An eye on the future for defeating hydrocephalus, ciliary dyskinesia-related hydrocephalus: review article

Congenital hydrocephalus affects approximately one in 1000 newborn children and is fatal in approximately 50% of untreated cases. The currently known management protocols usually necessitate multiple interventions and long-term use of healthcare resources due to a relatively high incidence of complications, and many of them mostly provide a treatment of the effect rather than the cause of cerebrospinal fluid flow reduction or outflow obstruction. Future studies discussing etiology specific hydrocephalus alternative treatments are needed. We systematically reviewed the available literature on the effect of ciliary abnormality on congenital hydrocephalus pathogenesis, to open a discussion on the feasibility of factoring ciliary abnormality in future research on hydrocephalus treatment modalities. Although there are different forms of ciliopathies, we focused in this review on primary ciliary dyskinesia. There is growing evidence of association of other ciliary syndromes and hydrocephalus, such as the reduced generation of multiple motile cilia, which is distinct from primary ciliary dyskinesia. Data for this review were identified by searching PubMed using the search terms 'hydrocephalus,' 'Kartagener syndrome,' 'primary ciliary dyskinesia,' and 'immotile cilia syndrome.' Only articles published in English and reporting human patients were included. Seven studies met our inclusion criteria, reporting 12 cases of hydrocephalus associated with primary ciliary dyskinesia. The patients had variable clinical presentations, genetic backgrounds, and ciliary defects. The ependymal water propelling cilia differ in structure and function from the mucus propelling cilia, and there is a possibility of isolated non-syndromic ependymal ciliopathy causing only hydrocephalus with growing evidence in the literature for the association ependymal ciliary abnormality and hydrocephalus. Abdominal and thoracic situs in children with hydrocephalus can be evaluated, and secondary damage of ependymal cilia causing hydrocephalus in cases with generalized ciliary abnormality can be considered.

Progressive liver, kidney, and heart degeneration in children and adults affected by TULP3 mutations

Organ fibrosis is a shared endpoint of many diseases, yet underlying mechanisms are not well understood. Several pathways governed by the primary cilium, a sensory antenna present on most vertebrate cells, have been linked with fibrosis. Ciliopathies usually start early in life and represent a considerable disease burden. We performed massively parallel sequencing by using cohorts of genetically unsolved individuals with unexplained liver and kidney failure and correlated this with clinical, imaging, and histopathological analyses. Mechanistic studies were conducted with a vertebrate model and primary cells. We detected bi-allelic deleterious variants in TULP3, encoding a critical adaptor protein for ciliary trafficking, in a total of 15 mostly adult individuals, originating from eight unrelated families, with progressive degenerative liver fibrosis, fibrocystic kidney disease, and hypertrophic cardiomyopathy with atypical fibrotic patterns on histopathology. We recapitulated the human phenotype in adult zebrafish and confirmed disruption of critical ciliary cargo composition in several primary cell lines derived from affected individuals. Further, we show interaction between TULP3 and the nuclear deacetylase SIRT1, with roles in DNA damage repair and fibrosis, and report increased DNA damage ex vivo. Transcriptomic studies demonstrated upregulation of profibrotic pathways with gene clusters for hypertrophic cardiomyopathy and WNT and TGF-β signaling. These findings identify variants in TULP3 as a monogenic cause for progressive degenerative disease of major organs in which affected individuals benefit from early detection and improved clinical management. Elucidation of mechanisms crucial for DNA damage repair and tissue maintenance will guide novel therapeutic avenues for this and similar genetic and non-genomic diseases.

