Potential Benefit of Channel Activators in Loss-of-Function Primary Potassium Channelopathies Causing Heredoataxia.

Potassium channels (KCN) are transmembrane complexes that regulate the resting membrane potential and the duration of action potentials in cells. The opening of KCN brings about an efflux of K+ ions that induces cell repolarization after depolarization, returns the transmembrane potential to its resting state, and enables for continuous spiking ability. The aim of this work was to assess the role of KCN dysfunction in the pathogenesis of hereditary ataxias and the mechanisms of action of KCN opening agents (KCO). In consequence, a review of the ad hoc medical literature was performed. Among hereditary KCN diseases causing ataxia, mutated Kv3.3, Kv4.3, and Kv1.1 channels provoke spinocerebellar ataxia (SCA) type 13, SCA19/22, and episodic ataxia type 1 (EA1), respectively. The K+ efflux was found to be reduced in experimental models of these diseases, resulting in abnormally prolonged depolarization and incomplete repolarization, thereby interfering with repetitive discharges in the cells. Hence, substances able to promote normal spiking activity in the cerebellum could provide symptomatic benefit. Although drugs used in clinical practice do not activate Kv3.3 or Kv4.3 directly, available KCO probably could ameliorate ataxic symptoms in SCA13 and SCA19/22, as verified with acetazolamide in EA1, and retigabine in a mouse model of hypokalemic periodic paralysis. To summarize, ataxia could possibly be improved by non-specific KCO in SCA13 and SCA19/22. The identification of new specific KCO agents will undoubtedly constitute a promising therapeutic strategy for these diseases.

Myoclonus improvement after seizures in progressive myoclonic epilepsy type 7: a case report.

BACKGROUND: Progressive Myoclonic Epilepsy (PME) is a group of rare diseases that are difficult to differentiate from one another based on phenotypical characteristics. CASE REPORT: We report a case of PME type 7 due to a pathogenic variant in KCNC1 with myoclonus improvement after epileptic seizures. DISCUSSION: Myoclonus improvement after seizures may be a clue to the diagnosis of Progressive Myoclonic Epilepsy type 7.

A novel KCNC1 gain-of-function variant causing developmental and epileptic encephalopathy: "Precision medicine" approach with fluoxetine.

Variable phenotypes, including developmental encephalopathy with (DEE) or without seizures and myoclonic epilepsy and ataxia due to potassium channel mutation, are caused by pathogenetic variants in KCNC1, encoding for Kv3.1 channel subunits. In vitro, channels carrying most KCNC1 pathogenic variants display loss-of-function features. Here, we describe a child affected by DEE with fever-triggered seizures, caused by a novel de novo heterozygous missense KCNC1 variant (c.1273G>A; V425M). Patch-clamp recordings in transiently transfected CHO cells revealed that, compared to wild-type, Kv3.1 V425M currents (1) were larger, with membrane potentials between -40 and +40 mV; (2) displayed a hyperpolarizing shift in activation gating; (3) failed to inactivate; and (4) had slower activation and deactivation kinetics, consistent with a mixed functional pattern with prevalent gain-of-function effects. Exposure to the antidepressant drug fluoxetine inhibited currents expressed by both wild-type and mutant Kv3.1 channels. Treatment of the proband with fluoxetine led to a rapid and prolonged clinical amelioration, with the disappearance of seizures and an improvement in balance, gross motor skills, and oculomotor coordination. These results suggest that drug repurposing based on the specific genetic defect may provide an effective personalized treatment for KCNC1-related DEEs.

Progressive myoclonus epilepsy KCNC1 variant causes a developmental dendritopathy.

