A zebrafish morpholino knockdown model targeting ahi1 enables efficient phenotypic assessment of ciliopathy-related defects and functional evaluation of variants of uncertain significance. This assay clarifies the impact of VUSs, supporting zebrafish morphants as a reliable platform for validating ciliopathy-associated genetic variants.

Disruption of the complex processes underlying central nervous system development leads to a broad spectrum of brain malformations and neurodevelopmental disorders, often with a genetic cause. Here, we report bi-allelic pathogenic variants in fibronectin type III and SPRY domain-containing 1-like (FSD1L), encoding a protein of unknown function, in eleven individuals, including five fetuses from six unrelated families. The phenotype ranges from severe hydrocephalus, corpus callosum agenesis, and absent pyramid decussation to a neurodevelopmental syndrome characterized by severe intellectual disability, spastic tetraparesis, reduced vision, and epilepsy, associated with corpus callosum agenesis/hypoplasia, mild ventricular dilation, optic nerve hypoplasia, and white matter reduction. This phenotype closely resembles that observed in L1 syndrome, caused by pathogenic variants in L1CAM, encoding a neural adhesion molecule. The knockdown of Fsd1l in mouse embryos recapitulated the ventricular dilation observed in affected fetuses. Immunohistochemical studies in human control fetuses revealed that FSD1L localized to neurons with commissural fate and projection neurons during human development. Induced pluripotent stem cell (iPSC)-derived neural progenitor cells from affected individuals failed to differentiate into premature neurons and to properly form neurospheres while undergoing increased cell death. In neural progenitors, FSD1L localized with microtubules of the mitotic spindle during M phase and to the transition zone and along the axoneme of the primary cilium during interphase. In line with this, fibroblasts from affected individuals exhibited marked alterations of the mitotic spindle and reduced ciliogenesis and ciliary length compared to control cells. Our findings define FSD1L as a microtubule-associated protein implicated in neuronal differentiation, axon guidance, and fasciculation.

Background and Objectives:Pathogenic variants in KIF5C, encoding a neuronal kinesin motor protein, cause a rare neurodevelopmental disorder characterized by profound global developmental delay/intellectual disability mainly associated with absent speech and severe motor disability, epilepsy, and behavioral problems. Methods:Three individuals with KIF5C variants were evaluated through clinical, neuroimaging, and genetic assessments, and their findings were compared with previously reported cases. A PubMed search using the term "KIF5C″ was performed on March 2, 2025; only English-language articles with detailed clinical descriptions of participants were included. Results:Two participants carried the recurrent c.709G > A, p.(Glu237Lys) variant, whereas 1 had a novel substitution, c.606C > G, p.(Ser202Arg). All individuals exhibited severe neurodevelopmental impairment. Neuroimaging revealed complex brain malformations, particularly anterior-predominant pachygyria, as well as white matter and cerebellar abnormalities; 1 participant lacked overt cortical malformations. Discussion:These findings emphasize that KIF5C-related disorder displays a broader clinical, genetic, and neuroimaging spectrum than previously recognized and may, in some cases, occur without the classic cortical malformations. The presence of white matter and cerebellar involvement suggests that KIF5C variants may disrupt multiple neurodevelopmental processes. Expanding the recognized phenotype will enhance early diagnosis, deepen our understanding of the disease's clinical spectrum, and inform both management strategies and genetic counseling.

Primary cilia are ubiquitous organelles, which play essential roles in sensing and transducing cellular signals and in mediating key developmental pathways. Pathogenic variants in genes encoding for ciliary proteins give rise to a spectrum of disorders termed primary ciliopathies. The archetypal neurodevelopmental ciliopathy is Joubert syndrome. However, in the past decade, primary cilia have been implicated in several other neurological disorders, including neurodevelopmental disorders, malformations of cortical development, neurodegenerative disorders, and psychiatric disorders. Therapeutic approaches for cilia-related disorders are still scarce. Strategies based on gene therapy and antisense oligonucleotides show promising results, especially for the treatment of retinal ciliopathies, and are currently moving towards clinical translation. Other approaches based on drug repurposing or the use of small molecules, despite positive results in a variety of cellular and animal models, are still in the experimental stage.