Dawn and dusk peaks of outer segment phagocytosis, and visual cycle function require Rab28

RAB28 is a farnesylated, ciliary G-protein. Patient variants in RAB28 are causative of autosomal recessive cone-rod dystrophy (CRD), an inherited human blindness. In rodent and zebrafish models, the absence of Rab28 results in diminished dawn, photoreceptor, outer segment phagocytosis (OSP). Here, we demonstrate that Rab28 is also required for dusk peaks of OSP, but not for basal OSP levels. This study further elucidated the molecular mechanisms by which Rab28 controls OSP and inherited blindness. Proteomic profiling identified factors whose expression in the eye or whose expression at dawn and dusk peaks of OSP is dysregulated by loss of Rab28. Notably, transgenic overexpression of Rab28, solely in zebrafish cones, rescues the OSP defect in rab28 KO fish, suggesting rab28 gene replacement in cone photoreceptors is sufficient to regulate Rab28-OSP. Rab28 loss also perturbs function of the visual cycle as retinoid levels of 11-cRAL, 11cRP, and atRP are significantly reduced in larval and adult rab28 KO retinae (p < .05). These data give further understanding on the molecular mechanisms of RAB28-associated CRD, highlighting roles of Rab28 in both peaks of OSP, in vitamin A metabolism and in retinoid recycling.

Mechanisms of Weight Control by Primary Cilia

A primary cilium, a hair-like protrusion of the plasma membrane, is a pivotal organelle for sensing external environmental signals and transducing intracellular signaling. An interesting linkage between cilia and obesity has been revealed by studies of the human genetic ciliopathies Bardet-Biedl syndrome and Alström syndrome, in which obesity is a principal manifestation. Mouse models of cell type-specific cilia dysgenesis have subsequently demonstrated that ciliary defects restricted to specific hypothalamic neurons are sufficient to induce obesity and hyperphagia. A potential mechanism underlying hypothalamic neuron cilia-related obesity is impaired ciliary localization of G protein-coupled receptors involved in the regulation of appetite and energy metabolism. A well-studied example of this is melanocortin 4 receptor (MC4R), mutations in which are the most common cause of human monogenic obesity. In the paraventricular hypothalamus neurons, a blockade of ciliary trafficking of MC4R as well as its downstream ciliary signaling leads to hyperphagia and weight gain. Another potential mechanism is reduced leptin signaling in hypothalamic neurons with defective cilia. Leptin receptors traffic to the periciliary area upon leptin stimulation. Moreover, defects in cilia formation hamper leptin signaling and actions in both developing and differentiated hypothalamic neurons. The list of obesity-linked ciliary proteins is expending and this supports a tight association between cilia and obesity. This article provides a brief review on the mechanism of how ciliary defects in hypothalamic neurons facilitate obesity.

Patient-Patient Similarity-Based Screening of a Clinical Data Warehouse to Support Ciliopathy Diagnosis

A timely diagnosis is a key challenge for many rare diseases. As an expanding group of rare and severe monogenic disorders with a broad spectrum of clinical manifestations, ciliopathies, notably renal ciliopathies, suffer from important underdiagnosis issues. Our objective is to develop an approach for screening large-scale clinical data warehouses and detecting patients with similar clinical manifestations to those from diagnosed ciliopathy patients. We expect that the top-ranked similar patients will benefit from genetic testing for an early diagnosis. The dependence and relatedness between phenotypes were taken into account in our similarity model through medical concept embedding. The relevance of each phenotype to each patient was also considered by adjusted aggregation of phenotype similarity into patient similarity. A ranking model based on the best-subtype-average similarity was proposed to address the phenotypic overlapping and heterogeneity of ciliopathies. Our results showed that using less than one-tenth of learning sources, our language and center specific embedding provided comparable or better performances than other existing medical concept embeddings. Combined with the best-subtype-average ranking model, our patient-patient similarity-based screening approach was demonstrated effective in two large scale unbalanced datasets containing approximately 10,000 and 60,000 controls with kidney manifestations in the clinical data warehouse (about 2 and 0.4% of prevalence, respectively). Our approach will offer the opportunity to identify candidate patients who could go through genetic testing for ciliopathy. Earlier diagnosis, before irreversible end-stage kidney disease, will enable these patients to benefit from appropriate follow-up and novel treatments that could alleviate kidney dysfunction.

