Background Disrupted RNA processing is increasingly recognized as a key driver of severe neurodevelopmental disorders. Variants in the Integrator catalytic subunit INTS11 and its binding partner BRAT1 lead to clinically overlapping phenotypes, yet only the molecular function of INTS11 has been relatively well characterized. In contrast, the mechanistic contribution of BRAT1 to RNA metabolism and disease has remained unclear, leaving major gaps in variant interpretation and diagnostic classification.Methods We employed an integrated genetic, molecular, and in vivo approach to investigate the impact of INTS11 and BRAT1 mutations on U small nuclear RNA (U snRNA) processing. Patient-derived fibroblasts and lymphoblastoid cells were analysed by western blotting, RT-qPCR and fluorescence in situ hybridization to assess U1 snRNA 3 '-end processing and nuclear retention. To validate the functional consequences of Integrator deficiency in vivo, we generated and characterized an ints11 knockout zebrafish model.Results We identified novel biallelic variants in INTS11 and BRAT1 in individuals with overlapping neurodevelopmental features. While defective snRNA processing is anticipated in INTS11 deficiency, this study provides the first direct demonstration of impaired U1 snRNA processing across multiple INTS11-mutated patient cells. Critically, we show that BRAT1 mutations also compromise U1 snRNA 3 '-end processing, leading to nuclear accumulation of unprocessed transcripts. These findings provide direct evidence of BRAT1's role in RNA processing and establish Integrator dysfunction as a primary pathogenic mechanism in BRAT1-associated neurological disease. The magnitude of U1 snRNA misprocessing closely correlates with clinical severity across the BRAT1 cohort, highlighting its potential as a diagnostic biomarker. Consistently, the ints11 knockout zebrafish model recapitulates core patient features - including microcephaly, neurodevelopmental defects, and U snRNA processing defects - further validating the causal role of Integrator deficiency in vivo.Conclusions Our results redefine BRAT1-associated neurological disorders as Integrator-related diseases driven by RNA processing defects. Nuclear accumulation of unprocessed U1 snRNAs emerges as a robust biomarker for variant interpretation, disease severity, and patient stratification, particularly in BRAT1 cases. These findings broaden the clinical and molecular spectrum of Integrator dysfunction and provide a foundation for improved diagnostic and translational approaches.

The Thanatos-associated (THAP) protein family, named after the Greek god of death, comprises zinc-finger proteins characterized by a DNA-binding domain called the THAP domain. Although THAP1 and THAP11 have been extensively studied, the broader family of twelve human THAP-domain containing proteins is increasingly recognized as an important but underexplored group of transcriptional regulators. Evidence now links THAP proteins to a wide range of cellular processes, including cell-cycle progression, DNA repair, apoptosis, proteostasis, and mitochondrial function. Dysregulation of these proteins has also been implicated in cancer and neurological disorders, underscoring their medical relevance. In this review, we summarize current knowledge of their structure, localization, transcriptional roles, and disease associations. We also present new structural analyses that shed light on conserved and divergent features across the THAP family. Finally, we will highlight their newly appreciated functions in stem and progenitor cell biology.

