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Pseudo-TORCH Syndrome (PTS) encompasses a heterogeneous group of genetic disorders that may clinically and radiologically resemble congenital TORCH infections. These mimickers present with overlapping features manifested as intracranial and systemic abnormalities. Collagen type IV alpha 1 chain (COL4A1)-related diseases, characterized by autosomal dominant inheritance, exhibit a diverse phenotypic spectrum involving cerebrovascular, renal, ophthalmological, cardiac, and muscular abnormalities. Cerebrovascular manifestations range from small-vessel brain disease to large vessel abnormalities, resulting in intracerebral hemorrhage, periventricular leukoencephalopathy, and ventriculomegaly. Additional features include cortical malformations, eye defects, arrhythmias, renal disease, muscular abnormalities, and hematological manifestations. Age of onset varies widely, and phenotypic variability exists even among individuals with the same variant. In this study, we present two cases of COL4A1-related disorder mimicking congenital TORCH infections, highlighting the importance of recognizing genetic mimics in clinical practice.
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BACKGROUND: Acute metabolic crises in inborn errors of metabolism (such as urea cycle disorders, organic acidemia, maple syrup urine disease, and mitochondrial disorders) are neurological emergencies requiring management in the pediatric intensive care unit (PICU). There is a paucity of data pertaining to electroencephalograms (EEG) characteristics in this cohort. We hypothesized that the incidence of background abnormalities and seizures in this cohort would be high. Neuromonitoring data from our center's PICU over 10 years are presented in this article. METHODS: Data were collected by retrospective chart review for patients with the aforementioned disorders who were admitted to the PICU at our institution because of metabolic/neurologic symptoms from 2008 to 2018. Descriptive statistics (χ2 test or Fisher's exact test) were used to study the association between EEG parameters and outcomes. RESULTS: Our cohort included 40 unique patients (8 with urea cycle disorder, 7 with organic acidemia, 3 with maple syrup urine disease, and 22 with mitochondrial disease) with 153 admissions. Presenting symptoms included altered mentation (36%), seizures (41%), focal weakness (5%), and emesis (28%). Continuous EEG was ordered in 34% (n = 52) of admissions. Twenty-three admissions were complicated by seizures, including eight manifesting as status epilepticus (seven nonconvulsive and one convulsive). Asymmetry and focal slowing on EEG were associated with seizures. Moderate background slowing or worse was noted in 75% of EEGs. Among those patients monitored on EEG, 4 (8%) died, 3 (6%) experienced a worsening of their Pediatric Cerebral Performance Category (PCPC) score as compared to admission, and 44 (86%) had no change (or improvement) in their PCPC score during admission. CONCLUSIONS: This study shows a high incidence of clinical and subclinical seizures during metabolic crisis in patients with inborn errors of metabolism. EEG background features were associated with risk of seizures as well as discharge outcomes. This is the largest study to date to investigate EEG features and risk of seizures in patients with neurometabolic disorders admitted to the PICU. These data may be used to inform neuromonitoring protocols to improve mortality and morbidity in inborn errors of metabolism.
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Urea cycle disorders (UCD) are inherited diseases resulting from deficiency in one of six enzymes or two carriers that are required to remove ammonia from the body. UCD may be associated with neurological damage encompassing a spectrum from asymptomatic/mild to severe encephalopathy, which results in most cases from Hyperammonemia (HA) and elevation of other neurotoxic intermediates of metabolism. Electroencephalography (EEG), Magnetic resonance imaging (MRI) and Proton Magnetic resonance spectroscopy (MRS) are noninvasive measures of brain function and structure that can be used during HA to guide management and provide prognostic information, in addition to being research tools to understand the pathophysiology of UCD associated brain injury. The Urea Cycle Rare disorders Consortium (UCDC) has been invested in research to understand the immediate and downstream effects of hyperammonemia (HA) on brain using electroencephalogram (EEG) and multimodal brain MRI to establish early patterns of brain injury and to track recovery and prognosis. This review highlights the evolving knowledge about the impact of UCD and HA in particular on neurological injury and recovery and use of EEG and MRI to study and evaluate prognostic factors for risk and recovery. It recognizes the work of others and discusses the UCDC's prior work and future research priorities.