Adult Presentation of Joubert Syndrome Presenting With Dysphagia: A Case Report

Joubert syndrome (JS) is a rare autosomal recessive disease affecting the cilium, an intracellular organelle. It has a wide spectrum of presentations with the involvement of multiple genes. JS has multiple subtypes that are either pure JS or JS with other organ involvement such as the kidneys, liver, and others. However, all subtypes share the involvement of the cerebellar peduncles and the brainstem, which presents as "a molar tooth sign" on magnetic resonance imaging, hypotonia, and intellectual disability. It has a higher prevalence among children with few able to survive to adulthood. Unfortunately, survivors live with debilitating comorbidities. Here, we present the case of a 20-year-old patient who presented with a new onset of dysphagia that led to a diagnosis of JS.

Idiopathic intracranial hypertension in a child with Bardet-Biedl syndrome

BACKGROUND

Bardet-Biedl syndrome (BBS) is known to be associated with hydrocephalus, but not with idiopathic intracranial hypertension (IIH). Case presentation: We describe such a case and propose the pathogenesis. We also discuss the challenges of diagnosis, treatment, and monitoring outcomes in this population that is already at high risk of vision loss from retinal dystrophy.

CONCLUSION

IIH can result from a combination of risk factors in conjunction with the underlying dysfunctional cilia in BBS patients. Monitoring disease progression is difficult, and as such IIH may be underdiagnosed or missed. Management must be adjusted to account for BBS patients' impaired metabolic and renal physiology. It is important that clinicians be aware of these challenges in this vulnerable population, and regular monitoring should be done to avoid preventable vision loss.

Modeling Human Primary Microcephaly With hiPSC-Derived Brain Organoids Carrying CPAP-E1235V Disease-Associated Mutant Protein

The centrosome is composed of a pair of centrioles and serves as the major microtubule-organizing center (MTOC) in cells. Centrosome dysfunction has been linked to autosomal recessive primary microcephaly (MCPH), which is a rare human neurodevelopmental disorder characterized by small brain size with intellectual disability. Recently, several mouse models carrying mutated genes encoding centrosomal proteins have been generated to address the genotype-phenotype relationships in MCPH. However, several human-specific features were not observed in the mouse models during brain development. Herein, we generated isogenic hiPSCs carrying the gene encoding centrosomal CPAP-E1235V mutant protein using the CRISPR-Cas9 genome editing system, and examined the phenotypic features of wild-type and mutant hiPSCs and their derived brain organoids. Our results showed that the CPAP-E1235V mutant perturbed the recruitment of several centriolar proteins involved in centriole elongation, including CEP120, CEP295, CENTROBIN, POC5, and POC1B, onto nascent centrioles, resulting in the production of short centrioles but long cilia. Importantly, our wild-type hiPSC-derived brain organoid recapitulated many cellular events seen in the developing human brain, including neuronal differentiation and cortical spatial lamination. Interestingly, hiPSC-CPAP-E1235V-derived brain organoids induced p53-dependent neuronal cell death, resulting in the production of smaller brain organoids that mimic the microcephaly phenotype. Furthermore, we observed that the CPAP-E1235V mutation altered the spindle orientation of neuronal progenitor cells and induced premature neuronal differentiation. In summary, we have shown that the hiPSC-derived brain organoid coupled with CRISPR/Cas9 gene editing technology can recapitulate the centrosome/centriole-associated MCPH pathological features. Possible mechanisms for MCPH with centriole/centrosome dysfunction are discussed.

Human iPSC-Derived Retinal Organoids and Retinal Pigment Epithelium for Novel Intronic RPGR Variant Assessment for Therapy Suitability

