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

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.

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.

Glucose transporter-1 deficiency syndrome with extreme phenotypic variability in a five-generation family carrying a novel SLC2A1 variant

BACKGROUND AND PURPOSE

Glucose transporter-1 (GLUT1) deficiency syndrome (GLUT1-DS) is a metabolic disorder due to reduced expression of GLUT1, a glucose transporter of the central nervous system. GLUT1-DS is caused by heterozygous SLC2A1 variants that mostly arise de novo. Here, we report a large family with heterogeneous phenotypes related to a novel SLC2A1 variant.

METHODS

We present clinical and genetic features of a five-generation family with GLUT1-DS.

RESULTS

The 14 (nine living) affected members had heterogeneous phenotypes, including seizures (11/14), behavioral disturbances (5/14), mild intellectual disability (3/14), and/or gait disabilities (2/14). Brain magnetic resonance imaging revealed hippocampal sclerosis in the 8-year-old proband, who also had drug-responsive absences associated with attention-deficit/hyperactivity disorder. His 52-year-old father, who had focal epilepsy since childhood, developed paraparesis related to a reversible myelitis associated with hypoglycorrhachia. Molecular study detected a novel heterozygous missense variant (c.446C>T) in exon 4 of SLC2A1 (NM: 006516.2) that cosegregated with the illness. This variant causes an amino acid replacement (p.Pro149Leu) at the fourth transmembrane segment of GLUT1, an important domain located at its catalytic core.

CONCLUSIONS

Our study illustrates the extremely heterogenous phenotypes in familial GLUT1-DS, ranging from milder classic phenotypes to more subtle neurological disorder including paraparesis. This novel SLC2A1 variant (c.446C>T) provides new insight into the pathophysiology of GLUT1-DS.

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.

GLUT1DS focus on dysarthria

RESEARCH PURPOSE

GLUT1 deficiency syndrome (GLUT1DS) is a rare genetic disorder caused by a mutation in the SLC2A1 gene that limits the transport of glucose across the blood-brain barrier. Speech disorders and dysarthria are typical findings in patients with GLUT1DS, but have never been deeply phenotyped. The aim of the present study was to characterize speech abilities in a sample of patients with GLUT1DS.

RESULTS

30 patients with GLUT1DS were recruited. We reported impairments in different speech and oromotor domains: the speech was characterized by dysarthria, inaccurate articulation of consonants, abnormal nasal resonance, errors in intonation and prosody and low intelligibility. We observed difficulties in motor planning and programming. Moreover, we observed a significant difference between the dysarthric level of impairment with genotype groups.

CONCLUSIONS

The presence of a speech disorder in patients with GLUT1DS represents a core feature of the syndrome. Our findings suggest that patients with GLUT1DS would benefit from a comprehensive neurocognitive assessment to detect strengths and weaknesses of the speech profile. Understanding the speech and language phenotype in GLUT1DS is critical for planning early intervention to positively influence the global development of patients with GLUT1DS.

Brain microvascular endothelial cell metabolism and its ties to barrier function

Brain microvascular endothelial cells, which lie at the interface between blood and brain, are critical to brain energetics. These cells must precisely balance metabolizing nutrients for their own demands with transporting nutrients into the brain to sustain parenchymal cells. It is essential to understand this integrated metabolism and transport so that we can develop better diagnostics and therapeutics for neurodegenerative diseases such as Alzheimer's disease, multiple sclerosis, and traumatic brain injury. In this chapter, we first describe brain microvascular endothelial cell metabolism and how these cells regulate both blood flow and nutrient transport. We then explain the impact of brain microvascular endothelial cell metabolism on the integrity of the blood-brain barrier, as well as how metabolites produced by the endothelial cells impact other brain cells. We detail some ways that cell metabolism is typically measured experimentally and modeled computationally. Finally, we describe changes in brain microvascular endothelial cell metabolism in aging and neurodegenerative diseases. At the end of the chapter, we highlight areas for future research in brain microvascular endothelial cell metabolism. The goal of this chapter is to underscore the importance of nutrient metabolism and transport at the brain endothelium for cerebral health and neurovascular disease treatment.

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.

