Pathophysiology of mitochondrial disease causing epilepsy and status epilepticus

Liver transplantation for mitochondrial DNA depletion syndrome caused by MPV17 deficiency: a case report and literature review

Objective

To study the effectiveness of liver transplantation (LT) in treating mitochondrial DNA depletion syndrome (MDS) caused by the MPV17 gene variant.

Case presentation

A boy aged 2.8 years presented with edema of the lower limbs and abdomen, which persisted for over 10 days and was of unknown origin; this was accompanied by abnormal liver function, intractable hypoglycemia, and hyperlactatemia. During the second week of onset, he developed acute-on-chronic liver failure and was diagnosed with MDS due to homozygous variant c.293C>T in the MPV17 gene. Subsequently, he underwent LT from a cadaveric donor. At follow-up after 15 months, his liver function was found to be normal, without any symptoms. Additionally, a literature review was performed that included MDS patients with the MPV17 variant who underwent LT. The results demonstrated that the survival rates for MDS patients who underwent LT were 69.5%, 38.6%, 38.6%, and 38.6% at 1-year, 5-year, 10-year, and 20-year intervals, respectively. Sub-group analyses revealed the survival rate of MDS patients with isolated liver disease (83.33%, 5/6) was higher than that of hepatocerebral MDS patients (44.44%, 8/18). Fifteen variants were identified in the MPV17 gene, and patients with the c.293C>T (p.P98l) variant exhibited the highest survival rate.

Conclusion

Hepatocerebral MDS patients without neurological symptoms may benefit from LT.

Clinical and radiological description of 120 pediatric stroke-like episodes

BACKGROUND AND PURPOSE

Stroke-like episodes (SLEs) are defined as acute onset of neurological symptoms mimicking a stroke and radiological lesions non-congruent to vascular territory. We aimed to analyze the acute clinical and radiological features of SLEs to determine their pathophysiology.

METHODS

We performed a monocenter retrospective analysis of 120 SLEs in 60 children over a 20-year period. Inclusion criteria were compatible clinical symptoms and stroke-like lesions on brain magnetic resonance imaging (MRI; performed for all 120 events) with focal hyperintensity on diffusion-weighted imaging in a non-vascular territory.

RESULTS

Three groups were identified: children with mitochondrial diseases (n = 22) involving mitochondrial DNA mutations (55%) or nuclear DNA mutations (45%); those with other metabolic diseases or epilepsy disorders (n = 22); and those in whom no etiology was found despite extensive investigations (n = 16). Age at first SLE was younger in the group with metabolic or epilepsy disorders (18 months vs. 128 months; p < 0.0001) and an infectious trigger was more frequent (69% vs. 20%; p = 0.0001). Seizures occurred in 75% of episodes, revealing 50% episodes of SLEs and mainly leading to status epilepticus (90%). Of the 120 MRI scans confirming the diagnosis, 28 were performed within a short and strict 48-h period and were further analyzed to better understand the underlying mechanisms. The scans showed primary cortical hyperintensity (n = 28/28) with decreased apparent diffusion coefficient in 52% of cases. Systematic hyperperfusion was found on spin labeling sequences when available (n = 18/18).

CONCLUSION

Clinical and radiological results support the existence of a vicious circle based on two main mechanisms: energy deficit and neuronal hyperexcitability at the origin of SLE.

A case report: New-onset refractory status epilepticus in a patient with FASTKD2-related mitochondrial disease

Objectives

New-onset refractory status epilepticus (NORSE) is associated with high morbidity and mortality. Despite extensive work-up, the underlying etiology remains unknown in 50% of affected individuals. Mitochondrial disorders represent rare causes of NORSE. Biallelic variants in FASTKD2 were reported as a cause of infantile encephalomyopathy with refractory epilepsy.

Case description

In the study, we report a previously healthy 14-year-old with a new, homozygous FASTKD2 variant presenting with NORSE. Following a seizure-free period of 7 years, he experienced another super-refractory SE and subsequently developed drug-resistant focal epilepsy, mild myopathy, optic atrophy, and discrete psychomotor slowing. Structural MRI at the time of NORSE showed right temporo-parieto-occipital FLAIR hyperintensity and diffusion restriction, with extensive right hemispheric atrophy at the age of 22 years. Whole-exome sequencing revealed a novel homozygous loss of function variant [c.(1072C>T);(1072C>T)] [p.(Arg358Ter);(Arg358Ter)] in FASTKD2 (NM_001136193), resulting in a premature termination codon in the protein-coding region and loss of function of FASTKD2. Oxidative phosphorylation (OXPHOS) in muscle and skin fibroblasts was unremarkable.

Conclusion

This is the first case of a normally developed adolescent with a new homozygous loss of function variant in FASTKD2, manifesting with NORSE. The phenotypical spectrum of FASTKD2-related mitochondrial disease is heterogeneous, ranging from recurrent status epilepticus and refractory focal epilepsy in an adolescent with normal cognitive development to severe forms of infantile mitochondrial encephalopathy. Although mitochondrial diseases are rare causes of NORSE, clinical features such as young age at onset and multi-system involvement should trigger genetic testing. Early diagnosis is essential for counseling and treatment considerations.

Gene variations of glutamate metabolism pathway and epilepsy

Background

Epilepsy is a paroxysmal disorder of the brain, caused by an imbalance of neuronal excitation and inhibition. Glutamate is the most important excitatory neurotransmitter in the brain and plays an important role in epileptogenesis. Mutations in genes at any step/component of the glutamate metabolic pathway may lead to the development of epilepsy or epileptic encephalopathy.

Methods

Clinical history of 3 epilepsy patients with genetic variations of the glutamate metabolism pathway was collected. Electroencephalogram recording and magnetic resonance imaging  were performed in each patient. We also reviewed recent literature for a variety of the genetic variations involved in epilepsy.

Results

Case 1 was a SLC1A2 mutation-carrier diagnosed with developmental and epileptic encephalopathy (DEE) 41, whose seizures decreased after start of the ketogenic diet. Case 2 carried a GRIN2A gene mutation and was seizure-free for three years after taking levetiracetam and vitamin B6. Case 3 was a GRIN2B mutation-carrier  diagnosed with DEE 27, who seizures diminished after taking oxcarbazepine.

