Exome capture reveals ZNF423 and CEP164 mutations, linking renal ciliopathies to DNA damage response signaling.

Nephronophthisis-related ciliopathies (NPHP-RC) are degenerative recessive diseases that affect kidney, retina, and brain. Genetic defects in NPHP gene products that localize to cilia and centrosomes defined them as "ciliopathies." However, disease mechanisms remain poorly understood. Here, we identify by whole-exome resequencing, mutations of MRE11, ZNF423, and CEP164 as causing NPHP-RC. All three genes function within the DNA damage response (DDR) pathway. We demonstrate that, upon induced DNA damage, the NPHP-RC proteins ZNF423, CEP164, and NPHP10 colocalize to nuclear foci positive for TIP60, known to activate ATM at sites of DNA damage. We show that knockdown of CEP164 or ZNF423 causes sensitivity to DNA damaging agents and that cep164 knockdown in zebrafish results in dysregulated DDR and an NPHP-RC phenotype. Our findings link degenerative diseases of the kidney and retina, disorders of increasing prevalence, to mechanisms of DDR.

Neuropathy target esterase activity defines phenotypes among PNPLA6 disorders.

Biallelic pathogenic variants in the PNPLA6 gene cause a broad spectrum of disorders leading to gait disturbance, visual impairment, anterior hypopituitarism and hair anomalies. PNPLA6 encodes neuropathy target esterase (NTE), yet the role of NTE dysfunction on affected tissues in the large spectrum of associated disease remains unclear. We present a systematic evidence-based review of a novel cohort of 23 new patients along with 95 reported individuals with PNPLA6 variants that implicate missense variants as a driver of disease pathogenesis. Measuring esterase activity of 46 disease-associated and 20 common variants observed across PNPLA6-associated clinical diagnoses unambiguously reclassified 36 variants as pathogenic and 10 variants as likely pathogenic, establishing a robust functional assay for classifying PNPLA6 variants of unknown significance. Estimating the overall NTE activity of affected individuals revealed a striking inverse relationship between NTE activity and the presence of retinopathy and endocrinopathy. This phenomenon was recaptured in vivo in an allelic mouse series, where a similar NTE threshold for retinopathy exists. Thus, PNPLA6 disorders, previously considered allelic, are a continuous spectrum of pleiotropic phenotypes defined by an NTE genotype:activity:phenotype relationship. This relationship, and the generation of a preclinical animal model, pave the way for therapeutic trials, using NTE as a biomarker.

The landscape of submicroscopic structural variants at the OPN1LW/OPN1MW gene cluster on Xq28 underlying blue cone monochromacy.

Blue cone monochromacy (BCM) is an X-linked retinal disorder characterized by low vision, photoaversion, and poor color discrimination. BCM is due to the lack of long-wavelength-sensitive and middle-wavelength-sensitive cone photoreceptor function and caused by mutations in the OPN1LW/OPN1MW gene cluster on Xq28. Here, we investigated the prevalence and the landscape of submicroscopic structural variants (SVs) at single-base resolution in BCM patients. We found that about one-third (n = 73) of the 213 molecularly confirmed BCM families carry an SV, most commonly deletions restricted to the OPN1LW/OPN1MW gene cluster. The structure and precise breakpoints of the SVs were resolved in all but one of the 73 families. Twenty-two families-all from the United States-showed the same SV, and we confirmed a common ancestry of this mutation. In total, 42 distinct SVs were identified, including 40 previously unreported SVs, thereby quadrupling the number of precisely mapped SVs underlying BCM. Notably, there was no "region of overlap" among these SVs. However, 90% of SVs encompass the upstream locus control region, an essential enhancer element. Its minimal functional extent based on deletion mapping in patients was refined to 358 bp. Breakpoint analyses suggest diverse mechanisms underlying SV formation as well as in one case the gene conversion-based exchange of a 142-bp deletion between opsin genes. Using parsimonious assumptions, we reconstructed the composition and copy number of the OPN1LW/OPN1MW gene cluster prior to the mutation event and found evidence that large gene arrays may be predisposed to the occurrence of SVs at this locus.

