What do parents expect from a genetic diagnosis of their child with intellectual disability?

BACKGROUND

Caring for a child with intellectual disability (ID) has been associated with increased social and psychological burdens. Diagnostic and prognostic uncertainty may enhance emotional stress in families.

METHOD

The present authors assessed the motivations, expectations, mental health, physical health and the quality of life of 194 parents whose children with intellectual disability were undergoing a genetic diagnostic workup.

RESULTS

Most parents considered a diagnosis highly relevant for their own emotional relief, their child's therapies and education, or family planning. Parental mental health was significantly lower compared with the normative sample, but physical health was not different. The severity of the child's intellectual disability correlated negatively with their parents' mental and physical health, quality of life, and positively with parental anxiety.

CONCLUSION

Healthcare providers should be aware of the disadvantages facing families with intellectually disabled children. Receiving practical, social and psychological support as well as genetic testing might be particularly relevant for families with severely disabled children.

Ketogenic diet as a successful early treatment modality for SCN2A mutation

SCN2A mutations have been described in a very broad spectrum of clinical phenotypes including benign (familial) neonatal/infantile seizures and early infantile epileptic encephalopathies (EIEE) as Ohtahara syndrome (OS), Dravet syndrome (DS), epilepsy of infancy with migrating focal seizures and West syndrome (WS). Treatment modalities for epilepsy caused by SCN2A mutations mainly consist of sodium channel blockers but ketogenic diet (KD) is also considered as an option of treatment for intractible seizures caused by SCN2A mutations. Because of the wide nature of the heterogeneity of mutations related to SCN2A gene, the clinical phenotypes vary in severity and treatment response to KD has been reported to be controversial. We present a patient diagnosed with OS associated with a novel SCN2A mutation (c.408G > A, p.Met136lle; OMIM®: 182390) who had a complete resolution of seizures and EEG abnormalities with KD commenced at 39 days of age. As far as we are aware our case is the youngest patient with SCN2A mutation treated with KD with complete resolution of epilepsy at an early age and has been seizure free of antiepileptic medications for a long duration.

Scn2a haploinsufficient mice display a spectrum of phenotypes affecting anxiety, sociability, memory flexibility and ampakine CX516 rescues their hyperactivity

Background

Mutations of the SCN2A gene encoding a voltage-gated sodium channel alpha-II subunit Nav1.2 are associated with neurological disorders such as epilepsy, autism spectrum disorders, intellectual disability, and schizophrenia. However, causal relationships and pathogenic mechanisms underlying these neurological defects, especially social and psychiatric features, remain to be elucidated.

Methods

We investigated the behavior of mice with a conventional or conditional deletion of Scn2a in a comprehensive test battery including open field, elevated plus maze, light-dark box, three chambers, social dominance tube, resident-intruder, ultrasonic vocalization, and fear conditioning tests. We further monitored the effects of the positive allosteric modulator of AMPA receptors CX516 on these model mice.

Results

Conventional heterozygous Scn2a knockout mice (Scn2a^KO/+) displayed novelty-induced exploratory hyperactivity and increased rearing. The increased vertical activity was reproduced by heterozygous inactivation of Scn2a in dorsal-telencephalic excitatory neurons but not in inhibitory neurons. Moreover, these phenotypes were rescued by treating Scn2a^KO/+ mice with CX516. Additionally, Scn2a^KO/+ mice displayed mild social behavior impairment, enhanced fear conditioning, and deficient fear extinction. Neuronal activity was intensified in the medial prefrontal cortex of Scn2a^KO/+ mice, with an increase in the gamma band.

Conclusions

Scn2a^KO/+ mice exhibit a spectrum of phenotypes commonly observed in models of schizophrenia and autism spectrum disorder. Treatment with the CX516 ampakine, which ameliorates hyperactivity in these mice, could be a potential therapeutic strategy to rescue some of the disease phenotypes.

Electronic supplementary material

The online version of this article (10.1186/s13229-019-0265-5) contains supplementary material, which is available to authorized users.

Further corroboration of distinct functional features in SCN2A variants causing intellectual disability or epileptic phenotypes

BACKGROUND

Deleterious variants in the voltage-gated sodium channel type 2 (Na_v1.2) lead to a broad spectrum of phenotypes ranging from benign familial neonatal-infantile epilepsy (BFNIE), severe developmental and epileptic encephalopathy (DEE) and intellectual disability (ID) to autism spectrum disorders (ASD). Yet, the underlying mechanisms are still incompletely understood.

METHODS

To further elucidate the genotype-phenotype correlation of SCN2A variants we investigated the functional effects of six variants representing the phenotypic spectrum by whole-cell patch-clamp studies in transfected HEK293T cells and in-silico structural modeling.

RESULTS

The two variants p.L1342P and p.E1803G detected in patients with early onset epileptic encephalopathy (EE) showed profound and complex changes in channel gating, whereas the BFNIE variant p.L1563V exhibited only a small gain of channel function. The three variants identified in ID patients without seizures, p.R937C, p.L611Vfs*35 and p.W1716*, did not produce measurable currents. Homology modeling of the missense variants predicted structural impairments consistent with the electrophysiological findings.