Conclusions

Preclinical and clinical evidence supports the therapeutic potential of glutamatergic signaling-targeting treatments for epilepsy. More studies are needed to discover novel DEE-related genetic mutations in the glutamate metabolic pathway.

Rodent Models of Audiogenic Epilepsy: Genetic Aspects, Advantages, Current Problems and Perspectives

Animal models of epilepsy are of great importance in epileptology. They are used to study the mechanisms of epileptogenesis, and search for new genes and regulatory pathways involved in the development of epilepsy as well as screening new antiepileptic drugs. Today, many methods of modeling epilepsy in animals are used, including electroconvulsive, pharmacological in intact animals, and genetic, with the predisposition for spontaneous or refractory epileptic seizures. Due to the simplicity of manipulation and universality, genetic models of audiogenic epilepsy in rodents stand out among this diversity. We tried to combine data on the genetics of audiogenic epilepsy in rodents, the relevance of various models of audiogenic epilepsy to certain epileptic syndromes in humans, and the advantages of using of rodent strains predisposed to audiogenic epilepsy in current epileptology.

Delay in diagnosing a patient with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome who presented with status epilepticus and lactic acidosis: a case report

Background

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episode syndrome is a rare mitochondrial genetic disorder that can present with a variety of clinical manifestations, including stroke, hearing loss, seizures, and lactic acidosis. The most common genetic mutation associated with this syndrome is M.3243A>G. The main underlying mechanism of the disease relates to protein synthesis, energy depletion, and nitric oxide deficiency. Controlling disease complications and improving patient quality of life are the primary aims of treatment options.

Case presentation

A 28-year-old Arabic female visited Al-Amiri Hospital in Kuwait. The patient was newly diagnosed with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episode syndrome following her admission as a case of status epilepticus requiring further investigation. The patient’s seizures were controlled, and she was evaluated to rule out the most serious complications by carrying out appropriate clinical, laboratory, and radiological imaging. The patient was discharged from the hospital after 2 weeks with a follow-up plan.

Conclusion

This case report emphasizes the importance of considering mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episode syndrome as a potential cause of status epilepticus with lactic acidosis in a young female patient with a past history of stroke-like episodes. It also stresses the most important workup to rule out every possible life-threatening complication to improve patients’ lives.

Decrease of MtDNA copy number affects mitochondrial function and involves in the pathological consequences of ischaemic stroke

The mtDNA copy number can affect the function of mitochondria and play an important role in the development of diseases. However, there are few studies on the mechanism of mtDNA copy number variation and its effects in IS. The specific mechanism of mtDNA copy number variation is still unclear. In this study, mtDNA copy number of 101 IS patients and 101 normal controls were detected by qRT‐PCR, the effect of D‐loop variation on mtDNA copy number of IS patients was explored. Then, a TFAM gene KD‐OE PC12 cell model was constructed to explore the effect of mtDNA copy number variation on mitochondrial function. The results showed that the mtDNA copy number level of the IS group was significantly lower than that of the normal control group (p < 0.05). The relative expression of TFAM gene mRNA in the cells of the OGD/R treatment group was significantly lower than that of the control group (p < 0.05). In addition, after TFAM gene knockdown and over‐expression plasmids were transfected into HEK 293T cells, mtDNA copy number and ATP production level of Sh‐TFAM transfection group was significantly decreased (p < 0.05), while mtDNA copy number and ATP production level of OE‐TFAM transfected group were significantly higher than that of blank control group and OE‐ctrl negative control group (p < 0.01). Our study demonstrated that mitochondrial D‐loop mutation and TFAM gene dysfunction can cause the decrease of mtDNA copy number, thus affecting the mitochondrial metabolism and function of nerve cells, participating in the pathological damage mechanism of IS.

Management of Status Epilepticus, Refractory Status Epilepticus, and Super-refractory Status Epilepticus

PURPOSE OF REVIEW

Status epilepticus is a serious condition caused by disorders and diseases that affect the central nervous system. In status epilepticus, hypersynchronous epileptic activity lasts longer than the usual duration of isolated self-limited seizures (time t1), which causes neuronal damage or alteration of neuronal networks at a certain time point (time t2), depending on the type of and duration of status epilepticus. The successful management of status epilepticus includes both the early termination of seizure activity and the earliest possible identification of a causative etiology, which may require independent acute treatment. In nonconvulsive status epilepticus, patients present only with subtle clinical signs or even without any visible clinical manifestations. In these cases, EEG allows for the assessment of cerebral function and identification of patterns in need of urgent treatment.

RECENT FINDINGS

In 2015, the International League Against Epilepsy proposed a new definition and classification of status epilepticus, encompassing four axes: symptomatology, etiology, EEG, and age. Various validation studies determined the practical usefulness of EEG criteria to identify nonconvulsive status epilepticus. The American Clinical Neurophysiology Society has incorporated these criteria into their most recent critical care EEG terminology in 2021. Etiology, age, symptomatology, and the metabolic demand associated with an increasing duration of status epilepticus are the most important determinants of prognosis. The consequences of status epilepticus can be visualized in vivo by MRI studies.

SUMMARY

The current knowledge about status epilepticus allows for a more reliable diagnosis, earlier treatment, and improved cerebral imaging of its consequences. Outcome prediction is a soft tool for estimating the need for intensive care resources.

Super-refractory status epilepticus (SRSE): A case series of 22 pediatric patients

BACKGROUND

Super-refractory Status Epilepticus (SRSE) is a rare condition in which SE persists or recurs ≥24 h after the onset of anesthesia. Although its characteristics are well defined in adulthood, only few studies on children are available.

METHODS

we retrospectively analyzed the population of patients with SRSE aged <18 years treated in the Pediatric Intensive Care Unit of the Bambino Gesù Pediatric Hospital. We assessed clinical history, etiology, neuroimaging, electro-clinical features of SRSE, treatments and neurological status after SRSE cessation.

