Targeting heterozygous dominant negative variant of KCNA2 using Gapmer ASO for the treatment of drug-resistant epilepsy.

A missense mutation c.1220C>G of KCN2A gene was recently identified in an infant with epilepsy. KCNA2 encodes KV1.2 subunits that form voltage-gated potassium channels (VGKC) via tetrameric assembly. The mutation results in amino acid change P407R at the highly conserved PVP motif. Functional characterization revealed that mutant KV1.2_P407R subunits formed loss-of-function channels and suppressed both KV1.2 and KV1.1 channel activities. Hetero-tetrameric assembly of the KV1.2_P407R subunits with other neuronal voltage-gated potassium channels of Shaker subfamily could lead to general deficit of repolarizing potassium current and potentially underlie the enhanced seizure susceptibility. Indeed, expression of human KV1.2_P407R in early postnatal rat cortical neurons or genetically engineered hESC-derived neurons disclosed broadening of action potential duration and early afterdepolarization (EAD), associating with reduced potassium current. We hypothesize that Gapmer antisense oligonucleotides (ASOs) targeted to c.1220C>G mutation will selectively degrade the mutant mRNA while allowing the remaining wild-type (WT) subunits to form functional channels. As a proof of principle, delivery of Gapmer packaged in lipid nanoparticle into cortical neurons selectively suppressed KV1.2_P407R over the WT protein expression, reversing the broadening of action potential duration, abrogating the EAD and leading to overall increase in potassium current.

Molecular and Phenotypic Characterization of the RORB-Related Disorder.

BACKGROUND AND OBJECTIVES: Heterozygous variants in RAR-related orphan receptor B (RORB) have recently been associated with susceptibility to idiopathic generalized epilepsy. However, few reports have been published so far describing pathogenic variants of this gene in patients with epilepsy and intellectual disability (ID). In this study, we aimed to delineate the epilepsy phenotype associated with RORB pathogenic variants and to provide arguments in favor of the pathogenicity of variants. METHODS: Through an international collaboration, we analyzed seizure characteristics, EEG data, and genotypes of a cohort of patients with heterozygous variants in RORB. To gain insight into disease mechanisms, we performed ex vivo cortical electroporation in mouse embryos of 5 selected variants, 2 truncating and 3 missense, and evaluated on expression and quantified changes in axonal morphology. RESULTS: We identified 35 patients (17 male, median age 10 years, range 2.5-23 years) carrying 32 different heterozygous variants in RORB, including 28 single-nucleotide variants or small insertions/deletions (12 missense, 12 frameshift or nonsense, 2 splice-site variants, and 2 in-frame deletions), and 4 microdeletions; de novo in 18 patients and inherited in 10. Seizures were reported in 31/35 (89%) patients, with a median age at onset of 3 years (range 4 months-12 years). Absence seizures occurred in 25 patients with epilepsy (81%). Nineteen patients experienced a single seizure type: absences, myoclonic absences, or absences with eyelid myoclonia and focal seizures. Nine patients had absence seizures combined with other generalized seizure types. One patient had presented with absences associated with photosensitive occipital seizures. Three other patients had generalized tonic-clonic seizures without absences. ID of variable degree was observed in 85% of the patients. Expression studies in cultured neurons showed shorter axons for the 5 tested variants, both truncating and missense variants, supporting an impaired protein function. DISCUSSION: In most patients, the phenotype of the RORB-related disorder associates absence seizures with mild-to-moderate ID. In silico and in vitro evaluation of the variants in our cohort, including axonal morphogenetic experiments in cultured neurons, supports their pathogenicity, showing a hypomorphic effect.

Parents' priorities for decision-making of pediatric epilepsy treatments and perceived needs for decision support in multi-ethnic Asian clinical setting: A qualitative analysis.

