Genetic testing in benign familial epilepsies of the first year of life: Clinical and diagnostic significance

Channelopathies in epilepsy: an overview of clinical presentations, pathogenic mechanisms, and therapeutic insights

Pathogenic variants in genes encoding ion channels are causal for various pediatric and adult neurological conditions. In particular, several epilepsy syndromes have been identified to be caused by specific channelopathies. These encompass a spectrum from self-limited epilepsies to developmental and epileptic encephalopathies spanning genetic and acquired causes. Several of these channelopathies have exquisite responses to specific antiseizure medications (ASMs), while others ASMs may prove ineffective or even worsen seizures. Some channelopathies demonstrate phenotypic pleiotropy and can cause other neurological conditions outside of epilepsy. This review aims to provide a comprehensive exploration of the pathophysiology of seizure generation, ion channels implicated in epilepsy, and several genetic epilepsies due to ion channel dysfunction. We outline the clinical presentation, pathogenesis, and the current state of basic science and clinical research for these channelopathies. In addition, we briefly look at potential precision therapy approaches emerging for these disorders.

A Girl with PRRT2 Mutation Presenting with Benign Familial Infantile Seizures Followed by Autistic Regression

Benign familial infantile seizure (BFIS) is an autosomal dominant infantile-onset epilepsy syndrome with a typically benign prognosis. It is commonly associated with heterozygous mutations of the PRRT2 gene located on chromosome 16p11.2. The frameshift heterozygous mutation (c.649dupC, p.Arg217Profs∗8) in PRRT2 is responsible for the majority of BFIS cases. In this report, we present a rare case of a girl with a confirmed clinical and genetic diagnosis of BFIS due to a frameshift heterozygous mutation in PRRT2 (c.649dupC). She exhibited typical neurodevelopment until 15 months of age, followed by an unexpected severe autistic regression. In addition to BFIS, PRRT2 mutations are also associated with paroxysmal kinesigenic dyskinesia (PKD) and infantile convulsions and paroxysmal choreoathetosis (ICCA), indicating a complex genotype-phenotype heterogeneity in PRRT2 mutations. This clinical observation highlights the possibility that BFIS patients with PRRT2 mutations may not always have a benign neurodevelopmental prognosis, emphasizing the need for long-term clinical follow-up.

Neurodevelopmental outcomes in a cohort of Australian families with self-limited familial epilepsy of neonatal/infantile onset

OBJECTIVES

To determine: i) seizure recurrence; ii) developmental disability; iii) co-morbidities and risk factors in self-limited familial neonatal and/or infantile epilepsy (SeLFE) in a multigenerational study.

METHODS

Families were retrospectively recruited from epilepsy databases (2021-2022) in 2 paediatric hospitals, Sydney, Australia. Eligible families had 2 first degree relatives with seizures and underwent genetic testing. Demographics/clinical data were collected from interviews and medical records. Vineland Adaptive Behaviour Scales-Third Edition measured adaptive function.

RESULTS

Fifteen families participated. Fourteen had a genetic diagnosis (93%): 11 pathogenic; PRRT2 (n=4), KCNQ2 (n=3), SCN2A (n=4), 3 likely pathogenic; KCNQ2 (n=1), SCN8A (n=2). Seizures affected 73 individuals (ages 1-76 years); 30 children and 20 adults had in-depth phenotyping. Ten of 50 individuals (20%) had seizure recurrence, aged 8-65 years. Median time from last neonatal/infantile seizure was 11.8/12.8 years. Predictors of recurrence were high seizure number (p=0.05) and longer treatment duration (p=0.03). Seven children had global developmental delay (GDD): mild (n=4), moderate (n=1) and severe (n=2). Vineland-3 identified 3 had low-average and 3 had mild-moderately impaired functioning. The majority (82%) were average. GDD was associated with older age at last seizure (p=0.03), longer epilepsy duration (p=0.02), and higher number of anti-seizure medications (p=0.05). Four children had speech delay, 5 (10%) had Autism Spectrum Disorder. Paroxysmal kinesiogenic dyskinesia (n=5) occurred in 4 families and hemiplegic migraine (n=8) in 3 families.

CONCLUSIONS

Individuals with SeLFE have a small risk of recurrent seizures (20%) and neurodevelopmental disability. Significant predictors are higher seizure number and longer epilepsy duration. Developmental surveillance is imperative.

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.

A case presentation of paroxysmal hypnogenic dyskinesia: clinical features and management

Paroxysmal Hypnogenic Dyskinesia (PHD) is a rare movement disorder characterized by involuntary movements, including chorea, athetosis, ballismus, and dystonia, which occur during the Non-Rapid Eye Movement (NREM) sleep stage. Therefore, the diagnosis of PHD is highly crucial due to the presence of differential diagnoses such as epilepsy and other sleep disorders. Although numerous mutations have been identified, the etiology of PHD, which arises from dysregulation in basal ganglia functions, remains unclear. We wanted to present a case of a nineteen-year-old girl diagnosed with PHD to draw attention to the diagnosis, etiology, and treatment of PHD.

Supplementary Information

The online version contains supplementary material available at 10.1007/s41105-023-00499-5.

KCNQ2-Related Epilepsy: Genotype-Phenotype Relationship with Tailored Antiseizure Medication (ASM)-A Systematic Review

BACKGROUND

Autosomal dominant mutations of the KCNQ2 gene can cause two epileptic disorders: benign familial neonatal seizures (BFNS) and developmental epileptic encephalopathy (DEE). This systematic review aims to identify the best reported therapy for these patients, relating to phenotype, neurodevelopmental outcome, and an eventual correlation between phenotype and genotype.

METHODS

We searched on PubMed using the search terms "KCNQ2" AND "therapy" and "KCNQ2" AND "treatment"; we found 304 articles. Of these, 29 met our criteria. We collected the data from 194 patients. All 29 articles were retrospective studies.

RESULTS

In all, 104 patients were classified as DEE and 90 as BFNS. After treatment began, 95% of BFNS patients became seizure free, whereas the seizures stopped only in 73% of those with DEE. Phenobarbital and sodium channel blockers were the most used treatment in BFNS. Most of the DEE patients (95%) needed polytherapy for seizure control and even that did not prevent subsequent developmental impairment (77%).Missense mutations were discovered in 96% of DEE patients; these were less common in BFNS (50%), followed by large deletion (16%), truncation (16%), splice donor site (10%), and frameshift (7%).

CONCLUSION

Phenobarbital or carbamazepine appears to be the most effective antiseizure medication for children with a "benign" variant. On the contrary, polytherapy is often needed for DEE patients, even if it does not seem to improve neurological outcomes. In DEE patients, most mutations were located in S4 and S6 helix, which could serve as a potential target for the development of more specific treatment in the future.

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.

Clinical and genetic analysis of benign familial infantile epilepsy caused by PRRT2 gene variant

Objective

This study presents the clinical phenotypes and genetic analysis of seven patients with benign familial infantile epilepsy (BFIE) diagnosed by whole-exome sequencing.

