Clinical Aspects of Glucose Transporter Type 1 Deficiency: Information From a Global Registry

Metabolic pathways and genes involved in treatable and non-treatable metabolic epilepsies. A comprehensive review and metabolic pathway analysis

More than 600 different metabolic disorders can lead to a clinical picture, where seizures are a main neurological manifestation, either as the primary clinical finding or as a part of a more complex phenotype. For these metabolic disorders, the term "metabolic epilepsy" is commonly used. About one in six metabolic epilepsies is treatable, constituting a well-defined subset of metabolic disorders, which is amenable to treatment targeting the primary cause of the seizures and reducing or preventing associated complications. However, the majority of metabolic disorders currently lack effective treatment, making them a major challenge both in clinical practice and in research. Herein, we provide an overview of both treatable and non-treatable metabolic epilepsies and discuss our current understanding of these disorders. We also perform pathway analysis in order to compare the pathways in which the genes associated with treatable and non-treatable metabolic epilepsies take part. This approach may orientate the research to particular pathways and explore novel treatment algorithms.

Diagnosis and treatment recommendations for glucose transporter 1 deficiency syndrome

BACKGROUND

Glucose transporter 1 deficiency syndrome (Glut1DS) was initially reported by De Vivo and colleagues in 1991. This disease arises from mutations in the SLC2A1 and presents with a broad clinical spectrum. It is a treatable neuro-metabolic condition, where prompt diagnosis and initiation of ketogenic dietary therapy can markedly enhance the prognosis. However, due to its rarity, Glut1DS is susceptible to misdiagnosis or missed diagnosis, which can lead to delayed treatment and irreversible dysfunction of the central nervous system. To promote diagnostic awareness and effective treatments, the recommendations for diagnosis and treatment have been developed.

METHODS

The panel on Glut1DS included 28 participants from the members of the Ketogenic Diet Professional Committee of the Chinese Epilepsy Association and Chinese experts with extensive experience in managing Glut1DS. All authors extensively reviewed the literature, and the survey results were discussed in detail over several online meetings. Following multiple deliberative sessions, all participants approved the final manuscript for submission.

RESULTS

Early diagnosis and timely treatment of Glut1DS are crucial for improving prognosis. Physicians should be alert to suspiction of this disease if the following clinical manifestations appear: seizures, episodic or persistent movement disorders (often triggered by fasting, fatigue, or exercise), delayed motor and cognitive development. Characteristic clinical presentations may include seizures combined with movement disorders, episodic eye-head movements, and paroxysmal exercise-induced dyskinesia (PED). In these cases, genetic testing should be promptly completed, and a lumbar puncture should be performed if necessary. The ketogenic diet is internationally recognized as the first-line treatment; the earlier it is started, the better the prognosis. It can effectively control seizures and improve motor disorders. Antiepileptic drug treatment is generally ineffective or provides limited symptom improvement before starting the ketogenic diet.

CONCLUSION

The recommendations provide clinicians with a relatively systematic guide for the rapid identification, diagnosis, and timely treatment of Glut1DS.

Clinical and genetic analysis of children with glucose transporter type 1 deficiency syndrome

Glucose transporter type 1 deficiency syndrome (GLUT1-DS) is a rare metabolic encephalopathy with a wide variety of clinical phenotypes. In the present study, 15 patients diagnosed with GLUT1-DS were selected, all of whom had obvious clinical manifestations and complete genetic testing. Their clinical data and genetic reports were collated. All patients were provided with a ketogenic diet (KD) and an improvement in their symptoms was observed during a follow-up period of up to 1 year. The results revealed that the 15 cases had clinical symptoms, such as convulsions or dyskinesia. Although none had a cerebrospinal fluid/glucose ratio <0.4, the genetic report revealed that all had the solute carrier family 2 member 1 gene variant, and their clinical symptoms basically improved following the use of the KD. GLUT1-DS is a genetic metabolic disease that causes a series of neurological symptoms due to glucose metabolism disorders in the brain. Low glucose levels in cerebrospinal fluid and genetic testing are key diagnostic criteria, and the KD is a highly effective treatment option. By summarizing and analyzing patients with GLUT1-DS, summarizing clinical characteristics and expanding their gene profile, the findings of the present study may be of clinical significance for the early recognition and diagnosis of the disease, so as to conduct early treatment and shorten the duration of brain energy deficiency. This is of utmost importance for improving the prognosis and quality of life of affected children.

Triheptanoin Did Not Show Benefit versus Placebo for the Treatment of Paroxysmal Movement Disorders in Glut1 Deficiency Syndrome: Results of a Randomized Phase 3 Study

BACKGROUND

Paroxysmal movement disorders are common in Glut1 deficiency syndrome (Glut1DS). Not all patients respond to or tolerate ketogenic diets.

OBJECTIVES

The objective was to evaluate the effectiveness and safety of triheptanoin in reducing the frequency of disabling movement disorders in patients with Glut1DS not receiving a ketogenic diet.

METHODS

UX007G-CL301 was a randomized, double-blind, placebo-controlled, phase 3 crossover study. After a 6-week run-in, eligible patients were randomized 1:1 to the first sequence (triheptanoin/placebo or placebo/triheptanoin) titration plus maintenance, followed by washout and the opposite sequence titration plus maintenance. The placebo (safflower oil) matched the appearance, taste, and smell of triheptanoin. Open-label triheptanoin was administered in the extension. The frequency of disabling paroxysmal movement disorder events per 4 weeks (recorded by diary during maintenance; primary endpoint) was assessed by Wilcoxon rank-sum test.

