Characteristics of KCNQ 2 variants causing either benign neonatal epilepsy or developmental and epileptic encephalopathy

KCNQ2 mutations cause unique neonatal behavior arrests without motor seizures: Functional characterization

OBJECTIVE

KCNQ2 gene mutation usually manifests as neonatal seizures in the first week of life. Nonsense mutations cause a unique self-limited familial neonatal epilepsy (SLFNE), which is radically different from developmental epileptic encephalopathy (DEE). However, the exact underlying mechanisms remain unclear.

METHODS

The proband, along with their mother and grandmother, carried the c.1342C > T (p.Arg448Ter) mutation in the KCNQ2 gene. The clinical phenotypes, electroencephalography (EEG) findings, and neurodevelopmental outcomes were comprehensively surveyed. The mutant variants were transfected into HEK293 cells to investigate functional changes.

RESULTS

The proband exhibited behavior arrests, autonomic and non-motor neonatal seizures with changes in heart rate and respiration. EEG exhibited focal sharp waves. Seizures were remitted after three months of age. The neurodevelopmental outcomes at three years of age were unremarkable. A functional study demonstrated that the currents of p.Arg448Ter were non-functional in homomeric p.Arg448Ter compared with that of the KCNQ2 wild type. However, the current density and V1/2 exhibited significant improvement and close to that of the wild-type after transfection with heteromeric KCNQ2 + p.Arg448Ter and KCNQ2 + KCNQ3 + p.Arg448Ter respectively. Channel expression on the cell membrane was not visible after homomeric transfection, but not after heteromeric transfection. Retigabine did not affect homomeric p.Arg448Ter but improved heteromeric p. Arg448Ter + KCNQ2 and heteromeric KCNQ2 + Arg448Ter + KCNQ3.

CONCLUSIONS

The newborn carrying the p. Arg448Ter mutation presented frequent behavioral arrests, autonomic, and non-motor neonatal seizures. This unique pattern differs from KCNQ2 seizures, which typically manifest as motor seizures. Although p.Arg448Ter is a non-sense decay, the functional study demonstrated an almost-full compensation mechanism after transfection of heteromeric KCNQ2 and KCNQ3.

Plural molecular and cellular mechanisms of pore domain KCNQ2 encephalopathy

KCNQ2 variants in children with neurodevelopmental impairment are difficult to assess due to their heterogeneity and unclear pathogenic mechanisms. We describe a child with neonatal-onset epilepsy, developmental impairment of intermediate severity, and KCNQ2 G256W heterozygosity. Analyzing prior KCNQ2 channel cryoelectron microscopy models revealed G256 as a node of an arch-shaped non-covalent bond network linking S5, the pore turret, and the ion path. Co-expression with G256W dominantly suppressed conduction by wild-type subunits in heterologous cells. Ezogabine partly reversed this suppression. G256W/+ mice have epilepsy leading to premature deaths. Hippocampal CA1 pyramidal cells from G256W/+ brain slices showed hyperexcitability. G256W/+ pyramidal cell KCNQ2 and KCNQ3 immunolabeling was significantly shifted from axon initial segments to neuronal somata. Despite normal mRNA levels, G256W/+ mouse KCNQ2 protein levels were reduced by about 50%. Our findings indicate that G256W pathogenicity results from multiplicative effects, including reductions in intrinsic conduction, subcellular targeting, and protein stability. These studies provide evidence for an unexpected and novel role for the KCNQ2 pore turret and introduce a valid animal model of KCNQ2 encephalopathy. Our results, spanning structure to behavior, may be broadly applicable because the majority of KCNQ2 encephalopathy patients share variants near the selectivity filter.

Novel KCNQ2 missense variant expands the genotype spectrum of DEE7

BACKGROUND

KCNQ is a voltage-gated K + channel that controls neuronal excitability and is mutated in epilepsy and autism spectrum disorder (ASD). We focus on the KV7.2 voltage-gated potassium channel gene (KCNQ2), which is known for its association with developmental delay and various seizures (including self-limited benign familial neonatal epilepsy and epileptic encephalopathy). But the pathogenicity of many variants remains unproven, potentially leading to misinterpretation of their functional consequences.

METHODS

In this study, we studied a patient who visited Nanhua Hospital. Targeted next-generation sequencing and Sanger sequencing were used to identify the pathogenic variants. Meanwhile, computational models, including hydrogen bonding and docking analyses, suggest that variants cause functional impairment. In addition, functional validation was performed in the drosophila to further evaluate the missense variant in the KCNQ2 gene as the cause of this patient.

RESULTS

A new missense variant in the KCNQ2 gene was identified: NM_172107.4:c.1007C > A(p.ALa336Glu), which resulted in the change from alanine to glutamate at amino acid position 336 in the KCNQ2 gene. After computational modeling, including hydrogen bond analysis and docking analysis, it is indicated that the variants cause functional impairment. Furthermore, RNAi-mediated KCNQ knockout in flies led to the onset of epileptic behavior, lifespan and climbing capacity were affected, expression of the normal human KCNQ2 rescues the in flies RNAi-mediated KCNQ knockout behavioral abnormalities.

CONCLUSION

Our findings expands the genetic profile of KCNQ2 and enhances the genotype - phenotype link.

A Novel KCNQ2 Variant in a Patient with a Combined Tremor Syndrome

Background

Tremor disorders have various genetic causes.

Case report

A 60-year-old female with a family history of tremor presented a combined tremor syndrome, transient episodes of loss of contact and speech disturbances, as well as distal painful symptoms. Genetic screening revealed a novel heterozygous missense variant in the KCNQ2 gene.

Discussion

The KCNQ2 protein regulates action potential firing, and mutations in its gene are associated with epilepsy and neuropathic pain. The identified variant, although of uncertain significance, may disrupt KCNQ2 function and also play a role in tremor pathogenesis. This case highlights the importance of genetic screening in combined tremor disorders.

MLe-KCNQ2: An Artificial Intelligence Model for the Prognosis of Missense KCNQ2 Gene Variants

Despite the increasing availability of genomic data and enhanced data analysis procedures, predicting the severity of associated diseases remains elusive in the absence of clinical descriptors. To address this challenge, we have focused on the KV7.2 voltage-gated potassium channel gene (KCNQ2), known for its link to developmental delays and various epilepsies, including self-limited benign familial neonatal epilepsy and epileptic encephalopathy. Genome-wide tools often exhibit a tendency to overestimate deleterious mutations, frequently overlooking tolerated variants, and lack the capacity to discriminate variant severity. This study introduces a novel approach by evaluating multiple machine learning (ML) protocols and descriptors. The combination of genomic information with a novel Variant Frequency Index (VFI) builds a robust foundation for constructing reliable gene-specific ML models. The ensemble model, MLe-KCNQ2, formed through logistic regression, support vector machine, random forest and gradient boosting algorithms, achieves specificity and sensitivity values surpassing 0.95 (AUC-ROC > 0.98). The ensemble MLe-KCNQ2 model also categorizes pathogenic mutations as benign or severe, with an area under the receiver operating characteristic curve (AUC-ROC) above 0.67. This study not only presents a transferable methodology for accurately classifying KCNQ2 missense variants, but also provides valuable insights for clinical counseling and aids in the determination of variant severity. The research context emphasizes the necessity of precise variant classification, especially for genes like KCNQ2, contributing to the broader understanding of gene-specific challenges in the field of genomic research. The MLe-KCNQ2 model stands as a promising tool for enhancing clinical decision making and prognosis in the realm of KCNQ2-related pathologies.

Improved classification and pathogenicity assessment by comprehensive functional studies in a large data set of KCNQ2 variants

AIMS

The paucity of functional annotations on hundreds of KCNQ2 variants impedes the diagnosis and treatment of KCNQ2-related disorders. The aims of this work were to determine the functional properties of 331 clinical KCNQ2 variants, interpreted the pathogenicity of 331 variants using functional data，and explored the association between homomeric channel functions and phenotypes.

MAIN METHODS

We collected 145 KCNQ2 variants from 232 epilepsy patients and 186 KCNQ2 missense variants from the ClinVar database. Whole-cell patch-clamp recording was used to classify the function of 331 variants. Subsequently, we proposed 24 criteria for the pathogenicity interpretation of KCNQ2 variants and used them to assess pathogenicity of 331 variants. Finally, we analyzed the clinical phenotypes of patients carrying these variants, and explored the correlations between functional mechanisms and phenotypes.

