Intergenic sequences harboring potential enhancer elements contribute to Axenfeld-Rieger syndrome by regulating PITX2.

Recent studies have uncovered that noncoding sequence variants may relate to Axenfeld-Rieger syndrome (ARS), a rare developmental anomaly with genetic heterogeneity. However, how these genomic regions are functionally and structurally associated with ARS is still unclear. In this study, we performed genome-wide linkage analysis and whole-genome sequencing in a Chinese family with ARS and identified a heterozygous deletion of about 570 kb (termed LOH-1) in the intergenic sequence between paired-like homeodomain transcription factor 2 (PITX2) and family with sequence similarity 241 member A. Knockout of LOH-1 homologous sequences caused ARS phenotypes in mice. RNA-Seq and real-time quantitative PCR revealed a significant reduction in Pitx2 gene expression in LOH-1-/- mice, while forkhead box C1 expression remained unchanged. ChIP-Seq and bioinformatics analysis identified a potential enhancer region (LOH-E1) within LOH-1. Deletion of LOH-E1 led to a substantial downregulation of the PITX2 gene. Mechanistically, we found a sequence (hg38 chr4:111,399,594-111,399,691) that is on LOH-E1 could regulate PITX2 by binding to RAD21, a critical component of the cohesin complex. Knockdown of RAD21 resulted in reduced PITX2 expression. Collectively, our findings indicate that a potential enhancer sequence that is within LOH-1 may regulate PITX2 expression remotely through cohesin-mediated loop domains, leading to ARS when absent.

In Vivo Assessment of Retinal Phenotypes in Axenfeld-Rieger Syndrome.

Purpose: Axenfeld-Rieger syndrome (ARS) is characterized by ocular anomalies including posterior embryotoxon, iridocorneal adhesions, corectopia/iris hypoplasia, and developmental glaucoma. Although anterior segment defects and glaucoma contribute to decreased visual acuity, the role of potential posterior segment abnormalities has not been explored. We used high-resolution retinal imaging to test the hypothesis that individuals with ARS have posterior segment pathology. Methods: Three individuals with FOXC1-ARS and 10 with PITX2-ARS completed slit-lamp and fundus photography, optical coherence tomography (OCT), OCT angiography, and adaptive optics scanning light ophthalmoscopy (AOSLO). Quantitative metrics were compared to previously published values for individuals with normal vision. Results: All individuals demonstrated typical anterior segment phenotypes. Average ganglion cell and inner plexiform layer thickness was lower in PITX2-ARS, consistent with the glaucoma history in this group. A novel phenotype of foveal hypoplasia was noted in 40% of individuals with PITX2-ARS (but none with FOXC1-ARS). Moreover, the depth and volume of the foveal pit were significantly lower in PITX2-ARS compared to normal controls, even excluding individuals with foveal hypoplasia. Analysis of known foveal hypoplasia genes failed to identify an alternative explanation. Foveal cone density was decreased in one individual with foveal hypoplasia and normal in six without foveal hypoplasia. Two individuals (one from each group) demonstrated non-foveal retinal irregularities with regions of photoreceptor anomalies on OCT and AOSLO. Conclusions: These findings implicate PITX2 in the development of the posterior segment, particularly the fovea, in humans. The identified posterior segment phenotypes may contribute to visual acuity deficits in individuals with PITX2-ARS.

Syndromic ciliopathy: a taiwanese single-center study.

