Background and ObjectivesDevelopmental and epileptic encephalopathies (DEEs) with early burst-suppression EEG (EIDEE-BS) are among the most severe neonatal epileptic syndromes, typically presenting in the first months of life with refractory seizures and profound neurodevelopmental impairment. Although variants in the KCNQ2, STXBP1, and SCN2A genes are recognized as major causes, the full genetic spectrum remains uncertain. We aimed to delineate the electroclinical characteristics, genetic etiologies, and long-term outcomes in a large MRI-negative EIDEE-BS cohort.MethodsWe retrospectively analyzed 110 patients with BS EEG enrolled from a database of 1,540 individuals with suspected genetic epilepsies (2008-2023). Clinical, EEG, and genetic data were systematically collected. Patients were stratified into 4 groups: KCNQ2, STXBP1, "other pathogenic variants," and "without a genetic diagnosis." EEG traces were reviewed independently, and outcomes were assessed through long-term follow-up.ResultsPathogenic or likely pathogenic variants were identified in 62.7% of patients and involved 23 genes, including 2 copy number variants. KCNQ2 (n = 24) and STXBP1 (n = 16) accounted for one-third of diagnoses, whereas SCN2A (n = 3) and KCNT1 (n = 2) were less frequent. In KCNQ2 cases, seizures and BS onset occurred earlier than in STXBP1 cases: mean 2 days vs 6 weeks for seizures and 3 days vs 2 months for BS, respectively. A typical BS pattern (bursts longer than suppressions) strongly correlated with KCNQ2 and STXBP1 variants. Novel associations were found with DPM1, GRIN2A, KCNT2, PIGO, PURA, WWOX, and candidate genes (KMT2E, SNAP25, and SYT1). Most variants were de novo heterozygous; however, recessive and X-linked inheritance patterns were also observed. Mortality was high (25%), primarily from status epilepticus and complications of severe disability. Most patients (72.5%) had persistent seizures at follow-up (a mean of 6.5 years), as well as profound intellectual disabilities, irrespective of genotype.DiscussionThis large series highlights the strong monogenic basis of EIDEE-BS. KCNQ2, STXBP1, and SCN2A were the most commonly affected genes. Early EEG features, particularly BS timing and morphology, can help anticipate the underlying genotype and guide precision therapy, including the early use of sodium channel blockers in selected cases. These findings support recent ILAE reclassification efforts and underscore the importance of comprehensive genomic testing for improved diagnosis and counseling.

Small nuclear RNAs (snRNAs) are essential components of the spliceosome. De novo variants in snRNA genes RNU4-2 (ReNU syndrome), RNU5B-1 and RNU2-2 have been linked to dominant neurodevelopmental disorders (NDDs), revealing a large unexpected contribution of noncoding RNA genes to genetic diseases. Here, through international collaborations, we analyze systematically 200 potentially functional snRNA genes in a French cohort of 34,329 people with rare disorders. We report RNU2-2 variants in 141 individuals, including 35 with recurrent dominant pathogenic variants and 91 affected members from 73 families with biallelic variants. Recessive RNU2-2 NDD is at least twice as frequent as the dominant form and often involves a de novo variant in trans with an inherited allele, consistent with the high mutability of snRNA genes. Dominant and recessive RNU2-2 NDDs share overlapping clinical features, with frequent epilepsy. Blood transcriptomics and DNA methylation analyses revealed subtle, variant-specific effects on splicing and episignatures. Our results support a gradient-of-impact model bridging dominant and recessive inheritance, and establish RNU2-2 variants as a principal contributor to NDDs, nearly as prevalent as ReNU syndrome.

