INTRODUCTION: Although there has been increasing recognition of the occurrence of non-epileptic involuntary movements in developmental and epileptic encephalopathies (DEEs), the spectrum of dystonic presentations associated with these conditions remains poorly described. We sought to expand the catalogue of dystonia-predominant phenotypes in monogenic DEEs, building on the recently introduced concept of an epilepsy-movement disorder spectrum. METHODS: Cases were identified from a whole-exome-sequenced cohort of 45 pediatric index patients with complex dystonia (67% sequenced as parent-child trios). Review of molecular findings in DEE-associated genes was performed. For five individuals with identified DEE-causing variants, detailed information about presenting phenotypic features and the natural history of disease was obtained. RESULTS: De-novo pathogenic and likely pathogenic missense variants in GABRA1, GABBR2, GNAO1, and FOXG1 gave rise to infantile-onset persistent and paroxysmal dystonic manifestations, beginning in the limb or truncal musculature and progressing gradually to a generalized state. Coexisting, less prominent movement-disorder symptoms were observed and included myoclonic, ballistic, and stereotypic abnormal movements as well as choreoathetosis. Dystonia dominated over epileptic neurodevelopmental comorbidities in all four subjects and represented the primary indication for molecular genetic analysis. We also report the unusual case of an adult female patient with dystonia, tremor, and mild learning disability who was found to harbor a pathogenic frameshift variant in MECP2. CONCLUSIONS: Dystonia can be a leading clinical manifestation in different DEEs. A monogenic basis of disease should be considered on the association of dystonia and developmental delay-epilepsy presentations, justifying a molecular screening for variants in DEE-associated genes.

2nd Department of Neurology Faculty of Medicine Comenius University University Hospital Bratislava Bratislava Slovakia

Department of Neurology Charles University 1st Faculty of Medicine and General University Hospital Prague Prague Czech Republic

Department of Neurology Medical University Innsbruck Innsbruck Austria

Department of Neurology P J Safarik University Kosice Slovak Republic; Department of Neurology University Hospital of L Pasteur Kosice Slovak Republic

Department of Neurology Zvolen Hospital Slovakia

Department of Neuropediatrics and Muscle Disorders University Medical Center Faculty of Medicine University of Freiburg Germany

Inborn Errors of Metabolism Pediatric Intensive Care Unit University Hospital of Nantes Nantes France

Institute of Neurogenomics Helmholtz Zentrum München Munich Germany

Institute of Neurogenomics Helmholtz Zentrum München Munich Germany; Technical University of Munich Munich Germany; School of Medicine Institute of Human Genetics

Institute of Neurogenomics Helmholtz Zentrum München Munich Germany; Technical University of Munich Munich Germany; School of Medicine Institute of Human Genetics; Lehrstuhl für Neurogenetik Technische Universität München Munich Germany; Munich Cluster for Systems Neurology SyNergy Munich Germany

Ludwig Maximilian University of Munich Munich Germany; Hospital for Neuropediatrics and Neurological Rehabilitation Centre of Epilepsy for Children and Adolescents Schoen Klinik Vogtareuth Vogtareuth Germany

MGZ Medical Genetics Center Munich Munich Germany; Department of Pediatrics Technical University of Munich School of Medicine Munich Germany

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