BACKGROUND: Syndromic ciliopathies are a group of congenital disorders characterized by broad clinical and genetic overlap, including obesity, visual problems, skeletal anomalies, mental retardation, and renal diseases. The hallmark of the pathophysiology among these disorders is defective ciliary functions or formation. Many different genes have been implicated in the pathogenesis of these diseases, but some patients still remain unclear about their genotypes. METHODS: The aim of this study was to identify the genetic causes in patients with syndromic ciliopathy. Patients suspected of or meeting clinical diagnostic criteria for any type of syndromic ciliopathy were recruited at a single diagnostic medical center in Southern Taiwan. Whole exome sequencing (WES) was employed to identify their genotypes and elucidate the mutation spectrum in Taiwanese patients with syndromic ciliopathy. Clinical information was collected at the time of patient enrollment. RESULTS: A total of 14 cases were molecularly diagnosed with syndromic ciliopathy. Among these cases, 10 had Bardet-Biedl syndrome (BBS), comprising eight BBS2 patients and two BBS7 patients. Additionally, two cases were diagnosed with Alström syndrome, one with Oral-facial-digital syndrome type 14, and another with Joubert syndrome type 10. A total of 4 novel variants were identified. A recurrent splice site mutation, BBS2: c.534 + 1G > T, was present in all eight BBS2 patients, suggesting a founder effect. One BBS2 patient with homozygous c.534 + 1G > T mutations carried a third ciliopathic allele, TTC21B: c.264_267dupTAGA, a nonsense mutation resulting in a premature stop codon and protein truncation. CONCLUSIONS: Whole exome sequencing (WES) assists in identifying molecular pathogenic variants in ciliopathic patients, as well as the genetic hotspot mutations in specific populations. It should be considered as the first-line genetic testing for heterogeneous disorders characterized by the involvement of multiple genes and diverse clinical manifestations.

[Genetic analysis of a fetus with cryptophthalmos due to variants of FREM2 gene].

OBJECTIVE: To explore the genetic etiology of a fetus with cryptophthalmos detected by prenatal ultrasonography. METHODS: A fetus undergoing induced labor at 32nd gestational week due to absence of bilateral eye fissures detected by prenatal ultrasonography in January 2017 was selected as the study subject. Umbilical cord blood sample from the fetus and peripheral blood samples from its parents were collected for the extraction of genomic DNA. Pathogenic variants were screened through whole exome sequencing (WES) and verified by Sanger sequencing. Pathogenicity of candidate variants was verified by bioinformatic analysis and protein structure simulation. Based on the results of genetic testing, prenatal diagnosis was provided to the couple upon their subsequent pregnancy. RESULTS: The couple had four adverse pregnancies previously. The aborted fetus was the fifth, with fused bilateral upper and lower eyelids, poorly developed eyeballs, adhesion of the cornea with the upper eyelid, low-set ears, and abnormal plantar creases, and was diagnosed with cryptophthalmos. WES and Sanger sequencing revealed that the fetus has harbored compound heterozygous variants of the FREM2 gene, namely c.4537G>A (p.D1513N) and c.7292C>T (p.T2431M). Both variants were unreported associated with cryptophthalmos previously. Protein structure simulation showed that they may lead to loss of hydrogen bonds in the protein product. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), both variants were predicted to be likely pathogenic (PM1_Supporting+PM2_Supporting+PM5+PP3+PP4; PM2_Supporting+PM3+PP3+PP4). The mother was performed prenatal diagnosis in her sixth pregnancy based on the variants detected in this family, and delivered a daughter with normal phenotype. CONCLUSION: The FREM2: c.4537G>A and c.7292C>T compound heterozygous variants probably underlay the pathogenesis of cryptophthalmos in this fetus. Above finding has enriched the mutational spectrum of the FREM2 gene.

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.

Joubert syndrome-derived induced pluripotent stem cells show altered neuronal differentiation in vitro.

Joubert syndrome (JS) is a recessively inherited congenital ataxia characterized by hypotonia, psychomotor delay, abnormal ocular movements, intellectual disability, and a peculiar cerebellar and brainstem malformation, the "molar tooth sign." Over 40 causative genes have been reported, all encoding for proteins implicated in the structure or functioning of the primary cilium, a subcellular organelle widely present in embryonic and adult tissues. In this paper, we developed an in vitro neuronal differentiation model using patient-derived induced pluripotent stem cells (iPSCs), to evaluate possible neurodevelopmental defects in JS. To this end, iPSCs from four JS patients harboring mutations in distinct JS genes (AHI1, CPLANE1, TMEM67, and CC2D2A) were differentiated alongside healthy control cells to obtain mid-hindbrain precursors and cerebellar granule cells. Differentiation was monitored over 31 days through the detection of lineage-specific marker expression by qRT-PCR, immunofluorescence, and transcriptomics analysis. All JS patient-derived iPSCs, regardless of the mutant gene, showed a similar impairment to differentiate into mid-hindbrain and cerebellar granule cells when compared to healthy controls. In addition, analysis of primary cilium count and morphology showed notable ciliary defects in all differentiating JS patient-derived iPSCs compared to controls. These results confirm that patient-derived iPSCs are an accessible and relevant in vitro model to analyze cellular phenotypes connected to the presence of JS gene mutations in a neuronal context.

