Next generation sequencing identifies mutations in Atonal homolog 7 (ATOH7) in families with global eye developmental defects

KIF11 Inhibition Induces Retinopathy Progression by Affecting Photoreceptor Cell Ciliogenesis and Cell Cycle Regulation in Development

Microcephaly with or without chorioretinopathy, lymphedema, or impaired intellectual development (MCLMR; OMIM 152950) is a rare autosomal dominant disorder, which is primarily characterized by defects in the central nervous system and retinal developmental anomalies. Kinesin-5 KIF11 has been discovered as a major causative gene for MCLMR. It has been well established that KIF11 is essential for microtubule organization, centrosome separation, and spindle assembly during mitosis. However, cellular and molecular mechanisms in the physiopathology of MCLMR remain largely unknown. In this study, KIF11-inhibition mouse models are generated, which reveal that chemical inhibition of KIF11 results in defects in retinal development, the formation of rosettes, photoreceptor ciliary alterations, and vision loss. Furthermore, it is demonstrated that KIF11 is essential for the formation, organization, and maintenance of primary cilia in photoreceptor cells, which further contributes to the organization of photoreceptor cells and the development of the retina. Using the developing mouse embryos as a model, it is revealed that KIF11 inhibition induces the formation of monopolar spindle and mitotic arrest, which further results in tetraploidy and apoptotic cell death. These findings uncover cellular mechanisms underlying the loss-of-function of KIF11 and retinopathy in MCLMR and further support the functions of KIF11 in development.

Genotype-Phenotype Spectrum of eyeGENE Patients With Familial Exudative Vitreoretinopathy: Novel Variants in Norrin/β-Catenin Signaling Pathway Genes

Purpose

To report the variants and genotype-phenotype correlations in patients with familial exudative vitreoretinopathy (FEVR) included in the eyeGENE database.

Methods

A retrospective study was conducted in a cohort of 122 eyeGENE patients from 114 families with FEVR. Clinical details and genetic test results were provided by referring clinicians and clinical laboratories in the eyeGENE network, respectively. Genotype and phenotype information was reviewed, and reported variants were reclassified.

Results

Genetic test reports of 50 probands revealed 52 variants in the four genes of the Norrin/β-catenin signaling pathway: LRP5, FZD4, TSPAN12, and NDP. Following variant reclassification, 35 of the reported variants were interpreted as pathogenic or likely pathogenic (12 in LRP5, 11 in FZD4, seven in TSPAN12 and five in NDP), providing a conclusive test result for nearly one-third (32%) of the probands. Among the reported variants, 18 were novel (34.6%) and two-thirds were missense. Retinal detachment was reported less in patients with variants in TSPAN12 (P = 0.017). One-third of the patients (33.3%) with an FZD4 variant had asymmetric findings. In contrast, asymmetry was less pronounced in patients with variants in TSPAN12 (11.1%).

Conclusions

This was one of the largest cohorts reviewed from North America, expanding the variant spectrum in FEVR. Among the eyeGENE FEVR patients, disease-associated variants in Norrin/β-catenin signaling pathway genes can explain one-third of the cohort. LRP5 and FZD4 variants were the most common. The genotype-phenotype correlations supported the phenotypic variability in FEVR.

Blind But Alive - Congenital Loss of atoh7 Disrupts the Visual System of Adult Zebrafish

Purpose

Vision is the predominant sense in most animal species. Loss of vision can be caused by a multitude of factors resulting in anatomic as well as behavioral changes. In mice and zebrafish, atoh7 mutants are completely blind as they fail to generate retinal ganglion cells (RGCs) during development. In contrast to mice, raising blind zebrafish to adulthood is challenging and this important model is currently missing in the field. Here, we report the phenotype of homozygous mutant adult zebrafish atoh7 mutants that have been raised using adjusted feeding and holding conditions.

Methods

The phenotype of adult mutants was characterized using classical histology and immunohistochemistry as well as optical coherence tomography. In addition, the optokinetic response was characterized.

Results

Adult atoh7 mutants display dark body pigmentation and significantly reduced body length. They fail to form RGCs, the resulting nerve fiber layer as well as the optic nerve, and consequently behave completely blindly. In contrast, increased amounts of other retinal neurons and Müller glia are formed. In addition, the optic tectum is anatomically reduced in size, presumably due to the missing retinal input.

Conclusions

Taken together, we provide a comprehensive characterization of a completely blind adult zebrafish mutant with focus on retinal and tectal morphology, as a useful model for glaucoma and optic nerve aplasia.

Dysfunction of Calcyphosine-Like gene impairs retinal angiogenesis through the MYC axis and is associated with familial exudative vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is a severe genetic disorder characterized by incomplete vascularization of the peripheral retina and associated symptoms that can lead to vision loss. However, the underlying genetic causes of approximately 50% of FEVR cases remain unknown. Here, we report two heterozygous variants in calcyphosine-like gene (CAPSL) that is associated with FEVR. Both variants exhibited compromised CAPSL protein expression. Vascular endothelial cell (EC)-specific inactivation of Capsl resulted in delayed radial/vertical vascular progression, compromised endothelial proliferation/migration, recapitulating the human FEVR phenotypes. CAPSL-depleted human retinal microvascular endothelial cells (HRECs) exhibited impaired tube formation, decreased cell proliferation, disrupted cell polarity establishment, and filopodia/lamellipodia formation, as well as disrupted collective cell migration. Transcriptomic and proteomic profiling revealed that CAPSL abolition inhibited the MYC signaling axis, in which the expression of core MYC targeted genes were profoundly decreased. Furthermore, a combined analysis of CAPSL-depleted HRECs and c-MYC-depleted human umbilical vein endothelial cells uncovered similar transcription patterns. Collectively, this study reports a novel FEVR-associated candidate gene, CAPSL, which provides valuable information for genetic counseling of FEVR. This study also reveals that compromised CAPSL function may cause FEVR through MYC axis, shedding light on the potential involvement of MYC signaling in the pathogenesis of FEVR.

Identification and Characterization of ATOH7-Regulated Target Genes and Pathways in Human Neuroretinal Development

The proneural transcription factor atonal basic helix-loop-helix transcription factor 7 (ATOH7) is expressed in early progenitors in the developing neuroretina. In vertebrates, this is crucial for the development of retinal ganglion cells (RGCs), as mutant animals show an almost complete absence of RGCs, underdeveloped optic nerves, and aberrations in retinal vessel development. Human mutations are rare and result in autosomal recessive optic nerve hypoplasia (ONH) or severe vascular changes, diagnosed as autosomal recessive persistent hyperplasia of the primary vitreous (PHPVAR). To better understand the role of ATOH7 in neuroretinal development, we created ATOH7 knockout and eGFP-expressing ATOH7 reporter human induced pluripotent stem cells (hiPSCs), which were differentiated into early-stage retinal organoids. Target loci regulated by ATOH7 were identified by Cleavage Under Targets and Release Using Nuclease with sequencing (CUT&RUN-seq) and differential expression by RNA sequencing (RNA-seq) of wildtype and mutant organoid-derived reporter cells. Additionally, single-cell RNA sequencing (scRNA-seq) was performed on whole organoids to identify cell type-specific genes. Mutant organoids displayed substantial deficiency in axon sprouting, reduction in RGCs, and an increase in other cell types. We identified 469 differentially expressed target genes, with an overrepresentation of genes belonging to axon development/guidance and Notch signaling. Taken together, we consolidate the function of human ATOH7 in guiding progenitor competence by inducing RGC-specific genes while inhibiting other cell fates. Furthermore, we highlight candidate genes responsible for ATOH7-associated optic nerve and retinovascular anomalies, which sheds light to potential future therapy targets for related disorders.

