Autosomal recessive familial exudative vitreoretinopathy is associated with mutations in LRP5

Genetic Evaluation for Monogenic Disorders of Low Bone Mass and Increased Bone Fragility: What Clinicians Need to Know

PURPOSE OF REVIEW

The purpose of this review is to outline the principles of clinical genetic testing and to provide practical guidance to clinicians in navigating genetic testing for patients with suspected monogenic forms of osteoporosis.

RECENT FINDINGS

Heritability assessments and genome-wide association studies have clearly shown the significant contributions of genetic variations to the pathogenesis of osteoporosis. Currently, over 50 monogenic disorders that present primarily with low bone mass and increased risk of fractures have been described. The widespread availability of clinical genetic testing offers a valuable opportunity to correctly diagnose individuals with monogenic forms of osteoporosis, thus instituting appropriate surveillance and treatment. Clinical genetic testing may identify the appropriate diagnosis in a subset of patients with low bone mass, multiple or unusual fractures, and severe or early-onset osteoporosis, and thus clinicians should be aware of how to incorporate such testing into their clinical practices.

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.

Deciphering a crucial dimeric interface governing Norrin dimerization and the pathogenesis of familial exudative vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is a hereditary eye disease that could cause blindness. It has been established that Norrin forms dimers to activate β-catenin signaling, yet the core interface for Norrin dimerization and the precise mechanism by which Norrin dimerization contributes to the pathogenesis of FEVR remain elusive. Here, we report an NDP variant, c.265T>C (p.Phe89Leu), that interrupted β-catenin signaling by disrupting Norrin dimerization. Structural and functional analysis revealed that the Phe-89 of one Norrin monomer interacts with Pro-98, Ser-101, Arg-121, and Ile-123 of another, forming two core symmetrical dimerization interfaces that are pivotal for the formation of a "hand-by-arm" dimer. Intriguingly, we proved that one of the two core symmetrical interfaces is sufficient for dimerization and activation of β-catenin signaling, with a substantial contribution from the Phe-89/Pro-98 interaction. Further functional analysis revealed that the disruption of both dimeric interfaces eliminates potential binding sites for LRP5, which could be partially restored by over-expression of TSPAN12. In conclusion, our findings unveil a core dimerization interface that regulates Norrin/LRP5 interaction, highlighting the essential role of Norrin dimerization on β-catenin signaling and providing potential therapeutic avenues for the treatment of FEVR.

The co-receptor Tspan12 directly captures Norrin to promote ligand-specific β-catenin signaling

Wnt/β-catenin signaling directs animal development and tissue renewal in a tightly controlled, cell- and tissue-specific manner. In the central nervous system, the atypical ligand Norrin controls angiogenesis and maintenance of the blood-brain barrier and blood-retina barrier through the Wnt/β-catenin pathway. Like Wnt, Norrin activates signaling by binding and heterodimerizing the receptors Frizzled (Fzd) and Low-density lipoprotein receptor-related protein 5 or 6 (LRP5/6), leading to membrane recruitment of the intracellular transducer Dishevelled (Dvl); this ultimately results in the stabilization of the transcriptional coactivator β-catenin. Unlike Wnt, the cysteine-knot ligand Norrin only signals through Fzd4 and additionally requires the co-receptor Tspan12; however, the mechanism underlying Tspan12-mediated signal enhancement is unclear. It has been proposed that Tspan12 integrates into the Norrin-Fzd4 complex to enhance Norrin-Fzd4 affinity or otherwise allosterically modulate Fzd4 signaling. Here, we measure direct, high-affinity binding between purified Norrin and Tspan12 in a lipid environment and use AlphaFold models to interrogate this interaction interface. We find that Tspan12 and Fzd4 can simultaneously bind Norrin and that a pre-formed Tspan12/Fzd4 heterodimer, as well as cells co-expressing Tspan12 and Fzd4, more efficiently capture low concentrations of Norrin than Fzd4 alone. We also show that Tspan12 competes with both heparan sulfate proteoglycans and LRP6 for Norrin binding and that Tspan12 does not impact Fzd4-Dvl affinity in the presence or absence of Norrin. Our findings suggest that Tspan12 does not allosterically enhance Fzd4 binding to Norrin or Dvl, but instead functions to directly capture Norrin upstream of signaling.

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.

