Early Infantile Epileptic Encephalopathy Research Articles

Syntaxin Binding Protein 1 Related Epilepsies

AbstractSyntaxin binding protein 1 (STXBP1), commonly known as MUNC18–1, is a member of SEC1 family membrane trafficking proteins; their function consists in controlling the soluble N-ethylmaleimide-sensitive factor attachment protein receptors complex assembly, making them essentials regulators of vesicle fusion. The precise function and molecular mechanism through which Munc18–1 contributes to neurotransmitter releasing is not entirely understood, but several evidences suggest its probable role in exocytosis. In 2008, heterozygous de novo mutations in neuronal protein Munc18–1 were first referred as a cause of Ohtahara syndrome development. Currently, a wide examination of the published data proved that 3.1% of patients with severe epilepsy carry a pathogenic de novo mutation including STXBP1 and approximately 10.2% of early onset epileptic encephalopathy is due to an aberrant STXBP1 form codified by the mutated gene. STXBP1 mutations can be associated to a wide clinical heterogeneity. All affected individuals show developmental delay and approximately the 95% of cases have seizures and early onset epileptic encephalopathy, characterized by infantile spasms as the main consistent feature. Burst suppression pattern and hypsarrhythmia are the most frequent EEG anomalies. Other neuronal disorders include Rett syndrome and behavioral and movement disorders. Mild dysmorphic features have been detected in a small number of cases. No genotype–phenotype correlation has been reported. Management of STXBP1 encephalopathy requires a multidisciplinary approach, including epilepsy control and neurological rehabilitation. About 25% of patients are refractory to standard therapy. A single or combined antiepileptic drugs may be required. Several studies described vigabatrin, valproic acid, levetiracetam, topiramate, clobazam, and oxcarbazepine as effective in seizure control. Lamotrigine, zonisamide, and phenobarbital are also commonly used. To date, it remains unclear which therapy is the most effective. Severe morbidity and high mortality are inevitable consequences in some of these patients.

Genetic Etiologies in Developmental and/or Epileptic Encephalopathy With Electrical Status Epilepticus During Sleep: Cohort Study.

BackgroundRecently, the electroencephalogram pattern of electrical status epilepticus during sleep (ESES) had been reported in some genetic disorders, and most of them were noted with developmental and epileptic encephalopathy (DEE) or epileptic encephalopathy (EE). This study aimed to determine the genetic etiologies and clinical characteristics of ESES in DEE/EE.MethodsWe performed a cohort study in cases of DEE or EE with ESES. Tio-based genetic testing was performed in 74 cases and was analyzed to identify underlying variants.ResultsPathogenic or likely pathogenic variants were identified in 17/74 cases, including KCNQ2 (n = 6), KCNA2 (n = 5), GRIN2A (n = 3), SLC9A6 (n = 1), HIVEP2 (n = 1), and RARS2 (n = 1). Eleven were boys. The median age at seizure onset was 6 months. ESES occurred at the mean age of 2.0 ± 1.2 years, predominant in the Rolandic region in 14 years. Twelve of 17 cases had the first stage of different epilepsy preceding ESES: 2/12 were diagnosed as Ohtahara syndrome, 2/12 were diagnosed as infantile spasms, 3/12 were diagnosed as DEE, and 5/12 were diagnosed as EE without the epileptic syndrome.ConclusionMonogenic variants explained over 20% of DEE/EE with ESES. ESES could be an age-related feature in genetic disorders and occurred after the first stage of different epilepsy. Both age-related factors and genetic etiology were suggested to play a role in the occurrence of ESES in genetic DEE/EE.

SCN2A and Its Related Epileptic Phenotypes

AbstractEpilepsies 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).

