Phenotypic analysis of epilepsy in the mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes-associated mitochondrial DNA A3243G mutation

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.

EEG: Current relevance and promising quantitative analyses

Electroencephalography (EEG) remains an essential tool, characterized by an excellent temporal resolution and offering a real window on cerebral functions. Surface EEG signals are mainly generated by the postsynaptic activities of synchronously activated neural assemblies. EEG is also a low-cost tool, easy to use at bed-side, allowing to record brain electrical activities with a low number or up to 256 surface electrodes. For clinical purpose, EEG remains a critical investigation for epilepsies, sleep disorders, disorders of consciousness. Its temporal resolution and practicability also make EEG a necessary tool for cognitive neurosciences and brain-computer interfaces. EEG visual analysis is essential in clinical practice and the subject of recent progresses. Several EEG-based quantitative analyses may complete the visual analysis, such as event-related potentials, source localizations, brain connectivity and microstates analyses. Some developments in surface EEG electrodes appear also, potentially promising for long term continuous EEGs. We overview in this article some recent progresses in visual EEG analysis and promising quantitative analyses.

Clinical features of epileptic seizures in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes

BACKGROUND AND PURPOSE

This study aimed to characterize the clinical features of epilepsy in mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) and analyze the clinical determinants for drug-resistant epilepsy in MELAS.

METHODS

A single-center, retrospective study was conducted to investigate the clinical features of epilepsy in patients with MELAS. Collected variables included seizure semiology, electroencephalography (EEG), muscle biopsy, genetic testing, neuroimaging findings, resting serum lactic value and modified Rankin scale (mRS) of patients with MELAS. We also investigated the differences between the adult-onset group and the child-onset group and analyzed the risk factors for drug-resistant epilepsy in MELAS.

RESULTS

We studied 97 patients (56 males: 41 females) with confirmed MELAS. Epileptic seizure occurred in 100.0% of patients and the initial symptom of 69.1% patients was epileptic seizure. The average age of disease onset was 21.0 years, ranging from 2 to 60 years. The seizure types of these patients with MELAS were variable, with generalized onset (51.5%) to be the most common type. The EEG changes in the patients with MELAS were mainly slow wave (90.9%) and epileptiform discharge (68.2%). The child-onset group with earlier seizure onset presented significantly higher resting serum lactic value (p = 0.0048) and lower incidence of stroke-like lesion in the brain (p = 0.003), especially in the temporal lobe (p < 0.001), compared with the adult-onset group. Importantly, drug-resistant epilepsy in MELAS was demonstrated to be closely related to the earlier age of seizure onset (p = 0.013), as well as the higher mRS score (p < 0.001) and higher resting serum lactic value (p = 0.009).

CONCLUSION

Early identification of MELAS should be considered among individuals with recurrent epilepsy through clinical screening. Age of seizure onset and resting serum lactic value may predict the development of drug-resistant epilepsy in MELAS. Close observation and appropriate anti-epileptic treatment are indispensable for individuals with MELAS to improve the prognosis. Further studies with larger sample size are required to further evaluate the risk factors of drug-resistant epilepsy in MELAS and provide guidance on treatment of MELAS.

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

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

Seizure Semiology, EEG, and Imaging Findings in Epilepsy Secondary to Mitochondrial Disease

Background: Identification of an underlying mitochondrial disorder can be challenging due to the significant phenotypic variability between and within specific disorders. Epilepsy can be a presenting symptom with several mitochondrial disorders. In this study, we evaluated clinical, electrophysiologic, and imaging features in patients with epilepsy and mitochondrial disorders to identify common features, which could aid in earlier identification of a mitochondrial etiology. Methods: This is a retrospective case series from January 2011 to December 2019 at a tertiary referral center of patients with epilepsy and a genetically confirmed diagnosis of a mitochondrial disorder. A total of 164 patients were reviewed with 20 patients fulfilling inclusion criteria. Results: A total of 20 patients (14 females, 6 males) aged 0.5-61 years with epilepsy and genetically confirmed mitochondrial disorders were identified. Status epilepticus occurred in 15 patients, with focal status epilepticus in 13 patients, including 9 patients with visual features. Abnormalities over the posterior cerebral regions were seen in 66% of ictal recordings and 44% of imaging studies. All the patients were on nutraceutical supplementation with no significant change in disease progression seen. At last follow-up, eight patients were deceased and the remainder had moderate-to-severe disability. Discussion: In this series of patients with epilepsy and mitochondrial disorders, we found increased propensity for seizures arising from the posterior cerebral regions. Over time, electroencephalogram (EEG) and imaging abnormalities increasingly occurred over the posterior cerebral regions. Focal seizures and focal status epilepticus with visual symptoms were common. Additional study is needed on nutraceutical supplementation in mitochondrial disorders.

