CAPRIN1 haploinsufficiency causes a neurodevelopmental disorder with language impairment, ADHD and ASD

Circular RNA hsa_circ_0000288 protects against epilepsy in mice by binding to and stabilizing caprin1 protein

Current anti-epileptic drugs remain to be unsatisfactory, new therapeutic approaches are needed. Circular RNA is a promising class of therapeutic RNAs. Recent studies have shown the role of circRNA in the pathologic process of epilepsy. In this study, we identified the circRNA in epileptic patients in remission that inhibited the epileptic course. By comparing the profiles of differentially expressed circRNAs in peripheral serum between patients in remission and those not in remission, we found that the level of hsa_circ_0000288 (circ288) was markedly elevated in the epileptic patients in remission. We established a kainic acid-induced status epilepticus model in mice. Overexpression of Circ288 by injecting adeno-associated virus (AAV)-circ288-overexpression vector into hippocampi significantly ameliorated epilepsy-induced neuronal injury, promoted hippocampus neurogenesis, and inhibited abnormal migration of newborn neurons into the dentate hilus. Moreover, circ288 overexpression significantly decreased the epileptiform discharges and the spontaneous seizures in the chronic phase of epileptogenesis and alleviated mood disorders (anxiety, depression), and cognitive deficits in epileptic mice. We revealed that circ288 directly bound to an RNA-binding protein caprin1 and inhibited its degradation. The protective action of circ288 was reversed by the knockdown of caprin1 in an in vitro epileptic model and lost in the neuron-specific caprin1 knockout mice (CaMK2α-Cre:Caprin1f/f). Overexpression of circ288 or caprin1 raised the mRNA level of NMDA receptor 3B, a negative modulator of NMDA receptors, suggesting the involvement of the carpin1-NMDA receptor 3B pathway in the role of circ288. Given the disadvantages of circ288 overexpression by a virus, we constructed exosomes-encapsulated circ288 (EXO-circ288) and demonstrated that tail vein injection of EXO-circ288 exerted robust protective effects. This study provides a new avenue for developing anti-epileptic therapeutic RNAs.

Derivation of the IGGi006-A stem cell line from a patient with CAPRIN1 haploinsufficiency

CAPRIN1 gene encodes a RNA-binding protein, abundant in the brain where it plays a crucial role, regulating the transport and translation of mRNAs of synaptic proteins.CAPRIN1 haploinsufficiency causes a neurodevelopmental disorder characterized by language impairment/speech delay, intellectual disability, attention deficit, hyperactivity disorder, and autism spectrum disorder. To understand the pathogenesis of this disorder and in view of future treatment, we generated human induced pluripotent stem cells (iPSCs) from a patient carrying the c.1744C>T CAPRIN1 variant. The line show marker expression for the pluripotency and the capacity to differentiate into the three germ layers.

CAPRIN1 Transcriptionally Activated PLPP4 to Inhibit DOX Sensitivity and Promote Breast Cancer Progression

BACKGROUND

Phospholipid phosphatase 4 (PLPP4) has been identified as a potential regulator of cancer cell dynamics, however, the role of PLPP4 in breast cancer (BC) progression and the sensitivity of BC cells to doxorubicin (DOX) remain elusive.

METHODS

The study analyzed the expression of PLPP4 and cell cycle-associated protein 1 (CAPRIN1) expression in BC tissues and cells using quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) and western blotting assays. Functional assays including colony formation, EdU, Transwell, and flow cytometry were employed to assess cellular behaviors. The sensitivity of BC cells to DOX was analyzed by CCK-8 assay and an in vivo xenograft model assay. The association between PLPP4 and CAPRIN1 was investigated using RNA immunoprecipitation assay and dual-luciferase reporter assay.

RESULTS

Upregulation of PLPP4 expression was observed in BC tissues and cells. Downregulation of PLPP4 expression in BC cells resulted in a suppression of their proliferative capacity, as well as a reduction in migratory and invasive capabilities. Additionally, this manipulation enhanced cell susceptibility to apoptosis and improved the sensitivity of these cells to DOX. When PLPP4 was knocked down in vivo in transplantable tumors, there was a marked enhancement in the responsiveness to DOX treatment. The transcription factor CAPRIN1 was found to regulate the expression of PLPP4 in the HCC1937 and MDA-MB-231 cell lines. Upregulation of CAPRIN1 was observed in both BC tissues and cells, and overexpression of PLPP4 reversed the effects of CAPRIN1 silencing on BC cell proliferation, migration, invasion, apoptosis, and DOX sensitivity.

