PURPOSE:TCF7L2 (OMIM 602228; HGNC:11641) is a transcription factor and a critical effector of the Wnt/ β-Catenin pathway. In 2021, 11 pediatric patients with monoallelic predicted loss-of-function (pLOF) TCF7L2 variants and syndromic features were observed. Characterization of patients with pLOF TCF7L2 variants and neurodevelopmental features-herein referred to as TCF7L2-related neurodevelopmental disorder-is urgently needed. METHODS:We leveraged multiple methods (eg, GeneMatcher, DECIPHER, literature review, and public/private repositories) to identify an international cohort of 76 patients with pLOF TCF7L2 variants and neurodevelopmental features and phenotypically characterized them. We also retrospectively searched for an independent cohort of adults with pLOF TCF7L2 variants (n = 11) from more than 60,000 PennMedicine BioBank patients. RESULTS:Among 76 patients with pLOF TCF7L2 variants, speech delay (95.3%), craniofacial dysmorphisms (73.3%), ophthalmologic conditions (65.5%), autism (62.1%), and orthopedic abnormalities (52.6%) were the most commonly observed. Phenotypic differences did not cluster by variant type or genomic locus. Among PennMedicine BioBank patients, an association of nominal significance with type 2 diabetes with renal manifestations (odds ratio = 5.8; P = .03) was detected, warranting further investigation. CONCLUSION:This study represents the most comprehensive characterization of TCF7L2-related neurodevelopmental disorder to date, a novel neurodevelopmental disorder, defining its genotypic and phenotypic spectra. We opened a Simons Searchlight natural history study that is now available for patient enrollment to enhance the understanding of this condition.

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.

INTRODUCTION:Type I 3-Methylglutaconic Aciduria (MGCA1) is a metabolic disorder inherited in an autosomal recessive manner. It is caused by a deficiency in the 3-methylglutaconyl-CoA hydratase encoded by the AUH gene, leading to abnormal excretion of urinary organic acids. While the pediatric phenotype encompasses a spectrum ranging from isolated developmental delay to severe forms with leukodystrophy, developmental delay, spastic tetraplegia and movement disorders, the adult phenotype corresponds to a leukodystrophy with spastic ataxia, progressive dementia, and optic neuropathy. Due to its rarity, MGCA1 is most likely underdiagnosed, or diagnosed with an important delay, leading to inadequate care or genetic counselling. A better understanding of the disease's phenotype is thus required to facilitate its clinical and genetic diagnosis, in turn favoring clinical care and genetic counselling. METHODS AND RESULTS:We report two new MGCA1 patients, including an adult male patient with pure, late-onset, and progressive cerebellar ataxia, without optic neuropathy or leukodystrophy. A young female patient case is also reported with moderate developmental delay and leukodystrophy, offering 14-year follow-up data under carnitine supplementation. In both cases, urinary organic acid chromatography was critical to the diagnostic process by demonstrating abnormal and specific urinary organic acids excretion. DISCUSSION AND CONCLUSION:The description of new, mild and/or late-onset phenotypes expands the clinical and radiological spectrum of MGCA1. Our results show that late-onset MGCA1 patients may present with pure cerebellar ataxia without leukodystrophy, contrasting with current knowledge. These results support the fact that AUH should always be sequenced in patients with pure cerebellar ataxia, but also that urinary organic acid chromatography being a simple, rapid, and cost-effective test, should be performed as a first-tier analysis in all patients with unresolved neurological symptoms. The importance of identifying MGCA1 patients is reinforced by the possibility of implementing a low-risk and possibly effective therapy with low-protein diet and L-carnitine supplementation.

De novo heterozygous variants in CUGBP Elav-like family member 2 (CELF2) have recently been associated with a rare neurodevelopmental disorder, yet the mechanisms linking specific variants to distinct clinical phenotypes remain poorly understood. Here, we reported a cohort of 18 individuals and provided evidence that variants causing CELF2 mislocalization, but not protein-null variants, were associated with seizures. Using proband-derived human cortical neurons and transgenic mouse models, we demonstrated that CELF2 underwent activity-dependent nucleocytoplasmic shuttling in excitatory neurons and that its cytoplasmic retention caused neuronal hyperactivity, elevated seizure susceptibility, and learning and memory deficits. We further found that cytoplasmic CELF2 regulated mRNAs critical for synaptic function and neuronal excitability and implicated in epileptic seizures and intellectual disability. Drug screening further identified AKT signaling as a key regulator of CELF2 nucleocytoplasmic shuttling and a candidate target for reversing neuronal hyperactivity. Together, our findings expand the clinical and genetic spectrum of CELF2-related neurodevelopmental disorders and establish a variant-specific mechanism that links CELF2 mislocalization to neuronal hyperactivity, seizures, and cognitive impairment.