KEY FINDINGS

In the homozygous state, 287 were classified as loss-of-function and 14 as gain-of-function. In the more clinically relative heterozygous state, 200 variants exhibited functional impairment, 121 of which showed dominant-negative effects on wild-type KCNQ2 subunits. After introducing functional data as strong-level evidence to interpret pathogenicity, over half of variants (169/331) were reclassified and 254 were classified as pathogenic/likely pathogenic. Moreover, dominant-negative effect and haploinsufficiency were identified as primary mechanisms in DEE/ID and SeLNE, respectively. The degree of impairment of channel function correlated with the phenotype severity.

SIGNIFICANCE

Our study reveals the possible cause of KCNQ2-related disorders at the molecular level, provides compelling evidence for clinical classification of KCNQ2 variants, and expands the knowledge of correlations between functional mechanisms and phenotypes.

Newly discovered variants in unexplained neonatal encephalopathy

BACKGROUND

The genetic background of neonatal encephalopathy (NE) is complicated and early diagnosis is beneficial to optimizing therapeutic strategy for patients.

METHODS

NE Patients with unclear etiology received regular clinical tests including ammonia test, metabolic screening test, amplitude-integrated electroencephalographic (aEEG) monitoring, brain Magnetic Resonance Imaging (MRI) scanning, and genetic test. The protein structure change was predicted using Dynamut2 and RoseTTAFold.

RESULTS

15 out of a total of 113 NE Patients were detected with newly reported pathogenic variants. In this sub-cohort, (1) seizure was the primary initial symptoms; (2) four patients had abnormal metabolic screening results, and two of them were also diagnosed with excessive blood ammonia concentration; (3) the brain MRI results were irregular in three infants and the brain waves were of moderate-severe abnormality in about a half of the patients. The novel pathogenic variants discovered in this study belonged to 12 genes, and seven of them were predicted to introduce a premature translation termination. In-silicon predictions showed that four variants were destructive to the protein structure of KCNQ2.

CONCLUSION

Our study expands the mutation spectrum of genes associated with NE and introduces new evidence for molecular diagnosis in this newborn illness.

Genetic Background of Epilepsy and Antiepileptic Treatments

Advanced identification of the gene mutations causing epilepsy syndromes is expected to translate into faster diagnosis and more effective treatment of these conditions. Over the last 5 years, approximately 40 clinical trials on the treatment of genetic epilepsies have been conducted. As a result, some medications that are not regular antiseizure drugs (e.g., soticlestat, fenfluramine, or ganaxolone) have been introduced to the treatment of drug-resistant seizures in Dravet, Lennox-Gastaut, maternally inherited chromosome 15q11.2-q13.1 duplication (Dup 15q) syndromes, and protocadherin 19 (PCDH 19)-clusterig epilepsy. And although the effects of soticlestat, fenfluramine, and ganaxolone are described as promising, they do not significantly affect the course of the mentioned epilepsy syndromes. Importantly, each of these syndromes is related to mutations in several genes. On the other hand, several mutations can occur within one gene, and different gene variants may be manifested in different disease phenotypes. This complex pattern of inheritance contributes to rather poor genotype-phenotype correlations. Hence, the detection of a specific mutation is not synonymous with a precise diagnosis of a specific syndrome. Bearing in mind that seizures develop as a consequence of the predominance of excitatory over inhibitory processes, it seems reasonable that mutations in genes encoding sodium and potassium channels, as well as glutamatergic and gamma-aminobutyric (GABA) receptors, play a role in the pathogenesis of epilepsy. In some cases, different pathogenic variants of the same gene can result in opposite functional effects, determining the effectiveness of therapy with certain medications. For instance, seizures related to gain-of-function (GoF) mutations in genes encoding sodium channels can be successfully treated with sodium channel blockers. On the contrary, the same drugs may aggravate seizures related to loss-of-function (LoF) variants of the same genes. Hence, knowledge of gene mutation-treatment response relationships facilitates more favorable selection of drugs for anticonvulsant therapy.

ILAE Genetic Literacy Series: Self-limited familial epilepsy syndromes with onset in neonatal age and infancy

The self-limited (familial) epilepsies with onset in neonates or infants, formerly called benign familial neonatal and/or infantile epilepsies, are autosomal dominant disorders characterized by neonatal- or infantile-onset focal motor seizures and the absence of neurodevelopmental complications. Seizures tend to remit during infancy or early childhood and are therefore called "self-limited". A positive family history for epilepsy usually suggests the genetic etiology, but incomplete penetrance and de novo inheritance occur. Here, we review the phenotypic spectrum and the genetic architecture of self-limited (familial) epilepsies with onset in neonates or infants. Using an illustrative case study, we describe important clues in recognition of these syndromes, diagnostic steps including genetic testing, management, and genetic counseling.

Functional characterization and in vitro pharmacological rescue of KCNQ2 pore mutations associated with epileptic encephalopathy

Mutations in the KCNQ2 gene encoding KV7.2 subunit that mediates neuronal M-current cause a severe form of developmental and epileptic encephalopathy (DEE). Electrophysiological evaluation of KCNQ2 mutations has been proved clinically useful in improving outcome prediction and choosing rational anti-seizure medications (ASMs). In this study we described the clinical characteristics, electrophysiological phenotypes and the in vitro response to KCNQ openers of five KCNQ2 pore mutations (V250A, N258Y, H260P, A265T and G290S) from seven patients diagnosed with KCNQ2-DEE. The KCNQ2 variants were transfected into Chinese hamster ovary (CHO) cells alone, in combination with KCNQ3 (1:1) or with wild-type KCNQ2 (KCNQ2-WT) and KCNQ3 in a ratio of 1:1:2, respectively. Their expression and electrophysiological function were assessed. When transfected alone or in combination with KCNQ3, none of these mutations affected the membrane expression of KCNQ2, but most failed to induce a potassium current except A265T, in which trace currents were observed when co-transfected with KCNQ3. When co-expressed with KCNQ2-WT and KCNQ3 (1:1:2), the currents at 0 mV of these mutations were decreased by 30%-70% compared to the KCNQ2/3 channel, which could be significantly rescued by applying KCNQ openers including the approved antiepileptic drug retigabine (RTG, 10 μM), as well as two candidates subjected to clinical trials, pynegabine (HN37, 1 μM) and XEN1101 (1 μM). These newly identified pathologic variants enrich the KCNQ2-DEE mutation hotspots in the pore-forming domain. This electrophysiological study provides a rational basis for personalized therapy with KCNQ openers in DEE patients carrying loss-of-function (LOF) mutations in KCNQ2.

Clinical analysis and functional characterization of KCNQ2-related developmental and epileptic encephalopathy

Background

Developmental and epileptic encephalopathy (DEE) is a condition characterized by severe seizures and a range of developmental impairments. Pathogenic variants in KCNQ2, encoding for potassium channel subunit, cause KCNQ2-related DEE. This study aimed to examine the relationships between genotype and phenotype in KCNQ2-related DEE.

Methods

In total, 12 patients were enrolled in this study for genetic testing, clinical analysis, and developmental evaluation. Pathogenic variants of KCNQ2 were characterized through a whole-cell electrophysiological recording expressed in Chinese hamster ovary (CHO) cells. The expression levels of the KCNQ2 subunit and its localization at the plasma membrane were determined using Western blot analysis.

Results

Seizures were detected in all patients. All DEE patients showed evidence of developmental delay. In total, 11 de novo KCNQ2 variants were identified, including 10 missense variants from DEE patients and one truncating variant from a patient with self-limited neonatal epilepsy (SeLNE). All variants were found to be loss of function through analysis of M-currents using patch-clamp recordings. The functional impact of variants on M-current in heteromericKCNQ2/3 channels may be associated with the severity of developmental disorders in DEE. The variants with dominant-negative effects in heteromeric channels may be responsible for the profound developmental phenotype.

Conclusion

The mechanism underlying KCNQ2-related DEE involves a reduction of the M-current through dominant-negative effects, and the severity of developmental disorders in DEE may be predicted by the impact of variants on the M-current of heteromericKCNQ2/3 channels.

Relationship Between Epileptic Activity and Developmental Outcome in KCNQ2-Related Epilepsy

BACKGROUND

We aim to describe a cohort of patients with KCNQ2-related epilepsy and evaluate the relationship between epileptic activity and developmental outcome. This topic is relevant for the selection of clinical end points in future clinical trials, since cessation of seizures may or may not be the most important outcome.

METHODS

This retrospective cohort study of children with self-limited (familial) neonatal epilepsy and developmental and epileptic encephalopathy due to pathogenic variants in KCNQ2 was conducted between 2019 and 2021. We collected clinical, therapeutic, and genetic information. Available electroencephalographic recordings were reviewed by a neurophysiologist. Gross motor function was determined using the Gross Motor Function Classification System (GMFCS). The Vineland Adaptive Behavior Composite standard score (ABC SS) was used to measure adaptive functioning.