Ciliopathies are rare genetic disorders characterized by significant genetic and phenotypic variability. Over 140 proteins localized to primary cilia, which are sensory organelles essential for vertebrate development, are implicated. TMEM17 encodes a transmembrane protein at the ciliary transition zone and was previously proposed as a potential ciliopathy gene, based on reports of individuals from two families with orofaciodigital syndrome type 6 (OFD6) and Joubert syndrome (JS). Here, we report two unrelated fetuses with occipital encephalocele, polydactyly, and kidney cysts, in whom exome sequencing identified a founder homozygous missense variant (Arg94Trp) in TMEM17, affecting a highly conserved residue. This expands the TMEM17-associated phenotypic spectrum to include Meckel syndrome (MKS). Comprehensive functional analyses of all known TMEM17 variants, using patient tissues/cells and a C. elegans model system, demonstrate a loss-of-function mechanism. Our study reveals severe functional consequences, including TMEM17 destabilization and mislocalization, anomalies in cilium composition and function, and abrogation of Sonic Hedgehog signaling. These experiments confirm the pathogenicity of all TMEM17 variants and underscore its essential role at the ciliary transition zone. Collectively, our findings establish TMEM17 as a bona fide ciliopathy gene, associated with a wide phenotypic spectrum ranging from viable syndromes (OFD6 and JS) to a fetal-lethal condition (MKS).

RNU4ATAC is a non-coding gene involved in the minor spliceosome, and is mutated in a spectrum of syndromic skeletal disorders with recessive inheritance. Recently, biallelic RNU4ATAC pathogenic variants were detected in five patients presenting a complex syndromic phenotype and a brain malformation resembling the 'molar tooth sign' (MTS). This is the hallmark of Joubert syndrome (JS), a neurodevelopmental ciliopathy with multiorgan involvement.We reanalysed exome sequencing (ES) from 53 patients with JS, who lacked coding variants in known JS-associated genes. Four RNU4ATAC variants (n.16G>A, n.51G>A, n.13C>T and n.30G>A) were identified in compound heterozygosity in three probands, accounting for 5.6% of negative cases. All patients displayed the MTS and clinical features overlapping those of JS and RNU4ATAC-related skeletal disorders.These findings expand the phenotypic spectrum of RNU4ATAC-related disorders to include a complex neurological-skeletal ciliopathy phenotype, and highlight the relevance of ES reanalysis to uncover non-coding variants often undetected by conventional diagnostics.

Studying ciliary genes in the context of the human central nervous system is crucial for understanding the underlying causes of neurodevelopmental ciliopathies. Here, we use pluripotent stem cell-derived spinal organoids to reveal distinct functions of the ciliopathy gene RPGRIP1L in humans and mice, and uncover an unexplored role for cilia in human axial patterning. Previous research has emphasized Rpgrip1l critical functions in mouse brain and spinal cord development through the regulation of SHH/GLI pathway. Here, we show that RPGRIP1L is not required for SHH activation or motoneuron lineage commitment in human spinal progenitors and that this feature is shared by another ciliopathy gene, TMEM67. Furthermore, human RPGRIP1L-mutant motoneurons adopt hindbrain and cervical identities instead of caudal brachial identity. Temporal transcriptome analysis reveals that this antero-posterior patterning defect originates in early axial progenitors and correlates with cilia loss. These findings provide important insights into the role of cilia in human neural development.

We generated iPSC line using skin fibroblasts obtained from a female patient affected by Joubert syndrome, caused by two compound heterozygous variants (c.143G > A; p.Gly48Glu and c.1784 T > G; p.Leu595Ter) in CPLANE1. We used Sendai -virus -based technique for reprogramming and then we applied karyotype analysis, to exclude possible acquired big rearrangements. We verified the presence of the same STR profile as fibroblasts, the stem cell state (by immunofluorescence and qPCR) and, finally, the pluripotency state (by in vitro trilineage differentiation).