Rett syndrome (RTT) is a severe X-linked neurodevelopmental disorder due to pathogenic variants in the methyl CpG binding protein 2 gene (MECP2). The discovery that deficits resulting from Mecp2 loss are reversible in mice has increased interest in gene therapy as a potential cure for RTT. We have previously evaluated the efficacy of a self-complementary AAV9 vector expressing a codon-optimized version of Mecp2 (scAAV9-MCO) delivered via a systemic approach in early symptomatic Mecp2-knock-out male (KO) mice. In the present study, focused ultrasound (FUS) was used to transiently disrupt the blood-brain barrier (BBB) in a RTT mouse model, thereby facilitating enhanced AAV delivery to the central nervous system (CNS). Our findings demonstrate that scAAV9-MCO administration, when combined with FUS, significantly improves survival, body weight, respiratory function, and locomotor activity, while restoring the excitatory-inhibitory synaptic balance in hippocampal neurons in treated KO mice relative to untreated animals. Quantification of the brain infection level revealed that 20-40% of cells are Mecp2-positive in the brain of KO mice following the treatment with scAAV9-MCO and FUS. This is a significant improvement compared to prior results without FUS. The evaluation of the protein levels indicates a possible overdose of Mecp2 protein in the brain cells. Nevertheless, these results demonstrate that using FUS following systemic administration of an AAV9 vector represents a significant improvement over classical gene therapy protocol for RTT.

BACKGROUND AND OBJECTIVES:Developmental and epileptic encephalopathies (DEEs) with early burst-suppression EEG (EIDEE-BS) are among the most severe neonatal epileptic syndromes, typically presenting in the first months of life with refractory seizures and profound neurodevelopmental impairment. Although variants in the KCNQ2, STXBP1, and SCN2A genes are recognized as major causes, the full genetic spectrum remains uncertain. We aimed to delineate the electroclinical characteristics, genetic etiologies, and long-term outcomes in a large MRI-negative EIDEE-BS cohort. METHODS:We retrospectively analyzed 110 patients with BS EEG enrolled from a database of 1,540 individuals with suspected genetic epilepsies (2008-2023). Clinical, EEG, and genetic data were systematically collected. Patients were stratified into 4 groups: KCNQ2, STXBP1, "other pathogenic variants," and "without a genetic diagnosis." EEG traces were reviewed independently, and outcomes were assessed through long-term follow-up. RESULTS:Pathogenic or likely pathogenic variants were identified in 62.7% of patients and involved 23 genes, including 2 copy number variants. KCNQ2 (n = 24) and STXBP1 (n = 16) accounted for one-third of diagnoses, whereas SCN2A (n = 3) and KCNT1 (n = 2) were less frequent. In KCNQ2 cases, seizures and BS onset occurred earlier than in STXBP1 cases: mean 2 days vs 6 weeks for seizures and 3 days vs 2 months for BS, respectively. A typical BS pattern (bursts longer than suppressions) strongly correlated with KCNQ2 and STXBP1 variants. Novel associations were found with DPM1, GRIN2A, KCNT2, PIGO, PURA, WWOX, and candidate genes (KMT2E, SNAP25, and SYT1). Most variants were de novo heterozygous; however, recessive and X-linked inheritance patterns were also observed. Mortality was high (25%), primarily from status epilepticus and complications of severe disability. Most patients (72.5%) had persistent seizures at follow-up (a mean of 6.5 years), as well as profound intellectual disabilities, irrespective of genotype. DISCUSSION:This large series highlights the strong monogenic basis of EIDEE-BS. KCNQ2, STXBP1, and SCN2A were the most commonly affected genes. Early EEG features, particularly BS timing and morphology, can help anticipate the underlying genotype and guide precision therapy, including the early use of sodium channel blockers in selected cases. These findings support recent ILAE reclassification efforts and underscore the importance of comprehensive genomic testing for improved diagnosis and counseling.