OBJECTIVE: To identify parents' priorities when making a decision on genetic testing and antiseizure drug (ASD) options for pediatric epilepsy and their support needs for informed decision-making in multi-ethnic Asian clinical settings. METHODS: Qualitative in-depth interviews, using a semi-structured interview guide, were conducted with purposively selected parents of pediatric patients with newly diagnosed epilepsy or known diagnosis of epilepsy (n = 26). Interviews were audio recorded and transcribed verbatim. Thematic analysis was undertaken to generate themes. RESULTS: Parents' narratives showed difficulty assimilating information, while knowledge deficit and emotional vulnerability led parents' desire to defer a decision for testing and ASDs to mitigate decisional burden. Priorities for decisions were primarily based on intuitive ideas of the treatment's risks and benefits, yet very few could elaborate on tradeoffs between risks and efficacy. Priorities outside the purview of the healthcare team, such as children's emotional wellbeing and family burden of ASD administration, were also considered important. Authority-of-medical-professional heuristic facilitated the ASD decision for parents who preferred shared rather than sole responsibility for a decision. Importantly, parents' support needs for informed decision-making were very much related to the availability of support mechanisms in post-treatment decisions owing to perceived uncertainty of the chosen ASD. CONCLUSIONS: Findings suggest that multiple priorities influenced ASD decision process. To address support needs of parents for informed decision-making, more consideration should be given to post-treatment decision support through the provision of educational opportunities, building peer support networks, and developing a novel communication channel between healthcare providers and parents.

Single-cell transcriptomics and surface epitope detection in human brain epileptic lesions identifies pro-inflammatory signaling.

Epileptogenic triggers are multifactorial and not well understood. Here we aimed to address the hypothesis that inappropriate pro-inflammatory mechanisms contribute to the pathogenesis of refractory epilepsy (non-responsiveness to antiepileptic drugs) in human patients. We used single-cell cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) to reveal the immunotranscriptome of surgically resected epileptic lesion tissues. Our approach uncovered a pro-inflammatory microenvironment, including extensive activation of microglia and infiltration of other pro-inflammatory immune cells. These findings were supported by ligand-receptor (LR) interactome analysis, which demonstrated potential mechanisms of infiltration and evidence of direct physical interactions between microglia and T cells. Together, these data provide insight into the immune microenvironment in epileptic tissue, which may aid the development of new therapeutics.

Unique Severe HyperEkplexia-Like Apneic Events (SHELAE) Improved by High-Dose Piracetam.

Breath-holding spells are common non-epileptic events with onset between 6 months and 18 months of age that are usually triggered by minor painful events or strong emotions. Symptomatic treatments for breath-holding spells include iron supplementation, glycopyrrolate and piracetam. Hyperekplexia is a rare non-epileptic disorder characterized by generalized hypertonia and exaggerated startle. Prolonged stiffening triggered by startle can lead to desaturation, cardiac asystole and sudden infant death. It is commonly treated with Clonazepam and other anti-epileptic drugs. Piracetam has been reported to be effective in some anecdotal cases. We describe a case of an infant with frequent hyperekplexia-like breath-holding events who failed to respond adequately to glycopyrrolate, pace-maker insertion and clonazepam, who had marked improvement in his symptoms with high dose Piracetam. High dose Piracetam should be considered in infants with similar severe hyperekplexia-like/breath-holding events as it may be beneficial in ameliorating the acute and chronic course in these children.

Gene therapy restores dopamine transporter expression and ameliorates pathology in iPSC and mouse models of infantile parkinsonism.

