Atypical GLUT1 deficiency with prominent movement disorder responsive to ketogenic diet

The diagnostic and prognostic role of cerebrospinal fluid biomarkers in glucose transporter 1 deficiency: a systematic review

The purpose of this study is to investigate the diagnostic and prognostic role of cerebrospinal fluid (CSF) biomarkers in the diagnostic work-up of glucose transporter 1 (GLUT1) deficiency. Reported here is a systematic review according to PRISMA guidelines collecting clinical and biochemical data about all published patients who underwent CSF analysis. Clinical phenotypes were compared between groups defined by the levels of CSF glucose (≤ 2.2 mmol/L versus > 2.2 mmol/L), CSF/blood glucose ratio (≤ 0.45 versus > 0.45), and CSF lactate (≤ 1 mmol/L versus > 1 mmol/L). Five hundred sixty-two patients fulfilled the inclusion criteria with a mean age at the diagnosis of 8.6 ± 6.7 years. Patients with CSF glucose ≤ 2.2 mmol/L and CSF/blood glucose ratio ≤ 0.45 presented with an earlier onset of symptoms (16.4 ± 22.0 versus 54.4 ± 45.9 months, p < 0.01; 15.7 ± 23.8 versus 40.9 ± 38.0 months, p < 0.01) and received an earlier molecular genetic confirmation (92.1 ± 72.8 versus 157.1 ± 106.2 months, p < 0.01). CSF glucose ≤ 2.2 mmol/L was consistently associated with response to ketogenic diet (p = 0.018) and antiseizure medications (p = 0.025). CSF/blood glucose ratio ≤ 0.45 was significantly associated with absence seizures (p = 0.048), paroxysmal exercise-induced dyskinesia (p = 0.046), and intellectual disability (p = 0.016) while CSF lactate > 1 mmol/L was associated with a response to antiseizure medications (p = 0.026) but not to ketogenic diet.Conclusions:This systematic review supported the diagnostic usefulness of lumbar puncture for the early identification of patients with GLUT1 deficiency responsive to treatments especially if they present with co-occurring epilepsy, movement, and neurodevelopmental disorders. What is Known: • Phenotypes of GLUT1 deficiency syndrome range between early epileptic and developmental encephalopathy to paroxysmal movement disorders and developmental impairment What is New: • CSF blood/glucose ratio may predict better than CSF glucose the diagnosis in children presenting with early onset absences • CSF blood/glucose ratio may predict better than CSF glucose the diagnosis in children presenting with paroxysmal exercise induced dyskinesia and intellectual disability. • CSF glucose may predict better than CSF blood/glucose and lactate the response to ketogenic diet and antiseizure medications.

Canine paroxysmal dyskinesia-a review

Paroxysmal dyskinesias (PDs) are a group of involuntary, hyperkinetic movement disorders that recur episodically and may last seconds to hours. An important feature of PD is that there is no loss of consciousness during the episode. Using a clinical classification, three main types of PDs have been distinguished in canine PD: (1) paroxysmal kinesigenic dyskinesia (PKD) that commences after (sudden) movements, (2) paroxysmal non-kinesigenic dyskinesia (PNKD) not associated with exercise and can occur at rest, and (3) paroxysmal exertion-induced dyskinesia (PED) associated with fatigue. Canine PDs are diagnosed based on the clinical presentation, history, and phenomenology. For the latter, a video recording of the paroxysmal event is extremely useful. An etiological classification of canine PDs includes genetic (proven and suspected), reactive (drug-induced, toxic, metabolic, and dietary), structural (neoplasia, inflammatory, and other structural causes), and unknown causes. In this review, an overview of all reported canine PDs is provided with emphasis on phenotype, genotype, and, where possible, pathophysiology and treatment for each reported canine PD.

Genetic Testing of Movements Disorders: A Review of Clinical Utility

Currently, pathogenic variants in more than 500 different genes are known to cause various movement disorders. The increasing accessibility and reducing cost of genetic testing has resulted in increasing clinical use of genetic testing for the diagnosis of movement disorders. However, the optimal use case(s) for genetic testing at a patient level remain ill-defined. Here, we review the utility of genetic testing in patients with movement disorders and also highlight current challenges and limitations that need to be considered when making decisions about genetic testing in clinical practice.

Highlights

The utility of genetic testing extends across multiple clinical and non-clinical domains. Here we review different aspects of the utility of genetic testing for movement disorders and the numerous associated challenges and limitations. These factors should be weighed on a case-by-case basis when requesting genetic tests in clinical practice.

Molecular Genetics of GLUT1DS Italian Pediatric Cohort: 10 Novel Disease-Related Variants and Structural Analysis

GLUT1 deficiency syndrome (GLUT1DS1; OMIM #606777) is a rare genetic metabolic disease, characterized by infantile-onset epileptic encephalopathy, global developmental delay, progressive microcephaly, and movement disorders (e.g., spasticity and dystonia). It is caused by heterozygous mutations in the SLC2A1 gene, which encodes the GLUT1 protein, a glucose transporter across the blood-brain barrier (BBB). Most commonly, these variants arise de novo resulting in sporadic cases, although several familial cases with AD inheritance pattern have been described. Twenty-seven Italian pediatric patients, clinically suspect of GLUT1DS from both sporadic and familial cases, have been enrolled. We detected by trios sequencing analysis 25 different variants causing GLUT1DS. Of these, 40% of the identified variants (10 out of 25) had never been reported before, including missense, frameshift, and splice site variants. Their structural mapping on the X-ray structure of GLUT1 strongly suggested the potential pathogenic effects of these novel disease-related mutations, broadening the genotypic spectrum heterogeneity found in the SLC2A1 gene. Moreover, 24% is located in a vulnerable region of the GLUT1 protein that involves transmembrane 4 and 5 helices encoded by exon 4, confirming a mutational hotspot in the SLC2A1 gene. Lastly, we investigated possible correlations between mutation type and clinical and biochemical data observed in our GLUT1DS cohort, revealing that splice site and frameshift variants are related to a more severe phenotype and low CSF parameters.