Methods

The clinical data of seven children with BFIE diagnosed at the Department of Neurology, Children's Hospital Affiliated to Zhengzhou University between December 2017 and April 2022 were retrospectively analyzed. Whole-exome sequencing was used to identify the genetic causes, and the variants were verified by Sanger sequencing in other family members.

Results

The seven patients with BFIE included two males and five females ranging in age between 3 and 7 months old. The main clinical phenotype of the seven affected children was the presence of focal or generalized tonic-clonic seizures, which was well controlled by anti-seizure medication. Cases 1 and 5 exhibited predominantly generalized tonic-clonic seizures accompanied by focal seizures while cases 2, 3, and 7 displayed generalized tonic-clonic seizures, and cases 4 and 6 had focal seizures. The grandmother and father of cases 2, 6, and 7 had histories of seizures. However, there was no family history of seizures in the remaining cases. Case 1 carried a de novo frameshift variant c.397delG (p.E133Nfs*43) in the proline-rich transmembrane protein 2 (PRRT2) gene while case 2 had a nonsense variant c.46G > T (p.Glu16*) inherited from the father, and cases 3-7 carried a heterozygous frameshift variant c.649dup (p.R217Pfs*8) in the same gene. In cases 3 and 4, the frameshift variant was de novo, while in cases 5-7, the variant was paternally inherited. The c.397delG (p.E133Nfs*43) variant is previously unreported.

Conclusion

This study demonstrated the effectiveness of whole-exome sequencing in the diagnosis of BFIE. Moreover, our findings revealed a novel pathogenic variant c.397delG (p.E133Nfs*43) in the PRRT2 gene that causes BFIE, expanding the mutation spectrum of PRRT2.

Functional analysis of a novel de novo SCN2A variant in a patient with seizures refractory to oxcarbazepine

Objective

We admitted a female patient with infantile onset epilepsy (<3-month-old). The use of oxcarbazepine exacerbated epileptic seizures in the patient. In the present study, we aimed to identify the genetic basis of the infantile onset epilepsy in the patient, and determine the correlations among genotype, phenotype, and clinical drug response.

Methods

We described the clinical characteristics of an infant with refractory epilepsy. Whole exome sequencing (WES) was used to screen for the pathogenic variant. Whole-cell patch-clamp was performed to determine functional outcomes of the variant.

Results

WES identified a novel de novo SCN2A variant (c.468 G > C, p.K156N) in the patient. In comparison with wildtype, electrophysiology revealed that SCN2A-K156N variant in transfected cells demonstrated reduced sodium current density, delayed activation and accelerated inactivation process of Na⁺ channel, all of which suggested a loss-of-function (LOF) of Na_v1.2 channel.

Conclusion

We showed the importance of functional analysis for a SCN2A variant with unknown significance to determine pathogenicity, drug reactions, and genotype-phenotype correlations. For patients suffering from early infantile epilepsies, the use of oxcarbazepine in some SCN2A-related epilepsies requires vigilance to assess the possibility of epilepsy worsening.

An accurate prediction model of digenic interaction for estimating pathogenic gene pairs of human diseases

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Numerous pathogenic interactions are yet to be revealed efficiently due to dimension burden.

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Existing methods are underpowered and inaccurate to estimate pathogenic interactions.

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We developed an accurate bioinformatic method to predict digenic interaction effects based on gene-level features.

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The new method created a valuable resource of genome-wide pathogenic digenic interactions.

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We found that known causal genes in Mendelian and Oligogenic diseases may be enriched with interactive effects for the first time.

Increasing evidence shows that genetic interaction across the entire genome may explain a non-trivial fraction of genetic diseases. Digenic interaction is the simplest manifestation of genetic interaction among genes. However, systematic exploration of digenic interactive effects on the whole genome is often discouraged by the high dimension burden. Thus, numerous digenic interactions are yet to be identified for many diseases. Here, we propose a Digenic Interaction Effect Predictor (DIEP), an accurate machine-learning approach to identify the genome-wide pathogenic coding gene pairs with digenic interaction effects. This approach achieved high accuracy and sensitivity in independent testing datasets, outperforming another gene-level digenic predictor (DiGePred). DIEP was also able to discriminate digenic interaction effect from bi-locus effects dual molecular diagnosis (pseudo-digenic). Using DIEP, we provided a valuable resource of genome-wide digenic interactions and demonstrated the enrichment of the digenic interaction effect in Mendelian and Oligogenic diseases. Therefore, DIEP will play a useful role in facilitating the genomic mapping of interactive causal genes for human diseases.

First reported case of an inherited PACS2 pathogenic variant with variable expression

Neonatal epilepsy, cerebellar dysgenesis and facial dysmorphisms may be associated with de novo PACS2 missense pathogenic variants (EIEE 66) (OMIM #618067). Here, we report a toddler boy with neonatal-onset seizures, developmental delay with hypotonia, facial dysmorphisms and prominence of the cisterna magna, mild inferior vermian and cerebellar hypoplasia. A nextgeneration epilepsy gene panel revealed a known pathogenic PACS2 missense variant, p.Glu209Lys, that was inherited from his mildly affected mother. We describe the first PACS2 pathogenic variant to be inherited, expanding the clinical spectrum, associated with a mild phenotype in the mother and a more severe phenotype in her son, in keeping with previously reported descriptions.

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.

KCNQ2-Related Neonatal Epilepsy Treated With Vitamin B6: A Report of Two Cases and Literature Review

Potassium Voltage-Gated Channel Subfamily Q Member 2 (KCNQ2) gene has been initially associated with "Benign familial neonatal epilepsy" (BFNE). Amounting evidence arising by next-generation sequencing techniques have led to the definition of new phenotypes, such as neonatal epileptic encephalopathy (NEE), expanding the spectrum of KCNQ2-related epilepsies. Pyridoxine (PN) dependent epilepsies (PDE) are a heterogeneous group of autosomal recessive disorders associated with neonatal-onset seizures responsive to treatment with vitamin B6 (VitB6). Few cases of neonatal seizures due to KCNQ2 pathogenic variants have been reported as successfully responding to VitB6. We reported two cases of KCNQ2-related neonatal epilepsies involving a 5-year-old male with a paternally inherited heterozygous mutation (c.1639C>T; p.Arg547Trp), and a 10-year-old female with a de novo heterozygous mutation (c.740C>T; p.Ser247Leu). Both children benefited from VitB6 treatment. Although the mechanisms explaining the efficacy of VitB6 in such patients remain unclear, this treatment option in neonatal-onset seizures is easily taken into account in Neonatal Intensive Care Units (NICUs). Further studies should be conducted to better define clinical guidelines and treatment protocols.

Genetic Epilepsy Syndromes

PURPOSE OF REVIEW

This article reviews the clinical features, typical EEG findings, treatment, prognosis, and underlying molecular etiologies of the more common genetic epilepsy syndromes. Genetic generalized epilepsy, self-limited focal epilepsy of childhood, self-limited neonatal and infantile epilepsy, select developmental and epileptic encephalopathies, progressive myoclonus epilepsies, sleep-related hypermotor epilepsy, photosensitive occipital lobe epilepsy, and focal epilepsy with auditory features are discussed. Also reviewed are two familial epilepsy syndromes: genetic epilepsy with febrile seizures plus and familial focal epilepsy with variable foci.