Studying developmental processes in the context of the human central nervous system is essential to understand neurodevelopmental diseases. In this paper we perform a comparative functional study of the ciliopathy gene RPGRIP1L in human and mouse spinal development using in vitro 3D differentiation of pluripotent stem cells. RPGRIP1L, a causal gene of severe neurodevelopmental ciliopathies such as Joubert and Meckel syndromes, encodes a scaffolding protein of the ciliary transition zone involved in ciliary gating. Previous work has identified a major role for Rpgrip1l in mouse brain and spinal cord development, via controlling the Sonic Hedgehog (SHH)/GLI pathway. We show that spinal organoids derived from Rpgrip1l mutant mouse embryonic stem cells faithfully recapitulate the loss of motoneurons and the strong reduction of SHH signaling observed in the mutant mice. In contrast, human induced pluripotent stem cells mutant for RPGRIP1L produce motoneurons and activate the SHH pathway at levels similar to wild types, a property shared by human iPSCs mutant for another ciliopathy gene TMEM67. Moreover, we show that, in human RPGRIP1L mutant organoids, motoneurons acquire a more anterior identity, expressing HOX genes and proteins normally present in the hindbrain while motoneurons from wild type organoids strictly display spinal identity. By performing a temporal transcriptome analysis throughout the differentiation process, we find that the anteroposterior specification defect arises in early axial progenitors and correlates with the loss of cilia in these cells. Thus, this study uncovers distinct functions in humans and mice for ciliopathy proteins and a novel role for RPGRIP1L in human spinal anteroposterior patterning. These findings have important implications for understanding the role of cilia in human spinal cord development and the pathogenic mechanisms of neurodevelopmental ciliopathies.

Joubert syndrome (JS) is a genetically heterogeneous neurodevelopmental ciliopathy. Despite exome sequencing (ES), several patients remain undiagnosed. This study aims to increase the diagnostic yield by uncovering cryptic variants through targeted ES reanalysis. We first focused on 26 patients in whom ES only disclosed heterozygous pathogenic coding variants in a JS gene. We reanalyzed raw ES data searching for copy number variants (CNVs) and intronic variants affecting splicing. We validated CNVs through real-time PCR or chromosomal microarray, and splicing variants through RT-PCR or minigenes. Cryptic variants were then searched in additional 44 ES-negative JS individuals. We identified cryptic “second hits” in 14 of 26 children (54%) and biallelic cryptic variants in 3 of 44 (7%), reaching a definite diagnosis in 17 of 70 (overall diagnostic gain 24%). We show that CNVs and intronic splicing variants are a common mutational mechanism in JS; more importantly, we demonstrate that a significant proportion of such variants can be disclosed simply through a focused reanalysis of available ES data, with a significantly increase of the diagnostic yield especially among patients previously found to carry heterozygous coding variants in the KIAA0586, CC2D2A and CPLANE1 genes.

We established two iPSC lines starting from skin fibroblasts of two healthy individuals using Sendai-virus-based technique. The obtained iPSCs were characterized showing same STR profile as starting fibroblasts, normal karyotype, loss of stemness vectors, expression of stemness markers, both through real-time PCR and immunofluorescence, (OCT4, SOX2, TRA-1–60, NANOG and SSEA4) and in vitro differentiation into three germ layers.