Rare genetic variants in ARID2 are responsible for a recently described neurodevelopmental condition called ARID2-related disorder (ARID2-RD). ARID2 belongs to PBAF, a unit of the SWI/SNF complex, which is a chromatin remodeling complex. This work aims to further delineate the phenotypic spectrum of ARID2-RD, providing clinicians with additional data for better care and aid in the future diagnosis of this condition. We obtained the genotypes and phenotypes of 27 previously unreported individuals with ARID2-RD and compared this series with findings in the literature. We also assessed peripheral blood DNA methylation profiles in individuals with ARID2-RD compared to episignatures of controls, unresolved cases, and other neurodevelopmental disorders. The main clinical features of ARID2-RD are developmental delay, speech disorders, intellectual disability (ID), behavior problems, short stature, and various dysmorphic and ectodermal features. Genome-wide differential methylation analysis revealed a global hypermethylated profile in ARID2-RD that could aid in reclassifying variants of uncertain significance. Our study doubles the number of reported individuals with ARID2 pathogenic variants to 53. It confirms loss-of-function as a pathomechanism and shows the absence of a clear genotype-phenotype correlation. We provide evidence for a unique DNA methylation episignature for ARID2-RD and further delineate the ARID2-associated phenotype.

Purpose AUTS2-related syndrome is characterized by developmental delay, autism spectrum disorder, and intellectual disability. From alternative promoters, AUTS2 encodes 2 distinct long and short isoforms encoding a putative transcriptional activator. Methods Through a European collaborative study, we collected clinical and genotype data on the largest AUTS2-related syndrome cohort of 58 patients harboring genomic rearrangements or single-nucleotide variants (SNVs). Results Pathogenic SNVs were recurrently found in individuals from different countries, suggesting mutational hotspots. Independent of the underlying defect at the AUTS2 locus, we observed that autistic behavior, hyperactivity, learning difficulties, and speech delay are common features of AUTS2-related syndrome. Among patients with SNVs, individuals carrying pathogenic variants affecting both longer and shorter AUTS2 transcripts showed a recognizable phenotype with microcephaly, brachycephaly, microretrognathia, broad nasal base, and anteverted nares. Behavioral disorders were more common in patients with variants affecting only the longer isoform. Arthrogryposis and stiff movements were only observed in patients with SNVs. Conclusion This study provides a comprehensive clinical characterization of AUTS2-related syndrome, reveals few genotype-phenotype correlations, and suggests that the disruption of the 2 distinct AUTS2 transcripts has a different impact on the clinical phenotype.

De novo variants are a leading cause of neurodevelopmental disorders (NDDs), but because every monogenic NDD is different and usually extremely rare, it remains a major challenge to understand the complete phenotype and genotype spectrum of any morbid gene. According to OMIM, heterozygous variants in KDM6B cause "neurodevelopmental disorder with coarse facies and mild distal skeletal abnormalities."Here, by examining the molecular and clinical spectrum of 85 reported individuals with mostly de novo (likely) pathogenic KDM6B variants, we demonstrate that this description is inaccurate and potentially misleading. Cognitive deficits are seen consistently in all individuals, but the overall phenotype is highly variable. Notably, coarse facies and distal skeletal anomalies, as defined by OMIM, are rare in this expanded cohort while other features are unexpectedly common (e.g., hypotonia, psychosis, etc.). Using 3D protein structure analysis and an innovative dual Drosophila gain-of-function assay, we demonstrated a disruptive effect of 11 missense/in-frame indels located in or near the enzymatic JmJC or Zn-containing domain of KDM6B. Consistent with the role of KDM6B in human cognition, we demonstrated a role for the Drosophila KDM6B ortholog in memory and behavior. Taken together, we accurately define the broad clinical spectrum of the KDM6B-related NDD, introduce an innovative functional testing paradigm for the assessment of KDM6B variants, and demonstrate a conserved role for KDM6B in cognition and behavior. Our study demonstrates the critical importance of international collaboration, sharing of clinical data, and rigorous functional analysis of genetic variants to ensure correct disease diagnosis for rare disorders.

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.