Contribution of whole genome sequencing in the molecular diagnosis of mosaic partial deletion of the NF1 gene in neurofibromatosis type 1.

Neurofibromatosis type 1 (NF1) is an autosomal dominant disease with complete penetrance but highly variable expressivity. In most patients, Next Generation Sequencing (NGS) technologies allow the identification of a loss-of-function pathogenic variant in the NF1 gene, a negative regulator of the RAS-MAPK pathway. We describe the 5-year diagnosis wandering of a patient with a clear NF1 clinical diagnosis, but no molecular diagnosis using standard molecular technologies. The patient presented with a typical NF1 phenotype but NF1 targeted NGS, NF1 transcript analysis, MLPA, and array comparative genomic hybridization failed to reveal a genetic aberration. After 5 years of unsuccessful investigations, trio WGS finally identified a de novo mosaic (VAF ~ 14%) 24.6 kb germline deletion encompassing the promoter and first exon of NF1. This case report illustrates the relevance of WGS to detect structural variants including copy number variants that would be missed by alternative approaches. The identification of the causal pathogenic variant allowed a tailored genetic counseling with a targeted non-invasive prenatal diagnosis by detecting the deletion in plasmatic cell-free DNA from the proband's pregnant partner. This report clearly highlights the need to make WGS a clinically accessible test, offering a tremendous opportunity to identify a molecular diagnosis for otherwise unsolved cases.

ROSAH syndrome mimicking chronic uveitis.

To suggest a unique missense variant candidate based on long-term ophthalmological changes and associated systemic signs described in five patients from two unrelated families affected by an autosomal dominant multi-systemic disorder including Retinal dystrophy, Optic nerve oedema, Splenomegaly, Anhidrosis and migraine Headaches, called ROSAH syndrome, related to a unique missense variant in ALPK1 gene. Observational longitudinal follow-up study of unrelated families. Clinical analysis of ophthalmological and systemic examinations was performed, followed by genetic analysis, including targeted Next Generation Sequencing (NGS) and Whole-Genome Sequencing (WGS). The ophthalmological phenotype showed extensive optic nerve swelling associated with early macular oedema and vascular leakage. The main associated systemic manifestations were recurrent fever, splenomegaly, anhidrosis, mild cytopenia, anicocytosis and hypersegmented polynuclear cells. WGS, shortened in the second family by the gene candidate suggestion, revealed in all patients the heterozygous missense variant c.710C>T; p.(Thr237Met) in ALPK1. The primary morbidity in ROSAH syndrome in this cohort appeared ophthalmological. Comprehensive, detailed phenotype changes aided by the advancement in genetic testing could allow an early genetic diagnosis of ROSAH syndrome and targeted treatment. The unique missense variant may be suggested as a target of gene correction therapy.

AnnotSV and knotAnnotSV: a web server for human structural variations annotations, ranking and analysis.

With the dramatic increase of pangenomic analysis, Human geneticists have generated large amount of genomic data including millions of small variants (SNV/indel) but also thousands of structural variations (SV) mainly from next-generation sequencing and array-based techniques. While the identification of the complete SV repertoire of a patient is getting possible, the interpretation of each SV remains challenging. To help identifying human pathogenic SV, we have developed a web server dedicated to their annotation and ranking (AnnotSV) as well as their visualization and interpretation (knotAnnotSV) freely available at the following address: https://www.lbgi.fr/AnnotSV/. A large amount of annotations from >20 sources is integrated in our web server including among others genes, haploinsufficiency, triplosensitivity, regulatory elements, known pathogenic or benign genomic regions, phenotypic data. An ACMG/ClinGen compliant prioritization module allows the scoring and the ranking of SV into 5 SV classes from pathogenic to benign. Finally, the visualization interface displays the annotated SV in an interactive way including popups, search fields, filtering options, advanced colouring to highlight pathogenic SV and hyperlinks to the UCSC genome browser or other public databases. This web server is designed for diagnostic and research analysis by providing important resources to the user.

