Joubert syndrome and related disorders

Syndromic Retinitis Pigmentosa: A Narrative Review

Retinitis pigmentosa (RP) encompasses inherited retinal dystrophies, appearing either as an isolated eye condition or as part of a broader systemic syndrome, known as syndromic RP. In these cases, RP includes systemic symptoms impacting other organs, complicating diagnosis and management. This review highlights key systemic syndromes linked with RP, such as Usher, Bardet-Biedl, and Alström syndromes, focusing on genetic mutations, inheritance, and clinical symptoms. These insights support clinicians in recognizing syndromic RP early. Ocular signs like nystagmus and congenital cataracts may indicate systemic disease, prompting genetic testing. Conversely, systemic symptoms may necessitate eye exams, even if vision symptoms are absent. Understanding the systemic aspects of these syndromes emphasizes the need for multidisciplinary collaboration among ophthalmologists, pediatricians, and other specialists to optimize patient care. The review also addresses emerging genetic therapies aimed at both visual and systemic symptoms, though more extensive studies are required to confirm their effectiveness. Overall, by detailing the genetic and clinical profiles of syndromic RP, this review seeks to aid healthcare professionals in diagnosing and managing these complex conditions more effectively, enhancing patient outcomes through timely, specialized intervention.

Prenatal diagnosis of Joubert syndrome: A case report

Joubert syndrome (JS) is a rare autosomal recessive disorder with brain stem and cerebellar malformations. Early diagnosis through Magnetic Resonance Imaging (MRI) and ultrasonography (US) is crucial for managing this condition. This report presents a JS case diagnosed at 24 weeks of pregnancy. A 25-year-old gravida 2, para 1 woman was referred at 24 weeks' gestation for suspected posterior fossa abnormalities. Ultrasound revealed normal cerebellar hemispheres but significant abnormalities in the cerebellar vermis, including the molar tooth sign and polydactyly, suggesting JS. The fetal MRI confirmed these findings. Following specialist consultations, the patient opted to terminate the pregnancy. A stillborn female infant was delivered, and genomic DNA sequencing identified a frameshift deletion in the AHI1 gene. Early prenatal diagnosis of JS is crucial for informed pregnancy management. The combination of ultrasonography, MRI, and genomic DNA sequencing proved effective for diagnosis.

Exome sequencing confirms the clinical diagnosis of both joubert syndrome and klinefelter syndrome with keratoconus in a han Chinese family

Introduction

Joubert syndrome a rare genetic disorder, is characterized by abnormalities in the development of the central nervous system with "molar signs" on magnetic resonance imaging of the brain and accompanied by cerebellar vermis hypoplasia, ataxia, hypotonia, and developmental delay. Keratoconus (KC) is a kind of genetically predisposed eye disease that causes blindness characterized by a dilated thinning of the central or paracentral cornea conically projected forward, highly irregular astigmatism, and severe visual impairment. Klinefelter syndrome is caused by an extra X chromosome in the cells of male patients, and the main phenotype is tall stature and dysplasia with secondary sex characteristics. This study was intended to identify the genetic etiology and determine the clinical diagnosis of one Han Chinese family with specific clinical manifestations of keratoconus and multiorgan involvement.

Methods

A comprehensive ocular and related general examination was performed on one patient and his asymptomatic parents and brother. Pathogenic genes were tested by exome sequencing. CNV-seq was used to verify the copy number variation, and peripheral blood was cultured for karyotype analysis. The pathogenicity of the identified variant was determined subject to ACMG guidelines. The Gene Expression Omnibus (GEO) dataset of keratoconus-related genes in the NCBI database was obtained to analyze the differentially expressed genes in corneal tissues of the keratoconus group and the normal control group, and analysis of protein-protein interaction networks (PPI) was performed.

Results

Proband, a 25-year-old male, had sudden loss of vision in the left eye for 1 week. Best corrected visual acuity (BCVA): 0.5 (-1.00DS/-5.00DC*29°) in the right eye, counting fingers/40 cm in the left eye. Slit-lamp microscopy of the right eye showed mild anterior protrusion of the cornea and thinning of the cone-topped cornea. The left eye showed marked thinning of the central region of the cornea, rounded edema in the form of a cone-like bulge, epithelial bullae, edema and turbidity of the stroma, and bulging of the Descemet's membrane. Cranial magnetic resonance imaging (MRI) revealed changes in the midbrain and cerebellum, with a "molar sign" and a "bat-winged" ventriculus quartus cerebri. General check-up: 168 cm in height, decreased muscle tone in all four limbs, knee jerk elicited, negative Babinski sign, abdominal reflexes elicited, finger-to-nose test positive, intentional tremor evident in both hands, positive Romberg's sign, instability of gait, level I intellectual disability, poor adaptive behavior, communication disorders, teeth all dentures, a peculiar face with blepharophimosis, wide inner canthus distance, mild ptosis, severe positive epicanthus, high palatal arches, exotropia, hypotrichosis of beard and face, inconspicuous prominentia laryngea, and short upper and lower limbs. Exome sequencing detected compound heterozygous frameshift variants M1:c.9279dup:p.His3094Thrfs*18 and M2:c.6515_6522del:p.Lys2172Thrfs*37 in the patient's CPLANE1 gene and the presence of duplication-type CNV on the X chromosome. Sanger sequencing showed that the mother and father carried the M1 and M2 variants, respectively, and the younger brother carried the M2 variant, which was a novel variant. CNV-seq analysis showed the presence of a duplication-type CNV Xp22.33-Xq28 (2757837-156030895) of approximately 155 Mb on the X chromosome of the proband, which was a de novo variant and carried by neither of the parents. The two heterozygous frameshift variants and duplication-type CNV were pathogenic according to the ACMG guidelines. Differential expression analysis of keratoconus-related genes showed that CPLANE1 was upregulated in the corneal tissues of keratoconus patients compared with normal controls, and such a difference was statistically significant (p = 0.000515, <0.05). PPI analysis showed that the CPLANE1-NPHP3 complex protein acted as a bridge between cilia and extracellular matrix tissue. According to the genetic test results and clinical phenotype analysis, the family was finally diagnosed with Joubert syndrome combined with Keratoconus and Klinefelter syndrome.

Discussion

In this study, we report a proband in a Han Chinese family with both Joubert syndrome and X-linked Klinefelter syndrome as well as keratoconus, and the phenotype spectrum of CPLANE1-Joubert syndrome may be expanded accordingly. Meanwhile, the significance of exome sequencing was emphasized in aiding the clinical diagnosis of complex cases, which is difficult to make.

Joubert syndrome presenting bilateral peroneal neuropathies: A case report

RATIONALE

Joubert syndrome (JS) is a rare genetic disorder that presents with various neurological symptoms, primarily involving central nervous system dysfunction. Considering the etiology of JS, peripheral nervous system abnormalities cannot be excluded; however, cases of JS accompanied by peripheral nervous system abnormalities have not yet been reported. Distinct radiological findings on brain magnetic resonance imaging were considered essential for the diagnosis of JS. However, recently, cases of JS with normal or nearly normal brain morphology have been reported. To date, there is no consensus on the most appropriate diagnostic method for JS when imaging-based diagnostic approach is challenging. This report describes the case of an adult patient who exhibited bilateral peroneal neuropathies and was finally diagnosed with JS through genetic testing.