RECENT FINDINGS

Recent years have seen considerable advances in our understanding of the genetic factors underlying genetic epilepsy syndromes. New therapies are emerging for some of these conditions; in some cases, these precision medicine approaches may dramatically improve the prognosis.

SUMMARY

Many recognizable genetic epilepsy syndromes exist, the identification of which is a crucial skill for neurologists, particularly those who work with children. Proper diagnosis of the electroclinical syndrome allows for appropriate treatment choices and counseling regarding prognosis and possible comorbidities.

PRRT2 mutation in a Japanese woman: Adult-onset focal epilepsy coexisting with movement disorders and cerebellar atrophy

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Mutation of the PRRT2 gene in a Japanese woman resulted in the c.604_607del variant.

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Her clinical features presented with focal epilepsy, cerebellar atrophy, paroxysmal kinesigenic dyskinesia, and paroxysmal non-kinesigenic dystonia (PNKD).

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Video-EEG monitoring revealed that her epilepsy arose from the left temporal region.

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Low dose lamotrigine was effective for her epilepsy and PNKD.

Proline-rich transmembrane protein 2 (PRRT2) was confirmed as the causative gene of paroxysmal kinesigenic dyskinesia (PKD) as shown by genome-wide linkage analyses. PRRT2 mutations are also associated with benign familial infantile seizures, infantile convulsions and choreoathetosis, and childhood absence epilepsy, but few reports have investigated adult-onset epilepsy. We describe here a rare presentation of adult-onset focal epilepsy with a PRRT2 mutation in a 31-year-old woman who showed cerebellar atrophy, familial paroxysmal kinesigenic dyskinesia, and paroxysmal non-kinesigenic dystonia. Video-electroencephalography (EEG) demonstrated focal impaired awareness seizures, in which ictal EEG changes showed left temporal onset with rhythmic theta activity over the left temporal region. Magnetic resonance imaging showed mild cerebellar atrophy. The administration of lamotrigine 50 mg/day resulted in freedom from her seizures and lamotrigine 150 mg/day reduced paroxysmal non-kinesigenic dystonia. Furthermore, she had a rare frameshift mutation, c.604_607del, p.Ser202fs of which the pathogenicity has been reported in ClinVar, but it has not been reported in Japan. Mutation of the PRRT2 gene can cause adult-onset epilepsy, paroxysmal non-kinesigenic movement disorder, and cerebellar atrophy, suggesting an expanding clinical phenotypic spectrum associated with PRRT2 mutations.

Genetic-cellular epilepsy: Clues to diagnosing newborns with neonatal seizures

OBJECTIVE

The aim of this study was to analyse clinical characteristics of newborns with genetic-cellular epilepsy (GCE) to compare them to those of newborns with seizures with other aetiologies and elucidate clues to the diagnosis of GCE.

METHODS

This retrospective single-centre study analysed data from an 8-year cohort of newborns with seizures from 2010-2017. Clinical, neurophysiological, laboratory, and imaging data and outcomes of children with GCE were compared to those of newborns with seizures with other aetiologies.

RESULTS

A total of 112 newborns (N = 68; 61% boys) were included. Hypoxic-ischaemic encephalopathy (N = 42; 29%) was the most common seizure aetiology; GCE (with pathogenic variants KCNQ2, KCNQ3, SCN2A, TBC1D24, CHD2, and STXBP) was diagnosed in 9 (6%). The group of newborns with GCE significantly differed from the group with seizures with other aetiologies in terms of family history of epilepsy (p = 0.000), neonatal epileptic status (NES) (p = 0.007), normal imaging studies (p = 0.000), and outcomes (p = 0.034), but did not differ regarding the type and age of seizure onset, number of antiepileptic drugs administered, and EEG results. Positive family history of epilepsy (p = 0.027), presence of NES (p = 0.041), and normal imaging studies (p = 0.002) were most indicative of the diagnosis of GCE. Probability of GCE with this combination was 0.92.

CONCLUSION

In a heterogenous group of newborns with seizures, a positive family history of epilepsy, presence of NES, and normal imaging studies were most indicative of the diagnosis of GCE.

PRRT2 Related Epilepsies: A Gene Review

PRRT2 encodes for proline-rich transmembrane protein 2 involved in synaptic vesicle fusion and presynaptic neurotransmitter release. Mutations in human PRRT2 have been related to paroxysmal kinesigenic dyskinesia (PKD), infantile convulsions with choreoathetosis, benign familial infantile epilepsies, and hemiplegic migraine. PRRT2 mutations cause neuronal hyperexcitability, which could be related to basal ganglia or cortical circuits dysfunction, leading to paroxysmal disorders. PRRT2 is expressed in the cerebral cortex, basal ganglia, and cerebellum. Approximately, 90% of pathogenic variants are inherited and 10% are de novo. Paroxysmal attacks in PKD are characterized by dystonia, choreoathetosis, and ballismus. In the benign familial infantile epilepsy (BFIE), seizures are usually focal with or without generalization, usually begin between 3 and 12 months of age and remit by 2 years of age. In 30% of cases of PRRT2-associated PKD, there is an association with BFIE, and this entity is referred to as PKD with infantile convulsions (PKD/IC). PRRT2 mutations are the cause of benign family childhood epilepsy and PKD/IC. On the other hand, PRRT2 mutations do not seem to correlate with other types of epilepsy. The increasing incidence of hemiplegic migraine in families with PRRT2-associated PKD or PKD/IC suggests a common disease pathway, and it is possible to assert that BFIE, paroxysmal kinesigenic dyskinesia, and PKD with IC belong to a continuous disease spectrum of PRRT2-associated diseases.

SCN2A and Its Related Epileptic Phenotypes

Epilepsies due to SCN2A mutations can present with a broad range of phenotypes that are still not fully understood. Clinical characteristics of SNC2A-related epilepsy may vary from neonatal benign epilepsy to early-onset epileptic encephalopathy, including Ohtahara syndrome and West syndrome, and epileptic encephalopathies occurring at later ages (usually within the first 10 years of life). Some patient may present with intellectual disability and/or autism or movement disorders and without epilepsy. The heterogeneity of the phenotypes associated to such genetic mutations does not always allow the clinician to address his suspect on this gene. For this reason, diagnosis is usually made after a multiple gene panel examination through next generation sequencing (NGS) or after whole exome sequencing (WES) or whole genome sequencing (WGS). Subsequently, confirmation by Sanger sequencing can be obtained. Mutations in SCN2A are inherited as an autosomal dominant trait. Most individuals diagnosed with SCN2A–benign familial neonatal-infantile seizures (BFNIS) have an affected parent; however, hypothetically, a child may present SCN2A-BNFNIS as the result of a de novo pathogenic variant. Almost all individuals with SCN2A and severe epileptic encephalopathies have a de novo pathogenic variant. SNC2A-related epilepsies have not shown a clear genotype–phenotype correlation; in some cases, a same variant may lead to different presentations even within the same family and this could be due to other genetic factors or to environmental causes. There is no “standardized” treatment for SCN2A-related epilepsy, as it varies in relation to the clinical presentation and the phenotype of the patient, according to its own gene mutation. Treatment is based mainly on antiepileptic drugs, which include classic wide-spectrum drugs, such as valproic acid, levetiracetam, and lamotrigine. However, specific agents, which act directly modulating the sodium channels activity (phenytoin, carbamazepine, oxcarbamazepine, lamotrigine, and zonisamide), have shown positive result, as other sodium channel blockers (lidocaine and mexiletine) or even other drugs with different targets (phenobarbital).

