1. Genotype-phenotype correlations in SCN8A-related disorders reveal prognostic and therapeutic implications
- Author
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Arve Vøllo, Stephen W. Scherer, Elena Gardella, Irina Mishina, María Vaccarezza, Jennifer L. Howe, Sebastian Lebon, Josua Kegele, Gaetan Lesca, Timo Roser, Silvia Masnada, Johannes Rebstock, Marga Buzatu, Damien Lederer, Ingo Borggraefe, Tobias Brünger, Ulrike B. S. Hedrich, Sergey Korostelev, Frédéric Bilan, Ahmed Eltokhi, M. Mahdi Motazacker, Karen E. Wain, Susanne Ruf, Manuela Pendziwiat, Lukas Sonnenberg, Yuanyuan Liu, Alice W Ho, Silvana Franceschetti, Jan Benda, Ethan M. Goldberg, Helene Verhelst, Julian Schubert, Juliann M. Savatt, Mathilde Nizon, Caroline Lund, Katherine B. Howell, Tobias Loddenkemper, Katherine L. Helbig, Cornelia Betzler, Roseline Caume, Francesca Darra, Richard J. Leventer, Christina Fenger, Pierangelo Veggiotti, Ilona Krey, Nancy Eisenhauer, Andrea Berger, Pasquale Striano, Heather E. Olson, An-Sofie Schoonjans, M Scott Perry, Stephan Lauxmann, Emmanuel Scalais, Petra Laššuthová, Monisa D. Wagner, Ilya V. Kanivets, A. A. Sharkov, P Y Billie Au, Mahmoud Koko, Siddharth Srivastava, Jakob Christensen, Artem Borovikov, Mette U Schmidt-Petersen, Anna Jansen, Judith S. Verhoeven, Johanna Krüger, Claudia M Bonardi, Shoji Ichikawa, Patrick May, Sabine Grønborg, Johannes R. Lemke, Marije Meuwissen, Katalin Sterbova, Mark Fitzgerald, Lucio Giordano, Holger Lerche, Mikhail Abramov, Bénédicte Gérard, Elena L. Dadali, Cecilia Altuzarra, Aster V. E. Harder, Stefano Sartori, Katrine M Johannesen, Sergey Kutsev, Maert Rannap, Renzo Guerrini, Dagmar Wieczorek, Laura Canafoglia, Annapurna Poduri, Christina E. Hoei-Hansen, Agathe Roubertie, Nils A Koch, Karen Müller-Schlüter, Chloe A Stutterd, Ngoc Minh Le, Pia Zacher, Constanze Heine, Sonja Walsh, Carla Marini, Federico Zara, Karl Martin Klein, Eva H. Brilstra, Guido Rubboli, Walid Fazeli, Judith Kroell-Seger, Rikke S. Møller, Dorota Hoffman-Zacharska, Michael Alber, Phillis Lakeman, Massimo Mastrangelo, Margarete Koch-Hogrebe, Ingo Helbig, Daniel Tibussek, Marketa Vlckova, Anne Destrée, Wen-Hann Tan, Haim Bassan, Dennis Lal, Patrizia Accorsi, Bert van der Zwaag, Cathrine E Gjerulfsen, Marion Gérard, Sara Matricardi, Thomas U. Mayer, Philippe Gelisse, Jong M. Rho, and Marie-Cécile Nassogne
- Subjects
medicine.medical_specialty ,Benign familial infantile epilepsy ,business.industry ,medicine.disease ,Gastroenterology ,Phenotype ,Epilepsy ,Electrophysiology ,Sodium channel blocker ,Internal medicine ,medicine ,Missense mutation ,Generalized epilepsy ,business ,Genotype-Phenotype Correlations - Abstract
We report detailed functional analyses and genotype-phenotype correlations in 433 individuals carrying disease-causing variants in SCN8A, encoding the voltage-gated Na+ channel NaV1.6. Five different clinical subgroups could be identified: 1) Benign familial infantile epilepsy (BFIE) (n=17, normal cognition, treatable seizures), 2) intermediate epilepsy (n=36, mild ID, partially pharmacoresponsive), 3) developmental and epileptic encephalopathy (DEE, n=191, severe ID, majority pharmacoresistant), 4) generalized epilepsy (n=21, mild to moderate ID, frequently with absence seizures), and 5) affected individuals without epilepsy (n=25, mild to moderate ID). Groups 1-3 presented with early-onset (median: four months) focal or multifocal seizures and epileptic discharges, whereas the onset of seizures in group 4 was later (median: 39 months) with generalized epileptic discharges. The epilepsy was not classifiable in 143 individuals. We performed functional studies expressing missense variants in ND7/23 neuroblastoma cells and primary neuronal cultures using recombinant tetrodotoxin insensitive human NaV1.6 channels and whole-cell patch clamping. Two variants causing DEE showed a strong gain-of-function (GOF, hyperpolarising shift of steady-state activation, strongly increased neuronal firing rate), and one variant causing BFIE or intermediate epilepsy showed a mild GOF (defective fast inactivation, less increased firing). In contrast, all three variants causing generalized epilepsy induced a loss-of-function (LOF, reduced current amplitudes, depolarising shift of steady-state activation, reduced neuronal firing). Including previous studies, functional effects were known for 165 individuals. All 133 individuals carrying GOF variants had either focal (76, groups 1-3), or unclassifiable epilepsy (37), whereas 32 with LOF variants had either generalized (14), no (11) or unclassifiable (5) epilepsy; only two had DEE. Computational modeling in the GOF group revealed a significant correlation between the severity of the electrophysiological and clinical phenotypes. GOF variant carriers responded significantly better to sodium channel blockers (SCBs) than to other anti-seizure medications, and the same applied for all individuals of groups 1-3.In conclusion, our data reveal clear genotype-phenotype correlations between age at seizure onset, type of epilepsy and gain- or loss-of-function effects of SCN8A variants. Generalized epilepsy with absence seizures is the main epilepsy phenotype of LOF variant carriers and the extent of the electrophysiological dysfunction of the GOF variants is a main determinant of the severity of the clinical phenotype in focal epilepsies. Our pharmacological data indicate that SCBs present a therapeutic treatment option in early onset SCN8A-related focal epilepsy.
- Published
- 2021