PATIENT CONCERNS AND DIAGNOSIS

A 27-year-old man visited our outpatient clinic due to a gait disturbance that started at a very young age. The patient exhibited difficulty maintaining balance, especially when walking slowly. Oculomotor apraxia was observed on ophthalmic evaluation. During diagnostic workups, including brain imaging and direct DNA sequencing, no conclusive findings were detected. Only nerve conduction studies revealed profound bilateral peroneal neuropathies. We performed whole genome sequencing to obtain a proper diagnosis and identify the gene mutation responsible for JS.

LESSONS

This case represents the first instance of peripheral nerve dysfunction in JS. Further research is needed to explore the association between JS and peripheral nervous system abnormalities. Detailed genetic testing may serve as a valuable tool for diagnosing JS when no prominent abnormalities are detected in brain imaging studies.

Frameshift Variant in AMPD2 in Cirneco dell'Etna Dogs with Retinopathy and Tremors

While the manifestations of many inherited retinal disorders are limited to loss of vision, others are part of a syndrome that affects multiple tissues, particularly the nervous system. Most syndromic retinal disorders are thought to be recessively inherited. Two dogs out of a litter of Cirneco dell' Etna dogs, both males, showed signs of retinal degeneration, along with tremors and signs described as either atypical seizures or paroxysmal dyskinesias, while the other two male littermates were normal. We named this oculo-neurological syndrome CONS (Cirneco oculo-neurological syndrome), and undertook homozygosity mapping and whole-genome sequencing to determine its potential genetic etiology. Notably, we detected a 1-bp deletion in chromosome 6 that was predicted to cause a frameshift and premature stop codon within the canine AMPD2 gene, which encodes adenosine monophosphate deaminase, an enzyme that converts adenosine 5'-monophosphate (AMP) to inosine 5'-monophosphate (IMP). Genotyping of the available Cirneco population suggested perfect segregation between cases and controls for the variant. Moreover, this variant was absent in canine genomic databases comprised of thousands of unaffected dogs. The AMPD2 genetic variant we identified in dogs presents with retinal manifestations, adding to the spectrum of neurological manifestations associated with AMPD2 variants in humans.

Cilia-related diseases

More and more attention is paid to diseases such as internal transfer and brain malformation which are caused by the abnormal morphogenesis of cilia. These cilia-related diseases are divided into two categories: ciliopathy resulting from defects of primary cilia and primary ciliary dyskinesia (PCD) caused by functional dysregulation of motile cilia. Cilia are widely distributed, and their related diseases can cover many human organs and tissues. Recent studies prove that primary cilia play a key role in maintaining homeostasis in the cardiovascular system. However, molecular mechanisms of cilia-related diseases remain elusive. Here, we reviewed recent research progresses on characteristics, molecular mechanisms and treatment methods of ciliopathy and PCD. Our review is beneficial to the further research on the pathogenesis and treatment strategies of cilia-related diseases.

Clinical and genetic characteristics of 36 children with Joubert syndrome

Background and aims

Joubert syndrome (JBTS, OMIM # 213300) is a group of ciliopathies characterized by mid-hindbrain malformation, developmental delay, hypotonia, oculomotor apraxia, and breathing abnormalities. Molar tooth sign in brain imaging is the hallmark for diagnosing JBTS. It is a clinically and genetically heterogeneous disorder involving mutations in more than 40 ciliopathy-related genes. However, long-term follow-up data are scarce, and further research is needed to determine the abundant phenotypes and genetics of this disorder. The study aimed to summarize clinical manifestations, particular appearance on cranial imaging, genetic data, and prognostic features of patients with JBTS.

Methods

A retrospective case review of 36 cases of JBTS from May 1986 to December 2021 was performed. Clinical data of JBTS patients with development retardation and molar tooth sign on cranial imaging as the main features were analyzed. Genetic testing was performed according to consent obtained from patients and their families. The Gesell Developmental Scale was used to evaluate the intelligence level before and after treatment. The children were divided into a purely neurological JBTS (pure JBTS) group and JBTS with multi-organ system involvement group and then followed up every 3-6 months.

Results

We enrolled 18 males and 18 females. Thirty-four (94.44%) cases had developmental delay, one patient (2.78%) had strabismus, and one patient (2.78%) had intermittent dizziness. There was one case co-morbid with Lesch-Nyhan syndrome. Three-quarters of cases had one or more other organ or system involvement, with a greater predilection for vision and hearing impairment. JBTS could also involve the skin. Thirty-one cases (86.11%) showed a typical molar tooth sign, and five cases showed a bat wing sign on cranial imaging. Abnormal video electroencephalogram (VEEG) result was obtained in 7.69% of cases. We found six JBTS-related novel gene loci variants: CPLANE1: c.4189 + 1G > A, c.3101T > C(p.Ile1034Thr), c.3733T > C (p.Cys1245Arg), c.4080G > A(p.Lys1360=); RPGRIP1l: c.1351-11A > G; CEP120: c.214 C > T(p.Arg72Cys). The CHD7 gene may be potentially related to the occurrence of JBTS. Analysis showed that the prognosis of pure JBTS was better than that of JBTS with neurological and non-neurological involvement after the formal rehabilitation treatment (P < 0.05). Of the three children with seizures, two cases had epilepsy with a poor prognosis, and another case had breath-holding spells.

Conclusion

Our findings indicate that early cranial imaging is helpful for the etiological diagnosis of children with unexplained developmental delay and multiple malformations. Patients with JBTS may have coexisting skin abnormalities. The novel gene loci of CPLANE1, RPGRIP1l, and CEP120 were associated with JBTS in our study and provided significant information to enrich the related genetic data. Future works investigating several aspects of the association between CHD7 gene and JBTS merit further investigation. The prognosis of children with pure JBTS is better than that of children with JBTS with non-neurological involvement.

Ciliopathies in pediatric endocrinology

Ciliopathies are a group of disorders that involve many organs and systems. In this review, we consider the role of the cilium in multiorgan pathology with a focus on endocrinological aspects. Identification of new genes and mutations is the major challenge in development of a tailored and appropriate therapy. It is expected that new mutations will be identified to characterize ciliopathies and promote new therapies.