RESULTS

Among 44 children (mean age 8.1 ± 4.0 years, 45.5% were male), 15 of 44 had S(F)NE, and 29 of 44 had DEE. Delayed seizure freedom was more frequent in DEE than in S(F)NE (P = 0.025), but no correlation was observed between age at seizure freedom and developmental outcome in patients with DEE. Multifocal interictal epileptiform abnormalities at epilepsy onset were more frequent in DEE than in S(F)NE (P = 0.014), and were associated with higher GMFCS (P = 0.027) and lower ABC SS (P = 0.048) in patients with DEE. Disorganized background activity at follow-up was more frequent in DEE than in S(F)NE (P = 0.001), and was associated with higher GMFCS levels (P = 0.009) and lower ABC SS (P = 0.005) in patients with DEE.

CONCLUSIONS

This study shows a partial correlation between epileptic activity and developmental outcome in KCNQ2-related epilepsy.

Nine patients with KCNQ2-related neonatal seizures and functional studies of two missense variants

Mutations in KCNQ2 encoding for voltage-gated K channel subunits underlying the neuronal M-current have been associated with infantile-onset epileptic disorders. The clinical spectrum ranges from self-limited neonatal seizures to epileptic encephalopathy and delayed development. Mutations in KCNQ2 could be either gain- or loss-of-function which require different therapeutic approaches. To better understand genotype-phenotype correlation, more reports of patients and their mutations with elucidated molecular mechanism are needed. We studied 104 patients with infantile-onset pharmacoresistant epilepsy who underwent exome or genome sequencing. Nine patients with neonatal-onset seizures from unrelated families were found to harbor pathogenic or likely pathogenic variants in the KCNQ2 gene. The p.(N258K) was recently reported, and p. (G279D) has never been previously reported. Functional effect of p.(N258K) and p.(G279D) has never been previously studied. The cellular localization study demonstrated that the surface membrane expression of Kv7.2 carrying either variant was decreased. Whole-cell patch-clamp analyses revealed that both variants significantly impaired Kv7.2 M-current amplitude and density, conductance depolarizing shift in voltage dependence of activation, membrane resistance, and membrane time constant (Tau), indicating a loss-of-function in both the homotetrameric and heterotetrameric with Kv7.3 channels. In addition, both variants exerted dominant-negative effects in heterotetrameric with Kv7.3 channels. This study expands the mutational spectrum of KCNQ2- related epilepsy and their functional consequences provide insights into their pathomechanism.

Potassium channelopathies associated with epilepsy-related syndromes and directions for therapeutic intervention

A number of mutations to members of several CNS potassium (K) channel families have been identified which result in rare forms of neonatal onset epilepsy, or syndromes of which one prominent characteristic is a form of epilepsy. Benign Familial Neonatal Convulsions or Seizures (BFNC or BFNS), also referred to as Self-Limited Familial Neonatal Epilepsy (SeLNE), results from mutations in 2 members of the K_V7 family (KCNQ) of K channels; while generally self-resolving by about 15 weeks of age, these mutations significantly increase the probability of generalized seizure disorders in the adult, in some cases they result in more severe developmental syndromes. Epilepsy of Infancy with Migrating Focal Seizures (EIMSF), or Migrating Partial Seizures of Infancy (MMPSI), is a rare severe form of epilepsy linked primarily to gain of function mutations in a member of the sodium-dependent K channel family, KCNT1 or SLACK. Finally, KCNMA1 channelopathies, including Liang-Wang syndrome (LIWAS), are rare combinations of neurological symptoms including seizure, movement abnormalities, delayed development and intellectual disabilities, with Liang-Wang syndrome an extremely serious polymalformative syndrome with a number of neurological sequelae including epilepsy. These are caused by mutations in the pore-forming subunit of the large-conductance calcium-activated K channel (BK channel) KCNMA1. The identification of these rare but significant channelopathies has resulted in a resurgence of interest in their treatment by direct pharmacological or genetic modulation. We will briefly review the genetics, biophysics and pharmacology of these K channels, their linkage with the 3 syndromes described above, and efforts to more effectively target these syndromes.

Epilepsy and Cognitive Impairment in Childhood and Adolescence: A Mini-Review

Managing epilepsy in people with an intellectual disability remains a therapeutic challenge and must take into account additional issues such as diagnostic difficulties and frequent drug resistance. Advances in genomic technologies improved our understanding of epilepsy and raised the possibility to develop patients-tailored treatments acting on the key molecular mechanisms involved in the development of the disease. In addition to conventional antiseizure medications (ASMs), ketogenic diet, hormone therapy and epilepsy surgery play an important role, especially in cases of drugresistance. This review aims to provide a comprehensive overview of the mainfactors influencing cognition in children and adolescents with epilepsy and the main therapeutic options available for the epilepsies associated with intellectual disability.

Measuring the inch stones for progress: Gross motor function in the developmental and epileptic encephalopathies

OBJECTIVE

Developmental and epileptic encephalopathies (DEE) entail moderate to profound impairments in gross motor skills and mobility, which are poorly quantified with clinical outcomes assessments (COA) used in neuro-typical populations. We studied the motor domain of the Adaptive Behavior Assessment System-3 for ages 0-5 years (ABAS) used outside of its intended age range with a focus on raw scores.

METHODS

In a cross-sectional survey, 117 parents of children with a variety of DEEs (ages 1-35 years, median = 9) completed the motor domain section of the ABAS. Floor and ceiling effects and associations with epilepsy-related factors were assessed with appropriate parametric and nonparametric statistical techniques. The sensitivity of the ABAS and additional measures of mobility borrowed from the cerebral palsy literature (Functional Activities Questionnaire (FAQ-22) walking level (FAQ-WL)) to different levels of the Functional Mobility Scale was determined.

RESULTS

ABAS motor scores corresponded to a median age equivalent of 20.5 months (Inter-Quartile Range (IQR) 8-34). Most raw scores corresponded to standardized scores > 2 standard deviations below the ABAS standardization sample mean. ABAS raw scores demonstrated minimal floor and ceiling effects (<5%). In linear regression models, scores increased with age under 6 years (p < 0.0001) but flattened out thereafter. Scores varied substantially by DEE group (p < 0.001) and decreased with higher convulsive seizure frequency (<0.0001) and number of seizure medications (p < 0.001). ABAS and other motor scores were sensitive to important differences in mobility as represented by the FMS at 5 yards. Further, they correlated with declines in mobility function from 5 to 500 yards.

SIGNIFICANCE

An out-of-range COA with raw scores may provide a measure of motor ability and mobility sensitive within the range of moderate to profound impairment seen in patients with DEE. This approach could shorten the time to appropriate COA development and ensure timely clinical trial readiness for novel therapies for rare DEEs.

Potassium channels and epilepsy

With the development and application of next-generation sequencing technology, the aetiological diagnosis of genetic epilepsy is rapidly becoming easier and less expensive. Additionally, there is a growing body of research into precision therapy based on genetic diagnosis. The numerous genes in the potassium ion channel family constitute the largest family of ion channels: this family is divided into different subtypes. Potassium ion channels play a crucial role in the electrical activity of neurons and are directly involved in the mechanism of epileptic seizures. In China, scientific research on genetic diagnosis and studies of precision therapy for genetic epilepsy are progressing rapidly. Many cases of epilepsy caused by mutation of potassium channel genes have been identified, and several potassium channel gene targets and drug candidates have been discovered. The purpose of this review is to briefly summarize the progress of research on the precise diagnosis and treatment of potassium ion channel-related genetic epilepsy, especially the research conducted in China. Here in, we review several large cohort studies on the genetic diagnosis of epilepsy in China in recent years, summarized the proportion of potassium channel genes. We focus on the progress of precison therapy on some hot epilepsy related potassium channel genes: KCNA1, KCNA2, KCNB1, KCNC1, KCND2, KCNQ2, KCNQ3, KCNMA1, and KCNT1.