Current Management of Patients with RPE65 Mutation Associated Inherited Retinal Degenerations in Europe: Results of a 2-Year Follow-Up Multinational Survey.

INTRODUCTION: The aim of this study was to evaluate the current management of RPE65 biallelic mutation-associated inherited retinal degeneration (RPE65-IRD) in Europe since market authorization of voretigene neparvovec (VN, LuxturnaTM) in 2018. By July 2022, over 200 patients have been treated outside the USA, of whom about 90% in Europe. We conducted among all centers of the European Vision Institute Clinical Research Network (EVICR.net) and health care providers (HCPs) of the European Reference Network dedicated to Rare Eye Diseases (ERN-EYE) the second multinational survey on management of IRDs in Europe elaborated by EVICR.net with a special focus on RPE65-IRD. METHODS: An electronic survey questionnaire with 48 questions specifically addressing RPE65-IRD (2019 survey 35) was developed and sent by June 2021 to 95 EVICR.net centers and 40 ERN-EYE HCPs and affiliated members. Of note, 11 centers are members of both networks. Statistical analysis was performed with Excel and R. RESULTS: The overall response rate was 44% (55/124); 26 centers follow RPE65 biallelic mutation-associated IRD patients. By June 2021, 8/26 centers have treated 57 RPE65-IRD cases (1-19/center, median 6) and 43 planned for treatment (range 0-10/center, median 6). The overall age range was 3-52 years, and on average 22% of the patients did not (yet) qualify for treatment (range 2-60%/center, median 15%). Main reasons were too advanced (range 0-100, median 75%) or mild disease (range 0-100, median 0). Eighty-three percent of centers (10/12) that follow RPE65 mutation-associated IRD patients treated with VN participate in the PERCEIVE registry (EUPAS31153, http://www.encepp.eu/encepp/viewResource.htm?id=37005). Quality of life and full-field stimulus test improvements had the highest scores of the survey-reported outcome parameters in VN treatment follow-up. CONCLUSION: This second multinational survey on management of RPE65-IRD by EVICR.net centers and ERN-EYE HCPs in Europe indicates that RPE65-IRD might be diagnosed more reliably in 2021 compared to 2019. By June 2021, 8/26 centers reported detailed results including VN treatment. Main reasons for non-treatment were too advanced or mild disease, followed by absence of 2 class 4 or 5 mutations on both alleles or because of a too young age. Patient satisfaction with treatment was estimated to be high by 50% of the centers.

Current Management of Inherited Retinal Degeneration Patients in Europe: Results of a 2-Year Follow-Up Multinational Survey by the European Vision Institute Clinical Research Network - EVICR.net.

INTRODUCTION: An increasing number of gene-specific therapies are being developed for inherited retinal degenerations (IRDs). Identification of well-characterized patients is an emerging need. We conducted the second multinational survey among the EVICR.net and ERN-EYE members to understand the management and treatment of IRDs in Europe and compared it to the 2019 survey. METHODS: An electronic survey questionnaire was developed and sent to 124 clinical centers (25 countries) by June/July 2021. Statistical analysis was performed with Excel and R. RESULTS: The overall response rate was 44% but varied among countries. Only 9% of responding centers do not see IRD patients (2019 survey 14%), 42% follow at least 200 patients per year, 18% follow 500-999, and 2% more than 1,000. Databases exist in 86% of the centers (local 86%; national web based 12%). IRD patients are referred to EVICR.net and ERN-EYE centers mainly by general ophthalmologists, patient self-referral, or medical retina specialists. Most IRD patients are first seen as adults. Signs and symptoms depend on age of onset: in infancy, nystagmus; at older age, night blindness and reduced visual field; reduced visual acuity is described at any age. Comprehensive ophthalmic examination always includes visual acuity and almost always visual field multimodal retinal imaging, electrophysiology, color vision testing, and refraction. Identification of genotypes is successful in 72% of centers in 40-80% of cases (2019 survey 69% of centers). The time for confirmation of the genetic diagnosis varies from 2-4 weeks to 24 months (2019 survey >4 weeks ≤10 years). Genetic testing is covered by public health service in 83%, private health insurance in 29%, research funds in 24%; 5% do not have access to genetic testing (2019 survey 15%). The most striking result is the high increase in the involvement of centers in natural history and gene therapy trials that more than doubled for the latter. DISCUSSION: This second multinational survey on management of IRDs in Europe highlights persistent important differences in the number of IRD patients managed per center, comparable diagnostic work-up, and increasing genotyping in diagnostic laboratories. The important increase in involvement of centers in natural history and gene therapy trials reflects the rapidly evolving field of gene therapy development. The survey provides important follow-up data for researchers, clinicians, caregivers, patient advocate groups, pharmaceutical companies, and investors.

