunction in ARMC9-deficient cells and zebrafish and ameliorated the ocular motility and motor deficits of a patient with ARMC9 deficiency. The present results provide a compelling mechanistic link, supported by evidence from human studies, between primary cilia and mitochondrial signaling. Importantly, our findings have significant implications for the development of therapeutic approaches targeting ciliopathies.

Emerging Multi-omic Approaches to the Molecular Diagnosis of Mitochondrial Disease and Available Strategies for Treatment and Prevention

Mitochondria are semi-autonomous organelles present in several copies within most cells in the human body that are controlled by the precise collaboration of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) encoding mitochondrial proteins. They play important roles in numerous metabolic pathways, such as the synthesis of adenosine triphosphate (ATP), the predominant energy substrate of the cell generated through oxidative phosphorylation (OXPHOS), intracellular calcium homeostasis, metabolite biosynthesis, aging, cell cycles, and so forth. Previous studies revealed that dysfunction of these multi-functional organelles, which may arise due to mutations in either the nuclear or mitochondrial genome, leads to a diverse group of clinically and genetically heterogeneous disorders. These diseases include neurodegenerative and metabolic disorders as well as cardiac and skeletal myopathies in both adults and newborns. The plethora of phenotypes and defects displayed leads to challenges in the diagnosis and treatment of mitochondrial diseases. In this regard, the related literature proposed several diagnostic options, such as high throughput mitochondrial genomics and omics technologies, as well as numerous therapeutic options, such as pharmacological approaches, manipulating the mitochondrial genome, increasing the mitochondria content of the affected cells, and recently mitochondrial diseases transmission prevention. Therefore, the present article attempted to review the latest advances and challenges in diagnostic and therapeutic options for mitochondrial diseases.

Valine and Inflammation Drive Epilepsy in a Mouse Model of ECHS1 Deficiency

ECHS1 Deficiency (ECHS1D) is a rare and devastating pediatric disease that currently has no defined treatments. This disorder results from missense loss-of-function mutations in the ECHS1 gene that result in severe developmental delays, encephalopathy, hypotonia, and early death. ECHS1 enzymatic activity is necessary for the beta-oxidation of fatty acids and the oxidation of branched-chain amino acids within the inner mitochondrial matrix. The pathogenesis of disease remains unknown, however it is hypothesized that disease is driven by an accumulation of toxic metabolites from impaired valine oxidation. To expand our knowledge on disease mechanisms, a novel mouse model of ECHS1D was generated that possesses a disease-associated knock-in (KI) allele and a knock-out (KO) allele. To investigate the behavioral phenotype, a battery of testing was performed at multiple time points, which included assessments of learning, motor function, endurance, sensory responses, and anxiety. Neurological abnormalities were assessed using wireless telemetry EEG recordings, pentylenetetrazol (PTZ) seizure induction, and immunohistochemistry. Metabolic perturbations were measured within the liver, serum, and brain using mass spectrometry and magnetic resonance spectroscopy. To test disease mechanisms, mice were subjected to disease pathway stressors and then survival, body weight gain, and epilepsy were assessed. Mice containing KI/KI or KI/KO alleles were viable with normal development and survival, and the presence of KI and KO alleles resulted in a significant reduction in ECHS1 protein. ECHS1D mice displayed reduced exercise capacity and pain sensation. EEG analysis revealed increased slow wave power that was associated with perturbations in sleep. ECHS1D mice had significantly increased epileptiform EEG discharges, and were sensitive to seizure induction, which resulted in death of 60% of ECHS1D mice. Under basal conditions, brain structure was grossly normal, although histological analysis revealed increased microglial activation in aged ECHS1D mice. Increased dietary valine only affected ECHS1D mice, which significantly exacerbated seizure susceptibility and resulted in death. Lastly, acute inflammatory challenge drove regression and early lethality in ECHS1D mice. In conclusion, we developed a novel model of ECHS1D that may be used to further knowledge on disease mechanisms and to develop therapeutics. Our data suggests altered metabolic signaling and inflammation may contribute to epilepsy in ECHS1D, and these alterations may be attributed to impaired valine metabolism.

Interferon-gamma contributes to disease progression in the Ndufs4(-/-) model of Leigh syndrome

AIM

Leigh syndrome (LS), the most common paediatric presentation of genetic mitochondrial dysfunction, is a multi-system disorder characterised by severe neurologic and metabolic abnormalities. Symmetric, bilateral, progressive necrotizing lesions in the brainstem are defining features of the disease. Patients are often symptom free in early life but typically develop symptoms by about 2 years of age. The mechanisms underlying disease onset and progression in LS remain obscure. Recent studies have shown that the immune system causally drives disease in the Ndufs4(-/-) mouse model of LS: treatment of Ndufs4(-/-) mice with the macrophage-depleting Csf1r inhibitor pexidartinib prevents disease. While the precise mechanisms leading to immune activation and immune factors involved in disease progression have not yet been determined, interferon-gamma (IFNγ) and interferon gamma-induced protein 10 (IP10) were found to be significantly elevated in Ndufs4(-/-) brainstem, implicating these factors in disease. Here, we aimed to explore the role of IFNγ and IP10 in LS.

METHODS

To establish the role of IFNγ and IP10 in LS, we generated IFNγ and IP10 deficient Ndufs4(-/-)/Ifng(-/-) and Ndufs4(-/-)/IP10(-/-) double knockout animals, as well as IFNγ and IP10 heterozygous, Ndufs4(-/-)/Ifng(+/-) and Ndufs4(-/-)/IP10(+/-), animals. We monitored disease onset and progression to define the impact of heterozygous or homozygous loss of IFNγ and IP10 in LS.

RESULTS

Loss of IP10 does not significantly impact the onset or progression of disease in the Ndufs4(-/-) model. IFNγ loss significantly extends survival and delays disease progression in a gene dosage-dependent manner, though the benefits are modest compared to Csf1r inhibition.

CONCLUSIONS

IFNγ contributes to disease onset and progression in LS. Our findings suggest that IFNγ targeting therapies may provide some benefits in genetic mitochondrial disease, but targeting IFNγ alone would likely yield only modest benefits in LS.

Elucidating the Role of OXPHOS Variants in Asthenozoospermia: Insights from Whole Genome Sequencing and an In Silico Analysis

Infertility is a global health challenge that affects an estimated 72.4 million people worldwide. Between 30 and 50% of these cases involve male factors, showcasing the complex nature of male infertility, which can be attributed to both environmental and genetic determinants. Asthenozoospermia, a condition characterized by reduced sperm motility, stands out as a significant contributor to male infertility. This study explores the involvement of the mitochondrial oxidative phosphorylation (OXPHOS) system, crucial for ATP production and sperm motility, in asthenozoospermia. Through whole-genome sequencing and in silico analysis, our aim was to identify and characterize OXPHOS gene variants specific to individuals with asthenozoospermia. Our analysis identified 680,099 unique variants, with 309 located within OXPHOS genes. Nine of these variants were prioritized due to their significant implications, such as potential associations with diseases, effects on gene expression, protein function, etc. Interestingly, none of these variants had been previously associated with male infertility, opening up new avenues for research. Thus, through our comprehensive approach, we provide valuable insights into the genetic factors that influence sperm motility, laying the foundation for future research in the field of male infertility.