Pathogenic KCNQ2 variants are the most common genetic cause of neonatal-onset epilepsies, with phenotypes ranging from self-limited (familial) neonatal epilepsy (SeL(F)NE) to severe developmental and epileptic encephalopathy (KCNQ2-DEE). Sodium channel blockers (SCBs) have shown promise for seizure control in these disorders, but their impact on neurodevelopmental outcomes and possible relationship with timing of initiation remain incompletely understood. We leveraged a large, multicentre international cohort comprising 282 individuals with pathogenic KCNQ2 variants to retrospectively assess the effectiveness of antiseizure medications (ASMs), particularly SCBs, on seizure control and neurodevelopment. Individuals were grouped according to the predicted variant-specific functional effects: loss-of-function (LOF) variants known to be associated with SeL(F)NE or DEE respectively, and gain-of-function (GOF) variants. Epilepsy course, ASM effectiveness, and neurodevelopmental milestones were systematically collected and analysed, including time-to-event and adjusted outcome analyses. SCBs, especially carbamazepine (CBZ) and oxcarbazepine (OXC), emerged as the most effective ASMs in both LOF groups. In LOF KCNQ2-DEE, time-to-event analyses showed that early SCB initiation (≤1 month) was associated with earlier seizure offset. Early SCB initiation was also associated with significantly more favourable neurodevelopmental outcomes, including higher rates of attaining major motor milestones. This association remained significant after adjustment for seizure control by 1 month and total ASM burden. Considerable phenotypic variability persisted, with some individuals experiencing severe impairment despite early seizure control and SCB initiation, suggesting that variant severity and additional genetic or biological modifiers contribute to outcome heterogeneity.Our results support the use of SCBs, particularly CBZ and OXC, as first-line therapy in (LOF) KCNQ2-DEE and SeL(F)NE. Earlier SCB initiation was associated with earlier seizure offset and more favourable developmental outcomes, underscoring the importance of early genetic diagnosis and timely SCB therapy. We however emphasise that early treatment is not universally transformative and further prospective work, including exploration of targeted therapies and standardised neurodevelopmental assessments, is needed to optimise long-term outcomes in this heterogeneous population.