Clinical manifestation and genetic analysis of a child with early infantile epileptic encephalopathy 42

To analyze the clinical phenotype and genetic characterization of a child with early infantile epileptic encephalopathy. The proband was subjected to history taking and was diagnosed based on his clinical manifestation, magnetic resonance imaging (MRI) and whole exome sequencing (WES). Sanger sequencing was carried out to determine the origin of pathogenic variant. The proband unconsciously tilts his head to one side with squint, which revealed an abnormal discharge. MRI indicated suspicious abnormal signal shadow in the left posterior frontal cortex in addition with inflammation signs in the right maxillary sinus and ethmoid sinus. WES revealed that the proband has carried a heterozygous c.5789G>A variant in the CACNAIA gene. The result of Sanger sequencing was in keeping with that of WES. Neither of his parents has carried the same variant. The heterozygous c.5789G>A variant of the CACNAIA gene probably underlay the early infantile epileptic encephalopathy 42 in the proband, which has a de novo origin.

Establishment of an induced pluripotent stem cell line (ZJSHi001-A) from a patient with epileptic encephalopathy carrying KCNB1 Glu330Asp mutation.

Early infantile epileptic encephalopathy 26 (EE26) is a form of epileptic encephalopathy, a heterogeneous group of severe childhood-onset epilepsies characterized by refractory seizures, neurodevelopmental impairment, and poor prognosis. A recent study has shown that the KCNB1 gene mutation is associated with EE26; yet, the exact mechanism remains unclear. In this study, we produced an induced pluripotent stem cell line (iPSC) with a heterozygous variant of the KCNB1 gene (c.990G>T, p.Glu330Asp). Induced iPSCs were generated from peripheral blood mononuclear cells (PBMCs) obtained from a female child aged 6 with KCNB1 gene c. 990G>T and p.Glu330Asp heterozygous mutation.

In Silico Predictions of KCNQ Variant Pathogenicity in Epilepsy

BackgroundVariants in KCNQ2 and KCNQ3 may cause benign neonatal familial seizures and early infantile epileptic encephalopathy. Previous reports suggest that in silico models cannot predict pathogenicity accurately enough for clinical use. Here we sought to establish a model to accurately predict the pathogenicity of KCNQ2 and KCNQ3 missense variants based on available in silico prediction models. MethodsClinVar and gnomAD databases of reported KCNQ2 and KCNQ3 missense variants in patients with neonatal epilepsy were accessed and classified as benign, pathogenic, or of uncertain significance. Sensitivity, specificity, and classification accuracy for prediction of pathogenicity were determined and compared for 10 widely used prediction algorithms program. A mathematical model of the variants (KCNQ Index) was created using their amino acid location and prediction algorithm scores to improve prediction accuracy. ResultsUsing clinically characterized variants, the free online tool PROVEAN accurately predicted pathogenicity 92% of the time and the KCNQ Index had an accuracy of 96%. However, when including the gnomAD database as benign variants, only the KCNQ Index was able to predict pathogenicity with an accuracy greater than 90% (sensitivity = 93% and specificity = 98%). No model could accurately predict the phenotype of variants. ConclusionWe show that KCNQ channel variant pathogenicity can be predicted by a novel KCNQ Index in neonatal epilepsy. However, more work is needed to accurately predict the patient’s epilepsy phenotype from in silico algorithms.

RHOBTB2 Mutations Expand the Phenotypic Spectrum of Alternating Hemiplegia of Childhood

To explore the phenotypic spectrum of RHOBTB2-related disorders and specifically to determine whether patients fulfill criteria for alternating hemiplegia of childhood (AHC), we report the clinical features of 11 affected individuals. Individuals with RHOBTB2-related disorders were identified through a movement disorder clinic at a specialist pediatric center, with additional cases identified through collaboration with other centers internationally. Clinical data were acquired through retrospective case-note review. Eleven affected patients were identified. All had heterozygous missense variants involving exon 9 of RHOBTB2, confirmed as de novo in 9 cases. All had a complex motor phenotype, including at least 2 different kinds of movement disorder, e.g., ataxia and dystonia. Many patients demonstrated several features fulfilling the criteria for AHC: 10 patients had a movement disorder including paroxysmal elements, and 8 experienced hemiplegic episodes. In contrast to classic AHC, commonly caused by mutations in ATP1A3, these events were reported later only in RHOBTB2 mutation-positive patients from 20 months of age. Seven patients had epilepsy, but of these, 4 patients achieved seizure freedom. All patients had intellectual disability, usually moderate to severe. Other features include episodes of marked skin color change and gastrointestinal symptoms, each in 4 patients. Although heterozygous RHOBTB2 mutations were originally described in early infantile epileptic encephalopathy type 64, our study confirms that they account for a more expansive clinical phenotype, including a complex polymorphic movement disorder with paroxysmal elements resembling AHC. RHOBTB2 testing should therefore be considered in patients with an AHC-like phenotype, particularly those negative for ATPA1A3 mutations.