Blood-brain barrier transporters: An overview of function, dysfunction in Alzheimer's disease and strategies for treatment

The blood-brain-barrier (BBB) has a major function in maintaining brain homeostasis by regulating the entry of molecules from the blood to the brain. Key players in BBB function are BBB transporters which are highly expressed in brain endothelial cells (BECs) and critical in mediating the exchange of nutrients and waste products. BBB transporters can also influence drug delivery into the brain by inhibiting or facilitating the entry of brain targeting therapeutics for the treatment of brain disorders, such as Alzheimer's disease (AD). Recent studies have shown that AD is associated with a disrupted BBB and transporter dysfunction, although their roles in the development in AD are not fully understand. Modulation of BBB transporter activity may pose a novel approach to enhance the delivery of drugs to the brain for enhanced treatment of AD. In this review, we will give an overview of key functions of BBB transporters and known changes in AD. In addition, we will discuss current strategies for transporter modulation for enhanced drug delivery into the brain.

The interplay between microbiota and brain-gut axis in epilepsy treatment

The brain-gut axis plays a vital role in connecting the cognitive and emotional centers of the brain with the intricate workings of the intestines. An imbalance in the microbiota-mediated brain-gut axis extends far beyond conditions like Irritable Bowel Syndrome (IBS) and obesity, playing a critical role in the development and progression of various neurological disorders, including epilepsy, depression, Alzheimer's disease (AD), and Parkinson's disease (PD). Epilepsy, a brain disorder characterized by unprovoked seizures, affects approximately 50 million people worldwide. Accumulating evidence suggests that rebuilding the gut microbiota through interventions such as fecal microbiota transplantation, probiotics, and ketogenic diets (KD) can benefit drug-resistant epilepsy. The disturbances in the gut microbiota could contribute to the toxic side effects of antiepileptic drugs and the development of drug resistance in epilepsy patients. These findings imply the potential impact of the gut microbiota on epilepsy and suggest that interventions targeting the microbiota, such as the KD, hold promise for managing and treating epilepsy. However, the full extent of the importance of microbiota in epilepsy treatment is not yet fully understood, and many aspects of this field remain unclear. Therefore, this article aims to provide an overview of the clinical and animal evidence supporting the regulatory role of gut microbiota in epilepsy, and of potential pathways within the brain-gut axis that may be influenced by the gut microbiota in epilepsy. Furthermore, we will discuss the recent advancements in epilepsy treatment, including the KD, fecal microbiota transplantation, and antiseizure drugs, all from the perspective of the gut microbiota.

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.

GLUT-1 changes in paediatric Huntington disease brain cortex and fibroblasts: an observational case-control study

BACKGROUND

Paediatric Huntington disease with highly expanded mutations (HE-PHD; >80 CAG repeats) presents atypically, compared to adult-onset Huntington disease (AOHD), with neurodevelopmental delay, epilepsy, abnormal brain glucose metabolism, early striatal damage, and reduced lifespan. Since genetic GLUT-1 deficiency syndrome shows a symptom spectrum similar to HE-PHD, we investigated the potential role of the two main glucose transporters, GLUT-1 and GLUT-3, in HE-PHD.

METHODS

We compared GLUT-1 and GLUT-3 protein expression in HE-PHD, juvenile-onset (JOHD), and AOHD brains (n = 2; n = 3; n = 6) and periphery (n = 3; n = 2; n = 2) versus healthy adult controls (n = 6; n = 6). We also investigated mitochondrial complexes and hexokinase-II protein expression.

FINDINGS

GLUT-1 and GLUT-3 expression were significantly lower in HE-PHD frontal cortex (p = 0.009, 95% [CI 13.4, 14.7]; p = 0.017, 95% [CI 14.2, 14.5]) versus controls. In fibroblasts, GLUT-1 and GLUT-3 expression were lower compared to controls (p < 0.0001, 95% [CI 0.91, 1.09]; p = 0.046, 95% [CI 0.93, 1.07]). In the frontal cortex, this occurred without evidence of extensive neuronal degeneration. Patients with HE-PHD had deregulated mitochondrial complex expression, particularly complexes II-III, levels of which were lower in frontal cortex versus controls (p = 0.027, 95% [CI 17.1, 17.6]; p = 0.002, 95% CI [16.6, 16.9]) and patients with AOHD (p = 0.052, 95% [CI 17.0, 17.6]; p = 0.002, 95% [CI 16.6, 16.7]). Hexokinase-II expression was also lower in HE-PHD frontal cortex and striatum versus controls (p = 0.010, 95% [CI 17.8, 18.2]; p = 0.045, 95% [CI 18.6, 18.7]) and in frontal cortex versus patients with AOHD (p = 0.013, 95% [CI 17.7, 18.1]). Expression JOHD levels were consistently different to those of HE-PHD but similar to those of AOHD.