Suspected Autosomal Recessive Polycystic Kidney Disease but Cerebellar Vermis Hypoplasia, Oligophrenia Ataxia, Coloboma, and Hepatic Fibrosis (COACH) Syndrome in Retrospect, A Delayed Diagnosis Aided by Genotyping and Reverse Phenotyping: A Case Report and A Review of the Literature

The clinical features of cerebellar vermis hypoplasia, oligophrenia, ataxia, coloboma, and hepatic fibrosis (COACH) characterize the rare autosomal recessive multisystem disorder called COACH syndrome. COACH syndrome belongs to the spectrum of Joubert syndrome and related disorders (JSRDs) and liver involvement distinguishes COACH syndrome from the rest of the JSRD spectrum. Developmental delay and oculomotor apraxia occur early but with time, these can improve and may not be readily apparent or no longer need active medical management. Congenital hepatic fibrosis and renal disease, on the other hand, may develop late, and the temporal incongruity in organ system involvement may delay the recognition of COACH syndrome. We present a case of a young adult presenting late to a Renal Genetics Clinic for evaluation of renal cystic disease with congenital hepatic fibrosis, clinically suspected to have autosomal recessive polycystic kidney disease. Following genetic testing, a reevaluation of his medical records from infancy, together with reverse phenotyping and genetic phasing, led to a diagnosis of COACH syndrome.

An infant with Joubert syndrome: A case report

Joubert syndrome is a rare neurological and developmental malfunction represented by decreased muscle tone, ataxia, and delayed developmental milestones. Joubert syndrome-related disorders, besides central nervous system, can involve other systems and thus can lead to multi-organ malfunction. We report a case of pure Joubert syndrome who presented with developmental delay, decreased muscle tone, and ataxia. Identification of molar tooth sign on magnetic resonance imaging studies assisted to make a definitive diagnosis. Detailed examination revealed no other significant findings of any organ of the body. Patient was managed conservatively with symptomatic treatment. Although these types of cases are rarely encountered, they can lead to multiple organ disabilities. Therefore, clinicians should always keep this diagnosis in mind whenever an infant presents with the aforementioned neurodevelopmental symptoms.

Joubert syndrome a rare entity and role of radiology: A case report

Introduction and importance

Case presentation

Clinical discussion

Conclusion

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Joubert syndrome (JS) is rare entity characterized by set of cerebellum and midbrain abnormalities.

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This case study highlighted a 17-month-old baby presented with typical JS features diagnosed radiologically.

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The patient was given multivitamins, and the parents were counseled, educated on other supportive therapies.

Congenital Brain Malformations: An Integrated Diagnostic Approach

Congenital brain malformations are abnormalities present at birth that can result from developmental disruptions at various embryonic or fetal stages. The clinical presentation is nonspecific and can include developmental delay, hypotonia, and/or epilepsy. An informed combination of imaging and genetic testing enables early and accurate diagnosis and management planning. In this article, we provide a streamlined approach to radiologic phenotyping and genetic evaluation of brain malformations. We will review the clinical workflow for brain imaging and genetic testing with up-to-date ontologies and literature references. The organization of this article introduces a streamlined approach for imaging-based etiologic classification into malformative, destructive, and migrational abnormalities. Specific radiologic ontologies are then discussed in detail, with correlation of key neuroimaging features to embryology and molecular pathogenesis.

Genotype-phenotype correlates in Joubert syndrome: A review

Joubert syndrome (JS) is a genetically heterogeneous primary ciliopathy characterized by a pathognomonic cerebellar and brainstem malformation, the “molar tooth sign,” and variable organ involvement. Over 40 causative genes have been identified to date, explaining up to 94% of cases. To date, gene‐phenotype correlates have been delineated only for a handful of genes, directly translating into improved counseling and clinical care. For instance, JS individuals harboring pathogenic variants in TMEM67 have a significantly higher risk of liver fibrosis, while pathogenic variants in NPHP1, RPGRIP1L, and TMEM237 are frequently associated to JS with renal involvement, requiring a closer monitoring of liver parameters, or renal functioning. On the other hand, individuals with causal variants in the CEP290 or AHI1 need a closer surveillance for retinal dystrophy and, in case of CEP290, also for chronic kidney disease. These examples highlight how an accurate description of the range of clinical symptoms associated with defects in each causative gene, including the rare ones, would better address prognosis and help guiding a personalized management. This review proposes to address this issue by assessing the available literature, to confirm known, as well as to propose rare gene‐phenotype correlates in JS.

Evolutionarily conserved genetic interactions between nphp-4 and bbs-5 mutations exacerbate ciliopathy phenotypes

Primary cilia are sensory and signaling hubs with a protein composition that is distinct from the rest of the cell due to the barrier function of the transition zone (TZ) at the base of the cilium. Protein transport across the TZ is mediated in part by the BBSome, and mutations disrupting TZ and BBSome proteins cause human ciliopathy syndromes. Ciliopathies have phenotypic variability even among patients with identical genetic variants, suggesting a role for modifier loci. To identify potential ciliopathy modifiers, we performed a mutagenesis screen on nphp-4 mutant Caenorhabditis elegans and uncovered a novel allele of bbs-5. Nphp-4;bbs-5 double mutant worms have phenotypes not observed in either individual mutant strain. To test whether this genetic interaction is conserved, we also analyzed zebrafish and mouse mutants. While Nphp4 mutant zebrafish appeared overtly normal, Bbs5 mutants exhibited scoliosis. When combined, Nphp4;Bbs5 double mutant zebrafish did not exhibit synergistic effects, but the lack of a phenotype in Nphp4 mutants makes interpreting these data difficult. In contrast, Nphp4;Bbs5 double mutant mice were not viable and there were fewer mice than expected carrying three mutant alleles. In addition, postnatal loss of Bbs5 in mice using a conditional allele compromised survival when combined with an Nphp4 allele. As cilia are still formed in the double mutant mice, the exacerbated phenotype is likely a consequence of disrupted ciliary signaling. Collectively, these data support an evolutionarily conserved genetic interaction between Bbs5 and Nphp4 alleles that may contribute to the variability in ciliopathy phenotypes.

AHI1 gene mutation in a consanguineous Iranian family affected by Joubert syndrome: A case report

This point of detected mutation could be considered as a novel mutational hotspot point that carried in patient ancestors. Moreover, the obtained results and family history suggest a precise genetic consulting and molecular prenatal evaluation for suspect individuals with a family history of mental and physical abnormalities.

Clinical and genetic heterogeneity of primary ciliopathies (Review)

Ciliopathies comprise a group of complex disorders, with involvement of the majority of organs and systems. In total, >180 causal genes have been identified and, in addition to Mendelian inheritance, oligogenicity, genetic modifications, epistatic interactions and retrotransposon insertions have all been described when defining the ciliopathic phenotype. It is remarkable how the structural and functional impairment of a single, minuscule organelle may lead to the pathogenesis of highly pleiotropic diseases. Thus, combined efforts have been made to identify the genetic substratum and to determine the pathophysiological mechanism underlying the clinical presentation, in order to diagnose and classify ciliopathies. Yet, predicting the phenotype, given the intricacy of the genetic cause and overlapping clinical characteristics, represents a major challenge. In the future, advances in proteomics, cell biology and model organisms may provide new insights that could remodel the field of ciliopathies.