The severe epilepsy syndromes of infancy: A population-based study.

To study the epilepsy syndromes among the severe epilepsies of infancy and assess their incidence, etiologies, and outcomes. A population-based cohort study was undertaken of severe epilepsies with onset before age 18months in Victoria, Australia. Two epileptologists reviewed clinical features, seizure videos, and electroencephalograms to diagnose International League Against Epilepsy epilepsy syndromes. Incidence, etiologies, and outcomes at age 2years were determined. Seventy-three of 114 (64%) infants fulfilled diagnostic criteria for epilepsy syndromes at presentation, and 16 (14%) had "variants" of epilepsy syndromes in which there was one missing or different feature, or where all classical features had not yet emerged. West syndrome (WS) and "WS-like" epilepsy (infantile spasms without hypsarrhythmia or modified hypsarrhythmia) were the most common syndromes, with a combined incidence of 32.7/100000 live births/year. The incidence of epilepsy of infancy with migrating focal seizures (EIMFS) was 4.5/100000 and of early infantile epileptic encephalopathy (EIEE) was 3.6/100000. Structural etiologies were common in "WS-like" epilepsy (100%), unifocal epilepsy (83%), and WS (39%), whereas single gene disorders predominated in EIMFS, EIEE, and Dravet syndrome. Eighteen (16%) infants died before age 2years. Development was delayed or borderline in 85 of 96 (89%) survivors, being severe-profound in 40 of 96 (42%). All infants with EIEE or EIMFS had severe-profound delay or were deceased, but only 19 of 64 (30%) infants with WS, "WS-like," or "unifocal epilepsy" had severe-profound delay, and only two of 64 (3%) were deceased. Three quarters of severe epilepsies of infancy could be assigned an epilepsy syndrome or "variant syndrome" at presentation. In this era of genomic testing and advanced brain imaging, diagnosing epilepsy syndromes at presentation remains clinically useful for guiding etiologic investigation, initial treatment, and prognostication.

Teaching NeuroImages: Ohtahara Syndrome due to Unilateral Perisylvian Polymicrogyria

A 10-month-old boy, born of nonconsanguineous parents, without any perinatal insult, presented with tonic spasms from the 13th day of life. He started having tonic seizures from 4 months of age, with global developmental delay. On examination, there were no neurocutaneous markers, facial dysmorphism, or focal neurologic deficits. EEG (figure) showed generalized and multifocal epileptiform discharges along with burst-suppression pattern. MRI of brain revealed left perisylvian polymicrogyria (figure).

Case Series of Early SCN1A-Related Developmental and Epileptic Encephalopathies.

ABSTRACTIntroduction:The developmental and epileptic encephalopathies (DEEs) are a heterogeneous group of rare neurodevelopmental disorders, characterized by early onset seizures that are often intractable, electroencephalographic abnormalities, developmental delay, or regression. The SCN1A pathogenic variants can present as DEE. They are characterized by early infantile seizure onset, profound intellectual disability, and a severe hyperkinetic movement disorder. Studies are lacking, hence we are reporting a case series of early SCN1A-related DEE. The objective of the study was to report clinical and molecular aspects of early SCN1A-related DEE.Materials and Methods:A retrospective chart review of children with DEEs secondary to SCN1A pathogenic variants from January 2015 to March 2020 in a tertiary care referral center from south India.Results:Out of eleven children, seven were boys. The mean age of presentation was 3.5 months. Nine children had seizures triggered by fever. All the children presented with focal and generalized seizures along with epileptic spasms. No focal neurological deficits were noted; routine testing, neuroimaging, and metabolic tests were normal in all the cases. In all the cases, hypsarrhythmia was noted on electroencephalogram (EEG). All the children had pathogenic variants in the SCN1A gene. Five children responded to steroids, one child responded to vigabatrin, and one child responded to stiripentol, but all of them had relapsed and were refractory to other antiepileptic drugs. At follow-up, all children had developmental delays and six of them had autistic features.Conclusion:Early SCN1A-related encephalopathies should be considered in the differential diagnosis of early infantile epileptic encephalopathies. Identification of this condition is important, as treatment and outcome are different from other epileptic encephalopathies.