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Encéfalo , Eletroencefalografia , Hiperamonemia , Imageamento por Ressonância Magnética , Espectroscopia de Prótons por Ressonância Magnética , Distúrbios Congênitos do Ciclo da Ureia , Animais , Encéfalo/diagnóstico por imagem , Encéfalo/metabolismo , Encéfalo/fisiopatologia , História do Século XXI , Hiperamonemia/diagnóstico por imagem , Hiperamonemia/história , Hiperamonemia/metabolismo , Hiperamonemia/fisiopatologia , Distúrbios Congênitos do Ciclo da Ureia/diagnóstico por imagem , Distúrbios Congênitos do Ciclo da Ureia/história , Distúrbios Congênitos do Ciclo da Ureia/metabolismo , Distúrbios Congênitos do Ciclo da Ureia/fisiopatologiaRESUMO
Microdeletion in the 16p11.2 loci lead to a distinct neurodevelopmental disorder with intellectual disability and autism spectrum disorder in addition to dysmorphia, macrocephaly, and increased body mass index. One of the deleted genes in this region is PRRT2 which codes for proline-rich transmembrane protein 2. Heterozygous variants in PRRT2 cause four distinct neurological disorders including benign familial infantile epilepsy (BFIE), paroxysmal kinesigenic dyskinesia (PKD), PKD with infantile convulsions, and familial hemiplegic migraine (FHM). A 13-year-old male with a known history of 16p11.2 deletion and resultant cognitive delay presented with sudden onset of headache, left-sided weakness, facial droop, and aphasia concerning for acute ischemic stroke. Magnetic resonance imaging of the brain was performed urgently which did not reveal any acute processes and his presentation met criteria for hemiplegic migraine. There have been reports of PKD and BFIE in this microdeletion syndrome; however, our proband is the first case that presented with FHM related to haploinsufficiency of PRRT2. This report highlights the importance of counseling patient families regarding acute paroxysmal presentations in this syndrome.
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Transtorno do Espectro Autista , Deficiência Intelectual , AVC Isquêmico , Enxaqueca com Aura , Adolescente , Transtorno do Espectro Autista/genética , Transtorno Autístico , Deleção Cromossômica , Transtornos Cromossômicos , Cromossomos , Cromossomos Humanos Par 16 , Distonia , Haploinsuficiência/genética , Humanos , Deficiência Intelectual/complicações , Deficiência Intelectual/genética , Masculino , Proteínas de Membrana/genética , Enxaqueca com Aura/complicações , Enxaqueca com Aura/genética , Mutação , Proteínas do Tecido Nervoso/genética , LinhagemRESUMO
Inborn errors of metabolism (IEM) are a unique class of genetic diseases due to mutations in genes involved in key metabolic pathways. The combined incidence of IEM has been estimated to be as high as 1:1000. Urea Cycle disorders (UCD), one class of IEM, can present with cerebral edema and represent a possible target to explore the utility of different neuromonitoring techniques during an hyperammonemic crisis. The last two decades have brought advances in the early identification and comprehensive management of UCD, including further understanding of neuroimaging patterns associated with neurocognitive function. Nonetheless, very important questions remain about the potential acute neurotoxic effects of hyperammonemia to better understand how to treat and prevent secondary brain injury. In this review, we describe existing neuromonitoring techniques that have been used in rare metabolic disorders to assess and allow amelioration of ongoing brain injury. Directions of future research should be focused on identifying new diagnostic approaches in the management of metabolic crises to optimize care and reduce long term morbidity and mortality in patients with IEM.
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Erros Inatos do Metabolismo , Distúrbios Congênitos do Ciclo da Ureia , Humanos , Incidência , Estudos Longitudinais , Erros Inatos do Metabolismo/diagnósticoRESUMO
CASE: We are reporting the third unrelated case of cerebral aspartate-glutamate carrier isoform 1 (AGC1) deficiency. Patient is a 21-month-old Yemeni male who presented with refractory seizure disorder and developmental arrest. Neuroimaging showed cerebral volume loss and diminished N-acetylaspartate (NAA) peak. Whole exome sequencing revealed a homozygous novel missense variant in the SLC25A12 gene. Patient's seizure frequency abated drastically following initiation of ketogenic diet. DISCUSSION AND CONCLUSION: Cerebral AGC1 deficiency results in dysfunction of mitochondrial malate aspartate shuttle, thereby prohibiting myelin synthesis. There are significant phenotypic commonalities between our patient and previously reported cases including intractable epilepsy, psychomotor delay, cerebral atrophy, and diminished NAA peak. Our report also provides evidence regarding beneficial effect of ketogenic diet in this rare neurometabolic epilepsy.
