A recurrent de novo variant supports KCNC2 involvement in the pathogenesis of developmental and epileptic encephalopathy

Kv3.1 Voltage-gated Potassium Channels Modulate Anxiety-like Behaviors in Female Mice

Inhibitory parvalbumin (PV) interneurons regulate the activity of neural circuits within brain regions involved in emotional processing, including the prefrontal cortex (PFC). Recently, rodent studies have implicated a stress-induced increase in prefrontal PV neuron activity in the development of anxiety behaviors, particularly in females. However, the mechanisms through which stress increases activity of prefrontal PV neurons remain unknown. The fast-spiking properties of PV neurons in part come from their expression of voltage-gated potassium (K+) ion channels, particularly Kv3.1 channels. We therefore suggest that stress-induced changes in Kv3.1 channels contribute to the appearance of an anxious phenotype following chronic stress in female mice. Here, we first showed that unpredictable chronic mild stress (UCMS) increased expression of Kv3.1 channels on prefrontal PV neurons in female mice, a potential mechanism underlying the previously observed hyperactivity of these neurons after stress. We then showed that female mice deficient in Kv3.1 channels displayed resilience to UCMS-induced anxiety-like behaviors. Altogether, our findings implicate Kv3.1 channels in the development of anxiety-like behaviors following UCMS, particularly in females, providing a novel mechanism to understand sex-specific vulnerabilities to stress-induced psychopathologies.

In-Depth Genomic Analysis: The New Challenge in Congenital Heart Disease

The use of next-generation sequencing has provided new insights into the causes and mechanisms of congenital heart disease (CHD). Examinations of the whole exome sequence have detected detrimental gene variations modifying single or contiguous nucleotides, which are characterised as pathogenic based on statistical assessments of families and correlations with congenital heart disease, elevated expression during heart development, and reductions in harmful protein-coding mutations in the general population. Patients with CHD and extracardiac abnormalities are enriched for gene classes meeting these criteria, supporting a common set of pathways in the organogenesis of CHDs. Single-cell transcriptomics data have revealed the expression of genes associated with CHD in specific cell types, and emerging evidence suggests that genetic mutations disrupt multicellular genes essential for cardiogenesis. Metrics and units are being tracked in whole-genome sequencing studies.

A structurally precise mechanism links an epilepsy-associated KCNC2 potassium channel mutation to interneuron dysfunction

De novo heterozygous variants in KCNC2 encoding the voltage-gated potassium (K+) channel subunit Kv3.2 are a recently described cause of developmental and epileptic encephalopathy (DEE). A de novo variant in KCNC2 c.374G > A (p.Cys125Tyr) was identified via exome sequencing in a patient with DEE. Relative to wild-type Kv3.2, Kv3.2-p.Cys125Tyr induces K+ currents exhibiting a large hyperpolarizing shift in the voltage dependence of activation, accelerated activation, and delayed deactivation consistent with a relative stabilization of the open conformation, along with increased current density. Leveraging the cryogenic electron microscopy (cryo-EM) structure of Kv3.1, molecular dynamic simulations suggest that a strong π-π stacking interaction between the variant Tyr125 and Tyr156 in the α-6 helix of the T1 domain promotes a relative stabilization of the open conformation of the channel, which underlies the observed gain of function. A multicompartment computational model of a Kv3-expressing parvalbumin-positive cerebral cortex fast-spiking γ-aminobutyric acidergic (GABAergic) interneuron (PV-IN) demonstrates how the Kv3.2-Cys125Tyr variant impairs neuronal excitability and dysregulates inhibition in cerebral cortex circuits to explain the resulting epilepsy.

Role of Potassium Ion Channels in Epilepsy: Focus on Current Therapeutic Strategies

BACKGROUND

Epilepsy is one of the prevalent neurological disorders characterized by disrupted synchronization between inhibitory and excitatory neurons. Disturbed membrane potential due to abnormal regulation of neurotransmitters and ion transport across the neural cell membrane significantly contributes to the pathophysiology of epilepsy. Potassium ion channels (KCN) regulate the resting membrane potential and are involved in neuronal excitability. Genetic alterations in the potassium ion channels (KCN) have been reported to result in the enhancement of the release of neurotransmitters, the excitability of neurons, and abnormal rapid firing rate, which lead to epileptic phenotypes, making these ion channels a potential therapeutic target for epilepsy. The aim of this study is to explore the variations reported in different classes of potassium ion channels (KCN) in epilepsy patients, their functional evaluation, and therapeutic strategies to treat epilepsy targeting KCN.