A novel de novo heterozygous variant of the KCNQ2 gene: Contribution to early‑onset epileptic encephalopathy in a female infant

Early-onset epileptic encephalopathy (EOEE) represents one of the most severe epilepsies, characterized by recurrent seizures during early infancy, electroencephalogram (EEG) abnormalities and varying degrees of neurodevelopmental delay. The KCNQ2 gene has been reported to have a major role in EOEE. In the present study, a 3-month-old female infant from the Chinese Lisu minority with EOEE was analyzed. Detailed clinical evaluations and next-generation sequencing were performed to investigate the clinical and genetic characteristics of this patient, respectively. Furthermore, the three-dimensional structure of the mutant protein was predicted by SWISS-Model and the expression of KCNQ2 protein in the patient was assessed by flow cytometry. It was observed that the patient presented with typical clinical features of EOEE, including repeated non-febrile seizures and significant EEG abnormalities. A novel heterozygous missense variant c.431G>C (p.R144P) in KCNQ2 was identified in the patient and the genotyping of KCNQ2 in the patient's parents suggested that this variant was de novo. Subsequently, the breakage of hydrogen bonds between certain amino acids was predicted by structural analysis of the mutant protein. Flow cytometric analysis detected a significant reduction buts not complete loss of native KCNQ2 protein expression in the patient (25.1%). In conclusion, a novel variant in KCNQ2 was confirmed as the genetic cause for EOEE in this patient. The present study expanded the pathogenic mutation spectrum of KCNQ2, enhanced the understanding of the molecular pathogenesis of EOEE and provided novel clues for research on the genotype-phenotype correlation in this disease.

Variable Expression of GABAA Receptor Subunit Gamma 2 Mutation in a Nuclear Family Displaying Developmental and Encephalopathic Phenotype

Mutations in GABA_A receptor subunit genes (GABRs) are a major etiology for developmental and epileptic encephalopathies (DEEs). This article reports a case of a genetic abnormality in GABRG2 and updates the pathophysiology and treatment development for mutations in DEEs based on recent advances. Mutations in GABRs, especially in GABRA1, GABRB2, GABRB3, and GABRG2, impair GABAergic signaling and are frequently associated with DEEs such as Dravet syndrome and Lennox-Gastaut syndrome, as GABAergic signaling is critical for early brain development. We here present a novel association of a microdeletion of GABRG2 with a diagnosed DEE phenotype. We characterized the clinical phenotype and underlying mechanisms, including molecular genetics, EEGs, and MRI. We then compiled an update of molecular mechanisms of GABR mutations, especially the mutations in GABRB3 and GABRG2 attributed to DEEs. Genetic therapy is also discussed as a new avenue for treatment of DEEs through employing antisense oligonucleotide techniques. There is an urgent need to define treatment targets and explore new treatment paradigms for the DEEs, as early deployment could alleviate long-term disabilities and improve quality of life for patients. This study highlights biomolecular targets for future therapeutic interventions, including via both pharmacological and genetic approaches.

Pyridoxine-responsive KCNQ2 epileptic encephalopathy: Additional cases and literature review

Background

Typical patients with KCNQ2 (OMIM# 602235) epileptic encephalopathy present early neonatal‐onset intractable seizures with a burst suppression EEG pattern and severe developmental delay or regression, and those patients always fail first‐line treatment with sodium channel blockers. Vitamin B6, either pyridoxine or pyridoxal 50‐phosphate, has been demonstrated to improve seizure control in intractable epilepsy.

Methods

Here, we collected and summarized the clinical data for four independent cases diagnosed with pyridoxine‐responsive epileptic encephalopathy, and their exome sequencing data. Moreover, we reviewed all published cases and summarized the clinical features, genetic variants, and treatment of pyridoxine‐responsive KCNQ2 epileptic encephalopathy.

Results

All four cases showed refractory seizures during the neonatal period or infancy, accompanied by global development delay. Four pathogenetic variants of KCNQ2 were uncovered and confirmed by Sanger sequencing: KCNQ2 [NM_172107.4: c.2312C > T (p.Thr771Ile), c.873G > C (p.Arg291Ser), c.652 T > A (p.Trp218Arg) and c.913‐915del (p. Phe305del)]. Sodium channel blockers and other anti‐seizure medications failed to control their seizures. The frequency of seizures gradually decreased after treatment with high‐dose pyridoxine. In case 1, case 2, and case 4, clinical seizures relapsed when pyridoxine was withdrawn, and seizures were controlled again when pyridoxine treatment was resumed.

Conclusion

Our study suggests that pyridoxine may be a promising adjunctive treatment option for patients with KCNQ2 epileptic encephalopathy.

ILAE classification and definition of epilepsy syndromes with onset in neonates and infants: Position statement by the ILAE Task Force on Nosology and Definitions

The International League Against Epilepsy (ILAE) Task Force on Nosology and Definitions proposes a classification and definition of epilepsy syndromes in the neonate and infant with seizure onset up to 2 years of age. The incidence of epilepsy is high in this age group and epilepsy is frequently associated with significant comorbidities and mortality. The licensing of syndrome specific antiseizure medications following randomized controlled trials and the development of precision, gene-related therapies are two of the drivers defining the electroclinical phenotypes of syndromes with onset in infancy. The principal aim of this proposal, consistent with the 2017 ILAE Classification of the Epilepsies, is to support epilepsy diagnosis and emphasize the importance of classifying epilepsy in an individual both by syndrome and etiology. For each syndrome, we report epidemiology, clinical course, seizure types, electroencephalography (EEG), neuroimaging, genetics, and differential diagnosis. Syndromes are separated into self-limited syndromes, where there is likely to be spontaneous remission and developmental and epileptic encephalopathies, diseases where there is developmental impairment related to both the underlying etiology independent of epileptiform activity and the epileptic encephalopathy. The emerging class of etiology-specific epilepsy syndromes, where there is a specific etiology for the epilepsy that is associated with a clearly defined, relatively uniform, and distinct clinical phenotype in most affected individuals as well as consistent EEG, neuroimaging, and/or genetic correlates, is presented. The number of etiology-defined syndromes will continue to increase, and these newly described syndromes will in time be incorporated into this classification. The tables summarize mandatory features, cautionary alerts, and exclusionary features for the common syndromes. Guidance is given on the criteria for syndrome diagnosis in resource-limited regions where laboratory confirmation, including EEG, MRI, and genetic testing, might not be available.

Clinical Study of 30 Novel KCNQ2 Variants/Deletions in KCNQ2-Related Disorders

Background

KCNQ2-related disorder is typically characterized as neonatal onset seizure and epileptic encephalopathy. The relationship between its phenotype and genotype is still elusive. This study aims to provide clinical features, management, and prognosis of patients with novel candidate variants of the KCNQ2 gene.

Methods

We enrolled patients with novel variants in the KCNQ2 gene from the China Neonatal Genomes Project between January 2018 and January 2021. All patients underwent next-generation sequencing tests and genetic data were analyzed by an in-house pipeline. The pathogenicity of variants was classified according to the guideline of the American College of Medical Genetics. Each case was evaluated by two geneticists back to back. Patients' information was acquired from clinical records.

Results

A total of 30 unrelated patients with novel variants in the KCNQ2 gene were identified, including 19 patients with single-nucleotide variants (SNVs) and 11 patients with copy number variants (CNVs). For the 19 SNVs, 12 missense variants and 7 truncating variants were identified. Of them, 36.8% (7/19) of the KCNQ2 variants were located in C-terminal regions, 15.7% (3/19) in segment S2, and 15.7% (3/19) in segment S4. Among them, 18 of 19 patients experienced seizures in the early neonatal period. However, one patient presented neurodevelopmental delay (NDD) as initial phenotype when he was 2 months old, and he had severe NDD when he was 3 years old. This patient did not present seizure but had abnormal electrographic background activity and brain imaging. Moreover, for the 11 patients with CNVs, 20q13.3 deletions involving EEF1A2, KCNQ2, and CHRNA4 genes were detected. All of them presented neonatal-onset seizures, responded to antiepileptic drugs, and had normal neurological development.

Conclusion

In this study, patients with novel KCNQ2 variants have variable phenotypes, whereas patients with 20q13.3 deletion involving EEF1A2, KCNQ2, and CHRNA4 genes tend to have normal neurological development.

Pharmacokinetics of XEN496, a Novel Pediatric Formulation of Ezogabine, Under Fed and Fasted Conditions: A Phase 1 Trial

INTRODUCTION

XEN496 is a novel, granular, immediate-release formulation of ezogabine intended for pediatric use. The objective of this study was to assess the effect of food on the pharmacokinetics (PK) of XEN496 and its N-acetyl metabolite (NAMR) in healthy volunteers.

METHODS

Twenty-four adult subjects were enrolled in this phase 1, single center, open-label, randomized, single-dose, two-way crossover study. Subjects received 400 mg XEN496 as an oral suspension in both fed and fasted states separated by a 6-day washout period. Serial blood samples were collected up to 48 h post-administration. PK parameters evaluated included maximum observed plasma concentration (C_max), time of maximum observed plasma concentration (T_max), and area under the concentration-time curve (AUC_(0-t) and AUC_inf). Safety was assessed by laboratory evaluations, physical exam, and adverse event monitoring.