A familial missense variant in the Alzheimer's disease gene SORL1 impairs its maturation and endosomal sorting

The SORL1 gene has recently emerged as a strong Alzheimer's Disease (AD) risk gene. Over 500 different variants have been identified in the gene and the contribution of individual variants to AD development and progression is still largely unknown. Here, we describe a family consisting of 2 parents and 5 offspring. Both parents were affected with dementia and one had confirmed AD pathology with an age of onset > 75 years. All offspring were affected with AD with ages at onset ranging from 53 years to 74 years. DNA was available from the parent with confirmed AD and 5 offspring. We identified a coding variant, p.(Arg953Cys), in SORL1 in 5 of 6 individuals affected by AD. Notably, variant carriers had severe AD pathology, and the SORL1 variant segregated with TDP-43 pathology (LATE-NC). We further characterized this variant and show that this Arginine substitution occurs at a critical position in the YWTD-domain of the SORL1 translation product, SORL1. Functional studies further show that the p.R953C variant leads to retention of the SORL1 protein in the endoplasmic reticulum which leads to decreased maturation and shedding of the receptor and prevents its normal endosomal trafficking. Together, our analysis suggests that p.R953C is a pathogenic variant of SORL1 and sheds light on mechanisms of how missense SORL1 variants may lead to AD.

A Literary Pediatric Retina Fellowship With Michael T. Trese, MD

Michael T. Trese, MD (1946-2022), a vitreoretinal surgeon, made significant contributions to the field of retina. Although most known for his work in pediatric retina surgery, he was a pioneer in areas such as medical retina, translational research, and telemedicine. This article reviews his major contributions to spread his knowledge more widely to vitreoretinal trainees and specialists. We discuss six areas where Trese made a lasting impact: lens-sparing vitrectomy, familial exudative vitreoretinopathy, congenital X-linked retinoschisis, autologous plasmin enzyme, regenerative medicine, and telemedicine. [Ophthalmic Surg Lasers Imaging Retina 2023;54:701-712.].

A familial missense variant in the Alzheimer's Disease gene SORL1 impairs its maturation and endosomal sorting

The SORL1 gene has recently emerged as a strong Alzheimer's Disease (AD) risk gene. Over 500 different variants have been identified in the gene and the contribution of individual variants to AD development and progression is still largely unknown. Here, we describe a family consisting of 2 parents and 5 offspring. Both parents were affected with dementia and one had confirmed AD pathology with an age of onset >75 years. All offspring were affected with AD with ages at onset ranging from 53yrs-74yrs. DNA was available from the parent with confirmed AD and 5 offspring. We identified a coding variant, p.(Arg953Cys), in SORL1 in 5 of 6 individuals affected by AD. Notably, variant carriers had severe AD pathology, and the SORL1 variant segregated with TDP-43 pathology (LATE-NC). We further characterized this variant and show that this Arginine substitution occurs at a critical position in the YWTD-domain of the SORL1 translation product, SORL1. Functional studies further show that the p.R953C variant leads to retention of the SORL1 protein in the endoplasmic reticulum which leads to decreased maturation and shedding of the receptor and prevents its normal endosomal trafficking. Together, our analysis suggests that p.R953C is a pathogenic variant of SORL1 and sheds light on mechanisms of how missense SORL1 variants may lead to AD.

Identifying novel candidate compounds for therapeutic strategies in retinopathy of prematurity via computational drug-gene association analysis

Purpose

Retinopathy of prematurity (ROP) is the leading cause of preventable childhood blindness worldwide. Although interventions such as anti-VEGF and laser have high success rates in treating severe ROP, current treatment and preventative strategies still have their limitations. Thus, we aim to identify drugs and chemicals for ROP with comprehensive safety profiles and tolerability using a computational bioinformatics approach.

Methods

We generated a list of genes associated with ROP to date by querying PubMed Gene which draws from animal models, human studies, and genomic studies in the NCBI database. Gene enrichment analysis was performed on the ROP gene list with the ToppGene program which draws from multiple drug-gene interaction databases to predict compounds with significant associations to the ROP gene list. Compounds with significant toxicities or without known clinical indications were filtered out from the final drug list.

Results

The NCBI query identified 47 ROP genes with pharmacologic annotations present in ToppGene. Enrichment analysis revealed multiple drugs and chemical compounds related to the ROP gene list. The top ten most significant compounds associated with ROP include ascorbic acid, simvastatin, acetylcysteine, niacin, castor oil, penicillamine, curcumin, losartan, capsaicin, and metformin. Antioxidants, NSAIDs, antihypertensives, and anti-diabetics are the most common top drug classes derived from this analysis, and many of these compounds have potential to be readily repurposed for ROP as new prevention and treatment strategies.