OBJECTIVE: Mutations in KCNC1 can cause severe neurological dysfunction, including intellectual disability, epilepsy, and ataxia. The Arg320His variant, which occurs in the voltage-sensing domain of the channel, causes a highly penetrant and specific form of progressive myoclonus epilepsy with severe ataxia, designated myoclonus epilepsy and ataxia due to potassium channel mutation (MEAK). KCNC1 encodes the voltage-gated potassium channel KV 3.1, a channel that is important for enabling high-frequency firing in interneurons, raising the possibility that MEAK is associated with reduced interneuronal function. METHODS: To determine how this variant triggers MEAK, we expressed KV 3.1bR320H in cortical interneurons in vitro and investigated the effects on neuronal function and morphology. We also performed electrophysiological recordings of oocytes expressing KV 3.1b to determine whether the mutation introduces gating pore currents. RESULTS: Expression of the KV 3.1bR320H variant profoundly reduced excitability of mature cortical interneurons, and cells expressing these channels were unable to support high-frequency firing. The mutant channel also had an unexpected effect on morphology, severely impairing neurite development and interneuron viability, an effect that could not be rescued by blocking KV 3 channels. Oocyte recordings confirmed that in the adult KV 3.1b isoform, R320H confers a dominant negative loss-of-function effect by slowing channel activation, but does not introduce potentially toxic gating pore currents. SIGNIFICANCE: Overall, our data suggest that, in addition to the regulation of high-frequency firing, KV 3.1 channels play a hitherto unrecognized role in neuronal development. MEAK may be described as a developmental dendritopathy.

Targeted therapy improves cellular dysfunction, ataxia, and seizure susceptibility in a model of a progressive myoclonus epilepsy.

The recurrent variant KCNC1-p.Arg320His causes progressive myoclonus epilepsy (EPM) type 7, defined by progressive myoclonus, epilepsy, and ataxia, and is without effective treatment. KCNC1 encodes the voltage-gated potassium channel subunit Kv3.1, specifically expressed in high-frequency-firing neurons. Variant subunits act via loss of function; hence, EPM7 pathogenesis may involve impaired excitability of Kv3.1-expressing neurons, while enhancing Kv3 activity could represent a viable therapeutic strategy. We generate a mouse model, Kcnc1-p.Arg320His/+, which recapitulates the core features of EPM7, including progressive ataxia and seizure susceptibility. Kv3.1-expressing cerebellar granule cells and neocortical parvalbumin-positive GABAergic interneurons exhibit abnormalities consistent with Kv3 channel dysfunction. A Kv3-specific positive modulator (AUT00206) selectively enhances the firing frequency of Kv3.1-expressing neurons and improves motor function and seizure susceptibility in Kcnc1-Arg320His/+ mice. This work identifies a cellular and circuit basis of dysfunction in EPM7 and demonstrates that Kv3 positive modulators such as AUT00206 have therapeutic potential for the treatment of EPM7.

Oxidative stress-related cellular aging causes dysfunction of the Kv3.1/KCNC1 channel reverted by melatonin.

The voltage-gated Kv3.1/KCNC1 channel is abundantly expressed in fast-spiking principal neurons and GABAergic inhibitory interneurons throughout the ascending auditory pathway and in various brain regions. Inactivating mutations in the KCNC1 gene lead to forms of epilepsy and a decline in the expression of the Kv3.1 channel is involved in age-related hearing loss. As oxidative stress plays a fundamental role in the pathogenesis of epilepsy and age-related hearing loss, we hypothesized that an oxidative insult might affect the function of this channel. To verify this hypothesis, the activity and expression of endogenous and ectopic Kv3.1 were measured in models of oxidative stress-related aging represented by cell lines exposed to 100 mM d-galactose. In these models, intracellular reactive oxygen species, thiobarbituric acid reactive substances, sulfhydryl groups of cellular proteins, and the activity of catalase and superoxide dismutase were dysregulated, while the current density of Kv3.1 was significantly reduced. Importantly, the antioxidant melatonin reverted all these effects. The reduction of function of Kv3.1 was not determined by direct oxidation of amino acid side chains of the protein channel or reduction of transcript or total protein levels but was linked to reduced trafficking to the cell surface associated with Src phosphorylation as well as metabolic and endoplasmic reticulum stress. The data presented here specify Kv3.1 as a novel target of oxidative stress and suggest that Kv3.1 dysfunction might contribute to age-related hearing loss and increased prevalence of epilepsy during aging. The pharmacological use of the antioxidant melatonin can be protective in this setting.