Structural Variant Disrupting the Expression of the Remote FOXC1 Gene in a Patient with Syndromic Complex Microphthalmia.

Ocular malformations (OMs) arise from early defects during embryonic eye development. Despite the identification of over 100 genes linked to this heterogeneous group of disorders, the genetic cause remains unknown for half of the individuals following Whole-Exome Sequencing. Diagnosis procedures are further hampered by the difficulty of studying samples from clinically relevant tissue, which is one of the main obstacles in OMs. Whole-Genome Sequencing (WGS) to screen for non-coding regions and structural variants may unveil new diagnoses for OM individuals. In this study, we report a patient exhibiting a syndromic OM with a de novo 3.15 Mb inversion in the 6p25 region identified by WGS. This balanced structural variant was located 100 kb away from the FOXC1 gene, previously associated with ocular defects in the literature. We hypothesized that the inversion disrupts the topologically associating domain of FOXC1 and impairs the expression of the gene. Using a new type of samples to study transcripts, we were able to show that the patient presented monoallelic expression of FOXC1 in conjunctival cells, consistent with the abolition of the expression of the inverted allele. This report underscores the importance of investigating structural variants, even in non-coding regions, in individuals affected by ocular malformations.

Bilateral Peters' anomaly, aniridia and Wilms tumour (WAGR syndrome) in monozygotic twins.

AIM: This study reports the bilateral association of Peters' anomaly and congenital aniridia in monozygotic twins subsequently diagnosed with Wilms tumour (WAGR syndrome). METHODS: Two monozygotic female twins were referred at age 2 months with bilateral corneal opacity. A diagnosis of Peters' anomaly associated to aniridia was made in both eyes of both twins. Physical examination and ultrasonography were carried out at 12 months of age to explore the possibility of WAGR-related anomalies, specifically Wilms tumour. DNA were isolated and subjected to whole exome sequencing. RESULTS: Peters' anomaly associated to aniridia in both eyes as well as bilateral Wilms tumour in both children were diagnosed. Exome analyses showed a large heterozygous deletion encompassing 6 648 473 bp in chromosome 11p13, using Integrative Genomics Viewer and AnnotSV software. CONCLUSION: WAGR syndrome is a rare contiguous gene deletion syndrome with a greater risk of developing Wilms tumour associated with Peters' anomaly and congenital aniridia. However, co-occurrence of both anomalies was rarely reported in twins, and never in both eyes of monozygotic twins. Here, we report the bilateral association of Peters' anomaly and congenital aniridia in monozygotic twins with WAGR syndrome.

High Incidence of CPLANE1-Related Joubert Syndrome in the Products of Conceptions from Early Pregnancy Losses

Background: The fetal monogenic causes of early pregnancy losses (EPLs) are mainly unknown, with only a few articles on the subject published. In our previous study of EPLs using whole-exome sequencing analysis, we confirmed a genetic diagnosis of CPLANE1-related Joubert syndrome (JS) in three EPLs from two couples and identified a relatively common CPLANE1 allele among our population (NM_001384732.1:c.1819delT;c.7817T>A, further after referred as "complex allele"). Pathogenic variants in the CPLANE1 (C5orf42) gene are reported to cause JS type 17, a primary ciliopathy with various system defects. Aims: To examine the hypothesis that the CPLANE1 "complex allele," whether homozygous or compound heterozygous, is a common cause of EPLs in our population. Study Design: Cohort study/case-control study.ontrol study. Methods: In this study, we used polymerase chain reaction-based methods to screen for CPLANE1 "complex allele" presence among 246 euploid EPLs (< 12 gestational weeks) from families in North Macedonia. We also investigated the impact of this allele in 650 women with EPLs versus 646 women with no history of pregnancy loss and at least one livebirth, matched by ethnic origin. Results: We found a high incidence of JS in the total study group of EPLs (2.03%), with a considerably higher incidence among Albanian families (6.25%). Although not statistically significant, women with EPLs had a higher allele frequency of the CPLANE1 "complex allele" (AF = 1.38%) than the controls (AF = 0.85%; p = 0.2). Albanian women had significantly higher frequency of the "complex allele" than the Macedonians (AF = 1.65% and 0.39%, respectively; p = 0.003). Conclusion: To the best of our knowledge, this is the highest reported incidence of fetal monogenic disease that might cause EPLs. Targeted screening for the CPLANE1 "complex allele" would be warranted in Albanian ethnic couples because it would detect one JS in every 16 euploid EPLs. Our findings have a larger impact on the pathogenesis of pregnancy loss and contribute to a better understanding of the pathogenicity of the variants in the CPLANE1 gene.