Conclusion

This bioinformatics analysis creates an unbiased approach for drug discovery by identifying compounds associated to the known genes and pathways of ROP. While predictions from bioinformatic studies require preclinical/clinical studies to validate their results, this technique could certainly guide future investigations for pathologies like ROP.

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.

Familial Exudative Vitreoretinopathy and Systemic Abnormalities in Patients With CTNNB1 Mutations

Purpose

Familial exudative vitreoretinopathy (FEVR) is an inherited vitreoretinopathy. This study aimed to analyze the ocular phenotypes and systemic features of patients with CTNNB1 mutations.

Methods

Whole exome sequencing was performed in the probands, and Sanger sequencing was used to verify the mutations and perform segregation analysis in the available family members. A luciferase assay was used to assess the effect of the mutant β-catenin on transcription. Comprehensive ocular examinations were performed on the probands and family members. Systemic features were evaluated and followed up.

Results

A total of 763 FEVR families were enrolled. Seven different CTNNB1 mutations, including 5 novels and 2 known mutations, were detected in 8 families, accounting for 1.05% of all FEVR families. Compared to wild-type CTNNB1, the CTNNB1 mutants failed to induce luciferase reporter activity in SuperTopFlash (STF) cells. Among the 16 eyes of the 8 probands, 2 (12.5%) eyes were classified as stage 2 FEVR, 8 (50.0%) as stage 4, and 6 (37.5%) as stage 5. All the patients had varying degrees of systemic abnormalities and presented with motor, speech, and developmental delays over time. Among the eight families with CTNNB1 mutations, seven were de novo mutations, and one proband inherited the mutation from his asymptomatic mother.

Conclusions

This study provides detailed descriptions of the ocular phenotypes of patients with CTNNB1 mutations that presented as severe FEVR, and accompanied with other systemic abnormalities. Five novel mutations identified in this study, expanded the mutation spectrum of CTNNB1-associated 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.

Kinesin-5 Eg5 is essential for spindle assembly, chromosome stability and organogenesis in development

Chromosome stability relies on bipolar spindle assembly and faithful chromosome segregation during cell division. Kinesin-5 Eg5 is a plus-end-directed kinesin motor protein, which is essential for spindle pole separation and chromosome alignment in mitosis. Heterozygous Eg5 mutations cause autosomal-dominant microcephaly, primary lymphedema, and chorioretinal dysplasia syndrome in humans. However, the developmental roles and cellular mechanisms of Eg5 in organogenesis remain largely unknown. In this study, we have shown that Eg5 inhibition leads to the formation of the monopolar spindle, chromosome misalignment, polyploidy, and subsequent apoptosis. Strikingly, long-term inhibition of Eg5 stimulates the immune responses and the accumulation of lymphocytes in the mouse spleen through the innate and specific immunity pathways. Eg5 inhibition results in metaphase arrest and cell growth inhibition, and suppresses the formation of somite and retinal development in zebrafish embryos. Our data have revealed the essential roles of kinesin-5 Eg5 involved in cell proliferation, chromosome stability, and organogenesis during development. Our findings shed a light on the cellular basis and pathogenesis in microcephaly, primary lymphedema, and chorioretinal dysplasia syndrome of Eg5-mutation-positive patients.

CTNND1 variants cause familial exudative vitreoretinopathy through Wnt/Cadherin axis

Familial exudative vitreoretinopathy (FEVR) is a hereditary disorder that can cause vision loss. The CTNND1 gene encodes a cellular adhesion protein p120-catenin (p120), which is essential for vascularization, yet the function of p120 in postnatal physiological angiogenesis remains unclear. Here, we applied whole-exome sequencing (WES) on 140 probands of FEVR families and identified three candidate variants in the human CTNND1 gene. We performed inducible deletion of Ctnnd1 in the postnatal mouse endothelial cells (ECs) and observed typical phenotypes of FEVR. Immunofluorescence of retina flat mounts also revealed immune responses, including reactive astrogliosis and microgliosis accompanied by abnormal Vegfa expression. Using an unbiased proteomics analysis in combination with in vivo or in vitro approaches, we propose that p120 is critical for the integrity of cadherin/catenin complex, and that p120 activates Wnt signaling activity by protecting β-catenin from Gsk3β-ubiquitin-guided degradation. Treatment of CTNND1-depleted HRECs with Gsk3β inhibitors LiCl or CHIR-99021 successfully enhanced cell proliferation by preventing β-catenin from degradation. Moreover, LiCl treatment increased vessel density in Ctnnd1-deficient mouse retinas. Functional analysis also revealed that variants in CTNND1 cause FEVR by compromising the expression of adherens junctions (AJs) and Wnt signaling activity. Additionally, genetic interactions between p120 and β-catenin or α-catenin revealed by double heterozygous deletion in mice further confirmed that p120 regulates vascular development through the Wnt/Cadherin axis. Together, we propose that CTNND1 is a novel candidate gene associated with FEVR, and that variants in CTNND1 can cause FEVR through the Wnt/Cadherin axis.