CONCLUSION

This study demonstrates that CAPRIN1 transcriptionally activates PLPP4 to inhibit DOX sensitivity and promote BC progression. Targeting PLPP4 may represent a novel therapeutic strategy to enhance the efficacy of DOX in BC patients.

Advances in the treatment of autism spectrum disorder: Wharton jelly mesenchymal stem cell transplantation

BACKGROUND

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder with multifaceted origins. In recent studies, neuroinflammation and immune dysregulation have come to the forefront in its pathogenesis. There are studies suggesting that stem cell therapy may be effective in the treatment of ASD.

AIM

To evolve the landscape of ASD treatment, focusing on the potential benefits and safety of stem cell transplantation.

METHODS

A detailed case report is presented, displaying the positive outcomes observed in a child who underwent intrathecal and intravenous Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) transplantation combined with neurorehabilitation.

RESULTS

The study demonstrates a significant improvement in the child's functional outcomes (Childhood Autism Rating Scale, Denver 2 Developmental Screening Test), especially in language and gross motor skills. No serious side effects were encountered during the 2-year follow-up.

CONCLUSION

The findings support the safety and effectiveness of WJ-MSC transplantation in managing ASD.

Electrostatics of salt-dependent reentrant phase behaviors highlights diverse roles of ATP in biomolecular condensates

Liquid-liquid phase separation (LLPS) involving intrinsically disordered protein regions (IDRs) is a major physical mechanism for biological membraneless compartmentalization. The multifaceted electrostatic effects in these biomolecular condensates are exemplified here by experimental and theoretical investigations of the different salt- and ATP-dependent LLPSs of an IDR of messenger RNA-regulating protein Caprin1 and its phosphorylated variant pY-Caprin1, exhibiting, for example, reentrant behaviors in some instances but not others. Experimental data are rationalized by physical modeling using analytical theory, molecular dynamics, and polymer field-theoretic simulations, indicating that interchain ion bridges enhance LLPS of polyelectrolytes such as Caprin1 and the high valency of ATP-magnesium is a significant factor for its colocalization with the condensed phases, as similar trends are observed for other IDRs. The electrostatic nature of these features complements ATP's involvement in π-related interactions and as an amphiphilic hydrotrope, underscoring a general role of biomolecular condensates in modulating ion concentrations and its functional ramifications.

Fission yeast Caprin protein is required for efficient heterochromatin establishment

Heterochromatin is a key feature of eukaryotic genomes that serves important regulatory and structural roles in regions such as centromeres. In fission yeast, maintenance of existing heterochromatic domains relies on positive feedback loops involving histone methylation and non-coding RNAs. However, requirements for de novo establishment of heterochromatin are less well understood. Here, through a cross-based assay we have identified a novel factor influencing the efficiency of heterochromatin establishment. We determine that the previously uncharacterised protein is an ortholog of human Caprin1, an RNA-binding protein linked to stress granule formation. We confirm that the fission yeast ortholog, here named Cpn1, also associates with stress granules, and we uncover evidence of interplay between heterochromatin integrity and ribonucleoprotein (RNP) granule formation, with heterochromatin mutants showing reduced granule formation in the presence of stress, but increased granule formation in the absence of stress. We link this to regulation of non-coding heterochromatic transcripts, since in heterochromatin-deficient cells, Cpn1 can be seen to colocalise with accumulating pericentromeric transcripts, and absence of Cpn1 leads to hyperaccumulation of these RNAs at centromeres. Together, our findings unveil a novel link between RNP homeostasis and heterochromatin assembly, and implicate Cpn1 and associated factors in facilitating efficient heterochromatin establishment by enabling removal of excess transcripts that would otherwise impair assembly processes.

