A simple blood test expedites the diagnosis of glucose transporter type 1 deficiency syndrome

Changes in pediatric referrals after the 2009 ketogenic diet consensus recommendations

BACKGROUND

In 2009, the International Ketogenic Diet Study Group published recommendations for children receiving ketogenic diet (KD) therapy for epilepsy. The document included a table listing epilepsy syndromes and conditions in which the KD has been particularly beneficial, hoping that physicians would refer children for the KD sooner.

PURPOSE

To measure the impact of these 2009 recommendations on referral practice, we compared children initiated on the KD at Johns Hopkins Hospital (JHH) 10 years before and after the recommendations.

RESULTS

Overall, children referred to the KD who met indications increased from the pre- to post-recommendation group, 44 % (112/256) to 69 % (175/255) (p < 0.001), with JHH neurologists specifically referring more frequently (10/112, 9 % to 58/175, 33 %) (p < 0.01). Referrals increased for Glut-1 deficiency (0 % to 2.4 %, p = 0.015), Dravet syndrome (0 % to 6.7 %, p < 0.01), Rett syndrome (0.4 % to 3 %, p = 0.018), and formula-fed only status (16 % to 31 %, p < 0.01). The chances of > 50 % seizure reduction for all children referred improved slightly between decades (56 % to 61 %, p = 0.30).

CONCLUSIONS

Following the 2009 recommendations, our study shows there was an increase in referrals for children with indications at our center. Referrals from neurologists at our own institution increased the most. Ketogenic diet efficacy improved slightly over time but did not reach significance.

Complete absence of GLUT1 does not impair human terminal erythroid differentiation

The Glucose transporter 1 (GLUT1) is one of the most abundant proteins within the erythrocyte membrane and is required for glucose and dehydroascorbic acid (Vitamin C precursor) transport. It is widely recognized as a key protein for red cell structure, function, and metabolism. Previous reports highlighted the importance of GLUT1 activity within these uniquely glycolysis-dependent cells, in particular for increasing antioxidant capacity needed to avoid irreversible damage from oxidative stress in humans. However, studies of glucose transporter roles in erythroid cells are complicated by species-specific differences between humans and mice. Here, using CRISPR-mediated gene editing of immortalized erythroblasts and adult CD34+ hematopoietic progenitor cells, we generate committed human erythroid cells completely deficient in expression of GLUT1. We show that absence of GLUT1 does not impede human erythroblast proliferation, differentiation, or enucleation. This work demonstrates for the first-time generation of enucleated human reticulocytes lacking GLUT1. The GLUT1-deficient reticulocytes possess no tangible alterations to membrane composition or deformability in reticulocytes. Metabolomic analyses of GLUT1-deficient reticulocytes reveal hallmarks of reduced glucose import, downregulated metabolic processes and upregulated AMPK-signalling, alongside alterations in antioxidant metabolism, resulting in increased osmotic fragility and metabolic shifts indicative of higher oxidant stress. Despite detectable metabolic changes in GLUT1 deficient reticulocytes, the absence of developmental phenotype, detectable proteomic compensation or impaired deformability comprehensively alters our understanding of the role of GLUT1 in red blood cell structure, function and metabolism. It also provides cell biological evidence supporting clinical consensus that reduced GLUT1 expression does not cause anaemia in GLUT1 deficiency syndrome.

Prospective Multicenter Validation of a Simple Blood Test for the Diagnosis of Glut1 Deficiency Syndrome

BACKGROUND AND OBJECTIVE

GLUT1 deficiency syndrome (Glut1DS) is a treatable neurometabolic disease that causes a wide range of neurologic symptoms in children and adults. However, its diagnosis relies on an invasive test, that is, a lumbar puncture (LP) to measure glycorrhachia, and sometimes complex molecular analyses of the SLC2A1 gene. This procedure limits the number of patients able to receive the standard of care. We wished to validate the diagnostic performance of METAglut1, a simple blood test that quantifies GLUT1 on the erythrocyte surface.

METHODS

We performed a multicenter validation study in France, involving 33 centers. We studied 2 patient cohorts: a prospective cohort consisting of patients with a clinical suspicion of Glut1DS explored through the reference strategy, that is, LP and analyses of the SLC2A1 gene, and a retrospective cohort that included patients previously diagnosed with Glut1DS. All patients were blind-tested with METAglut1.