RESULTS

We identified 22 children with median age at SRSE onset of 3.1 years (IQR 1.3-7.3) and SRSE duration of 22.0 days (IQR 11.2-30.5) Before SRSE, 17 patients (77.3%) had an abnormal neurological examination, 18 (81.8%) had a diagnosis of epilepsy, 8 of which already presented an episode of SE. Only 4 patients (18.2%) had New Onset SRSE. Eleven patients had a progressive etiology (PE), 9 had a remote etiology (RE) and 2 patients had an acute etiology (AE). Amongst PE the most frequent etiologies were mitochondrial diseases, while among RE they were Developmental Epileptic Encephalopathies of genetic origin. Time to SRSE cessation was significantly longer in PE (p = 0.04). After SRSE, 8 patients, (7 with PE) showed a significant worsening of neurological status. In this group, mean time at SE cessation was significantly longer (p = 0.05).

CONCLUSIONS

pediatric SRSE is mostly associated with progressive diseases and remote etiologies. Underlying etiology seems to impact both on SRSE duration and subsequent neurological evolution, however more studies are needed to confirm these findings.

IDH-mutated gliomas promote epileptogenesis through d-2-hydroxyglutarate-dependent mTOR hyperactivation

BACKGROUND

Uncontrolled seizures in patients with gliomas have a significant impact on quality of life and morbidity, yet the mechanisms through which these tumors cause seizures remain unknown. Here, we hypothesize that the active metabolite d-2-hydroxyglutarate (d-2-HG) produced by the IDH-mutant enzyme leads to metabolic disruptions in surrounding cortical neurons that consequently promote seizures.

METHODS

We use a complementary study of in vitro neuron-glial cultures and electrographically sorted human cortical tissue from patients with IDH-mutant gliomas to test this hypothesis. We utilize micro-electrode arrays for in vitro electrophysiological studies in combination with pharmacological manipulations and biochemical studies to better elucidate the impact of d-2-HG on cortical metabolism and neuronal spiking activity.

RESULTS

We demonstrate that d-2-HG leads to increased neuronal spiking activity and promotes a distinct metabolic profile in surrounding neurons, evidenced by distinct metabolomic shifts and increased LDHA expression, as well as upregulation of mTOR signaling. The increases in neuronal activity are induced by mTOR activation and reversed with mTOR inhibition.

CONCLUSION

Together, our data suggest that metabolic disruptions in the surrounding cortex due to d-2-HG may be a driving event for epileptogenesis in patients with IDH-mutant gliomas.

Linsitinib (OSI-906) modulates brain energy metabolism and seizure activity in the lithium-pilocarpine rat model

Background

Epileptic seizure is a process of energy accumulation, bursting, and depletion accompanied by the production, spread, and termination of epileptic discharges. The energy required for a seizure is mainly provided through mitochondrial production of ATP. Mitochondrial diseases often lead to epileptic seizures, and energy depletion caused by seizures can lead to mitochondrial dysfunction. The energy metabolism has become a key target for treatment of epileptic diseases.

Method

The effect of OSI-906, an insulin receptor (IR)/ insulin-like growth factor 1 receptor (IGF-1R) inhibitor, on behaviors and electroencephalographic activity in the lithium-pilocarpine rats were tested. 18F-FDG positron emission tomography (PET)/ computed tomography (CT) was performed to detect the relative whole-brain glucose uptake values. Electron microscopy was performed to observe the ultrastructure of neuronal and mitochondrial damage. The changes in blood glucose at different time points before and after the intervention were tested and the effects of OSI-906 on IR/IGF-1R and downstream Akt signaling in the context of seizures were evaluated.

Results

The OSI-906 treatment applied 3 days before the pilocarpine-induced seizures significantly reduced the seizure severity, prolonged the seizure latency and decreased the EEG energy density. MicroPET/CT revealed that 50 mg/kg of OSI-906 inhibited the 18F-FDG glucose uptake after epileptic seizures, suggesting that OSI-906, through inhibiting IR/IGF-1R and the downstream AKT signaling, may regulate the excessive energy consumption of the epileptic brain. The OSI-906 treatment also reduced the mitochondrial damage caused by epileptic seizures.

Conclusion

The IR/IGF-1R inhibitor OSI-906 can significantly reduce the sensitivity and severity of pilocarpine-induced seizures by inhibiting the IR/IGF-1R and the downstream Akt signaling pathway.

Super-Refractory Status Epilepticus: Prognosis and Recent Advances in Management

Super-refractory status epilepticus (SRSE) is a life-threatening neurological emergency with high morbidity and mortality. It is defined as “status epilepticus (SE) that continues or recurs 24 hours or more after the onset of anesthesia, including those cases in which SE recurs on the reduction or withdrawal of anesthesia.” This condition is resistant to normal protocols used in the treatment of status epilepticus and exposes patients to increased risks of neuronal death, neuronal injury, and disruption of neuronal networks if not treated in a timely manner. It is mainly seen in patients with severe acute onset brain injury or presentation of new-onset refractory status epilepticus (NORSE). The mortality, neurological deficits, and functional impairments are significant depending on the duration of status epilepticus and the resultant brain damage. Research is underway to find the cure for this devastating neurological condition. In this review, we will discuss the wide range of therapies used in the management of SRSE, provide suggestions regarding its treatment, and comment on future directions. The therapies evaluated include traditional and alternative anesthetic agents with antiepileptic agents. The other emerging therapies include hypothermia, steroids, immunosuppressive agents, electrical and magnetic stimulation therapies, emergent respective epilepsy surgery, the ketogenic diet, pyridoxine infusion, cerebrospinal fluid drainage, and magnesium infusion. To date, there is a lack of robust published data regarding the safety and effectiveness of various therapies, and there continues to be a need for large randomized multicenter trials comparing newer therapies to treat this refractory condition.

Epilepsy in Mitochondrial Diseases-Current State of Knowledge on Aetiology and Treatment

Mitochondrial diseases are a heterogeneous group of diseases resulting from energy deficit and reduced adenosine triphosphate (ATP) production due to impaired oxidative phosphorylation. The manifestation of mitochondrial disease is usually multi-organ. Epilepsy is one of the most common manifestations of diseases resulting from mitochondrial dysfunction, especially in children. The onset of epilepsy is associated with poor prognosis, while its treatment is very challenging, which further adversely affects the course of these disorders. Fortunately, our knowledge of mitochondrial diseases is still growing, which gives hope for patients to improve their condition in the future. The paper presents the pathophysiology, clinical picture and treatment options for epilepsy in patients with mitochondrial disease.

