Simultaneous impairment of neuronal and metabolic function of mutated gephyrin in a patient with epileptic encephalopathy

Synaptic inhibition is essential for shaping the dynamics of neuronal networks, and aberrant inhibition plays an important role in neurological disorders. Gephyrin is a central player at inhibitory postsynapses, directly binds and organizes GABAA and glycine receptors (GABAARs and GlyRs), and is thereby indispensable for normal inhibitory neurotransmission. Additionally, gephyrin catalyzes the synthesis of the molybdenum cofactor (MoCo) in peripheral tissue. We identified a de novo missense mutation (G375D) in the gephyrin gene (GPHN) in a patient with epileptic encephalopathy resembling Dravet syndrome. Although stably expressed and correctly folded, gephyrin-G375D was nonsynaptically localized in neurons and acted dominant-negatively on the clustering of wild-type gephyrin leading to a marked decrease in GABAAR surface expression and GABAergic signaling. We identified a decreased binding affinity between gephyrinG375D and the receptors, suggesting that Gly375 is essential for gephyrin–receptor complex formation. Surprisingly, gephyrinG375D was also unable to synthesize MoCo and activate MoCodependent enzymes. Thus, we describe a missense mutation that affects both functions of gephyrin and suggest that the identified defect at GABAergic synapses is the mechanism underlying the patient’s severe phenotype. 1 Department of Chemistry, Institute of Biochemistry, University of Cologne, Cologne, Germany 2 Neurogenetics Group, Department of Molecular Genetics, VIB, Antwerp, Belgium 3 Laboratory of Neurogenetics, Institute Born-Bunge, University of Antwerp, Antwerp, Belgium 4 GENOMED, Center for Medical Genetics, University of Antwerp, Antwerp, Belgium 5 Division Cell Physiology, Zoological Institute, Technische Universität Braunschweig, Braunschweig, Germany 6 Pediatric Neurology Clinic, Al Obregia Hospital, Bucharest, Romania 7 Department of Neurology, Pediatric Neurology, Psychiatry, Child and Adolescent Psychiatry, and Neurosurgery, Carol Davila University of Medicine and Pharmacy, Bucharest, Romania 8 Division of Genetic Medicine, Department of Pediatrics, University of Washington, Seattle, WA, USA 9 Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, UK 10 Center for Molecular Medicine Cologne (CMMC), University of Cologne, Cologne, Germany 11 Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Cologne, Germany 12 Psychiatric & Neurodevelopmental Genetics Unit, Department of Psychiatry, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA 13 Cologne Center for Genomics, Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Cologne, Germany 14 Department of Neuropediatrics, University Medical Faculty Giessen and Marburg, Giessen, Germany 15 Institute for Molecular Medicine Finland (FIMM), University of Helsinki, Helsinki, Finland 16 Program in Medical and Population Genetics, The Broad Institute of MIT and Harvard, Cambridge, MA, USA 17 The Stanley Center for Psychiatric Research, The Broad Institute of MIT and Harvard, Cambridge, MA, USA 18 Analytic and Translational Genetics Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA 19 Department of Neurology, Massachusetts General Hospital, Boston, MA, USA 20 Department of Neuropediatrics, University Medical Center Schleswig-Holstein, Christian Albrechts University, Kiel, Germany 21 Division of Neurology, The Children’s Hospital of Philadelphia, Philadelphia, PA, USA 22 Division of Neurology, Antwerp University Hospital, Antwerp, Belgium 23 Inserm U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, Paris, France 24 Centre de reference épilepsies rares, Epilepsy unit, AP-HP Groupe hospitalier Pitié-Salpêtrière, F-75013, Paris, France *Corresponding author. Tel: +1 650 333 4376; E-mail: b.dejanovic@uni-koeln.de **Corresponding author. Tel: +32 32 65 1022; Fax: +32 32 65 1112; E-mail: sarahweck@hotmail.com ***Corresponding author. Tel: +49 221 470 6440; Fax: +49 221 470 5092; E-mail: gschwarz@uni-koeln.de EuroEPINOMICS Dravet working group: B.P.C. Koeleman; E.H. Brilstra; S. Sisodiya; S. Baulac; C. Depienne; J. Serratosa; P. Striano; C. Marini; R. Guerrini; H. Caglayan; T. Talvik; D. Hoffman; S. von Spiczak; J. Jähn These authors contributed equally to this work Joint senior authors EMBO Molecular Medicine Vol 7 | No 12 | 2015 a 2015 The Authors. Published under the terms of the CC BY 4.0 license 1580