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Tayebi N, Leon‐Ricardo B, McCall K, Mehinovic E, Engelstad K, Huynh V, Turner TN, Weisenberg J, Thio LL, Hruz P, Williams RSB, De Vivo DC, Petit V, Haller G, Gurnett CA. Quantitative determination of SLC2A1 variant functional effects in GLUT1 deficiency syndrome. Ann Clin Transl Neurol 2023; 10:787-801. [PMID: 37000947 PMCID: PMC10187726 DOI: 10.1002/acn3.51767] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 03/08/2023] [Accepted: 03/12/2023] [Indexed: 04/03/2023] Open
Abstract
OBJECTIVE The goal of this study is to demonstrate the utility of a growth assay to quantify the functional impact of single nucleotide variants (SNVs) in SLC2A1, the gene responsible for Glut1DS. METHODS The functional impact of 40 SNVs in SLC2A1 was quantitatively determined in HAP1 cells in which SLC2A1 is required for growth. Donor libraries were introduced into the endogenous SLC2A1 gene in HAP1-Lig4KO cells using CRISPR/Cas9. Cell populations were harvested and sequenced to quantify the effect of variants on growth and generate a functional score. Quantitative functional scores were compared to 3-OMG uptake, SLC2A1 cell surface expression, CADD score, and clinical data, including CSF/blood glucose ratio. RESULTS Nonsense variants (N = 3) were reduced in cell culture over time resulting in negative scores (mean score: -1.15 ± 0.17), whereas synonymous variants (N = 10) were not depleted (mean score: 0.25 ± 0.12) (P < 2e-16). Missense variants (N = 27) yielded a range of functional scores including slightly negative scores, supporting a partial function and intermediate phenotype. Several variants with normal results on either cell surface expression (p.N34S and p.W65R) or 3-OMG uptake (p.W65R) had negative functional scores. There is a moderate but significant correlation between our functional scores and CADD scores. INTERPRETATION Cell growth is useful to quantitatively determine the functional effects of SLC2A1 variants. Nonsense variants were reliably distinguished from benign variants in this in vitro functional assay. For facilitating early diagnosis and therapeutic intervention, future work is needed to determine the functional effect of every possible variant in SLC2A1.
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Affiliation(s)
- Naeimeh Tayebi
- Department of NeurologyWashington University in St LouisSt LouisMissouriUSA
| | - Brian Leon‐Ricardo
- Department of NeurologyWashington University in St LouisSt LouisMissouriUSA
| | - Kevin McCall
- Department of NeurologyWashington University in St LouisSt LouisMissouriUSA
| | - Elvisa Mehinovic
- Department of GeneticsWashington University in St LouisSt LouisMissouriUSA
| | - Kristin Engelstad
- Department of NeurologyColumbia University Irving Medical CenterNew YorkNew YorkUSA
| | - Vincent Huynh
- Department of NeurologyColumbia University Irving Medical CenterNew YorkNew YorkUSA
| | - Tychele N. Turner
- Department of GeneticsWashington University in St LouisSt LouisMissouriUSA
| | - Judy Weisenberg
- Department of NeurologyWashington University in St LouisSt LouisMissouriUSA
| | - Liu L. Thio
- Department of NeurologyWashington University in St LouisSt LouisMissouriUSA
| | - Paul Hruz
- Department of PediatricsWashington University in St LouisSt LouisMissouriUSA
| | - Robin S. B. Williams
- Centre for Biomedical Sciences, Department of Biological SciencesRoyal Holloway University of LondonEghamUK
| | - Darryl C. De Vivo
- Department of NeurologyColumbia University Irving Medical CenterNew YorkNew YorkUSA
| | | | - Gabe Haller
- Department of NeurologyWashington University in St LouisSt LouisMissouriUSA
- Department of GeneticsWashington University in St LouisSt LouisMissouriUSA
- Department of Neurological SurgeryWashington University in St LouisSt LouisMissouriUSA
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Klepper J, Akman C, Armeno M, Auvin S, Cervenka M, Cross HJ, De Giorgis V, Della Marina A, Engelstad K, Heussinger N, Kossoff EH, Leen WG, Leiendecker B, Monani UR, Oguni H, Neal E, Pascual JM, Pearson TS, Pons R, Scheffer IE, Veggiotti P, Willemsen M, Zuberi SM, De Vivo DC. Glut1 Deficiency Syndrome (Glut1DS): State of the art in 2020 and recommendations of the international Glut1DS study group. Epilepsia Open 2020; 5:354-365. [PMID: 32913944 PMCID: PMC7469861 DOI: 10.1002/epi4.12414] [Citation(s) in RCA: 125] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2020] [Revised: 06/13/2020] [Accepted: 06/16/2020] [Indexed: 12/14/2022] Open
Abstract
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.