RESULTS

Forty-three patients (children, n = 16; adults, n = 27) were randomized and treated. There was no difference between triheptanoin and placebo in the mean (interquartile range) number of disabling paroxysmal movement disorder events (14.3 [4.7-38.3] vs. 11.8; [3.2-28.7]; Hodges-Lehmann estimated median difference: 1.46; 95% confidence interval, -1.12 to 4.36; P = 0.2684). Treatment-emergent adverse events were mild/moderate in severity and included diarrhea, vomiting, upper abdominal pain, headache, and nausea. Two patients discontinued the study because of non-serious adverse events that were predominantly gastrointestinal. The study was closed early during the open-label extension because of lack of effectiveness. Seven patients continued to receive triheptanoin compassionately.

CONCLUSION

There were no significant differences between the triheptanoin and placebo groups in the frequency of disabling movement disorder events during the double-blind maintenance period. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Case for supporting astrocyte energetics in glucose transporter 1 deficiency syndrome

In glucose transporter 1 deficiency syndrome (Glut1DS), glucose transport into brain is reduced due to impaired Glut1 function in endothelial cells at the blood-brain barrier. This can lead to shortages of glucose in brain and is thought to contribute to seizures. Ketogenic diets are the first-line treatment and, among many beneficial effects, provide auxiliary fuel in the form of ketone bodies that are largely metabolized by neurons. However, Glut1 is also the main glucose transporter in astrocytes. Here, we review data indicating that glucose shortage may also impact astrocytes in addition to neurons and discuss the expected negative biochemical consequences of compromised astrocytic glucose transport for neurons. Based on these effects, auxiliary fuels are needed for both cell types and adding medium chain triglycerides (MCTs) to ketogenic diets is a biochemically superior treatment for Glut1DS compared to classical ketogenic diets. MCTs provide medium chain fatty acids (MCFAs), which are largely metabolized by astrocytes and not neurons. MCFAs supply energy and contribute carbons for glutamine and γ-aminobutyric acid synthesis, and decanoic acid can also block α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptors. MCTs do not compete with metabolism of ketone bodies mostly occurring in neurons. Triheptanoin, an anaplerotic but also gluconeogenic uneven MCT, may be another potential addition to ketogenic diets, although maintenance of "ketosis" can be difficult. Gene therapy has also targeted both endothelial cells and astrocytes. Other approaches to increase fuel delivery to the brain currently investigated include exchange of Glut1DS erythrocytes with healthy cells, infusion of lactate, and pharmacological improvement of glucose transport. In conclusion, although it remains difficult to assess impaired astrocytic energy metabolism in vivo, astrocytic energy needs are most likely not met by ketogenic diets in Glut1DS. Thus, we propose prospective studies including monitoring of blood MCFA levels to find optimal doses for add-on MCT to ketogenic diets and assessing of short- and long-term outcomes.

GLUT-1DS resistant to ketogenic diet: from clinical feature to in silico analysis. An exemplificative case report with a literature review

Glucose transporter type 1 deficiency syndrome (GLUT-1DS) is characterized by alterations in glucose translocation through the blood-brain barrier (BBB) due to mutation involving the GLUT-1 transporter. The fundamental therapy is ketogenic diet (KD) that provide an alternative energetic substrate - ketone bodies that across the BBB via MCT-1 - for the brain. Symptoms are various and include intractable seizure, acquired microcephalia, abnormal ocular movement, movement disorder, and neurodevelopment delay secondary to an energetic crisis for persistent neuroglycopenia. KD is extremely effective in controlling epileptic seizures and has a positive impact on movement disorders and cognitive impairment. Cases of KD resistance are rare, and only a few of them are reported in the literature, all regarding seizure. Our study describes a peculiar case of GLUT-1DS due to a new deletion involving the first codon of SLC2A1 gene determining a loss of function with a resistance to KD admitted to hospital due to intractable episodes of dystonia. This patient presented a worsening of symptomatology at higher ketonemia values but without hyperketosis and showed a complete resolution of symptomatology while maintaining low ketonemia values. Our study proposes an in-silico genomic and proteomic analysis aimed at explaining the atypical response to KD exhibited by our patient. In this way, we propose a new clinical and research approach based on precision medicine and molecular modelling to be applied to patients with GLUT-1DS resistant to first-line treatment with ketogenic diet by in silico study of genetic and altered protein product.

Metabolic causes of pediatric developmental & epileptic encephalopathies (DEE)- genetic variant analysis in a south Indian cohort

PURPOSE

Drug-resistant epilepsy is seen in patients with inborn errors of metabolism and metabolic dysfunction in neurons is crucial to brain disorders associated with psychomotor impairment. Diagnostic rates of metabolic causes of developmental and epileptic encephalopathy (DEE) using next generation sequencing have been rarely studied in literature.

METHODS

A prospective hospital study was carried out in 384 children with DEE, who underwent genetic testing. Metabolic disorders were evaluated with biochemical blood/urine assays and when required CSF estimations performed.

RESULTS

A total of 154 pathogenic/likely pathogenic variants in 384 children were identified. Out of 384 children, 89 were clinically suspected to have probable or possible metabolic disorders. Pathogenic/likely pathogenic variants in metabolic genes were identified in 39 out of 89 (43.8 %) and promising VUS in 28 (31.4 %). These included variants for progressive myoclonus epilepsies (21; 53.8 %), DEE with focal/multifocal seizures (8; 20.5 %), generalized epilepsy (5;12.8 %), early myoclonic encephalopathy (2; 5.1 %), LGS (1; 2.6 %) and West syndrome (2; 5.1 %).

CONCLUSION

Our cohort demonstrates for the first time from the Indian subcontinent that identification of metabolic variants can guide investigations and has therapeutic implications in patients with variable DEE phenotypes. A high utility is noted with regard to diagnosis and prognostication, given the low yield of available biochemical tests, indicating cost-effectiveness of this approach.

