Follow-up of folinic acid supplementation for patients with cerebral folate deficiency and Kearns-Sayre syndrome

Mitochondrial Chronic Progressive External Ophthalmoplegia

BACKGROUND

Chronic progressive external ophthalmoplegia (CPEO) is a rare disorder that can be at the forefront of several mitochondrial diseases. This review overviews mitochondrial CPEO encephalomyopathies to enhance accurate recognition and diagnosis for proper management.

METHODS

This study is conducted based on publications and guidelines obtained by selective review in PubMed. Randomized, double-blind, placebo-controlled trials, Cochrane reviews, and literature meta-analyses were particularly sought.

DISCUSSION

CPEO is a common presentation of mitochondrial encephalomyopathies, which can result from alterations in mitochondrial or nuclear DNA. Genetic sequencing is the gold standard for diagnosing mitochondrial encephalomyopathies, preceded by non-invasive tests such as fibroblast growth factor-21 and growth differentiation factor-15. More invasive options include a muscle biopsy, which can be carried out after uncertain diagnostic testing. No definitive treatment option is available for mitochondrial diseases, and management is mainly focused on lifestyle risk modification and supplementation to reduce mitochondrial load and symptomatic relief, such as ptosis repair in the case of CPEO. Nevertheless, various clinical trials and endeavors are still at large for achieving beneficial therapeutic outcomes for mitochondrial encephalomyopathies.

KEY MESSAGES

Understanding the varying presentations and genetic aspects of mitochondrial CPEO is crucial for accurate diagnosis and management.

Metabolomic disorders: confirmed presence of potentially treatable abnormalities in patients with treatment refractory depression and suicidal behavior

BACKGROUND

Refractory depression is a devastating condition with significant morbidity, mortality, and societal cost. Approximately 15% of patients with major depressive disorder are refractory to currently available treatments. We hypothesized metabolic abnormalities contributing to treatment refractory depression are associated with distinct findings identifiable in the cerebrospinal fluid (CSF). Our hypothesis was confirmed by a previous small case-controlled study. Here we present a second, larger replication study.

METHODS

We conducted a case-controlled, targeted, metabolomic evaluation of 141 adolescent and adult patients with well-characterized history of depression refractory to three maximum-dose, adequate-duration medication treatments, and 36 healthy controls. Plasma, urine, and CSF metabolic profiling were performed by coupled gas chromatography/mass spectrometry, and high-performance liquid chromatography, electrospray ionization, tandem mass spectrometry.

RESULTS

Abnormalities were identified in 67 of 141 treatment refractory depression participants. The CSF abnormalities included: low cerebral folate (n = 20), low tetrahydrobiopterin intermediates (n = 11), and borderline low-tetrahydrobiopterin intermediates (n = 20). Serum abnormalities included abnormal acylcarnitine profile (n = 12) and abnormal serum amino acids (n = 20). Eighteen patients presented with two or more abnormal metabolic findings. Sixteen patients with cerebral folate deficiency and seven with low tetrahydrobiopterin intermediates in CSF showed improvement in depression symptom inventories after treatment with folinic acid and sapropterin, respectively. No healthy controls had a metabolite abnormality.

CONCLUSIONS

Examination of metabolic disorders in treatment refractory depression identified an unexpectedly large proportion of patients with potentially treatable abnormalities. The etiology of these abnormalities and their potential roles in pathogenesis remain to be determined.

Cerebral folate deficiency: A report of two affected siblings

Cerebral folate deficiency (CFD) is a rare progressive neurological condition characterized by normal blood folate level and low 5-methyltetrahydrofolate (5-MTHF) levels in the cerebrospinal fluid. Patients present with different neurological findings including hypotonia and microcephaly. Later, patients develop ataxia, seizures, para or quadri-plagia. Herein, we report two siblings; born to consanguineous parents; who had normal neurological development in early childhood. Subsequently they developed drug-resistant seizures, neurological regression, and spastic quadriplegia. After thorough investigations patients had brain MRI which showed abnormal white matter signals and ventricular dilatation, CSF with low 5-MTHF, and whole exome sequencing (WES) revealed a novel homozygous variant in FOLR1 (c.245A > G; p.Tyr82Cys) consistent with the diagnosis of cerebral folate deficiency. They were treated with folinic acid in addition to standard anti-seizure medications. WES aids in reaching CFD diagnosis due to FOLR1 pathogenic variants. These results can be used for future counselling to prevent recurrence in future pregnancies by preimplantation genetic testing prior to implanting the embryo in the uterus. Treatment with folinic acid was shown to improve the neurological symptoms namely reduced the seizures and spasticity.