A case of early infantile epileptic encephalopathy type 7 with partial response to pyridoxal Phosphate

A case of early infantile epileptic encephalopathy type 7 with partial response to pyridoxal Phosphate

Congenital disorders of glycosylation type IIb with MOGS mutations cause early infantile epileptic encephalopathy, dysmorphic features, and hepatic dysfunction

AimMOGS mutations cause congenital disorders of glycosylation type IIb (CDG-IIb or GCS1-CDG). The specific manifestations caused by the mutations in this gene remain unknown. We aimed to describe the clinical features of CDG- IIb and the effectiveness of urinary oligosaccharide analysis in the diagnosis of CDG- IIb. MethodsPatient 1 was analyzed with whole-exome sequencing (WES) to identify the causative gene of intractable epilepsy and severe developmental delay. After detecting MOGS mutation in patient 1, we analyzed patients 2 and 3 who were siblings and had clinical features similar to those in patient 1. Urinary oligosaccharide analysis was performed to confirm CDG- IIb diagnosis in patient 1. The clinical features of these patients were analyzed and compared with those in eight published cases. ResultsOur three patients presented with early infantile epileptic encephalopathy, generalized hypotonia, hepatic dysfunction and dysmorphic features. In two cases, compound heterozygous mutations in MOGS were identified by WES. Isolation and characterization of the urinary oligosaccharide was performed in one of these cases to confirm the diagnosis of CDG-IIb. Although the isoelectric focusing of transferrin (IEF-T) of serum in this patient was normal, urinary excretion of Hex4 corresponding to Glc3Man was observed by mass spectrometry. ConclusionThis report provides clinical manifestations of CDG-IIb with MOGS mutation. CDG-IIb shows a normal IEF profile of serum transferrin and cannot be detected by structural analysis of the patient’s glycoproteins. Characterization of urinary oligosaccharides should be considered to detect this disorder.

WWOX Loss of Function in Neurodevelopmental and Neurodegenerative Disorders.

The WWOX gene was initially discovered as a putative tumor suppressor. More recently, its association with multiple central nervous system (CNS) pathologies has been recognized. WWOX biallelic germline pathogenic variants have been implicated in spinocerebellar ataxia type 12 (SCAR12; MIM:614322) and in early infantile epileptic encephalopathy (EIEE28; MIM:616211). WWOX germline copy number variants have also been associated with autism spectrum disorder (ASD). All identified germline genomic variants lead to partial or complete loss of WWOX function. Importantly, large-scale genome-wide association studies have also identified WWOX as a risk gene for common neurodegenerative conditions such as Alzheimer’s disease (AD) and multiple sclerosis (MS). Thus, the spectrum of CNS disorders associated with WWOX is broad and heterogeneous, and there is little understanding of potential mechanisms at play. Exploration of gene expression databases indicates that WWOX expression is comparatively higher in the human cerebellar cortex than in other CNS structures. However, RNA in-situ hybridization data from the Allen Mouse Brain Atlas show that specific regions of the basolateral amygdala (BLA), the medial entorhinal cortex (EC), and deep layers of the isocortex can be singled out as brain regions with specific higher levels of Wwox expression. These observations are in close agreement with single-cell RNA-seq data which indicate that neurons from the medial entorhinal cortex, Layer 5 from the frontal cortex as well as GABAergic basket cells and granule cells from cerebellar cortex are the specific neuronal subtypes that display the highest Wwox expression levels. Importantly, the brain regions and cell types in which WWOX is most abundantly expressed, such as the EC and BLA, are intimately linked to pathologies and syndromic conditions in turn associated with this gene, such as epilepsy, intellectual disability, ASD, and AD. Higher Wwox expression in interneurons and granule cells from cerebellum points to a direct link to the described cerebellar ataxia in cases of WWOX loss of function. We now know that total or partial impairment of WWOX function results in a wide and heterogeneous variety of neurodegenerative conditions for which the specific molecular mechanisms remain to be deciphered. Nevertheless, these observations indicate an important functional role for WWOX in normal development and function of the CNS. Evidence also indicates that disruption of WWOX expression at the gene or protein level in CNS has significant deleterious consequences.