Unique prenatal manifestations of biallelic NDUFAF5 variants: expansion of phenotype

OBJECTIVE

Mitochondrial complex-I deficiency, nuclear type 16, is a rare autosomal recessive disorder caused by biallelic pathogenic variants in NDUFAF5 (C20orf7) (OMIM 618238). The aim of this study was to describe a severe early prenatal manifestation of this disorder, which was previously considered to occur only postnatally.

METHODS

This was a multicenter retrospective case series including five fetuses from three non-related families, which shared common sonographic abnormalities, including brain cysts, corpus callosal malformations, non-immune hydrops fetalis and growth restriction. Genetic evaluation included chromosomal microarray analysis and exome sequencing. Two fetuses from the same family were also available for pathology examination, including electron microscopy.

RESULTS

Chromosomal microarray analysis revealed no chromosomal abnormality in any of the tested cases. Trio exome sequencing demonstrated that three affected fetuses from three unrelated families were compound heterozygous or homozygous for likely pathogenic variants in NDUFAF5. No other causative variants were detected. The association between NDUFAF5 variants and fetal malformations was further confirmed by segregation analysis. Histological evaluation of fetal tissues and electron microscopy of the skeletal muscle, liver, proximal tubules and heart demonstrated changes that resembled postmortem findings in patients with mitochondrial depletion disorders as well as previously undescribed findings.

CONCLUSIONS

Mitochondrial complex-I deficiency and specifically biallelic mutations in NDUFAF5 have a role in abnormal fetal development, presenting with severe congenital malformations. Mitochondrial complex-I disorders should be considered in the differential diagnosis of corpus callosal malformations and brain cysts, especially when associated with extracranial abnormalities, such as fetal growth restriction and non-immune hydrops fetalis. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

Interleukin-6-elicited chronic neuroinflammation may decrease survival but is not sufficient to drive disease progression in a mouse model of Leigh syndrome

BACKGROUND

Mitochondrial diseases (MDs) are genetic disorders characterized by dysfunctions in mitochondria. Clinical data suggest that additional factors, beyond genetics, contribute to the onset and progression of this group of diseases, but these influencing factors remain largely unknown. Mounting evidence indicates that immune dysregulation or distress could play a role. Clinical observations have described the co-incidence of infection and the onset of the disease as well as the worsening of symptoms following infection. These findings highlight the complex interactions between MDs and immunity and underscore the need to better understand their underlying relationships.

RESULTS

We used Ndufs4 KO mice, a well-established mouse model of Leigh syndrome (one of the most relevant MDs), to test whether chronic induction of a neuroinflammatory state in the central nervous system before the development of neurological symptoms would affect both the onset and progression of the disease in Ndufs4 KO mice. To this aim, we took advantage of the GFAP-IL6 mouse, which overexpresses interleukin-6 (IL-6) in astrocytes and produces chronic glial reactivity, by generating a mouse line with IL-6 overexpression and NDUFS4 deficiency. IL-6 overexpression aggravated the mortality of female Ndufs4 KO mice but did not alter the main motor and respiratory phenotypes measured in any sex. Interestingly, an abnormal region-dependent microglial response to IL-6 overexpression was observed in Ndufs4 KO mice compared to controls.

CONCLUSION

Overall, our data indicate that chronic neuroinflammation may worsen the disease in Ndufs4 KO female mice, but not in males, and uncovers an abnormal microglial response due to OXPHOS dysfunction, which may have implications for our understanding of the effect of OXPHOS dysfunction in microglia.

Challenges and opportunities to bridge translational to clinical research for personalized mitochondrial medicine

Mitochondrial disorders are a group of rare and heterogeneous genetic diseases characterized by dysfunctional mitochondria leading to deficient adenosine triphosphate synthesis and chronic energy deficit in patients. The majority of these patients exhibit a wide range of phenotypic manifestations targeting several organ systems, making their clinical diagnosis and management challenging. Bridging translational to clinical research is crucial for improving the early diagnosis and prognosis of these intractable mitochondrial disorders and for discovering novel therapeutic drug candidates and modalities. This review provides the current state of clinical testing in mitochondrial disorders, discusses the challenges and opportunities for converting basic discoveries into clinical settings, explores the most suited patient-centric approaches to harness the extraordinary heterogeneity among patients affected by the same primary mitochondrial disorder, and describes the current outlook of clinical trials.

The mitochondrial tRNA MT-TW m.5537_5538insT variant presents with significant intra-familial clinical variability

Mitochondrial disorders can present with a wide range of clinical and biochemical phenotypes. Mitochondrial DNA variants may be influenced by factors such as degree of heteroplasmy and tissue distribution. We present a four-generation family in which 10 individuals carry a pathogenic mitochondrial variant (m.5537_5538insT, MT-TW gene) with differing levels of heteroplasmy and clinical features. This genetic variant has been documented in two prior reports, both in individuals with Leigh syndrome. In the current family, three individuals have severe mitochondrial symptoms including Leigh syndrome (patient 1, 100% in blood), MELAS (patient 2, 97% heteroplasmy in muscle), and MELAS-like syndrome (patient 3, 50% heteroplasmy in blood and 100% in urine). Two individuals have mild mitochondrial symptoms (patient 4, 50% in blood and 67% in urine and patient 5, 50% heteroplasmy in blood and 30% in urine). We observe that this variant is associated with multiple mitochondrial presentations and phenotypes, including MELAS syndrome for which this variant has not previously been reported. We also demonstrate that the level of heteroplasmy of the mitochondrial DNA variant correlates with the severity of clinical presentation; however, not with the specific mitochondrial syndrome.

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.

Schizophrenia-Like Psychotic Symptoms Associated to Leigh Syndrome

Introduction

Leigh syndrome (LS) is a mitochondrial disease characterized by subacute necrotizing encephalomyelopathy with an estimated incidence of 1:40,000 births. The comorbidity of psychotic symptoms noted in mitochondrial and psychiatric diseases has spurred interest in the effects of DNA mutations and psychiatric disorders. Case presentation. We report the case of a Tunisian 28-year-old male diagnosed with maternally inherited Leigh syndrome. He presented anxiety and auditory hallucinations, and he reported a vague, unsystematized delusion evolving since 6 months. Significant remission was observed at risperidone 3 mg/day. Discussion. The normality of explorations in our case raised the issue of the link between the two diseases, supporting the hypothesis that mitochondrial dysfunction maybe the primary origin of psychotic disorders.

Conclusion

The aim of our work is to study the relations between mitochondrial dysfunction and psychiatric symptoms. Further study of mitochondrial dysfunction in psychiatric disorders is expected to be useful for the development of cellular disease markers and new psychotropics.