Methylation gene KCNC1 is associated with overall survival in patients with seminoma.

The aim of the present study was to explore and verify the potential mechanism of seminoma progression. Data on 132 RNA­seq and 156 methylation sites from stage II/III and I seminoma specimens were downloaded from The Cancer Genome Atlas database. An initial filter of |fold­change| >2 and false discovery rate <0.05 were used to identify differentially expressed genes (DEGs) which were associated with differential methylation site genes; these genes were considered potential candidates for further investigation by survival analysis. Potassium voltage­gated channel subfamily C member 1 (KCNC1) expression was verified in seminoma human tissues and three seminoma cell lines. The invasive, proliferative and apoptotic abilities of the human testicular tumor Ntera­2 and normal human testis Hs1.Tes cell lines were assessed following aberrant KCNC1 expression. KCNC1 was identified as a DEG, in which hypermethylation inhibited its expression and it was associated with poor overall survival in patients with seminoma. The present results demonstrated that KCNC1 is negatively correlated with methylation. Due to the abnormal expression of KCNC1 in seminoma cells, it was suggested that KCNC1 could be used as a diagnostic indicator and therapeutic target for the progression of seminoma.

Progressive myoclonic epilepsy: myoclonic epilepsy and ataxia due to KCNC1 mutation (MEAK): a case report and review of the literature.

Progressive myoclonic epilepsy (PME) is characterized by prominent myoclonus and generalized or focal seizures. A recently described novel KCNC1 mutation is associated with a specific phenotype of progressive myoclonic epilepsy, which has been defined as myoclonic epilepsy and ataxia due to potassium channel mutation (MEAK). Our case illustrates a typical presentation of this disease and the potential for misdiagnosis as idiopathic generalized epilepsy during the early phase of the disease. Unique findings that may suggest an alternative diagnosis are a progressive myoclonus, prominent ataxia/dysmetria on examination, and abnormally high amplitude in the sensory evoked potential recording. We also report a brief review of the existing literature on MEAK. Early and accurate diagnosis with genetic testing may significantly help in counseling patients and families.

Encephalopathies with KCNC1 variants: genotype-phenotype-functional correlations.

OBJECTIVE: To analyze clinical phenotypes associated with KCNC1 variants other than the Progressive Myoclonus Epilepsy-causing variant p.Arg320His, determine the electrophysiological functional impact of identified variants and explore genotype-phenotype-physiological correlations. METHODS: Ten cases with putative pathogenic variants in KCNC1 were studied. Variants had been identified via whole-exome sequencing or gene panel testing. Clinical phenotypic data were analyzed. To determine functional impact of variants detected in the Kv 3.1 channel encoded by KCNC1, Xenopus laevis oocyte expression system and automated two-electrode voltage clamping were used. RESULTS: Six unrelated patients had a Developmental and Epileptic Encephalopathy and a recurrent de novo variant p.Ala421Val (c.1262C > T). Functional analysis of p.Ala421Val revealed loss of function through a significant reduction in whole-cell current, but no dominant-negative effect. Three patients had a contrasting phenotype of Developmental Encephalopathy without seizures and different KCNC1 variants, all of which caused loss of function with reduced whole-cell currents. Evaluation of the variant p.Ala513Val (c.1538C > T) in the tenth case, suggested it was a variant of uncertain significance. INTERPRETATION: These are the first reported cases of Developmental and Epileptic Encephalopathy due to KCNC1 mutation. The spectrum of phenotypes associated with KCNC1 is now broadened to include not only a Progressive Myoclonus Epilepsy, but an infantile onset Developmental and Epileptic Encephalopathy, as well as Developmental Encephalopathy without seizures. Loss of function is a key feature, but definitive electrophysiological separation of these phenotypes has not yet emerged.

Familial cases of progressive myoclonic epilepsy caused by maternal somatic mosaicism of a recurrent KCNC1 p.Arg320His mutation.