Background: Pathogenic KCNQ2 variants are the most common genetic cause of neonatal-onset epilepsies, with phenotypes ranging from self-limited (familial) neonatal epilepsy (SeL(F)NE) to severe developmental and epileptic encephalopathy (KCNQ2-DEE). Sodium channel blockers (SCBs) have shown promise for seizure control in these disorders, but their impact on neurodevelopmental outcomes and possible relationship with timing of initiation remain incompletely understood. Methods: We leveraged a large, multicentre international cohort comprising 282 individuals with KCNQ2 pathogenic variants to retrospectively assess the effectiveness of antiseizure medications (ASMs), particularly SCBs, on seizure control and neurodevelopment. Individuals were grouped according to the predicted variant-specific functional effects: loss-of-function (LOF) variants known to be associated with SeL(F)NE or DEE respectively, and gain-of-function (GOF) variants. Epilepsy course, ASM effectiveness, and neurodevelopmental milestones were systematically collected and analysed. Results: SCBs, especially carbamazepine (CBZ) and oxcarbazepine (OXC), emerged as the most effective ASMs in both LOF groups. In LOF KCNQ2-DEE, early SCB initiation within the first month of life was associated with significantly more favourable neurodevelopmental trajectories, including higher rates of achievement of major motor milestones. Early seizure freedom itself was a strong predictor of improved neurodevelopment, with the positive effect of SCBs likely mediated by their ability to control seizures. However, considerable phenotypic variability persisted, with some individuals experiencing severe impairment despite early seizure control and SCB initiation. Variant severity and possible genetic modifiers likely contribute to this heterogeneity, underscoring the need for precision therapies beyond nonspecific ASM approaches. Conclusion: Our results strongly support the use of SCBs as first-line therapy in (LOF) KCNQ2-DEE and SeL(F)NE due to their high effectiveness. Moreover, SCBs appear most beneficial when initiated during the neonatal period, with earlier treatment linked to earlier seizure offset and better developmental outcomes. These results highlight the importance of early genetic diagnosis and timely SCB therapy, and support CBZ or OXC as first-line agents. We however emphasise that early treatment is not universally transformative, and further work, including exploration of targeted therapies but also standardised neurodevelopmental assessments, is needed to optimise long-term outcomes in this heterogeneous population. ### Competing Interest Statement S.W. received consultancy fees from UCB, Xenon Pharmaceuticals, Lundbeck, Knopp Biosciences, Encoded Therapeutics, Angelini Pharma, and Roche. C.F. has served on scientific advisory board for longboard pharmaceuticals and biocodex and has received speaker honoraria from Nutricia, UCB, and Jazz Pharmaceuticals. S.A. is Deputy Editor for Epilepsia. He has received personal fees for lectures or advice from: Biocodex, Eisai, Encoded, GRIN therapeutics, Jazz Pharmaceuticals, Longboard, Lundbeck, Neuraxpharm, Nutricia, Mosaica, Proveca, Servier, Stoke, Stream neuroscience, UCB Pharma. He has been investigators for: Eisai, Lundbeck, Proveca, Takeda, UCB Pharma. I.E.S. has served on scientific advisory boards for Biocodex, BioMarin, CAMP4 Therapeutics, Chiesi, Eisai, Encoded Therapeutics, Knopp Biosciences, Longboard Pharmaceuticals, Mosaica Therapeutics, Takeda Pharmaceuticals, UCB; has received speaker honoraria from Akumentis, Biocodex, BioMarin, Chiesi, Eisai, GlaxoSmithKline, Liva Nova, Nutricia, Stoke Therapeutics, Zuellig Pharma; has received funding for travel from Biocodex, BioMarin, Eisai, Encoded Therapeutics, GlaxoSmithKline, Stoke Therapeutics, UCB; has served as an investigator for Anavex Life Sciences, Biohaven Ltd, Bright Minds Biosciences, Cerebral Therapeutics, Cerecin Inc, Cereval Therapeutics, Encoded Therapeutics, EpiMinder Inc, ES-Therapeutics, GW Pharma, Longboard Pharmaceuticals, Marinus, Neuren Pharmaceuticals, Neurocrine BioSciences, Ovid Therapeutics, Praxis Precision Medicines, Shanghai Zhimeng Biopharma, SK Life Science, Supernus Pharmaceuticals, Takeda Pharmaceuticals, UCB, Ultragenyx, Xenon Pharmaceuticals, Zogenix, Zynerba; and has consulted for Atheneum Partners, Biohaven Pharmaceuticals, Care Beyond Diagnosis, Cerecin Inc, Eisai, Epilepsy Consortium, Longboard Pharmaceuticals, Praxis, Stoke Therapeutics, UCB, Zynerba Pharmaceuticals; and is a Non-Executive Director of Bellberry Ltd and a Director of the Australian Academy of Health and Medical Sciences. She may accrue future revenue on pending patent WO61/010176 (filed: 2008): Therapeutic Compound; has a patent for SCN1A testing held by Bionomics Inc and licensed to various diagnostic companies; has a patent molecular diagnostic/theranostic target for benign familial infantile epilepsy (BFIE) [PRRT2] 2011904493 & 2012900190 and PCT/AU2012/001321 (TECH ID:2012-009). The remaining authors report no competing interests. ### Funding Statement C.M. received funding from University of Antwerp-BOF (FFB200262). S.W. received funding from Fonds Wetenschappelijk Onderzoek (FWO 1861424N), GSKE - UCB Award, European Partnership for Personalized Medicine (EPPerMed BEATKCNQ), KCNQ2e.v. L.V. and S.W. received funding from the European Joint Programme on Rare Disease JTC 2020 (TreatKCNQ). L.V. recieved funding from the Agence Nationale de la Recherche (ANR 19-CE17-0018-02). M.M. was supported by Aix Marseille Univ, Agence Nationale de la Recherche (ANR 19‐CE17‐0018‐02). A.T.G.C received funding from the National Health and Medical Research Council (NHMRC) Postgraduate Scholarship, Australia. E.C.C. received funding from the Jack Pribaz Foundation, the KCNQ2 Cure Alliance, the Miles Family Fund, and the parents of Raz Fisher. This work was supported by funding from the Australian National Health and Medical Research Council (GNT1091593, GNT1172897, GNT2006841, GNT2010562, GNT2033247) and Medical Research Future Fund Australia (GNT2007707). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Informed consent for participation and publication was obtained from all parents or legal guardians according to the Declaration of Helsinki. The study was approved by the Human Research Ethics Committees of the University Hospital of Antwerp (Belgium, number: 20/50/683) and the Committee for the Protection of Persons (Comite de Protection des Personnes Sud-Est III, France, IDRCB: 2020-A01363-36). Data are reported in line with the Strengthening Reporting of Observational Studies in Epidemiology (STROBE) statement. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data supporting the findings of this study are available to those eligible upon request to the corresponding author.