Mitochondrial Neurodegenerative Diseases: Three Mitochondrial Ribosomal Proteins as Intermediate Stage in the Pathway That Associates Damaged Genes with Alzheimer's and Parkinson's

Currently, numerous research endeavors are dedicated to unraveling the intricate nature of neurodegenerative diseases. These conditions are characterized by the gradual and progressive impairment of specific neuronal systems that exhibit anatomical or physiological connections. In particular, in the last twenty years, remarkable efforts have been made to elucidate neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. However, despite extensive research endeavors, no cure or effective treatment has been discovered thus far. With the emergence of studies shedding light on the contribution of mitochondria to the onset and advancement of mitochondrial neurodegenerative disorders, researchers are now directing their investigations toward the development of therapies. These therapies include molecules designed to protect mitochondria and neurons from the detrimental effects of aging, as well as mutant proteins. Our objective is to discuss and evaluate the recent discovery of three mitochondrial ribosomal proteins linked to Alzheimer's and Parkinson's diseases. These proteins represent an intermediate stage in the pathway connecting damaged genes to the two mitochondrial neurological pathologies. This discovery potentially could open new avenues for the production of medicinal substances with curative potential for the treatment of these diseases.

Neurodegeneration, Mitochondria, and Antibiotics

Neurodegenerative diseases are characterized by the progressive loss of neurons, synapses, dendrites, and myelin in the central and/or peripheral nervous system. Actual therapeutic options for patients are scarce and merely palliative. Although they affect millions of patients worldwide, the molecular mechanisms underlying these conditions remain unclear. Mitochondrial dysfunction is generally found in neurodegenerative diseases and is believed to be involved in the pathomechanisms of these disorders. Therefore, therapies aiming to improve mitochondrial function are promising approaches for neurodegeneration. Although mitochondrial-targeted treatments are limited, new research findings have unraveled the therapeutic potential of several groups of antibiotics. These drugs possess pleiotropic effects beyond their anti-microbial activity, such as anti-inflammatory or mitochondrial enhancer function. In this review, we will discuss the controversial use of antibiotics as potential therapies in neurodegenerative diseases.

Genetic aberration analysis of mitochondrial respiratory complex I implications in the development of neurological disorders and their clinical significance

Growing neurological diseases pose difficult challenges for modern medicine to diagnose and manage them effectively. Many neurological disorders mainly occur due to genetic alteration in genes encoding mitochondrial proteins. Moreover, mitochondrial genes exhibit a higher rate of mutation due to the generation of Reactive oxygen species (ROS) during oxidative phosphorylation operating in their vicinity. Among the different complexes of Electron transport chain (ETC), NADH: Ubiquinone oxidoreductase (Mitochondrial complex I) is the most important. This multimeric enzyme, composed of 44 subunits, is encoded by both nuclear and mitochondrial genes. It often exhibits mutations resulting in development of various neurological diseases. The most prominent diseases include leigh syndrome (LS), leber hereditary optic neuropathy (LHON), mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS), myoclonic epilepsy associated with ragged-red fibers (MERRF), idiopathic Parkinson's disease (PD) and, Alzheimer's disease (AD). Preliminary data suggest that mitochondrial complex I subunit genes mutated are frequently of nuclear origin; however, most of the mtDNA gene encoding subunits are also primarily involved. In this review, we have discussed the genetic origins of neurological disorders involving mitochondrial complex I and signified recent approaches to unravel the diagnostic and therapeutic potentials and their management.

Anti-AQP4-IgG-positive Leigh syndrome: A case report and review of the literature

BACKGROUND

Leigh syndrome (LS; OMIM: 256000) is a progressive neurodegenerative disease caused by genetic mutations resulting in mitochondrial oxidative phosphorylation defects. The prognosis is poor, with most children dying before the age of 2 years. MT-ATP6 variants are the most common mitochondrial DNA mutations in LS. MT-ATP6 variant-induced LS may trigger autoimmunity, and immunotherapy might be effective. Here, we present the first pediatric case of anti-aquaporin 4 (AQP4)-IgG-positive LS caused by an MT-ATP6 variant.

CASE

A 1-year-old boy was hospitalized due to recurrent fever, cough, and developmental regression. Two months previously, he had developed reduced responses to stimulation and psychomotor retardation. After admission, his condition deteriorated and respiratory failure ensued. Magnetic resonance imaging of the brain showed symmetrical small patchy abnormal signals around the third ventricle, pons, and dorsal periaqueductal gray matter in the dorsal medulla. Laboratory tests revealed anti-AQP4-IgG antibodies. Anti-infection, immunoglobulin, and glucocorticoid therapy were administered for symptomatic treatment. Genetic testing revealed a de novo homogeneous pathogenic variant of MT-ATP6 (m.9176T > C, mutation ratio: 99.97%). The patient was diagnosed with anti-AQP4-IgG-positive LS, treated with "cocktail therapy" (vitamins B1, B2, C, and E, l-carnitine, and coenzyme Q10), and discharged after his condition improved. A literature review revealed that LS-induced mitochondrial defects can impact the immune system; hence, immunotherapy and early mitochondrial cocktail therapy may improve outcomes.

CONCLUSION

Anti-AQP4-IgG-positive LS is very rare. Patients with LS with the m.9176T  > C variant of MT-ATP6 may be susceptible to autoimmune damage of the central nervous system. Early cocktail therapy combined with immunotherapy may improve their prognosis.

Case report: A unusual case of delayed propionic acidemia complicated with subdural hematoma

Background

Propionic acidemia (PA) is an inherited autosomal recessive metabolic disorder that is classified as early-onset or late-onset, depending on the onset time of clinical symptoms. It clinically manifests as numerous lesions in the brain, pancreas, liver, and muscle. Muscle biopsies show myopathic changes, which help to distinguish late-onset propionic acidemia from other metabolic diseases involving muscles.

Case presentation

A 19-year-old Chinese girl was admitted to the hospital because of poor eating and fatigue. Head magnetic resonance imaging suggested metabolic diseases, and we administered symptomatic support treatment. Her symptoms gradually worsened, and she began to show convulsions and disturbances of consciousness. Muscle pathology showed myopathy-like changes. The presence of organic acids in the blood and urine suggested PA. Genetic analyses identified two compound heterozygous mutations in the patient's PCCB gene, confirming the diagnosis of delayed PA.

Conclusions

The muscle pathological examination of late-onset PA provides valuable information that is helpful for distinguishing delayed-onset PA from metabolic diseases. In the absence of a history of trauma, subdural hematoma may be a very rare complication of late-onset PA and can be regarded as a poor prognostic sign; therefore, it is suggested to perform head computed tomography as part of the routine neurological evaluation of PA patients.

Neuropathological Findings in Short-Chain enoyl-CoA Hydratase 1 Deficiency (ECHS1D): Case Report and Differential Diagnosis

Short-chain enoyl-CoA hydratase 1 (ECHS1) is an enzyme that participates in the metabolism of valine, transforming methacrylyl-CoA in β-hydroxy-isobutyryl-CoA. There is an accumulation of intermediate acids and ammonium as a consequence of its deficit. This background generates a harmful environment for the brain causing neuronal death and severe brain lesions. We present a case of a 39 weeks newborn that died at 31 hours old. We found vacuolization in basal areas, brain stem, cerebellum and spinal cord white matter (spongiform myelinopathy). These vacuoles were periodic acid-Schiff stain negative, there were neither acompanion gliosis nor macrophagic reaction. These findings were suggestive of metabolism acid disorders. The final diagnosis was confirmed by genetic study by massive parallel sequencing, showing 2 previously described pathogenic variants (c.160C > T and c.394G > A) of short-chain enoyl-CoA hydratase 1 gene. To our knowledge, this is the first case reporting the histological changes in short-chain enoyl-CoA hydratase 1 deficiency. Histological study provides useful information to orientate the diagnostic and clarify the clinical manifestations, especially in hospitals where urine or blood samples are not taking routinely or where genetic studies may not be performed.Synopsis: The main neuropathological findings in Short-chain enoyl-CoA hydratase 1 deficiency are the presence of whitte matter vacuoles in basal areas, brain stem and spinal cord.