WGS Revealed Novel BBS5 Pathogenic Variants, Missed by WES, Causing Ciliary Structure and Function Defects.

Bardet-Biedl syndrome (BBS) is an autosomal recessive ciliopathy that affects multiple organs, leading to retinitis pigmentosa, polydactyly, obesity, renal anomalies, cognitive impairment, and hypogonadism. Until now, biallelic pathogenic variants have been identified in at least 24 genes delineating the genetic heterogeneity of BBS. Among those, BBS5 is a minor contributor to the mutation load and is one of the eight subunits forming the BBSome, a protein complex implied in protein trafficking within the cilia. This study reports on a European BBS5 patient with a severe BBS phenotype. Genetic analysis was performed using multiple next-generation sequencing (NGS) tests (targeted exome, TES and whole exome, WES), and biallelic pathogenic variants could only be identified using whole-genome sequencing (WGS), including a previously missed large deletion of the first exons. Despite the absence of family samples, the biallelic status of the variants was confirmed. The BBS5 protein's impact was confirmed on the patient's cells (presence/absence and size of the cilium) and ciliary function (Sonic Hedgehog pathway). This study highlights the importance of WGS and the challenge of reliable structural variant detection in patients' genetic explorations as well as functional tests to assess a variant's pathogenicity.

Comprehensive variant spectrum of the CNGA3 gene in patients affected by achromatopsia.

Achromatopsia (ACHM) is a congenital cone photoreceptor disorder characterized by impaired color discrimination, low visual acuity, photosensitivity, and nystagmus. To date, six genes have been associated with ACHM (CNGA3, CNGB3, GNAT2, PDE6C, PDE6H, and ATF6), the majority of these being implicated in the cone phototransduction cascade. CNGA3 encodes the CNGA3 subunit of the cyclic nucleotide-gated ion channel in cone photoreceptors and is one of the major disease-associated genes for ACHM. Herein, we provide a comprehensive overview of the CNGA3 variant spectrum in a cohort of 1060 genetically confirmed ACHM patients, 385 (36.3%) of these carrying "likely disease-causing" variants in CNGA3. Compiling our own genetic data with those reported in the literature and in public databases, we further extend the CNGA3 variant spectrum to a total of 316 variants, 244 of which we interpreted as "likely disease-causing" according to ACMG/AMP criteria. We report 48 novel "likely disease-causing" variants, 24 of which are missense substitutions underlining the predominant role of this mutation class in the CNGA3 variant spectrum. In addition, we provide extensive in silico analyses and summarize reported functional data of previously analyzed missense, nonsense and splicing variants to further advance the pathogenicity assessment of the identified variants.

Rare De Novo Missense Variants in RNA Helicase DDX6 Cause Intellectual Disability and Dysmorphic Features and Lead to P-Body Defects and RNA Dysregulation.