The RPGR gene encodes Retinitis Pigmentosa GTPase Regulator, a known interactor with ciliary proteins, which is involved in maintaining healthy photoreceptor cells. Variants in RPGR are the main contributor to X-linked rod-cone dystrophy (RCD), and RPGR gene therapy approaches are in clinical trials. Hence, elucidation of the pathogenicity of novel RPGR variants is important for a patient therapy opportunity. Here, we describe a novel intronic RPGR variant, c.1415 − 9A>G, in a patient with RCD, which was classified as a variant of uncertain significance according to current clinical diagnostic criteria. The variant lay several base pairs intronic to the canonical splice acceptor site, raising suspicion of an RPGR RNA splicing abnormality and consequent protein dysfunction. To investigate disease causation in an appropriate disease model, induced pluripotent stem cells were generated from patient fibroblasts and differentiated to retinal pigment epithelium (iPSC-RPE) and retinal organoids (iPSC-RO). Abnormal RNA splicing of RPGR was demonstrated in patient fibroblasts, iPSC-RPE and iPSC-ROs, leading to a predicted frameshift and premature stop codon. Decreased RPGR expression was demonstrated in these cell types, with a striking loss of RPGR localization at the ciliary transitional zone, critically in the photoreceptor cilium of the patient iPSC-ROs. Mislocalisation of rhodopsin staining was present in the patient’s iPSC-RO rod photoreceptor cells, along with an abnormality of L/M opsin staining affecting cone photoreceptor cells and increased photoreceptor apoptosis. Additionally, patient iPSC-ROs displayed an increase in F-actin expression that was consistent with an abnormal actin regulation phenotype. Collectively, these studies indicate that the splicing abnormality caused by the c.1415 − 9A>G variant has an impact on RPGR function. This work has enabled the reclassification of this variant to pathogenic, allowing the consideration of patients with this variant having access to gene therapy clinical trials. In addition, we have identified biomarkers of disease suitable for the interrogation of other RPGR variants of uncertain significance.

Prenatally detected encephalocele associated with a novel pathogenic TCTN3 variant: A case report and literature review

Primary cilia are a component of almost all vertebrate cells with a crucial role in sensing and transducing environmental signals during tissue development. Their dysfunction is known as ciliopathies and can manifest with a wide spectrum of clinical disorders. Overlapping features and molecular heterogeneity of ciliopathies make diagnoses distinctly challenging. In this group of diseases, tectonic genes, and their mutations play an important role. We present a first-trimester fetus with occipital encephalocele and OFD type IV caused by TCTN3 compound heterozygous pathogenic variants: c.1423_1429del (p.Arg475Serfs*10) and c.3G>A (initiator codon). A severe arm anomaly was described in our case, with two fingers along the atrophic forearm and polydactyly on other limbs. This could be a new phenotypic characteristic contributing to further understanding of TCTN3-related disorders as well as other tectonic proteins in ciliopathy spectrum diseases.

Expression of a Truncated Form of ODAD1 Associated with an Unusually Mild Primary Ciliary Dyskinesia Phenotype

Primary ciliary dyskinesia (PCD) is a rare lung disease caused by mutations that impair the function of motile cilia, resulting in chronic upper and lower respiratory disease, reduced fertility, and a high prevalence of situs abnormalities. The disease is genetically and phenotypically heterogeneous, with causative mutations in > 50 genes identified, and clinical phenotypes ranging from mild to severe. Absence of ODAD1 (CCDC114), a component of the outer dynein arm docking complex, results in a failure to assemble outer dynein arms (ODAs), mostly immotile cilia, and a typical PCD phenotype. We identified a female (now 34 years old) with an unusually mild clinical phenotype who has a homozygous non-canonical splice mutation (c.1502+5G>A) in ODAD1. To investigate the mechanism for the unusual phenotype, we performed molecular and functional studies of cultured nasal epithelial cells. We demonstrate that this splice mutation results in the expression of a truncated protein that is attached to the axoneme, indicating that the mutant protein retains partial function. This allows for the assembly of some ODAs and a significant level of ciliary activity that may result in the atypically mild clinical phenotype. The results also suggest that partial restoration of ciliary function by therapeutic agents could lead to significant improvement of disease symptoms.

Zebrafish and idiopathic scoliosis: the 'unknown knowns'

The etiology and heterogeneity of idiopathic scoliosis (IS) are poorly understood. Studies using scoliotic zebrafish models have indicated a potential link between ciliary defects and scoliosis. They may further explain the onset of IS partially. However, it is necessary to further interpret the link between this progress and clinical medicine.