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

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

Mitochondrial Myopathy, Encephalopathy, Lactic acidosis and Stroke-Like Episodes Syndrome Presenting With Anton-Babinski Syndrome and Concurrent Occipital Lobe Seizures

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is a complex group of disorders with multisystem involvement that have a wide range of biochemical and genetic defects. The earliest symptoms of MELAS typically include easy fatigability, muscle weakness, encephalopathy with stroke-like episodes, recurrent headaches and seizures. The pathogenesis of stroke-like episodes manifesting as focal deficits like acute cortical blindness is not fully understood. We present an eight-year-old, right-handed boy with MELAS confirmed by the presence of pathogenic missense variant mutation (mt.3243A>G) presenting with acute intermittent reversible episodes of cortical blindness and Anton-Babinski Syndrome secondary to concurrent occipital lobe seizures captured during video electroencephalography (V-EEG) monitoring, in addition to the neuro-imaging which was not consistent with acute ischemic stroke.

This case highlights the importance of the V-EEG monitoring besides clinical testing and radiographic correlation during acute cortical blindness episodes in MELAS as occipital lobe seizures could be a part of the symptomatology.

Levetiracetam administration is correlated with lower mortality in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes: a retrospective study

Background:

Studies on the relationship between antiepileptic drug (AED) administration and clinical outcomes in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) remain scarce. Levetiracetam (LEV) is an AED that is neuroprotective in various neurologic disorders. This study aimed to determine the impact of LEV on the outcome of MELAS.

Methods:

A retrospective, single-center study was performed based on a large cohort of patients with MELAS with a history of seizures (n = 102). Decisions on antiepileptic therapies were made empirically. Patients were followed up for 1 to 8 years (median, 4 years) and divided into 2 groups based on whether LEV was administered (LEV or non-LEV). The modified Rankin scale (mRS) scores and mortality risks were analyzed in all patients.

Results:

LEV, carbamazepine, benzodiazepines, topiramate, oxcarbazepine, valproate, and lamotrigine were administered in 48, 37, 18, 13, 11, 9, and 9 patients, singly or in combination, respectively. The mean mRS score of the LEV group (n = 48) was lower than that of the non-LEV group (n = 54; mean ± standard deviation, 2.79 ± 1.47 vs. 3.83 ± 1.93, P = 0.006) up to the end of the study. Nevertheless, there was no difference in the proportion of subjects without disability (mRS ranging 0–1) between the groups (P = 0.37). The multivariate regressions revealed that LEV treatment was associated with lower mRS scores (odds ratio 0.32, 95% confidence interval [CI] 0.15–0.68, P = 0.003) and mortality rates (hazard ratio 0.24, 95% CI 0.08–0.74, P = 0.013). There was a significant difference in the Kaplan-Meier survival curves between the groups (χ² = 4.29, P = 0.04).

Conclusions:

The LEV administration is associated with lower mortality in patients with MELAS in this retrospective study. Further laboratory research and prospective cohort studies are needed to confirm whether LEV has neuroprotective effects on patients with mitochondrial diseases.

Clinical syndromes associated with mtDNA mutations: where we stand after 30 years

The landmark year 1988 can be considered as the birthdate of mitochondrial medicine, when the first pathogenic mutations affecting mtDNA were associated with human diseases. Three decades later, the field still expands and we are not ‘scraping the bottom of the barrel’ yet. Despite the tremendous progress in terms of molecular characterization and genotype/phenotype correlations, for the vast majority of cases we still lack a deep understanding of the pathogenesis, good models to study, and effective therapeutic options. However, recent technological advances including somatic cell reprogramming to induced pluripotent stem cells (iPSCs), organoid technology, and tailored endonucleases provide unprecedented opportunities to fill these gaps, casting hope to soon cure the major primary mitochondrial phenotypes reviewed here. This group of rare diseases represents a key model for tackling the pathogenic mechanisms involving mitochondrial biology relevant to much more common disorders that affect our currently ageing population, such as diabetes and metabolic syndrome, neurodegenerative and inflammatory disorders, and cancer.