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Affiliation(s)
- Joerg Klepper
- Children's Hospital Aschaffenburg‐AlzenauAschaffenburgGermany
| | - Cigdem Akman
- Department of Neurology and PediatricsVagelos College of Physicians and Surgeons at Columbia UniversityNew YorkNYUSA
| | - Marisa Armeno
- Department of NutritionHospital Pediatria JP GarrahanBuenos AiresArgentina
| | - Stéphane Auvin
- Department of Pediatric NeurologyCHU Hôpital Robert DebreAPHPParisFrance
| | - Mackenzie Cervenka
- Department of NeurologyComprehensive Epilepsy CenterJohns Hopkins University School of MedicineBaltimoreMDUSA
| | - Helen J. Cross
- UCL NIHR BRC Great Ormond Street Institute of Child HealthLondonUK
| | | | - Adela Della Marina
- Department of Neuropediatrics, Developmental Neurology and Social Pediatrics, Centre for Neuromuscular Disorders in Children, University Hospital EssenUniversity of Duisburg‐EssenEssenGermany
| | - Kristin Engelstad
- Department of Neurology and PediatricsVagelos College of Physicians and Surgeons at Columbia UniversityNew YorkNYUSA
| | - Nicole Heussinger
- Department of Pediatric NeurologyParacelsus Medical Private UniversityNurembergGermany
| | - Eric H. Kossoff
- Departments of Neurology and PediatricsJohns Hopkins UniversityBaltimoreMDUSA
| | - Wilhelmina G. Leen
- Department of NeurologyCanisius Wilhemina HospitalNijmegenThe Netherlands
| | - Baerbel Leiendecker
- Department of Neuropediatrics, Developmental Neurology and Social Pediatrics, Centre for Neuromuscular Disorders in Children, University Hospital EssenUniversity of Duisburg‐EssenEssenGermany
| | - Umrao R. Monani
- Center for Motor Neuron Biology & DiseaseDepartments of Neurology and Pathology & Cell BiologyColumbia University Irving Medical CenterNew YorkNYUSA
| | - Hirokazu Oguni
- Department of PediatricsTokyo Women's Medical UniversityTokyoJapan
| | | | - Juan M. Pascual
- Departments of Neurology and Neurotherapeutics, Physiology and PediatricsEugene McDermott Center for Human Growth and DevelopmentThe University of Texas Southwestern Medical CenterDallasTXUSA
| | - Toni S. Pearson
- Mount Sinai Center for Headache & Pain MedicineNew YorkNYUSA
| | - Roser Pons
- First Department of PediatricsAgia Sofia HospitalUniversity of AthensAthensGreece
| | - Ingrid E. Scheffer
- Florey and Murdoch InstitutesAustin Health and Royal Children's HospitalThe University of MelbourneMelbourneVictoriaAustralia
| | - Pierangelo Veggiotti
- Pediatric Neurology V. Buzzi HospitalChild Neuropsychiatry University of MilanMilanItaly
| | - Michél Willemsen
- Department of Pediatric NeurologyRadboud University Medical CentreAmalia Children's HospitalNijmegenNetherlands
| | - Sameer M. Zuberi
- Royal Hospital for Children & College of Medical Veterinary & Life SciencesUniversity of GlasgowGlasgowUK
| | - Darryl C. De Vivo
- Department of Neurology and PediatricsVagelos College of Physicians and Surgeons at Columbia UniversityNew YorkNYUSA
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Winczewska-Wiktor A, Hoffman-Zacharska D, Starczewska M, Kaczmarek I, Badura-Stronka M, Steinborn B. Variety of symptoms of GLUT1 deficiency syndrome in three-generation family. Epilepsy Behav 2020; 106:107036. [PMID: 32247176 DOI: 10.1016/j.yebeh.2020.107036] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Revised: 03/06/2020] [Accepted: 03/06/2020] [Indexed: 10/24/2022]
Abstract
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.