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Sistemas de Transporte de Aminoácidos Acídicos/deficiência , Antiporters/deficiência , Dieta Cetogênica , Doenças Desmielinizantes Hereditárias do Sistema Nervoso Central/diagnóstico , Doenças Mitocondriais/diagnóstico , Proteínas de Transporte da Membrana Mitocondrial/genética , Transtornos Psicomotores/diagnóstico , Adulto , Sistemas de Transporte de Aminoácidos Acídicos/genética , Antiporters/genética , Epilepsia Resistente a Medicamentos/dietoterapia , Doenças Desmielinizantes Hereditárias do Sistema Nervoso Central/dietoterapia , Doenças Desmielinizantes Hereditárias do Sistema Nervoso Central/genética , Doenças Desmielinizantes Hereditárias do Sistema Nervoso Central/fisiopatologia , Humanos , Masculino , Doenças Mitocondriais/dietoterapia , Doenças Mitocondriais/genética , Doenças Mitocondriais/fisiopatologia , Mutação de Sentido Incorreto , Isoformas de Proteínas , Transtornos Psicomotores/dietoterapia , Transtornos Psicomotores/genética , Transtornos Psicomotores/fisiopatologia , Sequenciamento do Exoma , Adulto JovemRESUMO
CASE: We report a 15-year-old Indian girl born to a consanguineous couple, who presented with epilepsy, developmental delay, neuroregression, and episodes of alternating hemiparesis. In addition, she had one episode of rhabdomyolysis at the age of 7 years. Extensive genetic and metabolic work up through the years was unrevealing. Eventually a trio whole exome sequencing (WES) revealed homozygous single nucleotide variants in TANGO2 gene. DISCUSSION: TANGO2 related recurrent metabolic crises with encephalomyopathy and cardiac arrhythmias were described very recently and only 15 cases were reported in literature at the time of writing. Alternating hemiplegia of childhood which was seen in our patient, has not been described in previous patients with TANGO2 mutation, and thereby expands the emerging phenotypic spectrum of this novel entity. This report also reiterates the utility of WES in diagnosing newly recognized neurogenetic conditions.
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Translocador Nuclear Receptor Aril Hidrocarboneto/genética , Variação Genética/genética , Hemiplegia/diagnóstico por imagem , Hemiplegia/genética , Fenótipo , Polimorfismo de Nucleotídeo Único/genética , Adolescente , Feminino , Homozigoto , HumanosRESUMO
BACKGROUND: Exome sequencing (ES) is a useful tool in diagnosing suspected mitochondrial disease but can miss pathogenic variants for several reasons. Additional testing, such as muscle biopsy or biochemical testing, can be helpful in exome-negative cases. METHODS: We report a patient who presented with repeated episodes of lactic acidosis and failure to thrive. RESULTS: ES and mitochondrial sequencing were initially negative but clinical suspicion for mitochondrial disease remained high. After muscle biopsy showed evidence of mitochondrial dysfunction, the ES was reanalyzed and revealed novel variants in AARS2. CONCLUSION: This case demonstrates the importance of muscle biopsy and biochemical testing in evaluating patients with a high suspicion of mitochondrial disease, even in the genomics era. Closed-loop communication between molecular genetics laboratories and clinical geneticists is an important step to help establish diagnosis in unsolved cases.