Developmental and epileptic encephalopathies (DEEs) are a group of severe childhood-onset neurological disorders, often caused by rare genetic variants affecting brain development and excitability. Despite advances in genomic sequencing, a substantial proportion of DEE cases remain unsolved. Here, we identify THAP12 as a novel disease-causing gene associated with autosomal recessive DEE. Whole-genome sequencing in two siblings who presented with infantile spasms and progressed to Lennox-Gastaut syndrome revealed compound heterozygous variants in THAP12 , leading to a reduction in protein abundance, consistent with a loss-of-function mechanism. To confirm this mechanism in vivo , we generated mouse models carrying either of the two patient-specific alleles. Both homozygous and compound heterozygous animals exhibited embryonic lethality, confirming the essential and dosage-sensitive role of Thap12 during early development. Zebrafish loss-of-function models recapitulated major aspects of the human phenotype, including microcephaly, brain hypoplasia, abnormal neuronal activity, and increased seizure sensitivity. Transcriptomic profiling of larval zebrafish brains revealed dysregulation of cell cycle and apoptotic pathways, in line with increased cell death and reduced proliferation observed in mutant embryos. Notably, overexpression of wild-type human THAP12 mRNA rescued these in vivo phenotypes, while the patient-derived variants allele failed to do so. Altogether, our findings demonstrate that THAP12 is essential for early brain development and neuronal survival, and that biallelic loss-of-function variants in this gene underlie a previously unrecognized etiology of autosomal recessive DEE. These results provide a mechanistic framework linking, for the first time, THAP12 dysfunction to neurodevelopmental pathology and open new avenues for diagnosis in undiagnosed DEE cases.

Background Genome editing in human skeletal muscle research requires protocols that maximize delivery while preserving viability and clonal outgrowth. We sought to develop a reagent-free workflow for CRISPR/Cas9 editing in human immortalized myoblasts and to demonstrate its performance in two use cases, an IARS1 knockout and an MLIP homozygous knock-in. Methods We optimized electroporation parameters using a green fluorescent protein reporter to compare three electrical settings for transfection and survival in E6/E7 myoblasts, then applied ribonucleoprotein delivery for editing. We evaluated the effect of confluency at electroporation, performed single-cell cloning without antibiotics or fluorescence-activated sorting, and validated edits by high-resolution melting pre-screen followed by Sanger sequencing. Results Electroporation optimization identified one parameter set that maximized delivery while preserving viability. Performing electroporation at low confluency increased clonal outgrowth and editing rates. The workflow yielded an 84% success rate for IARS1 knockout and a 3.3% success rate for MLIP homozygous knock-in. High-resolution melting provided a very sensitive pre-screen, detecting 96% to 100% of actual edits, reducing the number of Sanger sequencing needed. Performance was reproducible across runs and myoblast lines and increasing single-cell seeding scaled yields without compromising purity. Conclusions This work provides a practical and reproducible selection-free protocol that couples electroporation optimization, low confluency editing, single-cell cloning, and high-resolution melting sorting to generate pure edited myoblast lines. The approach is applicable to disease modeling in neuromuscular research and clarifies feasibility boundaries for essential genes and homology-directed repair in these cells. ### Competing Interest Statement The authors have declared no competing interest. * CRISPR : Clustered Regularly Interspaced Short Palindromic Repeats FACS : Fluorescence-Activated Cell Sorting GFP : Green Fluorescent Protein HDR : Homology-Directed Repair hiMyo : Human immortalized myoblasts HRM : High-Resolution Melting IARS1 : Isoleucyl-tRNA Synthetase 1 KI : Knock-in KO : Knock-out MLIP : Muscular Lamin-Interacting Protein NHEJ : Non-Homologous End Joining RNP : Ribonucleoprotein Muscular Dystrophy Canada, https://ror.org/000hkd473

DNA replication and repair are basic yet essential molecular processes for all cells. RFC1 encodes the largest subunit of the Replication Factor C, an essential clamp-loader for DNA replication and repair. Intronic repeat expansion in RFC1 has recently been associated with so-called RFC1-related disorders, which mainly encompass late-onset cerebellar ataxias. However, the mechanisms making certain tissues more susceptible to defects in these universal pathways remain mysterious. Here, we provide the first investigation of RFC1 gene function in vivo using zebrafish. We showed that RFC1 is expressed in neural progenitor cells within the developing cerebellum, where it maintains their genomic integrity during neurogenic maturation. Accordingly, RFC1 loss-of-function leads to a severe cerebellar phenotype due to impaired neurogenesis of both Purkinje and granule cells. Our data point to a specific role of RFC1 in the developing cerebellum, paving the way for a better understanding of the pathogenic mechanisms underlying RFC1-related disorders.