[Embryonic development and congenital diseases of the orbit]. / Embryologische Entwicklung und angeborene Erkrankungen des Auges.

Many neuroradiologists focus primarily on the central nervous system and give little attention to other regions like the eye/orbit. It is easy to be deceived by the pitfall called satisfaction of search (also abbreviated SOS), despite most congenital eye diseases being easily recognized if one is aware of them. In this article, the most common congenital orbital abnormalities are described, and their basic prenatal causes are summarized.

Complex balanced intrachromosomal rearrangement involving PITX2 identified as a cause of Axenfeld-Rieger Syndrome.

Axenfeld-Rieger Syndrome (ARS) type 1 is a rare autosomal dominant condition characterized by anterior chamber anomalies, umbilical defects, dental hypoplasia, and craniofacial anomalies, with Meckel's diverticulum in some individuals. Here, we describe a clinically ascertained female of childbearing age with ARS for whom clinical targeted sequencing and deletion/duplication analysis followed by clinical exome and genome sequencing resulted in no pathogenic variants or variants of unknown significance in PITX2 or FOXC1. Advanced bioinformatic analysis of the genome data identified a complex, balanced rearrangement disrupting PITX2. This case is the first reported intrachromosomal rearrangement leading to ARS, illustrating that for patients with compelling clinical phenotypes but negative genomic testing, additional bioinformatic analysis are essential to identify subtle genomic abnormalities in target genes.

Joubert syndrome causing mutation in C2 domain of CC2D2A affects structural integrity of cilia and cellular signaling molecules.

Cilia are organelles extend from cells to sense external signals for tuning intracellular signaling for optimal cellular functioning. They have evolved sensory and motor roles in various cells for tissue organization and homeostasis in development and post-development. More than a thousand genes are required for cilia function. Mutations in them cause multisystem disorders termed ciliopathies. The null mutations in CC2D2A result in Meckel syndrome (MKS), which is embryonic lethal, whereas patients who have missense mutations in the C2 domain of CC2D2A display Joubert syndrome (JBTS). They survive with blindness and mental retardation. How C2 domain defects cause disease conditions is not understood. To answer this question, C2 domain of Cc2d2a (mice gene) was knocked down (KD) in IMCD-3 cells by shRNA. This resulted in defective cilia morphology observed by immunofluorescence analysis. To further probe the cellular signaling alteration in affected cells, gene expression profiling was done by RNAseq and compared with the controls. Bioinformatics analysis revealed that the differentially expressed genes (DEGs) have functions in cilia. Among the 61 cilia DEGs identified, 50 genes were downregulated and 11 genes were upregulated. These cilia genes are involved in cilium assembly, protein trafficking to the cilium, intraflagellar transport (IFT), cellular signaling like polarity patterning, and Hedgehog signaling pathway. This suggests that the C2 domain of CC2D2A plays a critical role in cilia assembly and molecular signaling hosted in cilia for cellular homeostasis. Taken together, the missense mutations in the C2 domain of CC2D2A seen in JBTS might have affected cilia-mediated signaling in neurons of the retina and brain.

Novel compound heterozygous variants in ARL13B lead to Joubert syndrome.

