KCNT1 gain of function in 2 epilepsy phenotypes is reversed by quinidine

Abstract

Objective Mutations in KCNT1 have been implicated in autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) and epilepsy of infancy with migrating focal seizures (EIMFS). More recently, a whole exome sequencing study of epileptic encephalopathies identified an additional de novo mutation in one proband with EIMFS. We aim to investigate the electrophysiological and pharmacological characteristics of hKCNT1 mutations and examine developmental expression levels. Methods Here we use a Xenopus laevis oocyte based automated two-electrode voltage-clamp assay. The effects of quinidine (100 and 300 µM) are also tested. Using quantitative RT-PCR, the relative levels of mouse brain mKcnt1 mRNA expression are determined. Results We demonstrate that KCNT1 mutations implicated in epilepsy cause a marked increase in function. Importantly, there was a significant group difference in gain-of-function between mutations associated with ADNFLE and EIMFS. Finally, exposure to quinidine significantly reduces this gain-of-function for all mutations studied. Interpretation These results establish direction for a targeted therapy and potentially exemplify a translational paradigm for in vitro studies informing novel therapies in a neuropsychiatric disease.

International Union of Basic and Clinical Pharmacology. C. Nomenclature and Properties of Calcium-Activated and Sodium-Activated Potassium Channels

“…Mutations in the gene for K Na 1.1 have also been documented in autism (Iossifov et al, 2014). When expressed in Xenopus oocytes, the disease-causing mutations in K Na 1.1 generate currents that are 3-to 22-fold greater than those of wild-type channels, with no change in levels of channel protein or mRNA (Barcia et al, 2012;Martin et al, 2014;Milligan et al, 2014). For a subset of these mutations, changes in voltage dependence or Na + sensitivity contribute to the increase in current Tang et al, 2016).…”

“…Quinidine is a very effective blocker of these channels in both expression systems and neurons (Bhattacharjee et al, 2003;Yang et al, 2006Yang et al, , 2007Milligan et al, 2014;Rizzo et al, 2016). It has been reported that quinidine ameliorated the symptoms of a patient with malignant migrating partial seizures in infancy, but because this agent blocks a wide variety of other channels, the mechanism is not known (Bearden et al, 2014).…”

A targeted resequencing gene panel for focal epilepsy

“…Functional assays that will be reported elsewhere have confirmed that this mutation activates KCNT1 channels similarly to previously reported NFLE-associated mutations. 23 The other 2 variants (in T2957 and T2958; table 3) are of uncertain significance at this time based on the TLE phenotype and unavailability of parental samples for segregation.…”

Classification of the epilepsies: New concepts for discussion and debate—Special report of the ILAE Classification Task Force of the Commission for Classification and Terminology

“…These mutations are associated with a gain of function of the mutant ion channel 16. This gain of function can be reversed in vitro by an “old” drug, quinidine, which targets the KCNT1 potassium channel 17. Quinidine is both an antiarrhythmic agent and antimalarial treatment.…”