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Affiliation(s)
- Anna Winczewska-Wiktor
- Department of Developmental Neurology, Poznan University of Medical Sciences, Przybyszewskiego 49, 60-355 Poznan, Poland.
| | - Dorota Hoffman-Zacharska
- Institute of Mother and Child, Department of Medical Genetics, ul. Kasprzaka 17A, 01-211 Warsaw, Poland.
| | - Monika Starczewska
- Department of Developmental Neurology, Poznan University of Medical Sciences, Przybyszewskiego 49, 60-355 Poznan, Poland.
| | - Izabela Kaczmarek
- The Neuropsychology Laboratory, Department of Developmental Neurology, Poznan University of Medical Sciences, Przybyszewskiego 49, 60-355 Poznan, Poland.
| | - Magdalena Badura-Stronka
- Department of Medical Genetics, Poznan University of Medical Sciences, Rokietnicka 8, 60-806 Poznań, Poland.
| | - Barbara Steinborn
- Department of Developmental Neurology, Poznan University of Medical Sciences, Przybyszewskiego 49, 60-355 Poznan, Poland.
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Pimentel AC, Barroso IG, Ferreira JMJ, Dias RO, Ferreira C, Terra WR. Molecular machinery of starch digestion and glucose absorption along the midgut of Musca domestica. JOURNAL OF INSECT PHYSIOLOGY 2018; 109:11-20. [PMID: 29803861 DOI: 10.1016/j.jinsphys.2018.05.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Revised: 04/30/2018] [Accepted: 05/23/2018] [Indexed: 06/08/2023]
Abstract
Until now there is no molecular model of starch digestion and absorption of the resulting glucose molecules along the larval midgut of Musca domestica. For addressing to this, we used RNA-seq analyses from seven sections of the midgut and carcass to evaluate the expression level of the genes coding for amylases, maltases and sugar transporters (SP). An amylase related protein (Amyrel) and two amylase sequences, one soluble and one with a predicted GPI-anchor, were identified. Three highly expressed maltase genes were correlated with biochemically characterized maltases: one soluble, other glycocalyx-associated, and another membrane-bound. SPs were checked as being apical or basal by proteomics of microvillar preparations and those up-regulated by starch were identified by real time PCR. From the 9 SP sequences with high expression in midgut, two are putative sugar sensors (MdSP4 and MdSP5), one is probably a trehalose transporter (MdSP8), whereas MdSP1-3, MdSP6, and MdSP9 are supposed to transport glucose into cells, and MdSP7 from cells to hemolymph. MdSP1, MdSP7, and MdSP9 are up-regulated by starch. Based on the data, starch is at first digested by amylase and maltases at anterior midgut, with the resulting glucose units absorbed at middle midgut. At this region, low pH, lysozyme, and cathepsin D open the ingested bacteria and fungi cells, freeing sugars and glycogen. This and the remaining dietary starch are digested by amylase and maltases at the end of middle midgut and up to the middle part of the posterior midgut, with resulting sugars being absorbed along the posterior midgut.
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Affiliation(s)
- André C Pimentel
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Avenida Professor Lineu Prestes, 748, São Paulo 05508-000, Brazil
| | - Ignacio G Barroso
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Avenida Professor Lineu Prestes, 748, São Paulo 05508-000, Brazil
| | - Jéssica M J Ferreira
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Avenida Professor Lineu Prestes, 748, São Paulo 05508-000, Brazil
| | - Renata O Dias
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Avenida Professor Lineu Prestes, 748, São Paulo 05508-000, Brazil
| | - Clélia Ferreira
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Avenida Professor Lineu Prestes, 748, São Paulo 05508-000, Brazil
| | - Walter R Terra
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Avenida Professor Lineu Prestes, 748, São Paulo 05508-000, Brazil.