Currently available therapies in mitochondrial disease

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

Folic acid inhibits 5-methyltetrahydrofolate transport across the blood-cerebrospinal fluid barrier: Clinical biochemical data from two cases

Objective

The use of folic acid (FA) has been discouraged in cerebral folate deficiency (CFD) because, theoretically, it could inhibit the transport of 5-methyltetrahydrofolic acid (5MTHF) across the blood-cerebrospinal fluid (CSF) barrier. We present the clinical biochemical data of two cases with CFD to support this hypothesis.

Methods

We measured CSF and serum 5MTHF concentrations in a patient with Kearns-Sayre syndrome (KSS) and a patient homozygous for MTHFR C677T polymorphism before and during folate supplementation therapy. To evaluate these 5MTHF concentrations, we also analyzed CSF and serum samples in pediatric patients without folate supplementation.

Results

Both patients had low CSF 5MTHF before treatment and high-dose FA therapy did not normalize CSF 5MTHF. There was a dissociation between serum total folate and 5MTHF concentrations during FA therapy, which was considered to be due to the appearance of unmetabolized FA. The addition of folinic acid did not improve low CSF 5MTHF in the KSS patient and the cessation of FA resulted in the normalization of CSF 5MTHF. In the patient homozygous for MTHFR C677T, minimization of the FA dosage resulted in the normalization of CSF 5MTHF and an increased CSF-to-serum 5MTHF ratio.

Conclusions

Our data suggest that excess supplementation of FA impaired 5MTHF transport across the blood-CSF barrier. In the treatment of CFD, supplementation of folinic acid or 5MTHF (in cases of impaired 5MTHF synthesis) is preferred over the use of FA. The reference values of CSF 5MTHF concentration based on 600 pediatric cases were also provided.

Cerebral Folate Deficiency Syndrome: Early Diagnosis, Intervention and Treatment Strategies

Cerebral folate deficiency syndrome (CFDS) is defined as any neuropsychiatric or developmental disorder characterized by decreased CSF folate levels in the presence of normal folate status outside the nervous system. The specific clinical profile appears to be largely determined by the presence or absence of intrauterine folate deficiency as well as postnatal age at which cerebral folate deficiency occurs. The primary cause of CFDS is identified as the presence of serum folate receptor-alpha (FRα) autoantibodies impairing folate transport across the choroid plexus to the brain whereas, in a minority of cases, mitochondrial disorders, inborn errors of metabolism and loss of function mutations of the FRα (FOLR1) gene are identified. Early recognition and diagnosis of CFDS and prompt intervention is important to improve prognosis with successful outcomes. In this article we focus on FRα autoimmunity and its different age-dependent clinical syndromes, the diagnostic criteria, and treatments to be considered, including prevention strategies in this at-risk population.

Endocrine Manifestations and New Developments in Mitochondrial Disease

Mitochondrial diseases are a group of common inherited diseases causing disruption of oxidative phosphorylation. Some patients with mitochondrial disease have endocrine manifestations, with diabetes mellitus being predominant but also include hypogonadism, hypoadrenalism, and hypoparathyroidism. There have been major developments in mitochondrial disease over the past decade that have major implications for all patients. The collection of large cohorts of patients has better defined the phenotype of mitochondrial diseases and the majority of patients with endocrine abnormalities have involvement of several other systems. This means that patients with mitochondrial disease and endocrine manifestations need specialist follow-up because some of the other manifestations, such as stroke-like episodes and cardiomyopathy, are potentially life threatening. Also, the development and follow-up of large cohorts of patients means that there are clinical guidelines for the management of patients with mitochondrial disease. There is also considerable research activity to identify novel therapies for the treatment of mitochondrial disease. The revolution in genetics, with the introduction of next-generation sequencing, has made genetic testing more available and establishing a precise genetic diagnosis is important because it will affect the risk for involvement for different organ systems. Establishing a genetic diagnosis is also crucial because important reproductive options have been developed that will prevent the transmission of mitochondrial disease because of mitochondrial DNA variants to the next generation.