NAT10 promotes ovarian cancer cell migration, invasion, and stemness via N4-acetylcytidine modification of CAPRIN1

Ovarian cancer (OC) is the most lethal gynecological tumor. N4-acetylcytidine (ac4C) modification, catalyzed by the acetyltransferase NAT10, is involved in the occurrence and development of cancers. This study aimed to investigate the role of NAT10 in OC and the underlying molecular mechanisms. The expression of NAT10 and CAPRIN1 in OC cells lines were measured using quantitative real-time polymerase chain reaction and immunoblotting. Biological behaviors of OC cells were evaluated using EdU, Transwell, sphere formation, and immunoblotting assays. The molecular mechanism of NAT10 function was analyzed using bioinformatics, ac4C- RNA immunoprecipitation, and actinomycin D treatment assay. The effect of NAT10 on OC progression in vivo was evaluated using xenograft tumor model. The results indicated that NAT10 and CAPRIN1 were highly expressed in OC cells. NAT10 knockdown suppressed OC cell proliferation, migration, invasiveness, stemness, and epithelial-mesenchymal transition in vitro, and impeded tumor growth in vivo. Additionally, CAPRIN1 expression was found to be positively related to NAT10 expression in OC. Silencing of NAT10 inhibited ac4C levels of CAPRIN1 and reduced its RNA stability. Moreover, overexpression of CAPRIN1 reversed the suppression of migration, invasion, and stemness caused by NAT10 knockdown, while knockdown of CAPRIN1 alone inhibited these malignant behaviors of OC cells. In conclusion, NAT10 promotes OC progression by promoting cellular migration, invasion, and stemness via upregulating CAPRIN1 expression. Mechanistically, NAT10 stabilizes CAPRIN1 by promoting its ac4C modification. These findings suggest that NAT10 may be a promising therapy target for OC.

The Role of Oxidative Stress in Autism Spectrum Disorder Pathophysiology, Diagnosis and Treatment

Autism spectrum disorder (ASD) is a significant health problem with no known single cause. There is a vast number of evidence to suggest that oxidative stress plays an important role in this disorder. The author of this article reviewed the current literature in order to summarise the knowledge on the subject. In this paper, the role of oxidative stress is investigated in the context of its influence on pathogenesis, the use of oxidative stress biomarkers as diagnostic tools and the use of antioxidants in ASD treatment. Given the heterogeneity of ASD aetiology and inadequate treatment approaches, the search for common metabolic traits is essential to find more efficient diagnostic tools and treatment methods. There are increasing data to suggest that oxidative stress is involved in the pathogenesis of ASD, both directly and through its interplay with inflammation and mitochondrial dysfunction. Oxidative stress biomarkers appear to have good potential to be used as diagnostic tools to aid early diagnosis of ASD. The results are most promising for glutathione and its derivatives and also for isoprostanses. Probably, complex dedicated multi-parametric metabolic panels may be used in the future. Antioxidants show good potential in ASD-supportive treatment. In all described fields, the data support the importance of oxidative stress but also a need for further research, especially in the context of sample size and, preferably, with a multicentre approach.

Harnessing the potential of human induced pluripotent stem cells, functional assays and machine learning for neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) affect 4.7% of the global population and are associated with delays in brain development and a spectrum of impairments that can lead to lifelong disability and even mortality. Identification of biomarkers for accurate diagnosis and medications for effective treatment are lacking, in part due to the historical use of preclinical model systems that do not translate well to the clinic for neurological disorders, such as rodents and heterologous cell lines. Human-induced pluripotent stem cells (hiPSCs) are a promising in vitro system for modeling NDDs, providing opportunities to understand mechanisms driving NDDs in human neurons. Functional assays, including patch clamping, multielectrode array, and imaging-based assays, are popular tools employed with hiPSC disease models for disease investigation. Recent progress in machine learning (ML) algorithms also presents unprecedented opportunities to advance the NDD research process. In this review, we compare two-dimensional and three-dimensional hiPSC formats for disease modeling, discuss the applications of functional assays, and offer insights on incorporating ML into hiPSC-based NDD research and drug screening.

Gas5 regulates early-life stress-induced anxiety and spatial memory

Early-life stress (ES) induced by maternal separation (MS) remains a proven causality of anxiety and memory deficits at later stages of life. Emerging studies have shown that MS-induced gene expression in the hippocampus is operated at the level of transcription. However, the extent of involvement of non-coding RNAs in MS-induced behavioural deficits remains unexplored. Here, we have investigated the role of synapse-enriched long non-coding RNAs (lncRNAs) in anxiety and memory upon MS. We observed that MS led to an enhancement of expression of the lncRNA growth arrest specific 5 (Gas5) in the hippocampus; accompanied by increased levels of anxiety and deficits in spatial memory. Gas5 knockdown in early life was able to reduce anxiety and partially rescue the spatial memory deficits of maternally separated adult mice. However, the reversal of MS-induced anxiety and memory deficits is not attributed to Gas5 activity during neuronal development as Gas5 RNAi did not influence spine development. Gene Ontology analysis revealed that Gas5 exerts its function by regulating RNA metabolism and translation. Our study highlights the importance of MS-regulated lncRNA in anxiety and spatial memory.