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5
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Park MS. Molecular Dynamics Simulations of the Human Glucose Transporter GLUT1. PLoS One 2015; 10:e0125361. [PMID: 25919356 PMCID: PMC4412407 DOI: 10.1371/journal.pone.0125361] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Accepted: 03/12/2015] [Indexed: 01/31/2023] Open
Abstract
Glucose transporters (GLUTs) provide a pathway for glucose transport across membranes. Human GLUTs are implicated in devastating diseases such as heart disease, hyper- and hypo-glycemia, type 2 diabetes and cancer. The human GLUT1 has been recently crystalized in the inward-facing open conformation. However, there is no other structural information for other conformations. The X-ray structures of E. coli Xylose permease (XylE), a glucose transporter homolog, are available in multiple conformations with and without the substrates D-xylose and D-glucose. XylE has high sequence homology to human GLUT1 and key residues in the sugar-binding pocket are conserved. Here we construct a homology model for human GLUT1 based on the available XylE crystal structure in the partially occluded outward-facing conformation. A long unbiased all atom molecular dynamics simulation starting from the model can capture a new fully opened outward-facing conformation. Our investigation of molecular interactions at the interface between the transmembrane (TM) domains and the intracellular helices (ICH) domain in the outward- and inward-facing conformation supports that the ICH domain likely stabilizes the outward-facing conformation in GLUT1. Furthermore, inducing a conformational transition, our simulations manifest a global asymmetric rocker switch motion and detailed molecular interactions between the substrate and residues through the water-filled selective pore along a pathway from the extracellular to the intracellular side. The results presented here are consistent with previously published biochemical, mutagenesis and functional studies. Together, this study shed light on the structure and functional relationships of GLUT1 in multiple conformational states.
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Affiliation(s)
- Min-Sun Park
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, United States of America
- * E-mail:
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6
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Raja M, Kinne RKH. Pathogenic mutations causing glucose transport defects in GLUT1 transporter: The role of intermolecular forces in protein structure-function. Biophys Chem 2015; 200-201:9-17. [PMID: 25863194 DOI: 10.1016/j.bpc.2015.03.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Revised: 03/12/2015] [Accepted: 03/17/2015] [Indexed: 12/14/2022]
Abstract
Two families of glucose transporter - the Na(+)-dependent glucose cotransporter-1 (SGLT family) and the facilitated diffusion glucose transporter family (GLUT family) - play a crucial role in the translocation of glucose across the epithelial cell membrane. How genetic mutations cause life-threatening diseases like GLUT1-deficiency syndrome (GLUT1-DS) is not well understood. In this review, we have combined previous functional data with our in silico analyses of the bacterial homologue of GLUT members, XylE (an outward-facing, partly occluded conformation) and previously proposed GLUT1 homology model (an inward-facing conformation). A variety of native and mutant side chain interactions were modeled to highlight the potential roles of mutations in destabilizing protein-protein interaction hence triggering structural and functional defects. This study sets the stage for future studies of the structural properties that mediate GLUT1 dysfunction and further suggests that both SGLT and GLUT families share conserved domains that stabilize the transporter structure/function via a similar mechanism.
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Affiliation(s)
- Mobeen Raja
- Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany; Molecular Structure and Function, The Peter Gilgan Centre for Research and Learning, The Hospital for Sick Children, 686 Bay Street, Toronto, ON M5G 0A4, Canada.
| | - Rolf K H Kinne
- Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany.