Most inherited neurodegenerative disorders are incurable, and often only palliative treatment is available. Precision medicine has great potential to address this unmet clinical need. We explored this paradigm in dopamine transporter deficiency syndrome (DTDS), caused by biallelic loss-of-function mutations in SLC6A3, encoding the dopamine transporter (DAT). Patients present with early infantile hyperkinesia, severe progressive childhood parkinsonism, and raised cerebrospinal fluid dopamine metabolites. The absence of effective treatments and relentless disease course frequently leads to death in childhood. Using patient-derived induced pluripotent stem cells (iPSCs), we generated a midbrain dopaminergic (mDA) neuron model of DTDS that exhibited marked impairment of DAT activity, apoptotic neurodegeneration associated with TNFα-mediated inflammation, and dopamine toxicity. Partial restoration of DAT activity by the pharmacochaperone pifithrin-µ was mutation-specific. In contrast, lentiviral gene transfer of wild-type human SLC6A3 complementary DNA restored DAT activity and prevented neurodegeneration in all patient-derived mDA lines. To progress toward clinical translation, we used the knockout mouse model of DTDS that recapitulates human disease, exhibiting parkinsonism features, including tremor, bradykinesia, and premature death. Neonatal intracerebroventricular injection of human SLC6A3 using an adeno-associated virus (AAV) vector provided neuronal expression of human DAT, which ameliorated motor phenotype, life span, and neuronal survival in the substantia nigra and striatum, although off-target neurotoxic effects were seen at higher dosage. These were avoided with stereotactic delivery of AAV2.SLC6A3 gene therapy targeted to the midbrain of adult knockout mice, which rescued both motor phenotype and neurodegeneration, suggesting that targeted AAV gene therapy might be effective for patients with DTDS.

KMT2B-related disorders: expansion of the phenotypic spectrum and long-term efficacy of deep brain stimulation.

Heterozygous mutations in KMT2B are associated with an early-onset, progressive and often complex dystonia (DYT28). Key characteristics of typical disease include focal motor features at disease presentation, evolving through a caudocranial pattern into generalized dystonia, with prominent oromandibular, laryngeal and cervical involvement. Although KMT2B-related disease is emerging as one of the most common causes of early-onset genetic dystonia, much remains to be understood about the full spectrum of the disease. We describe a cohort of 53 patients with KMT2B mutations, with detailed delineation of their clinical phenotype and molecular genetic features. We report new disease presentations, including atypical patterns of dystonia evolution and a subgroup of patients with a non-dystonic neurodevelopmental phenotype. In addition to the previously reported systemic features, our study has identified co-morbidities, including the risk of status dystonicus, intrauterine growth retardation, and endocrinopathies. Analysis of this study cohort (n = 53) in tandem with published cases (n = 80) revealed that patients with chromosomal deletions and protein truncating variants had a significantly higher burden of systemic disease (with earlier onset of dystonia) than those with missense variants. Eighteen individuals had detailed longitudinal data available after insertion of deep brain stimulation for medically refractory dystonia. Median age at deep brain stimulation was 11.5 years (range: 4.5-37.0 years). Follow-up after deep brain stimulation ranged from 0.25 to 22 years. Significant improvement of motor function and disability (as assessed by the Burke Fahn Marsden's Dystonia Rating Scales, BFMDRS-M and BFMDRS-D) was evident at 6 months, 1 year and last follow-up (motor, P = 0.001, P = 0.004, and P = 0.012; disability, P = 0.009, P = 0.002 and P = 0.012). At 1 year post-deep brain stimulation, >50% of subjects showed BFMDRS-M and BFMDRS-D improvements of >30%. In the long-term deep brain stimulation cohort (deep brain stimulation inserted for >5 years, n = 8), improvement of >30% was maintained in 5/8 and 3/8 subjects for the BFMDRS-M and BFMDRS-D, respectively. The greatest BFMDRS-M improvements were observed for trunk (53.2%) and cervical (50.5%) dystonia, with less clinical impact on laryngeal dystonia. Improvements in gait dystonia decreased from 20.9% at 1 year to 16.2% at last assessment; no patient maintained a fully independent gait. Reduction of BFMDRS-D was maintained for swallowing (52.9%). Five patients developed mild parkinsonism following deep brain stimulation. KMT2B-related disease comprises an expanding continuum from infancy to adulthood, with early evidence of genotype-phenotype correlations. Except for laryngeal dysphonia, deep brain stimulation provides a significant improvement in quality of life and function with sustained clinical benefit depending on symptoms distribution.

Pro-inflammatory, IL-17 pathways dominate the architecture of the immunome in pediatric refractory epilepsy.