Monoallelic IFT140 pathogenic variants are an important cause of the autosomal dominant polycystic kidney-spectrum phenotype

Autosomal dominant polycystic kidney disease (ADPKD), characterized by progressive cyst formation/expansion, results in enlarged kidneys and often end stage kidney disease. ADPKD is genetically heterogeneous; PKD1 and PKD2 are the common loci (∼78% and ∼15% of families) and GANAB, DNAJB11, and ALG9 are minor genes. PKD is a ciliary-associated disease, a ciliopathy, and many syndromic ciliopathies have a PKD phenotype. In a multi-cohort/-site collaboration, we screened ADPKD-diagnosed families that were naive to genetic testing (n = 834) or for whom no PKD1 and PKD2 pathogenic variants had been identified (n = 381) with a PKD targeted next-generation sequencing panel (tNGS; n = 1,186) or whole-exome sequencing (WES; n = 29). We identified monoallelic IFT140 loss-of-function (LoF) variants in 12 multiplex families and 26 singletons (1.9% of naive families). IFT140 is a core component of the intraflagellar transport-complex A, responsible for retrograde ciliary trafficking and ciliary entry of membrane proteins; bi-allelic IFT140 variants cause the syndromic ciliopathy, short-rib thoracic dysplasia (SRTD9). The distinctive monoallelic phenotype is mild PKD with large cysts, limited kidney insufficiency, and few liver cysts. Analyses of the cystic kidney disease probands of Genomics England 100K showed that 2.1% had IFT140 LoF variants. Analysis of the UK Biobank cystic kidney disease group showed probands with IFT140 LoF variants as the third most common group, after PKD1 and PKD2. The proximity of IFT140 to PKD1 (∼0.5 Mb) in 16p13.3 can cause diagnostic confusion, and PKD1 variants could modify the IFT140 phenotype. Importantly, our studies link a ciliary structural protein to the ADPKD spectrum.

Molecular mechanisms underlying the role of the centriolar CEP164-TTBK2 complex in ciliopathies

Cilia formation is essential for human life. One of the earliest events in the ciliogenesis program is the recruitment of tau-tubulin kinase 2 (TTBK2) by the centriole distal appendage component CEP164. Due to the lack of high-resolution structural information on this complex, it is unclear how it is affected in human ciliopathies such as nephronophthisis. Furthermore, it is poorly understood if binding to CEP164 influences TTBK2 activities. Here, we present a detailed biochemical, structural, and functional analysis of the CEP164-TTBK2 complex and demonstrate how it is compromised by two ciliopathic mutations in CEP164. Moreover, we also provide insights into how binding to CEP164 is coordinated with TTBK2 activities. Together, our data deepen our understanding of a crucial step in cilia formation and will inform future studies aimed at restoring CEP164 functionality in a debilitating human ciliopathy.

Primary cilium in kidney development, function and disease

The primary cilium is a hair-like, microtubule-based organelle that is covered by the cell membrane and extends from the surface of most vertebrate cells. It detects and translates extracellular signals to direct various cellular signaling pathways to maintain homeostasis. It is mainly distributed in the proximal and distal tubules and collecting ducts in the kidney. Specific signaling transduction proteins localize to primary cilia. Defects in cilia structure and function lead to a class of diseases termed ciliopathies. The proper functioning of primary cilia is essential to kidney organogenesis and the maintenance of epithelial cell differentiation and proliferation. Persistent cilia dysfunction has a role in the early stages and progression of renal diseases, such as cystogenesis and acute tubular necrosis (ATN). In this review, we focus on the central role of cilia in kidney development and illustrate how defects in cilia are associated with renal disease progression.

Case Report: Sequential Liver After Kidney Transplantation in a Patient With Sensenbrenner Syndrome (Cranioectodermal Dysplasia)

Sensenbrenner syndrome, also known as cranioectodermal dysplasia (CED), is a rare ciliopathy clinically characterized by congenital craniofacial, skeletal, and ectodermal defects. Chronic kidney and liver insufficiency are also present in this disorder. Cranioectodermal dysplasia is an autosomal recessive and heterogeneous genetic disease. Six genes (IFT122, WDR35, IFT140, IFT43, IFT52, and WDR19) are known to be associated with this syndrome. Until 2021 more than 70 patients have been reported with CED, however, an orthotopic liver transplantation has been reported only in one case. Here, we present a case report of sequential liver-after-kidney transplantation in a male patient affected by CED. The kidney and liver transplantation was performed at the age of 7 and 12 years, respectively. Patients with Sensenbrenner syndrome require a multidisciplinary medical management and should regularly be followed-up by hepatologists and nephrologists, as the liver and kidney diseases are the major cause of morbidity and mortality.