Spectrum of Mutations in NDP Resulting in Ocular Disease; a Systematic Review

Aims and Rationale: The inner retina is supplied by three intraretinal capillary plexi whereas the outer retina is supplied by the choroidal circulation: NDP is essential for normal intraretinal vascularisation. Pathogenic variants in NDP (Xp11.3) may result in either a severe retinal phenotype associated with hearing loss (Norrie Disease) or a moderate retinal phenotype (Familial Exudative Vitreoretinopathy, FEVR). However, little is known about whether the nature or location of the NDP variant is predictive of severity. In this systematic review we summarise all reported NDP variants and draw conclusions about whether the nature of the NDP variant is predictive of the severity of the resulting ocular pathology and associated hearing loss and intellectual disability.

Findings: 201 different variants in the NDP gene have been reported as disease-causing. The pathological phenotype that may result from a disease-causing NDP variant is quite diverse but generally comprises a consistent cluster of features (retinal hypovascularisation, exudation, persistent foetal vasculature, tractional/exudative retinal detachment, intellectual disability and hearing loss) that vary predictably with severity. Previous reviews have found no clear pattern in the nature of NDP mutations that cause either FEVR or Norrie disease, with the exception that mutations affecting cysteine residues have been associated with Norrie Disease and that visual loss amongst patients with Norrie disease tends to be more severe if the NDP mutation results in an early termination of translation as opposed to a missense related amino acid change. A key limitation of previous reviews has been variability in the case definition of Norrie disease and FEVR amongst authors. We thus reclassified patients into two groups based only on the severity of their retinal disease. Of the reported pathogenic variants that have been described in more than one patient, we found that any given variant caused an equivalent severity of retinopathy each time it was reported with very few exceptions. We therefore conclude that specific NDP mutations generally result in a consistent retinal phenotype each time they arise. Reports by different authors of the same variant causing either FEVR or Norrie disease conflict primarily due to variability in the authors’ respective case definitions rather than true differences in disease severity.

FZD4 in a Large Chinese Population With Familial Exudative Vitreoretinopathy: Molecular Characteristics and Clinical Manifestations

Purpose

The purpose of this study was to establish a genotype-phenotype correlation of familial exudative vitreoretinopathy (FEVR) caused by FZD4 gene mutations.

Methods

Six hundred fifty-one probands and their family members were recruited based on a clinical diagnosis of FEVR between 2015 and 2021 at Zhongshan Ophthalmic Center. Ocular examinations were performed in all participants. Targeted gene panel sequencing and whole-exome sequencing were performed in the probands, and Sanger sequencing was used to verify the mutations and segregation analysis was performed in the family members.

Results

Fifty-one FZD4 mutations (24 novels and 27 known) were detected in 84 families. Of these 168 eyes with FEVR, the eyes at stages 1, 2, 3, 4, and 5 were 29 (17.3%), 15 (8.9%), 19 (11.3%), 55 (32.7%), and 12 (7.1%), respectively. Exact stage of 38 (22.6%) eyes could not be determined. The FEVR phenotypes were more severe in the probands than the phenotypes in the family members (P < 0.001). The families were divided into two groups, probands that inherited the variant from the mother, and probands that inherited the variant from the father. In addition, the FEVR stage differences between these two groups were different (P < 0.05). Despite the mutations being located in different domains of FZD4, no significant differences were identified among the domains in terms of FEVR staging, retinal folds, retinal detachment, temporal midperipheral vitreoretinal interface abnormality, and foveal hypoplasia.

Conclusions

The FZD4 probands had severer phenotype than the family members, and the FEVR stage difference was greater between the probands and mothers than that between the probands and fathers.

Ocular manifestations of Chinese patients with copy number variants in the NDP gene

PURPOSE

Familial exudative vitreoretinopathy (FEVR) and Norrie disease (ND) are genetic disorders that can be caused by mutations in the NDP gene and affect retinal vasculature growth and development. This study aimed to describe the copy number variations (CNVs) in the NDP gene in Chinese FEVR families and the associated phenotypes.