ObjectiveCarbamazepine is the first line treatment for patients affected by KCNQ2 developmental and epileptic encephalopathy. It is efficient to reduce or stop seizures in this context. However, its effect on the neurodevelopmental outcomes is debated. The aim of this study was to evaluate the efficacy of long-term oral administration of carbamazepine in a mouse model of Kcnq2 dysfunction.MethodsMice were treated at weaning and during 70 days. The impact on seizures was measured, and blood samples were collected every week. At 3 months of age, all mice were tested using the Water T-maze and Barnes maze tests to evaluate their cognitive abilities. Brain tissue was collected to measure carbamazepine and carbamazepine-epoxide concentrations.ResultsAfter 70 days of carbamazepine treatment, the impact on seizures was strong in the Kcnq2-DEE mice, with 1 out of 12 treated knock-in mice having a seizure compared to 8 out of 13 mice receiving the vehicle. Carbamazepine efficacy on seizures was progressive and correlated to an accumulation of carbamazepine-epoxide in the brain. The cognitive abilities of treated knock-in mice at 3 months of age were similar to those of wild-type mice.SignificanceIn addition to validating this knock-in model as a model of anticonvulsant efficacy, these results reveal that carbamazepine-epoxide accumulates in the brain when given over a long period of time. They also show that chronic treatment with carbamazepine strongly impacts cognitive abilities in a mouse model of Kcnq2-DEE, questioning current treatment strategies in human patients.Plain Language SummaryThis study evaluated the long-term effects of a treatment with an antiepileptic drug called carbamazepine (CBZ). It was performed in a mouse model of a severe form of genetic epilepsy. The results showed that a chronic treatment with CBZ effectively reduced seizures. Treated mice also showed improved cognitive abilities. An accumulation of a modified form of CBZ was measured in the brain of the treated animals. These findings call for a reevaluation of the long-term effects of CBZ treatment in humans, as the animal data suggest potential beneficial effects that may not yet be fully appreciated in clinical practice.

Variants in spliceosomal small nuclear RNA (snRNA) genes RNU4-2 (ReNU syndrome), RNU5B-1, and RNU2-2 have recently been linked to dominant neurodevelopmental disorders (NDDs), revealing a major, previously overlooked role for noncoding snRNAs in human disease. Here, we systematically analysed 200 potentially functional snRNA genes in a French cohort comprising 26,911 individuals with rare disorders and through international collaborations. We identify de novo and biallelic variants in RNU2-2 associated with both dominant and recessive NDDs in 126 individuals from 108 unrelated families. Recessive RNU2-2 NDD is at least twice as frequent as the dominant NDD caused by n.4G>A and n.35A>G, and often arises from a de novo variant in trans with an inherited allele, reflecting the high mutability of snRNA genes. Dominant and recessive RNU2-2-NDDs share overlapping clinical features with frequent epilepsy. Blood transcriptomics and DNA methylation analyses revealed subtle, variant-specific effects on splicing and episignatures. Our findings support a gradient-of-impact model and a continuum between dominant and recessive inheritance, establishing RNU2-2 variants as a frequent cause of NDDs, nearly as prevalent as ReNU syndrome.

Pathogenic variants in gamma-aminobutyric acid type A (GABAA) receptor subunit genes are increasingly associated with epilepsy and neurodevelopmental disorders. Pathogenic variants in GABRA2, encoding the alpha-2 subunit of GABAA receptors, have been recently reported. This study aims to better delineate the phenotypic spectrum of GABRA2 pathogenic variants. We conducted a retrospective multicenter study, analyzing six new patients with GABRA2 pathogenic variants identified through a French national collaboration. Clinical, electroencephalographic (EEG), and genetic data were reviewed alongside a literature analysis of eight previously reported cases. Two distinct electroclinical phenotypes were identified. The most severe, in four of six patients, featured early infantile developmental and epileptic encephalopathy with an EEG pattern of rapid rhythms suggestive of GABAergic hyperactivity. The milder phenotype, in two of six patients, included later onset, drug-responsive epilepsy with moderate developmental delay. A literature review confirmed these phenotypes and supported genotype-phenotype correlations, with transmembrane domain variants more frequently associated with severe phenotypes. This study refines the phenotypic spectrum of GABRA2-related disorders, highlighting two distinct electroclinical phenotypes. The identification of a recognizable EEG pattern of unusual rapid rhythms for age may be a biomarker for early diagnosis of a severe phenotype and suggests a potential underlying gain-of-function mechanism, to be confirmed by functional studies.