Effects of Sodium Lactate Infusion in Two Girls with Glucose Transporter 1 Deficiency Syndrome

BACKGROUND

Glucose is an important fuel for the brain. In glucose transporter 1 deficiency syndrome (GLUT1DS), the transport of glucose across the blood-brain barrier is limited. Most individuals with GLUT1DS present with developmental problems, epilepsy, and (paroxysmal) movement disorders, and respond favorably to the ketogenic diet. Similar to ketones, lactate is an alternative energy source for the brain. The aim of this study is to investigate whether intravenous infusion of sodium lactate in children with GLUT1DS has beneficial effects on their epilepsy.

METHODS

We performed a proof of principle study with two subjects with GLUT1DS who were not on a ketogenic diet and suffered from absence epilepsy. After overnight fasting, sodium lactate (600 mmol/L) was infused during 120 minutes, under video electroencephalographic (EEG) recording and monitoring of serum lactate, glucose, electrolytes, and pH. Furthermore, the EEGs were compared with pre-/postprandial EEGs of both subjects, obtained shortly before the study.

RESULTS

Fasting EEGs of both subjects showed frequent bilateral, frontocentral polyspike and wave complexes. In one subject, no more epileptic discharges were seen postprandially and after the start of lactate infusion. The EEG of the other subject did not change, neither postprandially nor after lactate infusion. Serum pH, lactate, and sodium changed temporarily during the study.

CONCLUSION

This study suggests that sodium lactate infusion is possible in individuals with GLUT1DS, and may have potential therapeutic effects. Cellular abnormalities, beyond neuronal energy failure, may contribute to the underlying disease mechanisms of GLUT1DS, explaining why not all individuals respond to the supplementation of alternative energy sources.

A concise study of acetazolamide in glucose transporter type 1 deficiency (G1D) epilepsy

Epilepsy constitutes the most common paroxysmal manifestation of glucose transporter type 1 deficiency (G1D) and is generally considered medication-refractory. It can also prove therapeutic diet-resistant. We examined acetazolamide effects in G1D motivated by several longstanding and recent observations: First, the electrographic spike-waves characteristic of absence seizures often resemble those of G1D and, since the 1950s, they have occasionally been treated successfully with acetazolamide, well before G1D was segregated from absence epilepsy as a distinct syndrome. Second, synaptic inhibitory neuron failure characterizes G1D and, in other experimental models, this can be ameliorated by drugs that modify cellular chloride gradient such as acetazolamide. Third, acetazolamide potently stimulates model cell glucose transport in vitro. Seventeen antiepileptic drug or therapeutic diet-refractory individuals with G1D treated with acetazolamide were thus identified via medical record review complemented by worldwide individual survey. Acetazolamide was tolerated and decreased seizures in 76% of them, with 58% of all persons studied experiencing seizure reductions by more than one-half, including those who first manifested myoclonic-astatic epilepsy or infantile spams. Eighty-eight percent of individuals with G1D continued taking acetazolamide for over 6 months, indicating sustained tolerability and efficacy. The results provide a novel avenue for the treatment and mechanistic investigation of G1D.

Expanding genotype-phenotype correlations in FOXG1 syndrome: results from a patient registry

BACKGROUND

We refine the clinical spectrum of FOXG1 syndrome and expand genotype-phenotype correlations through evaluation of 122 individuals enrolled in an international patient registry.

METHODS

The FOXG1 syndrome online patient registry allows for remote collection of caregiver-reported outcomes. Inclusion required documentation of a (likely) pathogenic variant in FOXG1. Caregivers were administered a questionnaire to evaluate clinical severity of core features of FOXG1 syndrome. Genotype-phenotype correlations were determined using nonparametric analyses.

RESULTS

We studied 122 registry participants with FOXG1 syndrome, aged < 12 months to 24 years. Caregivers described delayed or absent developmental milestone attainment, seizures (61%), and movement disorders (58%). Participants harbouring a missense variant had a milder phenotype. Compared to individuals with gene deletions (0%) or nonsense variants (20%), missense variants were associated with more frequent attainment of sitting (73%). Further, individuals with missense variants (41%) achieved independent walking more frequently than those with gene deletions (0%) or frameshift variants (6%). Presence of epilepsy also varied by genotype and was significantly more common in those with gene deletions (81%) compared to missense variants (47%). Individuals with gene deletions were more likely to have higher seizure burden than other genotypes with 53% reporting daily seizures, even at best control. We also observed that truncations preserving the forkhead DNA binding domain were associated with better developmental outcomes.

CONCLUSION

We refine the phenotypic spectrum of neurodevelopmental features associated with FOXG1 syndrome. We strengthen genotype-driven outcomes, where missense variants are associated with a milder clinical course.

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.

Combination of triheptanoin with the ketogenic diet in Glucose transporter type 1 deficiency (G1D)

Fuel influx and metabolism replenish carbon lost during normal neural activity. Ketogenic diets studied in epilepsy, dementia and other disorders do not sustain such replenishment because their ketone body derivatives contain four carbon atoms and are thus devoid of this anaplerotic or net carbon donor capacity. Yet, in these diseases carbon depletion is often inferred from cerebral fluorodeoxyglucose-positron emission tomography. Further, ketogenic diets may prove incompletely therapeutic. These deficiencies provide the motivation for complementation with anaplerotic fuel. However, there are few anaplerotic precursors consumable in clinically sufficient quantities besides those that supply glucose. Five-carbon ketones, stemming from metabolism of the food supplement triheptanoin, are anaplerotic. Triheptanoin can favorably affect Glucose transporter type 1 deficiency (G1D), a carbon-deficiency encephalopathy. However, the triheptanoin constituent heptanoate can compete with ketogenic diet-derived octanoate for metabolism in animals. It can also fuel neoglucogenesis, thus preempting ketosis. These uncertainties can be further accentuated by individual variability in ketogenesis. Therefore, human investigation is essential. Consequently, we examined the compatibility of triheptanoin at maximum tolerable dose with the ketogenic diet in 10 G1D individuals using clinical and electroencephalographic analyses, glycemia, and four- and five-carbon ketosis. 4 of 8 of subjects with pre-triheptanoin beta-hydroxybutyrate levels greater than 2 mM demonstrated a significant reduction in ketosis after triheptanoin. Changes in this and the other measures allowed us to deem the two treatments compatible in the same number of individuals, or 50% of persons in significant beta-hydroxybutyrate ketosis. These results inform the development of individualized anaplerotic modifications to the ketogenic diet.ClinicalTrials.gov registration NCT03301532, first registration: 04/10/2017.

