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Published on: August 20, 2019
Molecular and Phenotypic Characterization of the RORB-Related Disorder
Zeynep Gokce-Samar1, Annalisa Vetro1, Julitta De Bellescize1
1From the Department of Pediatric Clinical Epileptology (Z.G.-S., J.D.B., A.A.A.), Sleep Disorders and Functional Neurology, University Hospitals of Lyon, HCL, Member of ERN Epicare, France; Neuroscience Department (A.V., T.P., R.G.) IRCCS, Children's Hospital Meyer, Member of ERN Epicare, and University of Florence, Italy; Univ Lyon (L.M., N.P., D.S., N.C., J.C., G.L.), Univ Lyon 1, CNRS, INSERM, Physiopathologie et Génétique du Neurone et du Muscle, UMR5261, U1315, Institut NeuroMyoGène, France; Pediatric Neurology Unit (C.M.K., J.F.), University Hospitals of Geneva, Switzerland; Child Neurology and Psychiatric Unit (C.M., E.C.), Children's Hospital G. Salesi, Azienda Universitaria Ospedaliera delle Marche, Ancona, Italy; Department of Neurology (B.M.A.), University Hospitals of Montpellier; Department of Genetics (D.S., N.C., A. Labalme, G.L.), University Hospitals of Lyon, HCL, Member of ERN Epicare, France; Paediatric Epilepsy Research (A.A.A.), Child Neurology Department, Member of the ERN EpiCARE, San Juan de Dios Children's Hospital, Barcelona, Spain; Division of Neurology (V.A.C., S.M.R., I.H.), and The Epilepsy NeuroGenetics Initiative (ENGIN) (V.A.C., S.M.R., K.L.H., I.H.), Children's Hospital of Philadelphia, PA; Department of Neurology (V.A.C., S.M.R., I.H.), University of Pennsylvania Perelman School of Medicine, Philadelphia; Univ Rouen Normandie (F.L., G.N.), Inserm U1245 and CHU Rouen, Department of Genetics and Reference Center for Developmental Disorders; Department of Pediatric Neurology (G.A.M., A. Lebas), University Hospitals of Rouen; Department of Pediatric Neurology (H.O.T.), Hospital of Alpes Léman, Annemasse, France; Department of Pediatric Neurology (A.R.), Barcelona Children's Hospital, University of Barcelona, Spain; Developmental Neurosciences (A.N., M.A.K., K.R., R.S.), Zayed Centre for Research, University College of London, Great Ormond Street Hospital, Institute of Child Health, United Kingdom; Institute of Medical Genetics (P.J.), University of Zürich; Department of Neuropediatrics (G. Ramantani, K.S.), University Children's Hospital and University of Zürich, Switzerland; Department of Neurology (M.K.), Medical University of Vienna, Austria; Division of Pediatric Neurology, Developmental Medicine and Social Pediatrics (L.G.), Department of Pediatrics, Dr. von Hauner Children's Hospital, Ludwig-Maximilians-University, Munich, Germany; Institute of Human Genetics (S.V.), Medical University of Innsbruck, Innsbruck, Austria; Werner-Forßmann-Krankenhaus (S.V., S.T.), Eberswalde, Germany; Pediatric Neurology Discipline (D.C.), Neurosciences Department, Carol Davila University of Medicine Bucharest; Pediatric Neurology Clinic (D.C.), Al Obregia Hospital, Center of Expertise for Pediatric Neurology Rare Disorders, Member of ERN EpiCARE, Bucharest, Romania; Institute of Clinical Molecular Biology (M.P., I.H.), Christian-Albrechts-University of Kiel, Germany; Mission Fullerton Genetics Center (C.H.-E.), Asheville, NC; Department of Neurology (I.K.), Svt. Luka's Institute of Child Neurology and Epilepsy, Moscow; Department of Medical Genetics (I.R.), Kazan State University, Russia; Division of Child Neurology (D.S.R.), Department of Pediatrics, UPMC Children's Hospital of Pittsburgh, PA; Department of Molecular and Human Genetics (J.A.R.), Baylor College of Medicine, Houston, TX; Division of Clinical Genetics and Dysmorphology (M.A., K.G., J.M.G.), Cedars-Sinai Medical Center, Los Angeles, CA; Department of Neurology (A.I.), University Hospitals of Armand Trousseau, AP-HP, Paris; Department of Pediatric Neurology (N.V.), University Hospitals of Marseille, AP-HM; Univ. Lille (T.S.), CHU Lille, ULR7364, RADEME, Institute of Medical Genetics; Department of Clinical Genetics (R.C.), CHU Lille, France; Institute of Human Genetics (P.Z., S.N., K.P., T.B., I.M., M.R., R.A.J.), University of Leipzig Medical Center, Germany; Institute of Human Genetics (S.T.), Medical University of Innsbruck, Austria; Department of Biomedical and Health Informatics (DBHi) (I.H.), Children's Hospital of Philadelphia, PA; Department of Pediatric Neurology (F.E.J., K.K.), Brain Center UMC Utrecht, Member of ERN Epicare, Utrecht, the Netherlands; Department of Neurology (G. Rudolf), Strasbourg University Hospital; and Nantes Université (S.K.), CHU Nantes, Service de Génétique Médicale, and CNRS, INSERM, l'institut du thorax, France.
Background And Objectives:
Heterozygous variants in RAR-related orphan receptor B (RORB) have recently been associated with susceptibility to idiopathic generalized epilepsy. However, few reports have been published so far describing pathogenic variants of this gene in patients with epilepsy and intellectual disability (ID). In this study, we aimed to delineate the epilepsy phenotype associated with RORB pathogenic variants and to provide arguments in favor of the pathogenicity of variants.
Methods:
Through an international collaboration, we analyzed seizure characteristics, EEG data, and genotypes of a cohort of patients with heterozygous variants in RORB. To gain insight into disease mechanisms, we performed ex vivo cortical electroporation in mouse embryos of 5 selected variants, 2 truncating and 3 missense, and evaluated on expression and quantified changes in axonal morphology.
Results:
We identified 35 patients (17 male, median age 10 years, range 2.5-23 years) carrying 32 different heterozygous variants in RORB, including 28 single-nucleotide variants or small insertions/deletions (12 missense, 12 frameshift or nonsense, 2 splice-site variants, and 2 in-frame deletions), and 4 microdeletions; de novo in 18 patients and inherited in 10. Seizures were reported in 31/35 (89%) patients, with a median age at onset of 3 years (range 4 months-12 years). Absence seizures occurred in 25 patients with epilepsy (81%). Nineteen patients experienced a single seizure type: absences, myoclonic absences, or absences with eyelid myoclonia and focal seizures. Nine patients had absence seizures combined with other generalized seizure types. One patient had presented with absences associated with photosensitive occipital seizures. Three other patients had generalized tonic-clonic seizures without absences. ID of variable degree was observed in 85% of the patients. Expression studies in cultured neurons showed shorter axons for the 5 tested variants, both truncating and missense variants, supporting an impaired protein function.
Discussion:
In most patients, the phenotype of the RORB-related disorder associates absence seizures with mild-to-moderate ID. In silico and in vitro evaluation of the variants in our cohort, including axonal morphogenetic experiments in cultured neurons, supports their pathogenicity, showing a hypomorphic effect.
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