Sodium channelopathies of skeletal muscle and brain

Voltage-gated sodium channels initiate action potentials in nerve, skeletal muscle, and other electrically excitable cells. Mutations in them cause a wide range of diseases. These channelopathy mutations affect every aspect of sodium channel function, including voltage sensing, voltage-dependent activation, ion conductance, fast and slow inactivation, and both biosynthesis and assembly. Mutations that cause different forms of periodic paralysis in skeletal muscle were discovered first and have provided a template for understanding structure, function, and pathophysiology at the molecular level. More recent work has revealed multiple sodium channelopathies in the brain. Here we review the well-characterized genetics and pathophysiology of the periodic paralyses of skeletal muscle and then use this information as a foundation for advancing our understanding of mutations in the structurally homologous α-subunits of brain sodium channels that cause epilepsy, migraine, autism, and related comorbidities. We include studies based on molecular and structural biology, cell biology and physiology, pharmacology, and mouse genetics. Our review reveals unexpected connections among these different types of sodium channelopathies.

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.

The ILAE classification of seizures and the epilepsies: Modification for seizures in the neonate. Position paper by the ILAE Task Force on Neonatal Seizures

Seizures are the most common neurological emergency in the neonatal period and in contrast to those in infancy and childhood, are often provoked seizures with an acute cause and may be electrographic-only. Hence, neonatal seizures may not fit easily into classification schemes for seizures and epilepsies primarily developed for older children and adults. A Neonatal Seizures Task Force was established by the International League Against Epilepsy (ILAE) to develop a modification of the 2017 ILAE Classification of Seizures and Epilepsies, relevant to neonates. The neonatal classification framework emphasizes the role of electroencephalography (EEG) in the diagnosis of seizures in the neonate and includes a classification of seizure types relevant to this age group. The seizure type is determined by the predominant clinical feature. Many neonatal seizures are electrographic-only with no evident clinical features; therefore, these are included in the proposed classification. Clinical events without an EEG correlate are not included. Because seizures in the neonatal period have been shown to have a focal onset, a division into focal and generalized is unnecessary. Seizures can have a motor (automatisms, clonic, epileptic spasms, myoclonic, tonic), non-motor (autonomic, behavior arrest), or sequential presentation. The classification allows the user to choose the level of detail when classifying seizures in this age group.

A Novel Kv7.3 Variant in the Voltage-Sensing S4 Segment in a Family With Benign Neonatal Epilepsy: Functional Characterization and in vitro Rescue by β-Hydroxybutyrate

Pathogenic variants in KCNQ2 and KCNQ3, paralogous genes encoding Kv7.2 and Kv7.3 voltage-gated K⁺ channel subunits, are responsible for early-onset developmental/epileptic disorders characterized by heterogeneous clinical phenotypes ranging from benign familial neonatal epilepsy (BFNE) to early-onset developmental and epileptic encephalopathy (DEE). KCNQ2 variants account for the majority of pedigrees with BFNE and KCNQ3 variants are responsible for a much smaller subgroup, but the reasons for this imbalance remain unclear. Analysis of additional pedigrees is needed to further clarify the nature of this genetic heterogeneity and to improve prediction of pathogenicity for novel variants. We identified a BFNE family with two siblings and a parent affected. Exome sequencing on samples from both parents and siblings revealed a novel KCNQ3 variant (c.719T>G; p.M240R), segregating in the three affected individuals. The M240 residue is conserved among human Kv7.2-5 and lies between the two arginines (R5 and R6) closest to the intracellular side of the voltage-sensing S₄ transmembrane segment. Whole cell patch-clamp recordings in Chinese hamster ovary (CHO) cells revealed that homomeric Kv7.3 M240R channels were not functional, whereas heteromeric channels incorporating Kv7.3 M240R mutant subunits with Kv7.2 and Kv7.3 displayed a depolarizing shift of about 10 mV in activation gating. Molecular modeling results suggested that the M240R substitution preferentially stabilized the resting state and possibly destabilized the activated state of the Kv7.3 subunits, a result consistent with functional data. Exposure to β-hydroxybutyrate (BHB), a ketone body generated during the ketogenic diet (KD), reversed channel dysfunction induced by the M240R variant. In conclusion, we describe the first missense loss-of-function (LoF) pathogenic variant within the S₄ segment of Kv7.3 identified in patients with BFNE. Studied under conditions mimicking heterozygosity, the M240R variant mainly affects the voltage sensitivity, in contrast to previously analyzed BFNE Kv7.3 variants that reduce current density. Our pharmacological results provide a rationale for the use of KD in patients carrying LoF variants in Kv7.2 or Kv7.3 subunits.

Clinical spectrum and genotype-phenotype correlations in PRRT2 Italian patients

Prrt2 is a neuron-specific protein expressed at axonal and pre-synaptic domains, involved in synaptic neurotransmitter release and modulation of intrinsic excitability. Mutations in PRRT2 cause a spectrum of autosomal dominant paroxysmal neurological disorders including epilepsy, movement disorders, and hemiplegic migraine and show incomplete penetrance and variable expressivity. We assessed the diagnostic rate of PRRT2 in a cohort of Italian patients with epilepsy and/or paroxysmal kinesigenic dyskinesia (PKD) and evaluated genotype-phenotype correlations. Clinical data were collected using a structured questionnaire. Twenty-seven out of 55 (49.1%) probands carried PRRT2 heterozygous pathogenic variants, including six previously known genotypes and one novel missense mutation. A family history of epilepsy starting in the first year of life and/or PKD was strongly suggestive of a PRRT2 pathogenic variant. Epilepsy patients harbouring PRRT2 pathogenic variants showed earlier seizure onset and more frequent clusters compared with PRRT2-negative individuals with epilepsy. Moreover, we did also identify individuals with PRRT2 pathogenic variants with atypical age at onset, i.e. childhood-onset epilepsy and infantile-onset PKD. However, the lack of a clear correlation between specific PRRT2 genotypes and clinical manifestations and the high incidence of asymptomatic carriers suggest the involvement of additional factors in modulating expressivity of PRRT2-related disorders. Finally, our study supports the pleiotropic and multifaceted physiological role of PRRT2 gene which is emerging from experimental neuroscience.