GLUT1-DS Italian registry: past, present, and future: a useful tool for rare disorders

BACKGROUND

GLUT1 deficiency syndrome is a rare, genetically determined neurological disorder for which Ketogenic Dietary Treatment represents the gold standard and lifelong treatment. Patient registries are powerful tools providing insights and real-world data on rare diseases.

OBJECTIVE

To describe the implementation of a national web-based registry for GLUT1-DS.

METHODS

This is a retrospective and prospective, multicenter, observational registry developed in collaboration with the Italian GLUT1-DS association and based on an innovative, flexible and configurable cloud computing technology platform, structured according to the most rigorous requirements for the management of patient's sensitive data. The Glut1 Registry collects baseline and follow-up data on the patient's demographics, history, symptoms, genotype, clinical, and instrumental evaluations and therapies.

RESULTS

Five Centers in Italy joined the registry, and two more Centers are currently joining. In the first two years of running, data from 67 patients (40 females and 27 males) have been collected. Age at symptom onset was within the first year of life in most (40, 60%) patients. The diagnosis was formulated in infancy in almost half of the cases (34, 51%). Symptoms at onset were mainly paroxysmal (mostly epileptic seizure and paroxysmal ocular movement disorder) or mixed paroxysmal and fixed symptoms (mostly psychomotor delay). Most patients (53, 79%) are currently under Ketogenic dietary treatments.

CONCLUSIONS

We describe the principles behind the design, development, and deployment of the web-based nationwide GLUT1-DS registry. It represents a stepping stone towards a more comprehensive understanding of the disease from onset to adulthood. It also represents a virtuous model from a technical, legal, and organizational point of view, thus representing a possible paradigmatic example for other rare disease registry implementation.

Maximum dose, safety, tolerability and ketonemia after triheptanoin in glucose transporter type 1 deficiency (G1D)

Augmentation of anaplerosis, or replenishment of carbon lost during intermediary metabolic transitions, is desirable in energy metabolism defects. Triheptanoin, the triglyceride of 7-carbon heptanoic acid, is anaplerotic via direct oxidation or 5-carbon ketone body generation. In this context, triheptanoin can be used to treat Glucose transporter type 1 deficiency encephalopathy (G1D). An oral triheptanoin dose of 1 g/Kg/day supplies near 35% of the total caloric intake and impacted epilepsy and cognition in G1D. This provided the motivation to establish a maximum, potentially greater dose. Using a 3 + 3 dose-finding approach useful in oncology, we studied three age groups: 4-6, 6.8-10 and 11-16 years old. This allowed us to arrive at a maximum tolerated dose of 45% of daily caloric intake for each group. Safety was ascertained via analytical blood measures. One dose-limiting toxicity, occurring in 1 of 6 subjects, was encountered in the middle age group in the context of frequently reduced gastrointestinal tolerance for all groups. Ketonemia following triheptanoin was determined in another group of G1D subjects. In them, β-ketopentanoate and β-hydroxypentanoate concentrations were robustly but variably increased. These results enable the rigorous clinical investigation of triheptanoin in G1D by providing dosing and initial tolerability, safety and ketonemic potential.ClinicalTrials.gov registration: NCT03041363, first registration 02/02/2017.

Red blood cells as glucose carriers to the human brain: Modulation of cerebral activity by erythrocyte exchange transfusion in Glut1 deficiency (G1D)

Red blood cells circulating through the brain are briefly but closely apposed to the capillary endothelium. We hypothesized that this contact provides a nearly direct pathway for metabolic substrate transfer to neural cells that complements the better characterized plasma to endothelium transfer. While brain function is considered independent of normal fluctuations in blood glucose concentration, this is not borne out by persons with glucose transporter I (GLUT1) deficiency (G1D). In them, encephalopathy is often ameliorated by meal or carbohydrate administration, and this enabled us to test our hypothesis: Since red blood cells contain glucose, and since the red cells of G1D individuals are also deficient in GLUT1, replacing them with normal donor cells via exchange transfusion could augment erythrocyte to neural cell glucose transport via mass action in the setting of unaltered erythrocyte count or plasma glucose abundance. This motivated us to perform red blood cell exchange in 3 G1D persons. There were rapid, favorable and unprecedented changes in cognitive, electroencephalographic and quality-of-life measures. The hypothesized transfer mechanism was further substantiated by in vitro measurement of direct erythrocyte to endothelial cell glucose flux. The results also indicate that the adult intellect is capable of significant enhancement without deliberate practice.      ClinicalTrials.gov registration: NCT04137692 https://clinicaltrials.gov/ct2/show/NCT04137692.