METHODS

This study recruited 651 FEVR families. SeqCNV was used to analyze the CNVs in the families without mutations in known FEVR-associated genes. Multiplex ligation-dependent probe amplification and semiquantitative multiplex PCR were performed to verify the NDP CNVs. The probands and family members underwent complete ocular examinations.

RESULTS

NDP CNVs were identified in four patients from three unrelated families, accounting for 15% of the patients with NDP mutations and 0.46% of the entire FEVR cohort. Exon 2 deletions were detected in two families, and whole gene deletion was identified in one family. The affected individuals were born blind with total retinal detachment.

CONCLUSIONS

The findings confirm that CNVs are a common NDP mutation type. The CNV-associated phenotype is congenital blindness with total retinal detachment. Antenatal genetic analyses and fetal ultrasound can facilitate early diagnosis and interventions in patients with NDP mutations.

LMBR1L regulates proliferation and migration of endothelial cells through Norrin/β-catenin signaling

Precise Norrin/β-catenin signaling is critical for proper angiogenesis. Dysregulation of the signaling leads various diseases, of which retinal exudative vitreoretinopathy is the most prevalent. Here, we used global knockout mouse model to show that endothelial cells-derived limb region 1 like (LMBR1L), a transmembrane protein of unknown function in angiogenesis, is essential for retinal vascular development. In vitro experiments revealed that LMBR1L depletion resulted in aberrant activation of Norrin/β-catenin signaling pathway via decreased ubiquitination of FZD4, increased Norrin co-receptor LRP5 and p-GSK3β-Ser9 expression level, which caused accumulation of β-catenin. Moreover, inhibition of LMBR1L in human retinal microvascular endothelial cells (HRECs) caused increased proliferation ability and defective cell migration, which might due to upregulated expression levels of the AJ components. Treatment of p-GSK3β-Ser9 inhibitor AR-A014418 restored the phenotypes in LMBR1L-null HRECs, which further demonstrated the important regulatory role of LMBR1L in Norrin/β-catenin signaling pathway. Taken together, our data unravels an essential role of LMBR1L in angiogenesis.

Five novel copy number variations detected in patients with familial exudative vitreoretinopathy

Purpose

Familial exudative vitreoretinopathy (FEVR) is an inherited retinal vascular disease genetically heterogeneous with multiple causative genes. The aim of this study is to report five novel copy number variation (CNV) regions in FEVR patients and to investigate the possible contributions of novel CNVs to FEVR.

Methods

In this study, 824 FEVR families were collected. All cases were performed using the targeted next generation sequencing (NGS) assay, and families with no definite pathogenic mutations in FEVR genes were screened for CNVs according to the NGS results. Droplet digital polymerase chain reaction (ddPCR) testing was introduced to validate the screened CNV regions. We also reviewed the clinical presentations of the probands and affected family members associated with the novel CNVs and conducted segregation analysis.

Results

Five CNVs in five patients were detected in this study: heterozygous deletions of kinesin family member 11 (KIF11) exons 2-4, KIF11 exon 11, KIF11 exons 1-10, tetraspanin-12 (TSPAN12) exons 1-3, and low-density lipoprotein receptor-related protein 5 (LRP5) exons 19-21. Among the five affected families, TSPAN12 exons 1-3 heterozygous deletion and LRP5 exons 19-21 heterozygous deletion originate from the mother and the father of the proband, respectively. No other family members manifested as FEVR except for the probands. The correlation between disease severity and CNV loci seems uncertain.

Conclusions

Five novel CNV loci in FEVR patients were uncovered in this study, including one maternally-inherited and one paternally-inherited CNV region. Though there is no evidence of co-segregation between these CNVs and FEVR, our findings suggest novel genetic risk factors for FEVR.

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.

Identification of a novel mutation in KIF11 with functional analysis in a cohort of 516 familial patients with exudative vitreoretinopathy

Purpose

To identify a novel mutation in KIF11 with clinical and functional analysis among 516 familial patients with exudative vitreoretinopathy (FEVR).

Methods

Next-generation sequencing was performed on 516 patients with FEVR between January 2015 and October 2017. Clinical data were collected from patient charts, including sex, age at presentation, visual acuity if available, axial length, stage, and systemic clinical findings. Protein and mRNA levels were detected with western blotting and real-time quantitative PCR, respectively. Mass spectrometry was used to analyze the interacting protein of KIF11.