Therapy Prospects for Mitochondrial DNA Maintenance Disorders

Mitochondrial DNA depletion and multiple deletions syndromes (MDDS) constitute a group of mitochondrial diseases defined by dysfunctional mitochondrial DNA (mtDNA) replication and maintenance. As is the case for many other mitochondrial diseases, the options for the treatment of these disorders are rather limited today. Some aggressive treatments such as liver transplantation or allogeneic stem cell transplantation are among the few available options for patients with some forms of MDDS. However, in recent years, significant advances in our knowledge of the biochemical pathomechanisms accounting for dysfunctional mtDNA replication have been achieved, which has opened new prospects for the treatment of these often fatal diseases. Current strategies under investigation to treat MDDS range from small molecule substrate enhancement approaches to more complex treatments, such as lentiviral or adenoassociated vector-mediated gene therapy. Some of these experimental therapies have already reached the clinical phase with very promising results, however, they are hampered by the fact that these are all rare disorders and so the patient recruitment potential for clinical trials is very limited.

Mitochondrial dynamics in health and disease

In animals, mitochondria are mainly organised into an interconnected tubular network extending across the cell along a cytoskeletal scaffold. Mitochondrial fission and fusion, as well as distribution along cytoskeletal tracks, are counterbalancing mechanisms acting in concert to maintain a mitochondrial network tuned to cellular function. Balanced mitochondrial dynamics permits quality control of the network including biogenesis and turnover, and distribution of mitochondrial DNA, and is linked to metabolic status. Cellular and organismal health relies on a delicate balance between fission and fusion, and large rearrangements in the mitochondrial network can be seen in response to cellular insults and disease. Indeed, dysfunction in the major components of the fission and fusion machineries including dynamin-related protein 1 (DRP1), mitofusins 1 and 2 (MFN1, MFN2) and optic atrophy protein 1 (OPA1) and ensuing imbalance of mitochondrial dynamics can lead to neurodegenerative disease. Altered mitochondrial dynamics is also seen in more common diseases. In this review, the machinery involved in mitochondrial dynamics and their dysfunction in disease will be discussed.

The Dichotomous Role of Inflammation in the CNS: A Mitochondrial Point of View

Innate immune response is one of our primary defenses against pathogens infection, although, if dysregulated, it represents the leading cause of chronic tissue inflammation. This dualism is even more present in the central nervous system, where neuroinflammation is both important for the activation of reparatory mechanisms and, at the same time, leads to the release of detrimental factors that induce neurons loss. Key players in modulating the neuroinflammatory response are mitochondria. Indeed, they are responsible for a variety of cell mechanisms that control tissue homeostasis, such as autophagy, apoptosis, energy production, and also inflammation. Accordingly, it is widely recognized that mitochondria exert a pivotal role in the development of neurodegenerative diseases, such as multiple sclerosis, Parkinson's and Alzheimer's diseases, as well as in acute brain damage, such in ischemic stroke and epileptic seizures. In this review, we will describe the role of mitochondria molecular signaling in regulating neuroinflammation in central nervous system (CNS) diseases, by focusing on pattern recognition receptors (PRRs) signaling, reactive oxygen species (ROS) production, and mitophagy, giving a hint on the possible therapeutic approaches targeting mitochondrial pathways involved in inflammation.

Mechanism of Action of Ketogenic Diet Treatment: Impact of Decanoic Acid and Beta-Hydroxybutyrate on Sirtuins and Energy Metabolism in Hippocampal Murine Neurons

The ketogenic diet (KD), a high-lipid and low-carbohydrate diet, has been used in the treatment of epilepsy, neurodegenerative disorders, inborn errors of metabolism and cancer; however, the exact mechanism/s of its therapeutic effect is not completely known. We hypothesized that sirtuins (SIRT)—a group of seven NAD-dependent enzymes and important regulators of energy metabolism may be altered under KD treatment. HT22 hippocampal murine neurons were incubated with two important KD metabolites–beta-hydroxybutyrate (BHB) (the predominant ketone body) and decanoic acid (C10), both accumulating under KD. Enzyme activity, protein, and gene expressions of SIRT 1-4, enzyme capacities of the mitochondrial respiratory chain complexes (MRC), citrate synthase (CS) and gene expression of monocarboxylate transporters were measured in control (untreated) and KD-treated cells. Incubation with both–BHB and C10 resulted in significant elevation of SIRT1 enzyme activity and an overall upregulation of the MRC. C10 incubation showed prominent increases in maximal activities of complexes I + III and complex IV of the MRC and ratios of their activities to that of CS, pointing towards a more efficient functioning of the mitochondria in C10-treated cells.

The Study of Genetic Susceptibility and Mitochondrial Dysfunction in Mesial Temporal Lobe Epilepsy

The aim of this study is to investigate the mitochondrial dysfunction and pathogenic role of the mitochondrial genome in the progression of mesial temporal lobe epilepsy (MTLE) in vivo and in vitro. Mitochondrial DNA (mtDNA) and nuclear DNA were detected in the hippocampal samples and peripheral blood of patients with MTLE. Mitochondrial functions were detected in vivo and in vitro. In 20 patients with MTLE, mtDNA mutations involving single or multiple deletions in the hippocampus were found in 5 patients but were not detected in the peripheral blood. Two patients carried pathogenic mutations of RELN, both in the hippocampus and blood. A pathogenic mutation of DNA2 was found in the hippocampus of the 2 patients with multiple deletions but not in the blood samples. The mtDNA copy numbers showed dynamic changes in the MTLE models. In MTLE patients, low metabolism in mesial temporal lobe and hippocampus was observed by using PET-CT. Under electron microscope, the mitochondrial cristae were disordered, the density of mitochondrial matrix decreased and even vacuolated in the hippocampus neurons. In the MTLE rat models, there were dynamic changes in mitochondrial morphology; the ATP production rate decreased in the acute phase, the latent phase, and the chronic phase. Mitochondrial enzyme complex I activity decreased in both acute and chronic phases, and there was no significant difference in latent period. Decreased mitochondrial membrane potential and calcium homeostasis were detected in the epileptic cell models. We first identified somatic mutations in mtDNA in MTLE patients and comprehensively evaluated mitochondrial dysfunction in the pathogenesis of MTLE in vivo and in vitro. This evidence supports the environmental and modifying genetic interactions that contribute to the development of MTLE.