Identification of Glucose Transport Modulators In Vitro and Method for Their Deep Learning Neural Network Behavioral Evaluation in Glucose Transporter 1-Deficient Mice

Metabolic flux augmentation via glucose transport activation may be desirable in glucose transporter 1 (Glut1) deficiency syndrome (G1D) and dementia, whereas suppression might prove useful in cancer. Using lung adenocarcinoma cells that predominantly express Glut1 relative to other glucose transporters, we screened 9,646 compounds for effects on the accumulation of an extracellularly applied fluorescent glucose analog. Five drugs currently prescribed for unrelated indications or preclinically characterized robustly enhanced intracellular fluorescence. Additionally identified were 37 novel activating and nine inhibitory compounds lacking previous biologic characterization. Because few glucose-related mechanistic or pharmacological studies were available for these compounds, we developed a method to quantify G1D mouse behavior to infer potential therapeutic value. To this end, we designed a five-track apparatus to record and evaluate spontaneous locomotion videos. We applied this to a G1D mouse model that replicates the ataxia and other manifestations cardinal to the human disorder. Because the first two drugs that we examined in this manner (baclofen and acetazolamide) exerted various impacts on several gait aspects, we used deep learning neural networks to more comprehensively assess drug effects. Using this method, 49 locomotor parameters differentiated G1D from control mice. Thus, we used parameter modifiability to quantify efficacy on gait. We tested this by measuring the effects of saline as control and glucose as G1D therapy. The results indicate that this in vivo approach can estimate preclinical suitability from the perspective of G1D locomotion. This justifies the use of this method to evaluate our drugs or other interventions and sort candidates for further investigation. SIGNIFICANCE STATEMENT: There are few or no activators and few clinical inhibitors of glucose transport. Using Glut1-rich cells exposed to a glucose analog, we identified, in highthroughput fashion, a series of novel modulators. Some were drugs used to modify unrelated processes and some represented large but little studied chemical compound families. To facilitate their preclinical efficacy characterization regardless of potential mechanism of action, we developed a gait testing platform for deep learning neural network analysis of drug impact on Glut1-deficient mouse locomotion.

Perioperative management of surgical orthodontic treatment in a patient with glucose transporter 1 deficiency: report of a case and review of the literature

INTRODUCTION

Glucose transporter 1 (GLUT1) deficiency is a rare cerebral metabolic disorder caused by the shortage of glucose supply to the brain. For this disease, ketogenic diet therapy is essential. In addition, perioperative management requires not only the continuation of ketogenic diet therapy but also the management of nausea/vomiting, diarrhea, seizures, and infection. However, there have been few reports regarding oral and maxillofacial surgery.

CASE PRESENTATION

We describe a patient with GLUT1 deficiency who underwent orthognathic surgery. An 18-year-old man was referred to our hospital with the chief complaint of mandibular regression. Surgical tolerance was assessed by a fasting test and tooth extraction under general anesthesia, and orthognathic surgery was then performed. For orthognathic surgery, the mandibular dentition had scissor-like occlusion, and it was difficult to arrange the mandible. Therefore, we decided to perform maxillary osteotomy first. After the mandibular dentition was arranged by maxillary osteotomy, sagittal split ramus osteotomy (SSRO) was performed. Intermaxillary fixation (IMF) was necessary for SSRO, and caution was needed to prevent suffocation. The orthognathic surgery was successful, although complications, such as vomiting, diarrhea, and seizures, developed.

CONCLUSION

Surgical orthodontic treatment in GLUT1 deficiency can be performed relatively safely by maintaining the diet, taking measures against epilepsy and vomiting, and using antimicrobial agents in close collaboration with pediatricians, anesthesiologists, pharmacists, and nutritionists.

Metabolic modulation of synaptic failure and thalamocortical hypersynchronization with preserved consciousness in Glut1 deficiency

Individuals with glucose transporter type I deficiency (G1D) habitually experience nutrient-responsive epilepsy associated with decreased brain glucose. However, the mechanistic association between blood glucose concentration and brain excitability in the context of G1D remains to be elucidated. Electroencephalography (EEG) in G1D individuals revealed nutrition time-dependent seizure oscillations often associated with preserved volition despite electrographic generalization and uniform average oscillation duration and periodicity, suggesting increased facilitation of an underlying neural loop circuit. Nonlinear EEG ictal source localization analysis and simultaneous EEG/functional magnetic resonance imaging converged on the thalamus-sensorimotor cortex as one potential circuit, and 18F-deoxyglucose positron emission tomography (18F-DG-PET) illustrated decreased glucose accumulation in this circuit. This pattern, reflected in a decreased thalamic to striatal 18F signal ratio, can aid with the PET imaging diagnosis of the disorder, whereas the absence of noticeable ictal behavioral changes challenges the postulated requirement for normal thalamocortical activity during consciousness. In G1D mice, 18F-DG-PET and mass spectrometry also revealed decreased brain glucose and glycogen, but preserved tricarboxylic acid cycle intermediates, indicating no overall energy metabolism failure. In brain slices from these animals, synaptic inhibition of cortical pyramidal neurons and thalamic relay neurons was decreased, and neuronal disinhibition was mitigated by metabolic sources of carbon; tonic-clonic seizures were also suppressed by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor inhibition. These results pose G1D as a thalamocortical synaptic disinhibition disease associated with increased glucose-dependent neuronal excitability, possibly in relation to reduced glycogen. Together with findings in other metabolic defects, inhibitory neuron dysfunction is emerging as a modulable mechanism of hyperexcitability.

Glut1 deficiency syndrome throughout life: clinical phenotypes, intelligence, life achievements and quality of life in familial cases

Background

Glut1 deficiency syndrome (Glut1-DS) is a rare metabolic encephalopathy. Familial forms are poorly investigated, and no previous studies have explored aspects of Glut1-DS over the course of life: clinical pictures, intelligence, life achievements, and quality of life in adulthood.

Clinical, biochemical and genetic data in a cohort of familial Glut1-DS cases were collected from medical records. Intelligence was assessed using Raven’s Standard Progressive Matrices and Raven’s Colored Progressive Matrices in adults and children, respectively. An ad hoc interview focusing on life achievements and the World Health Organization Quality of Life Questionnaire were administered to adult subjects.