Liver Cirrhosis in Woman with Ciliopathy Syndrome

Ciliopathy syndrome is a congenital abnormality of structure and/or function of cilia, which causes pleiotropic disorder, including liver cirrhosis. This study aimed to describe a unique case of liver cirrhosis with possible aetiology of ciliopathy syndrome. A 44 year-old woman with chief complain of hematemesis had diabetes mellitus, obesity, dyslipidaemia, amenorrhoea and often became unconscious. We found short stature, brachydactyly, hyperpigmented maculae in trunk and four limbs, and hepatosplenomegaly. The laboratory results showed: haemoglobin 7.4 g/dl; albumin 2.42 g/dl; urea 84.8 mg/dl; creatinine 2.4 mg/dl; prolactin 138.8 ng/ml, while HBsAg was negative and anti-HCV was non-reactive. Abdominal ultrasonography showed liver cirrhosis; endoscopy showed grade 3 oesophageal varicose; FibroScan showed 75 kPa; liver biopsy showed hydropic degeneration and cirrhosis; and head CT scan showed chronic lacunar infarction of corona radiata and mega cisterna magna occipital. We reported female with oesophageal varicose rupture, short stature, brachydactyly, obesity, diabetes mellitus, dyslipidaemia, hyperpigmented maculae, liver cirrhosis and mega cisterna magna, which was likely to suffer from ciliopathy syndrome.

Aurora A and AKT Kinase Signaling Associated with Primary Cilia

Dysregulation of kinase signaling is associated with various pathological conditions, including cancer, inflammation, and autoimmunity; consequently, the kinases involved have become major therapeutic targets. While kinase signaling pathways play crucial roles in multiple cellular processes, the precise manner in which their dysregulation contributes to disease is dependent on the context; for example, the cell/tissue type or subcellular localization of the kinase or substrate. Thus, context-selective targeting of dysregulated kinases may serve to increase the therapeutic specificity while reducing off-target adverse effects. Primary cilia are antenna-like structures that extend from the plasma membrane and function by detecting extracellular cues and transducing signals into the cell. Cilia formation and signaling are dynamically regulated through context-dependent mechanisms; as such, dysregulation of primary cilia contributes to disease in a variety of ways. Here, we review the involvement of primary cilia-associated signaling through aurora A and AKT kinases with respect to cancer, obesity, and other ciliopathies.

Update of genetic variants in CEP120 and CC2D2A-With an emphasis on genotype-phenotype correlations, tissue specific transcripts and exploring mutation specific exon skipping therapies

BACKGROUND

Mutations in ciliary genes cause a spectrum of both overlapping and distinct clinical syndromes (ciliopathies). CEP120 and CC2D2A are paradigmatic examples for this genetic heterogeneity and pleiotropy as mutations in both cause Joubert syndrome but are also associated with skeletal ciliopathies and Meckel syndrome, respectively. The molecular basis for this phenotypical variability is not understood but basal exon skipping likely contributes to tolerance for deleterious mutations via tissue-specific preservation of the amount of expressed functional protein.

METHODS

We systematically reviewed and annotated genetic variants and clinical presentations reported in CEP120- and CC2D2A-associated disease and we combined in silico and ex vivo approaches to study tissue-specific transcripts and identify molecular targets for exon skipping.

RESULTS

We confirmed more severe clinical presentations associated with truncating CC2D2A mutations. We identified and confirmed basal exon skipping in the kidney, with possible relevance for organ-specific disease manifestations. Finally, we proposed a multimodal approach to classify exons amenable to exon skipping. By mapping reported variants, 14 truncating mutations in 7 CC2D2A exons were identified as potentially rescuable by targeted exon skipping, an approach that is already in clinical use for other inherited human diseases.

CONCLUSION

Genotype-phenotype correlations for CC2D2A support the deleteriousness of null alleles and CC2D2A, but not CEP120, offers potential for therapeutic exon skipping approaches.