CONCLUSIONS

Our findings support the hypothesis that complete loss-of-function variants lead to ID without seizures, small gain-of-function variants cause BFNIE and EE variants exhibit variable but profound Na_v1.2 gating changes. Moreover, structural modeling was able to predict the severity of the variant impact, supporting a potential role of structural modeling as a prognostic tool. Our study on the functional consequences of SCN2A variants causing the distinct phenotypes of EE, BFNIE and ID contributes to the elucidation of mechanisms underlying the broad phenotypic variability reported for SCN2A variants.

Clinical spectrum of STX1B-related epileptic disorders

OBJECTIVE

The aim of this study was to expand the spectrum of epilepsy syndromes related to STX1B, encoding the presynaptic protein syntaxin-1B, and establish genotype-phenotype correlations by identifying further disease-related variants.

METHODS

We used next-generation sequencing in the framework of research projects and diagnostic testing. Clinical data and EEGs were reviewed, including already published cases. To estimate the pathogenicity of the variants, we used established and newly developed in silico prediction tools.

RESULTS

We describe 17 new variants in STX1B, which are distributed across the whole gene. We discerned 4 different phenotypic groups across the newly identified and previously published patients (49 patients in 23 families): (1) 6 sporadic patients or families (31 affected individuals) with febrile and afebrile seizures with a benign course, generally good drug response, normal development, and without permanent neurologic deficits; (2) 2 patients with genetic generalized epilepsy without febrile seizures and cognitive deficits; (3) 13 patients or families with intractable seizures, developmental regression after seizure onset and additional neuropsychiatric symptoms; (4) 2 patients with focal epilepsy. More often, we found loss-of-function mutations in benign syndromes, whereas missense variants in the SNARE motif of syntaxin-1B were associated with more severe phenotypes.

CONCLUSION

These data expand the genetic and phenotypic spectrum of STX1B-related epilepsies to a diverse range of epilepsies that span the International League Against Epilepsy classification. Variants in STX1B are protean and contribute to many different epilepsy phenotypes, similar to SCN1A, the most important gene associated with fever-associated epilepsies.

Novel SCN2A mutation in a family associated with juvenile-onset myoclonus: Case report

RATIONALE

The phenotypic spectrum caused by SCN2A mutations includes benign neonatal/infantile seizures, Ohtahara syndrome, infantile spasms, West syndrome, and other unclassified epileptic phenotypes. Mutations in SCN2A have been implicated in neonatal seizure cases. Here, we described a Chinese family with 2 members having juvenile-onset myoclonus and identified a novel SCN2A point mutation within this family.

PATIENT CONCERNS

The 21-year-old male proband suffered from frequent myoclonus at 11 years old with subsequent progressive ataxia. His elder maternal half-sister also experienced myoclonus. Genomic DNA of the patients was extracted from the peripheral blood cells of the proband, elder maternal half-sister, parents, and uncle of the proband. Targeted next-generation sequencing was used to screen gene mutations in the proband. The potential functional effects of mutations within SCN2A were predicted In silico analyses.

DIAGNOSES

Genetic testing revealed a novel SCN2A variant, c.T4820C, which contains a highly conserved amino acid substitution within segment S5 (p.V1607A). This mutation was predicted to produce a dysfunctional Nav1.2 protein by Mutation Taster and Protein Variation Effect Analyzer (PROVEAN). Genotype-phenotype correlation showed an incomplete penetrance of p.V1607A.

INTERVENTIONS

The proband was treated by multiple antiepileptic drugs. These included carbamazepine, oxcarbazepine, valproate, and topiramate.

OUTCOMES

The duration of follow up was 2 years, and the proband developed drug-resistant epilepsy.

LESSONS

The case gives us the lesson that SCN2A mutation can contribute to juvenile-onset myoclonus. Our findings extend the spectrums of SCN2A mutations and the clinical features of patients with SCN2A mutations.

Genetic testing in a cohort of patients with potential epilepsy with myoclonic-atonic seizures

Epilepsy with myoclonic-atonic seizures (EMAS) accounts for 1-2% of all childhood-onset epilepsies. EMAS has been shown to have an underlying genetic component, however the genetics of this disorder is not yet well understood. The purpose of this study was to review genetic testing results for a cohort of EMAS patients. A retrospective chart review was conducted for 77 patients evaluated at Children's Hospital Colorado with a potential diagnosis of EMAS. Genetic testing and biochemical testing was reviewed. Family history data was also collected. Seventy-seven percent of the cohort had at least one genetic test performed, and a molecular diagnosis was reached for six patients. Thirty-seven patients had a microarray, six of which identified a copy number variant. Only one was felt to contribute to the phenotype (2p16.3 deletion including NRXN1). Fifty-one patients had an epilepsy panel, two of which were positive (likely pathogenic variant in SCN1A, pathogenic variant in GABRG2). Of the six patients who had whole exome sequencing, two were negative, three were positive or likely positive, and one had multiple variants not felt to explain the phenotype. While EMAS is widely accepted to have a strong genetic component, the diagnostic yield of genetic testing remains low. This may be because several genes now thought to be associated with EMAS are not included on the more commonly ordered epilepsy panels, or have only recently been added to them.

