Advances toward precision therapeutics for developmental and epileptic encephalopathies

Voltage-gated potassium channels as a potential therapeutic target for the treatment of neurological and psychiatric disorders

Voltage-gated potassium channels are a widely distributed subgroup of potassium channels responsible for the efflux of potassium in the repolarisation of the cell membrane, and hence contribute to the latency and propagation of action potentials. As they are causal to synaptic transmission, alterations to the structure of these channels can lead to a variety of neurological and psychiatric diseases. The Kv3 subfamily of voltage-gated potassium channels are found on many neurons in the brain, including inhibitory interneurons where they contribute to fast-frequency firing. Changes to the firing ability of these interneurons can lead to an imbalance of inhibitory and excitatory neurotransmission. To date, we have little understanding of the mechanism by which excitatory and inhibitory inputs become imbalanced. This imbalance is associated with cognitive deficits seen across neurological and neuropsychiatric disorders, which are currently difficult to treat. In this review, we collate evidence supporting the hypothesis that voltage-gated potassium channels, specifically the Kv3 subfamily, are central to many neurological and psychiatric disorders, and may thus be considered as an effective drug target. The collective evidence provided by the studies reviewed here demonstrates that Kv3 channels may be amenable to novel treatments that modulate the activity of these channels, with the prospect of improved patient outcome.

A Case Report of Parental Germline Mosaicism in the PCDH19 Gene of Two Iranian Siblings

Introduction

Developmental and epileptic encephalopathy 9 (DEE9) is caused by pathogenic variants in the PCDH19 gene. The clinical features include early-onset seizures that are often provoked by fever and display clustered seizures, mild to profound intellectual disability, autistic traits, and behavioral disturbances. DEE9 is characterized by an unusual X-linked pattern where heterozygous females or rarely mosaic hemizygous males are affected, but hemizygous males and homozygous females are asymptomatic. In recent years, an increasing number of female and male patients with PCDH19-related epilepsy and symptoms have been reported.

Methods

Here, we report two additional female patients with DEE9 who are siblings. After analyzing karyotype testing results, whole-exome sequencing (WES) was performed for the proband. Then, Sanger sequencing was carried out for proband, her affected sister, and parents.

Results

Sequencing results revealed that our two patients had a heterozygous frameshift variant (NM_001184880.2: c.1091delC, p.P364Rfs*4) in the PCDH19 gene. We also reviewed previously reported cases with this mutation in detail.

Conclusion

This is the first report of germline mosaicism in the PCDH19 gene in the Iranian population and expanded the phenotypic spectrum of DEE9. Genetic testing has become an effective way of determining the diagnosis. Parental germline mosaicism should be considered when providing genetic counseling for X-linked/autosomal dominant disorders. This report also emphasizes the importance of considering prenatal diagnosis (PND) in such cases.

Radiprodil, a selective GluN2B negative allosteric modulator, rescues audiogenic seizures in mice carrying the GluN2A(N615S) mutation

BACKGROUND AND PURPOSE

GRIN-related disorders are neurodevelopmental disorders caused by mutations in N-methyl-D-aspartate receptor (NMDAR) subunit genes. A large fraction of these mutations lead to a 'gain of function' (GoF) of the NMDAR. Patients present with a range of symptoms including epilepsy, intellectual disability, behavioural and motor. Controlling seizures is a significant unmet medical need in most patients with GRIN-related disorders. Although several hundred GRIN mutations have been identified in humans, until recently none of the mouse models carrying Grin mutations/deletions showed an epileptic phenotype. The two recent exceptions both carry mutations of GluN2A. The aim of this study was to assess the efficacy of radiprodil, a selective negative allosteric modulator of GluN2B-containing NMDARs, in counteracting audiogenic seizures (AGS) in a murine model carrying the GluN2A(N615S) homozygous mutation (Grin2aS/S mice).

EXPERIMENTAL APPROACH

Grin2aS/S mice were acutely treated with radiprodil at different doses before the presentation of a high-frequency acoustic stimulus commonly used for AGS induction.

KEY RESULTS

Radiprodil significantly and dose-dependently reduced the onset and severity of AGS in Grin2aS/S mice. Surprisingly, the results revealed a sex-dependent difference in AGS susceptibility and in the dose-dependent protection of radiprodil in the two genders. Specifically, radiprodil was more effective in female versus male mice.

CONCLUSION AND IMPLICATIONS

Overall, our data clearly show that radiprodil, a GluN2B selective negative allosteric modulator, may have the potential to control seizures in patients with GRIN2A GoF mutations. Further studies are warranted to better understand the sex-dependent effects observed in this study.

Pathophysiology to Risk Factor and Therapeutics to Treatment Strategies on Epilepsy

Epilepsy represents a condition in which abnormal neuronal discharges or the hyperexcitability of neurons occur with synchronicity, presenting a significant public health challenge. Prognostic factors, such as etiology, electroencephalogram (EEG) abnormalities, the type and number of seizures before treatment, as well as the initial unsatisfactory effects of medications, are important considerations. Although there are several third-generation antiepileptic drugs currently available, their multiple side effects can negatively affect patient quality of life. The inheritance and etiology of epilepsy are complex, involving multiple underlying genetic and epigenetic mechanisms. Different neurotransmitters play crucial roles in maintaining the normal physiology of different neurons. Dysregulations in neurotransmission, due to abnormal transmitter levels or changes in their receptors, can result in seizures. In this review, we address the roles played by various neurotransmitters and their receptors in the pathophysiology of epilepsy. Furthermore, we extensively explore the neurological mechanisms involved in the development and progression of epilepsy, along with its risk factors. Furthermore, we highlight the new therapeutic targets, along with pharmacological and non-pharmacological strategies currently employed in the treatment of epileptic syndromes, including drug interventions employed in clinical trials related to epilepsy.

How have the recent updated epilepsy classifications impacted on diagnosis and treatment?

INTRODUCTION

Epilepsies are a diverse group of disorders which differ regarding prognosis for seizure control and associated comorbidities. Accurate classification is critical to choose the highest yield investigations and best therapeutic options and to provide the most accurate prognoses regarding the expected degree of seizure control, possible remission, and risk of associated comorbidities to patients and their families. This article reviews the recent updates in epilepsy classification to illustrate how accurate classification impacts care for persons with epilepsy.

AREAS COVERED

The authors discuss the ILAE 2017 Classification of the Epilepsies along with the modification of the classification for neonatal seizures and epilepsies. They also discuss the ILAE position papers on Epilepsy syndromes in neonates and infants and children of variable age and the Idiopathic Generalized Epilepsies.

EXPERT OPINION

Accurate epilepsy classification allows selection of the highest yield investigations, choice of optimal therapies, and accurate prognostication of seizures (likelihood of response to antiseizure treatments and likelihood of remission with age), as well as comorbidities (likelihood, type, and severity). As we move into the era of disease modifying therapy, early accurate identification of underlying causes with timely introduction of specific treatments will be crucial to lessen the severity of epilepsy, with improved seizure control and attenuation of associated comorbidities.