Parkinsonism in Genetic Neurodevelopmental Disorders: A Systematic Review

Background

With advances in clinical genetic testing, associations between genetic neurodevelopmental disorders and parkinsonism are increasingly recognized. In this review, we aimed to provide a comprehensive overview of reports on parkinsonism in genetic neurodevelopmental disorders and summarize findings related to genetic diagnosis, clinical features and proposed disease mechanisms.

Methods

A systematic literature review was conducted in PubMed and Embase on June 15, 2021. Search terms for parkinsonism and genetic neurodevelopmental disorders, using generic terms and the Human Phenotype Ontology, were combined. Study characteristics and descriptive data were extracted from the articles using a modified version of the Cochrane Consumers and Communication Review Group's data extraction template. The protocol was registered in PROSPERO (CRD42020191035).

Results

The literature search yielded 208 reports for data-extraction, describing 69 genetic disorders in 422 patients. The five most reported from most to least frequent were: 22q11.2 deletion syndrome, beta-propeller protein-associated neurodegeneration, Down syndrome, cerebrotendinous xanthomatosis, and Rett syndrome. Notable findings were an almost equal male to female ratio, an early median age of motor onset (26 years old) and rigidity being more common than rest tremor. Results of dopaminergic imaging and response to antiparkinsonian medication often supported the neurodegenerative nature of parkinsonism. Moreover, neuropathology results showed neuronal loss in the majority of cases. Proposed disease mechanisms included aberrant mitochondrial function and disruptions in neurotransmitter metabolism, endosomal trafficking, and the autophagic-lysosomal and ubiquitin-proteasome system.

Conclusion

Parkinsonism has been reported in many GNDs. Findings from this study may provide clues for further research and improve management of patients with GNDs and/or parkinsonism.

Principles and functions of metabolic compartmentalization

Metabolism has historically been studied at the levels of whole cells, whole tissues and whole organisms. As a result, our understanding of how compartmentalization-the spatial and temporal separation of pathways and components-shapes organismal metabolism remains limited. At its essence, metabolic compartmentalization fulfils three important functions or 'pillars': establishing unique chemical environments, providing protection from reactive metabolites and enabling the regulation of metabolic pathways. However, how these pillars are established, regulated and maintained at both the cellular and systemic levels remains unclear. Here we discuss how the three pillars are established, maintained and regulated within the cell and discuss the consequences of dysregulation of metabolic compartmentalization in human disease. Organelles are increasingly emerging as 'command-and-control centres' and the increased understanding of metabolic compartmentalization is revealing new aspects of metabolic homeostasis, with this knowledge being translated into therapies for the treatment of cancer and certain neurodegenerative diseases.

Stroke-like Episodes in Inherited Neurometabolic Disorders

Stroke-like episodes (SLEs) are significant clinical manifestations of metabolic disorders affecting the central nervous system. Morphological equivalents presented in neuroimaging procedures are described as stroke-like lesions (SLLs). It is crucial to distinguish SLEs from cerebral infarction or intracerebral hemorrhage, mainly due to the variety in management. Another significant issue to underline is the meaning of the main pathogenetic hypotheses in the development of SLEs. The diagnostic process is based on the patient’s medical history, physical and neurological examination, neuroimaging techniques and laboratory and genetic testing. Implementation of treatment is generally symptomatic and includes L-arginine supplementation and adequate antiepileptic management. The main aim of the current review was to summarize the basic and actual knowledge about the occurrence of SLEs in various inherited neurometabolic disorders, discuss the possible pathomechanism of their development, underline the role of neuroimaging in the detection of SLLs and identification of the electroencephalographic patterns as well as histological abnormalities in inherited disorders of metabolism.

Leigh's disease, a fatal finding in the common world: A case report

Leigh syndrome is a neurodegenerative mitochondrial disorder of childhood characterized by symmetrical spongiform lesions in the brain. The clinical presentation of Leigh's syndrome can vary significantly. However, in the majority of cases, it usually presents as a progressive neurological disease involving motor and cognitive development. It is common to see signs and symptoms of the midbrain and brainstem involvement. Limited data are present on the brain processes occurring in Leigh's syndrome which can be attributed to fatal respiratory failure. Raised lactate levels in the blood and/or cerebrospinal fluid are noted. Magnetic resonance imaging (MRI) findings such as necrotic, symmetrical lesions in the BG/brain stem are helpful in arriving at the diagnosis of Leigh's syndrome. It's of utmost importance to determine whether fatal respiratory failure can be predicted based on clinical characteristics and findings on MRI. In our report, we presented 3 cases from rural India, including a 2-year-old male child presenting with UMN lesion signs, a 3-month-old female infant with delayed developmental milestones with lab results suggestive of Leigh's disease, and a 12-year-old female child with epistaxis and generalized weakness. As discussed above, all 3 cases presented differently with a variety of signs and symptoms and would have gone undiagnosed without the use of brain imaging. The study concluded with the impression that while MRI is essential to the initial diagnosis of Leigh's disease, MRI alone cannot be used to predict fatal respiratory failure in patients with Leigh's disease. In any dilemma regarding diagnosis even with MRI, molecular studies remain the gold standard.

Human iPSC-derived cerebral organoids model features of Leigh syndrome and reveal abnormal corticogenesis

Leigh syndrome (LS) is a rare, inherited neurometabolic disorder that presents with bilateral brain lesions caused by defects in the mitochondrial respiratory chain and associated nuclear-encoded proteins. We generated human induced pluripotent stem cells (iPSCs) from three LS patient-derived fibroblast lines. Using whole-exome and mitochondrial sequencing, we identified unreported mutations in pyruvate dehydrogenase (GM0372, PDH; GM13411, MT-ATP6/PDH) and dihydrolipoyl dehydrogenase (GM01503, DLD). These LS patient-derived iPSC lines were viable and capable of differentiating into progenitor populations, but we identified several abnormalities in three-dimensional differentiation models of brain development. LS patient-derived cerebral organoids showed defects in neural epithelial bud generation, size and cortical architecture at 100 days. The double mutant MT-ATP6/PDH line produced organoid neural precursor cells with abnormal mitochondrial morphology, characterized by fragmentation and disorganization, and showed an increased generation of astrocytes. These studies aim to provide a comprehensive phenotypic characterization of available patient-derived cell lines that can be used to study Leigh syndrome.