Cerebral Manifestations of Mitochondrial Disorders

This review aims at summarizing and discussing previous and recent findings concerning the cerebral manifestations of mitochondrial disorders (MIDs). MIDs frequently present as mitochondrial multiorgan disorder syndrome (MIMODS) either already at onset or later in the course. After the muscle, the brain is the organ second most frequently affected in MIMODS. Cerebral manifestations of MIDs are variable and may present with or without a lesion on imaging or functional studies, but there can be imaging/functional lesions without clinical manifestations. The most well-known cerebral manifestations of MIDs include stroke-like episodes, epilepsy, headache, ataxia, movement disorders, hypopituitarism, muscle weakness, psychiatric abnormalities, nystagmus, white and gray matter lesions, atrophy, basal ganglia calcification, and hypometabolism on 2-deoxy-2-[fluorine-18]fluoro-D-glucose positron-emission tomography. For most MIDs, only symptomatic therapy is currently available. Symptomatic treatment should be supplemented by vitamins, cofactors, and antioxidants. In conclusion, cerebral manifestations of MIDs need to be recognized and appropriately managed because they strongly determine the outcome of MID patients.

Cortical venous disease severity in MELAS syndrome correlates with brain lesion development

PURPOSE

MELAS syndrome is a mitochondrial disorder typified by recurrent stroke-like episodes, seizures, and progressive brain injury. Abnormal mitochondria have been found in arterial walls implicating a vasculogenic etiology. We have observed abnormal cortical vein T2/FLAIR signal in MELAS patients, potentially representing wall thickening and sluggish flow. We sought to examine the relationship of hyperintense veins and brain lesions in MELAS.

METHODS

Imaging databases at two children's hospitals were searched for brain MRIs from MELAS patients. Artifact, sedated exams, and lack of 2D-T2/FLAIR sequences were exclusion criteria. Each exam was assigned a venous score based on number of T2/FLAIR hyperintense veins: 1 = <10, 2 = 10 to 20, 3 = >20. Cumulative brain lesions and venous score in MELAS and aged-matched normal exams were compared by Mann-Whitney test.

RESULTS

A total of 106 exams from 14 unique MELAS patients (mean 16 ± 3 years) and 30 exams from normal aged-matched patients (mean 15 ± 3 years) were evaluated. Median venous score between MELAS and control patients significantly differed (3 versus 1; p < 0.001). In the MELAS group, venous score correlated with presence (median = 3) or absence (median = 1) of cumulative brain lesions. In all 8 MELAS patients who developed lesions, venous hyperintensity was present prior to, during, and after lesion onset. Venous score did not correlate with brain lesion acuity.

CONCLUSION

Abnormal venous signal correlates with cumulative brain lesion severity in MELAS syndrome. Cortical venous stenosis, congestion, and venous ischemia may be mechanisms of brain injury. Identification of cortical venous pathology may aid in diagnosis and could be predictive of lesion development.

Mitochondrial multiorgan disorder syndrome score generated from definite mitochondrial disorders

OBJECTIVES

Mitochondrial disorders (MIDs) frequently present as mitochondrial multiorgan disorder syndrome (MIMODS) at onset or evolve into MIMODS during the course. This study aimed to find which organs and/or tissues are most frequently affected by MIMODS, which are the most frequent abnormalities within an affected organ, whether there are typical MIMODS patterns, and to generate an MIMODS score to assess the diagnostic probability for an MID.

METHODS

This is a retrospective evaluation of clinical, biochemical, and genetic investigations of adult patients with definite MIDs. A total of 36 definite MID patients, 19 men and 17 women, aged 29-82 years were included in this study. The diagnosis was based on genetic testing (n=21), on biochemical investigations (n=17), or on both (n=2).

RESULTS

The number of organs most frequently affected was 4 ranging from 1 to 9. MIMODS was diagnosed in 97% of patients. The organs most frequently affected were the muscle (97%), central nervous system (CNS; 72%), endocrine glands (69%), heart (58%), intestines (55%), and peripheral nerves (50%). The most frequent CNS abnormalities were leukoencephalopathy, prolonged visually evoked potentials, and atrophy. The most frequent endocrine abnormalities included thyroid dysfunction, short stature, and diabetes. The most frequent cardiac abnormalities included arrhythmias, systolic dysfunction, and hypertrophic cardiomyopathy. The most frequent MIMODS patterns were encephalomyopathy, encephalo-myo-endocrinopathy, and encepalo-myo-endocrino-cardiopathy. The mean ± 2SD MIMODS score was 35.97±27.6 (range =11-71). An MIMODS score >10 was regarded as indicative of an MID.

CONCLUSION

Adult MIDs manifest as MIMODS in the vast majority of the cases. The organs most frequently affected in MIMODS are muscles, CNS, endocrine glands, and heart. An MIMODS score >10 suggests an MID.

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.

Stroke-like episodes, peri-episodic seizures, and MELAS mutations

PURPOSE

Stroke-like episodes (SLEs) are a hallmark of various mitochondrial disorders, in particular MELAS syndrome. SLEs manifest with vasogenic oedema (DWI and ADC hyperintensity) or partial cytotoxic oedema (DWI hyperintensity, ADC hypointensity) in the acute and subacute stage, and with gyriform T1-hyperintensity (cortical necrosis) in the chronic stage.