Next-generation sequencing to genetically diagnose a diverse range of inherited eye disorders in 15 consanguineous families from Pakistan

Inherited retinal dystrophies (IRDs) are characterized by photoreceptor dysfunction or degeneration. Clinical and phenotypic overlap between IRDs makes the genetic diagnosis very challenging and comprehensive genomic approaches for accurate diagnosis are frequently required. While there are previous studies on IRDs in Pakistan, causative genes and variants are still unknown for a significant portion of patients. Therefore, there is a need to expand the knowledge of the genetic spectrum of IRDs in Pakistan. Here, we recruited 52 affected and 53 normal individuals from 15 consanguineous Pakistani families presenting non-syndromic and syndromic forms of IRDs. We employed single molecule Molecular Inversion Probes (smMIPs) based panel sequencing and whole genome sequencing to identify the probable disease-causing variants in these families. Using this approach, we obtained a 93% genetic solve rate and identified 16 (likely) causative variants in 14 families, of which seven novel variants were identified in ATOH7, COL18A1, MERTK, NDP, PROM1, PRPF8 and USH2A while nine recurrent variants were identified in CNGA3, CNGB1, HGSNAT, NMNAT1, SIX6 and TULP1. The novel MERTK variant and one recurrent TULP1 variant explained the intra-familial locus heterogeneity in one of the screened families while two recurrent CNGA3 variants explained compound heterozygosity in another family. The identification of variants in known disease-associated genes emphasizes the utilization of time and cost-effective screening approaches for rapid diagnosis. The timely genetic diagnosis will not only identify any associated systemic issues in case of syndromic IRDs, but will also aid in the acceleration of personalized medicine for patients affected with IRDs.

Integrative transcriptomic profiling of ncRNAs and mRNAs in developing mouse lens

In recent years, burgeoning research has underscored the pivotal role of non-coding RNA in orchestrating the growth, development, and pathogenesis of various diseases across organisms. However, despite these advances, our understanding of the specific contributions of long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) to lens development remains notably limited. Clarifying the intricate gene regulatory networks is imperative for unraveling the molecular underpinnings of lens-related disorders. In this study, we aimed to address this gap by conducting a comprehensive analysis of the expression profiles of messenger RNAs (mRNAs), lncRNAs, and circRNAs at critical developmental time points of the mouse lens, encompassing both embryonic (E10.5, E12.5, and E16.5) and postnatal stages (P0.5, P10.5, and P60). Leveraging RNA-sequencing technology, we identified key transcripts pivotal to lens development. Our analysis revealed differentially expressed (DE) mRNAs, lncRNAs, and circRNAs across various developmental stages. Particularly noteworthy, there were 1831 co-differentially expressed (CO-DE) mRNAs, 150 CO-DE lncRNAs, and 13 CO-DE circRNAs identified during embryonic stages. Gene Ontology (GO) enrichment analysis unveiled associations primarily related to lens development, DNA conformational changes, and angiogenesis among DE mRNAs and lncRNAs. Furthermore, employing protein-protein interaction networks, mRNA-lncRNA co-expression networks, and circRNA-microRNA-mRNA networks, we predicted candidate key molecules implicated in lens development. Our findings underscore the pivotal roles of lncRNAs and circRNAs in this process, offering fresh insights into the pathogenesis of lens-related disorders and paving the way for future exploration in this field.

Retinopathy With Variant of Unknown Significance and Atypical Chorioretinal Coloboma in the Setting of Prematurity

A 37-week-old girl underwent ophthalmic examination. Born at 32 weeks, the infant weighed 680 grams and received high-flow nasal cannula for respiratory distress of the newborn. Dilated fundus examination of the right eye revealed an atypical chorioretinal coloboma; the left eye revealed hyperpigmentary changes in the macula. Fluorescein angiography of both eyes showed retinal vascularization to zone II. Genetic testing revealed a heterozygous variant of uncertain significance in the catenin Alpha 1 (CTNNA1) gene. CTNNA1 gene abnormalities have been implicated as causes of familial exudative vitreoretinopathy (FEVR). It is important to recognize possible simultaneous retinopathy of prematurity and FEVR. [Ophthalmic Surg Lasers Imaging Retina 2024;55:285-288.].

Identification of Novel FZD4 Mutations in Familial Exudative Vitreoretinopathy and Investigating the Pathogenic Mechanisms of FZD4 Mutations

Purpose

The purpose of this study is to report five novel FZD4 mutations identified in familial exudative vitreoretinopathy (FEVR) and to analyze and summarize the pathogenic mechanisms of 34 of 96 reported missense mutations in FZD4.

Methods

Five probands diagnosed with FEVR and their family members were enrolled in the study. Ocular examinations and targeted gene panel sequencing were conducted on all participants. Plasmids, each carrying 29 previously reported FZD4 missense mutations and five novel mutations, were constructed based on the selection of mutations from each domain of FZD4. These plasmids were used to investigate the effects of mutations on protein expression levels, Norrin/β-catenin activation capacity, membrane localization, norrin binding ability, and DVL2 recruitment ability in HEK293T, HEK293STF, and HeLa cells.

Results

All five novel mutations (S91F, V103E, C145S, E160K, C377F) responsible for FEVR were found to compromise Norrin/β-catenin activation of FZD4 protein. After reviewing a total of 34 reported missense mutations, we categorized all mutations based on their functional changes: signal peptide mutations, cysteine mutations affecting disulfide bonds, extracellular domain mutations influencing norrin binding, transmembrane domain (TM) 1 and TM7 mutations impacting membrane localization, and intracellular domain mutations affecting DVL2 recruitment.

Conclusions

We expanded the spectrum of FZD4 mutations relevant to FEVR and experimentally demonstrated that missense mutations in FZD4 can be classified into five categories based on different functional changes.

Characterization of a novel heterozygous frameshift variant in NDP gene that causes familial exudative vitreoretinopathy in female patients

Familial exudative vitreoretinopathy (FEVR) is a severe inherited disease characterized by defective retinal vascular development. With genetic and clinical heterogeneity, FEVR can be inherited in different patterns and characterized by phenotypes ranging from moderate visual defects to complete vision loss. This study was conducted to unravel the genetic and functional etiology of a 4-month-old female FEVR patient. Targeted gene panel and Sanger sequencing were utilized for genetic evaluation. Luciferase assays, western blot, quantitive real-time PCR, and immunocytochemistry were performed to verify the functional defects in the identified candidate variant. Here, we report a 4-month-old girl with bilateral retinal folds and peripheral avascularization, and identified a novel frameshift heterozygous variant c.37dup (p.Leu13ProfsTer13) in NDP. In vitro experiments revealed that the Leu13ProfsTer13 variant led to a prominent decrease in protein levels instead of mRNA levels, resulting in compromised Norrin/β-catenin signaling activity. Human androgen receptor assay further revealed that a slight skewing of X chromosome inactivation could partially cause FEVR. Thus, the pathogenic mechanism by which heterozygous frameshift or nonsense variants in female carriers cause FEVR might largely result from a loss-of-function variant in one X chromosome allele and a slightly skewed X-inactivation. Further recruitment of more FEVR-affected females carrying NDP variants and genotype-phenotype correlation analysis can ultimately offer valuable information for the prognosis prediction of FEVR.

Investigating the Impact of Dimer Interface Mutations on Norrin's Secretion and Norrin/β-Catenin Pathway Activation

Purpose

This study aimed to investigate the impact of 21 NDP mutations located at the dimer interface, focusing on their potential effects on protein assembly, secretion efficiency, and activation of the Norrin/β-catenin signaling pathway.

Methods

The expression level, secretion efficiency, and protein assembly of mutations were analyzed using Western blot. The Norrin/β-catenin signaling pathway activation ability after overexpression of mutants or supernatant incubation of mutant proteins was tested in HEK293STF cells. The mutant norrin and wild-type (WT) FZD4 were overexpressed in HeLa cells to observe their co-localization. Immunofluorescence staining was conducted in HeLa cells to analyze the subcellular localization of Norrin and the Retention Using Selective Hook (RUSH) assay was used to dynamically observe the secretion process of WT and mutant Norrin.

Results

Four mutants (A63S, E66K, H68P, and L103Q) exhibited no significant differences from WT in all evaluations. The other 17 mutants presented abnormalities, including inadequate protein assembly, reduced secretion, inability to bind to FZD4 on the cell membrane, and decreased capacity to activate Norrin/β-catenin signaling pathway. The RUSH assay revealed the delay in endoplasmic reticulum (ER) exit and impairment of Golgi transport.

Conclusions

Mutations at the Norrin dimer interface may lead to abnormal protein assembly, inability to bind to FZD4, and decreased secretion, thus contributing to compromised Norrin/β-catenin signaling. Our results shed light on the pathogenic mechanisms behind a significant proportion of NDP gene mutations in familial exudative vitreoretinopathy (FEVR) or Norrie disease.