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Suls A, Dedeken P, Goffin K, Van Esch H, Dupont P, Cassiman D, Kempfle J, Wuttke TV, Weber Y, Lerche H, Afawi Z, Vandenberghe W, Korczyn AD, Berkovic SF, Ekstein D, Kivity S, Ryvlin P, Claes LRF, Deprez L, Maljevic S, Vargas A, Van Dyck T, Goossens D, Del-Favero J, Van Laere K, De Jonghe P, Van Paesschen W. Paroxysmal exercise-induced dyskinesia and epilepsy is due to mutations in SLC2A1, encoding the glucose transporter GLUT1. Brain 2008; 131:1831-44. [PMID: 18577546 PMCID: PMC2442425 DOI: 10.1093/brain/awn113] [Citation(s) in RCA: 258] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Paroxysmal exercise-induced dyskinesia (PED) can occur in isolation or in association with epilepsy, but the genetic causes and pathophysiological mechanisms are still poorly understood. We performed a clinical evaluation and genetic analysis in a five-generation family with co-occurrence of PED and epilepsy (n = 39), suggesting that this combination represents a clinical entity. Based on a whole genome linkage analysis we screened SLC2A1, encoding the glucose transporter of the blood-brain-barrier, GLUT1 and identified heterozygous missense and frameshift mutations segregating in this and three other nuclear families with a similar phenotype. PED was characterized by choreoathetosis, dystonia or both, affecting mainly the legs. Predominant epileptic seizure types were primary generalized. A median CSF/blood glucose ratio of 0.52 (normal >0.60) in the patients and a reduced glucose uptake by mutated transporters compared with the wild-type as determined in Xenopus oocytes confirmed a pathogenic role of these mutations. Functional imaging studies implicated alterations in glucose metabolism in the corticostriate pathways in the pathophysiology of PED and in the frontal lobe cortex in the pathophysiology of epileptic seizures. Three patients were successfully treated with a ketogenic diet. In conclusion, co-occurring PED and epilepsy can be due to autosomal dominant heterozygous SLC2A1 mutations, expanding the phenotypic spectrum associated with GLUT1 deficiency and providing a potential new treatment option for this clinical syndrome.
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Affiliation(s)
- Arvid Suls
- Neurogenetics Group,VIB Department of Molecular Genetics, University of Antwerp, Antwerpen, Belgium
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8
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Pascual JM, Wang D, Yang R, Shi L, Yang H, De Vivo DC. Structural signatures and membrane helix 4 in GLUT1: inferences from human blood-brain glucose transport mutants. J Biol Chem 2008; 283:16732-42. [PMID: 18387950 PMCID: PMC2423257 DOI: 10.1074/jbc.m801403200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2008] [Indexed: 12/11/2022] Open
Abstract
Exon IV of SLC2A1, a multiple facilitator superfamily (MFS) transporter gene, is particularly susceptible to mutations that cause GLUT1 deficiency syndrome, a human encephalopathy that results from decreased glucose flux through the blood-brain barrier. Genotyping of 100 patients revealed that in a third of them who harbor missense mutations in the GLUT1 transporter, transmembrane domain 4 (TM4), encoded by SLC2A1 exon IV, contains mutant residues that have the periodicity of one face of a kinked alpha-helix. Arg-126, located at the amino terminus of TM4, is the locus for most of the mutations followed by other arginine and glycine residues located elsewhere in the transporter but conserved among MFS proteins. The Arg-126 mutants were constructed and assayed for protein expression, targeting, and transport capacity in Xenopus oocytes. The role of charge at position 126, as well as its accessibility, was investigated in R126H by determining its activity as a function of extracellular pH. The results indicate that intracellular charges at the MFS TM2-3 and TM8-9 signature loops and flanking TMs 3, 5, and 6 are critical for the structure of GLUT1 as are TM glycines and that TM4, located at the catalytic core of MFS proteins, forms a helix that surfaces into the extracellular solution where another proton facilitates transport.
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Affiliation(s)
- Juan M Pascual
- Department of Neurology, The University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
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9
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Bergeron MJ, Simonin A, Bürzle M, Hediger MA. Inherited epithelial transporter disorders--an overview. J Inherit Metab Dis 2008; 31:178-87. [PMID: 18415698 DOI: 10.1007/s10545-008-0861-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/30/2007] [Revised: 02/12/2008] [Accepted: 02/13/2008] [Indexed: 01/11/2023]
Abstract
In the late 1990s, the identification of transporters and transporter-associated genes progressed substantially due to the development of new cloning approaches such as expression cloning and, subsequently, to the implementation of the human genome project. Since then, the role of many transporter genes in human diseases has been elucidated. In this overview, we focus on inherited disorders of epithelial transporters. In particular, we review genetic defects of the genes encoding glucose transporters (SLC2 and SLC5 families) and amino acid transporters (SLC1, SLC3, SLC6 and SLC7 families).