The post-transcriptional modification of tRNAs plays a crucial role in tRNA structure and function. Pathogenic variants in tRNA-modification enzymes have been implicated in a wide range of human neurodevelopmental and neurological disorders. However, the molecular basis for many of these disorders remains unknown. Here, we describe a comprehensive cohort of 43 individuals from 31 unrelated families with bi-allelic variants in tRNA methyltransferase 1 (TRMT1). These individuals present with a neurodevelopmental disorder universally characterized by developmental delay and intellectual disability, accompanied by variable behavioral abnormalities, epilepsy, and facial dysmorphism. The identified variants include ultra-rare TRMT1 variants, comprising missense and predicted loss-of-function variants, which segregate with the observed clinical pathology. Our findings reveal that several variants lead to mis-splicing and a consequent loss of TRMT1 protein accumulation. Moreover, cells derived from individuals harboring TRMT1 variants exhibit a deficiency in tRNA modifications catalyzed by TRMT1. Molecular analysis reveals distinct regions of TRMT1 required for tRNA-modification activity and binding. Notably, depletion of Trmt1 protein in zebrafish is sufficient to induce developmental and behavioral phenotypes along with gene-expression changes associated with disrupted cell cycle, immune response, and neurodegenerative disorders. Altogether, these findings demonstrate that loss of TRMT1-catalyzed tRNA modifications leads to intellectual disability and provides insight into the molecular underpinnings of tRNA-modification deficiency caused by pathogenic TRMT1 variants.

The interstitial 6p microdeletion syndrome is characterized by dysmorphic facies and structural heart, kidney, brain, and musculoskeletal differences. RREB1 haploinsufficiency and consequent abnormal RAS-MAPK pathway signaling have been proposed as a driver of the disease phenotype; however, apart from a single case report, the phenotype of intragenic RREB1 variants is unknown. Here we present a cohort of 6 individuals with truncating RREB1 variants. Phenotypes include mild dysmorphisms, congenital heart disease, genitourinary malformations, dental anomalies, and developmental delay. Our data support RREB1 as a currently under-recognized cause of a RASopathy phenotype with features that overlap with Noonan, Costello, and Cardiofaciocutaneous syndromes.

Severe loss of function variants in the splicing regulatory protein RBM10 are known to cause TARP syndrome, a rare X-linked recessive congenital syndrome. In recent years, individuals with milder phenotypes have been published, suggesting a broader phenotypic spectrum. We report 37 new individuals with RBM10 variants and compare to 34 published cases. We find that the phenotype can be described as an 'RBM10-phenotypic spectrum' which can be further subdivided into two phenotypic groups, TARP syndrome (TARPS) and RBM10 Associated Intellectual Disability (RAID). Based on phenotype characterizations and functional studies, we describe a clear genotype-phenotype correlation. Splicing analysis of blood samples and CRISPR-edited cells representing different degrees of functional loss of RBM10 demonstrated a pattern of more exon inclusion in response to increased loss of RBM10 function (LOF). More inclusion was correlated with increasing phenotype severity. Functional studies of missense variants from the different phenotypic groups confirm this genotype-phenotype correlation and show that different molecular mechanisms can explain the underlying pathological alterations in RBM10 protein function. Interestingly, we show that some missense variants in the RNA binding, RRM2 domain of RBM10 alter RBM10 activity from splicing inhibition to stimulation, likely due to altered RNA binding characteristics. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by a grant from The Lundbeck Foundation (R286-2018-1739 to JMVB and BSA), Natur og Univers, Det Frie Forskningsraad (0135-00459B and 3103-00329A to BSA), The fund to support clinical research careers in the Region of Southern Denmark (Region Syddanmarks pulje for kliniske forskerkarriereforloeb) (CFA), and California Center for Rare Diseases within the UCLA Institute for Precision Health (SN, MT, LKW) . The Euro-MRX project, where the first family had their X-chromosome exome sequencing per-formed, was financially supported by the EU FP7 project GENCODYS, grant no. 241995. Several authors of this publication are members of the European Reference Network on Rare Con-genital Malformations and Rare Intellectual Disability ERN-ITHACA. [EU Framework Partnership Agreement ID: 3HP-HP-FPA ERN-01-2016/739516] This study makes use of data generated by the DECIPHER community. A full list of centers who contributed to the generation of the data is available from https://deciphergenomics.org/about/stats and via email from contact{at}deciphergenomics.org. DECIPHER is hosted by EMBL-EBI and funding for the DECIPHER project was provided by the Wellcome Trust [WT223718/Z/21/Z]. This study utilized the GeneMatcher platform, a founding member of the Matchmaker Ex-change project, to identify potential matches, data shared through the seqr platform (funding provid-ed by National Institutes of Health grants R01HG009141 and UM1HG008900), and use data shared through the PhenomeCentral repository (funded by Genome Canada and Canadian Institute of Health Research). ### 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: Approval for studies of families with RBM10 variants is obtained from The Regional Committee of Southern Denmark on Health Research Ethics (Project-ID: S-20180082). 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 RBM10 CRISPR RNA-seq data is deposited in the ArrayExpress database (https://www.ebi.ac.uk/bi-ostudies/arrayexpress) under accession number E-MTAB-15267. Patient RNA-seq data is not avail-able due to ethical restrictions. The analytical code is available upon request. Values for all presented data are reported in the Supporting Data Values file.