Loss-of-function of kinesin-5 KIF11 causes microcephaly, chorioretinopathy, and developmental disorders through chromosome instability and cell cycle arrest

Kinesin motors play a fundamental role in development by controlling intracellular transport, spindle assembly, and microtubule organization. In humans, patients carrying mutations in KIF11 suffer from an autosomal dominant inheritable disease called microcephaly with or without chorioretinopathy, lymphoedema, or mental retardation (MCLMR). While mitotic functions of KIF11 proteins have been well documented in centrosome separation and spindle assembly, cellular mechanisms underlying KIF11 dysfunction and MCLMR remain unclear. In this study, we generate KIF11-inhibition chick and zebrafish models and find that KIF11 inhibition results in microcephaly, chorioretinopathy, and severe developmental defects in vivo. Notably, loss-of-function of KIF11 causes the formation of monopolar spindle and chromosome misalignment, which finally contribute to cell cycle arrest, chromosome instability, and cell death. Our results demonstrate that KIF11 is crucial for spindle assembly, chromosome alignment, and cell cycle progression of progenitor stem cells, indicating a potential link between polyploidy and MCLMR. Our data have revealed that KIF11 inhibition cause microcephaly, chorioretinopathy, and development disorders through the formation of monopolar spindle, polyploid, and cell cycle arrest.

Aberrant gene expression yet undiminished retinal ganglion cell genesis in iPSC-derived models of optic nerve hypoplasia

BACKGROUND

Optic nerve hypoplasia (ONH), the leading congenital cause of permanent blindness, is characterized by a retinal ganglion cell (RGC) deficit at birth. Multifactorial developmental events are hypothesized to underlie ONH and its frequently associated neurologic and endocrine abnormalities; however, environmental influences are unclear and genetic underpinnings are unexplored. This work investigates the genetic contribution to ONH RGC production and gene expression using patient induced pluripotent stem cell (iPSC)-derived retinal organoids (ROs).

MATERIALS AND METHODS

iPSCs produced from ONH patients and controls were differentiated to ROs. RGC genesis was assessed using immunofluorescence and flow cytometry. Flow-sorted BRN3+ cells were collected for RNA extraction for RNA-Sequencing. Differential gene expression was assessed using DESeq2 and edgeR. PANTHER was employed to identify statistically over-represented ontologies among the differentially expressed genes (DEGs). DEGs of high interest to ONH were distinguished by assessing function, mutational constraint, and prior identification in ONH, autism and neurodevelopmental disorder (NDD) studies.

RESULTS

RGC genesis and survival were similar in ONH and control ROs. Differential expression of 70 genes was identified in both DESeq2 and edgeR analyses, representing a ~ 4-fold higher percentage of DEGs than in randomized study participants. DEGs showed trends towards over-representation of validated NDD genes and ONH exome variant genes. Among the DEGs, RAPGEF4 and DMD had the greatest number of disease-relevant features.

CONCLUSIONS

ONH genetic background was not associated with impaired RGC genesis but was associated with DEGs exhibiting disease contribution potential. This constitutes some of the first evidence of a genetic contribution to ONH.

Frameshift variants in the C-terminal of CTNNB1 cause familial exudative vitreoretinopathy by AXIN1-mediated ubiquitin-proteasome degradation condensation

The β-catenin has two intrinsically disordered regions in both C- and N-terminal domains that trigger the formation of phase-separated condensates. Variants in its C-terminus are associated with familial exudative vitreoretinopathy (FEVR), yet the pathogenesis and the role of these variants in inducing abnormal condensates, are unclear. In this study, we identified a novel heterozygous frameshift variant, c.2104-2105insCC (p.Gln703ProfsTer33), in CTNNB1 from a FEVR-affected family. This variant encodes an unstable truncated protein that was unable to activate Wnt signal transduction, which could be rescued by the inhibition of proteasome or phosphorylation. Further functional experiments revealed the propensity of the Gln703ProfsTer33 variant to form cytoplasmic condensates, exhibiting a lower turnover rate after fluorescent bleaching due to enhanced interaction with AXIN1. LiCl, which specifically blocks GSK3β-mediated phosphorylation, restored signal transduction, cell proliferation, and junctional integrity in primary human retinal microvascular endothelial cells over-expressed with Gln703ProfsTer33. Finally, experiments on two reported FEVR-associated mutations in the C-terminal domain of β-catenin exhibited several functional defects similar to the Gln703ProfsTer33. Together, our findings unravel that the C-terminal region of β-catenin is pivotal for the regulation of AXIN1/β-catenin interaction, acting as a switch to mediate nucleic and cytosolic condensates formation that is implicated in the pathogenesis of FEVR.

OCULAR FEATURES ASSOCIATED WITH MUTATIONS IN ATOH7 GENE OVERLAP THOSE WITH FAMILIAL EXUDATIVE VITREORETINOPATHY

BACKGROUND/PURPOSE

To report the ocular findings in three patients with a mutation in the ATOH7 gene.

METHODS

The clinical findings were collected from the medical records including those for magnetic resonance imaging. Three patients of two families who had poor vision since infancy were studied. Genetic testing of the ATOH7 gene was performed.

RESULTS

The three patients had varying degrees of intraocular vascular proliferation associated with advanced retinal detachments as falciform retinal folds or total retinal detachments. This state is referred to as congenital retinal nonattachment. One eye of a sibling had fluorescein angiographic findings of excessive branching of the retinal vessels and fluorescent dye leakage that were consistent with those of familial exudative vitreoretinopathy. Bilateral hypoplasia of the optic nerve was found in all three patients by magnetic resonance imaging. Genetic analysis showed a known in-frame deletion of the ATOH7 gene in all three patients.

CONCLUSION

This is the first report of a patient with a mutation in the ATOH7 gene that had typical vascular patterns of familial exudative vitreoretinopathy in the peripheral retina. The ocular features associated with mutations in the ATOH7 gene overlap those with familial exudative vitreoretinopathy at the early and advanced stages.

Management and outcomes of posterior persistent fetal vasculature

PURPOSE

To describe the clinical features, management and outcomes of posterior persistent fetal vasculature (PFV) and suggest a management algorithm.

DESIGN

Retrospective consecutive case series.

PARTICIPANTS

All children diagnosed with posterior PFV and treated or followed at the Rothschild Foundation Hospital in France between June 2011 and September 2021.

METHODS

Retrospective analysis of the clinical characteristics of posterior PFV. We reported at diagnosis: age, gender, presenting symptoms, intraocular pressure (IOP), visual acuity (VA). Patients were divided in four group depending on severity and involvement or not of the anterior segment. We reported the vitreoretinal surgical techniques used.

MAIN OUTCOME MEASURES

Anatomical results, ocular hypertension, BCVA, presence of post-operative adverse events and additional surgical interventions were recorded at each follow-up visit.

RESULTS

A total of 96 patients were included. Median age at diagnosis was 8 months (mean 18.9±30.9 months) with a mean follow-up of 27±31.2 months. Although PFV is often an isolated disease, it was associated with a systemic disease in 8% of cases. Posterior PFV was associated with anterior involvement in 62 eyes (64%). Forty-one eyes (42.7%) were microphthalmic and were more frequently associated with severe PFV [53% vs. 25%; (p=0.01)]. Surgery was performed in 85 patients (89%). Of them, 69 (81%) were a total success, 5 (6%) were a partial success due to a persistent limited peripheral retinal detachment (RD), and 11 (13%) were a failure due to persistent total RD after surgery. Twenty-four eyes presented post-operative adverse events including ocular hypertension requiring eye drop medication (6.6%), secondary cell proliferation around the IOL (7.7%), intravitreal hemorrhages (6.6%), persistent tractional RD (9.9%). A second surgery was performed in 15 patients (16%). At last follow-up, VA could be measured in logMAR in 43 children (45%), was light perception in 21 eyes (22%), and no light perception or impossible to assess in 32 eyes (33%).

CONCLUSIONS

In our case-series, most of patients presenting PFV with posterior involvement received complex vitreoretinal surgery. Goals of the surgery varies, and include retinal flattening, reduction of vitreoretinal traction, freeing of the visual axis and aesthetic concerns. We proposed a surgical and medical management algorithm for PFV.

Unrecognized ROPER in a child with a novel pathogenic variant in ZNF408 gene

BACKGROUND

Familial exudative vitreoretinopathy (FEVR) is a rare hereditary disorder characterized by abnormal or incomplete retinal angiogenesis commonly inherited in an autosomal dominant fashion. Up to 50% of FEVR cases are linked to known genetic mutations affecting retinal vasculature development.

PURPOSE

To report a case, a novel pathogenic variant of the ZNF408 gene associated with a case of FEVR in a premature male.

MATERIALS AND METHODS

Case report.

