Mitochondrial Strokes: Diagnostic Challenges and Chameleons.

Mitochondrial stroke-like episodes (SLEs) are a hallmark of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). They should be suspected in anyone with an acute/subacute onset of focal neurological symptoms at any age and are usually driven by seizures. Suggestive features of an underlying mitochondrial pathology include evolving MRI lesions, often originating within the posterior brain regions, the presence of multisystemic involvement, including diabetes, deafness, or cardiomyopathy, and a positive family history. The diagnosis of MELAS has important implications for those affected and their relatives, given it enables early initiation of appropriate treatment and genetic counselling. However, the diagnosis is frequently challenging, particularly during the acute phase of an event. We describe four cases of mitochondrial strokes to highlight the considerable overlap that exists with other neurological disorders, including viral and autoimmune encephalitis, ischemic stroke, and central nervous system (CNS) vasculitis, and discuss the clinical, laboratory, and imaging features that can help distinguish MELAS from these differential diagnoses.

Pregnancy in MNGIE: a clinical and metabolic honeymoon.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an inherited disease caused by a deficiency in thymidine phosphorylase and characterized by elevated systemic deoxyribonucleotides and gastrointestinal (GI) and neurological manifestations. We report the clinical and biochemical manifestations that were evaluated in a single patient before, during, and after pregnancy, over a period of 7 years. GI symptoms significantly improved, and plasma deoxyribonucleotide concentrations decreased during pregnancy. Within days after delivery, the patient's digestive symptoms recurred, coinciding with a rapid increase in plasma deoxyribonucleotide concentrations. We hypothesize that the clinico-metabolic improvements could be attributed to the enzyme replacement action of the placental thymidine phosphorylase.

Interrater agreement of classification of photoparoxysmal electroencephalographic response.

Our goal was to assess the interrater agreement (IRA) of photoparoxysmal response (PPR) using the classification proposed by a task force of the International League Against Epilepsy (ILAE), and a simplified classification system proposed by our group. In addition, we evaluated IRA of epileptiform discharges (EDs) and the diagnostic significance of the electroencephalographic (EEG) abnormalities. We used EEG recordings from the European Reference Network (EpiCARE) and Standardized Computer-based Organized Reporting of EEG (SCORE). Six raters independently scored EEG recordings from 30 patients. We calculated the agreement coefficient (AC) for each feature. IRA of PPR using the classification proposed by the ILAE task force was only fair (AC = 0.38). This improved to a moderate agreement by using the simplified classification (AC = 0.56; P = .004). IRA of EDs was almost perfect (AC = 0.98), and IRA of scoring the diagnostic significance was moderate (AC = 0.51). Our results suggest that the simplified classification of the PPR is suitable for implementation in clinical practice.

Successful liver transplantation in mitochondrial neurogastrointestinal encephalomyopathy (MNGIE).

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a fatal disorder characterized by progressive gastrointestinal dysmotility, peripheral neuropathy, leukoencephalopathy, skeletal myopathy, ophthalmoparesis, and ptosis. MNGIE stems from deficient thymidine phosphorylase activity (TP) leading to toxic elevations of plasma thymidine. Hematopoietic stem cell transplant (HSCT) restores TP activity and halts disease progression but has high transplant-related morbidity and mortality. Liver transplant (LT) was reported to restore TP activity in two adult MNGIE patients. We report successful LT in four additional MNGIE patients, including a pediatric patient. Our patients were diagnosed between ages 14 months and 36 years with elevated thymidine levels and biallelic pathogenic variants in TYMP. Two patients presented with progressive gastrointestinal dysmotility, and three demonstrated progressive peripheral neuropathy with two suffering limitations in ambulation. Two patients, including the child, had liver dysfunction and cirrhosis. Following LT, thymidine levels nearly normalized in all four patients and remained low for the duration of follow-up. Disease symptoms stabilized in all patients, with some manifesting improvements, including intestinal function. No patient died, and LT appeared to have a more favorable safety profile than HSCT, especially when liver disease is present. Follow-up studies will need to document the long-term impact of this new approach on disease outcome. Take Home Message: Liver transplantation is effective in stabilizing symptoms and nearly normalizing thymidine levels in patients with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) and may have an improved safety profile over hematopoietic stem cell transplant.