An epilepsy-associated ACTL6B variant captures neuronal hyperexcitability in a human induced pluripotent stem cell model.

ACTL6B is a component of the neuronal BRG1/brm‐associated factor (nBAF) complex, which is required for chromatin remodeling in postmitotic neurons. We recently reported biallelic pathogenic variants in ACTL6B in patients diagnosed with early infantile epileptic encephalopathy, subtype 76 (EIEE‐76), presenting with severe, global developmental delay, epileptic encephalopathy, cerebral atrophy, and abnormal central nervous system myelination. However, the pathophysiological mechanisms underlying their phenotype is unknown. Here, we investigate the molecular pathogenesis of ACTL6B p.(Val421_Cys425del) using in silico 3D protein modeling predictions and patient‐specific induced pluripotent stem cell‐derived neurons. We found neurons derived from EIEE‐76 patients showed impaired accumulation of ACTL6B compared to unaffected relatives, caused by reduced protein stability. Furthermore, EIEE‐76 patient‐derived neurons had dysregulated nBAF target gene expression, including genes important for neuronal development and disease. Multielectrode array system analysis unveiled elevated electrophysiological activity of EIEE‐76 patients‐derived neurons, consistent with the patient phenotype. Taken together, our findings validate a new model for EIEE‐76 and reveal how reduced ACTL6B expression affects neuronal function.

Two novel PCDH19 mutations in Russian patients with epilepsy with intellectual disability limited to females: a case report

BackgroundEpilepsy with intellectual disability limited to females (Epileptic encephalopathy, early infantile, 9; EIEE9) is a rare early infantile epileptic encephalopathy characterized by an unusual X-linked inheritance: females with heterozygous mutations are affected, while hemizygous males are not.Case presentationWe describe the clinical and molecular characteristics of 2 Russian patients with EIEE9 (females, ages 3 years and 7 years). In these patients seizures developed at the age of 3 years. Additionally, for our patients and for cases described in the literature we searched for a possible relationship between the type and localization of the mutation and the EIEE9 clinical phenotype.ConclusionsWe identified two novel PCDH19 mutations in EIEE9 patients: a missense mutation in exon 1 (c.1236C > A, p.Asp412Glu) and a frameshift in exon 3 (c.2386_2387insGTCT, p.Thr796fs). We conclude that the age of seizure onset and the presence of intellectual disability may depend not on the type and localization of PCDH19 mutations, but on the X-inactivation status. The study also highlights the need to screen for EIEE9 among young female epilepsy patients.

The phenotype and treatment of SCN2A-related developmental and epileptic encephalopathy.