INTERPRETATION

Our data suggest a dysfunctional hypometabolic state occurring specifically in paediatric Huntington disease brains.

FUNDING

'5 × 1000' Personal Income Tax donation to LIRH Foundation; Italian Ministry of HealthRC2301MH04 and RF-2016-02364123 to CSS.

Experimental pharmacology: Targeting metabolic pathways

Since the discovery of the treatment for Wilson disease a growing number of treatable inherited dystonias have been identified and their search and treatment have progressively been implemented in the clinics of patients with dystonia. While waiting for gene therapy to be more widely and adequately translated into the clinical setting, the efforts to divert the natural course of dystonia reside in unveiling its pathogenesis. Specific metabolic treatments can rewrite the natural history of the disease by preventing neurotoxic metabolite accumulation or interfering with the cell accumulation of damaging metabolites, restoring energetic cell fuel, supplementing defective metabolites, and supplementing the defective enzyme. A metabolic derangement of cell homeostasis is part of the progression of many non-metabolic genetic lesions and could be the target for possible metabolic approaches. In this chapter, we provided an update on treatment strategies for treatable inherited dystonias and an overview of genetic dystonias with new experimental therapeutic approaches available or close to clinical translation.

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.

Timing of Ketogenic Dietary Therapy (KDT) Introduction and Its Impact on Cognitive Profiles in Children with Glut1-DS—A Preliminary Study

The aim of this research was to characterize cognitive abilities in patients with Glut1-Deficiency syndrome (Glut1DS) following ketogenic diet therapy (KDT). Methods: The cognitive profiles of eight children were assessed using the Wechsler Intelligence Scale (WISC-IV). The effect of ketogenic diet therapy (KDT) on individual subareas of intelligence was analyzed considering the potential influence of speech motor impairments. Results: Patients with Glut1DS showed a wide range of cognitive performance levels. Some participants showed statistically and clinically significant discrepancies between individual subdomains of intelligence. Both variables, KDT initiation as well as duration, had a positive effect on the overall IQ score. Significant correlations were partially found between the time of KDT initiation and the level of IQ scores, depending on the presence of expressive language test demands of the respective subtests of the WISC-IV. Accordingly, the participants benefited les in the linguistic cognitive domain. The discrepancies in cognitive performance profiles of patients with Glut1DS can be attributed to the possibility of a negative distortion of the results due to the influence of speech motor impairments. Conclusions: The individual access skills of test persons should be more strongly considered in test procedures for the assessment of intelligence to reduce the negative influence of motor deficits on test performance. Specific characterization and systematization of the speech disorder are indispensable for determining the severity of speech motor impairment in Glut1DS. Therefore, a stronger focus on dysarthria during diagnosis and therapy is necessary.

Association between cerebrospinal fluid parameters and developmental and neurological status in glucose transporter 1 deficiency syndrome

OBJECTIVE

In glucose transporter 1 deficiency syndrome (Glut1DS), cerebrospinal fluid glucose (CSFG) and CSFG to blood glucose ratio (CBGR) show significant differences among groups classified by phenotype or genotype. The purpose of this study was to investigate the association between these biochemical parameters and Glut1DS severity.

METHODS

The medical records of 45 patients who visited Osaka University Hospital between March 2004 and December 2021 were retrospectively examined. Neurological status was determined using the developmental quotient (DQ), assessed using the Kyoto Scale of Psychological Development 2001, and the Scale for the Assessment and Rating of Ataxia (SARA). CSF parameters included CSFG, CBGR, and CSF lactate (CSFL).

RESULTS

CSF was collected from 41 patients, and DQ and SARA were assessed in 24 and 27 patients, respectively. Simple regression analysis showed moderate associations between neurological status and biochemical parameters. CSFG resulted in a higher R² than CBGR in these analyses. CSF parameters acquired during the first year of life were not comparable to those acquired later. CSFL was measured in 16 patients (DQ and SARA in 11 and 14 patients, respectively). Although simple regression analysis also showed moderate associations between neurological status and CSFG and CSFL, the multiple regression analysis for DQ and SARA resulted in strong associations through the use of a combination of CSFG and CSFL as explanatory variables.

CONCLUSION

The severity of Glut1DS can be predicted from CSF parameters. Glucose and lactate are independent contributors to the developmental and neurological status in Glut1DS.