Developmental brain abnormalities and acute encephalopathy in a patient with myopathy with extrapyramidal signs secondary to pathogenic variants in MICU1

Mitochondria play a variety of roles in the cell, far beyond their widely recognized role in ATP generation. One such role is the regulation and sequestration of calcium, which is done with the help of the mitochondrial calcium uniporter (MCU) and its regulators, MICU1 and MICU2. Genetic variations in MICU1 and MICU2 have been reported to cause myopathy, developmental disability and neurological symptoms typical of mitochondrial disorders. The symptoms of MICU1/2 deficiency have generally been attributed to calcium regulation in the metabolic and biochemical roles of mitochondria. Here, we report a female child with heterozygous MICU1 variants and multiple congenital brain malformations on MRI. Specifically, she shows anterior perisylvian polymicrogyria, dysmorphic basal ganglia, and cerebellar dysplasia in addition to white matter abnormalities. These novel findings suggest that MICU1 is necessary for proper neurodevelopment through a variety of potential mechanisms, including calcium-mediated regulation of the neuronal cytoskeleton, Miro1-MCU complex-mediated mitochondrial movement, or enhancing ATP production. This case provides new insight into the molecular pathogenesis of MCU dysfunction and may represent a novel diagnostic feature of calcium-based mitochondrial disease.

Advances in the treatment of mitochondrial epilepsies

Epilepsy is frequently a severe and sinister symptom in primary mitochondrial diseases, a group of more than 350 different genetic disorders characterized by mitochondrial dysfunction and extreme clinical and biochemical heterogeneity. Mitochondrial epilepsy is notoriously difficult to manage, principally because the vast majority of primary mitochondrial diseases currently lack effective therapies. Treating the underlying mitochondrial disorder is likely to be a more effective strategy than using traditional antiepileptic drugs. This review, initially presented at the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures at the Francis Crick Institute in London, summarizes the currently available and emerging therapies for mitochondrial epilepsy. Potentially treatable mitochondrial diseases include disorders of coenzyme Q₁₀ biosynthesis and a group of mitochondrial respiratory chain complex I subunit and assembly factor defects that respond to riboflavin (vitamin B2). Approaches that have been adopted in actively recruiting clinical trials include redox modulation, harnessing mitochondrial biogenesis, using rapamycin to target mitophagy, nucleoside supplementation, and gene and cell therapies. Most of the clinical trials are at an early stage (Phase 1 or 2) and none of the currently active trials is specifically targeting mitochondrial epilepsy. This article is part of the Special Issue "Proceedings of the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures".

Epileptic phenotypes in children with early-onset mitochondrial diseases

OBJECTIVES

To determine the prevalence of epilepsy in children with early-onset mitochondrial diseases (MDs) and to evaluate the epileptic phenotypes and associated features.

MATERIALS AND METHODS

Children affected by MD with onset during the first year of life were enrolled. Patients were classified according to their mitochondrial phenotype, and all findings in patients with epilepsy versus patients without were compared. The epileptic features were analyzed.

RESULTS

The series includes 129 patients (70 females) with median age at disease onset of 3 months. The median time of follow-up was 5 years. Non-syndromic mitochondrial encephalopathy and pyruvate dehydrogenase complex deficiency were the main mitochondrial diseases associated with epilepsy (P < 0.05). Seizures occurred in 48%, and the presence of epilepsy was significantly associated with earlier age at disease onset, presence of perinatal manifestations, and early detection of developmental delay and regression (P < 0.001). Epileptic encephalopathy (EE) with spasms and EE with prominent focal seizures were the most detected epileptic syndromes (37% and 27.4%). Several seizure types were recorded in 53.2%, with the unusual association of generalized and focal epileptic pattern. Disabling epilepsy was detected in 63% and was associated with early seizure onset, presence of several seizure types, epileptic syndrome featuring EE, and the recurrence of episodes of status epilepticus and epilepsia partialis continua (P < 0.05).

CONCLUSIONS

Epilepsy in children with early-onset MD may be a presenting or a prominent symptom in a multisystemic clinical presentation. Epilepsy-related factors could determine a worst seizure outcome, leading to a more severe burned of the disease.

Defined neuronal populations drive fatal phenotype in a mouse model of Leigh syndrome

Mitochondrial deficits in energy production cause untreatable and fatal pathologies known as mitochondrial disease (MD). Central nervous system affectation is critical in Leigh Syndrome (LS), a common MD presentation, leading to motor and respiratory deficits, seizures and premature death. However, only specific neuronal populations are affected. Furthermore, their molecular identity and their contribution to the disease remains unknown. Here, using a mouse model of LS lacking the mitochondrial complex I subunit Ndufs4, we dissect the critical role of genetically-defined neuronal populations in LS progression. Ndufs4 inactivation in Vglut2-expressing glutamatergic neurons leads to decreased neuronal firing, brainstem inflammation, motor and respiratory deficits, and early death. In contrast, Ndufs4 deletion in GABAergic neurons causes basal ganglia inflammation without motor or respiratory involvement, but accompanied by hypothermia and severe epileptic seizures preceding death. These results provide novel insight in the cell type-specific contribution to the pathology, dissecting the underlying cellular mechanisms of MD.

Identification of a Loss-of-Function Mutation in the Context of Glutaminase Deficiency and Neonatal Epileptic Encephalopathy

Importance

The identification and understanding of the monogenic causes of neurodevelopmental disorders are of high importance for personalized treatment and genetic counseling.

Objective

To identify and characterize novel genes for a specific neurodevelopmental disorder characterized by refractory seizures, respiratory failure, brain abnormalities, and death in the neonatal period; describe the outcome of glutaminase deficiency in humans; and understand the underlying pathological mechanisms.

Design, Setting, and Participants

We performed exome sequencing of cases of neurodevelopmental disorders without a clear genetic diagnosis, followed by genetic and bioinformatic evaluation of candidate variants and genes. Establishing pathogenicity of the variants was achieved by measuring metabolites in dried blood spots by a hydrophilic interaction liquid chromatography method coupled with tandem mass spectrometry. The participants are 2 families with a total of 4 children who each had lethal, therapy-refractory early neonatal seizures with status epilepticus and suppression bursts, respiratory insufficiency, simplified gyral structures, diffuse volume loss of the brain, and cerebral edema. Data analysis occurred from October 2017 to June 2018.