RESULTS

We analyzed 428 patients in the prospective cohort, including 15 patients newly diagnosed with Glut1DS, and 67 patients in the retrospective cohort. METAglut1 was 80% sensitive and >99% specific for the diagnosis of Glut1DS. Concordance analyses showed a substantial agreement between METAglut1 and glycorrhachia. In the prospective cohort, the positive predictive value of METAglut1 was slightly higher than that of glycorrhachia. METAglut1 succeeded to identify patients with Glut1DS with SCL2A1 mosaicism and variants of unknown significance.

DISCUSSION

METAglut1 is an easily performed, robust, and noninvasive diagnostic test for the diagnosis of Glut1DS, which allows wide screening of children and adults, including those with atypical forms of this treatable condition.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that a positive METAglut1 test accurately distinguishes patients with suspected GLUT1 deficiency syndrome from other neurologic syndromes as compared with invasive and genetic testing.

Quantitative determination of SLC2A1 variant functional effects in GLUT1 deficiency syndrome

OBJECTIVE

The goal of this study is to demonstrate the utility of a growth assay to quantify the functional impact of single nucleotide variants (SNVs) in SLC2A1, the gene responsible for Glut1DS.

METHODS

The functional impact of 40 SNVs in SLC2A1 was quantitatively determined in HAP1 cells in which SLC2A1 is required for growth. Donor libraries were introduced into the endogenous SLC2A1 gene in HAP1-Lig4KO cells using CRISPR/Cas9. Cell populations were harvested and sequenced to quantify the effect of variants on growth and generate a functional score. Quantitative functional scores were compared to 3-OMG uptake, SLC2A1 cell surface expression, CADD score, and clinical data, including CSF/blood glucose ratio.

RESULTS

Nonsense variants (N = 3) were reduced in cell culture over time resulting in negative scores (mean score: -1.15 ± 0.17), whereas synonymous variants (N = 10) were not depleted (mean score: 0.25 ± 0.12) (P < 2e-16). Missense variants (N = 27) yielded a range of functional scores including slightly negative scores, supporting a partial function and intermediate phenotype. Several variants with normal results on either cell surface expression (p.N34S and p.W65R) or 3-OMG uptake (p.W65R) had negative functional scores. There is a moderate but significant correlation between our functional scores and CADD scores.

INTERPRETATION

Cell growth is useful to quantitatively determine the functional effects of SLC2A1 variants. Nonsense variants were reliably distinguished from benign variants in this in vitro functional assay. For facilitating early diagnosis and therapeutic intervention, future work is needed to determine the functional effect of every possible variant in SLC2A1.

Establishment of a flow cytometry screening method for patients with glucose transporter 1 deficiency syndrome

Objective

We assessed the usefulness of flow cytometry as a functional assay to measure glucose transporter 1 (GLUT1) levels on the surface of red blood cells (RBCs) from Japanese patients with glucose transporter 1 deficiency syndrome (Glut1DS).

Methods

We recruited 13 genetically confirmed Glut1DS patients with a solute carrier family 2 member 1 (SLC2A1) mutation (eight missense, one frameshift, two nonsense, and two deletion) and one clinically suspected Glut1DS-like patient without an SLC2A1 mutation, and collected whole blood with informed consent. We stained pelleted RBCs (1 μL) from the patients with a Glut1.RBD ligand and anti-glycophorin A antibody, which recognizes a human RBC membrane protein, and analyzed the cells using flow cytometry.

Results

Relative GLUT1 levels quantified by flow cytometry in 11 of 13 patients with definite Glut1DS were 90% below those of healthy controls. Relative GLUT1 levels were not reduced in two of 13 Glut1DS patients who had a missense mutation and no intellectual disability and one Glut1DS-like patient without an SLC2A1 mutation. Relative GLUT1 levels were significantly reduced in Glut1DS patients with an SLC2A1 mutation, more severe intellectual disability, and spasticity.

Conclusions

This method to detect GLUT1 levels on RBCs is simple and appears to be an appropriate screening assay to identify severe Glut1DS patients in the early stage before the development of irreversible neurologic damage caused by chronic hypoglycorrhachia.