Genetics of neonatal-onset epilepsies

Although the majority of seizures in neonates are related to acute brain injury, a substantial minority are the first symptom of a neonatal-onset epilepsy often linked to a pathogenic genetic variant. Historically, studies on neonatal seizures including treatment response and long-term consequences have lumped all etiologies together. However, etiology has been consistently shown to be the most important determinant of outcome. In the past few years, an increasing number of monogenic disorders have been described and might explain up to a third of neonatal-onset epilepsy syndromes previously included under the umbrella of Ohtahara syndrome and early myoclonic encephalopathy. In this chapter, we define the concept of genetic epilepsy and review the classification. Then, we review the most relevant monogenic neonatal-onset epilepsies, detail their underlying pathophysiologic mechanisms, and present their electroclinical phenotypes. We highlight that, in some cases, such as neonates with KCNQ2 or KCNT1 gene mutations, the early recognition of the electroclinical phenotype can lead to targeted diagnostic testing and precision medicine treatment, enabling the possibility of improved outcome.

De Novo Pathogenic Variants in CACNA1E Cause Developmental and Epileptic Encephalopathy with Contractures, Macrocephaly, and Dyskinesias

Developmental and epileptic encephalopathies (DEEs) are severe neurodevelopmental disorders often beginning in infancy or early childhood that are characterized by intractable seizures, abundant epileptiform activity on EEG, and developmental impairment or regression. CACNA1E is highly expressed in the central nervous system and encodes the α₁-subunit of the voltage-gated Ca_V2.3 channel, which conducts high voltage-activated R-type calcium currents that initiate synaptic transmission. Using next-generation sequencing techniques, we identified de novo CACNA1E variants in 30 individuals with DEE, characterized by refractory infantile-onset seizures, severe hypotonia, and profound developmental impairment, often with congenital contractures, macrocephaly, hyperkinetic movement disorders, and early death. Most of the 14, partially recurring, variants cluster within the cytoplasmic ends of all four S6 segments, which form the presumed Ca_V2.3 channel activation gate. Functional analysis of several S6 variants revealed consistent gain-of-function effects comprising facilitated voltage-dependent activation and slowed inactivation. Another variant located in the domain II S4-S5 linker results in facilitated activation and increased current density. Five participants achieved seizure freedom on the anti-epileptic drug topiramate, which blocks R-type calcium channels. We establish pathogenic variants in CACNA1E as a cause of DEEs and suggest facilitated R-type calcium currents as a disease mechanism for human epilepsy and developmental disorders.

Catatonia Associated With a SCN2A-Related Disorder in a 4-Year-Old Child

Catatonia is a rare, underdiagnosed syndrome in children. We report the case of a 4-year-old child admitted for recent social withdrawal alternating with psychomotor excitement, verbigeration, and a loss of toilet readiness. He had a history of neonatal seizures, had been stabilized with vigabatrin, and was seizure free without treatment for several months. The pediatric and psychiatric examination revealed motor stereotypes, mannerism, bilateral mydriasis, and visual hallucinations. Laboratory and brain imaging explorations were initially negative. Catatonic symptoms, as measured with the Pediatric Catatonia Rating Scale, significantly decreased after introducing lorazepam, the first-line recommended treatment of this condition. On the basis of the neonatal seizure history, complementary genetic investigations were performed and revealed a mutation in the SCN2A gene, which encodes the voltage-gated sodium channel Nav1.2. Catatonic symptoms progressively disappeared after reintroducing vigabatrin. At the syndromic level, catatonia in young children appears responsive to high-dose lorazepam and is well monitored by using the Pediatric Catatonia Rating Scale. This case reveals the need for wide-ranging explorations in early-onset catatonia because specific targeted treatments might be available.

Balanced Activity between Kv3 and Nav Channels Determines Fast-Spiking in Mammalian Central Neurons

Fast-spiking (FS) neurons can fire action potentials (APs) up to 1,000 Hz and play key roles in vital functions such as sound location, motor coordination, and cognition. Here we report that the concerted actions of Kv3 voltage-gated K⁺ (Kv) and Na⁺ (Nav) channels are sufficient and necessary for inducing and maintaining FS. Voltage-clamp analysis revealed a robust correlation between the Kv3/Nav current ratio and FS. Expressing Kv3 channels alone could convert ∼30%-60% slow-spiking (SS) neurons to FS in culture. In contrast, co-expression of either Nav1.2 or Nav1.6 together with Kv3.1 or Kv3.3, but not alone or with Kv1.2, converted SS to FS with 100% efficiency. Furthermore, RNA-sequencing-based genome-wide analysis revealed that the Kv3/Nav ratio and Kv3 expression levels strongly correlated with the maximal AP frequencies. Therefore, FS is established by the properly balanced activities of Kv3 and Nav channels and could be further fine-tuned by channel biophysical features and localization patterns.