Main Outcomes and Measures

Early neonatal epileptic encephalopathy with glutaminase deficiency and lethal outcome.

Results

A total of 4 infants from 2 unrelated families, each of whom died less than 40 days after birth, were included. We identified a homozygous frameshift variant p.(Asp232Glufs*2) in GLS in the first family, as well as compound heterozygous variants p.(Gln81*) and p.(Arg272Lys) in GLS in the second family. The GLS gene encodes glutaminase (Enzyme Commission 3.5.1.2), which plays a major role in the conversion of glutamine into glutamate, the main excitatory neurotransmitter of the central nervous system. All 3 variants probably lead to a loss of function and thus glutaminase deficiency. Indeed, glutamine was increased in affected children (available z scores, 3.2 and 11.7). We theorize that the potential reduction of glutamate and the excess of glutamine were a probable cause of the described physiological and structural abnormalities of the central nervous system.

Conclusions and Relevance

We identified a novel autosomal recessive neurometabolic disorder of loss of function of glutaminase that leads to lethal early neonatal encephalopathy. This inborn error of metabolism underlines the importance of GLS for appropriate glutamine homeostasis and respiratory regulation, signal transduction, and survival.

Synaptic energy metabolism and neuronal excitability, in sickness and health

Most of the energy produced in the brain is dedicated to supporting synaptic transmission. Glucose is the main fuel, providing energy and carbon skeletons to the cells that execute and support synaptic function: neurons and astrocytes, respectively. It is unclear, however, how glucose is provided to and used by these cells under different levels of synaptic activity. It is even more unclear how diseases that impair glucose uptake and oxidation in the brain alter metabolism in neurons and astrocytes, disrupt synaptic activity, and cause neurological dysfunction, of which seizures are one of the most common clinical manifestations. Poor mechanistic understanding of diseases involving synaptic energy metabolism has prevented the expansion of therapeutic options, which, in most cases, are limited to symptomatic treatments. To shed light on the intersections between metabolism, synaptic transmission, and neuronal excitability, we briefly review current knowledge of compartmentalized metabolism in neurons and astrocytes, the biochemical pathways that fuel synaptic transmission at resting and active states, and the mechanisms by which disorders of brain glucose metabolism disrupt neuronal excitability and synaptic function and cause neurological disease in the form of epilepsy.

Systems Biology Approaches Toward Understanding Primary Mitochondrial Diseases

Primary mitochondrial diseases form one of the most common and severe groups of genetic disease, with a birth prevalence of at least 1 in 5000. These disorders are multi-genic and multi-phenotypic (even within the same gene defect) and span the entire age range from prenatal to late adult onset. Mitochondrial disease typically affects one or multiple high-energy demanding organs, and is frequently fatal in early life. Unfortunately, to date there are no known curative therapies, mostly owing to the rarity and heterogeneity of individual mitochondrial diseases, leading to diagnostic odysseys and difficulties in clinical trial design. This review aims to discuss recent advances and challenges of systems approaches for the study of primary mitochondrial diseases. Although there has been an explosion in the generation of omics data, few studies have progressed toward the integration of multiple levels of omics. It is evident that the integration of different types of data to create a more complete representation of biology remains challenging, perhaps due to the scarcity of available integrative tools and the complexity inherent in their use. In addition, "bottom-up" systems approaches have been adopted for use in the iterative cycle of systems biology: from data generation to model prediction and validation. Primary mitochondrial diseases, owing to their complex nature, will most likely benefit from a multidisciplinary approach encompassing clinical, molecular and computational studies integrated together by systems biology to elucidate underlying pathomechanisms for better diagnostics and therapeutic discovery. Just as next generation sequencing has rapidly increased diagnostic rates from approximately 5% up to 60% over two decades, more recent advancing technologies are encouraging; the generation of multi-omics, the integration of multiple types of data, and the ability to predict perturbations will, ultimately, be translated into improved patient care.

Spectrum of movement disorders and neurotransmitter abnormalities in paediatric POLG disease

OBJECTIVES

To describe the spectrum of movement disorders and cerebrospinal fluid (CSF) neurotransmitter profiles in paediatric patients with POLG disease.

METHODS

We identified children with genetically confirmed POLG disease, in whom CSF neurotransmitter analysis had been undertaken. Clinical data were collected retrospectively. CSF neurotransmitter levels were compared to both standardised age-related reference ranges and to non-POLG patients presenting with status epilepticus.

RESULTS

Forty-one patients with POLG disease were identified. Almost 50% of the patients had documented evidence of a movement disorder, including non-epileptic myoclonus, choreoathetosis and ataxia. CSF neurotransmitter analysis was undertaken in 15 cases and abnormalities were seen in the majority (87%) of cases tested. In many patients, distinctive patterns were evident, including raised neopterin, homovanillic acid and 5-hydroxyindoleacetic acid levels.

CONCLUSIONS

Children with POLG mutations can manifest with a wide spectrum of abnormal movements, which are often prominent features of the clinical syndrome. Underlying pathophysiology is probably multifactorial, and aberrant monoamine metabolism is likely to play a role.

Proenkephalin Derived Peptides Are Involved in the Modulation of Mitochondrial Respiratory Control During Epileptogenesis

Epilepsies are a group of common neurological diseases exerting a strong burden on patients and society, often lacking clear etiology and effective therapeutical strategies. Early intervention during the development of epilepsy (epileptogenesis) is of great medical interest, though hampered by poorly characterized epileptogenetic processes. Using the intrahippocampal kainic acid mouse model of temporal lobe epilepsy, we investigated the functional role of the endogenous opioid enkephalin during epileptogenesis. We addressed three sequential questions: (1) How does enkephalin affect seizure threshold and how is it regulated during epileptogenesis? (2) Does enkephalin influence detrimental effects during epileptogenesis? (3) How is enkephalin linked to mitochondrial function during epileptogenesis?. In contrast to other neuropeptides, the expression of enkephalin is not regulated in a seizure dependent manner. The pattern of regulation, and enkephalin's proconvulsive effects suggested it as a potential driving force in epileptogenesis. Surprisingly, enkephalin deficiency aggravated progressive granule cell dispersion in kainic acid induced epileptogenesis. Based on reported beneficial effects of enkephalin on mitochondrial function in hypoxic/ischemic states, we hypothesized that enkephalin may be involved in the adaptation of mitochondrial respiration during epileptogenesis. Using high-resolution respirometry, we observed dynamic improvement of hippocampal mitochondrial respiration after kainic acid-injections in wild-type, but not in enkephalin-deficient mice. Thus, wild-type mice displayed higher efficiency in the use of mitochondrial capacity as compared to enkephalin-deficient mice. Our data demonstrate a Janus-headed role of enkephalin in epileptogenesis. In naive mice, enkephalin facilitates seizures, but in subsequent stages it contributes to neuronal survival through improved mitochondrial respiration.