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Doenças Mitocondriais , Músculo Esquelético , Fenótipo , Feminino , Humanos , Lactente , Alanina-tRNA Ligase , Biópsia , Exoma , Sequenciamento do Exoma , Doenças Mitocondriais/genética , Doenças Mitocondriais/diagnóstico , Doenças Mitocondriais/patologia , Músculo Esquelético/patologiaRESUMO
BACKGROUND: Ornithine transcarbamylase deficiency (OTCD) due to an X-linked OTC mutation, is responsible for moderate to severe hyperammonemia (HA) with substantial morbidity and mortality. About 80% of females with OTCD remain apparently "asymptomatic" with limited studies of their clinical characteristics and long-term health vulnerabilities. Multimodal neuroimaging studies and executive function testing have shown that asymptomatic females exhibit limitations when stressed to perform at higher cognitive load and had reduced activation of the prefrontal cortex. This retrospective study aims to improve understanding of factors that might predict development of defined complications and serious illness in apparent asymptomatic females. A proband and her daughter are presented to highlight the utility of multimodal neuroimaging studies and to underscore that asymptomatic females with OTCD are not always asymptomatic. METHODS: We review data from 302 heterozygote females with OTCD enrolled in the Urea Cycle Disorders Consortium (UCDC) longitudinal natural history database. We apply multiple neuroimaging modalities in the workup of a proband and her daughter. RESULTS: Among the females in the database, 143 were noted as symptomatic at baseline (Sym). We focused on females who were asymptomatic (Asx, n = 111) and those who were asymptomatic initially upon enrollment in study but who later became symptomatic sometime during follow-up (Asx/Sym, n = 22). The majority of Asx (86%) and Asx/Sym (75%) subjects did not restrict protein at baseline, and ~38% of Asx and 33% of Asx/Sym subjects suffered from mild to severe neuropsychiatric conditions such as mood disorder and sleep problems. The risk of mild to severe HA sometime later in life for the Asx and Asx/Sym subjects as a combined group was ~4% (5/133), with ammonia ranging from 77 to 470 µM and at least half (2/4) of subjects requiring hospital admission and nitrogen scavenger therapy. For this combined group, the median age of first HA crisis was 50 years, whereas the median age of first symptom which included neuropsychiatric and/or behavioral symptoms was 17 years. The multimodal neuroimaging studies in female heterozygotes with OTCD also underscore that asymptomatic female heterozygotes with OTCD (e.g., proband) are not always asymptomatic. CONCLUSIONS: Analysis of Asx and Asx/Sym females with OTCD in this study suggests that future evidence-based management guidelines and/or a clinical risk score calculator for this cohort could be useful management tools to reduce morbidity and improve long-term quality of life.
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Doença da Deficiência de Ornitina Carbomoiltransferase , Adolescente , Feminino , Humanos , Pessoa de Meia-Idade , Hiperamonemia/etiologia , Estudos Longitudinais , Doença da Deficiência de Ornitina Carbomoiltransferase/diagnóstico , Doença da Deficiência de Ornitina Carbomoiltransferase/genética , Estudos Retrospectivos , Distúrbios Congênitos do Ciclo da Ureia/epidemiologia , Doenças Assintomáticas , Bases de Dados FactuaisRESUMO
In the past couple of decades, literature in pediatric neurology and clinical genetics has identified hundreds of monogenic disorders that can masquerade as infantile cerebral palsy (CP). Accurate and prompt diagnosis in such cases may be challenging due to several reasons. There are commercial multigene CP panels, but their diagnostic yield is often limited compared with exome sequencing because of diverse etiologies that may mimic CP. We report one such case where a patient with spastic hemiplegia underwent a long diagnostic journey before genetic diagnosis was established with exome sequencing and appropriate management was started. TTC19-related mitochondrial complex III deficiency is an ultrarare disorder of energy metabolism that presents with bilateral lesions in the basal ganglia and a degenerative neuropsychiatric phenotype.
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Paralisia Cerebral , Doenças Mitocondriais , Transtornos dos Movimentos , Criança , Humanos , Paralisia Cerebral/diagnóstico , Paralisia Cerebral/genética , Paralisia Cerebral/patologia , Transtornos dos Movimentos/diagnóstico , Transtornos dos Movimentos/genética , Fenótipo , Doenças Mitocondriais/genética , Sequenciamento de Nucleotídeos em Larga EscalaRESUMO
The practice of child neurology has changed significantly in the past two decades as we have integrated genetic testing into our standard of care to achieve precise diagnoses and to guide management of many childhood neurological conditions. Despite this paradigm shift, there appears to be a gap in both clinical exposure to neurogenetic disorders and education provided to residents in ordering and interpreting genetic testing. We therefore conducted a national survey for child neurology trainees in all programs across the United States to delineate their perception of the adequacy of current training and didactics in genetic/neurogenetic disorders. The results revealed knowledge gaps related to ordering and interpreting genetic testing, managing acute metabolic emergencies, and identifying resources for referral of patients to clinical trials. Responders considered their current curriculum in neurogenetics to be insufficient and voted favorably for an educational platform using recorded lectures and interactive sessions.