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

Objective

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

Methods

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

Results

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

Conclusions

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

Genetic Links to Episodic Movement Disorders: Current Insights

Episodic or paroxysmal movement disorders (PxMD) are conditions, which occur episodically, are transient, usually have normal interictal periods, and are characterized by hyperkinetic disorders, including ataxia, chorea, dystonia, and ballism. Broadly, these comprise paroxysmal dyskinesias (paroxysmal kinesigenic and non-kinesigenic dyskinesia [PKD/PNKD], paroxysmal exercise-induced dyskinesias [PED]) and episodic ataxias (EA) types 1-9. Classification of paroxysmal dyskinesias has traditionally been clinical. However, with advancement in genetics and the discovery of the molecular basis of several of these disorders, it is becoming clear that phenotypic pleiotropy exists, that is, the same variant may give rise to a variety of phenotypes, and the classical understanding of these disorders requires a new paradigm. Based on molecular pathogenesis, paroxysmal disorders are now categorized as synaptopathies, transportopathies, channelopathies, second-messenger related disorders, mitochondrial or others. A genetic paradigm also has an advantage of identifying potentially treatable disorders, such as glucose transporter 1 deficiency syndromes, which necessitates a ketogenic diet, and ADCY5-related disorders, which may respond to caffeine. Clues for a primary etiology include age at onset below 18 years, presence of family history and fixed triggers and attack duration. Paroxysmal movement disorder is a network disorder, with both the basal ganglia and the cerebellum implicated in pathogenesis. Abnormalities in the striatal cAMP turnover pathway may also be contributory. Although next-generation sequencing has restructured the approach to paroxysmal movement disorders, the genetic underpinnings of several entities remain undiscovered. As more genes and variants continue to be reported, these will lead to enhanced understanding of pathophysiological mechanisms and precise treatment.

Paroxysmal movement disorders: Paroxysmal dyskinesia and episodic ataxia

Paroxysmal movement disorders have traditionally been classified into paroxysmal dyskinesia (PxD), which consists in attacks of involuntary movements (mainly dystonia and/or chorea) without loss of consciousness, and episodic ataxia (EA), which features spells of cerebellar dysfunction with or without interictal neurological manifestations. In this chapter, PxD will be discussed first according to the trigger-based classification, thus reviewing clinical, genetic, and molecular features of paroxysmal kinesigenic dyskinesia, paroxysmal nonkinesigenic dyskinesia, and paroxysmal exercise-induced dyskinesia. EA will be presented thereafter according to their designated gene or genetic locus. Clinicogenetic similarities among paroxysmal movement disorders have progressively emerged, which are herein highlighted along with growing evidence that their pathomechanisms overlap those of epilepsy and migraine. Advances in our comprehension of the biological pathways underlying paroxysmal movement disorders, which involve ion channels as well as proteins associated with the vesical synaptic cycle or implicated in neuronal energy metabolism, may represent the cornerstone for defining a shared pathophysiologic framework and developing target-specific therapies.

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

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

Metabolic contributions to neuronal deficits caused by genomic disruption of schizophrenia risk gene SETD1A

Regulation of neuronal metabolism during early brain development is crucial for directing synaptic plasticity and proper circuit formation. Alterations in neuronal glycolysis or mitochondrial function are associated with several neuropsychiatric disorders, including schizophrenia. Recently, loss-of-function mutations in SETD1A, a histone methyltransferase, have been linked to increased schizophrenia risk and global developmental delay. Here, we show that heterozygous disruption of SETD1A in human induced pluripotent stem cell (hiPSC)-derived neurons results in reduced neurite outgrowth and spontaneous activity, two phenotypes commonly associated with schizophrenia, as well as alterations in metabolic capacity. Furthermore, supplementing culture media with metabolic intermediates ameliorated changes in neurite outgrowth and spontaneous activity, suggesting that metabolic dysfunction contributes to neuronal phenotypes caused by SETD1A haploinsufficiency. These findings highlight a previously unknown connection between SETD1A function, metabolic regulation, and neuron development, and identifies alternative avenues for therapeutic development.

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.

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.

