Phenotypic and functional assessment of two novel KCNQ2 gain-of-function variants Y141N and G239S and effects of amitriptyline treatment.

While loss-of-function (LoF) variants in KCNQ2 are associated with a spectrum of neonatal-onset epilepsies, gain-of-function (GoF) variants cause a more complex phenotype that precludes neonatal-onset epilepsy. In the present work, the clinical features of three patients carrying a de novo KCNQ2 Y141N (n ​= ​1) or G239S variant (n ​= ​2) respectively, are described. All three patients had a mild global developmental delay, with prominent language deficits, and strong activation of interictal epileptic activity during sleep. Epileptic seizures were not reported. The absence of neonatal seizures suggested a GoF effect and prompted functional testing of the variants. In vitro whole-cell patch-clamp electrophysiological experiments in Chinese Hamster Ovary cells transiently-transfected with the cDNAs encoding Kv7.2 subunits carrying the Y141N or G239S variants in homomeric or heteromeric configurations with Kv7.2 subunits, revealed that currents from channels incorporating mutant subunits displayed increased current densities and hyperpolarizing shifts of about 10 ​mV in activation gating; both these functional features are consistent with an in vitro GoF phenotype. The antidepressant drug amitriptyline induced a reversible and concentration-dependent inhibition of current carried by Kv7.2 Y141N and G239S mutant channels. Based on in vitro results, amitriptyline was prescribed in one patient (G239S), prompting a significant improvement in motor, verbal, social, sensory and adaptive behavior skillsduring the two-year-treatment period. Thus, our results suggest that KCNQ2 GoF variants Y141N and G239S cause a mild DD with prominent language deficits in the absence of neonatal seizures and that treatment with the Kv7 channel blocker amitriptyline might represent a potential targeted treatment for patients with KCNQ2 GoF variants.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Allan Bayat reports financial support was provided by Novo Nordisk Foundation. Francesco Miceli reports financial support was provided by Ministry of Education and Merit. Edward C. Cooper reports financial support was provided by Jack Pribaz Foundation and Miles Family Fund. Sarah Weckhuysen reports financial support was provided by FWO, GSKE, KCNQ2-Cure, Jack Pribaz Foundation, KCNQ2e.v., European Joint Programme on Rare Disease JTC 2020 (TreatKCNQ). Maurizio Taglialatela reports financial support was provided by Ministry of Education and Merit. Maurizio Taglialatela reports financial support was provided by Italian Ministry of Health. Maurizio Taglialatela reports was provided by European Joint Programme on Rare Disease JTC 2020 (TreatKCNQ). Sarah Weckhuysen reports a relationship with UCB, Xenon Pharmaceuticals, Lundbeck, Knopp Biosciences, Angelini Pharma, Roche, Biohaven and Encoded Therapeutics that includes: consulting or advisory. Edward C. Cooper reports a relationship with Xenon Pharmaceuticals and Knopp Biosciences that includes: consulting or advisory and funding grants. Rikke Steensbjerre Moller reports a relationship with EISAI, UCB, Orion and Angelini Pharma that includes: consulting or advisory and speaking and lecture fees.
(Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)