Neurology 2017 01 4;88(5):483-492. Epub 2017 Jan 4.
From the Danish Epilepsy Centre (R.S.M., K.M.J., M.N.), Dianalund; Institute for Regional Health Services (R.S.M., K.M.J., M.N.), University of Southern Denmark, Odense; Department of Neurology and Epileptology (T.V.W., S.V., H.L., S.M.), Hertie Institute for Clinical Brain Research, and Department of Neurosurgery (T.V.W.), University of Tübingen; Department of Neuropediatrics (I.H., M.P., S.v.S., H.M.), University Medical Center Schleswig-Holstein, Kiel, Germany; Division of Neurology (I.H., S.H., H.D.), The Children's Hospital of Philadelphia, PA; Neuroscience Department (C.M., R.G.), Children's Hospital Anna Meyer-University of Florence, Italy; Department of Genetics (E.H.B., M.S., K.L.v.G.), University Medical Center Utrecht, the Netherlands; Department of Neurology and Neurorehabilitation (U.V., I.T., T.T.), Children's Clinic of Tartu University Hospital, Estonia; Department of Pediatric Neurology and Epilepsy Center (I.B.), LMU Munich, Germany; Department of Pediatrics (I.T., T.T.), University of Tartu; Tallinn Children's Hospital (I.T.), Tallinn, Estonia; Clinic for Neuropediatrics and Neurorehabilitation (G.K., C.B., H.H.), Epilepsy Center for Children and Adolescents, Schön Klinik Vogtareuth, Germany; Paracelsus Medical Private University (G.K.), Salzburg, Austria; Neuropeadiatric Department (L.L.F.), Hospices Civils de Lyon; Department of Genetics (G.L., N.C.), Lyon University Hospitals; Claude Bernard Lyon I University (G.L., N.C.); Lyon Neuroscience Research Centre (G.L., N.C.), CNRS UMR5292, INSERM U1028; Epilepsy, Sleep and Pediatric Neurophysiology Department (J.d.B.), Lyon University Hospitals, France; Clinic for Pediatric Neurology (S.B.), Pediatric Department, University Hospital, Herlev, Denmark; Kleinwachau (N.H.), Sächsisches Epilepsiezentrum Radeberg, Dresden; Department of Neuropediatrics/Epilepsy Center (J.J.), University Medical Center Freiburg; Department of General Paediatrics (S.S.), Division of Child Neurology and Inherited Metabolic Diseases, Centre for Paediatrics and Adolescent Medicine, University Hospital Heidelberg; Department of Women and Child Health (S.S.), Hospital for Children and Adolescents, University of Leipzig Hospitals and Clinics, Germany; Department of Pediatrics (C.T.M., H.C.M.), Division of Genetic Medicine, University of Washington, Seattle; Amplexa Genetics (L.H.G.L., H.A.D.), Odense, Denmark; Northern German Epilepsy Center for Children and Adolescents (S.v.S.), Schwentinental-Raisdorf, Germany; Wilhelm Johannsen Centre for Functional Genome Research (Y.M., N.T.), Department of Cellular and Molecular Medicine, University of Copenhagen; Danish Epilepsy Center (G.R.), Filadelfia/University of Copenhagen, Denmark; Department of Diagnostics (J.R.L.), Institute of Human Genetics, University of Leipzig; and Svt. Luka's Institute of Child Neurology and Epilepsy (K.M.), Moscow, Russia. Dr Maljevic is currently at the Florey Institute of Neuroscience and Mental Health, Melbourne, Australia.
Objective: To examine the role of mutations in GABRB3 encoding the β subunit of the GABA receptor in individual patients with epilepsy with regard to causality, the spectrum of genetic variants, their pathophysiology, and associated phenotypes.
Methods: We performed massive parallel sequencing of GABRB3 in 416 patients with a range of epileptic encephalopathies and childhood-onset epilepsies and recruited additional patients with epilepsy with GABRB3 mutations from other research and diagnostic programs.
Results: We identified 22 patients with heterozygous mutations in GABRB3, including 3 probands from multiplex families. The phenotypic spectrum of the mutation carriers ranged from simple febrile seizures, genetic epilepsies with febrile seizures plus, and epilepsy with myoclonic-atonic seizures to West syndrome and other types of severe, early-onset epileptic encephalopathies. Electrophysiologic analysis of 7 mutations in Xenopus laevis oocytes, using coexpression of wild-type or mutant β, together with α and γ subunits and an automated 2-microelectrode voltage-clamp system, revealed reduced GABA-induced current amplitudes or GABA sensitivity for 5 of 7 mutations.
Conclusions: Our results indicate that GABRB3 mutations are associated with a broad phenotypic spectrum of epilepsies and that reduced receptor function causing GABAergic disinhibition represents the relevant disease mechanism.