The human RNA helicase DDX6 is an essential component of membrane-less organelles called processing bodies (PBs). PBs are involved in mRNA metabolic processes including translational repression via coordinated storage of mRNAs. Previous studies in human cell lines have implicated altered DDX6 in molecular and cellular dysfunction, but clinical consequences and pathogenesis in humans have yet to be described. Here, we report the identification of five rare de novo missense variants in DDX6 in probands presenting with intellectual disability, developmental delay, and similar dysmorphic features including telecanthus, epicanthus, arched eyebrows, and low-set ears. All five missense variants (p.His372Arg, p.Arg373Gln, p.Cys390Arg, p.Thr391Ile, and p.Thr391Pro) are located in two conserved motifs of the RecA-2 domain of DDX6 involved in RNA binding, helicase activity, and protein-partner binding. We use functional studies to demonstrate that the first variants identified (p.Arg373Gln and p.Cys390Arg) cause significant defects in PB assembly in primary fibroblast and model human cell lines. These variants' interactions with several protein partners were also disrupted in immunoprecipitation assays. Further investigation via complementation assays included the additional variants p.Thr391Ile and p.Thr391Pro, both of which, similarly to p.Arg373Gln and p.Cys390Arg, demonstrated significant defects in P-body assembly. Complementing these molecular findings, modeling of the variants on solved protein structures showed distinct spatial clustering near known protein binding regions. Collectively, our clinical and molecular data describe a neurodevelopmental syndrome associated with pathogenic missense variants in DDX6. Additionally, we suggest DDX6 join the DExD/H-box genes DDX3X and DHX30 in an emerging class of neurodevelopmental disorders involving RNA helicases.

First evidence of SOX2 mutations in Peters' anomaly: Lessons from molecular screening of 95 patients.

Peters' anomaly (PA) is a rare anterior segment dysgenesis characterized by central corneal opacity and irido-lenticulo-corneal adhesions. Several genes are involved in syndromic or isolated PA (B3GLCT, PAX6, PITX3, FOXE3, CYP1B1). Some copy number variations (CNVs) have also been occasionally reported. Despite this genetic heterogeneity, most of patients remain without genetic diagnosis. We retrieved a cohort of 95 individuals with PA and performed genotyping using a combination of comparative genomic hybridization, whole genome, exome and targeted sequencing of 119 genes associated with ocular development anomalies. Causative genetic defects involving 12 genes and CNVs were identified for 1/3 of patients. Unsurprisingly, B3GLCT and PAX6 were the most frequently implicated genes, respectively in syndromic and isolated PA. Unexpectedly, the third gene involved in our cohort was SOX2, the major gene of micro-anophthalmia. Four unrelated patients with PA (isolated or with microphthalmia) were carrying pathogenic variants in this gene that was never associated with PA before. Here we described the largest cohort of PA patients ever reported. The genetic bases of PA are still to be explored as genetic diagnosis was unavailable for 2/3 of patients. Nevertheless, we showed here for the first time the involvement of SOX2 in PA, offering new evidence for its role in corneal transparency and anterior segment development.

Contribution of Whole-Genome Sequencing and Transcript Analysis to Decipher Retinal Diseases Associated with MFSD8 Variants.

Biallelic gene defects in MFSD8 are not only a cause of the late-infantile form of neuronal ceroid lipofuscinosis, but also of rare isolated retinal degeneration. We report clinical and genetic data of seven patients compound heterozygous or homozygous for variants in MFSD8, issued from a French cohort with inherited retinal degeneration, and two additional patients retrieved from a Swiss cohort. Next-generation sequencing of large panels combined with whole-genome sequencing allowed for the identification of twelve variants from which seven were novel. Among them were one deep intronic variant c.998+1669A>G, one large deletion encompassing exon 9 and 10, and a silent change c.750A>G. Transcript analysis performed on patients' lymphoblastoid cell lines revealed the creation of a donor splice site by c.998+1669A>G, resulting in a 140 bp pseudoexon insertion in intron 10. Variant c.750A>G produced exon 8 skipping. In silico and in cellulo studies of these variants allowed us to assign the pathogenic effect, and showed that the combination of at least one severe variant with a moderate one leads to isolated retinal dystrophy, whereas the combination in trans of two severe variants is responsible for early onset severe retinal dystrophy in the context of late-infantile neuronal ceroid lipofuscinosis.

Neurotrophic Keratitis Due to Congenital Corneal Anesthesia with Deafness, Hypotonia, Intellectual Disability, Face Abnormality and Metabolic Disorder: A New Syndrome?