RESULTS

A 10-month-old male who was born prematurely at 34 weeks' gestation in the Dominican Republic was referred for persistent avascular retina. The baby was treated with bilateral intravitreal ranibizumab injections for retinopathy of prematurity (ROP) with the presence of plus disease. Fundus examination several months after treatment revealed the absence of tortuosity of the vessels with avascular periphery; fluorescein angiography (FA) confirmed peripheral avascularity and demonstrated irregular sprouts of vascularization in the absence of neovascularization. We performed genetic testing under the suspicion of FEVR and results identified a heterozygous mutation in the ZNF408 gene on chromosome 11, c.1307 C > T.

CONCLUSION

FEVR is an important differential diagnosis in premature infants with retinopathy, as clinical presentation can overlap with common findings in ROP. Maintaining high suspicion for the disease is especially critical in cases with findings unusual for ROP. FEVR in the presence of prematurity has been well described, falling under the proposed term ROPER. Genetic testing is key to confirm diagnosis.

A comprehensive functional analysis on the pathogenesis of novel TSPAN12 and NDP variants in familial exudative vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is an inherited blinding disorder; however, the known FEVR-associated variants account for approximately only 50% cases. Currently, the pathogenesis of most reported variants is not well studied, we aim to identify novel variants from FEVR-associated genes and perform a comprehensive functional analysis to uncover the pathogenesis of variants that cause FEVR. Using targeted gene panel and Sanger sequencing, we identified six novel and three known variants in TSPAN12 and NDP. These variants were demonstrated to cause significant inhibition of Norrin/β-catenin pathway by dual-luciferase reporter assay and western blot analysis. Structural analysis and co-immunoprecipitation revealed compromised interactions between missense variants and binding partners in the Norrin/β-catenin pathway. Immunofluorescence and subcellular protein extraction were performed to reveal the abnormal subcellular trafficking. Additionally, over-expression of TSPAN12 successfully enhanced the Norrin/β-catenin signaling activity by strengthening the binding affinity of mutant Norrin with FZD4 or LRP5. Together, these observations expanded the spectrum of FEVR-associated variants for the genetic counseling and prenatal diagnosis of FEVR, as well providing a potential therapeutic strategy for the treatment of FEVR.

Novel truncating variants in CTNNB1 cause familial exudative vitreoretinopathy

BACKGROUND

Familial exudative vitreoretinopathy (FEVR) is an inheritable blinding disorder with clinical and genetic heterogeneity. Heterozygous variants in the CTNNB1 gene have been reported to cause FEVR. However, the pathogenic basis of CTNNB1-associated FEVR has not been fully explored.

METHODS

Whole-exome sequencing was performed on the genomic DNA of probands. Dual-luciferase reporter assay, western blotting and co-immunoprecipitation were used to characterise the impacts of variants. Quantitative real-time PCR, EdU (5-ethynyl-2'-deoxyuridine) incorporation assay and immunocytochemistry were performed on the primary human retinal microvascular endothelial cells (HRECs) to investigate the effect of CTNNB1 depletion on the downstream genes involved in Norrin/β-catenin signalling, cell proliferation and junctional integrity, respectively. Transendothelial electrical resistance assay was applied to measure endothelial permeability. Heterozygous endothelial-specific Ctnnb1-knockout mouse mice were generated to verify FEVR-like phenotypes in the retina.

RESULTS

We identified two novel heterozygous variants (p.Leu103Ter and p.Val199LeufsTer11) and one previously reported heterozygous variant (p.His369ThrfsTer2) in the CTNNB1 gene. These variants caused truncation and degradation of β-catenin that reduced Norrin/β-catenin signalling activity. Additionally, knockdown (KD) of CTNNB1 in HRECs led to diminished mRNA levels of Norrin/β-catenin targeted genes, reduced cell proliferation and compromised junctional integrity. The Cre-mediated heterozygous deletion of Ctnnb1 in mouse endothelial cells (ECs) resulted in FEVR-like phenotypes. Moreover, LiCl treatment partially rescued the defects in CTNNB1-KD HRECs and EC-specific Ctnnb1 heterozygous knockout mice.

CONCLUSION

Our findings reinforced the current pathogenesis of Norrin/β-catenin for FEVR and expanded the causative variant spectrum of CTNNB1 for the prenatal diagnosis and genetic counselling of FEVR.

Clinical characteristics and mutation spectrum in 33 Chinese families with familial exudative vitreoretinopathy

OBJECTIVE

To explore the clinical manifestations and search for the variants of six related genes (LRP5, FZD4, TSPAN12, NDP, KIF11 and ZNF408) in Chinese patients with familial exudative vitreoretinopathy (FEVR), and investigate the correlation between the genetic variants and the clinical characteristics.

PATIENTS AND METHODS

Clinical data, including the retinal artery angle, acquired from wide-field fundus imaging, structural and microvascular features of the retina obtained from optical coherence tomography (OCT) and OCT angiography (OCTA) were collected from 33 pedigrees. Furthermore, mutation screening was performed. Variants filtering, bioinformatics analysis and Sanger sequencing were conducted to verify the variants.

RESULTS

Twenty-one variants were successfully detected in 16 of 33 families, of which 10 variants were newly identified. The proportion of variants in LRP5, FZD4, TSPAN12, NDP and KIF11 was 38.1% (8/21), 33.3% (7/21), 19.1% (4/21), 4.8% (1/21) and 4.8% (1/21), respectively. Three new variants were considered to be pathogenic or likely pathogenic. The FEVR group tended to exhibit a smaller retinal artery angle, higher incidence of foveal hypoplasia and lower vascular density compared to the control group. Patients who harboured variants of FZD4 exhibited greater severity of FEVR than those with LRP5 variants. However, those who harboured LRP5 variants tended to possess lower foveal vascular density.

CONCLUSIONS

Six known pathogenic genes were screened in 33 pedigrees with FEVR in our study, which revealed 10 novel variants. These findings enrich the clinical features and mutation spectrum in Chinese patients with FEVR, revealing the genotype-phenotype relationship, and contributing to the diagnosis and treatment of the disease.Key messagesWe identified 21 variants in 5 genes (LRP5, FZD4, TSPAN12, NDP and KIF11) associated with FEVR, 10 of which are novel (three were pathogenic or likely pathogenic).The proportion of variants was the highest for the LRP5 gene.FZD4 variants may be responsible for greater FEVR severity than LRP5 variants.

Zfp503/Nlz2 Is Required for RPE Differentiation and Optic Fissure Closure

Purpose

Uveal coloboma is a congenital eye malformation caused by failure of the optic fissure to close in early human development. Despite significant progress in identifying genes whose regulation is important for executing this closure, mutations are detected in a minority of cases using known gene panels, implying additional genetic complexity. We have previously shown knockdown of znf503 (the ortholog of mouse Zfp503) in zebrafish causes coloboma. Here we characterize Zfp503 knockout (KO) mice and evaluate transcriptomic profiling of mutant versus wild-type (WT) retinal pigment epithelium (RPE)/choroid.

Methods

Zfp503 KO mice were generated by gene targeting using homologous recombination. Embryos were characterized grossly and histologically. Patterns and level of developmentally relevant proteins/genes were examined with immunostaining/in situ hybridization. The transcriptomic profile of E11.5 KO RPE/choroid was compared to that of WT.

Results

Zfp503 is dynamically expressed in developing mouse eyes, and loss of its expression results in uveal coloboma. KO embryos exhibit altered mRNA levels and expression patterns of several key transcription factors involved in eye development, including Otx2, Mitf, Pax6, Pax2, Vax1, and Vax2, resulting in a failure to maintain the presumptive RPE, as evidenced by reduced melanin pigmentation and its differentiation into a neural retina-like lineage. Comparison of RNA sequencing data from WT and KO E11.5 embryos demonstrated reduced expression of melanin-related genes and significant overlap with genes known to be dynamically regulated at the optic fissure.

Conclusions

These results demonstrate a critical role of Zfp503 in maintaining RPE fate and optic fissure closure.