Ciliary Hedgehog signaling regulates cell survival to build the facial midline

Craniofacial defects are among the most common phenotypes caused by ciliopathies, yet the developmental and molecular etiology of these defects is poorly understood. We investigated multiple mouse models of human ciliopathies (including Tctn2, Cc2d2a, and Tmem231 mutants) and discovered that each displays hypotelorism, a narrowing of the midface. As early in development as the end of gastrulation, Tctn2 mutants displayed reduced activation of the Hedgehog (HH) pathway in the prechordal plate, the head organizer. This prechordal plate defect preceded a reduction of HH pathway activation and Shh expression in the adjacent neurectoderm. Concomitant with the reduction of HH pathway activity, Tctn2 mutants exhibited increased cell death in the neurectoderm and facial ectoderm, culminating in a collapse of the facial midline. Enhancing HH signaling by decreasing the gene dosage of a negative regulator of the pathway, Ptch1, decreased cell death and rescued the midface defect in both Tctn2 and Cc2d2a mutants. These results reveal that ciliary HH signaling mediates communication between the prechordal plate and the neurectoderm to provide cellular survival cues essential for development of the facial midline.

Expanding the Phenotype of the FAM149B1-Related Ciliopathy and Identification of Three Neurogenetic Disorders in a Single Family

Biallelic truncating FAM149B1 variants result in cilia dysfunction and have been reported in four infants with Joubert syndrome and orofaciodigital syndrome type VI, respectively. We report here on three adult siblings, 18 to 40 years of age, homozygous for the known FAM149B1 c.354_357delinsCACTC (p.Gln118Hisfs*20) variant. Detailed clinical examinations were performed including ocular and gait analyses, skeletal- and neuroimaging. All three patients presented with neurological and oculomotor symptoms since birth and mild skeletal dysplasia in infancy resulting in characteristic gait abnormalities. We document mild skeletal dysplasia, abnormal gait with increased hip rotation and increased external foot rotation, ataxia, variable polydactyly, ocular Duane syndrome, progressive ophthalmoplegia, nystagmus, situs inversus of the retinal vessels, olfactory bulb aplasia, and corpus callosal dysgenesis as novel features in FAM149B1-ciliopathy. We show that intellectual disability is mild to moderate and retinal, renal and liver function is normal in these affected adults. Our study thus expands the FAM149B1-related Joubert syndrome to a mainly neurological and skeletal ciliopathy phenotype with predominant oculomotor dysfunction but otherwise stable outcome in adults. Diagnosis of FAM149B1-related disorder was impeded by segregation of multiple neurogenetic disorders in the same family, highlighting the importance of extended clinical and genetic studies in families with complex phenotypes.

Cilia kinases in skeletal development and homeostasis

Primary cilia are dynamic compartments that regulate multiple aspects of cellular signaling. The production, maintenance, and function of cilia involve more than 1000 genes in mammals, and their mutations disrupt the ciliary signaling which manifests in a plethora of pathological conditions-the ciliopathies. Skeletal ciliopathies are genetic disorders affecting the development and homeostasis of the skeleton, and encompass a broad spectrum of pathologies ranging from isolated polydactyly to lethal syndromic dysplasias. The recent advances in forward genetics allowed for the identification of novel regulators of skeletogenesis, and revealed a growing list of ciliary proteins that are critical for signaling pathways implicated in bone physiology. Among these, a group of protein kinases involved in cilia assembly, maintenance, signaling, and disassembly has emerged. In this review, we summarize the functions of cilia kinases in skeletal development and disease, and discuss the available and upcoming treatment options.