Increased burden of rare risk variants across gene expression networks predisposes to sporadic Parkinson's disease

Alpha-synuclein (αSyn) is an intrinsically disordered protein that accumulates in the brains of patients with Parkinson's disease and forms intraneuronal inclusions called Lewy Bodies. While the mechanism underlying the dysregulation of αSyn in Parkinson's disease is unclear, it is thought that prionoid cell-to-cell propagation of αSyn has an important role. Through a high throughput screen, we recently identified 38 genes whose knock down modulates αSyn propagation. Follow up experiments were undertaken for two of those genes, TAX1BP1 and ADAMTS19, to study the mechanism with which they regulate αSyn homeostasis. We used a recently developed M17D neuroblastoma cell line expressing triple mutant (E35K+E46K+E61K) "3K" αSyn under doxycycline induction. 3K αSyn spontaneously forms inclusions that show ultrastructural similarities to Lewy Bodies. Experiments using that cell line showed that TAX1BP1 and ADAMTS19 regulate how αSyn interacts with lipids and phase separates into inclusions, respectively, adding to the growing body of evidence implicating those processes in Parkinson's disease. Through RNA sequencing, we identified several genes that are differentially expressed after knock-down of TAX1BP1 or ADAMTS19. Burden analysis revealed that those differentially expressed genes (DEGs) carry an increased frequency of rare risk variants in Parkinson's disease patients versus healthy controls, an effect that was independently replicated across two separate cohorts (GP2 and AMP-PD). Weighted gene co-expression network analysis (WGCNA) showed that the DEGs cluster within modules in regions of the brain that develop high degrees of αSyn pathology (basal ganglia, cortex). We propose a novel model for the genetic architecture of sporadic Parkinson's disease: increased burden of risk variants across genetic networks dysregulates pathways underlying αSyn homeostasis, thereby leading to pathology and neurodegeneration.

A multiomic atlas of the aging hippocampus reveals molecular changes in response to environmental enrichment

Aging involves the deterioration of organismal function, leading to the emergence of multiple pathologies. Environmental stimuli, including lifestyle, can influence the trajectory of this process and may be used as tools in the pursuit of healthy aging. To evaluate the role of epigenetic mechanisms in this context, we have generated bulk tissue and single cell multi-omic maps of the male mouse dorsal hippocampus in young and old animals exposed to environmental stimulation in the form of enriched environments. We present a molecular atlas of the aging process, highlighting two distinct axes, related to inflammation and to the dysregulation of mRNA metabolism, at the functional RNA and protein level. Additionally, we report the alteration of heterochromatin domains, including the loss of bivalent chromatin and the uncovering of a heterochromatin-switch phenomenon whereby constitutive heterochromatin loss is partially mitigated through gains in facultative heterochromatin. Notably, we observed the multi-omic reversal of a great number of aging-associated alterations in the context of environmental enrichment, which was particularly linked to glial and oligodendrocyte pathways. In conclusion, our work describes the epigenomic landscape of environmental stimulation in the context of aging and reveals how lifestyle intervention can lead to the multi-layered reversal of aging-associated decline.

Neuroplasticity of children in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that encompasses a range of symptoms including difficulties in verbal communication, social interaction, limited interests, and repetitive behaviors. Neuroplasticity refers to the structural and functional changes that occur in the nervous system to adapt and respond to changes in the external environment. In simpler terms, it is the brain's ability to learn and adapt to new environments. However, individuals with ASD exhibit abnormal neuroplasticity, which impacts information processing, sensory processing, and social cognition, leading to the manifestation of corresponding symptoms. This paper aims to review the current research progress on ASD neuroplasticity, focusing on genetics, environment, neural pathways, neuroinflammation, and immunity. The findings will provide a theoretical foundation and insights for intervention and treatment in pediatric fields related to ASD.

Cell cycle associated protein 1 associates with immune infiltration and ferroptosis in gastrointestinal cancer

Background

Cell Cycle-Associated Protein 1 (CAPRIN1) play an important role in cell proliferation, oxidative stress, and inflammatory response. Nonetheless, its role in tumor immunity and ferroptosis is largely unknown in gastrointestinal cancer patients.