Neurotrophic keratitis is a rare degenerative disease of the cornea that can lead to corneal ulceration, scarring, and significant visual impairment. It most commonly occurs in adults and is rarely diagnosed in children. Congenital corneal anesthesia is an extremely rare condition that requires appropriate ophthalmologists' attention in making diagnosis and treatment decisions. This condition usually presents in infancy or early childhood and is characterized by rare blinking rate, decreased tearing or a corneal ulcer that is unresponsive to treatment. In this case report, we describe a patient with multiple systemic and neurological disorders who presented to the ophthalmology department due to corneal erosion unresponsive to treatment. Brain magnetic resonance imaging confirmed bilateral trigeminal hypoplasia and the diagnosis of neurotrophic keratopathy due to bilateral congenital corneal anesthesia was made. The discrepancy between clinical signs and symptoms or treatment non-response in cases of corneal erosions should alert the ophthalmologists to suspect trigeminal dysfunction. MRI is the gold standard to confirm congenital corneal anesthesia and to differentiate from other possible neurotrophic keratitis causes.

Periodontal (formerly type VIII) Ehlers-Danlos syndrome: Description of 13 novel cases and expansion of the clinical phenotype.

Periodontal Ehlers-Danlos syndrome (pEDS) is a rare condition caused by pathogenic variants in the C1R and C1S genes, encoding subunits C1r and C1s of the first component of the classical complement pathway. It is characterized by early-onset periodontitis with premature tooth loss, pretibial hyperpigmentation and skin fragility. Rare arterial complications have been reported, but venous insufficiency is rarely described. Here we report 13 novel patients carrying heterozygous pathogenic variants in C1R and C1S including three novel C1S variants (c.962G > C, c.961 T > G and c.961 T > A). In addition to the pEDS phenotype, three patients and one relative displayed widespread venous insufficiency leading to persistent varicose leg ulcers. One patient suffered an intracranial aneurysm with familial vascular complications including thoracic and abdominal aortic aneurysm and dissection and intracranial aneurysm rupture. This work confirms that vascular complications can occur, although they are not frequent, which leads us to propose to carry out a first complete non-invasive vascular evaluation at the time of the diagnosis in pEDS patients. However, larger case series are needed to improve our understanding of the link between complement pathway activation and connective tissue alterations observed in these patients, and to better assess the frequency, type and consequences of the vascular complications.

A BBS1 SVA F retrotransposon insertion is a frequent cause of Bardet-Biedl syndrome.

Bardet-Biedl syndrome (BBS) is a ciliopathy characterized by retinitis pigmentosa, obesity, polydactyly, cognitive impairment and renal failure. Pathogenic variants in 24 genes account for the molecular basis of >80% of cases. Toward saturated discovery of the mutational basis of the disorder, we carefully explored our cohorts and identified a hominid-specific SINE-R/VNTR/Alu type F (SVA-F) insertion in exon 13 of BBS1 in eight families. In six families, the repeat insertion was found in trans with c.1169 T > G, p.Met390Arg and in two families the insertion was found in addition to other recessive BBS loci. Whole genome sequencing, de novo assembly and SNP array analysis were performed to characterize the genomic event. This insertion is extremely rare in the general population (found in 8 alleles of 8 BBS cases but not in >10 800 control individuals from gnomAD-SV) and due to a founder effect. Its 2435 bp sequence contains hallmarks of LINE1 mediated retrotransposition. Functional studies with patient-derived cell lines confirmed that the BBS1 SVA-F is deleterious as evidenced by a significant depletion of both mRNA and protein levels. Such findings highlight the importance of dedicated bioinformatics pipelines to identify all types of variation.

WDR34, a candidate gene for non-syndromic rod-cone dystrophy.

Rod-cone dystrophy (RCD), also called retinitis pigmentosa, is characterized by rod followed by cone photoreceptor degeneration, leading to gradual visual loss. Mutations in over 65 genes have been associated with non-syndromic RCD explaining 60% to 70% of cases, with novel gene defects possibly accounting for the unsolved cases. Homozygosity mapping and whole-exome sequencing applied to a case of autosomal recessive non-syndromic RCD from a consanguineous union identified a homozygous variant in WDR34. Mutations in WDR34 have been previously associated with severe ciliopathy syndromes possibly associated with a retinal dystrophy. This is the first report of a homozygous mutation in WDR34 associated with non-syndromic RCD.