Results

In total, 304 of 516 patients were identified with at least one mutation in FEVR causative genes. Mutations in KIF11 were identified in 14.47% of all carriers. The novel mutation p. H718L accounted for the greatest proportion (12/44; 27.30%) among all mutations in KIF11. Fundus presentations in these 12 individuals varied from the avascular zone of the peripheral retina to total retinal detachment. The p. H718L mutation can reduce the proliferation of human retinal endothelial cells (HRECs) compared to the wild type. The mRNA level of vascular endothelial growth factor-α, transforming growth factor-α, metalloproteinase-1, and angiopoietin-like 4 were depressed in the KIF11 (p. H718L) groups under hypoxia stimuli. Mass spectrometry results demonstrated that eukaryotic elongation factor 2 (EEF2) was an interacting protein of KIF11 and that the p. H718L mutation can attenuate the binding activity.

Conclusions

Patients with the most frequent KIF11 mutation p. H718L showed typical FEVR presentations in this cohort. The mutation in KIF11 likely plays a role in the proliferation of HRECs, and the p. H718L mutation can reduce the proliferation.

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.

Whole-Gene Deletions of FZD4 Cause Familial Exudative Vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is an inherited disorder characterized by abnormalities in the retinal vasculature. The FZD4 gene is associated with FEVR, but the prevalence and impact of FZD4 copy number variation (CNV) on FEVR patients are unknown. The aim of this study was to better understand the genetic features and clinical manifestations of patients with FZD4 CNVs. A total of 651 FEVR families were recruited. Families negative for mutations in FEVR-associated genes were selected for CNV analysis using SeqCNV. Semiquantitative multiplex polymerase chain reaction and multiplex ligation-dependent probe amplification were conducted to verify the CNVs. Four probands were found to carry whole-gene deletions of FZD4, accounting for 5% (4/80) of probands with FZD4 mutations and 0.6% (4/651) of all FEVR probands. The four probands exhibited similar phenotypes of unilateral retinal folds. FEVR in probands with CNVs was not more severe than in probands with FZD4 missense mutations (p = 1.000). Although this is the first report of FZD4 CNVs and the associated phenotypes, the interpretation of FZD4 CNVs should be emphasized when analyzing the next-generation sequencing data of FEVR patients because of their high prevalence.

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.

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.

Pregnancy and lactation, a challenge for the skeleton

In this review we discuss skeletal adaptations to the demanding situation of pregnancy and lactation. Calcium demands are increased during pregnancy and lactation, and this is effectuated by a complex series of hormonal changes. The changes in bone structure at the tissue and whole bone level observed during pregnancy and lactation appear to largely recover over time. The magnitude of the changes observed during lactation may relate to the volume and duration of breastfeeding and return to regular menses. Studies examining long-term consequences of pregnancy and lactation suggest that there are small, site-specific benefits to bone density and that bone geometry may also be affected. Pregnancy- and lactation-induced osteoporosis (PLO) is a rare disease for which the pathophysiological mechanism is as yet incompletely known; here, we discuss and speculate on the possible roles of genetics, oxytocin, sympathetic tone and bone marrow fat. Finally, we discuss fracture healing during pregnancy and lactation and the effects of estrogen on this process.

Role of NDP- and FZD4-Related Novel Mutations Identified in Patients with FEVR in Norrin/β-Catenin Signaling Pathway

Mutations in NDP and FZD4 have been closely related to a series of retinal diseases including familial exudative vitreoretinopathy (FEVR). Our study was designed to identify novel NDP and FZD4 mutations by whole exome sequencing (WES) in a cohort of patients with a definitive diagnosis of FEVR and explore the underlying molecular mechanism. During 2016, we investigated fifty nonconsanguineous families with affected individuals exhibiting FEVR phenotype and WES identified one recently reported mutation: NDP c.127C>A (p.H43N), and five novel mutations: NDP c.129_131del (p.44del), NDP c.320_353del (p.R107Pfs), NDP c.321delG (p.L108Cfs), NDP c.377G>T (p.C126F), and FZD4 c.314T>G (p.M105R) that cosegragated with the abnormal fundus vascular manifestations in six families. All the mutations were perceived to be pathogenic or likely pathogenic according to the standards and guidelines from the American College of Medical Genetics and Genomics (ACMG) and predicted to be deleterious by a series of bioinformatics analyses. We systematically performed functional analyses on the six mutations utilizing the Topflash reporter assay, where all NDP and FZD4 mutants revealed at least 50% loss of wild-type activity. Immunoprecipitation finally demonstrated that the six mutations could degrade the Norrin-Frizzled-4 pair-binding effect to varying degrees. Finally, our study underscores the correlation between the FEVR phenotype and genotype in NDP and FZD4, extending the mutation spectrum, allowing a reliable assessment of FEVR recurrence and improving genetic counseling. Further, our findings provide essential evidence for the follow-up study of animal models and drug targets by Topflash assays and immunoprecipitation.