VARS2-linked mitochondrial encephalopathy: two case reports enlarging the clinical phenotype.

BACKGROUND: Mitochondrial respiratory chain consists of five complexes encoded by nuclear and mitochondrial genomes. Mitochondrial aminoacyl-tRNA synthetases are key enzymes in the synthesis of such complexes. Bi-allelic variants of VARS2, a nuclear gene encoding for valyl-tRNA (Val-tRNA) synthetase, are associated to several forms of mitochondrial encephalopathies or cardiomyoencephalopathies. Among these, the rare homozygous c.1100C > T (p.Thr367Ile) mutation variably presents with progressive developmental delay, axial hypotonia, limbs spasticity, drug-resistant epilepsy leading, in some cases, to premature death. Yet only six cases, of which three are siblings, harbouring this homozygous mutation have been described worldwide. CASE PRESENTATION: Hereby, we report two additional cases of two non-related young girls from Sardinia, born from non-consanguineous and healthy parents, carrying the aforesaid homozygous VARS2 variant. At onset both the patients presented with worsening psychomotor delay, muscle hypotonia and brisk tendon reflexes. Standard genetic tests were normal, as well as metabolic investigations. Brain MRI showed unspecific progressive abnormalities, such as corpus callosum hypoplasia (patient A) and cerebellar atrophy (patient A and B). Diagnosis was reached by adopting massive parallel next generation sequencing. Notably clinical phenotype of the first patient appears to be milder compared to previous known cases. The second patient eventually developed refractory epilepsy and currently presents with severe global impairment. Because no specific treatment is available as yet, both patients are treated with supporting antioxidant compounds along with symptomatic therapies. CONCLUSIONS: Given the paucity of clinical data about this very rare mitochondrial encephalopathy, our report might contribute to broaden the phenotypic spectrum of the disorder. Moreover, noteworthy, three out of five pedigrees so far described belong to the Northern Sardinia ethnicity.

PARL deficiency in mouse causes Complex III defects, coenzyme Q depletion, and Leigh-like syndrome.

The mitochondrial intramembrane rhomboid protease PARL has been implicated in diverse functions in vitro, but its physiological role in vivo remains unclear. Here we show that Parl ablation in mouse causes a necrotizing encephalomyelopathy similar to Leigh syndrome, a mitochondrial disease characterized by disrupted energy production. Mice with conditional PARL deficiency in the nervous system, but not in muscle, develop a similar phenotype as germline Parl KOs, demonstrating the vital role of PARL in neurological homeostasis. Genetic modification of two major PARL substrates, PINK1 and PGAM5, do not modify this severe neurological phenotype. Parl-/- brain mitochondria are affected by progressive ultrastructural changes and by defects in Complex III (CIII) activity, coenzyme Q (CoQ) biosynthesis, and mitochondrial calcium metabolism. PARL is necessary for the stable expression of TTC19, which is required for CIII activity, and of COQ4, which is essential in CoQ biosynthesis. Thus, PARL plays a previously overlooked constitutive role in the maintenance of the respiratory chain in the nervous system, and its deficiency causes progressive mitochondrial dysfunction and structural abnormalities leading to neuronal necrosis and Leigh-like syndrome.

The development of an in vitro cerebral organoid model for investigating the pathomolecular mechanisms associated with the central nervous system involvement in Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE).