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Affiliation(s)
- M J Bergeron
- Institute of Biochemistry and Molecular Medicine, University of Berne, Berne, Switzerland
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10
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Abstract
GLUT1 deficiency syndrome (GLUT1DS, OMIM 606777) is a treatable epileptic encephalopathy resulting from impaired glucose transport into the brain. The essential biochemical finding is a low glucose concentration in the cerebrospinal fluid (CSF; hypoglycorrhachia; mean 1.7 [SD 0.3mmol/L]) in the setting of normoglycaemia. CSF lactate is normal. Patients present with an early-onset epilepsy resistant to anticonvulsants, developmental delay, and a complex movement disorder. Hypotonic, ataxic, and dystonic features are most prominent. Speech is often severely affected. Some patients develop spasticity and secondary microcephaly. The phenotype is highly variable ranging from severe impairment to children without seizures. Electroencephalography (EEG) may show 2.5-4Hz spike-waves improving on food intake. Neuroimaging is uninformative. Most patients carry heterozygous de novo mutations in the GLUT1 gene (OMIM 138140, gene map locus 1p35-31.3). Autosomal dominant transmission and several mutational hot spots have been identified, but phenotype-genotype correlations are not yet apparent. Homozygous GLUT1 mutations presumably are lethal. The ketogenic diet is the treatment of choice as it provides an alternative fuel to the brain. It should be introduced early and maintained into puberty. Seizures are effectively controlled with the onset of ketosis, but might recur and require comedication. The effect on neurodevelopment appears less impressive. The increasing number of patients, molecular and biochemical analysis, recent research into ketogenic diet mechanisms, and the development of animal models for GLUT1DS have brought substantial insights in disease manifestations and mechanisms. This review summarizes data on 84 published cases and highlights recent advances in understanding this entity.
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Salas-Burgos A, Iserovich P, Zuniga F, Vera JC, Fischbarg J. Predicting the three-dimensional structure of the human facilitative glucose transporter glut1 by a novel evolutionary homology strategy: insights on the molecular mechanism of substrate migration, and binding sites for glucose and inhibitory molecules. Biophys J 2004; 87:2990-9. [PMID: 15326030 PMCID: PMC1304772 DOI: 10.1529/biophysj.104.047886] [Citation(s) in RCA: 147] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2004] [Accepted: 08/09/2004] [Indexed: 12/13/2022] Open
Abstract
The glucose transporters (GLUT/SLC2A) are members of the major facilitator superfamily. Here, we generated a three-dimensional model for Glut1 using a two-step strategy: 1), GlpT structure as an initial homology template and 2), evolutionary homology using glucose-6-phosphate translocase as a template. The resulting structure (PDB No. 1SUK) exhibits a water-filled passageway communicating the extracellular and intracellular domains, with a funnel-like exofacial vestibule (infundibulum), followed by a 15 A-long x 8 A-wide channel, and a horn-shaped endofacial vestibule. Most residues which, by mutagenesis, are crucial for transport delimit the channel, and putative sugar recognition motifs (QLS, QLG) border both ends of the channel. On the outside of the structure there are two positively charged cavities (one exofacial, one endofacial) delimited by ATP-binding Walker motifs, and an exofacial large side cavity of yet unknown function. Docking sites were found for the glucose substrate and its inhibitors: glucose, forskolin, and phloretin at the exofacial infundibulum; forskolin, and phloretin at an endofacial site next to the channel opening; and cytochalasin B at a positively charged endofacial pocket 3 A away from the channel. Thus, 1SUK accounts for practically all biochemical and mutagenesis evidence, and provides clues for the transport process.
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Affiliation(s)
- Alexis Salas-Burgos
- Department of Ophthalmology, College of Physicians & Surgeons, Columbia University, New York, New York 10032, USA
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Klepper J. Impaired glucose transport into the brain: the expanding spectrum of glucose transporter type 1 deficiency syndrome. Curr Opin Neurol 2004; 17:193-6. [PMID: 15021248 DOI: 10.1097/00019052-200404000-00018] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE OF REVIEW Glucose transporter type 1 deficiency syndrome (OMIM 606777) is a treatable epileptic encephalopathy resulting from impaired glucose transport into the brain. In recent years, the increasing number of patients has generated substantial insights into the manifestations and mechanisms of this disease. Current understanding of this novel disorder is reviewed, and recent advances in diagnosis and treatment are highlighted. RECENT FINDINGS The syndrome is now understood to be a complex neurological disorder. The clinical spectrum has recently been extended by infants with 'benign' transient hypoglycorrhachia, glucose transporter type 1 deficiency syndrome without seizures, and by adult cases. Other key findings in the last couple of years include (1) the description of electroencephalogram abnormalities, (2) a characteristic cerebral metabolic footprint in positron emission tomography imaging, and (3) the definition of molecular mechanisms and functional domains within the glucose transporter type 1 protein by in-vitro mutagenesis. The disease has also shed a new light on the mechanisms and the effectiveness of the ketogenic diet for seizure control. SUMMARY The syndrome is now well characterized in children and should be considered in any patient with intractable epilepsy. An effective therapy is available. The clinical spectrum and the molecular basis of the disease are increasingly heterogeneous and indicate complex pathogenic mechanisms that will ultimately lead to a classification on clinical, biochemical, and molecular grounds.