An in vitro model of glucose transporter 1 deficiency syndrome at the blood-brain barrier using induced pluripotent stem cells

Glucose is an important source of energy for the central nervous system. Its uptake at the blood-brain barrier (BBB) is mostly mediated via glucose transporter 1 (GLUT1), a facilitated transporter encoded by the SLC2A1 gene. GLUT1 Deficiency Syndrome (GLUT1DS) is a haploinsufficiency characterized by mutations in the SLC2A1 gene, resulting in impaired glucose uptake at the BBB and clinically characterized by epileptic seizures and movement disorder. A major limitation is an absence of in vitro models of the BBB reproducing the disease. This study aimed to characterize an in vitro model of GLUT1DS using human pluripotent stem cells (iPSCs). Two GLUT1DS clones were generated (GLUT1-iPSC) from their original parental clone iPS(IMR90)-c4 by CRISPR/Cas9 and differentiated into brain microvascular endothelial cells (iBMECs). Cells were characterized in terms of SLC2A1 expression, changes in the barrier function, glucose uptake and metabolism, and angiogenesis. GLUT1DS iPSCs and iBMECs showed comparable phenotype to their parental control, with exception of reduced GLUT1 expression at the protein level. Although no major disruption in the barrier function was reported in the two clones, a significant reduction in glucose uptake accompanied by an increase in glycolysis and mitochondrial respiration was reported in both GLUT1DS-iBMECs. Finally, impaired angiogenic features were reported in such clones compared to the parental clone. Our study provides the first documented characterization of GLUT1DS-iBMECs generated by CRISPR-Cas9, suggesting that GLUT1 truncation appears detrimental to brain angiogenesis and brain endothelial bioenergetics, but maybe not be detrimental to iBMECs differentiation and barriergenesis. Our future direction is to further characterize the functional outcome of such truncated product, as well as its impact on other cells of the neurovascular unit.

Phenotypic and Genotypic Spectrum of Early-Onset Developmental and Epileptic Encephalopathies-Data from a Romanian Cohort

Early-onset developmental epileptic encephalopathy (DEE) refers to an age-specific, diverse group of epilepsy syndromes with electroclinical anomalies that are associated with severe cognitive, behavioral, and developmental impairments. Genetic DEEs have heterogeneous etiologies. This study includes 36 Romanian patients referred to the Regional Centre for Medical Genetics Dolj for genetic testing between 2017 and 2020. The patients had been admitted to and clinically evaluated at Doctor Victor Gomoiu Children’s Hospital and Prof. Dr. Alexandru Obregia Psychiatry Hospital in Bucharest. Panel testing was performed using the Illumina® TruSight™ One “clinical exome” (4811 genes), and the analysis focused on the known genes reported in DEEs and clinical concordance. The overall diagnostic rate was 25% (9/36 cases). Seven cases were diagnosed with Dravet syndrome (likely pathogenic/pathogenic variants in SCN1A) and two with Genetic Epilepsy with Febrile Seizures Plus (SCN1B). For the diagnosed patients, seizure onset was <1 year, and the seizure type was generalized tonic-clonic. Four additional plausible variants of unknown significance in SCN2A, SCN9A, and SLC2A1 correlated with the reported phenotype. Overall, we are reporting seven novel variants. Comprehensive clinical phenotyping is crucial for variant interpretation. Genetic assessment of patients with severe early-onset DEE can be a powerful diagnostic tool for clinicians, with implications for the management and counseling of the patients and their families.

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

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

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.

Long-term outcome of developmental and epileptic encephalopathies

Developmental and epileptic encephalopathies are conditions where there is developmental impairment related to both the underlying etiology independent of epileptiform activity and the epileptic encephalopathy. Usually they have multiple etiologies. Therefore, long-term outcome is related to both etiology-related factors and epilepsy-related factors-age at onset of epilepsy, type(s) of seizure(s), type of electroencephalographic abnormalities, duration of the epileptic disorder. This paper focuses on long-term outcome of six developmental and epileptic encephalopathies with onset from the neonatal period to childhood: early epileptic encephalopathy with suppression bursts, West syndrome, Dravet syndrome, Lennox-Gastaut syndrome, epilepsy with myoclonic atonic seizures and epileptic encephalopathy with continuous spike and waves during slow-wave sleep including Landau-Kleffner syndrome. For each syndrome, definition, main etiologies if multiple, and long-term outcome are discussed.