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare disorder caused by mutations in the thymidine phosphorylase gene (TYMP), leading to secondary aberrations to the mitochondrial genome. The disease is characterised by gastrointestinal dysmotility, sensorimotor peripheral neuropathy and leukoencephalopathy. The understanding of the molecular mechanisms that underlie the central nervous system (CNS) is hindered by the lack of a representative disease model; to address this we have developed an in vitro 3-D cerebral organoid of MNGIE. Induced pluripotent stem cells (iPSCs) generated from peripheral blood mononuclear cells (PBMCs) of a healthy control and a patient with MNGIE were characterised to ascertain bona fide pluripotency through the evaluation of pluripotency markers and the differentiation to the germ layers. iPSC lines were differentiated into cerebral organoids. Thymidine phosphorylase expression in PBMCs, iPSCs and Day 92 organoids was evaluated by immunoblotting and intact organoids were sampled for histological evaluation of neural markers. iPSCs demonstrated the expression of pluripotency markers SOX2 and TRA1-60 and the plasticity to differentiate into the germ layers. Cerebral organoids stained positive for the neural markers GFAP, O4, Tuj1, Nestin, SOX2 and MBP. Consistent with the disease phenotypes, MNGIE cells did not display thymidine phosphorylase expression whereas control PBMCs and Day 92 organoids did. Remarkably, control iPSCs did not stain positive for thymidine phosphorylase. We have established for the first time a MNGIE iPSC line and cerebral organoid model, which exhibited the expression of cells relevant to the study of the disease, such as neural stem cells, astrocytes and myelinating oligodendrocytes.

QIL1-dependent assembly of MICOS complex-lethal mutation in C19ORF70 resulting in liver disease and severe neurological retardation.

Seven subunits of the mitochondrial contact site and cristae junction (CJ) organizing system (MICOS) in humans have been recently described in function and structure. QIL1 (also named MIC13) is a small complex that is crucial for the maintenance and assembling of MICOS. A novel mutation of an essential splice site in the C19orf70 gene encoding QIL1 induces severe mitochondrial encephalopathy, hepatopathy and lactate acidosis consistent with psychomotor retardation. In addition, bilateral kidney stones were observed. Disassembly of MICOS complex subunits displays lack of MIC10-MIC26-MIC27-QIL1 subcomplex, resulting in aberrant cristae structure and a loss of cristae junctions and contact sites. In liver and muscle tissue, the activity of the respiratory chain complexes (OXPHOS) was severely impaired. Defects in MICOS complex do not only affect mitochondrial architecture, but also mitochondrial fusion, metabolic signalling, lipid trafficking and cellular electric homeostasis.

Clinical, biochemical, and genetic features associated with VARS2-related mitochondrial disease.

In recent years, an increasing number of mitochondrial disorders have been associated with mutations in mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs), which are key enzymes of mitochondrial protein synthesis. Bi-allelic functional variants in VARS2, encoding the mitochondrial valyl tRNA-synthetase, were first reported in a patient with psychomotor delay and epilepsia partialis continua associated with an oxidative phosphorylation (OXPHOS) Complex I defect, before being described in a patient with a neonatal form of encephalocardiomyopathy. Here we provide a detailed genetic, clinical, and biochemical description of 13 patients, from nine unrelated families, harboring VARS2 mutations. All patients except one, who manifested with a less severe disease course, presented at birth exhibiting severe encephalomyopathy and cardiomyopathy. Features included hypotonia, psychomotor delay, seizures, feeding difficulty, abnormal cranial MRI, and elevated lactate. The biochemical phenotype comprised a combined Complex I and Complex IV OXPHOS defect in muscle, with patient fibroblasts displaying normal OXPHOS activity. Homology modeling supported the pathogenicity of VARS2 missense variants. The detailed description of this cohort further delineates our understanding of the clinical presentation associated with pathogenic VARS2 variants and we recommend that this gene should be considered in early-onset mitochondrial encephalomyopathies or encephalocardiomyopathies.

Charting the territory: Describing the functional abilities of children with progressive neurological conditions.