RESULTS

For XEN496, median T_max was 3 and 2 h in the fed and fasted states, respectively. AUC parameters in the fed and fasted states were equivalent, whereas food decreased C_max of XEN496 by 32% compared to the fasted state. The ratio of geometric means [90% CI] for C_max was 72% [64-82%]. For NAMR, food delayed T_max by 1 h, while C_max and AUC parameters were equivalent in the fed and fasted states. The safety profile of XEN496 in this study appeared comparable to that previously reported for ezogabine tablets.

CONCLUSION

The biopharmaceutical performance of XEN496 in this study was as expected for an immediate-release, granular dosage formulation, and generally comparable to that reported for ezogabine tablets. Future studies are needed to characterize the efficacy, safety, and PK of XEN496 in a pediatric population.

Genetic analysis using targeted exome sequencing of 53 Vietnamese children with developmental and epileptic encephalopathies

Developmental and epileptic encephalopathies (DEE) refers to a group of rare and severe neurodevelopmental disorders where genetic etiologies can play a major role. This study aimed to elucidate the genetic etiologies of a cohort of 53 Vietnamese patients with DEE. All patients were classified into known electroclinical syndromes where possible. Exome sequencing (ES) followed by a targeted analysis on 294 DEE-related genes was then performed. Patients with identified causative variants were followed for 6 months to determine the impact of genetic testing on their treatment. The diagnostic yield was 38.0% (20/53), which was significantly higher in the earlier onset group (<12 months) than in the later onset group (≥12 months). The 19 identified variants belonged to 11 genes with various cellular functions. Genes encoding ion channels especially sodium voltage-gated channel were the most frequently involved. Most variants were missense variants and located in key protein functional domains. Four variants were novel and four had been reported previously but in different phenotypes. Within 6 months of further follow-up, treatment changes were applied for six patients based on the identified disease-causing variants, with five patients showing a positive impact. This is the first study in Vietnam to analyze the genetics of DEE. This study confirms the strong involvement of genetic etiologies in DEE, especially early onset DEE. The study also contributes to clarify the genotype-phenotype correlations of DEE and highlights the efficacy of targeted ES in the diagnosis and treatment of DEE.

High-throughput evaluation of epilepsy-associated KCNQ2 variants reveals functional and pharmacological heterogeneity

Hundreds of genetic variants in KCNQ2 encoding the voltage-gated potassium channel KV7.2 are associated with early onset epilepsy and/or developmental disability, but the functional consequences of most variants are unknown. Absent functional annotation for KCNQ2 variants hinders identification of individuals who may benefit from emerging precision therapies. We employed automated patch clamp recordings to assess at, to our knowledge, an unprecedented scale the functional and pharmacological properties of 79 missense and 2 inframe deletion KCNQ2 variants. Among the variants we studied were 18 known pathogenic variants, 24 mostly rare population variants, and 39 disease-associated variants with unclear functional effects. We analyzed electrophysiological data recorded from 9,480 cells. The functional properties of 18 known pathogenic variants largely matched previously published results and validated automated patch clamp for this purpose. Unlike rare population variants, most disease-associated KCNQ2 variants exhibited prominent loss-of-function with dominant-negative effects, providing strong evidence in support of pathogenicity. All variants responded to retigabine, although there were substantial differences in maximal responses. Our study demonstrated that dominant-negative loss-of-function is a common mechanism associated with missense KCNQ2 variants. Importantly, we observed genotype-dependent differences in the response of KCNQ2 variants to retigabine, a proposed precision therapy for KCNQ2 developmental and epileptic encephalopathy.

A novel KCNQ2 missense variant in non-syndromic intellectual disability causes mild gain-of-function of Kv7.2 channel

BACKGROUND

Heterozygous variants of KCNQ2 can cause KCNQ2 associated neurodevelopmental disorder, mainly are benign (familial) neonatal or infantile epilepsy (B(F)NE or B(F)IE) and early-onset epileptic encephalopathy (EOEE). Moreover, some intermediate phenotypes, including intellectual disability (ID), and myokymia are related to the gene.

METHODS

We collected a non-syndromic ID male patient with a novel KCNQ2 missense variant. Whole cell electrophysiology, western blotting, and immunofluorescence were adopted to analyze the variant's functional alterations.

RESULTS

The patient presented with global developmental delay since his infancy. He still had profound ID but did not have epilepsy at the adolescence. The de novo KCNQ2 variant p.R75C (NM_172107) in the NH2 domain identified here showed a slightly hyperpolarized shift of activation curves and larger current density in homomeric configurations, which could be abolished in co-expression with Kv7.2 or Kv7.3 wild-type. Western blotting and immunocytochemistry supported that the expression of variant p.R75C is lower than the Kv7.2 wild-type. The findings indicated variant p.R75C cause mild gain-of-function (GOF) of Kv7.2 channel.

CONCLUSIONS

We report a non-syndromic ID patient with a KCNQ2 mild GOF variant, adding evidence for this rare clinical phenotype in the disorder. We propose that individuals with KCNQ2 GOF variants are prone to have cognitive impairments.

Early initial video-electro-encephalography combined with variant location predict prognosis of KCNQ2-related disorder

BACKGROUND

The clinical features of KCNQ2-related disorders range from benign familial neonatal seizures 1 to early infantile epileptic encephalopathy 7. The genotype-phenotypic association is difficult to establish.

OBJECTIVE

To explore potential factors in neonatal period that can predict the prognosis of neonates with KCNQ2-related disorder.

METHODS

Infants with KCNQ2-related disorder were retrospectively enrolled in our study in Children's Hospital of Fudan University in China from Jan 2015 to Mar 2020. All infants were older than age of 12 months at time of follow-up, and assessed by Bayley Scales of Infant and Toddler Development-Third Edition (BSID-III) or Wechsler preschool and primary scale of intelligence-fourth edition (WPPSI-IV), then divided into three groups based on scores of BSID-III or WPPSI-IV: normal group, mild impairment group, encephalopathy group. We collected demographic variables, clinical characteristics, neuroimaging data. Considered variables include gender, gestational age, birth weight, age of the initial seizures, early interictal VEEG, variant location, delivery type. Variables predicting prognosis were identified using multivariate ordinal logistic regression analysis.

RESULTS

A total of 52 infants were selected in this study. Early interictal video-electro-encephalography (VEEG) (β = 2.77, 1.20 to 4.34, P = 0.001), and variant location (β = 2.77, 0.03 to 5.5, P = 0.048) were independent risk factors for prognosis. The worse the early interictal VEEG, the worse the prognosis. Patients with variants located in the pore-lining domain or S4 segment are more likely to have a poor prognosis.

CONCLUSIONS

The integration of early initial VEEG and variant location can predict prognosis. An individual whose KCNQ2 variant located in voltage sensor, the pore domain, with worse early initial VEEG background, often had an adverse outcome.

PIP2-dependent coupling of voltage sensor and pore domains in Kv7.2 channel

Phosphatidylinositol-4,5-bisphosphate (PIP₂) is a signaling lipid which regulates voltage-gated K_v7/KCNQ potassium channels. Altered PIP₂ sensitivity of neuronal K_v7.2 channel is involved in KCNQ2 epileptic encephalopathy. However, the molecular action of PIP₂ on K_v7.2 gating remains largely elusive. Here, we use molecular dynamics simulations and electrophysiology to characterize PIP₂ binding sites in a human K_v7.2 channel. In the closed state, PIP₂ localizes to the periphery of the voltage-sensing domain (VSD). In the open state, PIP₂ binds to 4 distinct interfaces formed by the cytoplasmic ends of the VSD, the gate, intracellular helices A and B and their linkers. PIP₂ binding induces bilayer-interacting conformation of helices A and B and the correlated motion of the VSD and the pore domain, whereas charge-neutralizing mutations block this coupling and reduce PIP₂ sensitivity of K_v7.2 channels by disrupting PIP₂ binding. These findings reveal the allosteric role of PIP₂ in K_v7.2 channel activation.

Pant et al. describe the mechanism by which PIP2 might regulate homomeric Kv7.2 channels. They identify sites important in the binding of the PIP2 lipid to Kv7.2 channels and propose that the PIP2 binding to a specific site results in the coupling between the voltage sensor domain (VSD) and pore domain (PD), which stabilizes the open state of the channel.

In vitro and in vivo anti-epileptic efficacy of eslicarbazepine acetate in a mouse model of KCNQ2-related self-limited epilepsy

BACKGROUND AND PURPOSE

The KCNQ2 gene encodes for the K_v 7.2 subunit of non-inactivating potassium channels. KCNQ2-related diseases range from autosomal dominant neonatal self-limited epilepsy, often caused by KCNQ2 haploinsufficiency, to severe encephalopathies caused by KCNQ2 missense variants. In vivo and in vitro effects of the sodium channel blocker eslicarbazepine acetate (ESL) and eslicarbazepine metabolite (S-Lic) in a mouse model of self-limited neonatal epilepsy as a first attempt to assess the utility of ESL in the KCNQ2 disease spectrum was investigated.