Drug refractory epilepsy (RE) is a chronic neurological disease with varied etiology that represents a group of patients whose seizures do not respond to anti-epileptic drugs. The immune system may have a role in seizure and epilepsy development, but the specific mechanisms of inflammation that lead to epileptogenesis and contribute to RE are unknown. Here, we used mass cytometry to comprehensively study the immune system of pediatric patients with RE and compared their immune profile and function with patients with age-matched autoimmune encephalitis (AIE) and healthy controls. Patients with RE and AIE displayed similar immune profiles overall, with changes in CD4+ and CD8+ T-cell subsets and an unbalance toward pro-inflammatory IL-17 production. In addition, patients with RE uniquely showed an altered balance in natural killer cell subsets. A systems level intercellular network analysis identified rewiring of the immune system leading to loss of inhibitory/regulatory intercellular connections and emergence of pro-inflammatory pathogenic functions in neuro-inflammatory immune-cell networks in patients with AIE and RE. These data underscore the contribution of systemic inflammation to the pathogenesis of seizures and epileptogenesis and have direct translational implications in advancing diagnostics and therapeutics design.

Clinical and molecular characterization of KCNT1-related severe early-onset epilepsy.

OBJECTIVE: To characterize the phenotypic spectrum, molecular genetic findings, and functional consequences of pathogenic variants in early-onset KCNT1 epilepsy. METHODS: We identified a cohort of 31 patients with epilepsy of infancy with migrating focal seizures (EIMFS) and screened for variants in KCNT1 using direct Sanger sequencing, a multiple-gene next-generation sequencing panel, and whole-exome sequencing. Additional patients with non-EIMFS early-onset epilepsy in whom we identified KCNT1 variants on local diagnostic multiple gene panel testing were also included. When possible, we performed homology modeling to predict the putative effects of variants on protein structure and function. We undertook electrophysiologic assessment of mutant KCNT1 channels in a xenopus oocyte model system. RESULTS: We identified pathogenic variants in KCNT1 in 12 patients, 4 of which are novel. Most variants occurred de novo. Ten patients had a clinical diagnosis of EIMFS, and the other 2 presented with early-onset severe nocturnal frontal lobe seizures. Three patients had a trial of quinidine with good clinical response in 1 patient. Computational modeling analysis implicates abnormal pore function (F346L) and impaired tetramer formation (F502V) as putative disease mechanisms. All evaluated KCNT1 variants resulted in marked gain of function with significantly increased channel amplitude and variable blockade by quinidine. CONCLUSIONS: Gain-of-function KCNT1 pathogenic variants cause a spectrum of severe focal epilepsies with onset in early infancy. Currently, genotype-phenotype correlations are unclear, although clinical outcome is poor for the majority of cases. Further elucidation of disease mechanisms may facilitate the development of targeted treatments, much needed for this pharmacoresistant genetic epilepsy.

TBC1D24 Mutations in a Sibship with Multifocal Polymyoclonus.

BACKGROUND: Advances in molecular genetic technologies have improved our understanding of genetic causes of rare neurological disorders with features of myoclonus. CASE REPORT: A family with two affected siblings, presenting with multifocal polymyoclonus and neurodevelopmental delay, was recruited for whole-exome sequencing following unyielding diagnostic neurometabolic investigations. Compound heterozygous mutations in TBC1D24, a gene previously associated with various epilepsy phenotypes and hearing loss, were identified in both siblings. The mutations included a missense change c.457G>A (p.Glu157Lys), and a novel frameshift mutation c.545del (p.Thr182Serfs*6). DISCUSSION: We propose that TBC1D24-related diseases should be in the differential diagnosis for children with polymyoclonus.

Mutations in the histone methyltransferase gene KMT2B cause complex early-onset dystonia.