The Study of a 231 French Patient Cohort Significantly Extends the Mutational Spectrum of the Two Major Usher Genes MYO7A and USH2A.

Usher syndrome is an autosomal recessive disorder characterized by congenital hearing loss combined with retinitis pigmentosa, and in some cases, vestibular areflexia. Three clinical subtypes are distinguished, and MYO7A and USH2A represent the two major causal genes involved in Usher type I, the most severe form, and type II, the most frequent form, respectively. Massively parallel sequencing was performed on a cohort of patients in the context of a molecular diagnosis to confirm clinical suspicion of Usher syndrome. We report here 231 pathogenic MYO7A and USH2A genotypes identified in 73 Usher type I and 158 Usher type II patients. Furthermore, we present the ACMG classification of the variants, which comprise all types. Among them, 68 have not been previously reported in the literature, including 12 missense and 16 splice variants. We also report a new deep intronic variant in USH2A. Despite the important number of molecular studies published on these two genes, we show that during the course of routine genetic diagnosis, undescribed variants continue to be identified at a high rate. This is particularly pertinent in the current era, where therapeutic strategies based on DNA or RNA technologies are being developed.

Novel TTLL5 Variants Associated with Cone-Rod Dystrophy and Early-Onset Severe Retinal Dystrophy.

Variants of the TTLL5 gene, which encodes tubulin tyrosine ligase-like family member five, are a rare cause of cone dystrophy (COD) or cone-rod dystrophy (CORD). To date, only a few TTLL5 patients have been clinically and genetically described. In this study, we report five patients harbouring biallelic variants of TTLL5. Four adult patients presented either COD or CORD with onset in the late teenage years. The youngest patient had a phenotype of early onset severe retinal dystrophy (EOSRD). Genetic analysis was performed by targeted next generation sequencing of gene panels and assessment of copy number variants (CNV). We identified eight variants, of which six were novel, including two large multiexon deletions in patients with COD or CORD, while the EOSRD patient harboured the novel homozygous p.(Trp640*) variant and three distinct USH2A variants, which might explain the observed rod involvement. Our study highlights the role of TTLL5 in COD/CORD and the importance of large deletions. These findings suggest that COD or CORD patients lacking variants in known genes may harbour CNVs to be discovered in TTLL5, previously undetected by classical sequencing methods. In addition, variable phenotypes in TTLL5-associated patients might be due to the presence of additional gene defects.

Novel IQCE variations confirm its role in postaxial polydactyly and cause ciliary defect phenotype in zebrafish.

Polydactyly is one of the most frequent inherited defects of the limbs characterized by supernumerary digits and high-genetic heterogeneity. Among the many genes involved, either in isolated or syndromic forms, eight have been implicated in postaxial polydactyly (PAP). Among those, IQCE has been recently identified in a single consanguineous family. Using whole-exome sequencing in patients with uncharacterized ciliopathies, including PAP, we identified three families with biallelic pathogenic variations in IQCE. Interestingly, the c.895_904del (p.Val301Serfs*8) was found in all families without sharing a common haplotype, suggesting a recurrent mechanism. Moreover, in two families, the systemic phenotype could be explained by additional pathogenic variants in known genes (TULP1, ATP6V1B1). RNA expression analysis on patients' fibroblasts confirms that the dysfunction of IQCE leads to the dysregulation of genes associated with the hedgehog-signaling pathway, and zebrafish experiments demonstrate a full spectrum of phenotypes linked to defective cilia: Body curvature, kidney cysts, left-right asymmetry, misdirected cilia in the pronephric duct, and retinal defects. In conclusion, we identified three additional families confirming IQCE as a nonsyndromic PAP gene. Our data emphasize the importance of taking into account the complete set of variations of each individual, as each clinical presentation could finally be explained by multiple genes.