Cerebral Folate Deficiency, Folate Receptor Alpha Autoantibodies and Leucovorin (Folinic Acid) Treatment in Autism Spectrum Disorders: A Systematic Review and Meta-Analysis

The cerebral folate receptor alpha (FRα) transports 5-methyltetrahydrofolate (5-MTHF) into the brain; low 5-MTHF in the brain causes cerebral folate deficiency (CFD). CFD has been associated with autism spectrum disorders (ASD) and is treated with d,l-leucovorin (folinic acid). One cause of CFD is an autoantibody that interferes with the function of the FRα. FRα autoantibodies (FRAAs) have been reported in ASD. A systematic review was performed to identify studies reporting FRAAs in association with ASD, or the use of d,l-leucovorin in the treatment of ASD. A meta-analysis examined the prevalence of FRAAs in ASD. The pooled prevalence of ASD in individuals with CFD was 44%, while the pooled prevalence of CFD in ASD was 38% (with a significant variation across studies due to heterogeneity). The etiology of CFD in ASD was attributed to FRAAs in 83% of the cases (with consistency across studies) and mitochondrial dysfunction in 43%. A significant inverse correlation was found between higher FRAA serum titers and lower 5-MTHF CSF concentrations in two studies. The prevalence of FRAA in ASD was 71% without significant variation across studies. Children with ASD were 19.03-fold more likely to be positive for a FRAA compared to typically developing children without an ASD sibling. For individuals with ASD and CFD, meta-analysis also found improvements with d,l-leucovorin in overall ASD symptoms (67%), irritability (58%), ataxia (88%), pyramidal signs (76%), movement disorders (47%), and epilepsy (75%). Twenty-one studies (including four placebo-controlled and three prospective, controlled) treated individuals with ASD using d,l-leucovorin. d,l-Leucovorin was found to significantly improve communication with medium-to-large effect sizes and have a positive effect on core ASD symptoms and associated behaviors (attention and stereotypy) in individual studies with large effect sizes. Significant adverse effects across studies were generally mild but the most common were aggression (9.5%), excitement or agitation (11.7%), headache (4.9%), insomnia (8.5%), and increased tantrums (6.2%). Taken together, d,l-leucovorin is associated with improvements in core and associated symptoms of ASD and appears safe and generally well-tolerated, with the strongest evidence coming from the blinded, placebo-controlled studies. Further studies would be helpful to confirm and expand on these findings.

The role of nutrition in space exploration: Implications for sensorimotor, cognition, behavior and the cerebral changes due to the exposure to radiation, altered gravity, and isolation/confinement hazards of spaceflight

Multi-year crewed space exploration missions are now on the horizon; therefore, it is important that we understand and mitigate the physiological effects of spaceflight. The spaceflight hazards-radiation, isolation, confinement, and altered gravity-have the potential to contribute to neuroinflammation and produce long-term cognitive and behavioral effects-while the fifth hazard, distance from earth, limits capabilities to mitigate these risks. Accumulated evidence suggests that nutrition has an important role in optimizing cognition and reducing the risk of neurodegenerative diseases caused by neuroinflammation. Here we review the nutritional perspective of how these spaceflight hazards affect the astronaut's brain, behavior, performance, and sensorimotor function. We also assess potential nutrient/nutritional countermeasures that could prevent or mitigate spaceflight risks and ensure that crewmembers remain healthy and perform well during their missions. Just as history has taught us the importance of nutrition in terrestrial exploration, we must understand the role of nutrition in the development and mitigation of spaceflight risks before humans can successfully explore beyond low-Earth orbit.