METHODOLOGY

A review of all the relevant literature was carried out to compile this article.

RESULTS

A large number of variations have been reported in different genes encoding various classes of KCN. These genetic alterations in KCN have been shown to be responsible for disrupted firing properties of neurons. Antiepileptic drugs (AEDs) are the main therapeutic strategy to treat epilepsy. Some patients do not respond favorably to the AEDs treatment, resulting in pharmacoresistant epilepsy.

CONCLUSION

Further to address the challenges faced in treating epilepsy, recent approaches like optogenetics, chemogenetics, and genome editing, such as clustered regularly interspaced short palindromic repeats (CRISPR), are emerging as target-specific therapeutic strategies.

Successful use of a phage endolysin for treatment of chronic pelvic pain syndrome/chronic bacterial prostatitis

Chronic prostatitis (CP) is a common inflammatory condition of the prostate that is estimated to effect 2%-10% of the world's male population. It can manifest as perineal, suprapubic, or lower back pain and urinary symptoms occurring with either recurrent bacterial infection [chronic bacterial prostatitis (CBP)] or in the absence of evidence of bacterial infection [chronic pelvic pain syndrome (CPPS)]. Here, in the case of a 39 years-old CBP patient, we report the first successful use of a bacteriophage-derived muralytic enzyme (endolysin) to treat and resolve the disease. Bacteriological analysis of the patient's prostatic secretion and semen samples revealed a chronic Enterococcus faecalis prostate infection, supporting a diagnosis of CBP. The patient's E. faecalis strain was resistant to several antibiotics and developed resistance to others during the course of treatment. Previous treatment with multiple courses of antibiotics, bacteriophages, probiotics, and immunologic stimulation had failed to achieve long term eradication of the infection or lasting mitigation of the symptoms. A cloned endolysin gene, encoded by E. faecalis bacteriophage ϕEf11, was expressed, and the resulting gene product was purified to electrophoretic homogeneity. A seven-day course of treatment with the endolysin resulted in the elimination of the E. faecalis infection to below culturally detectable levels, and the abatement of symptoms to near normal levels. Furthermore, during the endolysin treatment, the patient experienced no untoward reactions. The present report demonstrates the effectiveness of an endolysin as a novel modality in managing a recalcitrant infection that could not be controlled by conventional antibiotic therapy.

Personalized structural biology reveals the molecular mechanisms underlying heterogeneous epileptic phenotypes caused by de novo KCNC2 variants

Whole-exome sequencing (WES) in the clinic has identified several rare monogenic developmental and epileptic encephalopathies (DEE) caused by ion channel variants. However, WES often fails to provide actionable insight for rare diseases, such as DEEs, due to the challenges of interpreting variants of unknown significance (VUS). Here, we describe a "personalized structural biology" (PSB) approach that leverages recent innovations in the analysis of protein 3D structures to address this challenge. We illustrate this approach in an Undiagnosed Diseases Network (UDN) individual with DEE symptoms and a de novo VUS in KCNC2 (p.V469L), the Kv3.2 voltage-gated potassium channel. A nearby KCNC2 variant (p.V471L) was recently suggested to cause DEE-like phenotypes. Computational structural modeling suggests that both affect protein function. However, despite their proximity, the p.V469L variant is likely to sterically block the channel pore, while the p.V471L variant is likely to stabilize the open state. Biochemical and electrophysiological analyses demonstrate heterogeneous loss-of-function and gain-of-function effects, as well as differential response to 4-aminopyridine treatment. Molecular dynamics simulations illustrate that the pore of the p.V469L variant is more constricted, increasing the energetic barrier for K+ permeation, whereas the p.V471L variant stabilizes the open conformation. Our results implicate variants in KCNC2 as causative for DEE and guide the interpretation of a UDN individual. They further delineate the molecular basis for the heterogeneous clinical phenotypes resulting from two proximal pathogenic variants. This demonstrates how the PSB approach can provide an analytical framework for individualized hypothesis-driven interpretation of protein-coding VUS.