Clinical heterogeneity and intrafamilial variability of Joubert syndrome in two siblings with CPLANE1 variants

Background

Joubert syndrome (JBTS) is a rare genetic disorder that is characterized by midbrain‐hindbrain malformations. Multiple variants in genes that affect ciliary function contribute to the genetic and clinical heterogeneity of JBTS and its subtypes. However, the correlation between genotype and phenotype has not been elucidated due to the limited number of patients available.

Methods

In this study, we observed different clinical features in two siblings from the same family. The older sibling was classified as a pure JBTS patient, whereas her younger sibling displayed oral‐facial‐digital defects and was therefore classified as an oral‐facial‐digital syndrome type VI (OFD VI) patient. Next, we performed human genetic tests to identify the potential pathogenic variants in the two siblings.

Results

Genetic sequencing indicated that both siblings harbored compound heterozygous variants of a missense variant (c.1067C>T, p.S356F) and a frameshift variant (c.8377_8378del, p.E2793Lfs*24) in CPLANE1 (NM_023073.3).

Conclusion

This study reports that two novel CPLANE1 variants are associated with the occurrence of JBTS and OFD VI. These results help elucidate the intrafamilial phenotypic variability associated with CPLANE1 variants.

Mutations in the exocyst component EXOC2 cause severe defects in human brain development

The exocyst, an octameric protein complex, is an essential component of the membrane transport machinery required for tethering and fusion of vesicles at the plasma membrane. We report pathogenic variants in an exocyst subunit, EXOC2 (Sec5). Affected individuals have severe developmental delay, dysmorphism, and brain abnormalities; variability associated with epilepsy; and poor motor skills. Family 1 had two offspring with a homozygous truncating variant in EXOC2 that leads to nonsense-mediated decay of EXOC2 transcript, a severe reduction in exocytosis and vesicle fusion, and undetectable levels of EXOC2 protein. The patient from Family 2 had a milder clinical phenotype and reduced exocytosis. Cells from both patients showed defective Arl13b localization to the primary cilium. The discovery of mutations that partially disable exocyst function provides valuable insight into this essential protein complex in neural development. Since EXOC2 and other exocyst complex subunits are critical to neuronal function, our findings suggest that EXOC2 variants are the cause of the patients’ neurological disorders.

Retinal dystrophy as part of TTC21B-associated ciliopathy

Background: TCC21B is a ciliary protein. The most common phenotypic features associated with TCC21B biallelic mutations are nephronophthisis and skeletal abnormalities. To date, retinal dystrophy has been reported in only one patient.Materials and Methods: Clinical evaluation included best-corrected visual acuity, cycloplegic refraction, fundus examination, fundus photography, retinal imaging by optical coherence tomography, full-field electroretinography, multifocal electroretinography, and visual evoked potentials. Genetic analysis included Whole Exome Sequencing and confirmation of the identified mutations in the patient and his parents by PCR amplification and direct sequencing.Results: A ten-year-old Caucasian male presented with nephronophthisis, high myopia and nycatalopia. Best-corrected visual acuity was preserved to 20/20 in each eye with significant myopic correction. Visual fields were constricted. Optical coherence tomography confirmed the lack of outer retinal layers in the perifoveal area on both eyes. Electroretinography confirmed significant retinal dystrophy. Whole Exome Sequencing revealed compound heterozygous mutations in the TTC21B gene.Conclusions: TTC21B is associated with ciliopathy, but retinal dystrophy is a rare finding in these patients. We report retinal dystrophy secondary to TTC21B mutations, and provide for the first time detailed clinical information of the ophthalmic phenotype.

Targeting the photoreceptor cilium for the treatment of retinal diseases

Photoreceptors, as polarised sensory neurons, are essential for light sensation and phototransduction, which are highly dependent on the photoreceptor cilium. Structural defects and/or dysfunction of the photoreceptor cilium caused by mutations in photoreceptor-specific genes or common ciliary genes can lead to retinal diseases, including syndromic and nonsyndromic diseases. In this review, we describe the structure and function of the photoreceptor cilium. We also discuss recent findings that underscore the dysregulation of the photoreceptor cilium in various retinal diseases and the therapeutic potential of targeting ciliary genes in these diseases.

Clinical Features and Molecular Genetics of Autosomal Recessive Ataxia in the Turkish Population

Background:

Autosomal recessive cerebellar ataxias (ARCAs) are a heterogeneous group of inherited neurodegenerative disorders. The aim of this study was to present the clinical and genetic features of patients with ataxia complaints and those genetically diagnosed with ARCAs.

Materials and Methods:

Thirty-one children with ARCA were retrospectively analyzed.

Results:

Fourteen (45.2%) were boys and 17 (54.8%) were girls with the mean age at onset of symptoms of 46.13 ± 26.30 months (12–120 months). Of the 31 patients, 21 (67.7%) were from consanguineous marriages. Eight patients had Friedreich’s ataxia, five had ataxia telangiectasia, three had L-2-hydroxyglutaric aciduria, three had Joubert syndrome, two had neuronal ceroid lipofuscinosis, two had megalencephalic leukoencephalopathy with subcortical cysts, two had ataxia with ocular motor oculomotor apraxia type 1, one had cytochrome c oxidase deficiency, one had autosomal recessive spastic ataxia of Charlevoix-Saguenay, one had Niemann-Pick type C, one had congenital disorders of glycosylation, one had adrenoleukodystrophy, and one had cobalamin transport disorder.

Conclusion:

The prevalence of hereditary ataxia can vary among countries. The consanguineous marriage is an important finding in these diseases. These genetic tests will increase the number of ARCA patients diagnosed.

Syndromic Inherited Retinal Diseases: Genetic, Clinical and Diagnostic Aspects

Inherited retinal diseases (IRDs), which are among the most common genetic diseases in humans, define a clinically and genetically heterogeneous group of disorders. Over 80 forms of syndromic IRDs have been described. Approximately 200 genes are associated with these syndromes. The majority of syndromic IRDs are recessively inherited and rare. Many, although not all, syndromic IRDs can be classified into one of two major disease groups: inborn errors of metabolism and ciliopathies. Besides the retina, the systems and organs most commonly involved in syndromic IRDs are the central nervous system, ophthalmic extra-retinal tissues, ear, skeleton, kidney and the cardiovascular system. Due to the high degree of phenotypic variability and phenotypic overlap found in syndromic IRDs, correct diagnosis based on phenotypic features alone may be challenging and sometimes misleading. Therefore, genetic testing has become the benchmark for the diagnosis and management of patients with these conditions, as it complements the clinical findings and facilitates an accurate clinical diagnosis and treatment.

Whole exome sequencing identified a novel missense alteration in CC2D2A causing Joubert syndrome 9 in a Pakhtun family

BACKGROUND

Joubert syndrome (JBTS) is a heterogenous disorder characterized by intellectual disability, developmental delays, molar tooth sign in brain imaging, hypotonia, ocular motor apraxia and overlapping features of ciliopathies. There are 36 clinical subtypes of JBTS, with an equal number of genes known so far for this phenotype.