Diverse Molecular Mechanisms Underlying Pathogenic Protein Mutations: Beyond the Loss-of-Function Paradigm

Most known disease-causing mutations occur in protein-coding regions of DNA. While some of these involve a loss of protein function (e.g., through premature stop codons or missense changes that destabilize protein folding), many act via alternative molecular mechanisms and have dominant-negative or gain-of-function effects. In nearly all cases, these non-loss-of-function mutations can be understood by considering interactions of the wild-type and mutant protein with other molecules, such as proteins, nucleic acids, or small ligands and substrates. Here, we review the diverse molecular mechanisms by which pathogenic mutations can have non-loss-of-function effects, including by disrupting interactions, increasing binding affinity, changing binding specificity, causing assembly-mediated dominant-negative and dominant-positive effects, creating novel interactions, and promoting aggregation and phase separation. We believe that increased awareness of these diverse molecular disease mechanisms will lead to improved diagnosis (and ultimately treatment) of human genetic disorders. Expected final online publication date for the Annual Review of Genomics and Human Genetics, Volume 23 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The clinical and biochemical hallmarks generally associated with GLUT1DS may be caused by defects in genes other than SLC2A1

Glucose transporter 1 deficiency syndrome (GLUT1DS) is a neurometabolic disorder caused by haploinsufficiency of the GLUT1 glucose transporter (encoded by SLC2A1) leading to defective glucose transport across the blood–brain barrier. This work describes the genetic analysis of 56 patients with clinical or biochemical GLUT1DS hallmarks. 55.4% of these patients had a pathogenic variant of SLC2A1, and 23.2% had a variant in one of 13 different genes. No pathogenic variant was identified for the remaining patients. Expression analysis of SLC2A1 indicated a reduction in SLC2A1 mRNA in patients with pathogenic variants of this gene, as well as in one patient with a pathogenic variant in SLC9A6, and in three for whom no candidate variant was identified. Thus, the clinical and biochemical hallmarks generally associated with GLUT1DS may be caused by defects in genes other than SLC2A1.

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.

Diagnostic and Clinical Manifestation Differences of Glucose Transporter Type 1 Deficiency Syndrome in a Family with SLC2A1 Gene Mutation

Glucose transporter type 1 deficiency syndrome is a rare genetic disease that manifests neurological symptoms such as mental impairment or movement disorders, mostly seen in pediatric patients. Here, we highlight the main symptoms, diagnostic difficulties, and genetic correlations of this disease based on different clinical presentations between the members of a family carrying the same mutation. In this report, we studied siblings—a 5-year-old girl and a 6-year-old boy—who were admitted to a pediatric ward with various neurological symptoms. Different diagnostic procedures such as lumbar puncture, electroencephalography, and MRI of the brain were performed on these patients. Whole genome sequencing identified mutations in the SLC2A1 and GLUT1-DS genes, following which a ketogenic diet was implemented. This diet modification resulted in a good clinical response. Our case report reveals patients with the same genetic mutations having distinctive clinical manifestations.

Evidence That Substantia Nigra Pars Compacta Dopaminergic Neurons Are Selectively Vulnerable to Oxidative Stress Because They Are Highly Metabolically Active

There are 400–500 thousand dopaminergic cells within each side of the human substantia nigra pars compacta (SNpc) making them a minuscule portion of total brain mass. These tiny clusters of cells have an outsized impact on motor output and behavior as seen in disorders such as Parkinson’s disease (PD). SNpc dopaminergic neurons are more vulnerable to oxidative stress compared to other brain cell types, but the reasons for this are not precisely known. Here we provide evidence to support the hypothesis that this selective vulnerability is because SNpc neurons sustain high metabolic rates compared to other neurons. A higher baseline requirement for ATP production may lead to a selective vulnerability to impairments in oxidative phosphorylation (OXPHOS) or genetic insults that impair Complex I of the electron transport chain. We suggest that the energy demands of the unique morphological and electrophysiological properties of SNpc neurons may be one reason these cells produce more ATP than other cells. We further provide evidence to support the hypothesis that transcription factors (TFs) required to drive induction, differentiation, and maintenance of midbrain dopaminergic neural progenitor cells which give rise to terminally differentiated SNpc neurons are uniquely involved in both developmental patterning and metabolism, a dual function unlike other TFs that program neurons in other brain regions. The use of these TFs during induction and differentiation may program ventral midbrain progenitor cells metabolically to higher ATP levels, allowing for the development of those specialized cell processes seen in terminally differentiated cells. This paper provides a cellular and developmental framework for understanding the selective vulnerability of SNpc dopaminergic cells to oxidative stress.

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.