Background KCNQ2-developmental and epileptic encephalopathy (KCNQ2-DEE) is a severe neurodevelopmental disorder (NDD) characterised by early-life seizures but persistent cognitive impairment. The absence of early, quantifiable preclinical biomarkers for neurodevelopmental dysfunction limits the evaluation of new treatments. We hypothesise that key brain maturation processes are altered early in disease development and could serve as biomarkers for neurodevelopmental dysfunction. Methods We performed longitudinal in-vivo brain imaging in 37 kcnq2Thr274Met/+ (KI) mice and 31 wild-type (WT) controls at three developmental stages: infancy (P14-21), juvenile (P32-42), and adulthood (P83-106). Resting-state functional MRI (rs-fMRI) assessed functional connectivity (FC), [18F]SynVesT-1 PET measured synaptic density, and diffusion tensor imaging (DTI) evaluated white and grey matter microstructure. Linear mixed models with Bonferroni correction were used to analyse genotype-by-age interactions across brain regions. Findings At infant age, KI mice showed increased FC relative to WT, particularly within the default mode-like network (DMLN). During the juvenile stage, KI mice exhibited modest elevated synaptic density across brain regions, most notably in the cerebellum. By adulthood, KI mice displayed reduced FC, especially within the DMLN, compared to WT. No significant microstructural genotype-by-age interactions were found. Interpretation KCNQ2-DEE disrupts neurodevelopment, with early hyperconnectivity and delayed synaptic pruning transitioning to adult hypoconnectivity. While this pattern is too subtle to use as a standalone biomarker, these findings establish a foundation for their use in longitudinal preclinical research targeting early therapeutic intervention. Funding Supported by the University of Antwerp, Fonds Wetenschappelijk Onderzoek, the Queen Elisabeth Medical Foundation, the European Joint Programme on Rare Disease, and Fondation Lejeune.

BACKGROUND:Epileptic disorders are a heterogeneous group of neurological conditions, with many cases linked to monogenic causes, particularly in developmental and epileptic encephalopathies (DEE). Identifying pathogenic variants aids treatment, prognosis, and family planning. In France, genetic testing is coordinated through the EpiGene network. METHODS:We analyzed clinical and genetic data from 2563 epilepsy patients referred to four diagnostic labs (2016-2023). Epilepsy syndromes were classified via pre-test questionnaires, and genotyping used various gene panels, including a 68-gene core panel. Multivariate logistic regression assessed diagnostic rates and genotype-phenotype correlations. RESULTS:Overall, 27.0% of patients had pathogenic/likely pathogenic variants, mainly within the core panel (24%). SCN1A and KCNQ2 were the most frequently mutated genes. Diagnostic yield varied by syndrome, with Dravet Syndrome Spectrum (DSS) and early-infantile DEE (EIDEE) showing the highest rates (41% and 34%, respectively). Genetic heterogeneity differed across syndromes, from DSS (predominantly SCN1A) to Infantile Epileptic Spasms Syndrome (IESS, 12%), involving ≥ 26 genes. Outside DEE, self-limited neonatal epilepsy (SeLNE) had the highest yield (50%). Earlier seizure onset was associated with a higher likelihood of a positive molecular diagnosis, whereas intellectual disability severity and drug resistance were not independently predictive of diagnostic outcome. Genotype-phenotype correlations highlighted that objective clinical data (e.g., age of onset) can outperform syndrome labels (e.g., EIDEE) in predicting diagnosis. CONCLUSION:This large cohort study refines the genetic landscape of epilepsy, informs classification challenges, and enhances genetic testing strategies, ultimately improving patient care and future research directions.