Loss-of-function mutation of ABCC9, the gene encoding the SUR2 subunit of ATP sensitive-potassium (KATP) channels, was recently associated with autosomal recessive ABCC9-related intellectual disability and myopathy syndrome (AIMS). Here we identify nine additional subjects, from seven unrelated families, harbouring different homozygous loss-of-function variants in ABCC9 and presenting with a conserved range of clinical features. All variants are predicted to result in severe truncations or in-frame deletions within SUR2, leading to the generation of non-functional SUR2-dependent KATP channels. Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness. Heterozygous parents do not show any conserved clinical pathology but report multiple incidences of intra-uterine fetal death, which were also observed in an eighth family included in this study. In vivo studies of abcc9 loss-of-function in zebrafish revealed an exacerbated motor response to pentylenetetrazole, a pro-convulsive drug, consistent with impaired neurodevelopment associated with an increased seizure susceptibility. Our findings define an ABCC9 loss-of-function-related phenotype, expanding the genotypic and phenotypic spectrum of AIMS and reveal novel human pathologies arising from KATP channel dysfunction.

Previously, we demonstrated that palmatine (PALM) – an isoquinoline alkaloid from Berberis sibrica radix, exerted antiseizure activity in the pentylenetetrazole (PTZ)-induced seizure assay in larval zebrafish. The aim of the present study was to more precisely characterize PALM as a potential anticonvulsant drug candidate. A range of zebrafish and mouse seizure/epilepsy models were applied in the investigation. Immunostaining analysis was conducted to assess the changes in mouse brains, while in silico molecular modelling was performed to determine potential targets for PALM. Accordingly, PALM had anticonvulsant effect in ethyl 2-ketopent-4-enoate (EKP)-induced seizure assay in zebrafish larvae as well as in the 6 Hz-induced psychomotor seizure threshold and timed infusion PTZ tests in mice. The protective effect in the EKP-induced seizure assay was confirmed in the local field potential recordings. PALM did not affect seizures in the gabra1a knockout line of zebrafish larvae. In the scn1Lab-/- zebrafish line, pretreatment with PALM potentiated seizure-like behaviour of larvae. Repetitive treatment with PALM, however, did not reduce development of PTZ-induced seizure activity nor prevent the loss of parvalbumin-interneurons in the hippocampus of the PTZ kindled mice. In silico molecular modelling revealed that the noted anticonvulsant effect of PALM in EKP-induced seizure assay might result from its interactions with glutamic acid decarboxylase and/or via AMPA receptor non-competitive antagonism. Our study has demonstrated the anticonvulsant activity of PALM in some experimental models of seizures, including a model of pharmacoresistant seizures induced by EKP. These results indicate that PALM might be a suitable new drug candidate but the precise mechanism of its anticonvulsant activity has to be determined.

We studied three brothers and a maternal half-brother featuring global developmental delay, mild to moderate intellectual disability, epilepsy, microcephaly, and strabismus. All had bilateral perisylvian and perirolandic polymicrogyria, while some also had malformations of the hippocampus (malrotation and dysplasia), cerebellum (heterotopias and asymmetric aplasia), corpus callosum dysgenesis, and brainstem asymmetric dysplasia. Exome sequencing showed that all four patients had a novel variant (c.1597C>T:p.Leu533Phe) on the KIF4A gene on chromosome X. We discuss how this variant is possibly pathogenic and could explain the reported phenotype.