Characterization of Unique Lens Morphology in a Cohort of Children with Familial Exudative Vitreoretinopathy

Purpose: To characterize the lens morphology and to measure the clinical features of familial exudative vitreoretinopathy (FEVR) in children. Methods: Unique lens changes were observed in a cohort of children with FEVR from March 2015 to November 2017 using slit lamp examination and all the patients underwent cycloplegic refraction, ultrasound A and B, keratometry and fundus fluorescein angiography. Results: Twelve eyes of eight children with FEVR had unique lens changes. The contraction of the posterior capsule caused unique lens changes resulting in myopia in nine eyes of six children and astigmatism in eight eyes of five children. Retinal lesions in the affected eyes were all stage 1 to 2. Six eyes of three patients underwent lensectomy and intraocular lens implantation due to high anisometropia which could not be corrected by conventional optical correction. During lensectomy, the opacification in the posterior capsule was found to be due to the fibrous membrane that protruded into the anterior vitreous and not due to lens opacification. Three patients had bilateral lensectomy, in two of whom significant macular involvement was observed in one eye and in one of whom significant macular involvement was observed in both eyes. After surgery visual acuity (VA) improved obviously in two eyes without significant macular involvement and did not improve in the four eyes which had significant macular involvement. Among the five patients who did not have lensectomy, one patient was lost to follow-up and one patient had VA improved in both eyes without significant macular involvement. The other three patients did not have much change in VA. Conclusions: Clinicians should be aware that when a high myopia or astigmatism does not match the corneal curvature and the length of the eye, one should check carefully the changes of lens and fundus after dilating the pupil, to avoid misdiagnosis and missed diagnosis.

Integrin-linked kinase controls retinal angiogenesis and is linked to Wnt signaling and exudative vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is a human disease characterized by defective retinal angiogenesis and associated complications that can result in vision loss. Defective Wnt/β-catenin signaling is an established cause of FEVR, whereas other molecular alterations contributing to the disease remain insufficiently understood. Here, we show that integrin-linked kinase (ILK), a mediator of cell-matrix interactions, is indispensable for retinal angiogenesis. Inactivation of the murine Ilk gene in postnatal endothelial cells results in sprouting defects, reduced endothelial proliferation and disruption of the blood-retina barrier, resembling phenotypes seen in established mouse models of FEVR. Retinal vascularization defects are phenocopied by inducible inactivation of the gene for α-parvin (Parva), an interactor of ILK. Screening genomic DNA samples from exudative vitreoretinopathy patients identifies three distinct mutations in human ILK, which compromise the function of the gene product in vitro. Together, our data suggest that defective cell-matrix interactions are linked to Wnt signaling and FEVR.

Integrin-linked kinase (ILK) is an important mediator of integrin signaling. Here Park et al. show that mice with endothelial-specific deletion of Ilk develop vascular defects that resemble familial exudative vitreoretinopathy, and identify mutations in ILK in patients with exudative vitreoretinopathy suggesting a potential role in human pathogenesis.

Familial Exudative Vitreoretinopathy-Related Disease-Causing Genes and Norrin/β-Catenin Signal Pathway: Structure, Function, and Mutation Spectrums

Familial exudative vitreoretinopathy (FEVR) is a hereditary ocular disorder characterized by incomplete vascularization/abnormality of peripheral retina. Four of the identified disease-causing genes of FEVR were NDP, FZD4, LRP5, and TSPAN12, the protein coded by which were the components of the Norrin/β-catenin signal pathway. In this review, we summarized and discussed the spectrum of mutations involving these four genes. By the end of 2017, the number of FEVR causing mutations reported for NDP, FZD4, LRP5, and TSPAN12 was, respectively, 26, 121, 58, and 40. Three most frequently reported mutations were c. 362G > A (p.R121Q) of NDP, c. 313A > G (p.M105V), and c.1282_1285delGACA (p.D428SfsX2) of FZD4. Mutations have a tendency to cluster in some “hotspots” domains which may be responsible for protein interactions.

Clinical and Molecular Characterization of Familial Exudative Vitreoretinopathy Associated With Microcephaly

PURPOSE

Familial exudative vitreoretinopathy (FEVR) is a rare finding in patients with genetic forms of microcephaly. This study documents the detailed phenotype and expands the range of genetic heterogeneity.

DESIGN

Retrospective case series.