Early Treatment with Quinidine in 2 Patients with Epilepsy of Infancy with Migrating Focal Seizures (EIMFS) Due to Gain-of-Function KCNT1 Mutations: Functional Studies, Clinical Responses, and Critical Issues for Personalized Therapy

Epilepsy of infancy with migrating focal seizures (EIMFS) is a rare early-onset developmental epileptic encephalopathy resistant to anti-epileptic drugs. The most common cause for EIMFS is a gain-of-function mutation in the KCNT1 potassium channel gene, and treatment with the KCNT1 blocker quinidine has been suggested as a rational approach for seizure control in EIMFS patients. However, variable results on the clinical efficacy of quinidine have been reported. In the present study, we provide a detailed description of the clinical, genetic, in vitro, and in vivo electrophysiological profile and pharmacological responses to quinidine of 2 EIMFS unrelated patients with a heterozygous de novo KCNT1 mutation: c.2849G>A (p.R950Q) in patient 1 and c.2677G>A (p.E893K) in patient 2. When expressed heterologously in CHO cells, KCNT1 channels carrying each variant showed gain-of-function effects, and were more effectively blocked by quinidine when compared to wild-type KCNT1 channels. On the basis of these in vitro results, add-on quinidine treatment was started at 3 and 16 months of age in patients 1 and 2, respectively. The results obtained reveal that quinidine significantly reduced seizure burden (by about 90%) and improved quality of life in both patients, but failed to normalize developmental milestones, which persisted as severely delayed. Based on the present experience, early quinidine intervention associated with heart monitoring and control of blood levels is among the critical factors for therapy effectiveness in EIMFS patients with KCNT1 gain-of-function mutations. Multicenter studies are needed to establish a consensus protocol for patient recruitment, quinidine treatment modalities, and outcome evaluation, to optimize clinical efficacy and reduce risks as well as variability associated to quinidine use in such severe developmental encephalopathy.

The NaV1.7 Channel Subtype as an Antinociceptive Target for Spider Toxins in Adult Dorsal Root Ganglia Neurons

Although necessary for human survival, pain may sometimes become pathologic if long-lasting and associated with alterations in its signaling pathway. Opioid painkillers are officially used to treat moderate to severe, and even mild, pain. However, the consequent strong and not so rare complications that occur, including addiction and overdose, combined with pain management costs, remain an important societal and economic concern. In this context, animal venom toxins represent an original source of antinociceptive peptides that mainly target ion channels (such as ASICs as well as TRP, Ca_V, K_V and Na_V channels) involved in pain transmission. The present review aims to highlight the Na_V1.7 channel subtype as an antinociceptive target for spider toxins in adult dorsal root ganglia neurons. It will detail (i) the characteristics of these primary sensory neurons, the first ones in contact with pain stimulus and conveying the nociceptive message, (ii) the electrophysiological properties of the different Na_V channel subtypes expressed in these neurons, with a particular attention on the Na_V1.7 subtype, an antinociceptive target of choice that has been validated by human genetic evidence, and (iii) the features of spider venom toxins, shaped of inhibitory cysteine knot motif, that present high affinity for the Na_V1.7 subtype associated with evidenced analgesic efficacy in animal models.

SCN2A mutation in an infant presenting with migrating focal seizures and infantile spasm responsive to a ketogenic diet

SCN2A mutations have been identified in various encephalopathy phenotypes, ranging from benign familial neonatal-infantile seizure (BFNIS) to more severe forms of epileptic encephalopathy such as Ohtahara syndrome or epilepsy of infancy with migrating focal seizure (EIMFS). Thus far, no particularly effective treatment is available for severe epileptic encephalopathy caused by SCN2A mutations in children. We present the case of a boy who developed seizures on the third day of life and received a diagnosis of EIMFS based on his clinical presentations and electroencephalography reports. Antiepileptic drugs, namely oxcarbazepine, phenytoin, valproate, levetiracetam, and clonazepam, as well as adrenocorticotropic hormone therapy failed to reduce the severity of the seizures. Seizure pattern changed to infantile spasm with extensor thrust since 5 months of age. A ketogenic diet consisting of a medium-chain triglyceride recipe was introduced at 8 months of age and the seizures were resolved in the following 10 months. A de novo mutation in SCN2A (c.573G > T; p.W191C) was proven through next-generation sequencing.

The phenotype of SCN8A developmental and epileptic encephalopathy

Objective

To delineate the electroclinical features of SCN8A infantile developmental and epileptic encephalopathy (EIEE13, OMIM #614558).

Methods

Twenty-two patients, aged 19 months to 22 years, underwent electroclinical assessment.