EXPERIMENTAL APPROACH

Effects of S-Lic on in vitro physiological and pathological hippocampal neuronal activity in slices from mice carrying a heterozygous deletion of Kcnq2 (Kcnq2^+/- ) and Kcnq2^+/+ mice were investigated. ESL in vivo efficacy was investigated in the 6-Hz psychomotor seizure model in both Kcnq2^+/- and Kcnq2^+/+ mice.

KEY RESULTS

S-Lic increased the amplitude and decreased the incidence of physiological sharp wave-ripples in a concentration-dependent manner and slightly decreased gamma oscillations frequency. 4-Aminopyridine-evoked seizure-like events were blocked at high S-Lic concentrations and substantially reduced in incidence at lower concentrations. These results were not different in Kcnq2^+/+ and Kcnq2^+/- mice, although the EC₅₀ estimation implicated higher efficacy in Kcnq2^+/- animals. In vivo, Kcnq2^+/- mice had a lower seizure threshold than Kcnq2^+/+ mice. In both genotypes, ESL dose-dependently displayed protection against seizures.

CONCLUSIONS AND IMPLICATIONS

S-Lic slightly modulates hippocampal oscillations and blocks epileptic activity in vitro and in vivo. Our results suggest that the increased excitability in Kcnq2^+/- mice is effectively targeted by S-Lic high concentrations, presumably by blocking diverse sodium channel subtypes.

Genetics in Epilepsy

The presence of unprovoked, recurrent seizures, particularly when drug resistant and associated with cognitive and behavioral deficits, warrants investigation for an underlying genetic cause. This article provides an overview of the major classes of genes associated with epilepsy phenotypes divided into functional categories along with the recommended work-up and therapeutic considerations. Gene discovery in epilepsy supports counseling and anticipatory guidance but also opens the door for precision medicine guiding therapy with a focus on those with disease-modifying effects.

Electrophysiological Biomarkers in Genetic Epilepsies

Precision treatments for epilepsy targeting the underlying genetic diagnoses are becoming a reality. Historically, the goal of epilepsy treatments was to reduce seizure frequency. In the era of precision medicine, however, outcomes such as prevention of epilepsy progression or even improvements in cognitive functions are both aspirational targets for any intervention. Developing methods, both in clinical trial design and in novel endpoints, will be necessary for measuring, not only seizures, but also the other neurodevelopmental outcomes that are predicted to be targeted by precision treatments. Biomarkers that quantitatively measure disease progression or network level changes are needed to allow for unbiased measurements of the effects of any gene-level treatments. Here, we discuss some of the promising electrophysiological biomarkers that may be of use in clinical trials of precision therapies, as well as the difficulties in implementing them.

In Silico Predictions of KCNQ Variant Pathogenicity in Epilepsy

BACKGROUND

Variants in KCNQ2 and KCNQ3 may cause benign neonatal familial seizures and early infantile epileptic encephalopathy. Previous reports suggest that in silico models cannot predict pathogenicity accurately enough for clinical use. Here we sought to establish a model to accurately predict the pathogenicity of KCNQ2 and KCNQ3 missense variants based on available in silico prediction models.

METHODS

ClinVar and gnomAD databases of reported KCNQ2 and KCNQ3 missense variants in patients with neonatal epilepsy were accessed and classified as benign, pathogenic, or of uncertain significance. Sensitivity, specificity, and classification accuracy for prediction of pathogenicity were determined and compared for 10 widely used prediction algorithms program. A mathematical model of the variants (KCNQ Index) was created using their amino acid location and prediction algorithm scores to improve prediction accuracy.

RESULTS

Using clinically characterized variants, the free online tool PROVEAN accurately predicted pathogenicity 92% of the time and the KCNQ Index had an accuracy of 96%. However, when including the gnomAD database as benign variants, only the KCNQ Index was able to predict pathogenicity with an accuracy greater than 90% (sensitivity = 93% and specificity = 98%). No model could accurately predict the phenotype of variants.

CONCLUSION

We show that KCNQ channel variant pathogenicity can be predicted by a novel KCNQ Index in neonatal epilepsy. However, more work is needed to accurately predict the patient's epilepsy phenotype from in silico algorithms.

Developmental and epileptic encephalopathies: what we do and do not know

Developmental encephalopathies, including intellectual disability and autistic spectrum disorder, are frequently associated with infant epilepsy. Epileptic encephalopathy is used to describe an assumed causal relationship between epilepsy and developmental delay. Developmental encephalopathies pathogenesis more independent from epilepsy is supported by the identification of several gene variants associated with both developmental encephalopathies and epilepsy, the possibility for gene-associated developmental encephalopathies without epilepsy, and the continued development of developmental encephalopathies even when seizures are controlled. Hence, 'developmental and epileptic encephalopathy' may be a more appropriate term than epileptic encephalopathy. This update considers the best studied 'developmental and epileptic encephalopathy' gene variants for illustrative support for 'developmental and epileptic encephalopathy' over epileptic encephalopathy. Moreover, the interaction between epilepsy and developmental encephalopathies is considered with respect to influence on treatment decisions. Continued research in genetic testing will increase access to clinical tests, earlier diagnosis, better application of current treatments, and potentially provide new molecular-investigated treatments.

Potassium channels as prominent targets and tools for the treatment of epilepsy

INTRODUCTION

K⁺ channels are of great interest to epilepsy research as mutations in their genes are found in humans with inherited epilepsy. At the level of cellular physiology, K+ channels control neuronal intrinsic excitability and are the main contributors to membrane repolarization of active neurons. Recently, a genetically modified voltage-dependent K⁺ channel has been patented as a remedy for epileptic seizures.

AREAS COVERED

We review the role of potassium channels in excitability, clinical and experimental evidence for the association of potassium channelopathies with epilepsy, the targeting of K+ channels by drugs, and perspectives of gene therapy in epilepsy with the expression of extra K+ channels in the brain.

EXPERT OPINION

Control over K+ conductance is of great potential benefit for the treatment of epilepsy. Nowadays, gene therapy affecting K+ channels is one of the most promising approaches to treat pharmacoresistant focal epilepsy.

Adult phenotype of KCNQ2 encephalopathy

BACKGROUND

Pathogenic KCNQ2 variants are a frequent cause of developmental and epileptic encephalopathy.

METHODS

We recruited 13 adults (between 18 years and 45 years of age) with KCNQ2 encephalopathy and reviewed their clinical, EEG, neuroimaging and treatment history.

RESULTS

While most patients had daily seizures at seizure onset, seizure frequency declined or remitted during childhood and adulthood. The most common seizure type was tonic seizures (early) infancy, and tonic-clonic and focal impaired awareness seizures later in life. Ten individuals (77%) were seizure-free at last follow-up. In 38% of the individuals, earlier periods of seizure freedom lasting a minimum of 2 years followed by seizure recurrence had occurred. Of the 10 seizure-free patients, 4 were receiving a single antiseizure medication (ASM, carbamazepine, lamotrigine or levetiracetam), and 2 had stopped taking ASM. Intellectual disability (ID) ranged from mild to profound, with the majority (54%) of individuals in the severe category. At last contact, six individuals (46%) remained unable to walk independently, six (46%) had limb spasticity and four (31%) tetraparesis/tetraplegia. Six (46%) remained non-verbal, 10 (77%) had autistic features/autism, 4 (31%) exhibited aggressive behaviour and 4 (31%) destructive behaviour with self-injury. Four patients had visual problems, thought to be related to prematurity in one. Sleep problems were seen in six (46%) individuals.

CONCLUSION

Seizure frequency declines over the years and most patients are seizure-free in adulthood. Longer seizure-free periods followed by seizure recurrence are common during childhood and adolescence. Most adult patients have severe ID. Motor, language and behavioural problems are an issue of continuous concern.