Voluntary Behavior and Training Conditions Modulate in vivo Extracellular Glucose and Lactate in the Mouse Primary Motor Cortex

Learning or performing new behaviors requires significant neuronal signaling and is metabolically demanding. The metabolic cost of performing a behavior is mitigated by exposure and practice which result in diminished signaling and metabolic requirements. We examined the impact of novel and habituated wheel running, as well as effortful behaviors on the modulation of extracellular glucose and lactate using biosensors inserted in the primary motor cortex of mice. We found that motor behaviors produce increases in extracellular lactate and decreases in extracellular glucose in the primary motor cortex. These effects were modulated by experience, novelty and intensity of the behavior. The increase in extracellular lactate appears to be strongly associated with novelty of a behavior as well as the difficulty of performing a behavior. Our observations are consistent with the view that a main function of aerobic glycolysis is not to fuel the current neuronal activity but to sustain new bio-infrastructure as learning changes neural networks, chiefly through the shuttling of glucose derived carbons into the pentose phosphate pathway for the biosynthesis of nucleotides.

SLC2A1 and Its Related Epileptic Phenotypes

Glucose transporter type 1 deficiency syndrome (GLUT1DS) is caused by heterozygous, mostly de novo, mutations in SLC2A1 gene encoding the glucose transporter GLUT1, the most relevant energy transporter in the blood–brain barrier. GLUT1DS includes a broad spectrum of neurologic disturbances, from severe encephalopathy with developmental delay, to epilepsy, movement disorders, acquired microcephaly and atypical mild forms. For diagnosis, lumbar puncture and genetic analysis are necessary and complementary; an immediate response to ketogenic diet supports the diagnosis in case of high suspicion of disease and negative exams. The ketogenic diet is the first-line treatment and should be established at the initial stages of disease.

NGS-Based Diagnosis of Treatable Neurogenetic Disorders in Adults: Opportunities and Challenges

The identification of neurological disorders by next-generation sequencing (NGS)-based gene panels has helped clinicians understand the underlying physiopathology, resulting in personalized treatment for some rare diseases. While the phenotype of distinct neurogenetic disorders is generally well-known in childhood, in adulthood, the phenotype can be unspecific and make the standard diagnostic approach more complex. Here we present three unrelated adults with various neurological manifestations who were successfully diagnosed using NGS, allowing for the initiation of potentially life-changing treatments. A 63-year-old woman with progressive cognitive decline, pyramidal signs, and bilateral cataract was treated by chenodeoxycholic acid following the diagnosis of cerebrotendinous xanthomatosis due to a homozygous variant in CYP27A1. A 32-year-old man with adult-onset spastic paraplegia, in whom a variant in ABCD1 confirmed an X-linked adrenoleukodystrophy, was treated with corticoids for adrenal insufficiency. The third patient, a 28-year-old woman with early-onset developmental delay, epilepsy, and movement disorders was treated with a ketogenic diet following the identification of a variant in SLC2A1, confirming a glucose transporter type 1 deficiency syndrome. This case study illustrates the challenges in the timely diagnosis of medically actionable neurogenetic conditions, but also the considerable potential for improving patient health through modern sequencing technologies.

Paroxysmal Genetic Movement Disorders and Epilepsy

Paroxysmal movement disorders include paroxysmal kinesigenic dyskinesia, paroxysmal non-kinesigenic dyskinesia, paroxysmal exercise-induced dyskinesia, and episodic ataxias. In recent years, there has been renewed interest and recognition of these disorders and their intersection with epilepsy, at the molecular and pathophysiological levels. In this review, we discuss how these distinct phenotypes were constructed from a historical perspective and discuss how they are currently coalescing into established genetic etiologies with extensive pleiotropy, emphasizing clinical phenotyping important for diagnosis and for interpreting results from genetic testing. We discuss insights on the pathophysiology of select disorders and describe shared mechanisms that overlap treatment principles in some of these disorders. In the near future, it is likely that a growing number of genes will be described associating movement disorders and epilepsy, in parallel with improved understanding of disease mechanisms leading to more effective treatments.

Exogenous Ketone Supplements Improved Motor Performance in Preclinical Rodent Models

Nutritional ketosis has been proven effective for neurometabolic conditions and disorders linked to metabolic dysregulation. While inducing nutritional ketosis, ketogenic diet (KD) can improve motor performance in the context of certain disease states, but it is unknown whether exogenous ketone supplements—alternatives to KDs—may have similar effects. Therefore, we investigated the effect of ketone supplements on motor performance, using accelerating rotarod test and on postexercise blood glucose and R-beta-hydroxybutyrate (R-βHB) levels in rodent models with and without pathology. The effect of KD, butanediol (BD), ketone-ester (KE), ketone-salt (KS), and their combination (KE + KS: KEKS) or mixtures with medium chain triglyceride (MCT) (KE + MCT: KEMCT; KS + MCT: KSMCT) was tested in Sprague-Dawley (SPD) and WAG/Rij (WR) rats and in GLUT-1 Deficiency Syndrome (G1D) mice. Motor performance was enhanced by KEMCT acutely, KE and KS subchronically in SPD rats, by KEKS and KEMCT groups in WR rats, and by KE chronically in G1D mice. We demonstrated that exogenous ketone supplementation improved motor performance to various degrees in rodent models, while effectively elevated R-βHB and in some cases offsets postexercise blood glucose elevations. Our results suggest that improvement of motor performance varies depending on the strain of rodents, specific ketone formulation, age, and exposure frequency.

Variety of symptoms of GLUT1 deficiency syndrome in three-generation family

OBJECTIVE

Glucose transporter type 1 deficiency (G1D) syndrome is generally a genetic disorder because of a mutation of the SLC2A1 gene. The clinical picture of G1D is heterogeneous. The aim of this paper was to present the case of G1D, recognized in a three-generation family, caused by missense mutation p.Arg92Trp in SLC2A1 gene, and showing high clinical heterogeneity and evolution of symptoms over time.

METHODS

Three-generation family members, showing symptoms suggesting G1D, have been characterized in terms of the clinical picture, electroencephalogram (EEG) recordings, brain neuroimaging, and the psychological assessment data. All subjects were offered genetic testing of the SLC2A1 gene.