Novel cerebrospinal fluid biomarkers of glucose transporter type 1 deficiency syndrome: Implications beyond the brain's energy deficit

We used next-generation metabolic screening to identify new biomarkers for improved diagnosis and pathophysiological understanding of glucose transporter type 1 deficiency syndrome (GLUT1DS), comparing metabolic cerebrospinal fluid (CSF) profiles from 12 patients to those of 116 controls. This confirmed decreased CSF glucose and lactate levels in patients with GLUT1DS and increased glutamine at group level. We identified three novel biomarkers significantly decreased in patients, namely gluconic + galactonic acid, xylose-α1-3-glucose, and xylose-α1-3-xylose-α1-3-glucose, of which the latter two have not previously been identified in body fluids. CSF concentrations of gluconic + galactonic acid may be reduced as these metabolites could serve as alternative substrates for the pentose phosphate pathway. Xylose-α1-3-glucose and xylose-α1-3-xylose-α1-3-glucose may originate from glycosylated proteins; their decreased levels are hypothetically the consequence of insufficient glucose, one of two substrates for O-glucosylation. Since many proteins are O-glucosylated, this deficiency may affect cellular processes and thus contribute to GLUT1DS pathophysiology. The novel CSF biomarkers have the potential to improve the biochemical diagnosis of GLUT1DS. Our findings imply that brain glucose deficiency in GLUT1DS may cause disruptions at the cellular level that go beyond energy metabolism, underlining the importance of developing treatment strategies that directly target cerebral glucose uptake.

One Molecule for Mental Nourishment and More: Glucose Transporter Type 1—Biology and Deficiency Syndrome

Glucose transporter type 1 (Glut1) is the main transporter involved in the cellular uptake of glucose into many tissues, and is highly expressed in the brain and in erythrocytes. Glut1 deficiency syndrome is caused mainly by mutations of the SLC2A1 gene, impairing passive glucose transport across the blood–brain barrier. All age groups, from infants to adults, may be affected, with age-specific symptoms. In its classic form, the syndrome presents as an early-onset drug-resistant metabolic epileptic encephalopathy with a complex movement disorder and developmental delay. In later-onset forms, complex motor disorder predominates, with dystonia, ataxia, chorea or spasticity, often triggered by fasting. Diagnosis is confirmed by hypoglycorrhachia (below 45 mg/dL) with normal blood glucose, 18F-fluorodeoxyglucose positron emission tomography, and genetic analysis showing pathogenic SLC2A1 variants. There are also ongoing positive studies on erythrocytes’ Glut1 surface expression using flow cytometry. The standard treatment still consists of ketogenic therapies supplying ketones as alternative brain fuel. Anaplerotic substances may provide alternative energy sources. Understanding the complex interactions of Glut1 with other tissues, its signaling function for brain angiogenesis and gliosis, and the complex regulation of glucose transportation, including compensatory mechanisms in different tissues, will hopefully advance therapy. Ongoing research for future interventions is focusing on small molecules to restore Glut1, metabolic stimulation, and SLC2A1 transfer strategies. Newborn screening, early identification and treatment could minimize the neurodevelopmental disease consequences. Furthermore, understanding Glut1 relative deficiency or inhibition in inflammation, neurodegenerative disorders, and viral infections including COVID-19 and other settings could provide clues for future therapeutic approaches.

ILAE classification and definition of epilepsy syndromes with onset in neonates and infants: Position statement by the ILAE Task Force on Nosology and Definitions

The International League Against Epilepsy (ILAE) Task Force on Nosology and Definitions proposes a classification and definition of epilepsy syndromes in the neonate and infant with seizure onset up to 2 years of age. The incidence of epilepsy is high in this age group and epilepsy is frequently associated with significant comorbidities and mortality. The licensing of syndrome specific antiseizure medications following randomized controlled trials and the development of precision, gene-related therapies are two of the drivers defining the electroclinical phenotypes of syndromes with onset in infancy. The principal aim of this proposal, consistent with the 2017 ILAE Classification of the Epilepsies, is to support epilepsy diagnosis and emphasize the importance of classifying epilepsy in an individual both by syndrome and etiology. For each syndrome, we report epidemiology, clinical course, seizure types, electroencephalography (EEG), neuroimaging, genetics, and differential diagnosis. Syndromes are separated into self-limited syndromes, where there is likely to be spontaneous remission and developmental and epileptic encephalopathies, diseases where there is developmental impairment related to both the underlying etiology independent of epileptiform activity and the epileptic encephalopathy. The emerging class of etiology-specific epilepsy syndromes, where there is a specific etiology for the epilepsy that is associated with a clearly defined, relatively uniform, and distinct clinical phenotype in most affected individuals as well as consistent EEG, neuroimaging, and/or genetic correlates, is presented. The number of etiology-defined syndromes will continue to increase, and these newly described syndromes will in time be incorporated into this classification. The tables summarize mandatory features, cautionary alerts, and exclusionary features for the common syndromes. Guidance is given on the criteria for syndrome diagnosis in resource-limited regions where laboratory confirmation, including EEG, MRI, and genetic testing, might not be available.