Cell fate decisions, transcription factors and signaling during early retinal development

The development of the vertebrate eyes is a complex process starting from anterior-posterior and dorso-ventral patterning of the anterior neural tube, resulting in the formation of the eye field. Symmetrical separation of the eye field at the anterior neural plate is followed by two symmetrical evaginations to generate a pair of optic vesicles. Next, reciprocal invagination of the optic vesicles with surface ectoderm-derived lens placodes generates double-layered optic cups. The inner and outer layers of the optic cups develop into the neural retina and retinal pigment epithelium (RPE), respectively. In vitro produced retinal tissues, called retinal organoids, are formed from human pluripotent stem cells, mimicking major steps of retinal differentiation in vivo. This review article summarizes recent progress in our understanding of early eye development, focusing on the formation the eye field, optic vesicles, and early optic cups. Recent single-cell transcriptomic studies are integrated with classical in vivo genetic and functional studies to uncover a range of cellular mechanisms underlying early eye development. The functions of signal transduction pathways and lineage-specific DNA-binding transcription factors are dissected to explain cell-specific regulatory mechanisms underlying cell fate determination during early eye development. The functions of homeodomain (HD) transcription factors Otx2, Pax6, Lhx2, Six3 and Six6, which are required for early eye development, are discussed in detail. Comprehensive understanding of the mechanisms of early eye development provides insight into the molecular and cellular basis of developmental ocular anomalies, such as optic cup coloboma. Lastly, modeling human development and inherited retinal diseases using stem cell-derived retinal organoids generates opportunities to discover novel therapies for retinal diseases.

Heterozygote loss-of-function variants in the LRP5 gene cause familial exudative vitreoretinopathy

BACKGROUND

Familial exudative vitreoretinopathy (FEVR) is an inherited ocular disease with clinical manifestations of aberrant retinal vasculature. We aimed to identify novel causative variants responsible for FEVR and provided evidence for the genetic counselling of FEVR.

METHODS

We applied whole-exome sequencing (WES) on the genomic DNA samples from the probands and performed Sanger sequencing for variant validation. Western blot analysis and luciferase assays were performed to test the expression levels and the activity of mutant proteins.

RESULTS

We identified one novel heterozygous nonsense variant, and three novel heterozygous frameshift variants including c.1801G>T (p.G601*), c.1965delC (p.H656Tfs*41), c.4445delC (p.S1482Cfs*17), and c.4482delC (p.P1495Rfs*4), which disabled the function of LRP5 on the Norrin/β-catenin signalling. Overexpression of variant-carrying LRP5 proteins resulted in down regulation of the protein levels of β-catenin and the Norrin/β-catenin signalling target genes c-Myc and Glut1.

CONCLUSION

Our study showed that four inherited LRP5 variants can cause autosomal dominant FEVR via down regulation of Norrin/β-catenin signalling and expanded the spectrum of FEVR-associated LRP5 variants.

Whole exome sequencing revealed 14 variants in NDP, FZD4, LRP5, and TSPAN12 genes for 20 families with familial exudative vitreoretinopathy

BACKGROUND

Familial exudative vitreoretinopathy (FEVR) is a complex form of blindness-causing retinal degeneration. This study investigated the potential disease-causing variants in 20 Chinese families with FEVR.

METHODS

All available family members underwent detailed ophthalmological examinations, including best-corrected visual acuity and fundus examination. All probands and most family members underwent fluorescein fundus angiography. Twenty probands underwent whole exome sequencing; 16 of them also underwent copy number variant and mitochondrial genome analysis. Bioinformatics analysis and Sanger sequencing of available family members were used to confirm the disease-causing gene variant.

RESULTS

Twenty families were diagnosed with FEVR based on clinical symptoms, fundus manifestations, and fundus fluorescein angiography. Whole exome sequencing revealed 14 variants in NDP, FZD4, LRP5, and TSPAN12 genes among the 13 families. These variants were predicted to be damaging or deleterious according to multiple lines of prediction algorithms; they were not frequently found in multiple population databases. Seven variants had not previously been reported to cause FEVR: c.1039T>G p.(Phe347Val) in the FZD4 gene; c.1612C>T p.(Arg538Trp) and c.3237-2A>C in the LRP5 gene; and c.77T>A p.(Ile26Asn), c.170dupT p.(Leu57Phe fsTer60), c.236T>G p.(Met79Arg) and c.550dupA p.(Arg184Lys fsTer16) in the TSPAN12 gene. We did not detect any variants in the remaining seven families.

CONCLUSIONS

These results expand the spectrum of variants in the NDP, FZD4, LRP5, and TSPAN12 genes and provide insights regarding accurate diagnosis, family genetic counseling, and future gene therapy for FEVR.

Reaching a FEVR Pitch: A Case Series of Familial Exudative Vitreoretinopathy in Northern Ireland

PURPOSE

To evaluate the heterogeneity of both the clinical features and genetics of familial exudative vitreoretinopathy (FEVR) in a Northern Irish population.

METHODS

A retrospective trawl of a secure pediatric database was completed, as well as communication with all Northern Ireland ophthalmologists to identify adult cases. Cases were cross-referenced with a regional genetics database. Data on patient demographics, clinical findings, genetic testing, and patient treatment were collected.

RESULTS

Sixteen patients were identified. Average age at presentation was 11.8 years (range: 4 months to 38 years). Earlier age at presentation was associated with more advanced disease and those presenting later had more subtle signs such as retinal tear or vitreous hemorrhage. Four types of gene mutations were identified in 7 patients (NDP, TSPAN12, FZD4, and KIF11). Thirteen patients had complications associated with FEVR and associated systemic conditions were found in 5 patients. Twelve eyes received active treatment to control disease.

CONCLUSIONS

FEVR is a sight-threatening disease affecting prenatal retinal angiogenesis with a spectrum of disease and diverse genetic basis. Clinicians should look for signs of systemic and other ophthalmic sequelae in patients with FEVR because this could point to a genetic cause. Vigilance should also be exercised in older patients with unexplained vitreous hemorrhage or retinal tear with consideration of widefield angiography if FEVR is suspected. [J Pediatr Ophthalmol Strabismus. 2022;59(2):102-109.].

Functional Characterization of an In-Frame Deletion in the Basic Domain of the Retinal Transcription Factor ATOH7

Basic helix–loop–helix (bHLH) transcription factors are evolutionarily conserved and structurally similar proteins important in development. The temporospatial expression of atonal bHLH transcription factor 7 (ATOH7) directs the differentiation of retinal ganglion cells and mutations in the human gene lead to vitreoretinal and/or optic nerve abnormalities. Characterization of pathogenic ATOH7 mutations is needed to understand the functions of the conserved bHLH motif. The published ATOH7 in-frame deletion p.(Arg41_Arg48del) removes eight highly conserved amino acids in the basic domain. We functionally characterized the mutant protein by expressing V5-tagged ATOH7 constructs in human embryonic kidney 293T (HEK293T) cells for subsequent protein analyses, including Western blot, cycloheximide chase assays, Förster resonance energy transfer fluorescence lifetime imaging, enzyme-linked immunosorbent assays and dual-luciferase assays. Our results indicate that the in-frame deletion in the basic domain causes mislocalization of the protein, which can be rescued by a putative dimerization partner transcription factor 3 isoform E47 (E47), suggesting synergistic nuclear import. Furthermore, we observed (i) increased proteasomal degradation of the mutant protein, (ii) reduced protein heterodimerization, (iii) decreased DNA-binding and transcriptional activation of a reporter gene, as well as (iv) inhibited E47 activity. Altogether our observations suggest that the DNA-binding basic domain of ATOH7 has additional roles in regulating the nuclear import, dimerization, and protein stability.

Catenin α 1 mutations cause familial exudative vitreoretinopathy by overactivating Norrin/β-catenin signaling

Familial exudative vitreoretinopathy (FEVR) is a severe retinal vascular disease that causes blindness. FEVR has been linked to mutations in several genes associated with inactivation of the Norrin/β-catenin signaling pathway, but these account for only approximately 50% of cases. We report that mutations in α-catenin (CTNNA1) cause FEVR by overactivating the β-catenin pathway and disrupting cell adherens junctions. We identified 3 heterozygous mutations in CTNNA1 (p.F72S, p.R376Cfs*27, and p.P893L) by exome sequencing and further demonstrated that FEVR-associated mutations led to overactivation of Norrin/β-catenin signaling as a result of impaired protein interactions within the cadherin-catenin complex. The clinical features of FEVR were reproduced in mice lacking Ctnna1 in vascular endothelial cells (ECs) or with overactivated β-catenin signaling by an EC-specific gain-of-function allele of Ctnnb1. In isolated mouse lung ECs, both CTNNA1-P893L and F72S mutants failed to rescue either the disrupted F-actin arrangement or the VE-cadherin and CTNNB1 distribution. Moreover, we discovered that compound heterozygous Ctnna1 F72S and a deletion allele could cause a similar phenotype. Furthermore, in a FEVR family, we identified a mutation of LRP5, which activates Norrin/β-catenin signaling, and the corresponding knockin mice exhibited a partial FEVR-like phenotype. Our study demonstrates that the precise regulation of β-catenin activation is critical for retinal vascular development and provides new insights into the pathogenesis of FEVR.