AAV-vector based gene therapy for mitochondrial disease: progress and future perspectives

Mitochondrial diseases are a group of rare, heterogeneous diseases caused by gene mutations in both nuclear and mitochondrial genomes that result in defects in mitochondrial function. They are responsible for significant morbidity and mortality as they affect multiple organ systems and particularly those with high energy-utilizing tissues, such as the nervous system, skeletal muscle, and cardiac muscle. Virtually no effective treatments exist for these patients, despite the urgent need. As the majority of these conditions are monogenic and caused by mutations in nuclear genes, gene replacement is a highly attractive therapeutic strategy. Adeno-associated virus (AAV) is a well-characterized gene replacement vector, and its safety profile and ability to transduce quiescent cells nominates it as a potential gene therapy vehicle for several mitochondrial diseases. Indeed, AAV vector-based gene replacement is currently being explored in clinical trials for one mitochondrial disease (Leber hereditary optic neuropathy) and preclinical studies have been published investigating this strategy in other mitochondrial diseases. This review summarizes the preclinical findings of AAV vector-based gene replacement therapy for mitochondrial diseases including Leigh syndrome, Barth syndrome, ethylmalonic encephalopathy, and others.

Chemical Exchange Saturation Transfer for Lactate-Weighted Imaging at 3 T MRI: Comprehensive In Silico, In Vitro, In Situ, and In Vivo Evaluations

Based on in silico, in vitro, in situ, and in vivo evaluations, this study aims to establish and optimize the chemical exchange saturation transfer (CEST) imaging of lactate (Lactate-CEST—LATEST). To this end, we optimized LATEST sequences using Bloch−McConnell simulations for optimal detection of lactate with a clinical 3 T MRI scanner. The optimized sequences were used to image variable lactate concentrations in vitro (using phantom measurements), in situ (using nine human cadaveric lower leg specimens), and in vivo (using four healthy volunteers after exertional exercise) that were then statistically analyzed using the non-parametric Friedman test and Kendall Tau-b rank correlation. Within the simulated Bloch−McConnell equations framework, the magnetization transfer ratio asymmetry (MTRasym) value was quantified as 0.4% in the lactate-specific range of 0.5−1 ppm, both in vitro and in situ, and served as the imaging surrogate of the lactate level. In situ, significant differences (p < 0.001) and strong correlations (τ = 0.67) were observed between the MTRasym values and standardized intra-muscular lactate concentrations. In vivo, a temporary increase in the MTRasym values was detected after exertional exercise. In this bench-to-bedside comprehensive feasibility study, different lactate concentrations were detected using an optimized LATEST imaging protocol in vitro, in situ, and in vivo at 3 T, which prospectively paves the way towards non-invasive quantification and monitoring of lactate levels across a broad spectrum of diseases.

Bezafibrate Rescues Mitochondrial Encephalopathy in Mice via Induction of Daily Torpor and Hypometabolic State

Leigh syndrome (LS) is one of the most common mitochondrial encephalopathy diseases in infants. To date, there is still an absence of effective therapy. Bezafibrate (BEZ), a pan-peroxisome proliferator-activated receptor (PPAR) agonist, ameliorates the phenotype of the mouse model of mitochondrial disease via an unclear mechanism. Here, we applied it to Ndufs4 knockout (KO) mice, a widely used LS animal model, to observe the therapeutic effects and metabolic changes associated with BEZ treatment to explore the therapeutic strategies for mitochondrial diseases. Administration of BEZ significantly enhances survival and attenuates disease progression in Ndufs4 KO mice. Decreased oxidative stress and stunted growth were also observed. As a PPAR agonist, we did not find mitochondrial biogenesis or enhanced metabolism upon BEZ treatment. On the contrary, mice with dietary BEZ showed daily torpor bouts and lower metabolic rates. We speculate that activating energy-saving metabolism in mice may be associated with the therapeutic effects of BEZ, but the exact mechanism of action requires further study.

Pleiotropic effects of mitochondria in aging

Aging is typified by a progressive decline in mitochondrial activity and stress resilience. Here, we review how mitochondrial stress pathways have pleiotropic effects on cellular and systemic homeostasis, which can comprise protective or detrimental responses during aging. We describe recent evidence arguing that defects in these conserved adaptive pathways contribute to aging and age-related diseases. Signaling pathways regulating the mitochondrial unfolded protein response, mitochondrial membrane dynamics, and mitophagy are discussed, emphasizing how their failure contributes to heteroplasmy and de-regulation of key metabolites. Our current understanding of how these processes are controlled and interconnected explains how mitochondria can widely impact fundamental aspects of aging.

Mitochondrial ribosomal protein genes connected with Alzheimer's and tellurite toxicity

Mitochondrial diseases are a group of genetic disorders characterized by dysfunctional mitochondria. Within eukaryotic cells, mitochondria contain their own ribosomes, which synthesize small amounts of proteins, all of which are essential for the biogenesis of the oxidative phosphorylation system. The ribosome is an evolutionarily conserved macromolecular machine in nature both from a structural and functional point of view, universally responsible for the synthesis of proteins. Among the diseases afflicting humans, those of ribosomal origin - either cytoplasmic ribosomes (80S) or mitochondrial ribosomes (70S) - are relevant. These are inherited or acquired diseases most commonly caused by either ribosomal protein haploinsufficiency or defects in ribosome biogenesis. Here we review the scientific literature about the recent advances on changes in mitochondrial ribosomal structural and assembly proteins that are implicated in primary mitochondrial diseases and neurodegenerative disorders, and their possible connection with metalloid pollution and toxicity, with a focus on MRPL44, NAM9 (MNA6) and GEP3 (MTG3), whose lack or defect was associated with resistance to tellurite. Finally, we illustrate the suitability of yeast Saccharomyces cerevisiae (S.cerevisiae) and the nematode Caenorhabditis elegans (C.elegans) as model organisms for studying mitochondrial ribosome dysfunctions including those involved in human diseases.

DNAJC30 defect: a frequent cause of recessive Leber hereditary optic neuropathy and Leigh syndrome

The recent description of biallelic DNAJC30 variants in Leber hereditary optic neuropathy (LHON) and Leigh syndrome challenged the longstanding assumption for LHON to be exclusively maternally inherited and broadened the genetic spectrum of Leigh syndrome, the most frequent paediatric mitochondrial disease. Herein, we characterize 28 so far unreported individuals from 26 families carrying a homozygous DNAJC30 p.Tyr51Cys founder variant, 24 manifesting with LHON, two manifesting with Leigh syndrome, and two remaining asymptomatic. This collection of unreported variant carriers confirms sex-dependent incomplete penetrance of the homozygous variant given a significant male predominance of disease and the report of asymptomatic homozygous variant carriers. The autosomal recessive LHON patients demonstrate an earlier age of disease onset and a higher rate of idebenone-treated and spontaneous recovery of vision in comparison to reported figures for maternally inherited disease. Moreover, the report of two additional patients with childhood- or adult-onset Leigh syndrome further evidences the association of DNAJC30 with Leigh syndrome, previously only reported in a single childhood-onset case.