RESULTS

We sequenced the SLC2A1 gene in the proband of the family and identified the c.274C > T variant (p.Arg92Trp). The presence of the same mutation was confirmed in all affected family members; however, significant variations in the clinical picture among them were observed. In addition to the typical symptoms for G1D (e.g., epilepsy, intellectual disability), patients presented movement disorders, stiffness, and dysarthria, as well as psychiatric symptoms. After using the ketogenic diet, epileptic seizures disappeared, but the rest of the symptoms were resistant to treatment.

CONCLUSIONS

Despite the same underlying mutation, clinical symptoms may vary among members of one family. Different clinical symptoms are observed depending on the patient's age. Not all symptoms occur in all patients within one family despite the same genetic background. However, the importance of early therapy for the clinical course of the disease requires further study.

Glut1 deficiency is a rare but treatable cause of childhood absence epilepsy with atypical features

Glucose transporter type 1 deficiency syndrome (GLUT1-DS) is a rare genetic disorder caused by pathogenic variants in SLC2A1, resulting in impaired glucose uptake through the blood-brain barrier. Our objective is to analyze the frequency of GLUT1-DS in patients with absences with atypical features. Sequencing analysis and detection of copy number variation of the SLC2A1 gene was carried out in patients with atypical absences including: early-onset absence, intellectual disability, additional seizure types, refractory epilepsy, associated movement disorders, as well as those who have first-degree relatives with absence epilepsy or atypical EEG ictal discharges. Of the 43 patients analyzed, pathogenic variations were found in 2 (4.6%). Six atypical characteristics were found in these 2 patients. The greater the number of atypical characteristics presenting in patients with absence seizures, the more likely they have a SLC2A1 mutation. Although GLUT1-DS is an infrequent cause of absence epilepsy, recognizing this disorder is important, since initiation of a ketogenic diet can reduce the frequency of seizures, the severity of the movement disorder, and also improve the quality of life of the patients and their families.

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".

Paroxysmal ocular movements - an early sign in Glut1 deficiency Syndrome

The authors describe a 3-year-old female, diagnosed with GLUT1 deficiency Syndrome, with a previously unreported mutation in exon 7 of the SLC2A1 gene: c.968_972 + 3del P. (Val323Alafs*53), characterized by a classic phenotypic of acquired microcephaly, developmental delay, ataxia, spasticity, and epilepsy. Ketogenic diet was started at the age of 30 months with epilepsy improvement. She presented paroxysmal ocular movements in the first 12 months of life, recently defined as "aberrant gaze saccades", that are present in the early phase of visual system development, being one of the first disease signs, but easily disregarded. Recognizing these particular ocular movements would allow an early diagnosis, followed by ketogenic diet implementation, improving significantly the prognosis and the neurological development of those children.

How Can a Ketogenic Diet Improve Motor Function?

A ketogenic diet (KD) is a normocaloric diet composed by high fat (80-90%), low carbohydrate, and low protein consumption that induces fasting-like effects. KD increases ketone body (KBs) production and its concentration in the blood, providing the brain an alternative energy supply that enhances oxidative mitochondrial metabolism. In addition to its profound impact on neuro-metabolism and bioenergetics, the neuroprotective effect of specific polyunsaturated fatty acids and KBs involves pleiotropic mechanisms, such as the modulation of neuronal membrane excitability, inflammation, or reactive oxygen species production. KD is a therapy that has been used for almost a century to treat medically intractable epilepsy and has been increasingly explored in a number of neurological diseases. Motor function has also been shown to be improved by KD and/or medium-chain triglyceride diets in rodent models of Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and spinal cord injury. These studies have proposed that KD may induce a modification in synaptic morphology and function, involving ionic channels, glutamatergic transmission, or synaptic vesicular cycling machinery. However, little is understood about the molecular mechanisms underlying the impact of KD on motor function and the perspectives of its use to acquire the neuromuscular effects. The aim of this review is to explore the conditions through which KD might improve motor function. First, we will describe the main consequences of KD exposure in tissues involved in motor function. Second, we will report and discuss the relevance of KD in pre-clinical and clinical trials in the major diseases presenting motor dysfunction.

Paroxysmal eye-head movements in Glut1 deficiency syndrome

Objective:

To describe a characteristic paroxysmal eye–head movement disorder that occurs in infants with Glut1 deficiency syndrome (Glut1 DS).

Methods:

We retrospectively reviewed the medical charts of 101 patients with Glut1 DS to obtain clinical data about episodic abnormal eye movements and analyzed video recordings of 18 eye movement episodes from 10 patients.

Results:

A documented history of paroxysmal abnormal eye movements was found in 32/101 patients (32%), and a detailed description was available in 18 patients, presented here. Episodes started before age 6 months in 15/18 patients (83%), and preceded the onset of seizures in 10/16 patients (63%) who experienced both types of episodes. Eye movement episodes resolved, with or without treatment, by 6 years of age in 7/8 patients with documented long-term course. Episodes were brief (usually <5 minutes). Video analysis revealed that the eye movements were rapid, multidirectional, and often accompanied by a head movement in the same direction. Eye movements were separated by clear intervals of fixation, usually ranging from 200 to 800 ms. The movements were consistent with eye–head gaze saccades. These movements can be distinguished from opsoclonus by the presence of a clear intermovement fixation interval and the association of a same-direction head movement.

Conclusions:

Paroxysmal eye–head movements, for which we suggest the term aberrant gaze saccades, are an early symptom of Glut1 DS in infancy. Recognition of the episodes will facilitate prompt diagnosis of this treatable neurodevelopmental disorder.

Ketone ester supplementation attenuates seizure activity, and improves behavior and hippocampal synaptic plasticity in an Angelman syndrome mouse model

Angelman syndrome (AS) is a rare genetic and neurological disorder presenting with seizures, developmental delay, ataxia, and lack of speech. Previous studies have indicated that oxidative stress-dependent metabolic dysfunction may underlie the phenotypic deficits reported in the AS mouse model. While the ketogenic diet (KD) has been used to protect against oxidative stress and has successfully treated refractory epilepsy in AS case studies, issues arise due to its strict adherence requirements, in addition to selective eating habits and weight issues reported in patients with AS. We hypothesized that ketone ester supplementation would mimic the KD as an anticonvulsant and improve the behavioral and synaptic plasticity deficits in vivo. AS mice were supplemented R,S-1,3-butanediol acetoacetate diester (KE) ad libitum for eight weeks. KE administration improved motor coordination, learning and memory, and synaptic plasticity in AS mice. The KE was also anticonvulsant and altered brain amino acid metabolism in AS treated animals. Our findings suggest that KE supplementation produces sustained ketosis and ameliorates many phenotypes in the AS mouse model, and should be investigated further for future clinical use.