METHODS

Whole exome sequencing (WES) and Sanger sequencing were performed for the molecular diagnosis of a Pakhtun family affected with Joubert syndrome type 9 (JBTS9).

RESULTS

A novel homozygous missense variant (c.4417C>G; Pro1473Ala) in exon 34 was identified in coiled-coil and C2 domains-containing the protein 2A (CC2D2A; NM_001080522) gene. The variant co-segregated in autosomal recessive fashion within the family and was not found in 200 ethnically matched unaffected individuals. In silico analyses supported the pathogenic effect of the altered CC2D2A protein.

CONCLUSIONS

To the best of our knowledge, this is the first report of CC2D2A alteration co-segragating with a JBTS9 phenotype in a Pakhtun family from Pakistan. Our findings broaden the pathogenic spectrum of JBTS9, adding a novel variant to CC2D2A variation pool. WES analysis is a successful molecular diagnostic tool for rare genetic disorders, especially in those populations where the marriage of cousins is more frequent. Efficient and accurate genetic testing and counselling of the affected families are helpful for patient management and for reducing the disease burden in future generations.

Joubert Syndrome: A Molar Tooth Sign in Disguise

Joubert syndrome (JS) is a rare genetic ciliopathy characterized by the aplasia or malformation of the midbrain and or hindbrain structures. It usually manifests during the early stages with nonspecific neurological symptoms that progress to involve multiple systems. Its presentation similarity to other neurological disorders makes the diagnosis difficult, hence causing a delay in treatment and worse prognosis due to complications. If undiagnosed during childhood, it often presents during adolescence with the most common complication of acute kidney injury due to nephronophthisis. Here, we present a case of JS in late adolescence with renal complications and other neurological abnormalities. We aim to emphasize the importance of its early diagnosis by physicians in childhood to prevent further complications. It also highlights the possible diagnostic value and significance of brain imaging in the early stages when only mild mental retardation signs may be the only clues.

Four novel compound heterozygous mutations in C5orf42 gene in patients with pure and mild Joubert syndrome

Joubert syndrome (JS) is a rare clinically and genetically heterogeneous disease. Using whole or targeted exome sequencing, we identified four novel compound heterozygous mutations in chromosome 5 open reading frame 42 gene (C5orf42), including c.2876C>T (missense mutation) and c.3921+1G>A (splicing mutation), c.2292 -2delA (splicing mutation) and c.4067C>T (missense mutation), c.6997_6998insT (frameshift mutation) and c.8710C>T (nonsense mutation), c.3981G>C (nonsense mutation) and c.230 _233del (frameshift mutation), in four Chinese JS families. They were all inherited from their heterozygosis parents in the autosomal recessive inheritance mode. Pure JS clinical manifestations and mild neuroimaging findings were found in these patients. These verified the previous findings that C5orf42 mutations generally resulted in a purely neurological Joubert phenotype, and neuroimaging findings were mild in JS with C5orf42 mutations. Our report analyzed these C5orf42 mutations-associated phenotypes and neuroimaging findings in JS and updated the genetic variation spectrum of JS caused by C5orf42.These will help clinicians and geneticists reach a more accurate diagnosis for JS.

Optic vesicle morphogenesis requires primary cilia

Arl13b is a gene known to regulate ciliogenesis. Functional alterations in this gene's activity have been associated with Joubert syndrome. We found that in Arl13 null mouse embryos the orientation of the optic cup is inverted, such that the lens is abnormally surrounded by an inverted optic cup whose retina pigmented epithelium is oddly facing the surface ectoderm. Loss of Arl13b leads to the disruption of optic vesicle's patterning and expansion of ventral fates. We show that this phenotype is consequence of miss-regulation of Sonic hedgehog (Shh) signaling and demonstrate that the Arl13b-/- eye phenotype can be rescued by deletion of Gli2, a downstream effector of the Shh pathway. This work identified an unexpected role of primary cilia during the morphogenetic movements required for the formation of the eye.

Co-occurrence of mutations in KIF7 and KIAA0556 in Joubert syndrome with ocular coloboma, pituitary malformation and growth hormone deficiency: a case report and literature review

Background

Joubert syndrome is a recessive neurodevelopmental disorder characterized by clinical and genetic heterogeneity. Clinical hallmarks include hypotonia, ataxia, facial dysmorphism, abnormal eye movement, irregular breathing pattern cognitive impairment and, the molar tooth sign is the pathognomonic midbrain-hindbrain malformation on magnetic resonance imaging. The disorder is predominantly caused by biallelic mutations in more than 30 genes encoding proteins with a pivotal role in morphology and function of the primary cilium. Oligogenic inheritance or occurrence of genetic modifiers has been suggested to contribute to the variability of the clinical phenotype. We report on a family with peculiar clinical spectrum Joubert syndrome molecularly and clinically dissecting a complex phenotype, in which hypogonadism, pituitary malformation and growth hormone deficiency occur as major features.

Case presentation

A 7 year-old male was enrolled in a dedicated “Undiagnosed Patients Program” for a peculiar form of Joubert syndrome complicated by iris and retinochoroidal coloboma, hypogonadism pituitary malformation, and growth hormone deficiency. The molecular basis of the complex phenotype was investigated by whole exome sequencing. The concomitant occurrence of homozygosity for mutations in KIF7 and KIAA0556 was identified, and the assessment of major clinical features associated with mutations in these two genes provided evidence that these two independent events represent the cause underlying the complexity of the present clinical phenotype.

Conclusion

Beside the clinical variability of Joubert syndrome, co-occurrence of mutations in ciliopathy-associated genes may contribute to increase the clinical complexity of the trait.

The Ciliary Protein Arl13b Functions Outside of the Primary Cilium in Shh-Mediated Axon Guidance

The small GTPase Arl13b is enriched in primary cilia and regulates Sonic hedgehog (Shh) signaling. During neural development, Shh controls patterning and proliferation through a canonical, transcription-dependent pathway that requires the primary cilium. Additionally, Shh controls axon guidance through a non-canonical, transcription-independent pathway whose connection to the primary cilium is unknown. Here we show that inactivation of Arl13b results in defective commissural axon guidance in vivo. In vitro, we demonstrate that Arl13b functions autonomously in neurons for their Shh-dependent guidance response. We detect Arl13b protein in axons and growth cones, far from its well-established ciliary enrichment. To test whether Arl13b plays a non-ciliary function, we used an engineered, cilia-localization-deficient Arl13b variant and found that it was sufficient to mediate Shh axon guidance in vitro and in vivo. Together, these results indicate that, in addition to its ciliary role in canonical Shh signaling, Arl13b plays a cilia-independent role in Shh-mediated axon guidance.