PURPOSE: A recurrent de novo mutation in KCNC1 (c.959G > A, p.Arg320His) has been identified recently as one of the important genetic causes of progress myoclonic epilepsy (PME). The clinical phenotype resulting from this mutation has been named as myoclonus epilepsy and ataxia due to potassium channel mutation (MEAK). This finding carries important clinical implications in that autosomal dominant inheritance and de novo occurrence need to be considered when conducting genetic tests in patients with PME. We present two familial cases of MEAK in siblings with a recurrent p.Arg320His mutation in KCNC1. METHOD: Whole exome sequencing and subsequent Sanger sequencing were performed for the cases and their parents. RESULTS: A recurrent p.Arg320His mutation in KCNC1 was identified in the two brothers who showed characteristic features of MEAK: near normal early development, onset of myoclonus around 10 years of age, infrequent generalized tonic-clonic seizures, relatively mild cognitive impairment, and generalized epileptiform discharges. Interestingly, the asymptomatic mother was suspected as being mosaic for this mutation. This finding could lead to misleading inheritance patterns and make genetic diagnosis of PME more complicated. CONCLUSIONS: Our familial MEAK cases show that consideration of parental mosaicism in addition to meticulous phenotyping is needed when conducting KCNC1 genetic testing.

Pharmacological rescue of mutated Kv3.1 ion-channel linked to progressive myoclonus epilepsies.

Progressive myoclonus epilepsies (PMEs) constitute a cluster of inherent, genetically diverse, rare seizure disorders characterized by ataxia, tonic-clonic seizures, and action myoclonus. Recently, a mutation in the KCNC1 gene (Arg320His) was described in a group of PME patients. The KCNC1 gene encodes the Kv3.1 potassium ion channel responsible for the rapid repolarization of the membrane potential following action potential firing in fast spiking GABAergic interneurons (FSI), thereby enabling high firing frequency. In the present study, we demonstrate that the Arg320His mutation cause a reduction in the Kv3.1 current amplitude and acts in a dominantly negative fashion. The mutation profoundly affects channel activation and deactivation kinetics, and we further find that it impairs recruitment of the Kv3.1 channel to the plasma membrane. The Kv3 activating compound, RE01, partly rescues the electrophysiological deficit, suggesting that pharmacological activation of Kv3.1 activity might be a feasible approach for treatment of this cohort of PME patients.

Myoclonus epilepsy and ataxia due to potassium channel mutation (MEAK) is caused by heterozygous KCNC1 mutations.

Progressive myoclonus epilepsy (PME) is a distinct group of seizure disorders characterized by gradual neurological decline with ataxia, myoclonus and recurring seizures. There are several forms of PME, among which the most recently described is MEAK - myoclonus epilepsy and ataxia due to potassium channel mutation. This particular subtype is caused by a recurrent de novo heterozygous mutation (c.959G>A, p.Arg320His) in the KCNC1 gene, which maps to chromosome 11 and encodes for the Kv3.1 protein (a subunit of the Kv3 subfamily of voltage-gated potassium channels). Loss of Kv3 function disrupts the firing properties of fast-spiking neurons, affects neurotransmitter release and induces cell death. Specifically regarding Kv3.1 malfunctioning, the most affected neurons include inhibitory GABAergic interneurons and cerebellar neurons. Impairment of the former cells is believed to contribute to myoclonus and seizures, whereas dysfunction of the latter to ataxia and tremor. Phenotypically, MEAK patients generally have a normal early development. At the age of 6 to 14 years, they present with myoclonus, which tends to progressively worsen with time. Tonic-clonic seizures may or may not be present, and some patients develop mild cognitive impairment following seizure onset. Typical electroencephalographic features comprise generalized epileptiform discharges and, in some cases, photosensitivity. Brain imaging is either normal or shows cerebellar atrophy. The identification of MEAK has both expanded the phenotypic and genotypic spectra of PME and established an emerging role for de novo mutations in PME.