Results

Sixteen of 22 patients had mildly delayed development since birth. Drug-resistant epilepsy started at a median age of 4 months, followed by developmental slowing, pyramidal/extrapyramidal signs (22/22), movement disorders (12/22), cortical blindness (17/22), sialorrhea, and severe gastrointestinal symptoms (15/22), worsening during early childhood and plateauing at age 5 to 9 years. Death occurred in 4 children, following extreme neurologic deterioration, at 22 months to 5.5 years. Nonconvulsive status epilepticus recurred in 14 of 22 patients. The most effective antiepileptic drugs were oxcarbazepine, carbamazepine, phenytoin, and benzodiazepines. EEG showed background deterioration, epileptiform abnormalities with a temporo-occipital predominance, and posterior delta/beta activity correlating with visual impairment. Video-EEG documented focal seizures (FS) (22/22), spasm-like episodes (8/22), cortical myoclonus (8/22), and myoclonic absences (1/22). FS typically clustered and were prolonged (<20 minutes) with (1) cyanosis, hypomotor, and vegetative semiology, sometimes unnoticed, followed by (2) tonic-vibratory and (3) (hemi)-clonic manifestations ± evolution to a bilateral tonic-clonic seizure. FS had posterior-temporal/occipital onset, slowly spreading and sometimes migrating between hemispheres. Brain MRI showed progressive parenchymal atrophy and restriction of the optic radiations.

Conclusions:

SCN8A developmental and epileptic encephalopathy has strikingly consistent electroclinical features, suggesting a global progressive brain dysfunction primarily affecting the temporo-occipital regions. Both uncontrolled epilepsy and developmental compromise contribute to the profound impairment (increasing risk of death) during early childhood, but stabilization occurs in late childhood.

Nonsyndromic intellectual disability with novel heterozygous SCN2A mutation and epilepsy

SCN2A mutations are primarily associated with a variety of epilepsy syndromes. Recently, SCN2A has been reported as a gene responsible for nonsyndromic intellectual disability or autism spectrum disorders. Here, we present a case of a 12-year-old girl with nonsyndromic intellectual disability who exhibited a heterozygous de novo missense mutation in SCN2A. She developed seizures during the course of illness. This case suggests that the phenotype of patients with heterozygous SCN2A mutations can be variable.

Nav1.2 haplodeficiency in excitatory neurons causes absence-like seizures in mice

Mutations in the SCN2A gene encoding a voltage-gated sodium channel Nav1.2 are associated with epilepsies, intellectual disability, and autism. SCN2A gain-of-function mutations cause early-onset severe epilepsies, while loss-of-function mutations cause autism with milder and/or later-onset epilepsies. Here we show that both heterozygous Scn2a-knockout and knock-in mice harboring a patient-derived nonsense mutation exhibit ethosuximide-sensitive absence-like seizures associated with spike-and-wave discharges at adult stages. Unexpectedly, identical seizures are reproduced and even more prominent in mice with heterozygous Scn2a deletion specifically in dorsal-telencephalic (e.g., neocortical and hippocampal) excitatory neurons, but are undetected in mice with selective Scn2a deletion in inhibitory neurons. In adult cerebral cortex of wild-type mice, most Nav1.2 is expressed in excitatory neurons with a steady increase and redistribution from proximal (i.e., axon initial segments) to distal axons. These results indicate a pivotal role of Nav1.2 haplodeficiency in excitatory neurons in epilepsies of patients with SCN2A loss-of-function mutations.

Genetic etiologies of the electrical status epilepticus during slow wave sleep: systematic review

Background

Electrical status epilepticus during slow-wave sleep (ESESS) which is also known as continuous spike-wave of slow sleep (CSWSS) is type of electroencephalographic (EEG) pattern which is seen in ESESS/CSWSS/epilepsy aphasia spectrum. This EEG pattern can occur alone or with other syndromes. Its etiology is not clear, however, brain malformations, immune disorders, and genetic etiologies are suspected to contribute. We aimed to perform a systematic review of all genetic etiologies which have been reported to associate with ESESS/CSWSS/epilepsy-aphasia spectrum. We further aimed to identify the common underlying pathway which can explain it. To our knowledge, there is no available systematic review of genetic etiologies of ESESS/CSWSS/epilepsy-aphasia spectrum. MEDLINE, EMBASE, PubMed and Cochrane review database were searched, using terms specific to electrical status epilepticus during sleep or continuous spike–wave discharges during slow sleep or epilepsy-aphasia spectrum and of studies of genetic etiologies. These included monogenic mutations and copy number variations (CNVs). For each suspected dosage-sensitive gene, further studies were performed through OMIM and PubMed database.