Histone lysine methylation, mediated by mixed-lineage leukemia (MLL) proteins, is now known to be critical in the regulation of gene expression, genomic stability, cell cycle and nuclear architecture. Despite MLL proteins being postulated as essential for normal development, little is known about the specific functions of the different MLL lysine methyltransferases. Here we report heterozygous variants in the gene KMT2B (also known as MLL4) in 27 unrelated individuals with a complex progressive childhood-onset dystonia, often associated with a typical facial appearance and characteristic brain magnetic resonance imaging findings. Over time, the majority of affected individuals developed prominent cervical, cranial and laryngeal dystonia. Marked clinical benefit, including the restoration of independent ambulation in some cases, was observed following deep brain stimulation (DBS). These findings highlight a clinically recognizable and potentially treatable form of genetic dystonia, demonstrating the crucial role of KMT2B in the physiological control of voluntary movement.

RARS2 mutations in a sibship with infantile spasms.

Pontocerebellar hypoplasia is a group of heterogeneous neurodevelopmental disorders characterized by reduced volume of the brainstem and cerebellum. We report two male siblings who presented with early infantile clonic seizures, and then developed infantile spasms associated with prominent isolated cerebellar hypoplasia/atrophy on magnetic resonance imaging (MRI). Using whole exome sequencing techniques, both were found to be compound heterozygotes for one previously reported and one novel mutation in the gene encoding mitochondrial arginyl-tRNA synthetase 2 (RARS2). Mutations in this gene have been classically described in pontocerebellar hypoplasia type six (PCH6), a phenotype characterized by early (often intractable) seizures, profound developmental delay, and progressive pontocerebellar atrophy. The electroclinical spectrum of PCH6 is broad and includes a number of seizure types: myoclonic, generalized tonic-clonic, and focal clonic seizures. Our report expands the characterization of the PCH6 disease spectrum and presents infantile spasms as an associated electroclinical phenotype.

Delineation of the movement disorders associated with FOXG1 mutations.

OBJECTIVE: The primary objective of this research was to characterize the movement disorders associated with FOXG1 mutations. METHODS: We identified patients with FOXG1 mutations who were referred to either a tertiary movement disorder clinic or tertiary epilepsy service and retrospectively reviewed medical records, clinical investigations, neuroimaging, and available video footage. We administered a telephone-based questionnaire regarding the functional impact of the movement disorders and perceived efficacy of treatment to the caregivers of one cohort of participants. RESULTS: We identified 28 patients with FOXG1 mutations, of whom 6 had previously unreported mutations. A wide variety of movement disorders were identified, with dystonia, choreoathetosis, and orolingual/facial dyskinesias most commonly present. Ninety-three percent of patients had a mixed movement disorder phenotype. In contrast to the phenotype classically described with FOXG1 mutations, 4 patients with missense mutations had a milder phenotype, with independent ambulation, spoken language, and normocephaly. Hyperkinetic involuntary movements were a major clinical feature in these patients. Of the symptomatic treatments targeted to control abnormal involuntary movements, most did not emerge as clearly beneficial, although 4 patients had a caregiver-reported response to levodopa. CONCLUSIONS: Abnormal involuntary movements are a major feature of FOXG1 mutations. Our study delineates the spectrum of movement disorders and confirms an expanding clinical phenotype. Symptomatic treatment may be considered for severe or disabling cases, although further research regarding potential treatment strategies is necessary.

Improving diagnosis and broadening the phenotypes in early-onset seizure and severe developmental delay disorders through gene panel analysis.