Clinical and Genetic Characteristics of Chinese Children With GLUT1 Deficiency Syndrome: Case Report and Literature Review

Objective: GLUT1 deficiency syndrome (GLUT1-DS) is a rare, treatable neurometabolic disorder. However, its diagnosis may be challenging due to the various and evolving phenotypes. Here we report the first Chinese familial cases with genetically confirmed GLUT1-DS and analyze the characteristics of Chinese children with GLUT1-DS from clinical, laboratory, and genetic aspects.

Methods: We reported a Chinese family with three members affected with GLUT1-DS and searched for relevant articles up to September 2020 from PubMed, WOS, CNKI, and WanFang databases. A total of 30 Chinese patients diagnosed with GLUT1-DS (three newly identified patients in one family and 27 previously reported ones) were included and analyzed in this study.

Results: The median age of onset of the 30 patients (male: 18, female: 12) was 8.5 months (range, 33 days to 10 years). Epileptic seizures were found in 25 patients, most with generalized tonic–clonic and focal ones. Movement disorders were found in 20 patients—frequently with ataxia and dystonia, developmental delay in 25 patients, and microcephaly only in six patients. The cerebrospinal fluid (CSF) analysis showed decreased CSF glucose (median: 1.63 mmol/L, range: 1.1–2.6 mmol/L) and glucose ratio of CSF to blood (median: 0.340; range: 0.215–0.484). The genetic testing performed in 28 patients revealed 27 cases with pathogenic variations of the SLC2A1 gene, including 10 missense, nine frameshift, three nonsense, three large fragment deletions, and two splice-site mutations. Most patients had a good response to the treatment of ketogenic diet or regular diet with increased frequency. Although three patients in this Chinese family carried the same pathogenic mutation c.73C > T (p.Q25X) in the SLC2A1 gene, their symptoms and responses to treatment were not exactly the same.

Conclusion: The clinical manifestations of GLUT1-DS are heterogeneous, even among family members sharing the same mutation. For children with unexplained epileptic seizures, developmental delay, and complex movement disorders, detection of low CSF glucose or SLC2A1 gene mutations is helpful for the diagnosis of GLUT1-DS. Early initiation of ketogenic diet treatment significantly improves the symptoms and prognosis of GLUT1-DS.

GLUT1 Deficiency Syndrome-Early Treatment Maintains Cognitive Development? (Literature Review and Case Report)

Glucose transporter type 1 (GLUT1) is the most important energy carrier of the brain across the blood-brain barrier, and a genetic defect of GLUT1 is known as GLUT1 deficiency syndrome (GLUT1DS). It is characterized by early infantile seizures, developmental delay, microcephaly, ataxia, and various paroxysmal neurological phenomena. In most cases, GLUT1DS is caused by heterozygous single-nucleotide variants (SNVs) in the SLC2A1 gene that provoke complete or severe impairment of the functionality and/or expression of GLUT1 in the brain. Despite the rarity of these diseases, GLUT1DS is 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. We present a clinical phenotype, biochemical analysis, electroencephalographic and neuropsychological features of an 11-month-old boy with myoclonic seizures, hypogammaglobulinemia, and mildly impaired gross motor development. Using sequence analysis and deletion/duplication testing, deletion of an entire coding sequence in the SLC2A1 gene was detected. Early introduction of a modified Atkins diet maintained a seizure-free period without antiseizure medications and normal cognitive development in the follow-up period. Our report summarizes the clinical features of GLUT1 syndromes and discusses the importance of early identification and molecular confirmation of GLUT1DS as a treatable metabolic disorder.

Precision medicine for genetic childhood movement disorders

Increasingly effective targeted precision medicine is either already available or in development for a number of genetic childhood movement disorders. Patient-centred, personalized approaches include the repurposing of existing treatments for specific conditions and the development of novel therapies that target the underlying genetic defect or disease mechanism. In tandem with these scientific advances, close collaboration between clinicians, researchers, affected families, and stakeholders in the wider community will be key to successfully delivering such precision therapies to children with movement disorders. What this paper adds Precision medicine for genetic childhood movement disorders is developing rapidly. Accurate diagnosis, disease-specific outcome measures, and collaborative multidisciplinary work will accelerate the progress of such strategies.