The classic view of the lysosome as a static recycling center has been replaced with one of a dynamic and mobile hub of metabolic regulation. This revised view raises new questions about how dysfunction of this organelle causes pathology in inherited lysosomal disorders. Here we provide evidence for increased lysosomal exocytosis in the developing cartilage of three lysosomal disease zebrafish models with distinct etiologies. Dysregulated exocytosis was linked to altered cartilage development, increased activity of multiple cathepsin proteases, and cathepsin- and TGFβ-mediated pathogenesis in these models. Moreover, inhibition of cathepsin activity or direct blockade of exocytosis with small molecule modulators improved the cartilage phenotypes, reinforcing a connection between excessive extracellular protease activity and cartilage pathogenesis. This study highlights the pathogenic consequences in early cartilage development arising from uncontrolled release of lysosomal enzymes via exocytosis, and suggests that pharmacological enhancement of this process could be detrimental during tissue development.

Abstract Disclosure: S. Parisien-La Salle: None. F. Nobilleau: None. J. Lamontagne: None. S. Éric: None. I. Bourdeau: None. Introduction: Animal research has been limited in pheochromocytomas and paragangliomas (PPGLs). Recently, Dona et al., described a sdhb mutated zebrafish model by introducing a 13 bp frameshift mutation at the sdhb exon1—intron1 boundary into the zebrafish sdhb gene that recapitulated features of PPGLs. Objective: To generate a new model of mutated sdhb zebrafish to further investigate the underlying metabolic and biochemical perturbations in vivo. Methods: We took advantage of the genetic accessibility of zebrafish embryo to generate loss-of-function model for sdhb using CRISPR/Cas9 technology. Three guide RNAs were designed and microinjected in one-cell stage zebrafish embryos to target the coding sequence of zebrafish sdhb gene. In order to control for the stress brought on by injections, we injected a group of zebrafish with Cas9 endonuclease as a control. At five days post fertilization, mutant and control zebrafish were flash frozen and sent for liquid chromatography mass spectrometry measurements of Krebs cycle metabolites and normetanephrines/metanephrines. All results were normalized to the control groups consisting of wild-type or Cas9 injected larvae. Sdhb expression was analyzed by RT-qPCR in sdhb mutants and wild-type zebrafish larvae. We also monitored survival and heart rate in sdhb mutant zebrafish, compared to wild-type and Cas9. Results: Firstly, we confirmed the significant reduction of sdhb expression in CRISPR-injected larvae compared to wild-type larvae at 5 dpf (0.0613 vs 1.000 p<0.0001). Our metabolic panel showed that succinate was up to 26 times more elevated in sdhb mutants than in wild-type fish extracts (sdhb: 26.51 p<0.0001). Lactate (sdhb: 5.27 p<0.0001), leucine (sdhb: 2.88 p<0.0001), arginine (sdhb: 1.50 p=0.0034) and HMG-CoA (sdhb: 1.36 p=0.0033) were also higher in sdhb mutants. Whereas aspartate (sdhb: 0.244 p<0.0001) and oxidized gluthiatone (sdhb: 0.64 p=0.0011) were significantly lower in sdhb mutants than in wild-types. In regards to functionality, normetanephrine and metanephrine levels were at least four folds higher in sdhb mutants than in Cas9 injected larvaes (4.06 p<0.0001 and 3.42 p<0.0001 respectively). Interestingly, this difference was more noticeable in the fish bathing medium than in larvae tissue extracts, suggesting an increased hormonal excretion (normetanephrines: 4.81 p<0.0001 and metanephrines: 9.40 p<0.0001). Finally, sdhb mutated zebrafish presented with a higher heart rate (148 vs 133 p<0.0001) and reduced lifespan (p<0.0001) when compared to the wild-type/Cas9 group. Conclusion: These findings confirm that the zebrafish is an ideal model for studying PPGLs and their associated genetic defects. Our approach allows the in vivo assessment of a large metabolic panel, opening avenues on new potential clinical metabolic biomarkers in a loss-of-function of the SDHB gene. Ref: Dona M, et al. Endocr Relat Cancer. 2021 Presentation: 6/1/2024