RNA-binding proteins play a key role in post-transcriptional events, such as mRNA splicing, transport, stability, translation and decay. Dysregulation of RNA life can have dramatic consequences. CELF RNA-binding proteins appear to be essential during embryo development. In this study, we identified 15 patients with heterozygous missense or loss-of-function variants in the CELF4 gene by exome or genome sequencing. All variants affecting the N-terminus of the protein are essential and sufficient for the RNA-binding and splicing activity or RRM domains. Most patients presented with neurodevelopmental disorders including global developmental delay/intellectual disability (11/14), seizures (9/15) and overweight/obesity (10/14) that began in childhood. Clinical features are similar to the reported celf4-mouse mutant phenotype. This study highlights the essential role of CELF4 in development and its involvement as a novel etiology of neurodevelopmental disorders with obesity.

SETD2 has an essential role in epigenetic regulation. SETD2 pathogenic variants cause neurodevelopmental disorders (SETD2-NDDs) that most commonly include various degrees of intellectual disability and behavioral disorders, macrocephaly, brain malformations, and generalized overgrowth. A distinctive DNA methylation episignature has been identified for Luscan-Lumish syndrome. A less common phenotype, denoted SETD2-NDD with multiple congenital anomalies, failure to thrive, and profound intellectual disability, has been reported in association with a particular pathogenic variant (p.Arg1740Trp). To date, about 50 patients have been described in the literature with SETD2 causative variants. We report here an individual with a phenotype distinct from SETD2-NDDs, including normal cognition, distinctive facial features, and multiple tumor histories, including a sacral osteoblastoma at age 7, a benign femoral bone tumor at age 17, a peritoneal pseudomyxoma at age 27, and a hypophyseal macroadenoma and a low-grade optochiasmatic glioma at age 37 years. Trio exome sequencing identified a de novo heterozygous missense variant of unknown significance (p.Ser1658Leu) in the SETD2 gene. DNA methylation study by EpiSign assay confirmed the presence of an episignature profile compatible with SETD2-related disorders. Given the implication of somatic SETD2 variants in benign and malignant tumors, the implication of these SETD2 constitutional variants in tumorigenesis is discussed.

De novo heterozygous variants in the CELF2 gene have recently been associated with a rare neurodevelopmental disorder. However, the mechanisms linking specific variants to distinct clinical phenotypes remain poorly understood. Here, we report a new cohort of 14 individuals with de novo CELF2 variants, providing evidence that variants causing CELF2 cytoplasmic mislocalization, but not its loss-of-function, are associated with seizures. Using proband induced pluripotent stem cell-derived neurons and transgenic mouse models, we show that CELF2 undergoes activity-dependent nucleocytoplasmic shuttling in excitatory neurons, and its cytoplasmic retention causes neuronal hyperexcitability, leading to learning and memory deficits. In the cytoplasm, CELF2 regulates mRNAs critical for synaptic functions and neuronal excitability implicated in epileptic seizures and intellectual disability. Through drug screening, we identify AKT signaling as a key regulator of CELF2 shuttling and a target for treating CELF2-associated hyperexcitability. Our findings expand the clinical and genetic spectrum of CELF2-related neurodevelopmental disorders and reveal variant-specific mechanisms that link CELF2 mislocalization to neuronal hyperexcitability, learning deficits, and epileptic seizures. One Sentence Summary:CELF2 variants link protein mislocalization to neuronal hyperexcitability, learning deficits, and epileptic seizures.