PRINCIPAL RESULTS

SLEs must be clearly distinguished from ischaemic stroke, since management of these two entities is different. SLEs may go along with or without seizures or epileptiform discharges on EEG. However, in MELAS syndrome seizures may also occur in the absence of SLEs. Focal and generalised seizures have been reported but it is currently unknown if the one or the other prevail. SLEs with and without seizures may respond to NO-precursors l-arginine, succinate, or citrulline. As a supportive measure a ketogenic diet should be initiated. Seizures prior to or during a SLE or paroxysmal EEG-activity during a SLE should be initially treated with antiepileptic drugs (AEDs) with low mitochondrion-toxicity. Only in case these AEDs are ineffective, AEDs with higher mitochondrion-toxicity should be added.

MAJOR CONCLUSIONS

All patients with SLEs need to have an EEG recorded irrespective if they have manifesting seizures or not. There are no mtDNA or nDNA mutations which predispose for SLEs with seizures.

Blepharophimosis Ptosis Epicanthus Inversus Syndrome With Congenital Hypothyroidism and Brachydactyly in a 7-Year-Old Girl

A 7-year-old female presented with blepharophimosis ptosis epicanthus inversus syndrome with congenital hypothyroidism and brachydactyly. She displayed typical manifestations of type II blepharophimosis ptosis epicanthus inversus syndrome (normal uterus position, ovarian volume, and normal serum hormone levels). She takes levothyroxine sodium daily due to her congenital hypothyroidism. Karyotype analysis and genetic analysis of FOXL2 coding sequence was found to be normal. mtDNA A3243G, A8344G, 8993, and 13513 genes were also normal. The absence of mutations excluded mitochondrial encephalomyopathies. To the best of our knowledge, this is the first reported case of blepharophimosis ptosis epicanthus inversus syndrome with congenital hypothyroidism and brachydactyly.

Toxicity of Antiepileptic Drugs to Mitochondria

Some of the side and beneficial effects of antiepileptic drugs (AEDs) are mediated via the influence on mitochondria. This is of particular importance in patients requiring AED treatment for mitochondrial epilepsy. AED treatment in patients with mitochondrial disorders should rely on the known influences of AEDs on these organelles. AEDs may influence various mitochondrial functions or structures in a beneficial or detrimental way. There are AEDs in which the toxic effect outweighs the beneficial effect, such as valproic acid (VPA), carbamazepine (CBZ), phenytoin (PHT), or phenobarbital (PB). There are, however, also AEDs in which the beneficial effect on mitochondria outweighs the mitochondrion-toxic effect, such as gabapentin (GBT), lamotrigine (LTG), levetiracetam (LEV), or zonisamide (ZNS). In the majority of the AEDs, however, information about their influence of mitochondria is lacking. In clinical practice mitochondrial epilepsy should be initially treated with AEDs with low mitochondrion-toxic potential. Only in cases of ineffectivity or severe mitochondrial epilepsy, mitochondrion-toxic AEDs should be given. This applies for AEDs given orally or intravenously.

CNF1 Enhances Brain Energy Content and Counteracts Spontaneous Epileptiform Phenomena in Aged DBA/2J Mice

Epilepsy, one of the most common conditions affecting the brain, is characterized by neuroplasticity and brain cell energy defects. In this work, we demonstrate the ability of the Escherichia coli protein toxin cytotoxic necrotizing factor 1 (CNF1) to counteract epileptiform phenomena in inbred DBA/2J mice, an animal model displaying genetic background with an high susceptibility to induced- and spontaneous seizures. Via modulation of the Rho GTPases, CNF1 regulates actin dynamics with a consequent increase in spine density and length in pyramidal neurons of rat visual cortex, and influences the mitochondrial homeostasis with remarkable changes in the mitochondrial network architecture. In addition, CNF1 improves cognitive performances and increases ATP brain content in mouse models of Rett syndrome and Alzheimer's disease. The results herein reported show that a single dose of CNF1 induces a remarkable amelioration of the seizure phenotype, with a significant augmentation in neuroplasticity markers and in cortex mitochondrial ATP content. This latter effect is accompanied by a decrease in the expression of mitochondrial fission proteins, suggesting a role of mitochondrial dynamics in the CNF1-induced beneficial effects on this epileptiform phenotype. Our results strongly support the crucial role of brain energy homeostasis in the pathogenesis of certain neurological diseases, and suggest that CNF1 could represent a putative new therapeutic tool for epilepsy.