A novel PDE6D mutation in a patient with Joubert syndrome type 22 (JBTS22)

Joubert syndrome (JS) is an autosomal or X-linked recessive syndrome principally characterized by hypotonia, ataxia, cognitive impairment, and a specific finding on brain imaging called a "molar tooth sign" (MTS), which can be isolated or in conjunction with variable organ involvement. The genetic basis of JS is heterogeneous, with over 35 ciliary genes being implicated in its pathogenesis. However, some of these genes (such as PDE6D) have been associated to JS only in single families, seeking confirmation. Here we report a boy, born to first cousin parents, presenting with developmental delay, hypotonia, microcephaly, post axial polydactyly, oculomotor apraxia, and MTS. Whole exome sequencing revealed the presence of a novel homozygous truncating variant in the PDE6D gene: NM_002601.3:c.367_368insG [p.(Leu123Cysfs*13)]. The variant was confirmed by Sanger sequencing and found at the heterozygous state in both parents. A review of the literature pertaining to the role of PDE6D in JS is discussed.

Late-onset hydrocephalus in a child with Joubert syndrome: a case report

INTRODUCTION

The ciliopathy "Joubert syndrome" was first described in 1969 by Dr. Marie Joubert and most subtypes follow an autosomal recessive inheritance. The complex disorder shows typical clinical features, such as hyperventilation, abnormal eye movements, and retardation. A pathognomonic midbrain-hindbrain malformation, the molar tooth sign, can be found on magnetic resonance imaging of the brainstem. There are a little more than 200 reports of Joubert syndrome in the literature.

CASE PRESENTATION

We report a case of a 9-year-old boy who developed a progressive hydrocephalus starting from the age of 4. He underwent VP shunt placement at 8 years, which relieved hydrocephalus-related clinical symptoms and put development of the macrocephalus to a halt.

CONCLUSION

Neonatal hydrocephalus due to the altered anatomy of the posterior fossa has been reported earlier, but to our knowledge, this is the first case of a delayed onset of hydrocephalus in a patient with Joubert syndrome.

Primary cilia proteins: ciliary and extraciliary sites and functions

Primary cilia are immotile organelles known for their roles in development and cell signaling. Defects in primary cilia result in a range of disorders named ciliopathies. Because this organelle can be found singularly on almost all cell types, its importance extends to most organ systems. As such, elucidating the importance of the primary cilium has attracted researchers from all biological disciplines. As the primary cilia field expands, caution is warranted in attributing biological defects solely to the function of this organelle, since many of these "ciliary" proteins are found at other sites in cells and likely have non-ciliary functions. Indeed, many, if not all, cilia proteins have locations and functions outside the primary cilium. Extraciliary functions are known to include cell cycle regulation, cytoskeletal regulation, and trafficking. Cilia proteins have been observed in the nucleus, at the Golgi apparatus, and even in immune synapses of T cells (interestingly, a non-ciliated cell). Given the abundance of extraciliary sites and functions, it can be difficult to definitively attribute an observed phenotype solely to defective cilia rather than to some defective extraciliary function or a combination of both. Thus, extraciliary sites and functions of cilia proteins need to be considered, as well as experimentally determined. Through such consideration, we will understand the true role of the primary cilium in disease as compared to other cellular processes' influences in mediating disease (or through a combination of both). Here, we review a compilation of known extraciliary sites and functions of "cilia" proteins as a means to demonstrate the potential non-ciliary roles for these proteins.

Clinical and experimental evidence suggest a link between KIF7 and C5orf42-related ciliopathies through Sonic Hedgehog signaling

Acrocallosal syndrome (ACLS) is an autosomal recessive neurodevelopmental disorder caused by KIF7 defects and belongs to the heterogeneous group of ciliopathies related to Joubert syndrome (JBTS). While ACLS is characterized by macrocephaly, prominent forehead, depressed nasal bridge, and hypertelorism, facial dysmorphism has not been emphasized in JBTS cohorts with molecular diagnosis. To evaluate the specificity and etiology of ACLS craniofacial features, we performed whole exome or targeted Sanger sequencing in patients with the aforementioned overlapping craniofacial appearance but variable additional ciliopathy features followed by functional studies. We found (likely) pathogenic variants of KIF7 in 5 out of 9 families, including the original ACLS patients, and delineated 1000 to 4000-year-old Swiss founder alleles. Three of the remaining families had (likely) pathogenic variants in the JBTS gene C5orf42, and one patient had a novel de novo frameshift variant in SHH known to cause autosomal dominant holoprosencephaly. In accordance with the patients' craniofacial anomalies, we showed facial midline widening after silencing of C5orf42 in chicken embryos. We further supported the link between KIF7, SHH, and C5orf42 by demonstrating abnormal primary cilia and diminished response to a SHH agonist in fibroblasts of C5orf42-mutated patients, as well as axonal pathfinding errors in C5orf42-silenced chicken embryos similar to those observed after perturbation of Shh signaling. Our findings, therefore, suggest that beside the neurodevelopmental features, macrocephaly and facial widening are likely more general signs of disturbed SHH signaling. Nevertheless, long-term follow-up revealed that C5orf42-mutated patients showed catch-up development and fainting of facial features contrary to KIF7-mutated patients.

Novel OFD1 frameshift mutation in a Chinese boy with Joubert syndrome: a case report and literature review

Joubert syndrome (JBTS) is a clinically and genetically heterogeneous group of ciliopathy with a key diagnostic feature of 'molar tooth sign' in brain MRI. So far, over 20 causative genes have been identified, but only one gene (OFD1) results in X-linked Joubert syndrome 10 (JBTS10). Six mutations in the OFD1 gene have been found to cause JBTS10. In this study, we identified a novel OFD1 mutation of c.2843_2844 delAA (p.Lys948ArgfsX) in a 3-month-old boy with a 'molar tooth sign' and clinical features of JBTS using targeted exome next-generation sequencing. The de-novo OFD1 mutation in exon 21 leads to a frameshift mutation generating a prematurely truncated protein and is predicted to partly reduce the function of the OFD1 protein. Our study expands the genotype-phenotype spectrum in JBTS and will have applications in prenatal and early diagnosis of the disorder. This is the first report of the OFD1 mutation causing JBTS in a Chinese population.

Photoreceptor Cilia and Retinal Ciliopathies

Photoreceptors are sensory neurons designed to convert light stimuli into neurological responses. This process, called phototransduction, takes place in the outer segments (OS) of rod and cone photoreceptors. OS are specialized sensory cilia, with analogous structures to those present in other nonmotile cilia. Deficient morphogenesis and/or dysfunction of photoreceptor sensory cilia (PSC) caused by mutations in a variety of photoreceptor-specific and common cilia genes can lead to inherited retinal degenerations (IRDs). IRDs can manifest as isolated retinal diseases or syndromic diseases. In this review, we describe the structure and composition of PSC and different forms of ciliopathies with retinal involvement. We review the genetics of the IRDs, which are monogenic disorders but genetically diverse with regard to causality.