Novel mutation in TSPAN12 associated with familial exudative vitreoretinopathy in a Chinese pedigree

BACKGROUND

Familial exudative vitreoretinopathy (FEVR) is a rare retinal disorder characterised by incomplete retinal vascular development. Symptoms vary widely from none to blindness even within the same family. Multiple genes related to the Wnt pathway have been found to be associated with FEVR. Recent studies identified tetraspanin 12 (TSPAN12) as a cause of the autosomal dominant inheritance form of FEVR. Here, we describe a novel TSPAN12 mutation in a Chinese family with FEVR.

METHODS

Targeted next-generation sequencing was performed on the proband to define the TSPAN12 mutation. Sanger sequencing was used to confirm the mutation in five family members (I-1, II-2, II-3, II-4, and III-3) in a three-generation FEVR pedigree. Ophthalmologic examinations and diagnostic imaging related to FEVR were performed.

RESULTS

The proband (II-3) was a 32-year-old man with early-stage peripheral retinal vascular anomalies, but no visual acuity problems. DNA sequencing identified a heterozygous missense mutation (c.241 G > A: p.Gly81Arg) in TSPAN12 in the proband. The mutation was in a highly conserved region and was predicted to affect the normal protein structure. The patient's father and daughter were also diagnosed with FEVR and carried the same mutation, with varying degrees of manifestations. Other family members had good vision and normal eye examinations with negative genetic testing.

CONCLUSIONS

We identified a novel missense mutation in TSPAN12 associated with autosomal dominant FEVR. These results will facilitate the diagnosis, prognosis, and genetic counselling for this disease. Further studies are needed to identify the mechanisms underlying clinical variations among individuals in the family.

Familial exudative vitreoretinopathy with TGFBR2 mutation without signs of Loeys-Dietz syndrome

Background: Familial exudative vitreoretinopathy (FEVR) is an inherited retinal disorder with high genetic heterogeneity, and it is characterized by a defect in the development of the retinal vascular system. Loeys-Dietz syndrome (LDS) is an autosomal dominant systemic connective tissue disorder that is caused by mutations in the genes related to transforming growth factor signaling systems including the TGFBR2 gene. Two earlier studies reported that patients with LDS from mutations in the TGFBR2 gene were associated with FEVR-like retinal phenotype. The purpose of this study was to determine the characteristics of a case of FEVR without systemic abnormalities who had a mutation in the TGFBR2 gene.Materials and Methods: The clinical appearances and surgical outcomes were determined from the medical records. Genetic analysis was performed by whole exome sequencing.Results: A 15-year-old boy was diagnosed with FEVR by the appearance of the peripheral retina of both eyes and a retinal detachment in the left eye. Whole exome sequencing revealed a heterozygous deletion mutation in the TGFBR2 gene. A de novo mutation was confirmed by examining the family members. No systemic abnormalities were detected in the patient including those associated with LDS.Conclusions: FEVR can be associated with a TGFBR2 mutation without showing signs of LDS.

Whole-Exome Sequencing Reveals Novel TSPAN12 Variants in Autosomal Dominant Familial Exudative Vitreoretinopathy

Background: Familial exudative vitreoretinopathy (FEVR), a group of rare inherited retinal vascular disorders, is the major cause of vision loss in juveniles. At present, the diagnosis of FEVR remains difficult due to its clinical and genetic heterogeneities. Aims: To identify the causative genetic variants in two unrelated FEVR-affected families: one Indian family and one Chinese Han family. Materials and Methods: Five affected patients from two families were recruited for this study. Whole-exome sequencing was applied to the probands, and Sanger sequencing was performed for validation. Stringent whole-exome sequence data analyses were performed to evaluate all of the identified pathogenic variants. Results: Two novel variants in the TSPAN12 gene, were identified: a missense variant c.437 T > G (p.Leu146Arg); and a nonsense variant c.477 C > A (p.Cys159*). Both variants cosegregated with the disease in the investigated FEVR-affected families. Additionally, both variants inactivated the ability of TSPAN12 protein to enhance Norrin/β-catenin signaling. Conclusion: This study expands the mutational spectrum of TSPAN12 for FEVR.

Whole-Exome Sequencing Identified DLG1 as a Candidate Gene for Familial Exudative Vitreoretinopathy

Purpose: Familial exudative vitreoretinopathy (FEVR) is a blinding retinal vascular disease. Clinically, FEVR is characterized by incomplete vascularization of the peripheral retina and pathological neovascularization. Only about 50% of FEVR cases can be explained by known FEVR disease gene variations. This study aimed to identify novel genes associated with the FEVR phenotype and explore their pathogenic mechanisms. Materials and Methods: Exome sequencing analyses were conducted on one Chinese family with FEVR whose affected members did not exhibit pathogenic variants in the known FEVR genes (verified using Sanger sequencing analysis). Functions of the affected proteins were evaluated using reporter assays. Western blot analysis was used to detect mutant protein expression and the genes' pathogenic mechanisms. Results: A rare novel heterozygous variant in DLG1 (c.1792A>G; p.S598G) was identified. The amino acid residues surrounding the identified variant are highly conserved among vertebrates. A luciferase reporter assay revealed that the mutant DLG1 protein DLG1-S598G lost its ability to activate Wnt signaling. Moreover, a knockdown (KD) of DLG1 in human primary retinal endothelial cells impaired tube formation. Mechanistically, DLG1 KD led to a reduction in phosphorylated VEGFR2, an essential receptor for the angiogenic potency that signals the vascular endothelial growth factor molecule. Conclusions: The data reported here demonstrate that DLG1 is a novel candidate gene for FEVR.

Genetic control of retinal ganglion cell genesis

Retinal ganglion cells (RGCs) are the only projection neurons in the neural retina. They receive and integrate visual signals from upstream retinal neurons in the visual circuitry and transmit them to the brain. The function of RGCs is performed by the approximately 40 RGC types projecting to various central brain targets. RGCs are the first cell type to form during retinogenesis. The specification and differentiation of the RGC lineage is a stepwise process; a hierarchical gene regulatory network controlling the RGC lineage has been identified and continues to be elaborated. Recent studies with single-cell transcriptomics have led to unprecedented new insights into their types and developmental trajectory. In this review, we summarize our current understanding of the functions and relationships of the many regulators of the specification and differentiation of the RGC lineage. We emphasize the roles of these key transcription factors and pathways in different developmental steps, including the transition from retinal progenitor cells (RPCs) to RGCs, RGC differentiation, generation of diverse RGC types, and central projection of the RGC axons. We discuss critical issues that remain to be addressed for a comprehensive understanding of these different aspects of RGC genesis and emerging technologies, including single-cell techniques, novel genetic tools and resources, and high-throughput genome editing and screening assays, which can be leveraged in future studies.

Atoh7-independent specification of retinal ganglion cell identity

Retinal ganglion cells (RGCs) relay visual information from the eye to the brain. RGCs are the first cell type generated during retinal neurogenesis. Loss of function of the transcription factor Atoh7, expressed in multipotent early neurogenic retinal progenitors leads to a selective and essentially complete loss of RGCs. Therefore, Atoh7 is considered essential for conferring competence on progenitors to generate RGCs. Despite the importance of Atoh7 in RGC specification, we find that inhibiting apoptosis in Atoh7-deficient mice by loss of function of Bax only modestly reduces RGC numbers. Single-cell RNA sequencing of Atoh7;Bax-deficient retinas shows that RGC differentiation is delayed but that the gene expression profile of RGC precursors is grossly normal. Atoh7;Bax-deficient RGCs eventually mature, fire action potentials, and incorporate into retinal circuitry but exhibit severe axonal guidance defects. This study reveals an essential role for Atoh7 in RGC survival and demonstrates Atoh7-dependent and Atoh7-independent mechanisms for RGC specification.