Paroxysmal Nonepileptic Events in Glut1 Deficiency

Movement disorders are a major feature of Glut1 deficiency. As recently identified in adults with paroxysmal exercise‐induced dystonia, similar events were reported in pediatric Glut1 deficiency. In a case series, parent videos of regular motor state and paroxysmal events were requested from children with Glut1 deficiency on clinical follow‐up. A questionnaire was sent out to 60 families. Videos of nonparoxysmal/paroxysmal states in 3 children illustrated the ataxic‐dystonic, choreatiform, and dyskinetic‐dystonic nature of paroxysmal events. Fifty‐six evaluated questionnaires confirmed this observation in 73% of patients. Events appeared to increase with age, were triggered by low ketosis, sleep deprivation, and physical exercise, and unrelated to sex, hypoglycorrhachia, SLC2A1 mutations, or type of ketogenic diet. We conclude that paroxysmal events are a major clinical feature in Glut1 deficieny, linking the pediatric disease to adult Glut1D‐associated exercise‐induced paroxysmal dyskinesias.

Glucose Transporter Type I Deficiency (G1D) at 25 (1990-2015): Presumptions, Facts, and the Lives of Persons With This Rare Disease

BACKGROUND

As is often the case for rare diseases, the number of published reviews and case reports of glucose transporter type I deficiency (G1D) approaches or exceeds that of original research. This can indicate medical interest, but also scientific stagnation.

METHODS

In assessing this state of affairs here, we focus not on what is peculiar or disparate about G1D, but on the assumptions that have reigned thus far undisputed, and critique them as a potential impediment to progress. To summarize the most common G1D phenotype, we trace the 25-year story of G1D in parallel with the natural history of one of two index patients, identified in 1990 by one of us (G.M.R.) and brought up to date by the other (J.M.P.) while later examining widely repeated but little-scrutinized statements. Among them are those that pertain to assumptions about brain fuels; energy failure; cerebrospinal glucose concentration; the purpose of ketogenic diet; the role of the defective blood-brain barrier; genotype-phenotype correlations; a bewildering array of phenotypes; ictogenesis, seizures, and the electroencephalograph; the use of mice to model the disorder; and what treatments may and may not be expected to accomplish.

RESULTS

We reach the forgone conclusion that the proper study of mankind-and of one of its ailments (G1D) -is man itself (rather than mice, isolated cells, or extrapolated inferences) and propose a framework for rigorous investigation that we hope will lead to a better understanding and to better treatments for this and for rare disorders in general.

CONCLUSIONS

These considerations, together with experience drawn from other disorders, lead, as a logical consequence, to the nullification of the view that therapeutic development (i.e., trials) for rare diseases could or should be accelerated without the most vigorous scientific scrutiny: trial and error constitute an inseparable couple, such that, at the present time, hastening the former is bound to precipitate the latter.

From splitting GLUT1 deficiency syndromes to overlapping phenotypes

INTRODUCTION

Glucose transporter type 1 deficiency syndrome (GLUT1DS) is a rare genetic disorder due to mutations or deletions in SLC2A1, resulting in impaired glucose uptake through the blood brain barrier. The classic phenotype includes pharmacoresistant epilepsy, intellectual deficiency, microcephaly and complex movement disorders, with hypoglycorrhachia, but milder phenotypes have been described (carbohydrate-responsive phenotype, dystonia and ataxia without epilepsy, paroxysmal exertion-induced dystonia). The aim of our study was to provide a comprehensive overview of GLUT1DS in a French cohort.

METHODS

265 patients were referred to the French national laboratory for molecular screening between July 2006 and January 2012. Mutations in SLC2A1 were detected in 58 patients, with detailed clinical data available in 24, including clinical features with a focus on their epileptic pattern and electroencephalographic findings, biochemical findings and neuroimaging findings.

RESULTS

53 point mutations and 5 deletions in SLC2A1 were identified. Most patients (87.5%) exhibited classic phenotype with intellectual deficiency (41.7%), epilepsy (75%) or movement disorder (29%) as initial symptoms at a medium age of 7.5 months, but diagnostic was delayed in most cases (median age at diagnostic 8 years 5 months). Sensitivity to fasting or exertion in combination with those 3 main symptoms were the main differences between mutated and negative patients (p < 0.001). Patients with myoclonic seizures (52%) evolved with more severe intellectual deficiency and movement disorders compared with those with Early Onset Absence Epilepsy (38%). Three patients evolved from a classic phenotype during early childhood to a movement disorder predominant phenotype at a late childhood/adulthood.

CONCLUSIONS

Our data confirm that the classic phenotype is the most frequent in GLUT1DS. Myoclonic seizures are a distinctive feature of severe forms. However a great variability among patients and overlapping through life from milder classic phenotype to paroxysmal-prominent- movement-disorder phenotype are possible, thus making it difficult to identify definite genotype-phenotype correlations.

Brain and behavioral perturbations in rats following Western diet access

Energy dense "Western" diets (WD) are known to cause obesity as well as learning and memory impairments, blood-brain barrier damage, and psychological disturbances. Impaired glucose (GLUT1) and monocarboxylate (MCT1) transport may play a role in diet-induced dementia development. In contrast, ketogenic diets (KD) have been shown to be neuroprotective. We assessed the effect of 10, 40 and 90 days WD, KD and Chow maintenance on spontaneous alternation (SA) and vicarious trial and error (VTE) behaviors in male rats, then analyzed blood glucose, insulin, and ketone levels; and hippocampal GLUT1 and MCT1 mRNA. Compared to Chow and KD, rats fed WD had increased 90 day insulin levels. SA was decreased in WD rats at 10, but not 40 or 90 days. VTE was perturbed in WD-fed rats, particularly at 10 and 90 days, indicating hippocampal deficits. WD rats had lower hippocampal GLUT1 and MCT1 expression compared to Chow and KD, and KD rats had increased 90 day MCT1 expression compared to Chow and WD. These data suggest that WD reduces glucose and monocarboxylate transport at the hippocampus, which may result in learning and memory deficits. Further, KD consumption may be useful for MCT1 transporter recovery, which may benefit cognition.