We aimed to delineate the phenotypic spectrum of SCN2A-related developmental and epileptic encephalopathy (DEE) and determine the effectiveness of various treatment modalities, including sodium channel blockers and the ketogenic diet. Eleven patients with SCN2A-related DEE were included in the study. The characteristics of SCN2A mutations, electroclinical features, clinical course, and response to treatment modalities were analysed. The 11 patients were aged between 0.4 and 9.7 years. The onset of seizures ranged from neonate (six patients) to infant (four patients), to childhood (one patient). Epilepsy presented as Ohtahara syndrome, West syndrome, epilepsy of infancy with migrating focal seizures (EIMFS), and focal epilepsy in neonatal- to infantile-onset patients. The only childhood-onset patient in our study presented with focal epilepsy with autism. Neonatal-to infantile-onset patients had drug-resistant epilepsy (9/10), however, sodium channel blockers were effective in all treated patients (9/9). The ketogenic diet (6/8) and high-dose steroid treatment (4/5) were also effective. The seizures in the childhood-onset patient worsened during treatment with sodium channel blockers. All mutations in neonatal- to infantile-onset patients were missense mutations, whereas the mutation in the childhood-onset patient was a truncation mutation. These results support earlier observations regarding the epilepsy syndromes and response to antiepileptic drugs in patients with SCN2A-related DEE.

Variant-specific changes in persistent or resurgent sodium current in SCN8A-related epilepsy patient-derived neurons.

Missense variants in the SCN8A voltage-gated sodium channel gene are linked to early-infantile epileptic encephalopathy type 13, also known as SCN8A-related epilepsy. These patients exhibit a wide spectrum of intractable seizure types, severe developmental delay, movement disorders, and elevated risk of sudden unexpected death in epilepsy. The mechanisms by which SCN8A variants lead to epilepsy are poorly understood, although heterologous expression systems and mouse models have demonstrated altered sodium current properties. To investigate these mechanisms using a patient-specific model, we generated induced pluripotent stem cells from three patients with missense variants in SCN8A: p.R1872>L (Patient 1); p.V1592>L (Patient 2); and p.N1759>S (Patient 3). Using small molecule differentiation into excitatory neurons, induced pluripotent stem cell-derived neurons from all three patients displayed altered sodium currents. Patients 1 and 2 had elevated persistent current, while Patient 3 had increased resurgent current compared to controls. Neurons from all three patients displayed shorter axon initial segment lengths compared to controls. Further analyses focused on one of the patients with increased persistent sodium current (Patient 1) and the patient with increased resurgent current (Patient 3). Excitatory cortical neurons from both patients had prolonged action potential repolarization. Using doxycycline-inducible expression of the neuronal transcription factors neurogenin 1 and 2 to synchronize differentiation of induced excitatory cortical-like neurons, we investigated network activity and response to pharmacotherapies. Both small molecule differentiated and induced patient neurons displayed similar abnormalities in action potential repolarization. Patient induced neurons showed increased burstiness that was sensitive to phenytoin, currently a standard treatment for SCN8A-related epilepsy patients, or riluzole, an FDA-approved drug used in amyotrophic lateral sclerosis and known to block persistent and resurgent sodium currents, at pharmacologically relevant concentrations. Patch-clamp recordings showed that riluzole suppressed spontaneous firing and increased the action potential firing threshold of patient-derived neurons to more depolarized potentials. Two of the patients in this study were prescribed riluzole off-label. Patient 1 had a 50% reduction in seizure frequency. Patient 3 experienced an immediate and dramatic seizure reduction with months of seizure freedom. An additional patient with a SCN8A variant in domain IV of Nav1.6 (p.V1757>I) had a dramatic reduction in seizure frequency for several months after starting riluzole treatment, but then seizures recurred. Our results indicate that patient-specific neurons are useful for modelling SCN8A-related epilepsy and demonstrate SCN8A variant-specific mechanisms. Moreover, these findings suggest that patient-specific neuronal disease modelling offers a useful platform for discovering precision epilepsy therapies.