Leukocytes mediate disease pathogenesis in the Ndufs4(KO) mouse model of Leigh syndrome

Symmetric, progressive, necrotizing lesions in the brainstem are a defining feature of Leigh syndrome (LS). A mechanistic understanding of the pathogenesis of these lesions has been elusive. Here, we report that leukocyte proliferation is causally involved in the pathogenesis of LS. Depleting leukocytes with a colony-stimulating factor 1 receptor inhibitor disrupted disease progression, including suppression of CNS lesion formation and a substantial extension of survival. Leukocyte depletion rescued diverse symptoms, including seizures, respiratory center function, hyperlactemia, and neurologic sequelae. These data reveal a mechanistic explanation for the beneficial effects of mTOR inhibition. More importantly, these findings dramatically alter our understanding of the pathogenesis of LS, demonstrating that immune involvement is causal in disease. This work has important implications for the mechanisms of mitochondrial disease and may lead to novel therapeutic strategies.

Activated microglia and neuroinflammation as a pathogenic mechanism in Leigh syndrome

Neuroinflammation is one of the main mechanisms leading to neuronal death and dysfunction in neurodegenerative diseases. The role of microglia as primary mediators of inflammation is unclear in Leigh syndrome (LS) patients. This study aims to elucidate the role of microglia in LS progression by a detailed multipronged analysis of LS neuropathology, mouse and human induced pluripotent stem cells models of Leigh syndrome. We described brain pathology in three cases of Leigh syndrome and performed immunohistochemical staining of autopsy brain of LS patients. We used mouse model of LS (Ndufs4^-/-) to study the effect of microglial partial ablation using pharmacologic approach. Genetically modified human induced pluripotent stem cell (iPS) derived neurons and brain organoid with Ndufs4 mutation were used to investigate the neuroinflammation in LS. We reported a novel observation of marked increased in Iba1+ cells with features of activated microglia, in various parts of brain in postmortem neuropathological examinations of three Leigh syndrome patients. Using an Ndufs4^-/- mouse model for Leigh syndrome, we showed that partial ablation of microglia by Pexidartinib initiated at the symptom onset improved neurological function and significantly extended lifespan. Ndufs4 mutant LS brain organoid had elevated NLRP3 and IL6 pro-inflammatory pathways. Ndufs4-mutant LS iPSC neurons were more susceptible to glutamate excitotoxicity, which was further potentiated by IL-6. Our findings of LS human brain pathology, Ndufs4-deficient mouse and iPSC models of LS suggest a critical role of activated microglia in the progression of LS encephalopathy. This study suggests a potential clinical application of microglial ablation and immunosuppression during the active phase of Leigh syndrome.

Leigh syndrome in an infant: autopsy and histopathology findings

Leigh syndrome is an inherited neurodegenerative disorder of infancy that typically manifests between 3 and 12 months of age. The common neurological manifestations are developmental delay or regression, progressive cognitive decline, dystonia, ataxia, brainstem dysfunction, epileptic seizures, and respiratory dysfunction. Although the disorder is clinically and genetically heterogeneous, the histopathological and radiological features characteristically show focal and bilaterally symmetrical, necrotic lesions in the basal ganglia and brainstem. The syndrome has a characteristic histopathological signature that helps in clinching the diagnosis. We discuss these unique findings on autopsy and radiology in a young infant who succumbed to a subacute, progressive neurological illness suggestive of Leigh syndrome. Our case highlights that Leigh syndrome should be considered in the differential diagnosis of infantile-onset, subacute neuroregression with dystonia and seizures, a high anion gap metabolic acidosis, normal ketones, elevated lactates in blood, brain, and urine, and bilateral basal ganglia involvement.

On the dynamic and even reversible nature of Leigh syndrome: Lessons from human imaging and mouse models

Leigh syndrome (LS) is a neurodegenerative disease characterized by bilaterally symmetric brainstem or basal ganglia lesions. More than 80 genes, largely impacting mitochondrial energy metabolism, can underlie LS, and no approved medicines exist. Described 70 years ago, LS was initially diagnosed by the characteristic, necrotic lesions on autopsy. It has been broadly assumed that antemortem neuroimaging abnormalities in these regions correspond to end-stage histopathology. However, clinical observations and animal studies suggest that neuroimaging findings may represent an intermediate state, that is more dynamic than previously appreciated, and even reversible. We review this literature, discuss related conditions that are treatable, and present two new LS cases with radiographic improvement. We review studies in which hypoxia reverses advanced LS in a mouse model. The fluctuating and potentially reversible nature of radiographic LS lesions will be important in clinical trial design. Better understanding of this plasticity could lead to new therapies.

Clinical, imaging, biochemical and molecular features in Leigh syndrome: a study from the Italian network of mitochondrial diseases

BACKGROUND

Leigh syndrome (LS) is a progressive neurodegenerative disorder associated with primary or secondary dysfunction of mitochondrial oxidative phosphorylation and is the most common mitochondrial disease in childhood. Numerous reports on the biochemical and molecular profiles of LS have been published, but there are limited studies on genetically confirmed large series. We reviewed the clinical, imaging, biochemical and molecular data of 122 patients with a diagnosis of LS collected in the Italian Collaborative Network of Mitochondrial Diseases database.

RESULTS

Clinical picture was characterized by early onset of several neurological signs dominated by central nervous system involvement associated with both supra- and sub-tentorial grey matter at MRI in the majority of cases. Extraneurological organ involvement is less frequent in LS than expected for a mitochondrial disorder. Complex I and IV deficiencies were the most common biochemical diagnoses, mostly associated with mutations in SURF1 or mitochondrial-DNA genes encoding complex I subunits. Our data showed SURF1 as the genotype with the most unfavorable prognosis, differently from other cohorts reported to date.

CONCLUSION

We report on a large genetically defined LS cohort, adding new data on phenotype-genotype correlation, prognostic factors and possible suggestions to diagnostic workup.

Convergent Canonical Pathways in Autism Spectrum Disorder from Proteomic, Transcriptomic and DNA Methylation Data

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental disorder with extensive genetic and aetiological heterogeneity. While the underlying molecular mechanisms involved remain unclear, significant progress has been facilitated by recent advances in high-throughput transcriptomic, epigenomic and proteomic technologies. Here, we review recently published ASD proteomic data and compare proteomic functional enrichment signatures with those of transcriptomic and epigenomic data. We identify canonical pathways that are consistently implicated in ASD molecular data and find an enrichment of pathways involved in mitochondrial metabolism and neurogenesis. We identify a subset of differentially expressed proteins that are supported by ASD transcriptomic and DNA methylation data. Furthermore, these differentially expressed proteins are enriched for disease phenotype pathways associated with ASD aetiology. These proteins converge on protein–protein interaction networks that regulate cell proliferation and differentiation, metabolism, and inflammation, which demonstrates a link between canonical pathways, biological processes and the ASD phenotype. This review highlights how proteomics can uncover potential molecular mechanisms to explain a link between mitochondrial dysfunction and neurodevelopmental pathology.