AIMS: Little is known about the functional abilities of children with progressive genetic, metabolic, or neurological conditions (PNCs). In this study, children with PNCs were followed over a 2-year period to assess their functional abilities over time. Specific aims were to: 1) describe the changes in functional skills and the effects of age for children with PNCs, 2) assess changes in these children's need for caregiver assistance over time, and 3) examine relationships between these children's functional skills and need for caregiver assistance. METHODS: This study involved a longitudinal, descriptive design with three assessments occurring at Baseline, Year 1, Year 2. Functional skills and caregiver assistance were assessed by the Pediatric Evaluation of Disability Inventory (PEDI). The PEDI questionnaire was completed at baseline and then yearly by parents, along with the assistance of a trained research assistant (RA). RESULTS: The study was completed with 83 children (mean age at Baseline=7.1yrs, SD=4.6). Mean Functional skills scores were in the low ranges at Baseline and did not change significantly across time points (F(2, 71)=0.437, p=0.58). Time point had no effect on caregiver assistance ratings (p<0.2); however, children required greater amounts of help with self-care at later time points than for other functional domains. Statistically significant correlations were found between PEDI-Functional skills and caregiver assistance ratings (r=0.80-0.90, p<0.01). CONCLUSIONS: Functional skills were low for these children overall, irrespective of age. In children with PNCs: 1) mean functional skills did not change significantly over time; 2) caregiver assistance scores remained stable and 3) functional skills and levels of caregiver assistance were strongly positively correlated. Further research to explore the long-term functional trajectory in children with a PNC is recommended.

Novel RRM2B Mutation and Severe Mitochondrial DNA Depletion: Report of 2 Cases and Review of the Literature.

Purpose To describe the clinical presentation and implications of mitochondrial DNA depletion disorder of two siblings with early fatal encephalomyopathy and a novel mutation in the RRM2B gene. The relevant literature is reviewed. Methods We describe two brothers aged 2.5 months and 1 month, respectively, who were hospitalized in a tertiary pediatric medical center for evaluation of focal seizures, hypotonia, poor feeding, failure to thrive, lactic acidosis, and developmental delay. The older brother also had seizures, and the younger had severe bilateral neurosensory deafness. Results Genetic sequencing of the RRM2B gene revealed the same novel mutation in both the siblings. Both children died due to respiratory failure at ages 3 and 2.5 months, respectively. Conclusion The combination of neonatal hypotonia, developmental delay, and lactic acidosis should raise a clinician's suspicion of a mitochondrial depletion disorder and prompt further genetic studies.

BCAP31-associated encephalopathy and complex movement disorder mimicking mitochondrial encephalopathy.

BCAP31, encoded by BCAP31, is involved in the export of transmembrane proteins from the endoplasmic reticulum. Pathogenic variants in BCAP31 results in global developmental delay, dystonia, deafness and dysmorphic features in males, called deafness, dystonia, and cerebral hypomyelination (DDCH) syndrome. We report a new patient with BCAP3-associated encephalopathy, DDCH syndrome, sensorineural hearing loss, generalized dystonia, and choreoathetosis. This 3.5-year-old boy had microcephaly and failure to thrive within the first 3 months of life. His brain MRI showed bilateral increased signal intensity in globus pallidus at age 3 months raising the suspicion of mitochondrial encephalopathy. His muscle biopsy revealed pleomorphic subsarcolemmal mitochondria collection in electron microscopy. Respiratory chain enzyme activities were normal in muscle. He was enrolled to a whole exome sequencing research study, which identified a hemizygous likely pathogenic truncating variant (c.533_536dup; p.Ser180AlafsX6) in BCAP31, inherited from his mother, who had sensorineural hearing loss and normal cognitive functions. We report a new patient with BCAP31-associated encephalopathy, DDCH syndrome, mimicking mitochondrial encephalopathy. We also report a heterozygous mother who has bilateral sensorineural hearing loss. This patient's clinical features, muscle histopathology, brain MRI features, and family history were suggestive of mitochondrial encephalopathy. Whole exome sequencing research study confirmed the diagnosis of BCAP31-associated encephalopathy, DDCH syndrome.