Mucopolysaccharidosis-Plus Syndrome: Report on a Polish Patient with a Novel VPS33A Variant with Comparison with Other Described Patients

Eleven patients from Yakutia with a new lysosomal disease assumed then as mucopolysaccharidosis-plus syndrome (MPS-PS) were reported by Gurinova et al. in 2014. Up to now, a total number of 39 patients have been reported; in all of them, the c.1492C>T (p.Arg498Trp) variant of the VPS33A gene was detected. Here, we describe the first Polish MPS-PS patient with a novel homozygous c.599G>C (p.Arg200Pro) VPS33A variant presenting over 12 years of follow-up with some novel clinical features, including fetal ascites (resolved spontaneously), recurrent joint effusion and peripheral edemas, normal growth, and visceral obesity. Functional analyses revealed a slight presence of chondroitin sulphate (only) in urine glycosaminoglycan electrophoresis, presence of sialooligosaccharides in urine by thin-layer chromatography, and normal results of lysosomal enzymes activity and lysosphingolipids concentration in dried blood spot. The comparison with other MPS-PS described cases was also provided. The presented description of the natural history of MPS-PS in our patient may broaden the spectrum of phenotypes in this disease.

Investigation of novel de novo KCNC2 variants causing severe developmental and early-onset epileptic encephalopathy

Purpose The voltage-gated potassium channel K_v3.2, encoded by KCNC2, facilitates fast-spiking GABAergic interneurons to fire action potentials at high frequencies. It is pivotal to maintaining excitation/inhibition balance in mammalian brains. This study identified two novel de novo KCNC2 variants, p.Pro470Ser (P470S) and p.Phe382Leu (F382L), in patients with early onset developmental and epileptic encephalopathy (DEE). Methods To examine the molecular basis of DEE, we studied the functional characteristics of variant channels using patch-clamp techniques and computational modeling. Results Whole-cell patch clamp recordings from infected HEK293 cells revealed that channel activation and deactivation kinetics strongly decreased in both K_v3.2 P470S and F382L variant channels. This decrease also occurred in K_v3.2 p.Val471Leu (V471L) channels, known to be associated with DEE. In addition, K_v3.2 F382L and V471L variants exhibited a significant increase in channel conductance and a ∼20 mV negative shift in the threshold for voltage-dependent activation. Simulations of model GABAergic interneurons revealed that all variants decreased neuronal firing frequency. Thus, the variants' net loss-of-function effects disinhibited neural networks. Conclusion Our findings provide compelling evidence supporting the role of KCNC2 as a disease-causing gene in human neurodevelopmental delay and epilepsy.

Emerging evidence of genotype–phenotype associations of developmental and epileptic encephalopathy due to KCNC2 mutation: Identification of novel R405G

Developmental and epileptic encephalopathies (DEEs) have high genetic heterogeneity, and DEE due to the potassium voltage-gated channel subfamily C member 2 (KCNC2) variant remains poorly understood, given the scarcity of related case studies. We report on two unrelated Chinese patients, an 11-year-old boy and a 5-year-old girl, diagnosed with global developmental delay (GDD), intellectual disability (ID), and focal impaired awareness seizure characterized by generalized spike and wave complexes on electroencephalogram (EEG) in the absence of significant brain lesions. Whole-exome sequencing (WES) and electrophysiological analysis were performed to detect genetic variants and evaluate functional changes of the mutant KCNC2, respectively. Importantly, we identified a novel gain-of-function KCNC2 variant, R405G, in both patients. Previously reported variants, V471L, R351K, T437A, and T437N, and novel R405G were found in multiple unrelated patients with DEE, showing consistent genotype–phenotype associations. These findings emphasize that the KCNC2 gene is causative for DEE and facilitates treatment and prognosis in patients with DEE due to KCNC2 mutations.