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Internato e Residência , Neurologia , Neurociências , Criança , Currículo , Educação de Pós-Graduação em Medicina , Humanos , Neurologia/educação , Inquéritos e Questionários , Estados UnidosRESUMO
The literature thoroughly describes the challenges of pediatric drug development for rare diseases. This includes (1) generating interest from sponsors, (2) small numbers of children affected by a particular disease, (3) difficulties with study design, (4) lack of definitive outcome measures and assessment tools, (5) the need for additional safeguards for children as a vulnerable population, and (6) logistical hurdles to completing trials, especially with the need for longer term follow-up to establish safety and efficacy. There has also been an increasing awareness of the need to engage patients and their families in drug development processes and to address inequities in access to pediatric clinical trials. The year 2020 ushered in yet another challenge-the COVID-19 pandemic. The pediatric drug development ecosystem continues to evolve to meet these challenges. This article will focus on several key factors including recent regulatory approaches and public health policies to facilitate pediatric rare disease drug development, emerging trends in product development (biologics, molecularly targeted therapies), innovations in trial design/endpoints and data collection, and current efforts to increase patient engagement and promote equity. Finally, lessons learned from COVID-19 about building adaptable pediatric rare disease drug development processes will be discussed.
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Produtos Biológicos , Tratamento Farmacológico da COVID-19 , Criança , Desenvolvimento de Medicamentos , Ecossistema , Humanos , Pandemias , Saúde Pública , Doenças Raras/tratamento farmacológicoRESUMO
Malate dehydrogenases (MDH) serve a critical role in maintaining equilibrium of the NAD+/NADH ratio between the mitochondria and cytosol through the catalysis of the oxidation of L-malate to oxaloacetate in a reversible, NADH-dependent manner. MDH2 encodes the mitochondrial isoform, which is integral to the tricarboxylic acid cycle and thus energy homeostasis. Recently, five patients harboring compound heterozygous MDH2 variants have been described, three with early-onset epileptic encephalopathy, one with a stroke-like episode, and one with dilated cardiomyopathy. Here, we describe an additional seven patients with biallelic variants in MDH2, the largest and most neurodevelopmentally and ethnically diverse cohort to-date, including homozygous variants, a sibling pair, non-European patients, and an adult. From these patients, we learn that MDH2 deficiency results in a biochemical signature including elevations of plasma lactate and the lactate:pyruvate ratio with urinary excretion of malate. It also results in a recognizable constellation of neuroimaging findings of anterior-predominant cerebral atrophy, subependymal cysts with ventricular septations. We also recognize MDH2 deficiency as a cause of Leigh syndrome. Taken with existing patient reports, we conclude that MDH2 deficiency is an emerging and likely under-recognized cause of infantile epileptic encephalopathy and provide a framework for medical evaluation of patients identified with biallelic MDH2 variants.
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The mitochondrial malate aspartate shuttle system (MAS) maintains the cytosolic NAD+/NADH redox balance, thereby sustaining cytosolic redox-dependent pathways, such as glycolysis and serine biosynthesis. Human disease has been associated with defects in four MAS-proteins (encoded by MDH1, MDH2, GOT2, SLC25A12) sharing a neurological/epileptic phenotype, as well as citrin deficiency (SLC25A13) with a complex hepatopathic-neuropsychiatric phenotype. Ketogenic diets (KD) are high-fat/low-carbohydrate diets, which decrease glycolysis thus bypassing the mentioned defects. The same holds for mitochondrial pyruvate carrier (MPC) 1 deficiency, which also presents neurological deficits. We here describe 40 (18 previously unreported) subjects with MAS-/MPC1-defects (32 neurological phenotypes, eight citrin deficiency), describe and discuss their phenotypes and genotypes (presenting 12 novel variants), and the efficacy of KD. Of 13 MAS/MPC1-individuals with a neurological phenotype treated with KD, 11 experienced benefits-mainly a striking effect against seizures. Two individuals with citrin deficiency deceased before the correct diagnosis was established, presumably due to high-carbohydrate treatment. Six citrin-deficient individuals received a carbohydrate-restricted/fat-enriched diet and showed normalisation of laboratory values/hepatopathy as well as age-adequate thriving. We conclude that patients with MAS-/MPC1-defects are amenable to dietary intervention and that early (genetic) diagnosis is key for initiation of proper treatment and can even be lifesaving.