Background: There is limited data on the utility, yield, and cost efficiency of genetic testing in adults with epilepsy. We aimed to describe the yield and utility of genetic panels in our adult epilepsy clinic. Methods: We performed a retrospective, cross-sectional study of all patients followed by an epileptologist at a Canadian tertiary care centre's epilepsy clinic between January 2016 and August 2021 for whom a genetic panel was ordered. A panel was generally ordered when the etiology was unknown or in the presence of a malformation of cortical development. We determined the yield of panel positivity and of confirmed genetic diagnoses. We also estimated the proportion of these diagnoses that were clinically actionable. Results: In total, 164 panels were ordered in 164 patients. Most had refractory epilepsy (80%), and few had comorbid intellectual disability (10%) or a positive family history of epilepsy (11%). The yield of panel positivity was 11%. Panel results were uncertain 49% of the time and negative 40% of the time. Genetic diagnoses were confirmed in 7 (4.3%) patients. These genetic conditions involved the following genes: SCARB2, DEPDC5, PCDH19, LGI1, SCN1A, MT-TL1, and CHRNA7. Of the seven genetic diagnoses, 5 (71%) were evaluated to be clinically actionable. Conclusion: We report a lower diagnostic yield for genetic panels in adults with epilepsy than what has so far been reported. Although the field of the genetics of epilepsy is a fast-moving one and more data is required, our findings suggest that guidelines for genetic testing in adults are warranted.

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The sodium leak channel (NALCN) gene encodes a sodium leak channel that plays an important role in the regulation of the resting membrane potential and the control of neuronal excitability. Mutations in the NALCN gene have been reported in patients with infantile hypotonia with psychomotor retardation and characteristic facies (IHPRF) and congenital contractures of the limbs and face with hypotonia and developmental delay (CLIFAHDD syndrome). We describe the case of a father with drug-resistant left temporo-orbitofrontal epilepsy and his son with mildly-symptomatic temporal epilepsy (only recurrent déjà vu auras) whose genetic panels identified a likely pathogenic deletion of exon 27 on the NALCN gene. Our study helps broaden the clinical spectrum of diseases associated with mutations in the NALCN gene.

Personalized medicine is currently one of the most promising tools which give hope to patients with no suitable or no available treatment. Patient-specific approaches are particularly needed for common diseases with a broad phenotypic spectrum as well as for rare and yet-undiagnosed disorders. In both cases, there is a need to understand the underlying mechanisms and how to counteract them. Even though, during recent years, we have been observing the blossom of novel therapeutic techniques, there is still a gap to fill between bench and bedside in a patient-specific fashion. In particular, the complexity of genotype-to-phenotype correlations in the context of neurological disorders has dampened the development of successful disease-modifying therapeutics. Animal modeling of human diseases is instrumental in the development of therapies. Currently, zebrafish has emerged as a powerful and convenient model organism for modeling and investigating various neurological disorders. This model has been broadly described as a valuable tool for understanding developmental processes and disease mechanisms, behavioral studies, toxicity, and drug screening. The translatability of findings obtained from zebrafish studies and the broad prospect of human disease modeling paves the way for developing tailored therapeutic strategies. In this review, we will discuss the predictive power of zebrafish in the discovery of novel, precise therapeutic approaches in neurosciences. We will shed light on the advantages and abilities of this in vivo model to develop tailored medicinal strategies. We will also investigate the newest accomplishments and current challenges in the field and future perspectives.

