Drosophila expressing mutant human KCNT1 transgenes make an effective tool for targeted drug screening in a whole animal model of KCNT1-epilepsy.

Mutations in the KCNT1 potassium channel cause severe forms of epilepsy which are poorly controlled with current treatments. In vitro studies have shown that KCNT1-epilepsy mutations are gain of function, significantly increasing K+ current amplitudes. To investigate if Drosophila can be used to model human KCNT1 epilepsy, we generated Drosophila melanogaster lines carrying human KCNT1 with the patient mutation G288S, R398Q or R928C. Expression of each mutant channel in GABAergic neurons gave a seizure phenotype which responded either positively or negatively to 5 frontline epilepsy drugs most commonly administered to patients with KCNT1-epilepsy, often with little or no improvement of seizures. Cannabidiol showed the greatest reduction of the seizure phenotype while some drugs increased the seizure phenotype. Our study shows that Drosophila has the potential to model human KCNT1- epilepsy and can be used as a tool to assess new treatments for KCNT1- epilepsy.

In silico model reveals the key role of GABA in KCNT1-epilepsy in infancy with migrating focal seizures.

OBJECTIVE: This study was undertaken to investigate how gain of function (GOF) of slack channel due to a KCNT1 pathogenic variant induces abnormal neuronal cortical network activity and generates specific electroencephalographic (EEG) patterns of epilepsy in infancy with migrating focal seizures. METHODS: We used detailed microscopic computational models of neurons to explore the impact of GOF of slack channel (explicitly coded) on each subtype of neurons and on a cortical micronetwork. Then, we adapted a thalamocortical macroscopic model considering results obtained in detailed models and immature properties related to epileptic brain in infancy. Finally, we compared simulated EEGs resulting from the macroscopic model with interictal and ictal patterns of affected individuals using our previously reported EEG markers. RESULTS: The pathogenic variants of KCNT1 strongly decreased the firing rate properties of γ-aminobutyric acidergic (GABAergic) interneurons and, to a lesser extent, those of pyramidal cells. This change led to hyperexcitability with increased synchronization in a cortical micronetwork. At the macroscopic scale, introducing slack GOF effect resulted in epilepsy of infancy with migrating focal seizures (EIMFS) EEG interictal patterns. Increased excitation-to-inhibition ratio triggered seizure, but we had to add dynamic depolarizing GABA between somatostatin-positive interneurons and pyramidal cells to obtain migrating seizure. The simulated migrating seizures were close to EIMFS seizures, with similar values regarding the delay between the different ictal activities (one of the specific EEG markers of migrating focal seizures due to KCNT1 pathogenic variants). SIGNIFICANCE: This study illustrates the interest of biomathematical models to explore pathophysiological mechanisms bridging the gap between the functional effect of gene pathogenic variants and specific EEG phenotype. Such models can be complementary to in vitro cellular and animal models. This multiscale approach provides an in silico framework that can be further used to identify candidate innovative therapies.

Additional observation of a de novo pathogenic variant in KCNT2 leading to epileptic encephalopathy with clinical features of frontal lobe epilepsy.

INTRODUCTION: KCNT2 was recently recognized as a gene associated with neurodevelopmental disorder and epilepsy. CASE REPORT: We present an additional observation of a 16-year-old male patient with a novel de novo KCNT2 likely pathogenic variant and review the five previously reported cases of de novo variants in this gene. DISCUSSION: Whole exome sequencing identified the missense variant c.725C > A p.(Thr242Asn), which was confirmed by Sanger sequencing. Our patient has a refractory stereotyped and monomorphic type of hyperkinetic focal motor seizure, similar to what is seen in frontal lobe epilepsy, occurring only during sleep. This type of seizure is not usually seen in epileptic encephalopathies.

Two Patients With KCNT1-Related Epilepsy Responding to Phenobarbital and Potassium Bromide.

KCNT1 encodes a sodium-activated potassium channel highly expressed in the brain, regulating hyperpolarization following repetitive firing. Mutations in KCNT1 were originally implicated in autosomal-dominant nocturnal frontal lobe epilepsy and epilepsy of infancy with migrating focal seizures. It is now known that there is variability in phenotypic expression and incomplete penetrance. We describe 2 patients with KCNT1-related epilepsy, one with epilepsy of infancy with migrating focal seizures and one with multifocal epilepsy. As most patients with KCNT1 variants have treatment-resistant epilepsy, drugs that specifically target the KCNT1 channel have been of great interest. Quinidine, a broad-spectrum potassium channel blocker, has shown promise; however, clinical trial results have been variable. Our patient with epilepsy of infancy with migrating focal seizures did not respond to a trial of quinidine at 6 weeks of age-one of the earliest reported quinidine trials in the literature for KCNT1-related epilepsy. This indicates that timing of treatment and response may not be related. Both patients responded to high-dose phenobarbital. The patient with epilepsy of infancy with migrating focal seizures also had a significant reduction in seizures with potassium bromide (KBr). Our data suggest that alternative therapies to quinidine should be considered as a therapeutic option for patients with KCNT1-related epilepsy. Although improved seizure control led to parent-reported improvements in neurodevelopment, it is unknown if phenobarbital and KBr impact the overall developmental trajectory of patients with KCNT1-related epilepsy. Further multicenter longitudinal studies are required.