Genetics of Paroxysmal Dyskinesia: Novel Variants Corroborate the Role of KCNA1 in Paroxysmal Dyskinesia and Highlight the Diverse Phenotypic Spectrum of KCNA1- and SLC2A1-Related Disorders

Paroxysmal dyskinesias (PxD) are rare movement disorders with characteristic episodes of involuntary mixed hyperkinetic movements. Scientific efforts and technical advances in molecular genetics have led to the discovery of a variety of genes associated with PxD; however, clinical and genetic information of rarely affected genes or infrequent variants is often limited. In our case series, we present two individuals with PxD including one with classical paroxysmal kinesigenic dyskinesia, who carry new likely pathogenic de novo variants in KCNA1 (p.Gly396Val and p.Gly396Arg). The gene has only recently been discovered to be causative for familial paroxysmal kinesigenic dyskinesia. We also provide genetic evidence for pathogenicity of two newly identified disease-causing variants in SLC2A1 (p.Met96Thr and p.Leu231Pro) leading to paroxysmal exercise-induced dyskinesia. Since clinical information of carriers of variants in known disease-causing genes is often scarce, we encourage to share clinical data of individuals with rare or novel (likely) pathogenic variants to improve disease understanding.

CACNA1A-associated epilepsy: Electroclinical findings and treatment response on seizures in 18 patients

CACNA1A pathogenic mutations are involved in various neurological phenotypes including episodic ataxia (EA2), spinocerebellar ataxia (SCA6), and familial hemiplegic migraine (FHM1). Epilepsy is poorly documented. We studied 18 patients (10 males) carrying de novo or inherited CACNA1A mutations, with median age of 2,5 years at epilepsy onset. Eight mutations were novel. Two variants known leading to gain of function (GOF) were found in 5 patients. Five other patients had non-sense variants leading to loss of function (LOF). Seizures were most often revealed by either status epilepticus (SE) (n = 8), eventually triggered by fever (n = 5), or absences/behavioural arrests (n = 7). Non-epileptic paroxysmal events were frequent and consisted in recurrent hemiplegic accesses (n = 9), jitteriness in the neonatal period (n = 6), and ocular paroxysmal events (n = 9). Most of the patients had early permanent cerebellar dysfunction (n = 16) and early moderate to severe global developmental delay (GDD)/intellectual deficiency (ID) (n = 17). MRI was often abnormal, with cerebellar (n = 8) and/or cerebral (n = 6) atrophy. Stroke-like occurred in 2 cases. Some antiepileptic drugs including topiramate, levetiracetam, lamotrigine and valproate were effective on seizures. Acetazolamide and calcium channel blockers were often effective when used. More than half of the patients had refractory epilepsy. CACNA1A mutation should be evoked in front of 2 main electro-clinical phenotypes that are associated with permanent cerebellar dysfunction and moderate to severe GDD/ID. The first one, found in all 5 patients with GOF variants, is characterized by intractable seizures, early and recurrent SE and hemiplegic accesses. The second, less severe, found in 5 patients with LOF variants, is characterized by refractory early onset absence seizures.

Sub-genic intolerance, ClinVar, and the epilepsies: A whole-exome sequencing study of 29,165 individuals

Both mild and severe epilepsies are influenced by variants in the same genes, yet an explanation for the resulting phenotypic variation is unknown. As part of the ongoing Epi25 Collaboration, we performed a whole-exome sequencing analysis of 13,487 epilepsy-affected individuals and 15,678 control individuals. While prior Epi25 studies focused on gene-based collapsing analyses, we asked how the pattern of variation within genes differs by epilepsy type. Specifically, we compared the genetic architectures of severe developmental and epileptic encephalopathies (DEEs) and two generally less severe epilepsies, genetic generalized epilepsy and non-acquired focal epilepsy (NAFE). Our gene-based rare variant collapsing analysis used geographic ancestry-based clustering that included broader ancestries than previously possible and revealed novel associations. Using the missense intolerance ratio (MTR), we found that variants in DEE-affected individuals are in significantly more intolerant genic sub-regions than those in NAFE-affected individuals. Only previously reported pathogenic variants absent in available genomic datasets showed a significant burden in epilepsy-affected individuals compared with control individuals, and the ultra-rare pathogenic variants associated with DEE were located in more intolerant genic sub-regions than variants associated with non-DEE epilepsies. MTR filtering improved the yield of ultra-rare pathogenic variants in affected individuals compared with control individuals. Finally, analysis of variants in genes without a disease association revealed a significant burden of loss-of-function variants in the genes most intolerant to such variation, indicating additional epilepsy-risk genes yet to be discovered. Taken together, our study suggests that genic and sub-genic intolerance are critical characteristics for interpreting the effects of variation in genes that influence epilepsy.

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.