Current and Emerging Clinical Treatment in Mitochondrial Disease

Primary mitochondrial disease (PMD) is a group of complex genetic disorders that arise due to pathogenic variants in nuclear or mitochondrial genomes. Although PMD is one of the most prevalent inborn errors of metabolism, it often exhibits marked phenotypic variation and can therefore be difficult to recognise. Current treatment for PMD revolves around supportive and preventive approaches, with few disease-specific therapies available. However, over the last decade there has been considerable progress in our understanding of both the genetics and pathophysiology of PMD. This has resulted in the development of a plethora of new pharmacological and non-pharmacological therapies at varying stages of development. Many of these therapies are currently undergoing clinical trials. This review summarises the latest emerging therapies that may become mainstream treatment in the coming years. It is distinct from other recent reviews in the field by comprehensively addressing both pharmacological non-pharmacological therapy from both a bench and a bedside perspective. We highlight the current and developing therapeutic landscape in novel pharmacological treatment, dietary supplementation, exercise training, device use, mitochondrial donation, tissue replacement gene therapy, hypoxic therapy and mitochondrial base editing.

Mitochondrial medicine therapies: rationale, evidence, and dosing guidelines

PURPOSE OF REVIEW

Primary mitochondrial disease is a highly heterogeneous but collectively common inherited metabolic disorder, affecting at least one in 4300 individuals. Therapeutic management of mitochondrial disease typically involves empiric prescription of enzymatic cofactors, antioxidants, and amino acid and other nutrient supplements, based on biochemical reasoning, historical experience, and consensus expert opinion. As the field continues to rapidly advance, we review here the preclinical and clinical evidence, and specific dosing guidelines, for common mitochondrial medicine therapies to guide practitioners in their prescribing practices.

RECENT FINDINGS

Since publication of Mitochondrial Medicine Society guidelines for mitochondrial medicine therapies management in 2009, data has emerged to support consideration for using additional therapeutic agents and discontinuation of several previously used agents. Preclinical animal modeling data have indicated a lack of efficacy for vitamin C as an antioxidant for primary mitochondrial disease, but provided strong evidence for vitamin E and N-acetylcysteine. Clinical data have suggested L-carnitine may accelerate atherosclerotic disease. Long-term follow up on L-arginine use as prophylaxis against or acute treatment for metabolic strokes has provided more data supporting its clinical use in individuals with mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome and Leigh syndrome. Further, several precision therapies have been developed for specific molecular causes and/or shared clinical phenotypes of primary mitochondrial disease.

SUMMARY

We provide a comprehensive update on mitochondrial medicine therapies based on current evidence and our single-center clinical experience to support or refute their use, and provide detailed dosing guidelines, for the clinical management of mitochondrial disease. The overarching goal of empiric mitochondrial medicines is to utilize therapies with favorable benefit-to-risk profiles that may stabilize and enhance residual metabolic function to improve cellular resiliency and slow clinical disease progression and/or prevent acute decompensation.

The Phenotypic Spectrum of 47 Czech Patients with Single, Large-Scale Mitochondrial DNA Deletions

Background: In this retrospective study, we analysed clinical, biochemical and molecular genetic data of 47 Czech patients with Single, Large-Scale Mitochondrial DNA Deletions (SLSMD). Methods: The diagnosis was based on the long-range PCR (LX-PCR) screening of mtDNA isolated from muscle biopsy in 15 patients, and from the buccal swab, urinary epithelial cells and blood in 32 patients. Results: A total of 57% patients manifested before the age of 16. We did not find any significant difference between paediatric and adult manifestation in either the proportion of patients that would develop extraocular symptoms, or the timespan of its progression. The survival rate in patients with Pearson Syndrome reached 60%. Altogether, five patients manifested with atypical phenotype not fulfilling the latest criteria for SLSMD. No correlation was found between the disease severity and all heteroplasmy levels, lengths of the deletion and respiratory chain activities in muscle. Conclusions: Paediatric manifestation of Progressive External Ophthalmoplegia (PEO) is not associated with a higher risk of multisystemic involvement. Contrary to PEO and Kearns-Sayre Syndrome Spectrum, Pearson Syndrome still contributes to a significant childhood mortality. SLSMD should be considered even in cases with atypical presentation. To successfully identify carriers of SLSMD, a repeated combined analysis of buccal swab and urinary epithelial cells is needed.