Symptomatic west syndrome secondary to glucose transporter-1(GLUT1) deficiency with complete response to 4:1 ketogenic diet

Glucose transporter type 1 (GLUT-1) deficiency is a rare cause of preventable intellectual disability. Intellectual disability is due to refractory seizures in infancy and reduced supply of glucose to the brain. The authors report a third born male child of consanguineous parentage who presented with infantile spasms. Initially, he had refractory convulsions of focal, generalised, and myoclonic jerks, not responding to multiple anticonvulsants. He also had choreoathetoid movements. On examination he had microcephaly. MRI of brain was normal and EEG showing diffuse slowing. CSF glucose was low compared to blood glucose, with normal lactate and without any cells, hence diagnosed as Glucose transporter-1 deficiency and started on ketogenic diet. With ketogenic diet, child was seizure free, anticonvulsants decreased to 2 from 5, and improvements in development were noted.

Glucide metabolism disorders (excluding glycogen myopathies)

Glucide metabolism comprises pathways for transport, intermediate metabolism, utilization, and storage of carbohydrates. Defects affect multiple organs and present as systemic diseases. Neurological symptoms result from hypoglycemia, lactic acidosis, or inadequate storage of complex glucide molecules in neurological tissues. In glycogen storage disorders hypoglycemia indicates hepatic involvement, weakness and muscle cramps muscle involvement. Hypoglycemia is also the leading neurological symptom in disorders of gluconeogenesis. Disorders of galactose and fructose metabolism are rare, detectable by neonatal screening, and manifest following dietary intake of these sugars. Rare defects within the pentose metabolism constitute a new area of inborn metabolic disorders and may present with neurological symptoms. Treatment of these disorders involves the avoidance of fasting, dietary treatment eliminating specific carbohydrates, and enzyme replacement therapy in individual glycogen storage diseases.GLUT1 deficiency syndrome, a specific disorder of glucose transport into brain, results in global developmental delay, early-onset epilepsy, and a complex movement disorder. Treatment with a high-fat, low-carbohydrate ketogenic diet provides ketones as an alternative fuel to the brain and restores brain energy metabolism. Recently paroxysmal exertion-induced dyskinesia and stomatin-deficient cryohydrocytosis have been identified as an allelic disorder to GLUT1 deficiency equally responding to a ketogenic diet.

Dietary Treatments and New Therapeutic Perspective in GLUT1 Deficiency Syndrome

OPINION STATEMENT

GLUT1 deficiency syndrome (GLUT1DS) results from impaired glucose transport into the brain: awareness of its wide phenotypic spectrum is a prerequisite in order to ensure an early diagnosis, treating the patients is the subsequent challenge to allow prompt compensation for the brain's lack of fuel. The ketogenic diet (KD) plays a primary role in the treatment of GLUT1DS because it provides ketone bodies as an alternative source to meet the demands of energy of the brain. Therefore, we recommend early initiation of the KD based on the assumption that early diagnosis and treatment improves the long term neurological outcome: the classic KD (4:1 or 3:1) at the present time is the most proven and effective in GLUT1DS. A KD should be continued at least until adolescence, although there are reports of good tolerability even in adulthood, possibly with a less rigorous ratio; in our experience seizure and movement disorder control can be achieved by a 2:1 ketogenic ratio but the relationship between ketosis and neurodevelopmental outcome remains undetermined. Other types of KDs can, therefore, be considered. The Modified Atkins diet, for example, is also well tolerated and provides effective symptom control; furthermore, this diet has the advantage of being easy to prepare and more palatable, which are important requirements for good compliance. Nevertheless, about 20 % of these patients have compliance trouble or the same diet loses its effectiveness over time; for these reasons, new therapeutic strategies are currently under investigation but further studies on pathophysiological mechanisms and potential effects of novel "diets" or "therapies" are needed for this new pathology.

The many faces of Glut1 deficiency syndrome

Glucose transporter protein type 1 deficiency syndrome is a metabolic disorder manifesting as cognitive impairment, acquired microcephaly, epilepsy, and/or movement disorder caused by mutations in the SLC2A1 gene. We describe a cohort of isolated and familial cases of glucose transporter protein type 1 deficiency syndrome, emphasizing seizure semiology, electroencephalographic (EEG) features, treatment response and mutation pathogenicity. SLC2A1 mutations were detected in 3 sporadic and 4 familial cases. In addition, mutations were identified in 9 clinically unaffected family members in 2 families. The phenotypic spectrum of glucose transporter protein type 1 deficiency is wider than previously recognized, with considerable intra-familial variation. Diagnosis requires either hypoglycorrachia followed by SLC2A1 sequencing or direct gene sequencing. A ketogenic diet should be the first line of treatment, but more flexible diets, like the Atkins modified diet, can also be followed. Carbonic anhydrase inhibitors, such as acetazolamide or zonisamide, can be effective for seizure control.

Metabolic epilepsy: an update

Inborn errors of metabolism comprise a large class of genetic diseases involving disorders of metabolism. Presentation is usually in the neonatal period or infancy but can occur at any time, even in adulthood. Seizures are frequent symptom in inborn errors of metabolism, with no specific seizure types or EEG signatures. The diagnosis of a genetic defect or an inborn error of metabolism often results in requests for a vast array of biochemical and molecular tests leading to an expensive workup. However a specific diagnosis of metabolic disorders in epileptic patients may provide the possibility of specific treatments that can improve seizures. In a few metabolic diseases, epilepsy responds to specific treatments based on diet or supplementation of cofactors (vitamin-responsive epilepsies), but for most of them specific treatment is unfortunately not available, and conventional antiepileptic drugs must be used, often with no satisfactory success. In this review we present an overview of metabolic epilepsies based on various criteria such as treatability, age of onset, seizure type, and pathogenetic background.