A Metabolic Paradigm for Epilepsy

There is a resurgence of interest in the role of metabolism in epilepsy. Long considered ancillary and acknowledged only in the context of clinical application of ketogenic diets, metabolic control of epilepsy is gaining momentum and mainstream interest among researchers. A metabolic paradigm for epilepsy rests upon known perturbations in three major interconnected metabolic nodes and therapeutic targets therefrom (i.e., glycolysis, mitochondria, and redox balance).

Mitochondrial diseases and status epilepticus

This narrative review focuses on the pathophysiology, diagnosis, and management of status epilepticus in the context of primary mitochondrial disease. Epilepsy is common in mitochondrial disease, reported in >20% of adult cases and 40%-60% of pediatric cohorts. Status epilepticus is less frequently reported and appears to be associated with particular subgroups of mitochondrial disorders, namely defects of the mitochondrial DNA and its maintenance, and disorders of mitochondrial translation and dynamics. Mechanisms underlying mitochondrial status epilepticus are incompletely understood, and may include bioenergetic failure, oxidative stress, immune dysfunction, and impaired mitochondrial dynamics. Treatments tried in mitochondrial status epilepticus include antiepileptic drugs, anesthetic agents, magnesium, high-dose steroids, immune globulins, vagus nerve stimulation, and surgical procedures, all with variable success. The outcome of mitochondrial status epilepticus is extremely poor, and effective therapeutic options have not been reported. Improved understanding of the mechanisms underpinning mitochondrial status epilepticus is needed in order to develop more effective treatments.

Recent perspectives of pediatric mitochondrial diseases

Mitochondrial disorders are amongst the most common groups of inborn errors of metabolism. They are caused by deficiencies in the final pathway of the cellular energy production, the mitochondrial respiratory chain. The disorders are clinically and genetically heterogeneous and the aetiology could be found in the mitochondrial, or in the nuclear genome. We searched important e-databases for the collection of latest literature on the mitochondrial disease especially in pediatric population. Most of the studies in the recent past have focused on the understanding of the clinical phenotypes and pathophysiological mechanisms. Leigh syndrome is a common severe, neurodegenerative disease of early childhood. A defect in the POLG gene is another common observation in most of the cases leading to Alpers syndrome. The review concludes that pediatric mitochondrial disorders are severe, progressive and usually multi-systemic. Further, whole genome sequencing is an excellent diagnostic option.

Anterior thalamic nuclei deep brain stimulation reduces disruption of the blood-brain barrier, albumin extravasation, inflammation and apoptosis in kainic acid-induced epileptic rats

Objective The therapeutic efficacy of anterior thalamic nuclei deep brain stimulation (ATN-DBS) against seizures has been largely accepted; however, the effects of ATN-DBS on disruption of the blood-brain barrier (BBB), albumin extravasation, inflammation and apoptosis still remain unclear. Methods Rats were distributed into four treatment groups: physiological saline (PS, N = 12), kainic acid (KA, N = 12), KA-sham-DBS (N = 12) and KA-DBS (N = 12). Seizures were monitored using video-electroencephalogram (EEG). One day after surgery, all rats were sacrificed. Then, samples were prepared for quantitative real-time PCR (qPCR), western blot, immunofluorescence (IF) staining, and transmission electron microscopy to evaluate the disruption of the BBB, albumin extravasation, inflammation, and apoptosis. Result Because of the KA injection, the disruption of the BBB, albumin extravasation, inflammation and apoptosis were more severe in the KA and the KA-sham-DBS groups compared to the PS group (all Ps < 0.05 or < 0.01). The ideal outcomes were observed in the KA-DBS group. ATN-DBS produced a 46.3% reduction in seizure frequency and alleviated the disruption of the BBB, albumin extravasation, inflammatory reaction and apoptosis in comparison to the KA-sham-DBS group (all Ps < 0.05 or < 0.01). Conclusion (1) Seizures can be reduced using ATN-DBS in the epileptogenic stage. (2) ATN-DBS can reduce the disruption of the BBB and albumin extravasation. (3) ATN-DBS has an anti-inflammatory effect in epileptic models.

Pannexin-1 channels in epilepsy

Pannexin-1 (Panx1) expression is raised in several animal seizure models and in resected human epileptic brain tissue, suggesting relevance to epilepsy. Multiple factors that are characteristic of seizures are thought to regulate Panx1 channel opening, including elevated levels of extracellular K⁺. Panx1, when open, 1) releases ATP, glutamate, and other metabolites into the extracellular medium, and 2) may depolarize the membrane due to a channel reversal potential around 0mV. Resultant ATP release from stimulated Panx1 can activate purinergic receptors, including P2X7 receptors. Glutamate and other signaling molecules released by Panx1 opening may have both excitatory and inhibitory actions on seizure generation. This review examines the critical and complex roles of Panx1 channels in epilepsy, which could provide a basis for future therapeutics.

Understanding the Epilepsy in POLG Related Disease

Epilepsy is common in polymerase gamma (POLG) related disease and is associated with high morbidity and mortality. Epileptiform discharges typically affect the occipital regions initially and focal seizures, commonly evolving to bilateral convulsive seizures which are the most common seizure types in both adults and children. Our work has shown that mtDNA depletion—i.e., the quantitative loss of mtDNA—in neurones is the earliest and most important factor of the subsequent development of cellular dysfunction. Loss of mtDNA leads to loss of mitochondrial respiratory chain (MRC) components that, in turn, progressively disables energy metabolism. This critically balanced neuronal energy metabolism leads to both a chronic and continuous attrition (i.e., neurodegeneration) and it leaves the neurone unable to cope with increased demand that can trigger a potentially catastrophic cycle that results in acute focal necrosis. We believe that it is the onset of epilepsy that triggers the cascade of damage. These events can be identified in the stepwise evolution that characterizes the clinical, Electroencephalography (EEG), neuro-imaging, and neuropathology findings. Early recognition with prompt and aggressive seizure management is vital and may play a role in modifying the epileptogenic process and improving survival.