Mitochondrial Cardiomyopathy with a Unique 99mTc-MIBI/123I-BMIPP Mismatch Pattern.

A 42-year-old man was referred to our hospital due to chest pain, diabetes mellitus, and sensorineural hearing loss. Transthoracic echocardiography revealed diffuse left ventricular hypokinesis. He was diagnosed with mitochondrial disease and a c.A3243G mutation was identified in his mitochondrial DNA. This case of mitochondrial cardiomyopathy demonstrated a low uptake of 123I-BMIPP, while the uptake of 99mTc-MIBI was preserved. In contrast, previous reports have noted the increased uptake of123I-BMIPP and the decreased uptake of 99mTc-MIBI. This is the first study to show this unique 99mTc-MIBI/123I-BMIPP mismatch pattern. We also discuss the relationships among the cardiac scintigraphy, cardiac magnetic resonance imaging, and histopathology findings.

Further delineation of a rare recessive encephalomyopathy linked to mutations in GFER thanks to data sharing of whole exome sequencing data.

BACKGROUND: Alterations in GFER gene have been associated with progressive mitochondrial myopathy, congenital cataracts, hearing loss, developmental delay, lactic acidosis and respiratory chain deficiency in 3 siblings born to consanguineous Moroccan parents by homozygosity mapping and candidate gene approach (OMIM#613076). Next generation sequencing recently confirmed this association by the finding of compound heterozygous variants in 19-year-old girl with a strikingly similar phenotype, but this ultra-rare entity remains however unknown from most of the scientific community. MATERIALS AND METHODS: Whole exome sequencing was performed as part of a "diagnostic odyssey" for suspected mitochondrial condition in 2 patients, presenting congenital cataracts, progressive encephalomyopathy and hypotrophy and detected unreported compound heterozygous variants in GFER. RESULTS: Thanks to an international data sharing, we found 2 additional patients carrying compound heterozygous variants in GFER. Reverse phenotyping confirmed the phenotypical similarities between the 4 patients. Together with the first literature reports, the review of these 8 cases from 4 unrelated families enables us to better describe this apparently homogeneous disorder, with the clinical and biological stigmata of mitochondrial disease. CONCLUSION: This report highlights the clinical utility of whole exome sequencing and reverse phenotyping for the diagnosis of ultra-rare diseases and underlines the importance of a broad data sharing for accurate clinical delineation of previously unrecognized entities.

A novel thymidine phosphorylase mutation in a Chinese MNGIE patient.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder associated with mitochondrial alterations. MNGIE is characterized by severe gastrointestinal dysmotility, cachexia, ophthalmoplegia, ptosis, peripheral neuropathy, and leukoencephalopathy. The condition is caused by mutation of the TYMP gene. We studied the clinical and biochemical characteristics of a family with MNGIE. The proband was a 48-year-old male presenting with diarrhea and progressive weight loss. He also had ptosis and exhibited eyeball fixation. His blood and cerebrospinal fluid lactate levels were elevated. Magnetic resonance imaging of the brain revealed diffuse leukoencephalopathy. Ragged red fibers and cytochrome c oxidase-deficient fibers were apparent on muscle biopsy. His vision and ptosis deteriorated significantly during follow-up. Our clinical diagnosis of MNGIE was confirmed by TYMP gene analysis. We discovered a homozygous TYMP c.1193-1216 dup-GGGCGCTGCCGCTGGCGCTGGTGC mutation (a duplication). Some of the family members were heterozygous for the mutation but had no clinical features. We predicted the function of this mutation using PredictProtein and found that the secondary structure had changed in the region of the helix and strand, the transmembrane region, and the protein-protein binding sites. The family described herein exhibited biochemically, genetically, and functionally confirmed MNGIE syndrome.