Seizures are the outward manifestation of abnormally excessive or synchronous brain activity. While seizures can be somewhat symptomatically managed with anti-epileptic drugs (AEDs), many patients are still refractory to the currently available AEDs. As a result, there is a need to identify new molecules with anti-seizure properties. Curcumin is the principle curcuminoid of Curcuma longa, or colloquially turmeric, and has been experimentally proven to have anti-convulsive properties, but its poor bioavailability has dampened further therapeutic interest. Hence, this study aimed to ask if structural analogues of curcumin with an adequate bioavailability could have an anti-seizure effect in vivo. To do so, we tested these analogues following a multipronged approach combining the use of several zebrafish seizure models (chemically-induced and genetic) and complementary assays (behavioural and brain activity). Overall, from the 68 analogues tested, we found 15 different derivatives that were able to significantly decrease the behavioural hyperactivity induced by pentylenetetrazol. Of those, only a few showed an effect on the hyperactivity phenotype of two genetic models of brain seizures that are the gabra1 and gabrg2 knockouts. Two analogues, CA 80(1) and CA 74(1), were able to significantly alleviate brain seizures of gabrg2-mutant larvae. As a result, these analogues are good candidates as novel anti-seizure agents.

Epilepsy is a common disorder of the brain characterized by spontaneous recurrent seizures, which develop gradually during a process called epileptogenesis. The mechanistic processes underlying the changes of brain tissue and networks toward increased seizure susceptibility are not fully understood. In rodents, injection of kainic acid (KA) ultimately leads to the development of spontaneous epileptic seizures, reflecting similar neuropathological characteristics as seen in patients with temporal lobe epilepsy (TLE). Although this model has significantly contributed to increased knowledge of epileptogenesis, it is technically demanding, costly to operate and hence not suitable for high-throughput screening of anti-epileptic drugs (AEDs). Zebrafish, a vertebrate with complementary advantages to rodents, is an established animal model for epilepsy research. Here, we generated a novel KA-induced epilepsy model in zebrafish larvae that we functionally and pharmacologically validated. KA was administered by pericardial injection at an early zebrafish larval stage. The epileptic phenotype induced was examined by quantification of seizure-like behavior using automated video recording, and of epileptiform brain activity measured via local field potential (LFP) recordings. We also assessed GFP-labeled GABAergic and RFP-labeled glutamatergic neurons in double transgenic KA-injected zebrafish larvae, and examined the GABA and glutamate levels in the larval heads by liquid chromatography with tandem mass spectrometry detection (LC-MS/MS). Finally, KA-injected larvae were exposed to five commonly used AEDs by immersion for pharmacological characterization of the model. Shortly after injection, KA induced a massive damage and inflammation in the zebrafish brain and seizure-like locomotor behavior. An abnormal reorganization of brain circuits was observed, a decrease in both GABAergic and glutamatergic neuronal population and their associated neurotransmitters. Importantly, these changes were accompanied by spontaneous and continuous epileptiform brain discharges starting after a short latency period, as seen in KA rodent models and reminiscent of human pathology. Three out of five AEDs tested rescued LFP abnormalities but did not affect the seizure-like behavior. Taken together, for the first time we describe a chemically-induced larval zebrafish epilepsy model offering unique insights into studying epileptogenic processes in vivo and suitable for high-throughput AED screening purposes and rapid genetic investigations.

Mutations in the chromatin remodeller-coding gene CHD7 cause CHARGE syndrome (CS). CS features include moderate to severe neurological and behavioural problems, clinically characterized by intellectual disability, attention-deficit/hyperactivity disorder and autism spectrum disorder. To investigate the poorly characterized neurobiological role of CHD7, we here generate a zebrafish chd7-/- model. chd7-/- mutants have less GABAergic neurons and exhibit a hyperactivity behavioural phenotype. The GABAergic neuron defect is at least in part due to downregulation of the CHD7 direct target gene paqr3b, and subsequent upregulation of MAPK/ERK signalling, which is also dysregulated in CHD7 mutant human cells. Through a phenotype-based screen in chd7-/- zebrafish and Caenorhabditis elegans, we show that the small molecule ephedrine restores normal levels of MAPK/ERK signalling and improves both GABAergic defects and behavioural anomalies. We conclude that chd7 promotes paqr3b expression and that this is required for normal GABAergic network development. This work provides insight into the neuropathogenesis associated with CHD7 deficiency and identifies a promising compound for further preclinical studies.