OBJECTIVE:Following the first French multicenter pilot study (AnDDI-Prenatome) focused on the implementation of prenatal exome sequencing (pES), this ancillary study aims to explore the ethical and clinical issues raised by pES within multidisciplinary prenatal diagnosis centers. METHODS:33 healthcare professionals involved in the management of couples undergoing prenatal diagnosis (PND) took part in focus groups (2 with clinical geneticists, 3 with professionals from multidisciplinary prenatal diagnosis centers (MPDC), 1 with biologists). Each focus group was analyzed using the thematic analysis method. RESULTS:Professionals emphasized the importance of having a clear understanding of pES and the criteria for its prescription. Geneticists highlighted the need for a framework to clarify the implications of consent for patients and stressed the importance of offering structured support to assist couples in their decision-making process. Biologists and geneticists expressed a desire for effective multidisciplinary coordination of the care pathway, particularly in situations where the results were uncertain. CONCLUSION:These results will help to establish French recommendations for the prescription of pES.

ABSTRACT Background Multiple molecular diagnoses (MMD) involve distinct or overlapping phenotypes. They are not so rare in the field of congenital anomalies, given an overall 3.5%–8% rate. Mainly, MMD imply distinct genotypes. Exceptionally, genotypes are linked, involving a causal CNV by itself, facing a SNV for a recessive disorder resulting in a dual diagnosis. Methods An unrelated couple was referred at 21 + 3 weeks of gestation for talipes equinovarus, cerebellar hypoplasia, clenched fists, elevated hemidiaphragm, and micrognathia. Chromosomal microarray and exome sequencing analyses were performed. Results Both identified a pathogenic de novo 22q11.21 deletion (22q11.2del). Fetal autopsy revealed additional features (postaxial polydactyly, facial features, and abnormal lung lobulation), atypical for 22q11.2del syndrome. At the clinician's request, exome sequencing reanalysis identified a paternally inherited SCARF2 variant, in trans to the 22q11.2del causing autosomal recessive Van den Ende–Gupta syndrome. This dual diagnosis explains the entire fetus phenotype. Discussion This is a novel case of dual diagnosis, first prenatal and second case of this ultrarare association. It reflects the crucial role of precise phenotypic description, combined with the importance of considering dual diagnosis in case of atypical clinical presentation. Finally, prenatal phenotypes remain a challenge given the paucity of available known prenatal data for most rare diseases. Trial Registration ClinicalTrial.gov ID: NCT05182242

The major spliceosome contains five small nuclear RNAs (snRNAs; U1, U2, U4, U5 and U6) essential for splicing. Variants in RNU4-2, encoding U4, cause a neurodevelopmental disorder called ReNU syndrome. We investigated de novo variants in 50 snRNA-encoding genes in a French cohort of 23,649 individuals with rare disorders and gathered additional cases through international collaborations. Altogether, we identified 145 previously unreported probands with (likely) pathogenic variants in RNU4-2 and 21 individuals with de novo and/or recurrent variants in RNU5B-1 and RNU5A-1, encoding U5. Pathogenic variants typically arose de novo on the maternal allele and cluster in regions critical for splicing. RNU4-2 variants mainly localize to two structures, the stem III and T-loop/quasi-pseudoknot, which position the U6 ACAGAGA box for 5' splice site recognition and associate with different phenotypic severity. RNU4-2 variants result in specific defects in alternative 5' splice site usage and methylation patterns (episignatures) that correlate with variant location and clinical severity. This study establishes RNU5B-1 as a neurodevelopmental disorder gene, suggests RNU5A-1 as a strong candidate and highlights the role of de novo variants in snRNAs.

Polypyrimidine tract-binding protein 1 (PTBP1) is a heterogeneous nuclear ribonucleoprotein primarily known for its alternative splicing activity. It shuttles between the nucleus and cytoplasm via partially overlapping N-terminal nuclear localization (NLS) and export (NES) signals. Despite its fundamental role in cell growth and differentiation, its involvement in human disease remains poorly understood. We identified 27 individuals from 25 families harboring de novo or inherited pathogenic variants - predominantly start-loss (89%) and, to a lesser extent, missense (11%) - affecting NES/NLS motifs. Affected individuals presented with a syndromic neurodevelopmental disorder and variable skeletal dysplasia with disproportionate short stature with short limbs. Intellectual functioning ranged from normal to moderately delayed. Start-loss variants led to translation initiation from an alternative downstream in-frame methionine, resulting in loss of the NES and the first half of the bipartite NLS, and increased cytoplasmic stability. Start-loss and missense variants shared a DNA methylation episignature in peripheral blood and altered nucleocytoplasmic distribution in vitro and in vivo with preferential accumulation in processing bodies, causing aberrant gene expression but normal RNA splicing. Transcriptomic analysis of patient-derived fibroblasts revealed dysregulated pathways involved in osteochondrogenesis and neurodevelopment. Overall, our findings highlight a cytoplasmic role for PTBP1 in RNA stability and disease pathogenesis.