Sub-Cellular Metabolomics Contributes Mitochondria-Specific Metabolic Insights to a Mouse Model of Leigh Syndrome

Direct injury of mitochondrial respiratory chain (RC) complex I by Ndufs4 subunit mutations results in complex I deficiency (CID) and a progressive encephalomyopathy, known as Leigh syndrome. While mitochondrial, cytosolic and multi-organelle pathways are known to be involved in the neuromuscular LS pathogenesis, compartment-specific metabolomics has, to date, not been applied to murine models of CID. We thus hypothesized that sub-cellular metabolomics would be able to contribute organelle-specific insights to known Ndufs4 metabolic perturbations. To that end, whole brains and skeletal muscle from late-stage Ndufs4 mice and age/sex-matched controls were harvested for mitochondrial and cytosolic isolation. Untargeted ¹H-NMR and semi-targeted LC-MS/MS metabolomics was applied to the resulting cell fractions, whereafter important variables (VIPs) were selected by univariate statistics. A predominant increase in multiple targeted amino acids was observed in whole-brain samples, with a more prominent effect at the mitochondrial level. Similar pathways were implicated in the muscle tissue, showing a greater depletion of core metabolites with a compartment-specific distribution, however. The altered metabolites expectedly implicate altered redox homeostasis, alternate RC fueling, one-carbon metabolism, urea cycling and dysregulated proteostasis to different degrees in the analyzed tissues. A first application of EDTA-chelated magnesium and calcium measurement by NMR also revealed tissue- and compartment-specific alterations, implicating stress response-related calcium redistribution between neural cell compartments, as well as whole-cell muscle magnesium depletion. Altogether, these results confirm the ability of compartment-specific metabolomics to capture known alterations related to Ndufs4 KO and CID while proving its worth in elucidating metabolic compartmentalization in said pathways that went undetected in the diluted whole-cell samples previously studied.

Bilateral horizontal gaze palsy in an 8-year-old girl: A rare case with NDUFS4 gene mutation

We report a patient with complex clinical presentation including multiple neurological symptoms and eye involvement. Upon genetic investigation, the patient was found to carry a novel homozygous mutation in the NDUFS4 gene, thus adding to the heterogeneity of Leigh syndrome clinical presentation.

Late-onset Leigh syndrome without delayed development in China: A case report

BACKGROUND

Leigh syndrome (LS) is one of the most common mitochondrial diseases in infants and children. LS often manifests as early-onset with delayed phenotypic development. However, late-onset LS with normal development and white matter lesions in the brain is rarely reported, thereby highlighting the phenotypic variability of LS expression.

CASE SUMMARY

We report a 12-year-old boy who presented with an unusual late-onset and fulminant form of LS that is maternally inherited without developmental delay. The patient was admitted to the hospital with symptoms of ptosis and somnolence, and died within 2 mo. Analysis of peripheral blood leukocytes showed a homoplasmic m.9176T>C mutation in the patient. Magnetic resonance imaging also revealed lesions in bilateral white matter as well as symmetrical lesions in the basal ganglia and brain stem. The patient was diagnosed with LS. The patient was treated with vitamin C, vitamin D, and adenosine-triphosphate. The patient died within 2 mo of hospital admission.

CONCLUSION

LS can present in both infants and older children with different phenotypes.

Metabolism navigates neural cell fate in development, aging and neurodegeneration

An uninterrupted energy supply is critical for the optimal functioning of all our organs, and in this regard the human brain is particularly energy dependent. The study of energy metabolic pathways is a major focus within neuroscience research, which is supported by genetic defects in the oxidative phosphorylation mechanism often contributing towards neurodevelopmental disorders and changes in glucose metabolism presenting as a hallmark feature in age-dependent neurodegenerative disorders. However, as recent studies have illuminated roles of cellular metabolism that span far beyond mere energetics, it would be valuable to first comprehend the physiological involvement of metabolic pathways in neural cell fate and function, and to subsequently reconstruct their impact on diseases of the brain. In this Review, we first discuss recent evidence that implies metabolism as a master regulator of cell identity during neural development. Additionally, we examine the cell type-dependent metabolic states present in the adult brain. As metabolic states have been studied extensively as crucial regulators of malignant transformation in cancer, we reveal how knowledge gained from the field of cancer has aided our understanding in how metabolism likewise controls neural fate determination and stability by directly wiring into the cellular epigenetic landscape. We further summarize research pertaining to the interplay between metabolic alterations and neurodevelopmental and psychiatric disorders, and expose how an improved understanding of metabolic cell fate control might assist in the development of new concepts to combat age-dependent neurodegenerative diseases, particularly Alzheimer's disease.

Selective symmetrical necrotizing encephalopathy secondary to primary mitochondrial disorder in a cat

A 2‐year‐old female cat was referred for progressive neurological signs indicative of involvement of the prosencephalon, cerebellum, and brainstem. Magnetic resonance imaging identified multifocal, bilateral, symmetrical lesions with strong contrast enhancement, affecting multiple areas of the brain. Neuropathology at necropsy showed demyelination, necrotic lesions, spongiosis, and neuropil edema with reactive astrogliosis and neovascularization. Ultrastructural study indicated mitochondrial polymorphism. Genetic investigations outlined 2 polymorphisms within the tRNA‐Leu^(UUR) gene of mitochondrial DNA. Imaging and neuropathological findings were consistent with selective symmetrical necrotizing encephalopathy, for which genetic investigations support mitochondrial pathogenesis.

Cerebral blood flow and acute episodes of Leigh syndrome in neurometabolic disorders

AIM

To investigate cerebral blood flow (CBF) in acute episodes of Leigh syndrome compared with basal state in patients carrying pathogenic mitochondrial disease gene variants responsible for neurometabolic disorders.

METHOD

Arterial spin labelling (ASL) magnetic resonance imaging (MRI) sequences were used to measure CBF in 27 patients with mitochondrial respiratory chain enzyme deficiencies, ascribed to pathogenic variants of reported disease genes who were undergoing either urgent neuroimaging for acute episodes of Leigh syndrome (Group I: 15 MRI, seven females, eight males; mean age 7y; range 7mo-14y) or routine brain MRI (Group II: 15 MRI, eight females, seven males; mean age 5y 2mo; range 2mo-12y).

RESULTS

Patients displayed markedly increased CBF in the striatum (2.8-fold greater, p<0.001 [1.05-2.53]) during acute episodes of Leigh syndrome compared to basal conditions. Detection of elevated CBF preceded identification of structural MRI lesions in four out of 15 cases.

INTERPRETATION

Our results suggest that increased CBF is an overt hallmark of Leigh syndrome episodes and ASL MRI sequences should facilitate early diagnosis of acute episodes of Leigh syndrome, especially during the first attack in young children, when structural MRI is insufficiently informative.

Hypoxia ameliorates brain hyperoxia and NAD+ deficiency in a murine model of Leigh syndrome

Leigh syndrome is a severe mitochondrial neurodegenerative disease with no effective treatment. In the Ndufs4-/- mouse model of Leigh syndrome, continuously breathing 11% O2 (hypoxia) prevents neurodegeneration and leads to a dramatic extension (~5-fold) in lifespan. We investigated the effect of hypoxia on the brain metabolism of Ndufs4-/- mice by studying blood gas tensions and metabolite levels in simultaneously sampled arterial and cerebral internal jugular venous (IJV) blood. Relatively healthy Ndufs4-/- and wildtype (WT) mice breathing air until postnatal age ~38 d were compared to Ndufs4-/- and WT mice breathing air until ~38 days old followed by 4-weeks of breathing 11% O2. Compared to WT control mice, Ndufs4-/- mice breathing air have reduced brain O2 consumption as evidenced by an elevated partial pressure of O2 in IJV blood (PijvO2) despite a normal PO2 in arterial blood, and higher lactate/pyruvate (L/P) ratios in IJV plasma revealed by metabolic profiling. In Ndufs4-/- mice, hypoxia treatment normalized the cerebral venous PijvO2 and L/P ratios, and decreased levels of nicotinate in IJV plasma. Brain concentrations of nicotinamide adenine dinucleotide (NAD+) were lower in Ndufs4-/- mice breathing air than in WT mice, but preserved at WT levels with hypoxia treatment. Although mild hypoxia (17% O2) has been shown to be an ineffective therapy for Ndufs4-/- mice, we find that when combined with nicotinic acid supplementation it provides a modest improvement in neurodegeneration and lifespan. Therapies targeting both brain hyperoxia and NAD+ deficiency may hold promise for treating Leigh syndrome.