Epilepsy-Related Voltage-Gated Sodium Channelopathies: A Review

Epilepsy is a disease characterized by abnormal brain activity and a predisposition to generate epileptic seizures, leading to neurobiological, cognitive, psychological, social, and economic impacts for the patient. There are several known causes for epilepsy; one of them is the malfunction of ion channels, resulting from mutations. Voltage-gated sodium channels (NaV) play an essential role in the generation and propagation of action potential, and malfunction caused by mutations can induce irregular neuronal activity. That said, several genetic variations in NaV channels have been described and associated with epilepsy. These mutations can affect channel kinetics, modifying channel activation, inactivation, recovery from inactivation, and/or the current window. Among the NaV subtypes related to epilepsy, NaV1.1 is doubtless the most relevant, with more than 1500 mutations described. Truncation and missense mutations are the most observed alterations. In addition, several studies have already related mutated NaV channels with the electrophysiological functioning of the channel, aiming to correlate with the epilepsy phenotype. The present review provides an overview of studies on epilepsy-associated mutated human NaV1.1, NaV1.2, NaV1.3, NaV1.6, and NaV1.7.

Heteromeric Kv7.2 current changes caused by loss-of-function of KCNQ2 mutations are correlated with long-term neurodevelopmental outcomes

Pediatric epilepsy caused by KCNQ2 mutations can manifest benign familial neonatal convulsions (BFNC) to neonatal-onset epileptic encephalopathy (EE). Patients might manifest mild to profound neurodevelopmental disabilities. We analysed c.853C > A (P285T) and three mutations that cause KCNQ2 protein changes in the 247 position: c.740C > T (S247L), c.740C > A (S247X), and c.740C > G (S247W). S247L, S247W, and P285T cause neonatal-onset EE and poor neurodevelopmental outcomes; S247X cause BFNC and normal outcome. We investigated the phenotypes correlated with human embryonic kidney 293 (HEK293) cell functional current changes. More cell-current changes and a worse conductance curve were present in the homomeric transfected S247X than in S247L, S247W, and P285T. But in the heteromeric channel, S247L, S247W and P285T had more current impairments than did S247X. The protein expressions of S247X were nonfunctional. The outcomes were most severe in S247L and S247W, and severity was correlated with heteromeric current. Current changes were more significant in cells with homomeric S247X, but currents were “rescued” after heteromeric transfection of KCNQ2 and KCNQ3. This was not the case in cells with S247L, S247W. Our findings support that homomeric current changes are common in KCNQ2 neonatal-onset EE and KCNQ2 BFNC; however, heteromeric functional current changes are correlated with long-term neurodevelopmental outcomes.

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.

Phenotypic spectrum and genetics of SCN2A-related disorders, treatment options, and outcomes in epilepsy and beyond

Pathogenic variants in the SCN2A gene are associated with a variety of neurodevelopmental phenotypes, defined in recent years through multicenter collaboration. Phenotypes include benign (self-limited) neonatal and infantile epilepsy and more severe developmental and epileptic encephalopathies also presenting in early infancy. There is increasing evidence that an important phenotype linked to the gene is autism and intellectual disability without epilepsy or with rare seizures in later childhood. Other associations of SCN2A include the movement disorders chorea and episodic ataxia. It is likely that as genetic testing enters mainstream practice that new phenotypic associations will be identified. Some missense, gain of function variants tend to present in early infancy with epilepsy, whereas other missense or truncating, loss of function variants present with later-onset epilepsies or intellectual disability only. Knowledge of both mutation type and functional consequences can guide precision therapy. Sodium channel blockers may be effective antiepileptic medications in gain of function, neonatal and infantile presentations.

Advances in genetic testing and optimization of clinical management in children and adults with epilepsy

Introduction: Epileptic disorders are a heterogeneous group of medical conditions with epilepsy as the common denominator. Genetic causes, electro-clinical features, and management significantly vary according to the specific condition.Areas covered: Relevant diagnostic advances have been achieved thanks to the advent of Next Generation Sequencing (NGS)-based molecular techniques. These revolutionary tools allow to sequence all coding (whole exome sequencing, WES) and non-coding (whole genome sequencing, WGS) regions of human genome, with a potentially huge impact on patient care and scientific research.Expert opinion: The application of these tests in children and adults with epilepsy has led to the identification of new causative genes, widening the knowledge on the pathophysiology of epilepsy and resulting in therapeutic implications. This review will explore the most recent advancements in genetic testing and provide up-to-date approaches for the choice of the correct test in patients with epilepsy.

Genetic potassium channel-associated epilepsies: Clinical review of the Kv family

Next-generation sequencing has enhanced discovery of many disease-associated genes in previously unexplained epilepsies, mainly in developmental and epileptic encephalopathies and familial epilepsies. We now classify these disorders according to the underlying molecular pathways, which encompass a diverse array of cellular and sub-cellular compartments/signalling processes including voltage-gated ion-channel defects. With the aim to develop and increase the use of precision medicine therapies, understanding the pathogenic mechanisms and consequences of disease-causing variants has gained major relevance in clinical care. The super-family of voltage-gated potassium channels is the largest and most diverse family among the ion channels, encompassing approximately 80 genes. Key potassium channelopathies include those affecting the K_V, K_Ca and K_ir families, a significant proportion of which have been implicated in neurological disease. As for other ion channel disorders, different pathogenic variants within any individual voltage-gated potassium channel gene tend to affect channel protein function differently, causing heterogeneous clinical phenotypes. The focus of this review is to summarise recent clinical developments regarding the key voltage-gated potassium (K_V) family-related epilepsies, which now encompasses approximately 12 established disease-associated genes, from the KCNA-, KCNB-, KCNC-, KCND-, KCNV-, KCNQ- and KCNH-subfamilies.

The clinical and genetic spectrum in infants with (an) unprovoked cluster(s) of focal seizures

BACKGROUND

Self-limited (familial) infantile epilepsy (S(F)IE), formerly known as benign (familial) infantile convulsions (B(F)IC), is an infantile cluster epilepsy with in rule a complete recovery. This form of epilepsy is most often caused by variations in the PRRT2 gene (OMIM #605751).

AIM

To describe the clinical and genetic spectrum of sudden onset clusters of focal seizures in infancy.

METHODS

We retrospectively reviewed all individuals, who presented with unprovoked infantile seizures and selected all infants who had unprovoked clustered focal seizures between 1 and 20 months of age. We described the clinical and genetic spectrum of this cohort.

RESULTS

The data of 23 patients from 21 families were collected. All had an initial diagnosis of S(F)IE which was adjusted in 5 individuals. In 12 individuals a pathogenic variation in PRRT2 gene or complete deletion was identified. Pathogenic variants in PCDH19 and KCNQ2 were found in respectively 3 and 1 individuals. One individual had a non-pathogenic variant in ATP1A3 and in 6 others no variants were identified. The mean cluster duration was 2.9 days (range 1-13) (see Table 1). Twelve infants had only one cluster. All patients had focal motor or non-motor seizures, in 12 (52%) followed by bilateral (tonic)clonic seizures. Positive family history was present in 74% of individuals. In 11/12 (92%) tested families, ≥1 family member carried the pathogenic PRRT2 variant. Age of seizure onset (ASO) averaged 6.2 months (range 2-20 months). Age of latest seizure averaged 16 months (range 2-92). In several interictal EEG (electroencephalogram) recordings multifocal spikes or spike-wave abnormalities were detected. Ictal EEG recordings detected primary focal abnormalities.