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Affiliation(s)
- Jörg Klepper
- Department of Pediatrics and Pediatric Neurology, University of Essen, Essen, Germany.
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Klepper J, Diefenbach S, Kohlschütter A, Voit T. Effects of the ketogenic diet in the glucose transporter 1 deficiency syndrome. Prostaglandins Leukot Essent Fatty Acids 2004; 70:321-7. [PMID: 14769490 DOI: 10.1016/j.plefa.2003.07.004] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2003] [Accepted: 07/01/2003] [Indexed: 11/23/2022]
Abstract
The ketogenic diet (KD), established to treat intractable childhood epilepsy, has emerged as the principal treatment of GLUT1 deficiency syndrome (OMIM 606777). This defect of glucose transport into the brain results in hypoglycorrhachia causing epilepsy, developmental delay, and a complex motor disorder in early childhood. Ketones provided by a high-fat, low-carbohydrate diet serve as an alternative fuel to the brain. Glucose, lactate, lipids, and ketones in blood and cerebrospinal fluid were investigated in five GLUT1-deficient patients before and on the KD. Hypoglycorrhachia was detected in the non-ketotic and ketotic state. In ketosis, lactate concentrations in the cerebrospinal fluid increased moderately. The CSF/blood ratio for acetoacetate was higher compared to beta-hydroxybutyrate. Free fatty acids did not enter the brain in significant amounts. Blood concentrations of essential fatty acids determined in 18 GLUT1-deficient patients on the KD were sufficient in all age groups. The effects of the KD in GLUT1 deficiency syndrome, particularly the course of blood lipids, are discussed in an illustrative case. In this syndrome, the KD effectively restores brain energy metabolism. Ketosis does not influence impaired GLUT1-mediated glucose transport into brain: hypoglycorrhachia, the biochemical hallmark of the disease, can be identified in GLUT1-deficient patients on a KD. The effects of ketosis on the concentrations of glucose, lactate, ketones, and fatty acids in blood and cerebrospinal fluid in this entity are discussed in view of previous data on ketosis in man.
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Affiliation(s)
- Jörg Klepper
- Department of Pediatric Neurology, University of Essen, Hufelandstrasse 55, D-45122 Essen, Germany.
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Lange P, Gertsen E, Monden I, Klepper J, Keller K. Functional consequences of an in vivo mutation in exon 10 of the human GLUT1 gene. FEBS Lett 2003; 555:274-8. [PMID: 14644427 DOI: 10.1016/s0014-5793(03)01247-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The functional consequences of an in vivo heterozygous insertion mutation in the human facilitated glucose transporter isoform 1 (GLUT1) gene were investigated. The resulting frameshift in exon 10 changed the primary structure of the C-terminus from 42 in native GLUT1 to 61 amino acid residues in the mutant. Kinetic studies on a patient's erythrocytes were substantiated by expressing the mutant cDNA in Xenopus laevis oocytes. K(m) and V(max) values were clearly decreased explaining pathogenicity. Targeting to the plasma membrane was comparable between mutant and wild-type GLUT1. Transport inhibition by cytochalasin B was more effective in the mutant than in the wild-type transporter. The substrate specificity of GLUT1 remained unchanged.
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Affiliation(s)
- Peter Lange
- Institute of Pharmacology, Freie Universität Berlin, Thielallee 67-73, D-14195 Berlin, Germany
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