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Citrulinemia , Dieta Cetogênica , Ácido Aspártico/metabolismo , Carboidratos , Humanos , Malatos , Proteínas de Transporte da Membrana Mitocondrial/genética , Proteínas de Transporte da Membrana Mitocondrial/metabolismo , Transportadores de Ácidos MonocarboxílicosRESUMO
In this review, we analyze medical and select ethical aspects of the increasing use of next-generation sequencing (NGS) based tests in newborn medicine. In the last five years, there have been several studies exploring the role of rapid exome sequencing (ES) and genome sequencing (GS) in critically ill newborns. While the advantages include a high diagnostic yield with potential changes in interventions, there have been ethical dilemmas surrounding consent, information about adult-onset diseases and resolution of variants of uncertain significance. Another active area of research includes a cohort of studies funded under Newborn Sequencing in Genomic Medicine and Public Health pertaining to the use of ES and GS in newborn screening (NBS). While these techniques may allow for screening for several genetic disorders that do not have a detectable biochemical marker, the high costs and long turnaround times of these tests are barriers in their utilization as public health screening tests. Discordant results between conventional NBS and ES-based NBS, as well as challenges with consent, are other potential pitfalls of this approach. Please see the Bush, Al-Hertani and Bodamer article in this Special Issue for the broader scope and further discussion.
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We report the case of a 3-year-old male patient who presented with a 3-day history of altered mental status, emesis, and abdominal pain in the setting of a viral illness. A rapid screening revealed a high ammonia level and after reviewing his proton magnetic resonance spectroscopy (1H MRS) which showed the classic triad of high glutamate, low choline, and myoinositol, a diagnosis of ornithine transcarbamylase deficiency (OTCD) was made within 6 hours of presentation. Therapy with sodium phenylbutyrate and sodium benzoate was initiated and patient was discharged after 3 days with no neurologic disability. Biochemical and molecular testing eventually confirmed the diagnosis. 1H MRS is a practical and fast neuroimaging modality that can aid in diagnosis of OTCD and enables faster initiation of treatment in acute settings.
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The urea cycle disorders (UCD) are rare genetic disorder due to a deficiency of one of six enzymes or two transport proteins that act to remove waste nitrogen in form of ammonia from the body. In this review, we focus on neuroimaging studies in OTCD and Arginase deficiency, two of the UCD we have extensively studied. Ornithine transcarbamylase deficiency (OTCD) is the most common of these, and X-linked. Hyperammonemia (HA) in OTCD is due to deficient protein handling. Cognitive impairments and neurobehavioral disorders have emerged as the major sequelae in Arginase deficiency and OTCD, especially in relation to executive function and working memory, impacting pre-frontal cortex (PFC). Clinical management focuses on neuroprotection from HA, as well as neurotoxicity from other known and yet unclassified metabolites. Prevention and mitigation of neurological injury is a major challenge and research focus. Given the impact of HA on neurocognitive function of UCD, neuroimaging modalities, especially multi-modality imaging platforms, can bring a wealth of information to understand the neurocognitive function and biomarkers. Such information can further improve clinical decision making, and result in better therapeutic interventions. In vivo investigations of the affected brain using multimodal neuroimaging combined with clinical and behavioral phenotyping hold promise. MR Spectroscopy has already proven as a tool to study biochemical aberrations such as elevated glutamine surrounding HA as well as to diagnose partial UCD. Functional Near Infrared Spectroscopy (fNIRS), which assesses local changes in cerebral hemodynamic levels of cortical regions, is emerging as a non-invasive technique and will serve as a surrogate to fMRI with better portability. Here we review two decades of our research using non-invasive imaging and how it has contributed to an understanding of the cognitive effects of this group of genetic conditions.
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We report a 5-year-old male with a PDHA1 variant who presented with alternating hemiplegia of childhood and later developed developmental regression, basal ganglia injury and episodic lactic acidosis. Enzyme assay in lymphocytes confirmed a diagnosis of Pyruvate Dehydrogenase Complex (PDC) deficiency. His mother who was heterozygous for the same variant suffered from ophthalmoplegia, chronic migraine and developed flaccid paralysis at 36 years of age. PDHA1 is the most common genetic cause of PDC deficiency and presents with a myriad of neurological phenotypes including neonatal form with lactic acidosis, non-progressive infantile encephalopathy, Leigh syndrome subtype and intermittent ataxia. The presentations in our 2 patients contribute to the clinical heterogeneity of this neurogenetic condition.