CONCLUSION

We described 23 individuals with unprovoked cluster(s) of focal seizures at infancy. It appears to be a heterogeneous group. Half of them had a pathogenic variation in PRRT2 gene. Most had only one cluster of seizures. When clusters reoccur frequently, when seizures are more therapy-resistant and when seizures persist beyond the age of 2 years, another diagnosis or causative gene is likely.

Kv2.1 voltage-gated potassium channels in developmental perspective

Kv2.1 voltage-gated potassium channels consist of two types of α-subunits: (a) electrically-active Kcnb1 α-subunits and (b) silent or modulatory α-subunits plus β-subunits that, similar to silent α-subunits, also regulate electrically-active subunits. Voltage-gated potassium channels were traditionally viewed, mainly by electrophysiologists, as regulators of the electrical activity of the plasma membrane in excitable cells, a role that is performed by transmembrane protein domains of α-subunits that form the electric pore. Genetic studies revealed a role for this region of α-subunits of voltage-gated potassium channels in human neurodevelopmental disorders, such as epileptic encephalopathy. The N- and C-terminal domains of α-subunits interact to form the cytoplasmic subunit of heterotetrameric potassium channels that regulate electric pores. Subsequent animal studies revealed the developmental functions of Kcnb1-containing voltage-gated potassium channels and illustrated their role during brain development and reproduction. These functions of potassium channels are discussed in this review in the context of regulatory interactions between electrically-active and regulatory subunits.

A novel homozygous KCNQ3 loss-of-function variant causes non-syndromic intellectual disability and neonatal-onset pharmacodependent epilepsy

OBJECTIVE

Heterozygous variants in KCNQ2 or, more rarely, KCNQ3 genes are responsible for early-onset developmental/epileptic disorders characterized by heterogeneous clinical presentation and course, genetic transmission, and prognosis. While familial forms mostly include benign epilepsies with seizures starting in the neonatal or early-infantile period, de novo variants in KCNQ2 or KCNQ3 have been described in sporadic cases of early-onset encephalopathy (EOEE) with pharmacoresistant seizures, various age-related pathological EEG patterns, and moderate/severe developmental impairment. All pathogenic variants in KCNQ2 or KCNQ3 occur in heterozygosity. The aim of this work was to report the clinical, molecular, and functional properties of a new KCNQ3 variant found in homozygous configuration in a 9-year-old girl with pharmacodependent neonatal-onset epilepsy and non-syndromic intellectual disability.

METHODS

Exome sequencing was used for genetic investigation. KCNQ3 transcript and subunit expression in fibroblasts was analyzed with quantitative real-time PCR and Western blotting or immunofluorescence, respectively. Whole-cell patch-clamp electrophysiology was used for functional characterization of mutant subunits.

RESULTS

A novel single-base duplication in exon 12 of KCNQ3 (NM_004519.3:c.1599dup) was found in homozygous configuration in the proband born to consanguineous healthy parents; this frameshift variant introduced a premature termination codon (PTC), thus deleting a large part of the C-terminal region. Mutant KCNQ3 transcript and protein abundance was markedly reduced in primary fibroblasts from the proband, consistent with nonsense-mediated mRNA decay. The variant fully abolished the ability of KCNQ3 subunits to assemble into functional homomeric or heteromeric channels with KCNQ2 subunits.

SIGNIFICANCE

The present results indicate that a homozygous KCNQ3 loss-of-function variant is responsible for a severe phenotype characterized by neonatal-onset pharmacodependent seizures, with developmental delay and intellectual disability. They also reveal difference in genetic and pathogenetic mechanisms between KCNQ2- and KCNQ3-related epilepsies, a crucial observation for patients affected with EOEE and/or developmental disabilities.

Gene mutations in paediatric epilepsies cause NMDA-pathy, and phasic and tonic GABA-pathy

The aim of this study was to disentangle mechanisms of epileptogenesis in monogenic epilepsies in children. We reviewed paediatric monogenic epilepsies excluding brain malformation or an inborn error of metabolism, but including the gene function whether there is loss-of-function or gain-of-function, age at gene expression when available, and associated epilepsy syndrome. Genes for which at least five patients with similar epilepsy phenotype had been reported were selected. Three mechanisms are shared by most monogenic epilepsies: (1) excess of N-methyl-d-aspartate (NMDA) transmission activation (NMDA-pathies); (2) abnormal gamma-aminobutyric acid (GABA) transmission with reduced inhibition (phasic GABA-pathies); and (3) tonic activation of extrasynaptic GABA_A receptors by extracellular GABA (tonic GABA-pathies). NMDA-pathies comprise early epileptic encephalopathy with suppression-burst, neonatal/infantile benign seizures, West and Lennox-Gastaut syndromes, and encephalopathy with continuous spike waves in slow sleep, thus brief seizures with major interictal spiking. Phasic GABA-pathies comprise mostly generalized epilepsy with febrile seizures plus and Dravet syndrome, thus long-lasting seizures with mild interictal spiking. Tonic GABA-pathies cause epilepsy with myoclonic-atonic seizures and Angelman syndrome, thus major high-amplitude slow-wave activity. This pathophysiological approach to monogenic epilepsies provides diagnostic clues and helps to guide treatment strategy. WHAT THIS PAPER ADDS: In paediatric monogenic epilepsies, electroclinical patterns point to three main mechanisms: NMDA-pathies, and phasic and tonic GABA-pathies. Antiepileptic treatment choice could be guided by each of these mechanisms.

PLPP/CIN-mediated NEDD4-2 S448 dephosphorylation regulates neuronal excitability via GluA1 ubiquitination

Neuronal precursor cell expressed developmentally downregulated 4-2 (NEDD4-2) is an E3 ubiquitin ligase to regulate ion transport by controlling cellular trafficking/endocytosis and lysosomal degradation of ion channels and transporters. Thus, NEDD4-2 is relevant to neuronal excitability and epileptic encephalopathies in human patients. However, the regulatory molecules for NEDD4-2 dephosphorylation have been still elusive. Here, we demonstrate that pyridoxal-5′-phosphate phosphatase/chronophin (PLPP/CIN) specifically dephosphorylated NEDD4-2 serine (S) 448 site. PLPP/CIN deletion inhibited NEDD4-2 ubiquitination, and diminished the responsiveness of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor (AMPAR) by facilitating NEDD4-2-mediated ubiquitination of GluA1 subunit under physiological condition. PLPP/CIN overexpression reversed these effects. These PLPP/CIN-mediated processes were required for the increased seizure severity and its progression in response to kainic acid (KA). Therefore, we suggest the novel function of PLPP/CIN as a NEDD4-2 phosphatase, which may be a potential therapeutic target for NEDD4-2-associated diseases as well as various neurological and psychiatric disorders, including epilepsy.