Results

The clinical picture in adults was characterized by paroxysmal exercise-induced dyskinesia (PED) (80%), fatigue (60%), low intelligence (60%), epilepsy (50%), and migraine (50%). However, 20% of the adults had higher-than-average intelligence. Quality of Life (QoL) seemed unrelated to the presence of PED or fatigue in adulthood. An association of potential clinical relevance, albeit not statistically significant, was found between intelligence and QoL. The phenotype of familial Glut1-DS in children was characterized by epilepsy (83.3%), intellectual disability (50%), and PED (33%).

Conclusion

The phenotype of familial Glut1-DS shows age-related differences: epilepsy predominates in childhood; PED and fatigue, followed by epilepsy and migraine, characterize the condition in adulthood. Some adults with familial Glut1-DS may lead regular and fulfilling lives, enjoying the same QoL as unaffected individuals. The disorder tends to worsen from generation to generation, with new and more severe symptoms arising within the same family. Epigenetic studies might be useful to assess the phenotypic variability in Glut1-DS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02513-4.

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.

Head circumference in glucose transporter 1 deficiency syndrome: Normal for individuals, abnormal as a group

In the literature, microcephaly is considered as part of the classical phenotype of glucose transporter 1 deficiency syndrome (GLUT1DS), and previous cohort studies reported a prevalence of microcephaly of around 50%. In our clinical experience, however, only very few patients with GLUT1DS appear to have microcephaly. Therefore, we conducted an observational study among a large cohort of Dutch patients with GLUT1DS to investigate the prevalence of microcephaly, defined as < 2 standard deviations (SD) below the mean. We analysed the head circumference of 54 patients and found a prevalence of microcephaly at last known measurement of 6.5%. Notably, none of the patients had a head circumference < -3 SD. However, we learned that 75.9% of the patients had a head circumference below 0 SD. This study shows that microcephaly occurs less often than previously thought in patients with GLUT1DS, and that primary or secondary microcephaly does not seem to be a sign for clinicians to suspect GLUT1DS. As a group, however, patients with GLUT1DS seem to have decreased head circumference compared to healthy individuals and as such, our study suggests that early brain development and brain growth may be compromised in GLUT1DS.

Shedding light on the phenotypic–genotypic correlation of rare treatable and potentially treatable pediatric movement disorders

Background

Advances in genetic science have led to the identification of many rare treatable pediatric movements disorders (MDs). We explored the phenotypic–genotypic spectrum of pediatric patients presenting with MDs. By this, we aimed at raising awareness about such rare disorders, especially in our region. Over the past 3 years, we reviewed the demographic data, clinical profile, molecular genetics and other diagnostic workups of pediatric patients presenting with MDs.

Results

Twelve patients were identified; however, only six patients were genetically confirmed. The phenomenology of MDs ranged from paroxysmal kinesigenic choreoathetosis (1 patient), exercise-induced dyskinesia (2 patients), ataxia (2 patients) and dystonia (2 patients). Whole-exome sequencing in addition to the functional studies for some patients revealed a specific genetic diagnosis being responsible for their MDs. The genetic diagnosis of our patients included infantile convulsions and paroxysmal choreoathetosis syndrome and episodic ataxia due to “pathogenic homozygous mutation of PRRT2 gene,” glucose transporter type 1 deficiency-exercise induced dyskinesia due to “De Novo pathogenic heterozygous missense mutation of exon 4 of SLC2A1 gene,” aromatic L amino acid decarboxylase deficiency due to “pathogenic homozygous mutation of the DDC gene,” myopathy with extrapyramidal signs due to “likely pathogenic homozygous mutations of the MICU1 gene,” mitochondrial trifunctional protein deficiency due to “homozygous variant of uncertain significance (VUS) of HADHB gene” and glutaric aciduria II with serine deficiency due to “homozygous VUS for both ETFDH and PHGDH genes.” After receiving the treatment as per recognized treatment protocols, two patients showed complete resolution of symptoms and the rest showed variable responses.

Conclusion

Identifying the genetic etiology of our patients guided us to provide either disease-specific treatment or redirected our management plan. Hence, highlighting the value of molecular genetic analysis to avoid the diagnostic odyssey and identify treatable MDs.

Study of paediatric patients with the clinical and biochemical phenotype of glucose transporter type 1 deficiency syndrome

INTRODUCTION

Glucose transporter type 1 (GLUT1) deficiency syndrome may present a range of phenotypes, including epilepsy, intellectual disability, and movement disorders. The majority of patients present low CSF glucose levels and/or defects in the SLC2A1 gene; however, some patients do not present low CSF glucose or SLC2A1 mutations, and may have other mutations in other genes with compatible phenotypes.

AIMS

We describe the clinical, biochemical, and genetic characteristics of the disease and perform a univariate analysis of a group of patients with clinical and biochemical phenotype of GLUT1 deficiency syndrome, with or without SLC2A1 mutations.

MATERIAL AND METHODS

The study included 13 patients meeting clinical and biochemical criteria for GLUT1 deficiency syndrome. SLC2A1 sequencing and multiplex ligation-dependent probe amplification were performed; exome sequencing was performed for patients with negative results.

RESULTS

Six patients presented the classic phenotype; 2 paroxysmal dyskinesia, 2 complex movement disorders, 2 early-onset absence seizures, and one presented drug-resistant childhood absence epilepsy. Six patients were positive for SLC2A1 mutations; in the other 5, another genetic defect was identified. No significant differences were observed between the 2 groups for age of onset, clinical presentation, microcephaly, intellectual disability, or response to ketogenic diet. Patients with SLC2A1 mutations presented more clinical changes in relation to diet (66.7%, vs 28.6% in the SLC2A1-negative group) and greater persistence of motor symptoms (66% vs 28.6%); these differences were not statistically significant. Significant differences were observed for CSF glucose level (34.5 vs 46mg/dL, P=.04) and CSF/serum glucose ratio (0.4 vs 0.48, P<.05).