Compound heterozygous alterations in intraflagellar transport protein CLUAP1 in a child with a novel Joubert and oral-facial-digital overlap syndrome

Disruption of normal ciliary function results in a range of diseases collectively referred to as ciliopathies. Here we report a child with a phenotype that overlapped with Joubert, oral–facial–digital, and Pallister–Hall syndromes including brain, limb, and craniofacial anomalies. We performed exome-sequence analysis on a proband and both parents, filtered for putative causative variants, and Sanger-verified variants of interest. Identified variants in CLUAP1 were functionally analyzed in a Xenopus system to determine their effect on ciliary function. Two variants in CLUAP1 were identified through exome-sequence analysis, Chr16:g.3558407T>G, c.338T>G, p.(Met113Arg) and Chr16:g.3570011C>T, c.688C>T, p.(Arg230Ter). These variants were rare in the Exome Aggregation Consortium (ExAC) data set of 65,000 individuals (one and two occurrences, respectively). Transfection of mutant CLUAP1 constructs into Xenopus embryos showed reduced protein levels p.(Arg230Ter) and reduced intraflagellar transport p.(Met113Arg). The genetic data show that these variants are present in an affected child, are rare in the population, and result in reduced, but not absent, intraflagellar transport. We conclude that biallelic mutations in CLUAP1 resulted in this novel ciliopathy syndrome in the proband.

Identification of 2 Potentially Relevant Gene Mutations Involved in Strabismus Using Whole-Exome Sequencing

Background

The etiology of strabismus has a genetic component. Our study aimed to localize the candidate causative gene mutant in a Chinese family with strabismus and to describe its underlying etiology.

Material/Methods

Genomic DNA was extracted from the affected individual and his parents in a Chinese pedigree with strabismus. The resulting exomes were sequenced by whole-exome sequencing. After variant calling and filtering, the candidate causative gene mutations were selected for the rarity and predicted damaging effect, which complied with the model of recessive disease transmission.

Results

We examined a Chinese strabismus pedigree with the parents unaffected and 2 offspring affected. Whole-exome sequencing and bioinformatics filtering identified 2 variants including Abelson helper integration site 1 (AHI1) gene and nebulin (NEB) gene. The variant in the AHI1 gene, c.A3257G (p.E1086G), and the altered amino acid had a damaging effect on the encoded protein predicted by Polyphen2. Moreover, this change was located in the conserved SH3 domain of AHI1. Biallelic pathogenic variant in AHI1 gene can cause Joubert syndrome-related disorders with oculomotor apraxia characteristics. Additionally, c.A914G mutation was found in nebulin (NEB) gene. Therefore, we concluded that AHI1 c.3257A>G and NEB c.914 A>G were potential causal variants in this strabismus pedigree.

Conclusions

We detected an AHI1 homozygous mutation in the affected individual. Whole-exome sequencing is a powerful way to identify causally relevant genes, improving the understanding of this disorder.

Abnormal glycosylation in Joubert syndrome type 10

BACKGROUND

The discovery of disease pathogenesis requires systematic agnostic screening of multiple homeostatic processes that may become deregulated. We illustrate this principle in the evaluation and diagnosis of a 5-year-old boy with Joubert syndrome type 10 (JBTS10). He carried the OFD1 mutation p.Gln886Lysfs*2 (NM_003611.2: c.2656del) and manifested features of Joubert syndrome.

METHODS

We integrated exome sequencing, MALDI-TOF mass spectrometry analyses of plasma and cultured dermal fibroblasts glycomes, and full clinical evaluation of the proband. Analyses of cilia formation and lectin staining were performed by immunofluorescence. Measurement of cellular nucleotide sugar levels was performed with high-performance anion-exchange chromatography with pulsed amperometric detection. Statistical analyses utilized the Student's and Fisher's exact t tests.

RESULTS

Glycome analyses of plasma and cultured dermal fibroblasts identified abnormal N- and O-linked glycosylation profiles. These findings replicated in two unrelated males with OFD1 mutations. Cultured fibroblasts from affected individuals had a defect in ciliogenesis. The proband's fibroblasts also had an abnormally elevated nuclear sialylation signature and increased total cellular levels of CMP-sialic acid. Ciliogenesis and each glycosylation anomaly were rescued by expression of wild-type OFD1.

CONCLUSIONS

The rescue of ciliogenesis and glycosylation upon reintroduction of WT OFD1 suggests that both contribute to the pathogenesis of JBTS10.

Tectonic 1 Is a Key Regulator of Cell Proliferation in Pancreatic Cancer

Pancreatic cancer is notoriously becoming one of the most devastating human cancers leading to death. However, clinical challenges still remain in diagnosis and treatment of this ticklish cancer. In the present study, the authors identified a new gene, Tectonic 1 (TCTN1), as a key regulator of cell proliferation in pancreatic cancer. Lentivirus-mediated short hairpin RNA (shRNA) was employed to knock down endogenous TCTN1 expression in PANC-1 pancreatic cancer cells. Knockdown of TCTN1 expression potently inhibited cell viability and proliferation, as determined by MTT and colony formation assays. Western blotting analysis also showed that knockdown of TCTN1 suppressed the expression of cdc2, while it induced that of p21 and p27. Flow cytometry analysis showed that depletion of TCTN1 in PANC-1 cells led to cell cycle arrest in the G2/M phase as well as apoptosis. Besides, depletion of TCTN1 led to the increase of Bax and cleavage of PARP-1, but the decrease of bcl2 by western blotting. The data indicate that TCTN1 is indispensable for pancreatic cancer cell proliferation, which provides a novel alternative to targeted therapy of pancreatic cancer and deserves further investigation.

Identification of a homozygous nonsense mutation in KIAA0556 in a consanguineous family displaying Joubert syndrome

Joubert Syndrome (JS) is an inherited ciliopathy associated with mutations in genes essential in primary cilium function. Whole exome sequencing in a multiplex consanguineous family from India revealed a KIAA0556 homozygous single base pair deletion mutation (c.4420del; p.Met1474Cysfs*11). Knockdown of the gene in zebrafish resulted in a ciliopathy phenotype, rescued by co-injection of wildtype cDNA. Affected siblings present a mild and classical form of Joubert syndrome allowing for further delineation of the JS associated genotypic spectrum.

X-Linked Candidate Genes for a Ciliopathy-Like Disorder

The ability to interrogate the genome via chromosomal microarray and sequencing-based technologies has accelerated the ability to rapidly and accurately define etiologies as well as new candidate genes related to genetic conditions. We describe a male patient with a lethal presentation of a multiple congenital anomaly syndrome that appeared consistent with a ciliopathy phenotype. The patient was found to have a novel maternally inherited 1.9-Mb X chromosome deletion including 4 known genes. Presently, the biological functions of these genes are not well delineated. However, at least one of these genes may be a promising candidate gene for this pattern of anomalies based on the function of related genes and information from publicly available copy number variant databases of control and affected individuals. These genes would bear further scrutiny in larger cohorts of patients with similar phenotypes.