Joubert syndrome (JBTS) is a systematic developmental disorder mainly characterized by a pathognomonic mid-hindbrain malformation. All known JBTS-associated genes encode proteins involved in the function of antenna-like cellular organelle, primary cilium, which plays essential roles in cellular signal transduction and development. Here, we identified four unreported variants in ARL13B in two patients with the classical features of JBTS. ARL13B is a member of the Ras GTPase family and functions in ciliogenesis and cilia-related signaling. The two missense variants in ARL13B harbored the substitutions of amino acids at evolutionarily conserved positions. Using model cell lines, we found that the accumulations of the missense variants in cilia were impaired and the variants showed attenuated functions in ciliogenesis or the trafficking of INPP5E. Overall, these findings expanded the ARL13B pathogenetic variant spectrum of JBTS.

Deep neurological phenotyping in oculo-dento-digital syndrome.

OBJECTIVES: Oculodentodigital dysplasia (ODDD) is a rare autosomal dominant congenital malformation syndrome characterized by high penetrance and great phenotypic heterogeneity. Neurological manifestations are thought to occur in about one third of cases, but systematic studies are not available. We performed deep neurological phenotyping of 10 patients in one ODDD pedigree. METHODS: Retrospective case series. We analyzed in depth the neurological phenotype of a three-generation family segregating the heterozygous c.416 T > C, p.(Ile139Thr) in GJA1. Clinical and neuroradiological features were retrospectively evaluated. Brain MRI and visual evoked potentials were performed in 8 and 6 cases, respectively. RESULTS: Central nervous system manifestations occurred in 5 patients, the most common being isolated ataxia either in isolation or combined with spasticity. Furthermore, sphincteric disturbances (neurogenic bladder and fecal incontinence) were recognized as the first manifestation in most of the patients. Subclinical electrophysiological alteration of the optic pathway occurred in all the examined patients. Neuroimaging was significant for supratentorial hypomyelination pattern and hyperintense superior cerebellar peduncle in all examined patients. CONCLUSION: The neurological involvement in ODDD carriers is often missed but peculiar clinical and radiological patterns can be recognized. Deep neurological phenotyping is needed to help untangle ODDD syndrome complexity and find genotype-phenotype correlations.

Penetrating keratoplasty in brittle Cornea syndrome: Case series and review of the literature.

It concerns three siblings (two 28 year old twin boys and a 25 year old woman) who presented a previous history of rupture of eyeball in one eye and very poor vision in the other. At the first ophthalmoscopic and instrumental evaluation, three patients presented with bluish sclera and keratoglobus in the intact eye. A genetic analysis with whole exome sequencing was then performed on the three siblings, identifying a biallelic variant of the PRDM5 gene that led to the diagnosis of Brittle Cornea Syndrome (BCS), a rare autosomal recessive disorder characterized by corneal thinning and blue sclera. To preserve the only intact eye from possible breakage, the three siblings were trained in using protective measures (polycarbonate goggles etc.) to carry out close monitoring of symptoms and were asked to continue with follow-up visits for ocular and systemic diseases associated with BCS. Given the poor best corrected visual acuity achievable with glasses and contact lenses, penetrating keratoplasty was performed, achieving good visual acuity maintained in the 2-year follow-up in two of the three patients. Knowledge of this pathology and its clinical manifestations is essential for early diagnosis and correct management of this rare but very debilitating pathology. To our knowledge, this is the first case series of BCS reported in an Albanian population.

Magnetic Resonance Imaging Findings and Genetic Testing Results in Children With Congenital Corneal Opacities.