Methods

Through comprehensive bioinformatics, we investigate CAPRIN1 expression patterns and its role in diagnosis, functional signaling pathways, tumor immune infiltration and ferroptosis of different gastrointestinal cancer subtypes. Besides, immunohistochemistry (IHC) and immune blot were used to validate our esophagus cancer clinical data. The ferroptotic features of CAPRIN1 in vitro were assessed through knockdown assays in esophagus cancer cells.

Results

CAPRIN1 expression was significantly upregulated, correlated with poor prognosis, and served as an independent risk factor for most gastrointestinal cancer. Moreover, CAPRIN1 overexpression positively correlated with gene markers of most infiltrating immune cells, and immune checkpoints. CAPRIN1 knockdown significantly decreased the protein level of major histocompatibility complex class I molecules. We also identified a link between CAPRIN1 and ferroptosis-related genes in gastrointestinal cancer. Knockdown of CAPRIN1 significantly increased the production of lipid reactive oxygen species and malondialdehyde. Inhibition of CAPRIN1 expression promoted ferroptotic cell death induced by RAS-selective lethal 3 and erastin in human esophagus cancer cells.

Conclusion

Collectively, our results demonstrate that CAPRIN1 is aberrantly expressed in gastrointestinal cancer, is associated with poor prognosis, and could potentially influence immune infiltration and ferroptosis.

Proteomic and transcriptomic profiling of brainstem, cerebellum and olfactory tissues in early- and late-phase COVID-19

Neurological symptoms, including cognitive impairment and fatigue, can occur in both the acute infection phase of coronavirus disease 2019 (COVID-19) and at later stages, yet the mechanisms that contribute to this remain unclear. Here we profiled single-nucleus transcriptomes and proteomes of brainstem tissue from deceased individuals at various stages of COVID-19. We detected an inflammatory type I interferon response in acute COVID-19 cases, which resolves in the late disease phase. Integrating single-nucleus RNA sequencing and spatial transcriptomics, we could localize two patterns of reaction to severe systemic inflammation, one neuronal with a direct focus on cranial nerve nuclei and a separate diffuse pattern affecting the whole brainstem. The latter reflects a bystander effect of the respiratory infection that spreads throughout the vascular unit and alters the transcriptional state of mainly oligodendrocytes, microglia and astrocytes, while alterations of the brainstem nuclei could reflect the connection of the immune system and the central nervous system via, for example, the vagus nerve. Our results indicate that even without persistence of severe acute respiratory syndrome coronavirus 2 in the central nervous system, local immune reactions are prevailing, potentially causing functional disturbances that contribute to neurological complications of COVID-19.

Using Machine Learning to Explore Shared Genetic Pathways and Possible Endophenotypes in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a heterogeneous condition, characterized by complex genetic architectures and intertwined genetic/environmental interactions. Novel analysis approaches to disentangle its pathophysiology by computing large amounts of data are needed. We present an advanced machine learning technique, based on a clustering analysis on genotypical/phenotypical embedding spaces, to identify biological processes that might act as pathophysiological substrates for ASD. This technique was applied to the VariCarta database, which contained 187,794 variant events retrieved from 15,189 individuals with ASD. Nine clusters of ASD-related genes were identified. The 3 largest clusters included 68.6% of all individuals, consisting of 1455 (38.0%), 841 (21.9%), and 336 (8.7%) persons, respectively. Enrichment analysis was applied to isolate clinically relevant ASD-associated biological processes. Two of the identified clusters were characterized by individuals with an increased presence of variants linked to biological processes and cellular components, such as axon growth and guidance, synaptic membrane components, or transmission. The study also suggested other clusters with possible genotype-phenotype associations. Innovative methodologies, including machine learning, can improve our understanding of the underlying biological processes and gene variant networks that undergo the etiology and pathogenic mechanisms of ASD. Future work to ascertain the reproducibility of the presented methodology is warranted.

Combined exome analysis and exome depth assessment achieve a high diagnostic yield in an epilepsy case series, revealing significant genomic heterogeneity and novel mechanisms

OBJECTIVES

Genetics of epilepsy are highly heterogeneous and complex. Lesions detected involve genes encoding various types of channels, transcription factors, and other proteins implicated in numerous cellular processes, such as synaptogenesis. Consequently, a wide spectrum of clinical presentations and overlapping phenotypes hinders differential diagnosis and highlights the need for molecular investigations toward delineation of underlying mechanisms and final diagnosis. Characterization of defects may also contribute valuable data on genetic landscapes and networks implicated in epileptogenesis.