The utility of next-generation sequencing technologies in diagnosis of Mendelian mitochondrial diseases and reflections on clinical spectrum

OBJECTIVES

Diagnostic process of mitochondrial disorders (MD) is challenging because of the clinical variability and genetic heterogeneity of these conditions. Next-Generation Sequencing (NGS) technology offers a high-throughput platform for nuclear MD.

METHODS

We included 59 of 72 patients that undergone WES and targeted exome sequencing panel suspected to have potential PMDs. Patients who were included in the analysis considering the possible PMD were reviewed retrospectively and scored according to the Mitochondrial Disease Criteria Scale.

RESULTS

Sixty-one percent of the patients were diagnosed with whole-exome sequencing (WES) (36/59) and 15% with targeted exome sequencing (TES) (9/59). Patients with MD-related gene defects were included in the mito group, patients without MD-related gene defects were included in the nonmito group, and patients in whom no etiological cause could be identified were included in the unknown etiology group. In 11 out of 36 patients diagnosed with WES, a TES panel was applied prior to WES. In 47 probands in 39 genes (SURF1, SDHAF1, MTO1, FBXL4, SLC25A12, GLRX5, C19oRF12, NDUFAF6, DARS2, BOLA3, SLC19A3, SCO1, HIBCH, PDHA1, PDHAX, PC, ETFA, TRMU, TUFM, NDUFS6, WWOX, UBCD TREX1, ATL1, VAC14, GFAP, PLA2G6, TPRKB, ATP8A2, PEX13, IGHMBP2, LAMB2, LPIN1, GFPT1, CLN5, DOLK) (20 mito group, 19 nonmito group) 59 variants (31 mito group, 18 nonmito group) were detected. Seven novel variants in the mito group (SLC25A12, GLRX5, DARS2, SCO1, PC, ETFA, NDUFS6), nine novel variants in the nonmito group (IVD, GCDH, COG4, VAC14, GFAP, PLA2G6, ATP8A2, PEX13, LPIN1) were detected.

CONCLUSIONS

We explored the feasibility of identifying pathogenic alleles using WES and TES in MD. Our results show that WES is the primary method of choice in the diagnosis of MD until at least all genes responsible for PMD are found and are highly effective in facilitating the diagnosis process.

Defective metabolic programming impairs early neuronal morphogenesis in neural cultures and an organoid model of Leigh syndrome

Leigh syndrome (LS) is a severe manifestation of mitochondrial disease in children and is currently incurable. The lack of effective models hampers our understanding of the mechanisms underlying the neuronal pathology of LS. Using patient-derived induced pluripotent stem cells and CRISPR/Cas9 engineering, we developed a human model of LS caused by mutations in the complex IV assembly gene SURF1. Single-cell RNA-sequencing and multi-omics analysis revealed compromised neuronal morphogenesis in mutant neural cultures and brain organoids. The defects emerged at the level of neural progenitor cells (NPCs), which retained a glycolytic proliferative state that failed to instruct neuronal morphogenesis. LS NPCs carrying mutations in the complex I gene NDUFS4 recapitulated morphogenesis defects. SURF1 gene augmentation and PGC1A induction via bezafibrate treatment supported the metabolic programming of LS NPCs, leading to restored neuronal morphogenesis. Our findings provide mechanistic insights and suggest potential interventional strategies for a rare mitochondrial disease.

Clinical exome sequencing reveals a mutation in PDHA1 in Leigh syndrome: A case of a Chinese boy with lethal neuropathy

Background

Leigh syndrome, the most common mitochondrial syndrome in pediatrics, has diverse clinical manifestations and is genetically heterogeneous. Pathogenic mutations in more than 75 genes of two genomes (mitochondrial and nuclear) have been identified. PDHA1 encoding the E1 alpha subunit is an X‐chromosome gene whose mutations cause pyruvate dehydrogenase complex deficiency.

Methods

Here, we have described a 12‐year‐old boy with lethal neuropathy who almost died of a sudden loss of breathing and successive cardiac arrest. Extracorporeal membrane oxygenation rescued his life. His diagnosis was corrected from Guillain–Barré syndrome to Leigh syndrome 1 month later by clinical exome sequencing. Furthermore, we used software to predict the protein structure caused by frameshift mutations. We treated the boy with vitamin B1, coenzyme Q10, and a ketogenic diet.

Results

A PDHA1 mutation (NM_000284.4:c.1167_1170del) was identified as the underlying cause. The amino acid mutation was p.Ser390LysfsTer33. Moreover, the protein structure prediction results suggested that the protein structure has changed. The parents of the child were negative, so the mutation was de novo. The comprehensive assessment of the mutation was pathogenic. His condition gradually improved after receiving treatment.

Conclusion

This case suggests that gene detection should be popularized to improve diagnosis accuracy, especially in developing countries such as China.

Delineating the neurological phenotype in children with defects in the ECHS1 or HIBCH gene

The neurological phenotype of 3-hydroxyisobutyryl-CoA hydrolase (HIBCH) and short-chain enoyl-CoA hydratase (SCEH) defects is expanding and natural history studies are necessary to improve clinical management. From 42 patients with Leigh syndrome studied by massive parallel sequencing, we identified five patients with SCEH and HIBCH deficiency. Fourteen additional patients were recruited through collaborations with other centres. In total, we analysed the neurological features and mutation spectrum in 19 new SCEH/HIBCH patients. For natural history studies and phenotype to genotype associations we also included 70 previously reported patients. The 19 newly identified cases presented with Leigh syndrome (SCEH, n = 11; HIBCH, n = 6) and paroxysmal dystonia (SCEH, n = 2). Basal ganglia lesions (18 patients) were associated with small cysts in the putamen/pallidum in half of the cases, a characteristic hallmark for diagnosis. Eighteen pathogenic variants were identified, 11 were novel. Among all 89 cases, we observed a longer survival in HIBCH compared to SCEH patients, and in HIBCH patients carrying homozygous mutations on the protein surface compared to those with variants inside/near the catalytic region. The SCEH p.(Ala173Val) change was associated with a milder form of paroxysmal dystonia triggered by increased energy demands. In a child harbouring SCEH p.(Ala173Val) and the novel p.(Leu123Phe) change, an 83.6% reduction of the protein was observed in fibroblasts. The SCEH and HIBCH defects in the catabolic valine pathway were a frequent cause of Leigh syndrome in our cohort. We identified phenotype and genotype associations that may help predict outcome and improve clinical management.