Results

Twenty-six studies out of the 136 identified studies satisfied our inclusion criteria. I51 cases were identified among those 26 studies. 16 studies reported 11 monogenic mutations: SCN2A (N = 6), NHE6/SLC9A6 (N = 1), DRPLA/ ATN1 (N = 1), Neuroserpin/SRPX2 (N = 1), OPA3 (N = 1), KCNQ2 (N = 2), KCNA2 (N = 5), GRIN2A (N = 34), CNKSR2 (N = 2), SLC6A1 (N = 2) and KCNB1 (N = 5). 10 studies reported 89 CNVs including 9 recurrent ones: Xp22.12 deletion encompassing CNKSR2 (N = 6), 16p13 deletion encompassing GRIN2A (N = 4), 15q11.2–13.1 duplication (N = 15), 3q29 duplication (N = 11), 11p13 duplication (N = 2), 10q21.3 deletion (N = 2), 3q25 deletion (N = 2), 8p23.3 deletion (N = 2) and 9p24.2 (N = 2). 68 of the reported genetic etiologies including monogenic mutations and CNVs were detected in patients with ESESS/CSWSS/epilepsy aphasia spectrum solely. The most common underlying pathway was channelopathy (N = 56).

Conclusions

Our review suggests that genetic etiologies have a role to play in the occurrence of ESESS/CSWSS/epilepsy-aphasia spectrum. The common underlying pathway is channelopathy. Therefore we propose more genetic studies to be done for more discoveries which can pave a way for proper drug identification. We also suggest development of common cut-off value for spike-wave index to ensure common language among clinicians and researchers.

Electronic supplementary material

The online version of this article (10.1186/s12863-018-0628-5) contains supplementary material, which is available to authorized users.

Neonatal epilepsy genetics

Neonatal epilepsy genetics is a rapidly expanding field with recent technological advances in genomics leading to an expanding list of genetic disorders associated with neonatal-onset epilepsy. The genetic causes of neonatal epilepsy can be grouped into the following categories: (i) malformations of cortical development, (ii) genetic-metabolic, (iii) genetic-vascular, (iv) genetic-syndromic, and (v) genetic-cellular. Clinically, epilepsy in the neonate shows phenotypic overlap with pathogenic variants in unrelated genes causing similar clinical presentation (locus heterogeneity) and variants in the same gene leading to a wide clinical spectrum ranging from benign familial neonatal seizures to more severe epileptic encephalopathies (variable expressivity). We suggest a diagnostic approach to obtaining a genetic diagnosis with emphasis on clinical features such as electro-clinical phenotype and magnetic resonance imaging findings. Rapid identification of genetic disorders with targeted treatments should be a clinical priority. Achieving a genetic diagnosis can be challenging in a rapidly changing genetic landscape, but is increasingly possible.

Neonatal epilepsies: Clinical management

Whereas the majority of seizures in neonates are related to acute brain injury, a substantial minority are the first symptom of a neonatal-onset epilepsy, often linked to a pathogenic genetic variant. This defect may disrupt cortical development (e.g., lissencephaly, focal cortical dysplasia), lead to metabolic changes (e.g., pyridoxine-dependent epilepsy, sulfite oxidase deficiency) or lead to cortical dysfunction without metabolic or macroscopic structural changes (e.g., channelopathies, STXBP1). Historically, studies on treatment response and long-term consequences of neonatal seizures have lumped all etiologies together. However, etiology has been consistently shown to be the most important determinant of outcome. Here, we address the elements differentiating neonatal-onset epilepsies from acute symptomatic seizures. We review some common neonatal-onset epilepsies and emphasize how pathognomonic electro-clinical phenotypes such as the ones associated with KCNQ2 or KCNT1 gene mutation, when recognized early, can lead to targeted diagnostic testing and precision medicine treatment, enabling the possibility of improved outcome.

Dynamic action potential clamp predicts functional separation in mild familial and severe de novo forms of SCN2A epilepsy

De novo variants in SCN2A developmental and epileptic encephalopathy (DEE) show distinctive genotype-phenotype correlations. The two most recurrent SCN2A variants in DEE, R1882Q and R853Q, are associated with different ages and seizure types at onset. R1882Q presents on day 1 of life with focal seizures, while infantile spasms is the dominant seizure type seen in R853Q cases, presenting at a median age of 8 months. Voltage clamp, which characterizes the functional properties of ion channels, predicted gain-of-function for R1882Q and loss-of-function for R853Q. Dynamic action potential clamp, that we implement here as a method for modeling neurophysiological consequences of a given epilepsy variant, predicted that the R1882Q variant would cause a dramatic increase in firing, whereas the R853Q variant would cause a marked reduction in action potential firing. Dynamic clamp was also able to functionally separate the L1563V variant, seen in benign familial neonatal-infantile seizures from R1882Q, seen in DEE, suggesting a diagnostic potential for this type of analysis. Overall, the study shows a strong correlation between clinical phenotype, SCN2A genotype, and functional modeling. Dynamic clamp is well positioned to impact our understanding of pathomechanisms and for development of disease mechanism-targeted therapies in genetic epilepsy.