The Newcastle Pediatric Mitochondrial Disease Scale: translation and cultural adaptation for use in Brazil.

OBJECTIVE: The aim of this study was to translate and adapt the Newcastle Paediatric Mitochondrial Disease Scale (NPMDS) to Portuguese for use in Brazil. METHODS: The scale was applied in 20 pediatric patients with mitochondrial disease, in three groups: myopathy (n = 4); Leigh syndrome (n = 8); and encephalomyopathy (n = 8). Scores were obtained for the various dimensions of the NPMDS, and comparisons were drawn between the groups. RESULTS: There was a statistically significant difference between the myopathy group and the Leigh syndrome group (p = 0.0085), as well as between the myopathy and encephalomyopathy groups (p = 0.01). CONCLUSIONS: The translation of the NPMDS, and its adaptation to the socioeconomic and cultural conditions in Brazil, make the NPMDS score useful as an additional parameter in the evaluation and monitoring of pediatric patients with MD in Brazil.

The Newcastle Pediatric Mitochondrial Disease Scale: translation and cultural adaptation for use in Brazil / Escala Pediátrica de Doença Mitocondrial de Newcastle: tradução e adaptação cultural para uso no Brasil

ABSTRACT Objective The aim of this study was to translate and adapt the Newcastle Paediatric Mitochondrial Disease Scale (NPMDS) to Portuguese for use in Brazil. Methods The scale was applied in 20 pediatric patients with mitochondrial disease, in three groups: myopathy (n = 4); Leigh syndrome (n = 8); and encephalomyopathy (n = 8). Scores were obtained for the various dimensions of the NPMDS, and comparisons were drawn between the groups. Results There was a statistically significant difference between the myopathy group and the Leigh syndrome group (p = 0.0085), as well as between the myopathy and encephalomyopathy groups (p = 0.01). Conclusions The translation of the NPMDS, and its adaptation to the socioeconomic and cultural conditions in Brazil, make the NPMDS score useful as an additional parameter in the evaluation and monitoring of pediatric patients with MD in Brazil.

RESUMO Objetivo O objetivo do presente estudo foi realizar a tradução e adaptação da escala NPMDS para a população brasileira. Métodos A escala foi aplicada em 20 crianças e adolescentes com doença mitocondrial (DM) divididos em três grupos: miopatia (n=4), síndrome de Leigh (n=8) e encefalomiopatia (n=8). Obteve-se os escores separados das dimensões da escala NPMDS, foram realizadas comparações entre os escores da NPMDS nos diferentes grupos. Conclusão A tradução da escala NPMDS e sua adequação as condições socioeconômicas e culturais de nossa população tornam este instrumento um parâmetro adicional na avaliação e acompanhamento de pacientes pediátricos com DM.

Mitochondrial Neurogastrointestinal Encephalomyopathy Presenting as Anorexia Nervosa.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare multisystemic autosomal recessive disorder mainly caused by mutations in the nuclear gene TYMP, encoding thymidine phosphorylase. It generally appears in childhood and is clinically characterized by severe gastrointestinal dysmotility, cachexia, ptosis, progressive external ophthalmoplegia, peripheral neuropathy, and diffuse leukoencephalopathy on brain magnetic resonance imaging. The disease is clinically heterogeneous with the main symptoms being gastrointestinal, with an important weight loss. Symptoms might worsen rapidly, and a timely diagnosis is vital. However, patients report retrospectively their first symptoms before the age of 12 years, but the delay in diagnosis varies from 5 to 10 years. In the present study, we report a case of an adolescent with MNGIE, which was initially, and erroneously, diagnosed as anorexia nervosa. To make a timely and accurate differential diagnosis, we will discuss the clinical differences and similarities between MNGIE and anorexia nervosa and the importance of a multidisciplinary evaluation.