MKS5 and CEP290 Dependent Assembly Pathway of the Ciliary Transition Zone

Cilia have a unique diffusion barrier (“gate”) within their proximal region, termed transition zone (TZ), that compartmentalises signalling proteins within the organelle. The TZ is known to harbour two functional modules/complexes (Meckel syndrome [MKS] and Nephronophthisis [NPHP]) defined by genetic interaction, interdependent protein localisation (hierarchy), and proteomic studies. However, the composition and molecular organisation of these modules and their links to human ciliary disease are not completely understood. Here, we reveal Caenorhabditis elegans CEP-290 (mammalian Cep290/Mks4/Nphp6 orthologue) as a central assembly factor that is specific for established MKS module components and depends on the coiled coil region of MKS-5 (Rpgrip1L/Rpgrip1) for TZ localisation. Consistent with a critical role in ciliary gate function, CEP-290 prevents inappropriate entry of membrane-associated proteins into cilia and keeps ARL-13 (Arl13b) from leaking out of cilia via the TZ. We identify a novel MKS module component, TMEM-218 (Tmem218), that requires CEP-290 and other MKS module components for TZ localisation and functions together with the NPHP module to facilitate ciliogenesis. We show that TZ localisation of TMEM-138 (Tmem138) and CDKL-1 (Cdkl1/Cdkl2/Cdkl3/Cdlk4 related), not previously linked to a specific TZ module, similarly depends on CEP-290; surprisingly, neither TMEM-138 or CDKL-1 exhibit interdependent localisation or genetic interactions with core MKS or NPHP module components, suggesting they are part of a distinct, CEP-290-associated module. Lastly, we show that families presenting with Oral-Facial-Digital syndrome type 6 (OFD6) have likely pathogenic mutations in CEP-290-dependent TZ proteins, namely Tmem17, Tmem138, and Tmem231. Notably, patient fibroblasts harbouring mutated Tmem17, a protein not yet ciliopathy-associated, display ciliogenesis defects. Together, our findings expand the repertoire of MKS module-associated proteins—including the previously uncharacterised mammalian Tmem80—and suggest an MKS-5 and CEP-290-dependent assembly pathway for building a functional TZ.

The transition zone is a barrier structure required to maintain the dynamic composition and functional integrity of the cilium. This study describes the pathway by which the transition zone is assembled during cilium formation.

The primary cilium is a structure found in most animal cell types. Much like an antenna, it is responsible for sensing extracellular signals, including light and small molecules, and conveying this information to the receiving cell and respective tissue or organ. At the base of the cilium is the transition zone (TZ), which acts as a “gate” to regulate the entry and exit of ciliary proteins required for signal transduction. Here, we use the nematode Caenorhabditis elegans as a model system to dissect how different proteins within the TZ assemble to form a functional barrier. We find that the TZ protein MKS-5 (Rpgrip1/Rpgrip1L orthologue) forms the foundation for two different assembly pathways involving two distinct modules: Nephronophthisis (NPHP) and Meckel syndrome (MKS). We show that at the base of the MKS module is CEP-290, another TZ protein that assembles MKS module proteins, including a novel TZ protein we identify as TMEM-218. CEP-290 also helps assemble a potentially separate submodule containing TMEM-138 and CDKL-1. Notably, we provide evidence that the MKS module protein TMEM-17 facilitates cilium formation and is disrupted in the human disorder (ciliopathy) Oral-Facial-Digital Syndrome type 6 (OFD6). Together, our findings provide essential insights into the assembly pathway of the ciliary TZ and suggest further connections between the transition zone and human health.

[Prenatal discovery of Joubert syndrome associated with small bowel volvulus]

Joubert syndrome and prenatal volvulus are difficult to diagnose during pregnancy. Joubert syndrome and related diseases should be considered in case of prenatal abnormal features of the fourth ventricle. Small bowel volvulus is also a surgical emergency because of the risk of intestinal necrosis before or after delivery. This type of condition justifies the transfer of pregnant women to a specialized hospital where the newborn may receive appropriate care. We report the case of a 31-week and 4-day gestational-age fetus in whom intrauterine growth retardation and small-bowel volvulus were diagnosed. Additional imaging revealed associated Joubert syndrome. This highlights the need for regular ultrasound monitoring during pregnancy and the comanagement of obstetricians and pediatricians to provide appropriate care before and after delivery.

TMEM67 mutations found in a case of Joubert syndrome with renal hypodysplasia

Joubert syndrome is a rare inherited cerebellar ataxia with the dysgenesis of the cerebellar vermis, called the molar tooth sign. The combination of a large number of causative genes, more than 27, and the various clinical features involving multiple organs has established many genotypic-phenotypic correlations in Joubert syndrome. TMEM67 is one of the genes that are relatively well established as contributing to Joubert syndrome with liver involvement. Here, we report a 2-month-old boy who was initially treated for urinary tract infection, which further led to the diagnosis of Joubert syndrome accompanied by renal hypodysplasia with two different mutations: c.2522A>C and c.1065 + 4Adel in TMEM67.

Nystagmus in a newborn: a manifestation of Joubert syndrome in the neonatal period

Joubert syndrome is a rare disorder, usually autosomal recessive, with a prevalence of 1:80,000 to 1:100,000. This disease presents most commonly as breathing irregularities, although the two major clinical criteria are hypotonia and developmental delay, sometimes associated with ocular movement abnormalities. The severity of the presentation varies, ranging from mild cases with normal intelligence to severe developmental delays associated with early death. We report a case of a newborn who presented to the emergency department for absent ocular fixation and torsional nystagmus without other neurological abnormalities. Her cranial MR showed cerebellar vermis agenesis and a molar tooth sign. Her laboratory evaluation, and renal and abdominal ultrasound were normal. An electroretinogram showed mixed retinal dystrophy and an AHI1 homozygous missense c.1981T>C mutation was identified (parents are carriers). Throughout infancy, she has shown mild developmental delay and hypotonia, but no respiratory abnormalities. Owing to variable expressivity, a high level of suspicion is required.

Clinical and genetic characteristics of Japanese nephronophthisis patients

BACKGROUND

Nephronophthisis (NPH) accounts for 4-5 % of end-stage renal disease occurring in childhood.

METHOD

We investigated the clinical context and characteristics of renal and extrarenal symptoms, as well as the NPHP genes, in 35 Japanese patients with clinical and histologic features suggesting NPH.

RESULTS

NPH occurred fairly uniformly throughout Japan irrespective of region or gender. In three families, NPH affected siblings. The median age of patients was 12.5 years. Renal abnormalities attributable to NPH discovered through mass screening, such as urine tests in school. However, NPH accounted for less than 50 % of children with abnormal findings, including incidentally discovered renal dysfunction during evaluation of extrarenal symptoms or during routine check-ups. Typical extrarenal manifestations leaded to discovery including anemia and delayed physical development. The urine often showed low gravity specific density and low molecular weight proteinuria. Frequent renal histologic findings included cystic dilation of tubules, mainly in the medulla, and irregularity of tubular basement membranes. Genetically abnormalities of NPHP1 were not common, with large deletions frequently noted. Compound heterozygotes showing single abnormalities in each of NPHP1, NPHP3, and NPHP4 were observed.

CONCLUSIONS

Our findings resemble those reported in Western populations.