PF-06526290 can both enhance and inhibit conduction through voltage-gated sodium channels

BACKGROUND AND PURPOSE

Pharmacological agents that either inhibit or enhance flux of ions through voltage-gated sodium (Na_v ) channels may provide opportunities for treatment of human health disorders. During studies to characterize agents that modulate Na_v 1.3 function, we identified a compound that appears to exhibit both enhancement and inhibition of sodium ion conduction that appeared to be dependent on the gating state that the channel was in. The objective of the current study was to determine if these different modulatory effects are mediated by the same or distinct interactions with the channel.

EXPERIMENTAL APPROACH

Electrophysiology and site-directed mutation were used to investigate the effects of PF-06526290 on Na_v channel function.

KEY RESULTS

PF-06526290 greatly slows inactivation of Na_v channels in a subtype-independent manner. However, upon prolonged depolarization to induce inactivation, PF-06526290 becomes a Na_v subtype-selective inhibitor. Mutation of the domain 4 voltage sensor modulates inhibition of Na_v 1.3 or Na_v 1.7 channels by PF-06526290 but has no effect on PF-06526290 mediated slowing of inactivation.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that distinct interactions may underlie the two modes of Na_v channel modulation by PF-06526290 and that a single compound can affect sodium channel function in several ways.

Genetic diagnosis in neonatal-onset epilepsies: Back to the future

Seizures are more frequent in newborns than in any other period of life. In most cases they are due to acute dysfunction of the central nervous system; however some can be true epileptic disorders with an early onset. Although rare, diagnosis of neonatal-onset epilepsies is rising as genetic testing increases. The spectrum of clinical severity associated with specific genes can vary widely with difficulties in providing genotype-phenotype correlations. Therefore, clinicians should strive in order to clearly delineate the clinical features associated with pathogenic genetic variants with the aim to guide the increasing use of genetic testing and improve clinical management.

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.

Association between SCN1A and SCN2A mutations and clinical/EEG features in Chinese patients from epilepsy or severe seizures

BACKGROUND

We investigated the association between SCN1A and SCN2A mutations and clinical phenotype and electroencephalography (EEG) features.

METHODS

In this study, 48 patients suffered from epilepsy or severe seizures with SCN1A and SCN2A mutations were recruited. Medical data and molecular diagnosis were analyzed.

RESULTS

A total of 47 mutations were identified, including 33 novel mutations. The onset of most epilepsy caused by SCN1A mutations (1-6 m) was later than that of SCN2A mutations (neonatal). SCN1A mutations included truncating mutations and missense mutations occurred in the crucial region were associated with more severe phenotypes and developmental delay (85.7%, P = 0.020). De novo mutations or truncating mutations of SCN2A mutations are mainly associated with severe phenotypes. The proportion of initial abnormal EEG of SCN2A mutation was higher than that of SCN1A mutation (54.2%, 100%). Patients with SCN1A mutations showed more focal epileptiform discharges (69.2%), while patients with SCN2A mutations had more multifocal epileptiform discharges (53.8%). Sodium channel blockers were less effective for patients with SCN1A mutations and SCN2A mutations with early seizures onset.

CONCLUSIONS

Our study expanded the mutation spectrum of the SCN1A and SCN2A, and led to a better understanding of the similarities and difference in the genetic and clinical features between the two genes.

Getting serious about the early-life epilepsies

Early-life epilepsies represent a group of many individually rare and often complex developmental brain disorders associated with lifelong devastating consequences and high risk for early mortality. The quantity and quality of evidence needed to guide the evaluation and treatment to optimize outcomes of affected children is minimal; most children are treated within an evidence-free practice zone based solely on anecdote and lore. The remarkable advances in diagnostics and therapeutics are implemented haphazardly with no systematic effort to understand their effects and value. This stands in stark contrast to the evidence-rich practice of the Children's Oncology Group, where standard of care treatments are identified through rigorous, multicenter research studies, and the vast majority of patients are treated on protocols developed from that research. As a consequence, overall mortality for childhood cancers has declined from ∼90% in the 1950s to ∼20% today. The situations of these 2 rare disease specialties are contrasted, and some suggestions for moving early-life epilepsy onto a fast track for success are offered. Chief amongst these is that early-life epilepsy should be treated with the same urgency as pediatric cancer. The best diagnostics and evidence-based treatments should be used in a systematic fashion right from the start, not after the child and family have been subjected to the ravages of the disorder for months or years. This will require unity and cooperation among physicians, researchers, and institutions across state and national borders.

Mutations in SCN3A cause early infantile epileptic encephalopathy

OBJECTIVE

Voltage-gated sodium (Na⁺ ) channels underlie action potential generation and propagation and hence are central to the regulation of excitability in the nervous system. Mutations in the genes SCN1A, SCN2A, and SCN8A, encoding the Na⁺ channel pore-forming (α) subunits Nav1.1, 1.2, and 1.6, respectively, and SCN1B, encoding the accessory subunit β₁ , are established causes of genetic epilepsies. SCN3A, encoding Nav1.3, is known to be highly expressed in brain, but has not previously been linked to early infantile epileptic encephalopathy. Here, we describe a cohort of 4 patients with epileptic encephalopathy and heterozygous de novo missense variants in SCN3A (p.Ile875Thr in 2 cases, p.Pro1333Leu, and p.Val1769Ala).