Emerging Concepts in Nutrient Needs

Dietary reference intakes (DRIs) are quantitative, nutrient intake-based standards used for assessing the diets and specific nutrient intakes of healthy individuals and populations and for informing national nutrition policy and nutrition programs. Because nutrition needs vary by age, sex, and physiological state, DRIs are often specified for healthy subgroups within a population. Diet is known to be the leading modifiable risk factor for chronic disease, and the prevalence of chronic disease is growing in all populations globally and across all subgroups, but especially in older adults. It is known that nutrient needs can change in some chronic disease and other clinical states. Disease states and/or disease treatment can cause whole-body or tissue-specific nutrient depletion or excess, resulting in the need for altered nutrient intakes. In other cases, disease-related biochemical dysfunction can result in a requirement for a nonessential nutrient, rendering it as conditionally essential, or result in toxicity for a food component at levels usually tolerated by healthy people, as seen in inborn errors of metabolism. Here we summarize examples from a growing body of literature of disease-altering nutrient requirements, supporting the need to give more consideration to special nutrient requirements in disease states.

Mitochondrial disorders and the eye

Mitochondria are cellular organelles that play a key role in energy metabolism and oxidative phosphorylation. Malfunctioning of mitochondria has been implicated as the cause of many disorders with variable inheritance, heterogeneity of systems involved, and varied phenotype. Metabolically active tissues are more likely to be affected, causing an anatomic and physiologic disconnect in the treating physicians' mind between presentation and underlying pathophysiology. We shall focus on disorders of mitochondrial metabolism relevant to an ophthalmologist. These disorders can affect all parts of the visual pathway (crystalline lens, extraocular muscles, retina, optic nerve, and retrochiasm). After the introduction reviewing mitochondrial structure and function, each disorder is reviewed in detail, including approaches to its diagnosis and most current management guidelines.

Cerebral folate deficiency: Analytical tests and differential diagnosis

Cerebral folate deficiency is typically defined as a deficiency of the major folate species 5-methyltetrahydrofolate in the cerebrospinal fluid (CSF) in the presence of normal peripheral total folate levels. However, it should be noted that cerebral folate deficiency is also often used to describe conditions where CSF 5-MTHF is low, in the presence of low or undefined peripheral folate levels. Known defects of folate transport are deficiency of the proton coupled folate transporter, associated with systemic as well as cerebral folate deficiency, and deficiency of the folate receptor alpha, leading to an isolated cerebral folate deficiency associated with intractable seizures, developmental delay and/or regression, progressive ataxia and choreoathetoid movement disorders. Inborn errors of folate metabolism include deficiencies of the enzymes methylenetetrahydrofolate reductase, dihydrofolate reductase and 5,10-methenyltetrahydrofolate synthetase. Cerebral folate deficiency is potentially a treatable condition and so prompt recognition of these inborn errors and initiation of appropriate therapy is of paramount importance. Secondary cerebral folate deficiency may be observed in other inherited metabolic diseases, including disorders of the mitochondrial oxidative phosphorylation system, serine deficiency, and pyridoxine dependent epilepsy. Other secondary causes of cerebral folate deficiency include the effects of drugs, immune response activation, toxic insults and oxidative stress. This review describes the absorption, transport and metabolism of folate within the body; analytical methods to measure folate species in blood, plasma and CSF; inherited and acquired causes of cerebral folate deficiency; and possible treatment options in those patients found to have cerebral folate deficiency.

Targeted versus untargeted omics - the CAFSA story

BACKGROUND

In 2009, untargeted metabolomics led to the delineation of a new clinico-biological entity called cerebellar ataxia with elevated cerebrospinal free sialic acid, or CAFSA. In order to elucidate CAFSA, we applied sequentially targeted and untargeted omic approaches.

METHODS AND RESULTS

First, we studied five of the six CAFSA patients initially described. Besides increased CSF free sialic acid concentrations, three patients presented with markedly decreased 5-methyltetrahydrofolate (5-MTHF) CSF concentrations. Exome sequencing identified a homozygous POLG mutation in two affected sisters, but failed to identify a causative gene in the three sporadic patients with high sialic acid but low 5-MTHF. Using targeted mass spectrometry, we confirmed that free sialic acid was increased in the CSF of a third known POLG-mutated patient. We then pursued pathophysiological analyses of CAFSA using mass spectrometry-based metabolomics on CSF from two sporadic CAFSA patients as well as 95 patients with an unexplained encephalopathy and 39 controls. This led to the identification of a common metabotype between the two initial CAFSA patients and three additional patients, including one patient with Kearns-Sayre syndrome. Metabolites of the CSF metabotype were positioned in a reconstruction of the human metabolic network, which highlighted the proximity of the metabotype with acetyl-CoA and carnitine, two key metabolites regulating mitochondrial energy homeostasis.