Phenotypic spectrum of glucose transporter type 1 deficiency syndrome (Glut1 DS)

Glut1 deficiency syndrome (Glut1 DS) was originally described in 1991 as a developmental encephalopathy characterized by infantile onset refractory epilepsy, cognitive impairment, and mixed motor abnormalities including spasticity, ataxia, and dystonia. The clinical condition is caused by impaired glucose transport across the blood brain barrier. The past 5 years have seen a dramatic expansion in the range of clinical syndromes that are recognized to occur with Glut1 DS. In particular, there has been greater recognition of milder phenotypes. Absence epilepsy and other idiopathic generalized epilepsy syndromes may occur with seizure onset in childhood or adulthood. A number of patients present predominantly with movement disorders, sometimes without any accompanying seizures. In particular, paroxysmal exertional dyskinesia is now a well-documented clinical feature that occurs in individuals with Glut1 DS. A clue to the diagnosis in patients with paroxysmal symptoms may be the triggering of episodes during fasting or exercise. Intellectual impairment may range from severe to very mild. Awareness of the broad range of potential clinical phenotypes associated with Glut1 DS will facilitate earlier diagnosis of this treatable neurologic condition. The ketogenic diet is the mainstay of treatment and nourishes the starving symptomatic brain during development.

Movement disorders in GLUT1 deficiency syndrome respond to the modified Atkins diet

BACKGROUND

Movement disorders are a prominent feature of glucose transporter-1 (GLUT1) deficiency syndrome (GLUT1DS). First-choice treatment is a ketogenic diet, but compliance is poor. We have investigated the effect of the modified Atkins diet as an alternative treatment for movement disorders in GLUT1DS.

METHODS

Four patients with GLUT1DS ages 15 to 30 years who had movement disorders as the most prominent feature were prospectively evaluated after initiation of the modified Atkins diet. Movement disorders included dystonia, ataxia, myoclonus, and spasticity, either continuous or paroxysmal, triggered by action or exercise. Duration of treatment ranged from 3 months to 16 months.

RESULTS

All patients reached mild to moderate ketosis and experienced remarkable improvement in the frequency and severity of paroxysmal movement disorders. Cognitive function also improved subjectively.

CONCLUSIONS

The modified Atkins diet is an effective and feasible alternative to the ketogenic diet for the treatment of GLUT1DS-related paroxysmal movement disorders in adolescence and adulthood.

Valproic acid enhances glucose transport in the cultured brain astrocytes of glucose transporter 1 heterozygous mice

Glucose transporter 1 facilitates glucose transport across the blood-brain barrier. By increasing histone acetylation at the SLC2A1 promotor, valproic acid could increase SLC2A1 gene expression. This study was designed to evaluate the effects of valproic acid on glucose transport in astrocyte cultures derived from SLC2A1 heterozygous mice. Primary astrocyte cultures were prepared from the cerebral cortex of 1-day-old neonatal mice. Cultured astrocytes were incubated with valproic acid (0.05, 0.5, and 5 mM) for 48 hours. On day 3, the glucose uptake capacity of the astrocytes was measured by using (14)C-2-Deoxy-d-glucose under zero-trans conditions. The heterozygous astrocyte glucose uptake treated with valproic acid (0.05 and 0.5 mM) for 48 hours was significantly increased compared with the untreated control heterozygous astrocytes. Our findings demonstrate that valproic acid increased glucose transport capacity in SLC2A1 heterozygous cerebral astrocytes.

Glut1 deficiency (G1D): epilepsy and metabolic dysfunction in a mouse model of the most common human phenotype

Brain glucose supplies most of the carbon required for acetyl-coenzyme A (acetyl-CoA) generation (an important step for myelin synthesis) and for neurotransmitter production via further metabolism of acetyl-CoA in the tricarboxylic acid (TCA) cycle. However, it is not known whether reduced brain glucose transporter type I (GLUT-1) activity, the hallmark of the GLUT-1 deficiency (G1D) syndrome, leads to acetyl-CoA, TCA or neurotransmitter depletion. This question is relevant because, in its most common form in man, G1D is associated with cerebral hypomyelination (manifested as microcephaly) and epilepsy, suggestive of acetyl-CoA depletion and neurotransmitter dysfunction, respectively. Yet, brain metabolism in G1D remains underexplored both theoretically and experimentally, partly because computational models of limited brain glucose transport are subordinate to metabolic assumptions and partly because current hemizygous G1D mouse models manifest a mild phenotype not easily amenable to investigation. In contrast, adult antisense G1D mice replicate the human phenotype of spontaneous epilepsy associated with robust thalamocortical electrical oscillations. Additionally, and in consonance with human metabolic imaging observations, thalamus and cerebral cortex display the lowest GLUT-1 expression and glucose uptake in the mutant mouse. This depletion of brain glucose is associated with diminished plasma fatty acids and elevated ketone body levels, and with decreased brain acetyl-CoA and fatty acid contents, consistent with brain ketone body consumption and with stimulation of brain beta-oxidation and/or diminished cerebral lipid synthesis. In contrast with other epilepsies, astrocyte glutamine synthetase expression, cerebral TCA cycle intermediates, amino acid and amine neurotransmitter contents are also intact in G1D. The data suggest that the TCA cycle is preserved in G1D because reduced glycolysis and acetyl-CoA formation can be balanced by enhanced ketone body utilization. These results are incompatible with global cerebral energy failure or with neurotransmitter depletion as responsible for epilepsy in G1D and point to an unknown mechanism by which glycolysis critically regulates cortical excitability.

Glut1 deficiency: when to suspect and how to diagnose?

Impaired glucose transport across the blood-brain barrier results in GLUT1 deficiency syndrome (GLUT1-DS), characterized by infantile seizures, developmental delay, acquired microcephaly, spasticity, ataxia, and hypoglycorrhachia. A part from this classic phenotype, clinical conditions associated with a deficiency of GLUT1 are highly variable and several atypical variants have been described; in particular, patients with movement disorders, but without seizures, with paroxysmal exertion-induced dyskinesia, have been reported. Most patients carry heterozygous de novo mutations in the GLUT1-gene but autosomal dominant and recessive transmission has been identified. Diagnosis is based on low cerebrospinal fluid glucose, in the absence of hypoglycemia, and it is confirmed by molecular analysis of the GLUT1-gene and by glucose uptake studies and immunoreactivity in human erythrocytes. Treatment with a ketogenic diet results in marked improvement of seizures and movement disorders. This review summarizes recent advances in understanding of GLUT1-DS and highlights the diagnostic and therapeutic approach to GLUT1-DS.