PURPOSE: This study investigates brain and globe abnormalities identified on magnetic resonance imaging (MRI) in children with congenital corneal opacities (CCO). DESIGN: Retrospective cohort study. METHODS: Clinical notes, radiology records, and genetic testing results were reviewed for patients diagnosed with corneal opacification within the first 6 months of life at a tertiary referral academic center between August 2008 and January 2018. Ocular findings, systemic anomalies, neuroimaging, and genetic testing results were summarized. RESULTS: A total of 135 patients presenting at age 1 day to 12 years (mean age, 1 year) were identified. Children with bilateral CCO were more likely to have systemic disease (P = 0.018). Of the entire cohort, 43 (31.8%) patients received MRI, of whom 27 (62.8%) had abnormal brain findings and 30 (69.7%) had abnormal orbital findings. The most common abnormal brain findings were ventriculomegaly (n = 16, 59.2%) and corpus callosum abnormalities (n = 10, 37.0%) followed by brainstem/pons anomalies (n = 5, 18.5%), and cerebellar anomalies (n = 2, 7.4%). Abnormal brain MRI findings were associated with the presence of neurologic (P = .003) and craniofacial (P = .034) disease. A total of 44 (32.1%) patients underwent genetic testing, of whom 29 (65.9%) had pathogenic results. CONCLUSIONS: More than 60% of the children with CCO who underwent MRI had abnormal brain and orbit findings that were correlated with significant neurologic disease. Furthermore, almost two-thirds of patients with CCO who underwent genetic testing had pathogenic results. These data demonstrate the value of systemic workup in children with CCO, and highlight the role of ophthalmologists in facilitating the diagnosis of systemic comorbidities associated with CCO.

Short-read whole genome sequencing identifies causative variants in most individuals with previously unexplained aniridia.

BACKGROUND: Classic aniridia is a highly penetrant autosomal dominant disorder characterised by congenital absence of the iris, foveal hypoplasia, optic disc anomalies and progressive opacification of the cornea. >90% of cases of classic aniridia are caused by heterozygous, loss-of-function variants affecting the PAX6 locus. METHODS: Short-read whole genome sequencing was performed on 51 (39 affected) individuals from 37 different families who had screened negative for mutations in the PAX6 coding region. RESULTS: Likely causative mutations were identified in 22 out of 37 (59%) families. In 19 out of 22 families, the causative genomic changes have an interpretable deleterious impact on the PAX6 locus. Of these 19 families, 1 has a novel heterozygous PAX6 frameshift variant missed on previous screens, 4 have single nucleotide variants (SNVs) (one novel) affecting essential splice sites of PAX6 5' non-coding exons and 2 have deep intronic SNV (one novel) resulting in gain of a donor splice site. In 12 out of 19, the causative variants are large-scale structural variants; 5 have partial or whole gene deletions of PAX6, 3 have deletions encompassing critical PAX6 cis-regulatory elements, 2 have balanced inversions with disruptive breakpoints within the PAX6 locus and 2 have complex rearrangements disrupting PAX6. The remaining 3 of 22 families have deletions encompassing FOXC1 (a known cause of atypical aniridia). Seven of the causative variants occurred de novo and one cosegregated with familial aniridia. We were unable to establish inheritance status in the remaining probands. No plausibly causative SNVs were identified in PAX6 cis-regulatory elements. CONCLUSION: Whole genome sequencing proves to be an effective diagnostic test in most individuals with previously unexplained aniridia.

Generation of iPSC line from a Joubert syndrome patient with compound heterozygous mutations in CPLANE1 gene.

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

Phenotypic variability in Joubert syndrome is partially explained by ciliary pathophysiology.

INTRODUCTION: Joubert syndrome (JS) arises from defects of primary cilia resulting in potential malformations of the brain, kidneys, eyes, liver, and limbs. Several of the 35+ genes associated with JS have recognized genotype/phenotype correlations, but most genes have not had enough reported individuals to draw meaningful conclusions. METHODS: A PubMed literature review identified 688 individuals with JS across 32 genes and 112 publications to bolster known genotype/phenotype relationships and identify new correlations. All included patients had the "molar tooth sign" and a confirmed genetic diagnosis. Individuals were categorized by age, ethnicity, sex and the presence of developmental disability/intellectual disability, hypotonia, abnormal eye movements, ataxia, visual impairment, renal impairment, polydactyly, and liver abnormalities. RESULTS: Most genes demonstrated unique phenotypic profiles. Grouping proteins based on physiologic interactions established stronger phenotypic relationships that reflect known ciliary pathophysiology. Age-stratified data demonstrated that end-organ disease is progressive in JS. Most genes demonstrated a significant skew towards having variants with either residual protein function or no residual protein function. CONCLUSION: This cohort demonstrates that clinically meaningful genotype/phenotype relationships exist within most JS-related genes and can be referenced to allow for more personalized clinical care.