Loss-of-function variants in the KCNQ5 gene are implicated in genetic generalized epilepsies
Johanna Krüger,
Julian Schubert,
Josua Kegele,
Audrey Labalme,
Miaomiao Mao,
Jacqueline Heighway,
Guiscard Seebohm,
Pu Yan,
Mahmoud Koko,
Kezban Aslan-Kara,
Hande Caglayan,
Bernhard J. Steinhoff,
Yvonne G. Weber,
Pascale Keo-Kosal,
Samuel F. Berkovic,
Michael S. Hildebrand,
Steven Petrou,
Roland Krause,
Patrick May,
Gaetan Lesca,
Snezana Maljevic,
Holger Lerche
Affiliations
Johanna Krüger
Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried-Müller-Straße 27, 72076 Tübingen, Germany
Julian Schubert
Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried-Müller-Straße 27, 72076 Tübingen, Germany
Josua Kegele
Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried-Müller-Straße 27, 72076 Tübingen, Germany
Audrey Labalme
Service de Génétique, Hospices Civils de Lyon, Groupement Hospitalier Est, 59 Boulevard Pine, 69677 Bron, France
Miaomiao Mao
Florey Institute of Neuroscience and Mental Health, University of Melbourne, 30 Royal Parade, Parkville 3052, VIC, Australia
Jacqueline Heighway
Florey Institute of Neuroscience and Mental Health, University of Melbourne, 30 Royal Parade, Parkville 3052, VIC, Australia
Guiscard Seebohm
Institute for Genetics of Heart Diseases (IfGH), Department of Cardiovascular Medicine, University Hospital Münster, Domagkstraße 3, 48149 Münster, Germany
Pu Yan
Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried-Müller-Straße 27, 72076 Tübingen, Germany
Mahmoud Koko
Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried-Müller-Straße 27, 72076 Tübingen, Germany
Kezban Aslan-Kara
Çukurova University, Faculty of Medicine, Department of Neurology, Balcali 01790, Saricam/Adana, Turkey
Hande Caglayan
Department of Molecular Biology and Genetics, Boğaziçi University, Bebek 34342, Istanbul, Turkey
Bernhard J. Steinhoff
Kork Epilepsy Center, Landstraße 1, 77694 Kehl-Kork, Germany
Yvonne G. Weber
Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried-Müller-Straße 27, 72076 Tübingen, Germany; Department of Epileptology and Neurology, University of Aachen, Pauwelsstraße 30, 52074 Aachen, Germany
Pascale Keo-Kosal
Epileptology, Sleep Disorders and Functional Pediatric Neurology, Member of ERN-EpiCARE; HFME, Hospices Civils de Lyon, 59 Boulevard Pinel, 69500 Bron, France
Samuel F. Berkovic
Epilepsy Research Centre, Department of Medicine, Austin Health, The University of Melbourne, 245 Burgundy Street, Heidelberg 3084,VIC, Australia
Michael S. Hildebrand
Epilepsy Research Centre, Department of Medicine, Austin Health, The University of Melbourne, 245 Burgundy Street, Heidelberg 3084,VIC, Australia
Steven Petrou
Florey Institute of Neuroscience and Mental Health, University of Melbourne, 30 Royal Parade, Parkville 3052, VIC, Australia
Roland Krause
Luxembourg Centre for Systems Biomedicine, University of Luxembourg, 6 Avenue du Swing, Belvaux 4367, Luxembourg
Patrick May
Luxembourg Centre for Systems Biomedicine, University of Luxembourg, 6 Avenue du Swing, Belvaux 4367, Luxembourg
Gaetan Lesca
Service de Génétique, Hospices Civils de Lyon, Groupement Hospitalier Est, 59 Boulevard Pine, 69677 Bron, France
Snezana Maljevic
Florey Institute of Neuroscience and Mental Health, University of Melbourne, 30 Royal Parade, Parkville 3052, VIC, Australia
Holger Lerche
Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried-Müller-Straße 27, 72076 Tübingen, Germany; Corresponding author at: Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University Hospital Tübingen, Hoppe‐Seyler‐Str. 3, 72076 Tübingen, Germany.
Summary: Background: De novo missense variants in KCNQ5, encoding the voltage-gated K+ channel KV7.5, have been described to cause developmental and epileptic encephalopathy (DEE) or intellectual disability (ID). We set out to identify disease-related KCNQ5 variants in genetic generalized epilepsy (GGE) and their underlying mechanisms. Methods: 1292 families with GGE were studied by next-generation sequencing. Whole-cell patch-clamp recordings, biotinylation and phospholipid overlay assays were performed in mammalian cells combined with homology modelling. Findings: We identified three deleterious heterozygous missense variants, one truncation and one splice site alteration in five independent families with GGE with predominant absence seizures; two variants were also associated with mild to moderate ID. All missense variants displayed a strongly decreased current density indicating a loss-of-function (LOF). When mutant channels were co-expressed with wild-type (WT) KV7.5 or KV7.5 and KV7.3 channels, three variants also revealed a significant dominant-negative effect on WT channels. Other gating parameters were unchanged. Biotinylation assays indicated a normal surface expression of the variants. The R359C variant altered PI(4,5)P2-interaction. Interpretation: Our study identified deleterious KCNQ5 variants in GGE, partially combined with mild to moderate ID. The disease mechanism is a LOF partially with dominant-negative effects through functional deficits. LOF of KV7.5 channels will reduce the M-current, likely resulting in increased excitability of KV7.5-expressing neurons. Further studies on network level are necessary to understand which circuits are affected and how this induces generalized seizures. Funding: DFG/FNR Research Unit FOR-2715 (Germany/Luxemburg), BMBF rare disease network Treat-ION (Germany), foundation ‘no epilep’ (Germany).