CONCLUSIONS

GLUT1 deficiency syndrome may be caused by mutations to genes other than SLC2A1 in patients with compatible phenotype, low CSF glucose level, and good response to the ketogenic diet.

Study of paediatric patients with the clinical and biochemical phenotype of glucose transporter type 1 deficiency syndrome

INTRODUCTION

Glucose transporter type 1 (GLUT1) deficiency syndrome may present a range of phenotypes, including epilepsy, intellectual disability, and movement disorders. The majority of patients present low CSF glucose levels and/or defects in the SLC2A1 gene; however, some patients do not present low CSF glucose or SLC2A1 mutations, and may have other mutations in other genes with compatible phenotypes.

AIMS

We describe the clinical, biochemical, and genetic characteristics of the disease and perform a univariate analysis of a group of patients with clinical and biochemical phenotype of GLUT1 deficiency syndrome, with or without SLC2A1 mutations.

MATERIAL AND METHODS

The study included 13 patients meeting clinical and biochemical criteria for GLUT1 deficiency syndrome. SLC2A1 sequencing and multiplex ligation-dependent probe amplification were performed; exome sequencing was performed for patients with negative results.

RESULTS

Six patients presented the classic phenotype; 2 paroxysmal dyskinesia, 2 complex movement disorders, 2 early-onset absence seizures, and one presented drug-resistant childhood absence epilepsy. Six patients were positive for SLC2A1 mutations; in the other 5, another genetic defect was identified. No significant differences were observed between the 2 groups for age of onset, clinical presentation, microcephaly, intellectual disability, or response to ketogenic diet. Patients with SLC2A1 mutations presented more clinical changes in relation to diet (66.7% vs. 28.6% in the SLC2A1-negative group) and greater persistence of motor symptoms (66% vs. 28.6%); these differences were not statistically significant. Significant differences were observed for CSF glucose level (34.5 vs. 46mg/dL, P=.04) and CSF/serum glucose ratio (0.4 vs. 0.48, P<.05).

CONCLUSIONS

GLUT1 deficiency syndrome may be caused by mutations to genes other than SLC2A1 in patients with compatible phenotype, low CSF glucose level, and good response to the ketogenic diet.

Lenticular nuclei to thalamic ratio on PET is useful for diagnosis of GLUT1 deficiency syndrome

PURPOSE

To establish an objective method of [¹⁸F]-fluorodeoxyglucose positron emission tomography (FDG-PET) that can assist in the diagnosis of glucose transporter 1 deficiency syndrome (GLUT1-DS).

METHODS

FDG-PET was performed in 8 patients with a mean age of 12.5 years (range, 2-22 years) with GLUT1-DS. Their PET findings were compared with those of 45 controls with a mean age of 11.2 years (range, 2-21 years) by statistical parametric mapping (SPM12, Welcome Neurological Institute). The controls had epilepsy of unknown etiology and normal MRI findings. The age-adjusted ratios of mean radioactivities in regions of interest (ROIs) of bilateral lenticular nuclei, thalami, and the whole cerebral cortex were also measured. The sensitivities and specificities of the ratios for the differential diagnosis of GLUT1-DS were also determined.

RESULTS

SPM showed significantly decreased uptake in bilateral thalami and increased uptake in bilateral lenticular nuclei in patients with GLUT1-DS. There were no areas in the cerebral cortex with significant differences between patients and controls. On ROI analysis, by setting the cut-off value of the age-adjusted lenticular nuclei/thalami radioactivity ratio to 1.54, patients with GLUT1-DS were differentiated from controls with sensitivity of 1.00 and specificity of 0.98.

CONCLUSION

The age-adjusted lenticular nuclei/thalami radioactivity ratio on PET can distinguish patients with GLUT1-DS from patients with epilepsy of unknown etiology with high sensitivity and specificity. It is important to pay attention to the metabolism of the lenticular nuclei and thalami on PET for the diagnosis of GLUT1-DS.

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.

Improving genetic diagnostics of skeletal muscle channelopathies

INTRODUCTION

Skeletal muscle channelopathies are rare inherited conditions that cause significant morbidity and impact on quality of life. Some subsets have a mortality risk. Improved genetic methodology and understanding of phenotypes have improved diagnostic accuracy and yield.

AREAS COVERED

We discuss diagnostic advances since the advent of next-generation sequencing and the role of whole exome and genome sequencing. Advances in genotype-phenotype-functional correlations have improved understanding of inheritance and phenotypes. We outline new phenotypes, particularly in the pediatric setting and consider co-existing mutations that may act as genetic modifiers. We also discuss four newly identified genes associated with skeletal muscle channelopathies.

EXPERT OPINION

Next-generation sequencing using gene panels has improved diagnostic rates, identified new mutations, and discovered patients with co-existing pathogenic mutations ('double trouble'). This field has previously focussed on single genes, but we are now beginning to understand interactions between co-existing mutations, genetic modifiers, and their role in pathomechanisms. New genetic observations in pediatric presentations of channelopathies broadens our understanding of the conditions. Genetic and mechanistic advances have increased the potential to develop treatments.

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.