METHODS

This study reports on genetic findings from exome sequencing (ES) data of 107 patients with variable types of seizures, with or without additional symptoms, in the context of neurodevelopmental disorders.

RESULTS

Multidisciplinary evaluation of ES, including ancillary detection of copy number variants (CNVs) with the ExomeDepth tool, supported a definite diagnosis in 59.8% of the patients, reflecting one of the highest diagnostic yields in epilepsy.

CONCLUSION

Emerging advances of next-generation technologies and 'in silico' analysis tools offer the possibility to simultaneously detect several types of variations. Wide assessment of variable findings, specifically those found to be novel and least expected, reflects the ever-evolving genetic landscape of seizure development, potentially beneficial for increased opportunities for trial recruitment and enrollment, and optimized, even personalized, medical management.

RNA degradation eliminates developmental transcripts during murine embryonic stem cell differentiation via CAPRIN1-XRN2

Embryonic stem cells (ESCs) are self-renewing and pluripotent. In recent years, factors that control pluripotency, mostly nuclear, have been identified. To identify non-nuclear regulators of ESCs, we screened an endogenously labeled fluorescent fusion-protein library in mouse ESCs. One of the more compelling hits was the cell-cycle-associated protein 1 (CAPRIN1). CAPRIN1 knockout had little effect in ESCs, but it significantly altered differentiation and gene expression programs. Using RIP-seq and SLAM-seq, we found that CAPRIN1 associates with, and promotes the degradation of, thousands of RNA transcripts. CAPRIN1 interactome identified XRN2 as the likely ribonuclease. Upon early ESC differentiation, XRN2 is located in the nucleus and colocalizes with CAPRIN1 in small RNA granules in a CAPRIN1-dependent manner. We propose that CAPRIN1 regulates an RNA degradation pathway operating during early ESC differentiation, thus eliminating undesired spuriously transcribed transcripts in ESCs.

Is bRaQCing bad? New roles for ribosome associated quality control factors in stress granule regulation

Maintenance of proteostasis is of utmost importance to cellular viability and relies on the coordination of many post-transcriptional processes to respond to stressful stimuli. Stress granules (SGs) are RNA-protein condensates that form after translation initiation is inhibited, such as during the integrated stress response (ISR), and may facilitate cellular adaptation to stress. The ribosome-associated quality control (RQC) pathway is a critical translation monitoring system that recognizes aberrant mRNAs encoding potentially toxic nascent peptides to target them for degradation. Both SG regulation and the RQC pathway are directly associated with translation regulation, thus it is of no surprise recent developments have demonstrated a connection between them. VCP's function in the stress activated RQC pathway, ribosome collisions activating the ISR, and the regulation of the 40S ribosomal subunit by canonical SG proteins during the RQC all connect SGs to the RQC pathway. Because mutations in genes that are involved in both SG and RQC regulation are associated with degenerative and neurological diseases, understanding the coordination and interregulation of SGs and RQC may shed light on disease mechanisms. This minireview will highlight recent advances in understanding how SGs and the RQC pathway interact in health and disease contexts.

CAPRIN1P512L causes aberrant protein aggregation and associates with early-onset ataxia

CAPRIN1 is a ubiquitously expressed protein, abundant in the brain, where it regulates the transport and translation of mRNAs of genes involved in synaptic plasticity. Here we describe two unrelated children, who developed early-onset ataxia, dysarthria, cognitive decline and muscle weakness. Trio exome sequencing unraveled the identical de novo c.1535C > T (p.Pro512Leu) missense variant in CAPRIN1, affecting a highly conserved residue. In silico analyses predict an increased aggregation propensity of the mutated protein. Indeed, overexpressed CAPRIN1^P512L forms insoluble ubiquitinated aggregates, sequestrating proteins associated with neurodegenerative disorders (ATXN2, GEMIN5, SNRNP200 and SNCA). Moreover, the CAPRIN1^P512L mutation in isogenic iPSC-derived cortical neurons causes reduced neuronal activity and altered stress granule dynamics. Furthermore, nano-differential scanning fluorimetry reveals that CAPRIN1^P512L aggregation is strongly enhanced by RNA in vitro. These findings associate the gain-of-function Pro512Leu mutation to early-onset ataxia and neurodegeneration, unveiling a critical residue of CAPRIN1 and a key role of RNA–protein interactions.