New mutations in KCNT2 gene causing early infantile epileptic encephalopathy type 57: Case study and literature review

Early infantile epileptic encephalopathy (EIEE) 57 belongs to a group of encephalopathies with early-onset and characterised by severe electroencephalogram abnormalities, seizures, developmental delay and intellectual disability. We carried out Whole Exome analysis using Next Generation Sequencing (NGS) and bioinformatic analysis performed to find mutation associated with the patient phenotypes. The effect of the mutation on protein structure analysed by PolyPhen2 and Swissmodel ExPASy. In this study, we evaluated two unrelated Turkish males diagnosed with EIEE type 57 to investigate the genetic cause of this disease. Whole exome sequencing revealed mutations in KCN2 gene, which is a member of Potassium channels (KCN) gene family associated with epileptic encephalopathies. Two mutations, c.545A>T (p.Asn182Ile and c.2638C>A (p.Leu880Met) were reported here as a novel mutation. Our findings implicate the genotype-phenotype correlation of these mutations. Furthermore, the computational analysis showed their effect on protein binding site and function suggesting their role in the development of early infantile epileptic encephalopathy 57.

Boricua Founder Variant in FRRS1L Causes Epileptic Encephalopathy With Hyperkinetic Movements.

To describe a founder mutation effect and the clinical phenotype of homozygous FRRS1L c.737_739delGAG (p.Gly246del) variant in 15 children of Puerto Rican (Boricua) ancestry presenting with early infantile epileptic encephalopathy (EIEE-37) with prominent movement disorder. EIEE-37 is caused by biallelic loss of function variants in the FRRS1L gene, which is critical for AMPA-receptor function, resulting in intractable epilepsy and dyskinesia. A retrospective, multicenter chart review of patients sharing the same homozygous FRRS1L (p.Gly246del) pathogenic variant identified by clinical genetic testing. Clinical information was collected regarding neurodevelopmental outcomes, neuroimaging, electrographic features and clinical response to antiseizure medications. Fifteen patients from 12 different families of Puerto Rican ancestry were homozygous for the FRRS1L (p.Gly246del) pathogenic variant, with ages ranging from 1 to 25 years. The onset of seizures was from 6 to 24 months. All had hypotonia, severe global developmental delay, and most had hyperkinetic involuntary movements. Developmental regression during the first year of life was common (86%). Electroencephalogram showed hypsarrhythmia in 66% (10/15), with many older children evolving into Lennox-Gastaut syndrome. Six patients demonstrated progressive volume loss and/or cerebellar atrophy on brain magnetic resonance imaging (MRI). We describe the largest cohort to date of patients with epileptic encephalopathy. We estimate that 0.76% of unaffected individuals of Puerto Rican ancestry carry this pathogenic variant due to a founder effect. Children homozygous for the FRRS1L (p.Gly246del) Boricua variant exhibit a very homogenous phenotype of early developmental regression and epilepsy, starting with infantile spasms and evolving into Lennox-Gastaut syndrome with hyperkinetic movement disorder.

Functional analysis of three Nav1.6 mutations causing early infantile epileptic encephalopathy

The voltage-gated sodium channel Nav1.6 is associated with more than 300 cases of epileptic encephalopathy. Nav1.6 epilepsy-causing mutations are spread over the entire channel's structure and only 10% of mutations have been characterized at the molecular level, with most of them being gain of function mutations. In this study, we analyzed three previously uncharacterized Nav1.6 epilepsy-causing mutations: G214D, N215D and V216D, located within a mutation hot-spot at the S3-S4 extracellular loop of Domain1. Voltage clamp experiments showed a 6–16 mV hyperpolarizing shift in the activation mid-point for all three mutants. V216D presented the largest shift along with decreased current amplitude, enhanced inactivation and a lack of persistent current. Recordings at hyperpolarized potentials indicated that all three mutants presented gating pore currents. Furthermore, trafficking experiments performed in cultured hippocampal neurons demonstrated that the mutants trafficked properly to the cell surface, with no significant differences regarding surface expression within the axon initial segment or soma compared to wild-type. These trafficking data suggest that the disease-causing consequences are due to only changes in the biophysical properties of the channel. Interestingly, the patient carrying the V216D mutation, which is the mutant with the greatest electrophysiological changes as compared to wild-type, exhibited the most severe phenotype. These results emphasize that these mutations will mandate unique treatment approaches, for normal sodium channel blockers may not work given that the studied mutations present gating pore currents. This study emphasizes the importance of molecular characterization of disease-causing mutations in order to improve the pharmacological treatment of patients.