BACKGROUND: We sought to investigate the diagnostic yield and mutation spectrum in previously reported genes for early-onset epilepsy and disorders of severe developmental delay. METHODS: In 400 patients with these disorders with no known underlying aetiology and no major structural brain anomaly, we analysed 46 genes using a combination of targeted sequencing on an Illumina MiSeq platform and targeted, exon-level microarray copy number analysis. RESULTS: We identified causative mutations in 71/400 patients (18%). The diagnostic rate was highest among those with seizure onset within the first two months of life (39%), although overall it was similar in those with and without seizures. The most frequently mutated gene was SCN2A (11 patients, 3%). Other recurrently mutated genes included CDKL5, KCNQ2, SCN8A (six patients each), FOXG1, MECP2, SCN1A, STXBP1 (five patients each), KCNT1, PCDH19, TCF4 (three patients each) and ATP1A3, PRRT2 and SLC9A6 (two patients each). Mutations in EHMT1, GABRB3, LGI1, MBD5, PIGA, UBE3A and ZEB2 were each found in single patients. We found mutations in a number of genes in patients where either the electroclinical features or dysmorphic phenotypes were atypical for the identified gene. In only 11 cases (15%) had the clinician sufficient certainty to specify the mutated gene as the likely cause before testing. CONCLUSIONS: Our data demonstrate the considerable utility of a gene panel approach in the diagnosis of patients with early-onset epilepsy and severe developmental delay disorders., They provide further insights into the phenotypic spectrum and genotype-phenotype correlations for a number of the causative genes and emphasise the value of exon-level copy number testing in their analysis.

GABRB3 mutations: a new and emerging cause of early infantile epileptic encephalopathy.

The gamma-aminobutyric acid type A receptor ß3 gene (GABRB3) encodes the ß3-subunit of the gamma-aminobutyric acid type A (GABAA ) receptor, which mediates inhibitory signalling within the central nervous system. Recently, GABRB3 mutations have been identified in a few patients with infantile spasms and Lennox-Gastaut syndrome. We report the clinical and electrographic features of a novel case of GABRB3-related early-onset epileptic encephalopathy. Our patient presented with neonatal hypotonia and feeding difficulties, then developed pharmacoresistant epileptic encephalopathy, characterized by multiple seizure types from 3 months of age. Electroencephalography demonstrated ictal generalized and interictal multifocal epileptiform abnormalities. Using a SureSelectXT custom multiple gene panel covering 48 early infantile epileptic encephalopathy/developmental delay genes, a novel de novo GABRB3 heterozygous missense mutation, c.860C>T (p.Thr287Ile), was identified and confirmed on Sanger sequencing. GABRB3 is an emerging cause of early-onset epilepsy. Novel genetic technologies, such as whole-exome/genome sequencing and multiple gene panels, will undoubtedly identify further cases, allowing more detailed electroclinical delineation of the GABRB3-related genotypic and phenotypic spectra.

Severe infantile epileptic encephalopathy due to mutations in PLCB1: expansion of the genotypic and phenotypic disease spectrum.

Homozygous deletions of chromosome 20p12.3, disrupting the promoter region and first three coding exons of the phospholipase C ß1 gene (PLCB1), have previously been described in two reports of early infantile epileptic encephalopathy (EIEE). Both children were born to consanguineous parents, one presented with infantile spasms, the other with migrating partial seizures of infancy. We describe an infant presenting with severe intractable epilepsy (without a specific EIEE electroclinical syndrome diagnosis) and neurodevelopmental delay associated with compound heterozygous mutations in PLCB1. A case note review and molecular genetic investigations were performed for a child, approximately 10 months of age, admitted to Johns Hopkins University Hospital for developmental delay and new-onset seizures. The patient presented at 6 months of age with developmental delay, followed by the onset of intractable, focal, and generalized seizures associated with developmental regression from 10 months of age. Presently, at 2 years of age, the child has severe motor and cognitive delays. Diagnostic microarray revealed a heterozygous 476kb deletion of 20p12.3 (encompassing PLCB1), which was also detected in the mother. The genomic breakpoints for the heterozygous deletion were determined. In order to investigate the presence of a second PLCB1 mutation, direct Sanger sequencing of the coding region and flanking intronic regions was undertaken, revealing a novel heterozygous intron 1 splice site variant (c.99+1G>A) in both the index individual and the father. Advances in molecular genetic testing have greatly improved diagnostic rates in EIEE, and this report further confirms the important role of microarray investigation in this group of disorders. PLCB1-EIEE is now reported in a number of different EIEE phenotypes and our report provides further evidence for phenotypic pleiotropy encountered in early infantile epilepsy syndromes.