Current challenges in the pathophysiology, diagnosis, and treatment of paroxysmal movement disorders

INTRODUCTION

Paroxysmal movement disorders mostly comprise paroxysmal dyskinesia and episodic ataxia, and can be the consequence of a genetic disorder or symptomatic of an acquired disease.

AREAS COVERED

In this review, the authors focused on certain hot-topic issues in the field: the respective contribution of the cerebellum and striatum to the generation of paroxysmal dyskinesia, the importance of striatal cAMP turnover in the pathogenesis of paroxysmal dyskinesia, the treatable causes of paroxysmal movement disorders not to be missed, with a special emphasis on the treatment strategy to bypass the glucose transport defect in paroxysmal movement disorders due to GLUT1 deficiency, and functional paroxysmal movement disorders.

EXPERT OPINION

Treatment of genetic causes of paroxysmal movement disorders is evolving towards precision medicine with targeted gene-specific therapy. Alteration of the cerebellar output and modulation of the striatal cAMP turnover offer new perspectives for experimental therapeutics, at least for paroxysmal movement disorders due to selected causes. Further characterization of cell-specific molecular pathways or network dysfunctions that are critically involved in the pathogenesis of paroxysmal movement disorders will likely result in the identification of new biomarkers and testing of innovative-targeted therapeutics.

Glut1 Deficiency Syndrome (Glut1DS): State of the art in 2020 and recommendations of the international Glut1DS study group

Glut1 deficiency syndrome (Glut1DS) is a brain energy failure syndrome caused by impaired glucose transport across brain tissue barriers. Glucose diffusion across tissue barriers is facilitated by a family of proteins including glucose transporter type 1 (Glut1). Patients are treated effectively with ketogenic diet therapies (KDT) that provide a supplemental fuel, namely ketone bodies, for brain energy metabolism. The increasing complexity of Glut1DS, since its original description in 1991, now demands an international consensus statement regarding diagnosis and treatment. International experts (n = 23) developed a consensus statement utilizing their collective professional experience, responses to a standardized questionnaire, and serial discussions of wide-ranging issues related to Glut1DS. Key clinical features signaling the onset of Glut1DS are eye-head movement abnormalities, seizures, neurodevelopmental impairment, deceleration of head growth, and movement disorders. Diagnosis is confirmed by the presence of these clinical signs, hypoglycorrhachia documented by lumbar puncture, and genetic analysis showing pathogenic SLC2A1 variants. KDT represent standard choices with Glut1DS-specific recommendations regarding duration, composition, and management. Ongoing research has identified future interventions to restore Glut1 protein content and function. Clinical manifestations are influenced by patient age, genetic complexity, and novel therapeutic interventions. All clinical phenotypes will benefit from a better understanding of Glut1DS natural history throughout the life cycle and from improved guidelines facilitating early diagnosis and prompt treatment. Often, the presenting seizures are treated initially with antiseizure drugs before the cause of the epilepsy is ascertained and appropriate KDT are initiated. Initial drug treatment fails to treat the underlying metabolic disturbance during early brain development, contributing to the long-term disease burden. Impaired development of the brain microvasculature is one such complication of delayed Glut1DS treatment in the postnatal period. This international consensus statement should facilitate prompt diagnosis and guide best standard of care for Glut1DS throughout the life cycle.

Clinical and Genetic Overview of Paroxysmal Movement Disorders and Episodic Ataxias