Biallelic SCN2A Gene Mutation Causing Early Infantile Epileptic Encephalopathy: Case Report and Review

The voltage-gated sodium channel neuronal type 2 alpha subunit (Na_vα1.2) encoded by the SCN2A gene causes early infantile epileptic encephalopathy (EIEE) inherited in an autosomal dominant manner. Clinically, it has variable presentations, ranging from benign familial infantile seizures (BFIS) to severe EIEE. Diagnosis is achieved through molecular DNA testing of the SCN2A gene. Herein, we report on a 30-month-old Saudi girl who presented on the fourth day of life with EIEE, normal brain magnetic resonance imaging (MRI), normal electroencephalography (EEG), and well-controlled seizures. Genetic investigation revealed a novel homozygous missense mutation (c.5242A > G; p.Asn1748Asp) in the SCN2A gene (NM_001040142.1). This is the first reported autosomal recessive inheritance of a disease allele in the SCN2A and therefore expands the molecular and inheritance spectrum of the SCN2A gene defects.

A de novo KCNQ2 Gene Mutation Associated With Non-familial Early Onset Seizures: Case Report and Revision of Literature Data

Among neonatal epileptic syndromes, benign familial neonatal seizures (BFNS) are often due to autosomal-dominant mutations of the KCNQ2 gene. Seizures are usually characterized by asymmetric tonic posturing with apnea with onset in the first 7 days of life; they may even occur more than 10 times per day or evolve into status epilepticus. The delivery course of our patient was uneventful and family history was negative; on the second day of life the baby became pale, rigid, and apnoic during breastfeeding and appeared jittery and irritable when stimulated or examined. At age 3 days, she experienced clusters of generalized tonic seizures with pallor, desaturation, bradycardia, and partial response to intravenous phenobarbital; during her 4th and 5th days of life, three episodes of tonic seizures were noticed. At age 6 days, the patient experienced about 10 episodes of tonic seizures involving both sides of the body, which gradually responded to intravenous phenytoin. Electroencephalograms revealed abnormalities but brain MRI was normal. The patient is seizure-free since postnatal day 21; she is now 12 months old with cognitive development within normal limits at Bayley III Scale and mild motor delay. The patient is on maintenance therapy with phenobarbital since she was 7 months old. A de novo heterozygous mutation (c.853C>T/p.P285S) in the KCNQ2 gene was identified. We therefore describe a case of de novo KCNQ2-related neonatal convulsions with necessity of multiple anticonvulsants for the control of seizures, mutation occurring in the pore channel of the voltage-gated potassium channel subfamily Q member 2 associated with a likely benign course; furthermore, the same mutation of the KCNQ2 gene and a similar one (c.854C>A/p.P285H) have already been described in association with Ohtahara syndrome. Probably acquired environmental, perinatal and genetic risk factors are very important in determining the different phenotype; we hope that the rapid progress of analysis tools in molecular diagnosis can also be used in the search of an individualized therapeutic approach for these patients.

Homomeric Kv7.2 current suppression is a common feature in KCNQ2 epileptic encephalopathy

OBJECTIVE

To gain insight into the mechanisms underlying KCNQ2 encephalopathy by examining the electrophysiologic properties of mutant Kv7.2 channels in different multimeric configurations.

METHODS

We analyzed the genotype-phenotype relationship in 4 patients with KCNQ2 encephalopathy and performed electrophysiologic analysis of M-currents mediated by homomeric Kv7.2 or heteromeric Kv7.2/Kv7.3 channels.

RESULTS

Negligible or no current was recorded in cells expressing homomeric E130K, W270R, or G281R de novo mutants, and it was reduced by more than 90% for the L243F maternally inherited mutant. The E130K and G281R mutants presented a marked dominant-negative behavior, whereas the current density was partially reduced (L243F) or not affected (W270R) when coexpressed with wild-type Kv7.2 subunits. In contrast, the extent of Kv7.3 "rescue," which yields negligible currents on its own, followed the sequence E130K > L243F > W270R, whereas no rescue was observed with the G281R mutant. No significant effects on current density were observed when subunits were expressed in a 0.5:0.5:1.0 (Kv7.2:mutant:Kv7.3) DNA ratio to mimic the genetic balance. There was an increase in sensitivity to phosphatidylinositol 4,5-bisphosphate (PIP₂ ) depletion for W270R/Kv7.3, but no substantial differences were observed when the mutated subunits were coexpressed with Kv7.2 or both Kv7.2 and Kv7.3.

SIGNIFICANCE

There was a marked disparity of the impact of these mutations on Kv7.2 function, which varied on association with Kv7.2 or Kv7.3 subunits. Current density of homomeric channels was the most reliable property relating Kv7.2 function to encephalopathy, but other factors are required to explain the milder phenotype for some individuals carrying the maternally inherited L243F mutation. We hypothesize that the role of homomeric Kv7.2 channels for fine-tuning neuronal connections during development is critical for the severity of the KCNQ2 encephalopathy.

Clinical outcome of recurrent afebrile seizures in children with benign convulsions associated with mild gastroenteritis

PURPOSE

To assess the clinical outcome and evolution of recurrent afebrile seizures in children initially diagnosed with benign convulsions associated with mild gastroenteritis (CwG).

METHODS

We reviewed and analyzed the medical records of 37 patients who were diagnosed as CwG at onset, followed by recurrent afebrile seizures and followed up for at least 24 months.

RESULTS

The follow-up period ranged from 2 to 7 years (median, 40.1 months).Three patterns of recurrent afebrile seizures were recorded: afebrile seizures associated with gastrointestinal infection (AS-GI, n = 25), afebrile seizures associated with non-gastrointestinal infection (AS-nGI, n = 9), and unprovoked seizures (US, n = 3). Twenty eight patients (75.7%) had a second episode within 6 months after the first seizures. Five cases (13.5%) suffered three episodes of afebrile seizures. Seizure characteristics of the three patterns were similar, manifesting as clustered seizures in the majority. Focal epileptic activities in interictal EEG were found in 3 cases (9.4%) at onset, 10 cases (28.6%) at the second episode, respectively. Six patients were prescribed anti-epileptic drugs with apparently good responses. During at least 2 years' follow-up, all the cases showed normal psychomotor development. Only one patient was diagnosed with epilepsy.

CONCLUSIONS

All the recurrent afebrile seizures initially diagnosed as CwG, irrespective of the kinds and frequency of relapses, showed favorable prognoses. CwG maybe falls within the category of situation-related seizures, rather than epilepsy.