Diagnostic and Management Strategies in Patients with Persistent Fetal Vasculature: Current Insights

Persistent fetal vasculature (PFV), previously known as persistent hyperplastic primary vitreous, is a developmental malformation of the eyes that is caused by a failure of the hyaloid vasculature to regress in utero. PFV has been reported for decades; however, our understanding of the pathophysiology/pathogenesis of PFV, and the diagnostic and treatment modalities for PFV have evolved over time, and these advancements have improved diagnosis, treatment, and outcomes. However and in spite of these advancements, the heterogeneity of this disease continues to make PFV a diagnostic challenge. Here, we review what is currently known about various important aspects of PFV to update and enhance the knowledge of ophthalmologists who encounter and manage PFV in clinical practice.

Identification of Novel Mutations in the FZD4 and NDP Genes in Patients with Familial Exudative Vitreoretinopathy in South India

Background: Familial exudative vitreoretinopathy (FEVR) is an inheritable retinal vascular disease, which often leads to severe vision loss and blindness in children. However, reported mutations can only account for 50-60% of patients with FEVR. The purpose of this study was to identify novel frizzled class receptor 4 (FZD4) and Norrin cystine knot growth factor NDP (NDP) mutations in a cohort of Indian patients with FEVR by whole-exome sequencing. Methods: We performed data filtering and bioinformatic analyses. Results: Two novel heterozygous mutations in FZD4 gene were identified, each in two different families: c.1499_1500del [p.500_500del] and c.G296C [p.C99S]. One novel mutation in NDP in another family was identified: c.A256G [p.K86E]. All FZD4 mutations affected conserved amino acid residues and were absent in 1000 control individuals. To assess the effect of these FZD4 mutations on the biological activity of the protein, we introduced each FZD4 mutation into FZD4 cDNA by the site-directed mutagenesis techniques. A Norrin/beta-catenin pathway-based luciferase reporter assay revealed that the c.1499_1500del failed to activate the luciferase reporter; in contrast, compared with the wild-type FZD4 protein, the, c.G296C [p.C99S] mutation exhibited increased luciferase reporter activity. Conclusion: Our study found two novel FZD4 mutations, with opposite effects regarding functional expression levels in Indian patients with FEVR and expands on the mutational spectrum of FZD4 in Indian FEVR patients.

The Atoh7 remote enhancer provides transcriptional robustness during retinal ganglion cell development

The retinal ganglion cell (RGC) competence factor ATOH7 is dynamically expressed during retinal histogenesis. ATOH7 transcription is controlled by a promoter-adjacent primary enhancer and a remote shadow enhancer (SE). Deletion of the ATOH7 human SE causes nonsyndromic congenital retinal nonattachment (NCRNA) disease, characterized by optic nerve aplasia and total blindness. We used genome editing to model NCRNA in mice. Deletion of the murine SE reduces Atoh7 messenger RNA (mRNA) fivefold but does not recapitulate optic nerve loss; however, SEdel/knockout (KO) trans heterozygotes have thin optic nerves. By analyzing Atoh7 mRNA and protein levels, RGC development and survival, and chromatin landscape effects, we show that the SE ensures robust Atoh7 transcriptional output. Combining SE deletion and KO and wild-type alleles in a genotypic series, we determined the amount of Atoh7 needed to produce a normal complement of adult RGCs, and the secondary consequences of graded reductions in Atoh7 dosage. Together, these data reveal the workings of an evolutionary fail-safe, a duplicate enhancer mechanism that is hard-wired in the machinery of vertebrate retinal ganglion cell genesis.

Transcriptome analysis of the zebrafish atoh7-/- Mutant, lakritz, highlights Atoh7-dependent genetic networks with potential implications for human eye diseases

Expression of the bHLH transcription protein Atoh7 is a crucial factor conferring competence to retinal progenitor cells for the development of retinal ganglion cells. Several studies have emerged establishing ATOH7 as a retinal disease gene. Remarkably, such studies uncovered ATOH7 variants associated with global eye defects including optic nerve hypoplasia, microphthalmia, retinal vascular disorders, and glaucoma. The complex genetic networks and cellular decisions arising downstream of atoh7 expression, and how their dysregulation cause development of such disease traits remains unknown. To begin to understand such Atoh7-dependent events in vivo, we performed transcriptome analysis of wild-type and atoh7 mutant (lakritz) zebrafish embryos at the onset of retinal ganglion cell differentiation. We investigated in silico interplays of atoh7 and other disease-related genes and pathways. By network reconstruction analysis of differentially expressed genes, we identified gene clusters enriched in retinal development, cell cycle, chromatin remodeling, stress response, and Wnt pathways. By weighted gene coexpression network, we identified coexpression modules affected by the mutation and enriched in retina development genes tightly connected to atoh7. We established the groundwork whereby Atoh7-linked cellular and molecular processes can be investigated in the dynamic multi-tissue environment of the developing normal and diseased vertebrate eye.

Genetics of syndromic ocular coloboma: CHARGE and COACH syndromes

Optic fissure closure defects result in uveal coloboma, a potentially blinding condition affecting between 0.5 and 2.6 per 10,000 births that may cause up to 10% of childhood blindness. Uveal coloboma is on a phenotypic continuum with microphthalmia (small eye) and anophthalmia (primordial/no ocular tissue), the so-called MAC spectrum. This review gives a brief overview of the developmental biology behind coloboma and its clinical presentation/spectrum. Special attention will be given to two prominent, syndromic forms of coloboma, namely, CHARGE (Coloboma, Heart defect, Atresia choanae, Retarded growth and development, Genital hypoplasia, and Ear anomalies/deafness) and COACH (Cerebellar vermis hypoplasia, Oligophrenia, Ataxia, Coloboma, and Hepatic fibrosis) syndromes. Approaches employed to identify genes involved in optic fissure closure in animal models and recent advances in live imaging of zebrafish eye development are also discussed.

Frizzled 4 regulates ventral blood vessel remodeling in the zebrafish retina

BACKGROUND

Familial exudative vitreoretinopathy (FEVR) is a rare congenital disorder characterized by a lack of blood vessel growth to the periphery of the retina with secondary fibrovascular proliferation at the vascular-avascular junction. These structurally abnormal vessels cause leakage and hemorrhage, while the fibroproliferative scarring results in retinal dragging, detachment and blindness. Mutations in the FZD4 gene represent one of the most common causes of FEVR.

METHODS

A loss of function mutation resulting from a 10-nucleotide insertion into exon 1 of the zebrafish fzd4 gene was generated using transcription activator-like effector nucleases (TALENs). Structural and functional integrity of the retinal vasculature was examined by fluorescent microscopy and optokinetic responses.

RESULTS

Zebrafish retinal vasculature is asymmetrically distributed along the dorsoventral axis, with active vascular remodeling on the ventral surface of the retina throughout development. fzd4 mutants exhibit disorganized ventral retinal vasculature with discernable tubular fusion by week 8 of development. Furthermore, fzd4 mutants have impaired optokinetic responses requiring increased illumination.

CONCLUSION

We have generated a visually impaired zebrafish FEVR model exhibiting abnormal retinal vasculature. These fish provide a tractable system for studying vascular biology in retinovascular disorders, and demonstrate the feasibility of using zebrafish for evaluating future FEVR genes identified in humans.

The Molecular Basis of Human Anophthalmia and Microphthalmia

Human eye development is coordinated through an extensive network of genetic signalling pathways. Disruption of key regulatory genes in the early stages of eye development can result in aborted eye formation, resulting in an absent eye (anophthalmia) or a small underdeveloped eye (microphthalmia) phenotype. Anophthalmia and microphthalmia (AM) are part of the same clinical spectrum and have high genetic heterogeneity, with >90 identified associated genes. By understanding the roles of these genes in development, including their temporal expression, the phenotypic variation associated with AM can be better understood, improving diagnosis and management. This review describes the genetic and structural basis of eye development, focusing on the function of key genes known to be associated with AM. In addition, we highlight some promising avenues of research involving multiomic approaches and disease modelling with induced pluripotent stem cell (iPSC) technology, which will aid in developing novel therapies.