Pathogenic variants in KCNQ2 cause intellectual deficiency without epilepsy: Broadening the phenotypic spectrum of a potassium channelopathy

High-throughput sequencing (HTS) improved the molecular diagnosis in individuals with intellectual deficiency (ID) and helped to broaden the phenotype of previously known disease-causing genes. We report herein four unrelated patients with isolated ID, carriers of a likely pathogenic variant in KCNQ2, a gene usually implicated in benign familial neonatal seizures (BFNS) or early onset epileptic encephalopathy (EOEE). Patients were diagnosed by targeted HTS or exome sequencing. Pathogenicity of the variants was assessed by multiple in silico tools. Patients' ID ranged from mild to severe with predominance of speech disturbance and autistic features. Three of the four variants disrupted the same amino acid. Compiling all the pathogenic variants previously reported, we observed a strong overlap between variants causing EOEE, isolated ID, and BFNS and an important intra-familial phenotypic variability, although missense variants in the voltage-sensing domain and the pore are significantly associated to EOEE (p < 0.01, Fisher test). Thus, pathogenic variants in KCNQ2 can be associated with isolated ID. We did not highlight strong related genotype-phenotype correlations in KCNQ2-related disorders. A second genetic hit, a burden of rare variants, or other extrinsic factors may explain such a phenotypic variability. However, it is of interest to study encephalopathy genes in non-epileptic ID patients.

Structural Mechanism of ω-Currents in a Mutated Kv7.2 Voltage Sensor Domain from Molecular Dynamics Simulations

Activation of voltage-gated ion channels is regulated by conformational changes of the voltage sensor domains (VSDs), four water- and ion-impermeable modules peripheral to the central, permeable pore domain. Anomalous currents, defined as ω-currents, have been recorded in response to mutations of residues on the VSD S4 helix and associated with ion fluxes through the VSDs. In humans, gene defects in the potassium channel Kv7.2 result in a broad range of epileptic disorders, from benign neonatal seizures to severe epileptic encephalopathies. Experimental evidence suggests that the R207Q mutation in S4, associated with peripheral nerve hyperexcitability, induces ω-currents at depolarized potentials, but the fine structural details are still elusive. In this work, we use atom-detailed molecular dynamics simulations and a refined model structure of the Kv7.2 VSD in the active conformation in a membrane/water environment to study the effect of R207Q and four additional mutations of proven clinical importance. Our results demonstrate that the R207Q mutant shows the most pronounced increase of hydration in the internal VSD cavity, a feature favoring the occurrence of ω-currents. Free energy and kinetics calculations of sodium permeation through the native and mutated VSD indicate as more favorable the formation of a cationic current in the latter. Overall, our simulations establish a mechanistic linkage between genetic variations and their physiological outcome, by providing a computational description that includes both thermodynamic and kinetic features of ion permeation associated with ω-currents.

Dyshomeostatic modulation of Ca2+-activated K+ channels in a human neuronal model of KCNQ2 encephalopathy

Mutations in KCNQ2, which encodes a pore-forming K⁺ channel subunit responsible for neuronal M-current, cause neonatal epileptic encephalopathy, a complex disorder presenting with severe early-onset seizures and impaired neurodevelopment. The condition is exceptionally difficult to treat, partially because the effects of KCNQ2 mutations on the development and function of human neurons are unknown. Here, we used induced pluripotent stem cells (iPSCs) and gene editing to establish a disease model and measured the functional properties of differentiated excitatory neurons. We find that patient iPSC-derived neurons exhibit faster action potential repolarization, larger post-burst afterhyperpolarization and a functional enhancement of Ca²⁺-activated K⁺ channels. These properties, which can be recapitulated by chronic inhibition of M-current in control neurons, facilitate a burst-suppression firing pattern that is reminiscent of the interictal electroencephalography pattern in patients. Our findings suggest that dyshomeostatic mechanisms compound KCNQ2 loss-of-function leading to alterations in the neurodevelopmental trajectory of patient iPSC-derived neurons.

Clinical characteristics of KCNQ2 encephalopathy

PURPOSE

KCNQ2 mutations are associated with benign familial neonatal epilepsy (BFNE) or developmental and epileptic encephalopathy (DEE). In this study, we aimed to delineate the phenotype of KCNQ2 encephalopathy and evaluate the treatment response.

METHODS

Thirteen patients of KCNQ2 encephalopathy were included in the study. Characteristics of KCNQ2 mutations, electroclinical features, clinical course, and response to the treatment were analyzed.

RESULTS

Age range of the thirteen patients was between 3 months and 20.9 years. The onset of seizures in 11 patients ranged from 1 to 3 days of age, while in the other two patients it was 7 and 40 days, respectively. Most common initial seizure types were tonic seizures. Initial EEGs were suppression burst pattern in seven patients and slow and disorganized background with multifocal epileptiform discharges in six patients. Initial epilepsy syndrome was Ohtahara syndrome in seven patients, neonatal focal seizure in five patients, and focal epilepsy beyond neonatal period in one patient. Sodium channel blockers including oxcarbazepine (OXC) (n = 3), lamotrigine (LTG) (n = 3), phenytoin (PHT) (n = 2), topiramate (TPM) (n = 2), and zonisamide (ZNS) (n = 1) were tried and found effective in eleven patients. Ultimately, 12 of 13 patients became seizure-free. However, developmental outcomes were poor.

CONCLUSIONS

Sodium channel blockers are effective in seizure control in these patients with KCNQ2 encephalopathy. Early recognition of KCNQ2 encephalopathy and early use of sodium channel blockers might be helpful in seizure control.

Genetic Interaction of H19 and TGFBR1 Polymorphisms with Risk of Epilepsy in a Chinese Population

PURPOSE

Long non-coding RNA H19 was highly expressed in the latent period of epilepsy, contributing to apoptosis of hippocampal neurons by targeting let-7b. Transforming growth factor beta receptor 1 (TGFBR1), a target of let-7b, is located on the susceptibility locus for epilepsy. In this context, we investigated the association between tagSNPs in long non-coding RNA H19 and transforming growth factor beta receptor 1 (TGFBR1) rs6478974 and the risk of epilepsy.

PATIENTS AND METHODS

The present study consisted of 302 patients with epilepsy and 612 age- and gender-matched controls. The polymorphisms were analyzed using a TaqMan allelic genotyping assay. H19 and TGFBR1 mRNA levels were determined using quantitative real-time polymerase chain reaction.

RESULTS

The TGFBR1 AT and TT genotypes emerged as a protective factor for the risk of epilepsy (AT vs AA: adjusted OR = 0.59, 95% CI: 0.39-0.89, P = 0.01; TT vs AA: adjusted OR = 0.53, 95% CI: 0.35-0.80, P = 0.002, respectively). The protective effect was also observed in recessive genetic model (adjusted OR = 0.56, 95% CI: 0.38-0.82, P = 0.003). Individuals carrying the rs6478974 TT genotype had lower levels of TGFBR1 mRNA. Moreover, the TCTAT and TCCAA haplotypes emerged as a risk factor for epilepsy and the rs3741219-rs2839698-rs6478974 was associated with an interactive effect on the risk of epilepsy.

CONCLUSION

The current study provides evidence of the rs6478974 TT genotype decreasing the susceptibility to epilepsy by reducing the levels of TGFBR1 mRNA.

Current and Future Uses of Continuous EEG in the NICU

Continuous EEG (cEEG) is a fundamental neurodiagnostic tool in the care of critically ill neonates and is increasingly recommended. cEEG enhances prognostication via assessment of the background brain activity, plays a role in predicting which neonates are at risk for seizures when combined with clinical factors, and allows for accurate diagnosis and management of neonatal seizures. Continuous EEG is the gold standard method for diagnosis of neonatal seizures and should be used for detection of seizures in high-risk clinical conditions, differential diagnosis of paroxysmal events, and assessment of response to treatment. High costs associated with cEEG are a limiting factor in its widespread implementation. Centralized remote cEEG interpretation, automated seizure detection, and pre-natal EEG are potential future applications of this neurodiagnostic tool.

KCNQ2 Encephalopathy and Responsiveness to Pyridoxal-5'-Phosphate

KCNQ2 mutations encompass a wide range of phenotypes, ranging from benign familial neonatal seizure to a clinical spectrum of early-onset epileptic encephalopathy that occurs in the early neonatal period. We report an infant with KCNQ2 encephalopathy presenting as neonatal seizure, initially controlled by two anticonvulsants. Electroencephalogram (EEG) showed repetitive multifocal epileptiform discharges, which remained similar after administration of intravenous pyridoxine injection. Seizure recurred at the age of 3 months preceded by an episode of minor viral infection, which occurred multiple times per day. No significant change in seizure frequency was observed after 5-day oral pyridoxine trial, but subsequently, there was dramatic seizure improvement with oral pyridoxal-5'-phosphate (PLP). We hope to alert clinicians that in patients with neonatal epileptic encephalopathy, particularly with known KCNQ2 mutations, intravenous injection of pyridoxine (preferably with EEG monitoring), followed by both oral trial of pyridoxine and PLP should be considered. KCNQ2 mutations should also be considered in vitamin B6-responsive patients.