Benign and severe early-life seizures: a round in the first year of life

BACKGROUND

At the onset, differentiation between abnormal non-epileptic movements, and epileptic seizures presenting in early life is difficult as is clinical diagnosis and prognostic evaluation of the various seizure disorders presenting at this age. Seizures starting in the first year of life including the neonatal period might have a favorable course, such as in infants presenting with benign familial neonatal epilepsy, febrile seizures simplex or acute symptomatic seizures. However, in some cases, the onset of seizures at birth or in the first months of life have a dramatic evolution with severe cerebral impairment. Seizure disorders starting in early life include the "epileptic encephalopathies", a group of conditions characterized by drug resistant seizures, delayed developmental skills, and intellective disability. This group of disorders includes early infantile epileptic encephalopathy also known as Ohtahara syndrome, early myoclonic encephalopathy, epilepsy of infancy with migrating focal seizures, infantile spasms syndrome (also known as West syndrome), severe myoclonic epilepsy in infancy (also known as Dravet syndrome) and, myoclonic encephalopathies in non-progressive disorder. Here we report on seizures manifesting in the first year of life including the neonatal period. Conditions with a benign course, and those with severe evolution are presented. At this early age, clinical identification of seizures, distinction of each of these disorders, type of treatment and prognosis is particularly challenging. The aim of this report is to present the clinical manifestations of each of these disorders and provide an updated review of the conditions associated with seizures in the first year of life.

Incorporating epilepsy genetics into clinical practice: a 360°evaluation

We evaluated a new epilepsy genetic diagnostic and counseling service covering a UK population of 3.5 million. We calculated diagnostic yield, estimated clinical impact, and surveyed referring clinicians and families. We costed alternative investigational pathways for neonatal onset epilepsy. Patients with epilepsy of unknown aetiology onset < 2 years; treatment resistant epilepsy; or familial epilepsy were referred for counseling and testing. We developed NGS panels, performing clinical interpretation with a multidisciplinary team. We held an educational workshop for paediatricians and nurses. We sent questionnaires to referring paediatricians and families. We analysed investigation costs for 16 neonatal epilepsy patients. Of 96 patients, a genetic diagnosis was made in 34% of patients with seizure onset < 2 years, and 4% > 2 years, with turnaround time of 21 days. Pathogenic variants were seen in SCN8A, SCN2A, SCN1A, KCNQ2, HNRNPU, GRIN2A, SYNGAP1, STXBP1, STX1B, CDKL5, CHRNA4, PCDH19 and PIGT. Clinician prediction was poor. Clinicians and families rated the service highly. In neonates, the cost of investigations could be reduced from £9362 to £2838 by performing gene panel earlier and the median diagnostic delay of 3.43 years reduced to 21 days. Panel testing for epilepsy has a high yield among children with onset < 2 years, and an appreciable clinical and financial impact. Parallel gene testing supersedes single gene testing in most early onset cases that do not show a clear genotype-phenotype correlation. Clinical interpretation of laboratory results, and in-depth discussion of implications for patients and their families, necessitate multidisciplinary input and skilled genetic counseling.

Screening for epilepsy-related gene variants can lead to effective, personalized treatment plans while reducing costs. UK and Danish scientists, led by Deb Pal, King’s College London, evaluated a new service within the UK that searches for genetic variants in patients that cause epilepsy. The authors assessed the impact of next-generation gene panel tests, as well as the necessary resources to make such a service effective. Genetic testing was most effective in patients with seizure onset under 2 years old (21% diagnosed) and yield even higher in neonatal-onset epilepsy (63% diagnosed). For many patients with pathogenic variants, the diagnoses allowed for recommendations on treatment or enrolment in clinical trials. The researchers found that diagnostic delay and financial burden in neonatal epilepsy could be drastically reduced with gene panel testing. The scheme was highly rated by users and patients alike.

Progress in Understanding and Treating SCN2A-Mediated Disorders

Advances in gene discovery for neurodevelopmental disorders have identified SCN2A dysfunction as a leading cause of infantile seizures, autism spectrum disorder, and intellectual disability. SCN2A encodes the neuronal sodium channel Na_V1.2. Functional assays demonstrate strong correlation between genotype and phenotype. This insight can help guide therapeutic decisions and raises the possibility that ligands that selectively enhance or diminish channel function may improve symptoms. The well-defined function of sodium channels makes SCN2A an important test case for investigating the neurobiology of neurodevelopmental disorders more generally. Here, we discuss the progress made, through the concerted efforts of a diverse group of academic and industry scientists as well as policy advocates, in understanding and treating SCN2A-related disorders.

Mechanisms of KCNQ1 channel dysfunction in long QT syndrome involving voltage sensor domain mutations

Mutations that induce loss of function (LOF) or dysfunction of the human KCNQ1 channel are responsible for susceptibility to a life-threatening heart rhythm disorder, the congenital long QT syndrome (LQTS). Hundreds of KCNQ1 mutations have been identified, but the molecular mechanisms responsible for impaired function are poorly understood. We investigated the impact of 51 KCNQ1 variants with mutations located within the voltage sensor domain (VSD), with an emphasis on elucidating effects on cell surface expression, protein folding, and structure. For each variant, the efficiency of trafficking to the plasma membrane, the impact of proteasome inhibition, and protein stability were assayed. The results of these experiments combined with channel functional data provided the basis for classifying each mutation into one of six mechanistic categories, highlighting heterogeneity in the mechanisms resulting in channel dysfunction or LOF. More than half of the KCNQ1 LOF mutations examined were seen to destabilize the structure of the VSD, generally accompanied by mistrafficking and degradation by the proteasome, an observation that underscores the growing appreciation that mutation-induced destabilization of membrane proteins may be a common human disease mechanism. Finally, we observed that five of the folding-defective LQTS mutant sites are located in the VSD S0 helix, where they interact with a number of other LOF mutation sites in other segments of the VSD. These observations reveal a critical role for the S0 helix as a central scaffold to help organize and stabilize the KCNQ1 VSD and, most likely, the corresponding domain of many other ion channels.

PRRT2 mutations in a cohort of Chinese families with paroxysmal kinesigenic dyskinesia and genotype-phenotype correlation reanalysis in literatures

PURPOSE OF THE STUDY

Though rare, children are susceptible to paroxysmal dyskinesias such as paroxysmal kinesigenic dyskinesia, and infantile convulsions and choreoathetosis. Recent studies showed that the cause of paroxysmal kinesigenic dyskinesia or infantile convulsions and choreoathetosis could be proline-rich transmembrane protein 2 (PRRT2) gene mutations.

MATERIAL AND METHODS

This study analysed PRRT2 gene mutations in 51 families with paroxysmal kinesigenic dyskinesia or infantile convulsions and choreoathetosis by direct sequencing. In particular, we characterize the genotype-phenotype correlation between age at onset and the types of PRRT2 mutations in all published cases.

RESULTS

Direct sequencing showed that 12 out of the 51 families had three different pathogenic mutations (c.649dupC, c.776dupG, c.649C>T) in the PRRT2 gene. No significant difference of age at onset between the patients with and without PRRT2 mutations was found in this cohort of patients. A total of 97 different PRRT2 mutations have been reported in 87 studies till now. The PRRT2 mutation classes are wide, and most mutations are frameshift mutations but the most common mutation remains c.649dupC. Comparisons of the age at onset in paroxysmal kinesigenic dyskinesia or infantile convulsions patients with different types of mutations showed no significant difference.

CONCLUSIONS

This study expands the clinical and genetic spectrums of Chinese patients with paroxysmal kinesigenic dyskinesia and infantile convulsions and choreoathetosis. No clear genotype-phenotype correlation between the age at onset and the types of mutations has been determined.