Glucose transporter type 1 deficiency syndrome and the ketogenic diet

Glucose transporter type 1 deficiency syndrome (GLUT1DS) is characterised by deficient glucose transport over the blood-brain barrier and reduced glucose availability in the brain. This causes epilepsy, movement disorders, and cognitive impairment. Treatment with ketogenic diet provides ketones as alternative energy source. However, not all GLUT1DS patients are on dietary treatment (worldwide registry: 77/181 [43%] of patients). The current 25-year experience allows evaluation of effects and tolerability of dietary treatment for GLUT1DS. To this end, literature was searched up to January 2019 for individual case reports and series reporting (side) effects of dietary treatment for GLUT1DS. Upon aggregation of data for analysis, we identified 270 GLUT1DS patients with dietary treatment with a mean follow-up of 53 months. Epilepsy improved for 83% of 230 patients and remained unchanged for 17%, movement disorders improved for 82% of 127 patients and remained unchanged for 17%, and cognition improved for 59% of 58 patients and remained stable for 40%. Effects on epilepsy were seen within days/weeks and were most pronounced in patients with early treatment initiation. Effects on movement disorders were noticed within months and were strongest in patients with higher cerebrospinal fluid-to-blood glucose ratio. Although side effects were minimal, 18% of 270 patients reported poor compliance. In individual patients, symptoms deteriorated upon low ketosis, poor compliance, or treatment discontinuation. Based on the good tolerability and strong favourable effect of dietary treatment on GLUT1DS symptoms, we advocate dietary treatment in all GLUT1DS patients and prompt diagnosis or screening to allow early treatment.

Failure of ketogenic diet therapy in GLUT1 deficiency syndrome

PURPOSE

Epilepsy in GLUT1 deficiency syndrome is generally drug-resistant; ketogenic diet (KD) therapy is the mainstay of therapy, as production of ketones provides the brain with an alternative energy source, bypassing the defect in GLUT1. Failure of KD therapy and risk factors for failure have been sparsely published.

METHODS

We performed a retrospective study of GLUT1DS patients with refractory epilepsy failing on KD therapy, to identify their clinical characteristics.

RESULTS

Failure of the ketogenic diet was due to KD inefficacy (poor effect despite adequate ketosis), as well as intolerance and an inability to attain ketosis. Our cohort of seven patients in whom KD therapy failed stood out for their advanced age at seizure onset, i.e. almost 4 years vs 8 months in large series, female sex, as well as their advanced age at diagnosis and initiation of KD therapy. EEG recordings during KD therapy can aid in the assessment of effectiveness of the KD therapy.

CONCLUSIONS

GLUT1DS is generally described as a treatable disorder and existing case series do not provide details of treatment failure. In select patients with GLUT1DS, KD therapy fails, rendering GLUT1DS an essentially untreatable disorder. Failure of the ketogenic diet was due to KD inefficacy (poor effect despite adequate ketosis), as well as intolerance and an inability to attain ketosis. Failure to reduce seizure frequency with deterioration of the EEG findings should lead to consideration of cessation of KD therapy.

Genetic mimics of cerebral palsy

The term "cerebral palsy mimic" is used to describe a number of neurogenetic disorders that may present with motor symptoms in early childhood, resulting in a misdiagnosis of cerebral palsy. Cerebral palsy describes a heterogeneous group of neurodevelopmental disorders characterized by onset in infancy or early childhood of motor symptoms (including hypotonia, spasticity, dystonia, and chorea), often accompanied by developmental delay. The primary etiology of a cerebral palsy syndrome should always be identified if possible. This is particularly important in the case of genetic or metabolic disorders that have specific disease-modifying treatment. In this article, we discuss clinical features that should alert the clinician to the possibility of a cerebral palsy mimic, provide a practical framework for selecting and interpreting neuroimaging, biochemical, and genetic investigations, and highlight selected conditions that may present with predominant spasticity, dystonia/chorea, and ataxia. Making a precise diagnosis of a genetic disorder has important implications for treatment, and for advising the family regarding prognosis and genetic counseling. © 2019 International Parkinson and Movement Disorder Society.

Synaptic energy metabolism and neuronal excitability, in sickness and health

Most of the energy produced in the brain is dedicated to supporting synaptic transmission. Glucose is the main fuel, providing energy and carbon skeletons to the cells that execute and support synaptic function: neurons and astrocytes, respectively. It is unclear, however, how glucose is provided to and used by these cells under different levels of synaptic activity. It is even more unclear how diseases that impair glucose uptake and oxidation in the brain alter metabolism in neurons and astrocytes, disrupt synaptic activity, and cause neurological dysfunction, of which seizures are one of the most common clinical manifestations. Poor mechanistic understanding of diseases involving synaptic energy metabolism has prevented the expansion of therapeutic options, which, in most cases, are limited to symptomatic treatments. To shed light on the intersections between metabolism, synaptic transmission, and neuronal excitability, we briefly review current knowledge of compartmentalized metabolism in neurons and astrocytes, the biochemical pathways that fuel synaptic transmission at resting and active states, and the mechanisms by which disorders of brain glucose metabolism disrupt neuronal excitability and synaptic function and cause neurological disease in the form of epilepsy.

Treatable Genetic Metabolic Epilepsies

OPINION STATEMENT

In the absence of a culprit epileptogenic lesion, pharmacoresistant seizures should prompt the physician to consider potentially treatable metabolic epilepsies, especially in the presence of developmental delays. Even though the anti-seizure treatment of the epilepsies remains symptomatic and usually tailored to an electroclinical phenotype rather than to an underlying etiology, a thorough metabolic workup might reveal a disease with an etiology-specific treatment. Early diagnosis is essential in the case of treatable metabolic epilepsies allowing timely intervention. Despite the advances in genetic testing, biochemical testing including cerebrospinal fluid studies are still needed to expedite the diagnostic workup and potential therapeutic trials. The diagnostician should have a high index of suspicion despite potential clinical digressions from seminal publications describing the initial cases, as these index patients may represent the most severe form of the condition rather than its most common presenting form. The often gratifying developmental outcome and seizure control with early treatment calls for a prompt diagnostic consideration of treatable metabolic diseases; even though relatively rare or potentially only seemingly so.