Using Paramecium as a Model for Ciliopathies

Paramecium has served as a model organism for the studies of many aspects of genetics and cell biology: non-Mendelian inheritance, genome duplication, genome rearrangements, and exocytosis, to name a few. However, the large number and patterning of cilia that cover its surface have inspired extraordinary ultrastructural work. Its swimming patterns inspired exquisite electrophysiological studies that led to a description of the bioelectric control of ciliary motion. A genetic dissection of swimming behavior moved the field toward the genes and gene products underlying ciliary function. With the advent of molecular technologies, it became clear that there was not only great conservation of ciliary structure but also of the genes coding for ciliary structure and function. It is this conservation and the legacy of past research that allow us to use Paramecium as a model for cilia and ciliary diseases called ciliopathies. However, there would be no compelling reason to study Paramecium as this model if there were no new insights into cilia and ciliopathies to be gained. In this review, we present studies that we believe will do this. For example, while the literature continues to state that immotile cilia are sensory and motile cilia are not, we will provide evidence that Paramecium cilia are clearly sensory. Other examples show that while a Paramecium protein is highly conserved it takes a different interacting partner or conducts a different ion than expected. Perhaps these exceptions will provoke new ideas about mammalian systems.

Case Report: Second Report of Joubert Syndrome Caused by Biallelic Variants in IFT74

Joubert syndrome (JBTS) is a rare ciliopathy characterized by developmental delay, hypotonia, and distinctive cerebellar and brain stem malformation called the molar tooth sign (MTS). We reported a 15-month-old female with dysmorphic features (flat nasal bridge, almond-shaped eye, and a minor midline notch in the upper lips), hypotonia, polydactyly, development delay, and MTS. Whole exome sequencing revealed biallelic heterozygous mutations c.535C>G(p.Q179E/c.853G>T) (p.E285^*) in IFT74, which were inherited from the parents. So far, only one article reported JBTS associated with IFT74 gene mutation, and this is the second report of the fifth patient with JBTS due to variants in IFT74. All five patients had developmental delay, postaxial polydactyly, subtle cleft of the upper lip, hypotonia, and MTS, but notably without renal and retinal anomalies or significant obesity, and they shared the same mutation c.535C>G(p.Q179E) in IFT74, and c.853G>T(p.E285^*) that we found was a new mutation in IFT74 that related with Joubert syndrome. Those findings highlight the need for the inclusion of IFT74 in gene panels for JBST testing.

A Genotype-Phenotype Analysis of the Bardet-Biedl Syndrome in Puerto Rico

Background

Bardet-Biedl syndrome is a complex heterogeneous ciliopathy caused by genetic mutations. Although establishing genotype-phenotype correlations has been challenging, some regional variations have been previously reported. Due to its relative geographic isolation, Puerto Rico has a greater prevalence of Bardet-Biedl syndrome than do other regions. We sought to characterize the most frequent genotypic variations in a local cohort of Bardet-Biedl syndrome patients and report any genotypic-phenotypic trends.

Methods

Twenty-seven patients from an ophthalmology clinic in Puerto Rico with genetically confirmed Bardet-Biedl syndrome took a questionnaire inquiring about their most common symptoms. Ophthalmological information was obtained from patient records. The frequencies of the genotypic variations and symptoms were calculated.

Results

In the study population, BBS1 was the most prevalent mutated gene, followed by BBS7. In the BBS1 group, we found homozygotes for c.1169T>G (p.Met390Arg) and c.1645G>T (p.Glu549*), and compound heterozygotes for c.1169T>G (p.Met390Arg) and c.1645G>T (p.Glu549*), with one patient having c.1645G>T (p.Glu549*) and c.432+1G>A (splice donor). All the BBS7 patients were homozygous for c.632C>T (p.Thr211Ile). Compared to BBS7, we found that BBS1 patients generally had a milder ocular and systemic phenotype. However, when analyzing different BBS1 variants, patients with mutations in c.1645G>T (p.Glu549*), both compound heterozygous and homozygous, had more severe systemic phenotypes, overall.

Conclusion

Our study was the first detailed genotype-phenotype analysis of the Bardet-Biedl syndrome in Puerto Rico. Genetic mutations in BBS1 and BBS7 seem to be the most common culprits behind Bardet-Biedl syndrome in this population. Although patients diagnosed with BBS1 are likely to display milder systemic features, this was not the case with our BBS1 patients having the c.1645G>T (p.Glu549*) mutation. Further studies should focus on the c.1645G>T (p.Glu549*) mutation's impact on the BBS1 gene and protein product.