Paroxysmal movement disorders (PMDs) are rare neurological diseases typically manifesting with intermittent attacks of abnormal involuntary movements. Two main categories of PMDs are recognized based on the phenomenology: Paroxysmal dyskinesias (PxDs) are characterized by transient episodes hyperkinetic movement disorders, while attacks of cerebellar dysfunction are the hallmark of episodic ataxias (EAs). From an etiological point of view, both primary (genetic) and secondary (acquired) causes of PMDs are known. Recognition and diagnosis of PMDs is based on personal and familial medical history, physical examination, detailed reconstruction of ictal phenomenology, neuroimaging, and genetic analysis. Neurophysiological or laboratory tests are reserved for selected cases. Genetic knowledge of PMDs has been largely incremented by the advent of next generation sequencing (NGS) methodologies. The wide number of genes involved in the pathogenesis of PMDs reflects a high complexity of molecular bases of neurotransmission in cerebellar and basal ganglia circuits. In consideration of the broad genetic and phenotypic heterogeneity, a NGS approach by targeted panel for movement disorders, clinical or whole exome sequencing should be preferred, whenever possible, to a single gene approach, in order to increase diagnostic rate. This review is focused on clinical and genetic features of PMDs with the aim to (1) help clinicians to recognize, diagnose and treat patients with PMDs as well as to (2) provide an overview of genes and molecular mechanisms underlying these intriguing neurogenetic disorders.

Usefulness of diagnostic tools in a GLUT1 deficiency syndrome patient with 2 inherited mutations

In some patients with GLUT1 deficiency syndrome (GLUT1-DS), the diagnosis can be difficult to reach. We report a child with 2 inherited mutations suggesting an autosomal recessive transmission of SLC2A1 mutations.

METHODS

The child and her parents were explored with erythrocyte 3-O-methyl-d-Glucose uptake, glucose uptake in oocytes expressing GLUT1 with the gene mutations and measure of the expression of GLUT1 at the surface of the circulating red blood cells by flow cytometry (METAglut1™ test).

RESULTS

Both erythrocyte glucose uptake and glucose uptake in oocyte with the patient's mutations did not support the diagnosis of a mild GLUT1-DS phenotype with autosomal recessive transmission of SLC2A1 mutations. Instead, GLUT-1 expression at the surface of the erythrocytes appeared to better correlate with the clinical phenotypes in this family.

CONCLUSION

The diagnostic value of these functional/expression tools need to be further studied with a focus on mild phenotype of GLUT1-DS.

The spectrum of paroxysmal dyskinesias

Paroxysmal dyskinesias (PxD) comprise a group of heterogeneous syndromes characterized by recurrent attacks of mainly dystonia and/or chorea, without loss of consciousness. PxD have been classified according to their triggers and duration as paroxysmal kinesigenic dyskinesia, paroxysmal nonkinesigenic dyskinesia and paroxysmal exertion-induced dyskinesia. Of note, the spectrum of genetic and nongenetic conditions underlying PxD is continuously increasing, but not always a phenotype–etiology correlation exists. This creates a challenge in the diagnostic work-up, increased by the fact that most of these episodes are unwitnessed. Furthermore, other paroxysmal disorders, included those of psychogenic origin, should be considered in the differential diagnosis. In this review, some key points for the diagnosis are provided, as well as the appropriate treatment and future approaches discussed.

Plasma oxysterols: biomarkers for diagnosis and treatment in spastic paraplegia type 5

The hereditary spastic paraplegias are an expanding and heterogeneous group of disorders characterized by spasticity in the lower limbs. Plasma biomarkers are needed to guide the genetic testing of spastic paraplegia. Spastic paraplegia type 5 (SPG5) is an autosomal recessive spastic paraplegia due to mutations in CYP7B1, which encodes a cytochrome P450 7α-hydroxylase implicated in cholesterol and bile acids metabolism. We developed a method based on ultra-performance liquid chromatography electrospray tandem mass spectrometry to validate two plasma 25-hydroxycholesterol (25-OHC) and 27-hydroxycholesterol (27-OHC) as diagnostic biomarkers in a cohort of 21 patients with SPG5. For 14 patients, SPG5 was initially suspected on the basis of genetic analysis, and then confirmed by increased plasma 25-OHC, 27-OHC and their ratio to total cholesterol. For seven patients, the diagnosis was initially based on elevated plasma oxysterol levels and confirmed by the identification of two causal CYP7B1 mutations. The receiver operating characteristic curves analysis showed that 25-OHC, 27-OHC and their ratio to total cholesterol discriminated between SPG5 patients and healthy controls with 100% sensitivity and specificity. Taking advantage of the robustness of these plasma oxysterols, we then conducted a phase II therapeutic trial in 12 patients and tested whether candidate molecules (atorvastatin, chenodeoxycholic acid and resveratrol) can lower plasma oxysterols and improve bile acids profile. The trial consisted of a three-period, three-treatment crossover study and the six different sequences of three treatments were randomized. Using a linear mixed effect regression model with a random intercept, we observed that atorvastatin decreased moderately plasma 27-OHC (∼30%, P < 0.001) but did not change 27-OHC to total cholesterol ratio or 25-OHC levels. We also found an abnormal bile acids profile in SPG5 patients, with significantly decreased total serum bile acids associated with a relative decrease of ursodeoxycholic and lithocholic acids compared to deoxycholic acid. Treatment with chenodeoxycholic acid restored bile acids profile in SPG5 patients. Therefore, the combination of atorvastatin and chenodeoxycholic acid may be worth considering for the treatment of SPG5 patients but the neurological benefit of these metabolic interventions remains to be evaluated in phase III therapeutic trials using clinical, imaging and/or electrophysiological outcome measures with sufficient effect sizes. Overall, our study indicates that plasma 25-OHC and 27-OHC are robust diagnostic biomarkers of SPG5 and shall be used as first-line investigations in any patient with unexplained spastic paraplegia.