METHODS

All patients presented with treatment-resistant epilepsy in the first year of life, severe to profound intellectual disability, and in 2 cases (both with the variant p.Ile875Thr), diffuse polymicrogyria.

RESULTS

Electrophysiological recordings of mutant channels revealed prominent gain of channel function, with a markedly increased amplitude of the slowly inactivating current component, and for 2 of 3 mutants (p.Ile875Thr and p.Pro1333Leu), a leftward shift in the voltage dependence of activation to more hyperpolarized potentials. Gain of function was not observed for Nav1.3 variants known or presumed to be inherited (p.Arg1642Cys and p.Lys1799Gln). The antiseizure medications phenytoin and lacosamide selectively blocked slowly inactivating over transient current in wild-type and mutant Nav1.3 channels.

INTERPRETATION

These findings establish SCN3A as a new gene for infantile epileptic encephalopathy and suggest a potential pharmacologic intervention. These findings also reinforce the role of Nav1.3 as an important regulator of neuronal excitability in the developing brain, while providing additional insight into mechanisms of slow inactivation of Nav1.3. Ann Neurol 2018;83:703-717.

De novo BK channel variant causes epilepsy by affecting voltage gating but not Ca2+ sensitivity

Epilepsy is one of the most common neurological diseases and it causes profound morbidity and mortality. We identified the first de novo variant in KCNMA1 (c.2984 A > G (p.(N995S)))-encoding the BK channel-that causes epilepsy, but not paroxysmal dyskinesia, in two independent families. The c.2984 A > G (p.(N995S)) variant markedly increased the macroscopic potassium current by increasing both the channel open probability and channel open dwell time. The c.2984 A > G (p.(N995S)) variant did not affect the calcium sensitivity of the channel. We also identified three other variants of unknown significance (c.1554 G > T (p.(K518N)), c.1967A > C (p.(E656A)), and c.3476 A > G (p.(N1159S))) in three separate patients with divergent epileptic phenotypes. However, these variants did not affect the BK potassium current, and are therefore unlikely to be disease-causing. These results demonstrate that BK channel variants can cause epilepsy without paroxysmal dyskinesia. The underlying molecular mechanism can be increased activation of the BK channel by increased sensitivity to the voltage-dependent activation without affecting the sensitivity to the calcium-dependent activation. Our data suggest that the BK channel may represent a drug target for the treatment of epilepsy. Our data highlight the importance of functional electrophysiological studies of BK channel variants in distinguishing whether a genomic variant of unknown significance is a disease-causing variant or a benign variant.

Ion Channels in Genetic Epilepsy: From Genes and Mechanisms to Disease-Targeted Therapies

Epilepsy is a common and serious neurologic disease with a strong genetic component. Genetic studies have identified an increasing collection of disease-causing genes. The impact of these genetic discoveries is wide reaching-from precise diagnosis and classification of syndromes to the discovery and validation of new drug targets and the development of disease-targeted therapeutic strategies. About 25% of genes identified in epilepsy encode ion channels. Much of our understanding of disease mechanisms comes from work focused on this class of protein. In this study, we review the genetic, molecular, and physiologic evidence supporting the pathogenic role of a number of different voltage- and ligand-activated ion channels in genetic epilepsy. We also review proposed disease mechanisms for each ion channel and highlight targeted therapeutic strategies.

Genetic analysis of benign familial epilepsies in the first year of life in a Chinese cohort

Benign familial epilepsies that present themselves in the first year of life include benign familial neonatal epilepsy (BFNE), benign familial neonatal-infantile epilepsy (BFNIE) and benign familial infantile epilepsy (BFIE). We used Sanger sequencing and targeted next-generation sequencing to detect gene mutations in a Chinese cohort of patients with these three disorders. A total of 79 families were collected, including 4 BFNE, 7 BFNIE, and 68 BFIE. Genetic testing led to the identification of gene mutations in 60 families (60 out of 79, 75.9%). A total of 42 families had PRRT2 mutations, 9 had KCNQ2 mutations, 8 had SCN2A mutations, and 1 had a GABRA6 mutation. In total three of four BFNE families were detected with KCNQ2 mutations. Mutations were detected in all BFNIE families, including 3 KCNQ2 mutations, 3 SCN2A mutations, and 1 PRRT2 mutation. Gene mutations were identified in 50 out of 68 BFIE families (73.5%), including 41 PRRT2 mutations (41 out of 68, 60.3%), 5 SCN2A mutations, 3 KCNQ2 mutations, and 1 GABRA6 mutation. Our results confirmed that mutations in KCNQ2, SCN2A, and PRRT2 are major genetic causes of benign familial epilepsy in the first year of life in the Chinese population. KCNQ2 is the major gene related to BFNE. PRRT2 is the main gene responsible for BFIE.