Differential diagnosis of chorea

Chorea is a common movement disorder that can be caused by a large variety of structural, neurochemical (including pharmacologic), or metabolic disturbances to basal ganglia function, indicating the vulnerability of this brain region. The diagnosis is rarely indicated by the simple phenotypic appearance of chorea, and can be challenging, with many patients remaining undiagnosed. Clues to diagnosis may be found in the patient's family or medical history, on neurologic examination, or upon laboratory testing and neuroimaging. Increasingly, advances in genetic medicine are identifying new disorders and expanding the phenotype of recognized conditions. Although most therapies at present are supportive, correct diagnosis is essential for appropriate genetic counseling, and ultimately, for future molecular therapies.

Milder phenotypes of glucose transporter type 1 deficiency syndrome

Glucose transporter type 1 deficiency syndrome (GLUT1DS) is a treatable condition resulting from impaired glucose transport into the brain. The classical presentation is with infantile-onset epilepsy and severe developmental delay. Non-classical phenotypes with movement disorders and early-onset absence epilepsy are increasingly recognized and the clinical spectrum is expanding. The hallmark is hypoglycorrhachia (cerebrospinal fluid [CSF] glucose<2.2 mmol/l) in the presence of normoglycaemia with a CSF/blood glucose ratio of less than 0.4. GLUT1DS is due to a mutation in the solute carrier family 2, member 1 gene (SLC2A1). We present five individuals (four males, one female), all of whom had a mild phenotype, highlighting the importance of considering this diagnosis in unexplained neurological disorders associated with mild learning difficulties, subtle motor delay, early-onset absence epilepsy, fluctuating gait disorders, and/or dystonia. The mean age at diagnosis was 8 years 8 months. This paper also shows phenotypical parallels between GLUT1DS and paroxysmal exertion-induced dyskinesia.

T295M-associated Glut1 deficiency syndrome with normal erythrocyte 3-OMG uptake

PURPOSE

Glucose transporter type 1 (Glut1) is expressed in vascular endothelial cells comprising blood-brain barrier. Glut1 deficiency syndrome is characterized by low cerebrospinal fluid (CSF) concentration of glucose with normoglycemia, infantile seizure, acquired microcephaly, developmental delay and ataxia. As Glut1 is also expressed in erythrocytes, the diagnosis is confirmed by a decreased uptake of 3-O-methylglucose (3-OMG) into erythrocytes. However, patients with T295M mutation in the Glut1 gene show normal 3-OMG uptake. An in vitro study has proved that the T295M affects efflux rather than influx of glucose, explaining the discrepancy. However, the normal 3-OMG uptake in erythrocytes still indicates a possibility that the phenotype associated with this particular mutation may be milder. We compared the phenotype of three T295M-associated patients with that of other Glut1-deficient patients.

PATIENTS AND METHODS

Two patients are from our clinic and one is a patient reported elsewhere. The phenotype and biochemical data of patients with mutations other than T295M were obtained from a review and our previous report.

RESULTS

Despite the normal 3-OMG uptake into erythrocytes, all patients with T295M showed decreased glucose levels in CSF (33, 31 and 38mg/dl, respectively). The levels were comparable to those in patients with mutations other than T295M (31±4.3mg/dl (n=45)). All patients had convulsion, ataxia, speech delay, microcephaly and spasticity.

CONCLUSION

Despite the normal 3-OMG uptake in erythrocytes, phenotype of T295M-associated Glut1 deficiency was not significantly different from that of patients with a deficient 3-OMG uptake, indicating that T295M affects the glucose transport at the blood-brain barrier as much as other mutations.

Pre- and postprandial electroencephalography in glucose transporter type 1 deficiency syndrome: an illustrative case to discuss the concept of carbohydrate responsiveness

Glucose transporter type 1 deficiency syndrome is an inborn error of glucose transport across the blood-brain barrier with hypoglychorrachia. Patients usually present developmental delay, movement disorders, seizures, and acquired microcephaly, variously associated and leading to different phenotypes. We report a 3-year-old girl affected by glucose transporter type 1 deficiency syndrome with carbohydrate responsiveness. Her history was characterized by worsening of ataxia with an increasing interval to the last food intake, occurrence of seizures in the morning before breakfast, slowing of electroencephalogram (EEG) background activity with the appearance of epileptiform discharges during preprandial recordings, and improvement of the electroclinical picture after food intake. By adding a new case to the pertinent literature, we stress the role of pre- and postprandial EEG recordings for the identification of individuals potentially affected by glucose transporter type 1 deficiency syndrome. We also provide a possible physiopathological interpretation of EEG changes related to food intake.

Paroxysmal exercise-induced dyskinesia, writer's cramp, migraine with aura and absence epilepsy in twin brothers with a novel SLC2A1 missense mutation

We report two monochorionic twins that progressively developed, between ages 5 and 10, a combination of episodic neurological disorders including paroxysmal exercise-induced dyskinesia, migraine without or with aura, absence seizures and writer's cramp. CSF/serum glucose ratio was moderately decreased in both patients. Mutational analysis of SLC2A1 gene identified a de novo heterozygous missense mutation in exon 4. This novel mutation has been previously showed to disrupt glucose transport in vitro. Both patients showed immediate and near-complete response to ketogenic diet. This clinical observation suggests that a high index of suspicion for GLUT1 deficiency syndrome is warranted in evaluating patients with multiple neurological paroxysmal events.