Clinical and Molecular Characteristics in 100 Chinese Pediatric Patients with m.3243A>G Mutation in Mitochondrial DNA

Background:

Mitochondrial diseases are a group of energy metabolic disorders with multisystem involvements. Variable clinical features present a major challenge in pediatric diagnoses. We summarized the clinical spectrum of m.3243A>G mutation in Chinese pediatric patients, to define the common clinical manifestations and study the correlation between heteroplasmic degree of the mutation and clinical severity of the disease.

Methods:

Clinical data of one-hundred pediatric patients with symptomatic mitochondrial disease harboring m.3243A>G mutation from 2007 to 2013 were retrospectively reviewed. Detection of m.3243A>G mutation ratio was performed by polymerase chain reaction (PCR)-restriction fragment length polymorphism. Correlation between m.3243A>G mutation ratio and age was evaluated. The differences in clinical symptom frequency of patients with low, middle, and high levels of mutation ratio were analyzed by Chi-square test.

Results:

Sixty-six patients (66%) had suffered a delayed diagnosis for an average of 2 years. The most frequent symptoms were seizures (76%), short stature (73%), elevated plasma lactate (70%), abnormal magnetic resonance imaging/computed tomography (MRI/CT) changes (68%), vomiting (55%), decreased vision (52%), headache (50%), and muscle weakness (48%). The mutation ratio was correlated negatively with onset age (r = −0.470, P < 0.001). Myopathy was more frequent in patients with a high level of mutation ratio. However, patients with a low or middle level of m.3243A>G mutation ratio were more likely to suffer hearing loss, decreased vision, and gastrointestinal disturbance than patients with a high level of mutation ratio.

Conclusions:

Our study showed that half of Chinese pediatric patients with m.3243A>G mutation presented seizures, short stature, abnormal MRI/CT changes, elevated plasma lactate, vomiting, and headache. Pediatric patients with these recurrent symptoms should be considered for screening m.3243A>G mutation. Clinical manifestations and laboratory abnormalities should be carefully monitored in patients with this point mutation.

Epilepsy Characteristics and Clinical Outcome in Patients With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes (MELAS)

BACKGROUND

Epileptic seizures in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) are heterogeneous with no pathognomonic features. We reviewed epilepsy characteristics and clinical outcome exclusively in a pediatric population.

METHODS

Twenty-two children and adolescents (13 males) with confirmed mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes due to mitochondrial DNA A3243G mutation and epilepsy were recruited. Clinical data including seizure semiology, treatment response, neuroimaging findings, and electroencephalography were analyzed. We also examined the effect of the age at seizure onset and initial symptoms on the clinical variables.

RESULTS

Seizure semiology and electroencephalography abnormalities showed no syndrome-specific findings. Focal seizures occurred in 21 of 22 subjects (95.5%), whereas generalized seizures developed in seven of 22 subjects (31.8%). Twenty of 22 subjects (90.9%) achieved partial to complete reduction of clinical seizures for more than one year with a combination of more than two antiepileptic drugs. The subgroup with earlier seizure onset presented significantly earlier and showed significantly higher rates of drug-resistant epilepsy compared with the late onset group, although there were no significant differences in the initial symptoms. The subjects with severe epileptic conditions tended to have more severe clinical dysfunction and more severe organ involvement.

CONCLUSIONS

Both focal and generalized seizures occurred in patients with MELAS. Epilepsy in this population is drug resistant, but a certain degree of clinical seizure reduction was achievable with antiepileptic drugs, with more favorable outcomes than historically expected. Close observation and active epilepsy treatment of individuals with MELAS episodes and earlier seizure onset might improve the prognosis.

The Cyclic Vomiting Syndrome Threshold: A Framework for Understanding Pathogenesis and Predicting Successful Treatments

Cyclic vomiting syndrome (CVS) is an uncommon, idiopathic disorder defined by recurrent, sudden-onset attacks of repetitive retching and vomiting that are separated by symptom-free intervals. CVS was long regarded as a disorder primarily experienced by children but is now known to present de novo in adulthood. Adult CVS has garnered more research attention over the past 20 years, and these efforts have identified some acute and prophylactic treatments for this disorder. However, CVS still lacks a unifying disease model, and this has hindered the development of new therapies. Here adult CVS is reframed as a neurogenic disorder, driven by various endophenotypic factors that shape patterns of activity within the neural circuits required for disease expression. The concept of the "CVS threshold" is put forth in parallel with exploring the remarkable similarity of adult CVS with features of chronic migraine, epilepsy, and panic disorder. Because of such shared neural mechanisms and overlapping endophenotypes, many therapies that have been developed for these other disorders could also be useful in managing CVS. This review seeks to achieve three primary aims: (1) to develop a comprehensive, explanatory framework for adult CVS pathogenesis, (2) to use this framework for identifying potentially novel therapies for CVS, and (3) to describe future research directions that are needed to move the field forward.

Ketogenic diets: from cancer to mitochondrial diseases and beyond

BACKGROUND

The employment of dietary strategies such as ketogenic diets, which force cells to alter their energy source, has shown efficacy in the treatment of several diseases. Ketogenic diets are composed of high fat, moderate protein and low carbohydrates, which favour mitochondrial respiration rather than glycolysis for energy metabolism.

DESIGN

This review focuses on how oncological, neurological and mitochondrial disorders have been targeted by ketogenic diets, their metabolic effects, and the possible mechanisms of action on mitochondrial energy homeostasis. The beneficial and adverse effects of the ketogenic diets are also highlighted.

RESULTS AND CONCLUSIONS

Although the full mechanism by which ketogenic diets improve oncological and neurological conditions still remains to be elucidated, their clinical efficacy has attracted many new followers, and ketogenic diets can be a good option as a co-adjuvant therapy, depending on the situation and the extent of the disease.