CONCLUSION

Our genetic and metabolomics analyses suggest that CAFSA is a heterogeneous entity related to mitochondrial DNA alterations either through POLG mutations or a mechanism similar to what is observed in Kearns-Sayre syndrome.

Pediatric mitochondrial diseases and the heart

PURPOSE OF REVIEW

Mitochondrial disorders are an increasingly recognized cause of heart dysfunction, with the primary manifestations being cardiomyopathy and conduction defects. This review focuses on the complex genetics of mitochondrial disease and recently discovered conditions that affect mitochondrial function.

RECENT FINDINGS

Next-generation sequencing techniques, especially whole-exome sequencing, have led to the discovery of a number of conditions that cause mitochondrial dysfunction and subsequent cardiac abnormalities. Nuclear DNA defects are the main cause of mitochondrial disease in children, with disease pathogenesis being related to either abnormalities in specific mitochondrial electron transport chain subunits or in proteins related to subunit or mitochondrial DNA maintenance, mitochondrial protein translation, lipid bilayer structure, or other aspects of mitochondrial function.

SUMMARY

Currently, symptomatic therapy using standard medications targeting relief of complications is the primary approach to treatment. There are no US Food and Drug Administration-approved therapies for the specific treatment of mitochondrial disease. However, on the basis of recent advances in understanding of the pathophysiology of these complex disorders, various novel approaches are either in clinical trials or in development.

Dietary Supplement for Core Symptoms of Autism Spectrum Disorder: Where Are We Now and Where Should We Go?

Autism spectrum disorders (ASDs) are a class of severe and chronic conditions and core symptoms are deficits in social interaction, language communication impairments, and repetitive/stereotyped behavior. Given the limitations of available treatments and substantially increased prevalence of the disease, additional interventions are needed. Since the use of dietary supplements for ASD is of high prevalence, up-to-date information about those supplements are required for both parents and clinicians. Relevant articles were identified through a systematic search of PubMed, EMBASE, Cochrane library, and PsychINFO databases (through May 2017). Current best evidences of 22 randomized controlled trials on 8 different dietary supplements for core symptoms of ASD were reviewed. For each supplement, this report focuses on the definition and potential therapeutic mechanisms, the latest advances, and discussion of study limitations and future directions. Most studies were small and short term, and there is little evidence to support effectiveness of dietary supplements for children with ASD.

Novel genetic and neuropathological insights in neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP)

INTRODUCTION

Neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP) is caused by m.8993T>G/C mutations in the mitochondrial adenosine triphosphate synthase subunit 6 gene (MT-ATP6). Traditionally, heteroplasmy levels between 70% and 90% lead to NARP, and >90% result in Leigh syndrome.

METHODS

In this study we report a 30-year-old man with NARP and m.8993T>G in MT-ATP6.

RESULTS

Although the patient carried the mutation in homoplasmic state in blood with similarly high levels in urine (94%) and buccal swab (92%), he presented with NARP and not the expected, more severe Leigh phenotype. The mutation could not be detected in any of the 3 analyzed tissues of the mother, indicating a large genetic shift between mother and offspring. Nerve biopsy revealed peculiar endoneurial Schwann cell nuclear accumulations, clusters of concentrically arranged Schwann cells devoid of myelinated axons, and degenerated mitochondria.

CONCLUSIONS

We emphasize the phenotypic variability of the m.8993T>G MT-ATP6 mutation and the need for caution in predictive counseling in such patients. Muscle Nerve 54: 328-333, 2016.