The spectrum of movement disorders in Glut-1 deficiency

To assess the spectrum of movement disorders, we reviewed video recordings and charts of 57 patients with Glut-1 deficiency. Eighty-nine percent of patients with Glut-1 deficiency syndrome had a disturbance of gait. The most frequent gait abnormalities were ataxic-spastic and ataxic. Action limb dystonia was observed in 86% of cases and mild chorea in 75%. Cerebellar action tremor was seen in 70% of patients, myoclonus in 16%, and dyspraxia in 21%. Nonepileptic paroxysmal events occurred in 28% of patients, and included episodes of ataxia, weakness, Parkinsonism and nonkinesogenic dyskinesias. The 40 patients (70%) who were on the ketogenic diet had less severe gait disturbances but more dystonia, chorea, tremor, myoclonus, dyspraxia, and paroxysmal events compared with the 17 patients on a conventional diet. Poor dietary compliance and low ketonuria appear to trigger the paroxysmal events in some patients. Gait disturbances and movement disorders are frequent in patients with Glut-1 deficiency and are signs of chronic and intermittent pyramidal, cerebellar and extrapyramidal circuit dysfunction. These clinical symptoms reflect chronic nutrient deficiency during brain development and may be mitigated by chronic ketosis.

Glucose transporter type 1 deficiency: ketogenic diet in three patients with atypical phenotype

Glucose transporter type I deficiency syndrome (GLUT-1 DS) is an inborn error of glucose transport characterized by seizures, developmental delay, spasticity, acquired microcephaly and ataxia. Diagnosis is based on the finding of low cerebrospinal fluid glucose, in the absence of hypoglycemia, and identification of GLUT-1 gene mutation on chromosome 1. The classic phenotype is a severe form of early onset epileptic encephalopathy, but patient with different clinical presentation have been reported expanding the clinical spectrum. In particular, many patients show a prominent movement disorder other than epilepsy. It is known that this disease represents a treatable condition and ketogenic diet (KD) is the elective treatment in GLUT-1 DS patients. We report on KD in three unrelated Italian GLUT-1 DS female patients, diagnosed in early adulthood, all presenting with an atypical phenotype. Preliminary results seem to demonstrate efficacy of KD on paroxysmal movement disorder while positive effect on cognitive impairment result less evident.

Glucose transporter-1 deficiency syndrome: the expanding clinical and genetic spectrum of a treatable disorder

Glucose transporter-1 deficiency syndrome is caused by mutations in the SLC2A1 gene in the majority of patients and results in impaired glucose transport into the brain. From 2004-2008, 132 requests for mutational analysis of the SLC2A1 gene were studied by automated Sanger sequencing and multiplex ligation-dependent probe amplification. Mutations in the SLC2A1 gene were detected in 54 patients (41%) and subsequently in three clinically affected family members. In these 57 patients we identified 49 different mutations, including six multiple exon deletions, six known mutations and 37 novel mutations (13 missense, five nonsense, 13 frame shift, four splice site and two translation initiation mutations). Clinical data were retrospectively collected from referring physicians by means of a questionnaire. Three different phenotypes were recognized: (i) the classical phenotype (84%), subdivided into early-onset (<2 years) (65%) and late-onset (18%); (ii) a non-classical phenotype, with mental retardation and movement disorder, without epilepsy (15%); and (iii) one adult case of glucose transporter-1 deficiency syndrome with minimal symptoms. Recognizing glucose transporter-1 deficiency syndrome is important, since a ketogenic diet was effective in most of the patients with epilepsy (86%) and also reduced movement disorders in 48% of the patients with a classical phenotype and 71% of the patients with a non-classical phenotype. The average delay in diagnosing classical glucose transporter-1 deficiency syndrome was 6.6 years (range 1 month-16 years). Cerebrospinal fluid glucose was below 2.5 mmol/l (range 0.9-2.4 mmol/l) in all patients and cerebrospinal fluid : blood glucose ratio was below 0.50 in all but one patient (range 0.19-0.52). Cerebrospinal fluid lactate was low to normal in all patients. Our relatively large series of 57 patients with glucose transporter-1 deficiency syndrome allowed us to identify correlations between genotype, phenotype and biochemical data. Type of mutation was related to the severity of mental retardation and the presence of complex movement disorders. Cerebrospinal fluid : blood glucose ratio was related to type of mutation and phenotype. In conclusion, a substantial number of the patients with glucose transporter-1 deficiency syndrome do not have epilepsy. Our study demonstrates that a lumbar puncture provides the diagnostic clue to glucose transporter-1 deficiency syndrome and can thereby dramatically reduce diagnostic delay to allow early start of the ketogenic diet.

Early-onset absence epilepsy caused by mutations in the glucose transporter GLUT1

Absence epilepsies of childhood are heterogeneous with most cases following complex inheritance. Those cases with onset before 4 years of age represent a poorly studied subset. We screened 34 patients with early-onset absence epilepsy for mutations in SLC2A1, the gene encoding the GLUT1 glucose transporter. Mutations leading to reduced protein function were found in 12% (4/34) of patients. Two mutations arose de novo, and two were familial. These findings suggest GLUT1 deficiency underlies a significant proportion of early-onset absence epilepsy, which has both genetic counseling and treatment implications because the ketogenic diet is effective in GLUT1 deficiency.

The expanding phenotype of GLUT1-deficiency syndrome

Transport of glucose from the bloodstream across the blood-brain barrier to the central nervous system is facilitated by glucose transport protein type 1 (GLUT1), the first member of the solute carrier family 2 (SLC2). Heterozygous mutations in the GLUT1/SLC2A1 gene, occurring de novo or inherited as an autosomal dominant trait, result in cerebral energy failure and a clinical condition termed GLUT1-deficiency syndrome (GLUT1-DS). Clinical features usually comprise motor and mental developmental delay, seizures with infantile onset, deceleration of head growth often resulting in acquired microcephaly, and a movement disorder with ataxia, dystonia, and spasticity. Subsequent to the delineation of this classic phenotype the variability of signs and symptoms in GLUT1-DS is being recognized. Patients with (i) carbohydrate-responsive symptoms, with (ii) predominant ataxia or dystonia, but without seizures, and with (iii) paroxysmal exertion-induced dyskinesia and seizures have been reported. Common laboratory hallmark in all phenotypes is the reduced glucose level in cerebrospinal fluid with lowered CSF-to-blood glucose ratio. Treatment with a ketogenic diet results in marked improvement of seizures and movement disorders.