Background Joubert syndrome (JS) is a neurodevelopmental ciliopathy characterised by a distinctive mid-hindbrain malformation, the ‘molar tooth sign’. Over 40 JS-associated genes are known, accounting for two-thirds of cases. Methods While most variants are novel or extremely rare, we report on 11 recurring variants in seven genes, including three known ‘founder variants’ in the Ashkenazi Jewish, Hutterite and Finnish populations. We evaluated variant frequencies in ~550 European patients with JS and compared them with controls (>15 000 Italian plus gnomAD), and with an independent cohort of ~600 JS probands from the USA. Results All variants were markedly enriched in the European JS cohort compared with controls. When comparing allele frequencies in the two JS cohorts, the Ashkenazim founder variant (TMEM216 c.218G>T) was significantly enriched in American compared with European patients with JS, while MKS1 c.1476T>G was about 10 times more frequent among European JS. Frequencies of other variants were comparable in the two cohorts. Genotyping of several markers identified four novel European founder haplotypes. Two recurrent variants (MKS1 c.1476T>G and KIAA0586 c.428delG), have been detected in homozygosity in unaffected individuals, suggesting they could act as hypomorphic variants. However, while fibroblasts from a MKS1 c.1476T>G healthy homozygote showed impaired ability to form primary cilia and mildly reduced ciliary length, ciliary parameters were normal in cells from a KIAA0586 c.428delG healthy homozygote. Conclusion This study contributes to understand the complex genetic landscape of JS, explain its variable prevalence in distinct geographical areas and characterise two recurrent hypomorphic variants.

NFIB belongs to the nuclear factor I (NFI) family of transcription factors that, by activating or repressing gene expression during embryogenesis, has a relevant role in the development of several organs including the brain. Heterozygous pathogenic variants of NFIB have recently been associated with developmental delay and mild-to-moderate intellectual disability, macrocephaly, nonspecific facial dysmorphisms, and corpus callosum dysgenesis. We identified a heterozygous missense variant in the NFIB gene in a 15-year-old boy with neurodevelopmental disorder and brain malformations, who inherited the variant from his substantially healthy mother presenting only minor physical and neuroanatomical defects.

Background The term congenital ocular motor apraxia (COMA), coined by Cogan in 1952, designates the incapacity to initiate voluntary eye movements performing rapid gaze shift, so called saccades. While regarded as a nosological entity by some authors, there is growing evidence that COMA designates merely a neurological symptom with etiologic heterogeneity. In 2016, we reported an observational study in a cohort of 21 patients diagnosed as having COMA. Thorough re-evaluation of the neuroimaging features of these 21 subjects revealed a previously not recognized molar tooth sign (MTS) in 11 of them, thus leading to a diagnostic reassignment as Joubert syndrome (JBTS). Specific MRI features in two further individuals indicated a Poretti–Boltshauser syndrome (PTBHS) and a tubulinopathy. In eight patients, a more precise diagnosis was not achieved. We pursued this cohort aiming at clarification of the definite genetic basis of COMA in each patient. Results Using a candidate gene approach, molecular genetic panels or exome sequencing, we detected causative molecular genetic variants in 17 of 21 patients with COMA. In nine of those 11 subjects diagnosed with JBTS due to newly recognized MTS on neuroimaging, we found pathogenic mutations in five different genes known to be associated with JBTS, including KIAA0586, NPHP1, CC2D2A, MKS1 , and TMEM67 . In two individuals without MTS on MRI, pathogenic variants were detected in NPHP1 and KIAA0586 , arriving at a diagnosis of JBTS type 4 and 23, respectively. Three patients carried heterozygous truncating variants in SUFU , representing the first description of a newly identified forme fruste of JBTS. The clinical diagnoses of PTBHS and tubulinopathy were confirmed by detection of causative variants in LAMA1 and TUBA1A , respectively. In one patient with normal MRI, biallelic pathogenic variants in ATM indicated variant ataxia telangiectasia. Exome sequencing failed to reveal causative genetic variants in the remaining four subjects, two of them with clear MTS on MRI. Conclusions Our findings indicate marked etiologic heterogeneity in COMA with detection of causative mutations in 81% (17/21) in our cohort and nine different genes being affected, mostly genes associated with JBTS. We provide a diagnostic algorithm for COMA.

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