Folate nutrition and blood-brain barrier dysfunction

Mammals require essential nutrients from dietary sources to support normal metabolic, physiological and neuronal functions, to prevent diseases of nutritional deficiency as well as to prevent chronic disease. Disease and/or its treatment can modify fundamental biological processes including cellular nutrient accretion, stability and function in cells. These effects can be isolated to a specific diseased organ in the absence of whole-body alterations in nutrient status or biochemistry. Loss of blood-brain barrier function, which occurs in in-born errors of metabolism and in chronic disease, can cause brain-specific folate deficiency and contribute to disease co-morbidity. The role of brain folate deficiency in neuropsychiatric disorders is reviewed, as well as emerging diagnostic and nutritional strategies to identify and address brain folate deficiency in blood-brain barrier dysfunction.

Neuromuscular Manifestations in Mitochondrial Diseases in Children

Mitochondrial diseases exhibit significant clinical and genetic heterogeneity. Mitochondria are highly dynamic organelles that are the major contributor of adenosine triphosphate, through oxidative phosphorylation. These disorders may be developed at any age, with isolated or multiple system involvement, and in any pattern of inheritance. Defects in the mitochondrial respiratory chain impair energy production and almost invariably involve skeletal muscle and peripheral nerves, causing exercise intolerance, cramps, recurrent myoglobinuria, or fixed weakness, which often affects extraocular muscles and results in droopy eyelids (ptosis), progressive external ophthalmoplegia, peripheral ataxia, and peripheral polyneuropathy. This review describes the main neuromuscular symptomatology through different syndromes reported in the literature and from our experience. We want to highlight the importance of searching for the "clue clinical signs" associated with inheritance pattern as key elements to guide the complex diagnosis process and genetic studies in mitochondrial diseases.

The homozygous R504C mutation in MTO1 gene is responsible for ONCE syndrome

We report clinical and biochemical finding from three unrelated patients presenting ONCE (Optic Neuropathy, Cardiomyopathy and Encephalopathy with lactic acidosis and combined oxidative phosphorylation deficiency) syndrome. Whole-exome sequencing (WES) of the three patients and the healthy sister of one of them was used to identify the carry gene. Clinical and biochemical findings were used to filter variants, and molecular, in silico and genetic studies were performed to characterize the candidate variants. Mitochondrial DNA (mtDNA) defects involving mutations, deletions or depletion were discarded, whereas WES uncovered a double homozygous mutation in the MTO1 gene (NM_001123226:c.1510C>T, p.R504C, and c.1669G>A, p.V557M) in two of the patients and the homozygous mutation p.R504C in the other. Therefore, our data confirm p.R504C as pathogenic mutation responsible of ONCE syndrome, and p.V557M as a rare polymorphic variant.

Pathophysiology of mitochondrial disease causing epilepsy and status epilepticus

Epilepsy is part of the clinical phenotype in nearly 40% of children with mitochondrial disease, yet the underlying molecular mechanisms remain poorly understood. Energy depletion has been postulated as the cause of mitochondrial epilepsy, but if this were the case, then 100% of patients with mitochondrial disease would be expected to present with seizures. This review explores other potential disease mechanisms underlying mitochondrial epilepsy, including oxidative stress, impaired calcium homeostasis, immune dysfunction, and deficiency of vitamins, cofactors, reducing equivalents, and other metabolites. Different mechanisms are likely to predominate in different mitochondrial disorders, since mitochondrial function varies between neurons and astrocytes, between different types of neurons, and in different brain regions. Systematic studies in cell and animal models of mitochondrial disease are needed in order to develop effective therapies for mitochondrial epilepsy. This article is part of a Special Issue entitled "Status Epilepticus".

Can folic acid have a role in mitochondrial disorders?

Cellular folate metabolism is highly compartmentalized, with mitochondria folate transport and metabolism being distinct from the well-known cytosolic folate metabolism. There is evidence supporting the association between low folate status and mitochondrial DNA (mtDNA) instability, and cerebral folate deficiency is relatively frequent in mitochondrial disorders. Furthermore, folinic acid supplementation has been reported to be beneficial not only in some patients with mitochondrial disease, but also in patients with relatively common diseases where folate deficiency might be an important pathophysiological factor. In this review, we focus on the evidence that supports the potential involvement of impaired folate metabolism in the pathophysiology of mitochondrial disorders.