The fibroblast growth factor 12 (FGF12) gene encodes a protein interacting with voltage-gated sodium channels. Two variants, p.(Arg52His) and p.(Gly50Ser), have repeatedly been associated with developmental and epileptic encephalopathy-47 (DEE47; Mendelian Inheritance in Man #617166) with poor outcome. We aim to refine the electroclinical phenotype and outcomes of 10 unpublished patients (2-38 years old) with these recurrent pathogenic variants in the FGF12 gene without DEE (p.[Arg52His], n = 4; p.[Gly50Ser], n = 6). The patients with p.(Gly50Ser) showed later and more explosive epilepsy onset, whereas p.(Arg52His) cases had gradual onset. All developed epilepsy before 5 months, with 70% achieving seizure remission by 6 months with antiseizure medication (ASM), leading to good neurodevelopmental outcomes (median follow-up = 6.8 years). In contrast, the patients with mild intellectual disability had persistent epilepsy despite ASM. Additionally, patients with favorable neurodevelopmental outcomes and FGF12 pathogenic variants showed no signs of cerebellar atrophy. Moreover, we did not find a clear correlation between treatment with sodium channel blockers, its timing, and neurodevelopmental outcome. Here, we expand the phenotypic spectrum of FGF12 pathogenic variants and underscore cases with favorable neurodevelopmental outcomes.

OBJECTIVE:Neonatal seizures initiate the onset of epilepsy in less than 20% of cases. Establishing accurate and prompt diagnosis for precision medicine, offering tailored care, and informing families about neurodevelopmental prognosis represents a significant challenge. We aim to describe the natural history of drug-resistant epilepsy and negative brain MRI with neonatal onset, and to identify predictors of neurodevelopmental outcomes. METHODS:We retrospectively analyzed demographic, clinical, electroencephalogram (EEG), and genetic data from neonates with epilepsy onset before 1 month of age, with no provoked cause, and a normal brain MRI, followed at a tertiary center from 2000 to 2020. Neonates with self-limited epilepsy (SLE) or those responding to phenobarbital without later epilepsy were excluded. RESULTS:Among 56 patients, 60% had a genetic etiology (KCNQ2, STXBP1, KCNT1, others). Most (96%) developed intellectual disability (ID); moderate ID without cerebral palsy (CP) was recorded in 11, and profound intellectual and multiple disabilities (PIMD) in 42. Only two patients had a favorable neurodevelopmental outcome without intellectual disability. An abnormal neurological exam at epilepsy onset was the sole risk factor for future PIMD. SIGNIFICANCE:Neonatal-onset pharmacoresistant epilepsies with a normal brain MRI are predominantly monogenic and lead to poor neurodevelopmental outcomes. An abnormal initial neurodevelopmental assessment predicts future PIMD. PLAIN LANGUAGE SUMMARY:Our study found that epilepsy starting in the neonatal period is often linked to a strong genetic component. The prognosis is generally poor, with frequent neurodevelopmental delays. An abnormal neurological examination during the neonatal period is a predictor of worse outcomes.

Purpose: This study aims to comprehensively delineate the phenotypic spectrum of ACTL6B-related disorders, previously associated with both autosomal recessive and autosomal dominant neurodevelopmental disorders. Molecularly, the role of the nucleolar protein ACTL6B in contributing to the disease has remained unclear. Methods: We identified 105 affected individuals, including 39 previously reported cases, and systematically analyzed detailed clinical and genetic data for all individuals. Additionally, we conducted knockdown experiments in neuronal cells to investigate the role of ACTL6B in ribosome biogenesis. Results: Biallelic variants in ACTL6B are associated with severe-to-profound global developmental delay/intellectual disability, infantile intractable seizures, absent speech, autistic features, dystonia, and increased lethality. De novo monoallelic variants result in moderate-to-severe global developmental delay/intellectual disability, absent speech, and autistic features, whereas seizures and dystonia were less frequently observed. Dysmorphic facial features and brain abnormalities, including hypoplastic corpus callosum, and parenchymal volume loss/atrophy, are common findings in both groups. We reveal that in the nucleolus, ACTL6B plays a crucial role in ribosome biogenesis, particularly in pre-rRNA processing. Conclusion: This study provides a comprehensive characterization of the clinical spectrum of both autosomal recessive and dominant forms of ACTL6B-associated disorders. It offers a comparative analysis of their respective phenotypes provides a plausible molecular explanation and suggests their inclusion within the expanding category of "ribosomopathies." (c) 2024 The Authors. Published by Elsevier Inc. on behalf of American College of Medical Genetics and Genomics. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