Comparative characterization of PCDH19 missense and truncating variants in PCDH19-related epilepsy

Missense and truncating variants in protocadherin 19 (PCDH19) cause PCDH19-related epilepsy. In this study, we aimed to investigate variations in distributional characteristics and the clinical implications of variant type in PCDH19-related epilepsy. We comprehensively collected PCDH19 missense and truncating variants from the literature and by sequencing six exons and intron–exon boundaries of PCDH19 in our cohort. We investigated the distribution of each type of variant using the cumulative distribution function and tested for associations between variant types and phenotypes. The distribution of missense variants in patients was clearly different from that of healthy individuals and was uniform throughout the extracellular cadherin (EC) domain, which consisted of six highly conserved domains. Truncating variants showed two types of distributions: (1) located from EC domain 1 to EC domain 4, and (2) located from EC domain 5 to the cytoplasmic domain. Furthermore, we also found that later onset seizures and milder intellectual disability occurred in patients with truncating variants located from EC domain 5 to the cytoplasmic domain compared with those of patients with other variants. Our findings provide the first evidence of two types of truncating variants in the PCDH19 gene with regard to distribution and the resulting clinical phenotype.

Familial neonatal seizures caused by the Kv7.3 selectivity filter mutation T313I

OBJECTIVE

A spectrum of seizure disorders is linked to mutations in Kv7.2 and Kv7.3 channels. Linking functional effects of identified mutations to their clinical presentation requires ongoing characterization of newly identified variants. In this study, we identified and functionally characterized a previously unreported mutation in the selectivity filter of Kv7.3.

METHODS

Next-generation sequencing was used to identify the Kv7.3[T313I] mutation in a family affected by neonatal seizures. Electrophysiological approaches were used to characterize the functional effects of this mutation on ion channels expressed in Xenopus laevis oocytes.

RESULTS

Substitution of residue 313 from threonine to isoleucine (Kv7.3[T313I]) likely disrupts a critical intersubunit hydrogen bond. Characterization of the mutation in homomeric Kv7.3 channels demonstrated a total loss of channel function. Assembly in heteromeric channels (with Kv7.2) leads to modest suppression of total current when expressed in Xenopus laevis oocytes. Using a Kv7 activator with distinct effects on homomeric Kv7.2 vs heteromeric Kv7.2/Kv7.3 channels, we demonstrated that assembly of Kv7.2 and Kv7.3[T313I] generates functional channels.

SIGNIFICANCE

Biophysical and clinical effects of the T313I mutation are consistent with Kv7.3 mutations previously identified in cases of pharmacoresponsive self-limiting neonatal epilepsy. These findings expand our description of functionally characterized Kv7 channel variants and report new methods to distinguish molecular mechanisms of channel mutations.

Genotype-phenotype correlations in patients with de novo KCNQ2 pathogenic variants

Objective

Early identification of de novo KCNQ2 variants in patients with epilepsy raises prognostic issues toward optimal management. We analyzed the clinical and genetic information from a cohort of patients with de novo KCNQ2 pathogenic variants to dissect genotype-phenotype correlations.

Methods

Patients with de novo KCNQ2 pathogenic variants were identified from Italy, Denmark, and Belgium. Atomic resolution Kv7.2 structures were also generated using homology modeling to map the variants.

Results

We included 34 patients with a mean age of 4.7 years. Median seizure onset was 2 days, mainly with focal seizures with autonomic signs. Twenty-two patients (65%) were seizure free at the mean age of 1.2 years. More than half of the patients (17/32) displayed severe/profound intellectual disability; however, 4 (13%) of them had a normal cognitive outcome.

A total of 28 de novo pathogenic variants were identified, most missense (25/28), and clustered in conserved regions of the protein; 6 variants recurred, and 7 were novel. We did not identify a relationship between variant position and seizure offset or cognitive outcome in patients harboring missense variants. Besides, recurrent variants were associated with overlapping epilepsy features but also variable evolution regarding the intellectual outcome.

Conclusions

We highlight the complexity of variant interpretation to assess the impact of a class of de novo KCNQ2 mutations. Genetic modifiers could be implicated, but the study paradigms to successfully address the impact of each single mutation need to be developed.

Efficacy of Intravenous Hydrocortisone Treatment in Refractory Neonatal Seizures: A Report on Three Cases

Neonatal seizures are the most common neurological emergency, and neonatal status epilepticus (NSE) remains a controversial entity, with no general consensus about its definition and treatment. Here, we report on three newborns with NSE refractory to first- and second-line antiepileptic drugs successfully treated with intravenous (IV) hydrocortisone. The patients had previously failed therapy with levetiracetam, phenobarbital and midazolam, showing persistent clinical and electrical seizures. Modulation of brain inflammation triggered during prolonged epileptic activity has been thought to potentially explain the beneficial effects of anti-inflammatory treatment.

Effect of total callosotomy on KCNQ2-related intractable epilepsy

AIM

To describe beneficial effects of callosotomy on KCNQ2-related intractable epilepsy.

CASE REPORT

Our patient was a 10-year-old girl who had developed epilepsy during the neonatal period, accompanied by a suppression-burst pattern on the electroencephalography (EEG). The patient showed profound psychomotor developmental delay since early infancy. Daily seizures of versive posturing and ocular deviation were transiently controlled by carbamazepine and valproate at the age of 1 year; however, the seizures gradually increased to up to 50 times per day. Ictal EEG and positron emission tomography revealed an epileptic focus in the left frontal lobe at age 5 years. Total callosotomy resulted in marked reduction of epileptic seizures thereafter, as well as improved responses to external auditory and visual stimuli. Whole exome sequencing at age 9 identified a de novo missense variant in KCNQ2 (NM_172107.3:c.563A > C:p.(Gln188Pro)).

CONCLUSION

This case supports that epilepsy surgery could benefit children with epileptic encephalopathy, even with the etiology of channelopathy.

Developmental and epileptic encephalopathy due to SZT2 genomic variants: Emerging features of a syndromic condition

Seizure threshold 2 (SZT2) gene mutations have been associated with developmental and epileptic encephalopathies (DEEs). Following a literature review, we collected 22 patients and identified the main clinical features related to SZT2 variants that are epilepsy with onset within the first years of life, intellectual disability (ID), macrocephaly with dysmorphic facial features, corpus callosum (CC) shape abnormalities, and cortical migration disorders. Moreover, we identified the c.7825T>G homozygous missense variant in SZT2 in two female siblings presenting with focal seizures, mild-moderate ID, behavioral disturbances, and facial dysmorphisms. Interictal Electroencephalogram (EEG) and ictal EEG were both informative and revealed, respectively, temporal bilateral asynchronous slow and epileptiform abnormalities and a focal onset in both of them. Neuroimaging study revealed a thick and abnormally shaped CC. Seizure threshold 2 has been identified as a component of the KICSTOR complex, a newly recognized protein complex involved in the mammalian target of rapamycin (mTOR) pathway. mTOR signaling dysregulation represents common pathogenetic mechanisms that can explain the presence of both epileptogenesis and ID. Even if few cases had been reported, a new clinical phenotype is emerging, and recent hypothesis of hyperactivation of mTORC1 signaling might also open to targeted treatments, challenging an early diagnosis as of paramount importance.

Epileptic channelopathies caused by neuronal Kv7 (KCNQ) channel dysfunction

Seizures are the most common neurological manifestation in the newborn period, with an estimated incidence of 1.8-3.5 per 1000 live births. Prolonged or intractable seizures have a detrimental effect on cognition and brain function in experimental animals and are associated with adverse long-term neurodevelopmental sequelae and an increased risk of post-neonatal epilepsy in humans. The developing brain is particularly susceptible to the potentially severe effects of epilepsy, and epilepsy, especially when refractory to medications, often results in a developmental and epileptic encephalopathy (DEE) with developmental arrest or regression. DEEs can be primarily attributed to genetic causes. Given the critical role of potassium (K⁺) currents with distinct subcellular localization, biophysical properties, modulation, and pharmacological profile in regulating intrinsic electrical properties of neurons and their responsiveness to synaptic inputs, it is not too surprising that genetic research in the past two decades has identified several K⁺ channel genes as responsible for a large fraction of DEE. In the present article, we review the genetically determined epileptic channelopathies affecting three members of the Kv7 family, namely Kv7.2 (KCNQ2), Kv7.3 (KCNQ3), and Kv7.5 (KCNQ5); we review the phenotypic spectrum of Kv7-related epileptic channelopathies, the different genetic and pathogenetic mechanisms, and the emerging genotype-phenotype correlations which may prove crucial for prognostic predictions, disease management, parental counseling, and individually tailored therapeutic attempts.