The glucose transporter type 1 (Glut1) syndromes

The glucose transporter type 1 (Glut1) is the most important energy carrier of the brain across the blood-brain barrier. In the early nineties, the first genetic defect of Glut1 was described and known as the Glut1 deficiency syndrome (Glut1-DS). It is characterized by early infantile seizures, developmental delay, microcephaly, and ataxia. Recently, milder variants have also been described. The clinical picture of Glut1 defects and the understanding of the pathophysiology of this disease have significantly grown. A special form of transient movement disorders, the paroxysmal exertion-induced dyskinesia (PED), absence epilepsies particularly with an early onset absence epilepsy (EOAE) and childhood absence epilepsy (CAE), myoclonic astatic epilepsy (MAE), episodic choreoathetosis and spasticity (CSE), and focal epilepsy can be based on a Glut1 defect. Despite the rarity of these diseases, the Glut1 syndromes are of high clinical interest since a very effective therapy, the ketogenic diet, can improve or reverse symptoms especially if it is started as early as possible. The present article summarizes the clinical features of Glut1 syndromes and discusses the underlying genetic mutations, including the available data on functional tests as well as the genotype-phenotype correlations. This article is part of the Special Issue "Individualized Epilepsy Management: Medicines, Surgery and Beyond".

Phenotypes, genotypes, and the management of paroxysmal movement disorders

As a consequence of the genomic revolution, a large number of publications describing paroxysmal movement disorders have been published in the last few years, shedding light on their molecular pathology. Routine gene testing is not necessary to guide treatment for typical forms of paroxysmal kinesigenic dyskinesia (PKD), paroxysmal nonkinesigenic dyskinesia (PNKD), and episodic ataxia type 1 or 2. It can, however, be helpful in the management of atypical or complex cases, especially for genetic counselling, treatment strategies, and the offer of preimplantation genetic diagnosis. Antiepileptic drugs remain the treatment of choice for PKD and episodic ataxia type 1, benzodiazepines are often useful for PNKD, and episodic ataxia type 2 benefits from acetazolamide regardless of the genetic etiology.

WHAT THE PAPER ADDS

A growing number of genes have been associated with classic and newly described paroxysmal movement disorders. Paroxysmal movement disorders share common mechanisms and clinical features with other neurological paroxysmal phenomena including epilepsy and migraine.

Triheptanoin for the treatment of brain energy deficit: A 14-year experience

Triheptanoin is an odd-chain triglyceride with anaplerotic properties-that is, replenishing the pool of metabolic intermediates in the Krebs cycle. Unlike even-chain fatty acids metabolized to acetyl-CoA only, triheptanoin can indeed provide both acetyl-CoA and propionyl-CoA, two key carbon sources for the Krebs cycle. Triheptanoin was initially used in patients with long-chain fatty acid oxidation disorders. The first demonstration of the possible benefit of triheptanoin for brain energy deficit came from a patient with pyruvate carboxylase deficiency, a severe metabolic disease that affects anaplerosis in the brain. In an open-label study, triheptanoin was then shown to decrease nonepileptic paroxysmal manifestations by 90% in patients with glucose transporter 1 deficiency syndrome, a disease that affects glucose transport into the brain. ³¹ P magnetic resonance spectroscopy studies also indicated that triheptanoin was able to correct bioenergetics in the brain of patients with Huntington disease, a neurodegenerative disease associated with brain energy deficit. Altogether, these studies indicate that triheptanoin can be a treatment for brain energy deficit related to altered anaplerosis and/or glucose metabolism. © 2017 Wiley Periodicals, Inc.