Genetics of anophthalmia and microphthalmia. Part 1: Non-syndromic anophthalmia/microphthalmia

Eye formation is the result of coordinated induction and differentiation processes during embryogenesis. Disruption of any one of these events has the potential to cause ocular growth and structural defects, such as anophthalmia and microphthalmia (A/M). A/M can be isolated or occur with systemic anomalies, when they may form part of a recognizable syndrome. Their etiology includes genetic and environmental factors; several hundred genes involved in ocular development have been identified in humans or animal models. In humans, around 30 genes have been repeatedly implicated in A/M families, although many other genes have been described in single cases or families, and some genetic syndromes include eye anomalies occasionally as part of a wider phenotype. As a result of this broad genetic heterogeneity, with one or two notable exceptions, each gene explains only a small percentage of cases. Given the overlapping phenotypes, these genes can be most efficiently tested on panels or by whole exome/genome sequencing for the purposes of molecular diagnosis. However, despite whole exome/genome testing more than half of patients currently remain without a molecular diagnosis. The proportion of undiagnosed cases is even higher in those individuals with unilateral or milder phenotypes. Furthermore, even when a strong gene candidate is available for a patient, issues of incomplete penetrance and germinal mosaicism make diagnosis and genetic counseling challenging. In this review, we present the main genes implicated in non-syndromic human A/M phenotypes and, for practical purposes, classify them according to the most frequent or predominant phenotype each is associated with. Our intention is that this will allow clinicians to rank and prioritize their molecular analyses and interpretations according to the phenotypes of their patients.

The polymorphisms of ATOH 7, ET-1 and ACE in non-arteritic anterior ischemic optic neuropathy

Non-arteritic anterior ischemic optic neuropathy (NAION) is a common cause of acute optic neuropathy in the elderly. The role of the genetic polymorphisms of Atonal Homolog 7 (ATOH7), Endothelin-1 (ET-1) and Angiotensin Converting Enzyme (ACE) in NAION and the combined effects of the gene-gene and gene-medical comorbidities on NAION were not clear. We conducted a perspective, case-control study. 71 NAION patients and 142 age and sex-matched healthy controls were enrolled. Single nucleotide polymorphisms of ATOH7 (rs1900004), ET-1 (rs5370) and ACE (rs1799752) were identified by polymerase chain reaction (PCR) method and all PCR products were screened with Sanger sequencing. The prevalence of genetic factors in NAION patients were compared to normal people, and assessed in conditional logistic regression models. The modified effects of gene-gene or gene-medical comorbidities on NAION development were assessed with a multiplicative model. A significant high risk was found in the T allele of ATOH7 in NAION, with an odds ratio (OR) of 1.55 (P = 0.04). Conditional logistic regression analysis, including diabetes and hypertension, revealed that ATOH7 TT genotype carriers conferred a significantly increased risk of NAION (TT/CC + CT, OR = 3.32, 95% confidence interval (CI) = 1.16-9.53, P = 0.03). Interaction analysis showed that ET-1 (P = 0.01), ACE (P = 0.046) and hypertension (P = 0.02) have modified effects on NAION development. Our results showed that the polymorphism of optic disc associated gene-ATOH7 conferred a significant risk of NAION. Combination of ATOH7 and ET-1, ATOH7 and ACE, as well as ATOH7 and hypertension, increased the susceptibility of NAION. Our data may be useful for NAION predicting.

Defects in the Cell Signaling Mediator β-Catenin Cause the Retinal Vascular Condition FEVR

Familial exudative vitreoretinopathy (FEVR) is an inherited blinding disorder characterized by the abnormal development of the retinal vasculature. The majority of mutations identified in FEVR are found within four genes that encode the receptor complex (FZD4, LRP5, and TSPAN12) and ligand (NDP) of a molecular pathway that controls angiogenesis, the Norrin-β-catenin signaling pathway. However, half of all FEVR-affected case subjects do not harbor mutations in these genes, indicating that further mutated genes remain to be identified. Here we report the identification of mutations in CTNNB1, the gene encoding β-catenin, as a cause of FEVR. We describe heterozygous mutations (c.2142_2157dup [p.His720^∗] and c.2128C>T [p.Arg710Cys]) in two dominant FEVR-affected families and a de novo mutation (c.1434_1435insC [p.Glu479Argfs^∗18]) in a simplex case subject. Previous studies have reported heterozygous de novo CTNNB1 mutations as a cause of syndromic intellectual disability (ID) and autism spectrum disorder, and somatic mutations are linked to many cancers. However, in this study we show that Mendelian inherited CTNNB1 mutations can cause non-syndromic FEVR and that FEVR can be a part of the syndromic ID phenotype, further establishing the role that β-catenin signaling plays in the development of the retinal vasculature.

Genetic causes of optic nerve hypoplasia

Optic nerve hypoplasia (ONH) is the most common congenital optic nerve anomaly and a leading cause of blindness in the USA. Although most cases of ONH occur as isolated cases within their respective families, the advancement in molecular diagnostic technology has made us realise that a substantial fraction of cases has identifiable genetic causes, typically de novo mutations. An increasing number of genes has been reported, mutations of which can cause ONH. Many of the genes involved serve as transcription factors, participating in an intricate multistep process critical to eye development and neurogenesis in the neural retina. This review will discuss the respective genes and mutations, human phenotypes, and animal models that have been created to gain a deeper understanding of the disorders. The identification of the underlying gene and mutation provides an important step in diagnosis, medical care and counselling for the affected individuals and their families. We envision that future research will lead to further disease gene identification, but will also teach us about gene-gene and gene-environment interactions relevant to optic nerve development. How much of the functional impairment of the various forms of ONH is a reflection of altered morphogenesis versus neuronal homeostasis will determine the prospect of therapeutic intervention, with the ultimate goal of improving the quality of life of the individuals affected with ONH.

Genetic Advances in Microphthalmia

Congenital ocular anomalies such as anophthalmia and microphthalmia (AM) are severe craniofacial malformations in human. The etiologies of these ocular globe anomalies are diverse but the genetic origin appears to be a predominant cause. Until recently, genetic diagnosis capability was rather limited in AM patients and only a few genes were available for routine genetic testing. While some issues remain poorly understood, knowledge regarding the molecular basis of AM dramatically improved over the last years with the development of new molecular screening technologies. Thus, the genetic cause is now identifiable in more than 50% of patients with a severe bilateral eye phenotype and in around 30% of all AM patients taken together. Such advances in the knowledge of these genetic bases are important as they improve the quality of care, in terms of diagnosis, prognosis, and genetic counseling delivered to the patients and their families.

KIF11 mutations are a common cause of autosomal dominant familial exudative vitreoretinopathy

BACKGROUND/AIMS

To identify KIF11 mutations in patients with familial exudative vitreoretinopathy (FEVR) and to describe the associated phenotypes.

METHODS

Mutation analysis in a cohort of patients in a single institute was conducted. Bioinformatics was performed for whole exome sequencing, and the variants were confirmed by Sanger sequencing. Clinical data and DNA samples were collected from 814 unrelated Chinese probands, including 34 with FEVR, at the Pediatric and Genetic Eye Clinic, Zhongshan Ophthalmic Centre, Guangzhou, China.

RESULTS

Four novel heterozygous truncation mutations in KIF11, including c.131_132dupAT (p.P45Ifs*92), c.2230C>T (p.Q744*), c.2863C>T (p.Q955*) and c.2952_2955delGCAG (p.G985Ifs*6), were detected in four of 34 probands with FEVR. Combined with our previously identified mutations in FEVR cases (n=14), KIF11 mutations were identified in 8.3% (4/48) of all probands with FEVR. Ocular phenotypes documented in patients with KIF11 mutations showed a significant great variability of FEVR from the avascular zone in the peripheral retina to bilateral complete retinal detachment. Analysis of available family members in family QT1314 and QT937 showed segregation of KIF11 mutations with the phenotype of FEVR as expected. The family QT964 with two affected siblings and unaffected parents demonstrated a peculiar somatic mosaicism in the mother who had a low copy number variant (about 7% in her leucocyte DNA).

CONCLUSIONS

Identification of mutations in 8.3% patients suggests KIF11 mutations as a common cause of FEVR. Patients with KIF11 mutations showed typical, but variable, signs of FEVR with or without microcephaly, lymphoedema and mental retardation.

Complex genetics of familial exudative vitreoretinopathy and related pediatric retinal detachments

Familial exudative vitreoretinopathy (FEVR) is a hereditary vitreoretinal disorder that can cause various types of retinal detachments. The abnormalities in eyes with FEVR are caused by poor vascularization in the peripheral retina. The genetics of FEVR is highly heterogeneous, and mutations in the genes for Wnt signaling and a transcription factor have been reported to be responsible for FEVR. These factors have been shown to be the regulators of the pathophysiological pathways of retinal vascular development. Studies conducted to identify the causative genes of FEVR have uncovered a diverse and complex relationship between FEVR and other diseases; for example, Norrie disease, a Mendelian-inherited disease; retinopathy of prematurity, a multifactorial genetic disease; and Coats disease, a nongenetic disease, associated with pediatric retinal detachments.