E3 ubiquitin ligases have been linked to developmental diseases including autism, Angelman syndrome (UBE3A), and Johanson-Blizzard syndrome (JBS) (UBR1). Here, we report variants in the E3 ligase UBR5 in 29 individuals presenting with a neurodevelopmental syndrome that includes developmental delay, autism, intellectual disability, epilepsy, movement disorders, and/or genital anomalies. Their phenotype is distinct from JBS due to the absence of exocrine pancreatic insufficiency and the presence of autism, epilepsy, and, in some probands, a movement disorder. E3 ubiquitin ligases are responsible for transferring ubiquitin to substrate proteins to regulate a variety of cellular functions, including protein degradation, protein-protein interactions, and protein localization. Knocking out ubr-5 in C. elegans resulted in a lower movement score compared to the wild type, supporting a role for UBR5 in neurodevelopment. Using an in vitro autoubiquitination assay and confocal microscopy for the human protein, we found decreased ubiquitination activity and altered cellular localization in several variants found in our cohort compared to the wild type. In conclusion, we found that variants in UBR5 cause a neurodevelopmental syndrome that can be associated with a movement disorder, reinforcing the role of the UBR protein family in a neurodevelopmental disease that differs from previously described ubiquitin-ligase-related syndromes. We also provide evidence for the pathogenic potential loss of UBR5 function with functional experiments in C. elegans and in vitro ubiquitination assays.

Intellectual Disability (ID) is the major cause of handicap, affecting nearly 3% of the general population, and is highly genetically heterogenous with more than a thousand genes involved. Exome sequencing performed in two independent families identified the same missense variant, p.(Gly611Ser), in the NDST1 (N-deacetylase/N-sulfotransferase member 1) gene. This variant had been previously found in ID patients of two other families but has never been functionally characterized. The NDST1 gene encodes a bifunctional enzyme that catalyzes both N-deacetylation and N-sulfation of N-acetyl-glucosamine residues during heparan sulfate (HS) biosynthesis. This step is essential because it influences the downstream enzymatic modifications and thereby determines the overall structure and sulfation degree of the HS polysaccharide chain. To discriminate between a rare polymorphism and a pathogenic variant, we compared the enzymatic properties of wild-type and mutant NDST1 proteins. We found that the p.(Gly611Ser) variant results in a complete loss of N-sulfotransferase activity while the N-deacetylase activity is retained. NDST1 shows the highest and the most homogeneous expression in the human cerebral structures compared to the other members of the NDST gene family. These results indicate that a loss of NDST1 N-sulfation activity is associated with impaired cognitive functions.

BRAT1 biallelic variants are associated with rigidity and multifocal seizure syndrome, lethal neonatal (RMFSL), and neurodevelopmental disorder associating cerebellar atrophy with or without seizures syndrome (NEDCAS). To date, forty individuals have been reported in the literature. We collected clinical and molecular data from 57 additional cases allowing us to study a large cohort of 97 individuals and draw phenotype-genotype correlations. Fifty-nine individuals presented with BRAT1-related RMFSL phenotype. Most of them had no psychomotor acquisition (100%), epilepsy (100%), microcephaly (91%), limb rigidity (93%), and died prematurely (93%). Thirty-eight individuals presented a non-lethal phenotype of BRAT1-related NEDCAS phenotype. Seventy-six percent of the patients in this group were able to walk and 68% were able to say at least a few words. Most of them had cerebellar ataxia (82%), axial hypotonia (79%) and cerebellar atrophy (100%). Genotype-phenotype correlations in our cohort revealed that biallelic nonsense, frameshift or inframe deletion/insertion variants result in the severe BRAT1-related RMFSL phenotype (46/46; 100%). In contrast, genotypes with at least one missense were more likely associated with NEDCAS (28/34; 82%). The phenotype of patients carrying splice variants was variable: 41% presented with RMFSL (7/17) and 59% with NEDCAS (10/17).