METHODS

Twelve patients (10 families) with a diagnosis of FEVR and microcephaly were ascertained from pediatric genetic eye clinics and underwent full clinical assessment including retinal imaging. Molecular investigations included candidate gene Sanger sequencing, whole-exome sequencing (WES), and whole-genome sequencing (WGS).

RESULTS

All patients had reduced vision and nystagmus. Six were legally blind. Two probands carried bi-allelic LRP5 variants, both presenting with bilateral retinal folds. A novel homozygous splice variant, and 2 missense variants were identified. Subsequent bone density measurement identified osteoporosis in one proband. Four families had heterozygous KIF11 variants. Two probands had a retinal fold in one eye and chorioretinal atrophy in the other; the other 2 had bilateral retinal folds. Four heterozygous variants were found, including 2 large deletions not identified on Sanger sequencing or WES. Finally, a family of 2 children with learning difficulties, abnormal peripheral retinal vasculogenesis, and rod-cone dystrophy were investigated. They were found to have bi-allelic splicing variants in TUBGCP6. Three families remain unsolved following WES and WGS.

CONCLUSIONS

Molecular diagnosis has been achieved in 7 of 10 families investigated, including a previously unrecognized association with LRP5. WGS enabled molecular diagnosis in 3 families after prior negative Sanger sequencing of the causative gene. This has enabled patient-specific care with targeted investigations and accurate family counseling.

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.

Whole-Exome Sequencing Analysis Identified Novel Mutations in the TSPAN12 Gene in Chinese Families with Familial Exudative Vitreoretinopathy

Background: Familial exudative vitreoretinopathy (FEVR, OMIM 133780), characterized by incomplete retinal vascular development and pathological neovascularization, is a severe inherited retinal disorder. Mutations in 10 genes have been reported to be associated with FEVR, but this still leaves ∼50% of FEVR cases to be genetically explained. Purpose: The purpose of this study was to identify novel FEVR-causing mutations and explore the causative mutations in Chinese FEVR families. Methods: Whole-exome sequencing was performed to analyze the genomic DNA of the probands from 121 Chinese FEVR families. Sanger sequencing was carried out to verify all identified mutations. Luciferase assays were used to test the activity of a mutant protein in the Norrin-β-catenin signaling pathway. Results: Four novel heterozygous TSPAN12 (Tetraspanin 12) mutations, including two single-base substitution mutations and two small-deletion mutations, were identified in these FEVR families: c.1A>G (p.0), c.614G>A (p.G205D), c.695delT (p.V232Gfs*7), and c.833_842del (p.L278Qfs*25). Conclusion: This study revealed the causative mutations in four Chinese FEVR families and identified four novel FEVR-causing mutations, thus expanding the mutation spectrum of FEVR in the Chinese population.

An FEVR-associated mutation in ZNF408 alters the expression of genes involved in the development of vasculature

Familial exudative vitreoretinopathy (FEVR) is an inherited retinal disorder hallmarked by an abnormal development of retinal vasculature. A missense mutation in ZNF408 (p.H455Y) was reported to underlie autosomal dominant FEVR in a large Dutch family, and ZNF408 was shown to play a role in the development of vasculature. Nonetheless, little is known about the molecular mechanism of ZNF408-associated FEVR. To investigate this, an in vitro model of ZNF408-associated FEVR was generated by overexpressing wild-type and p.H455Y ZNF408 in human umbilical vein endothelial cells. Cells overexpressing mutant ZNF408 were unable to form a capillary-like network in an in vitro tube formation assay, thereby mimicking the clinical feature observed in patients with FEVR. Intriguingly, transcriptome analysis revealed that genes involved in the development of vasculature were deregulated by the p.H455Y mutation. Chromatin immunoprecipitation showed that p.H455Y ZNF408 has reduced DNA-binding ability, as compared to the wild-type protein. The fact that the p.H455Y mutation disrupts the expression of genes important for the development of vasculature sheds further light on the molecular mechanisms underlying ZNF408-associated FEVR.

Genetic variants of TSPAN12 gene in patients with retinopathy of prematurity

Genetic susceptibility to retinopathy of prematurity (ROP) has been reported. However, no virulence genes are currently known for ROP. This study aimed to assess FZD4, LRP5, TSPAN12, and NDP, which are known virulence genes involved in familial exudative vitreoretinopathy, an ailment that shares some symptoms with ROP. After approval from the parents of diseased infants, blood samples from 29 Han patients with ROP were collected for genomic DNA extraction. Direct sequencing was used to assess the four candidate genes, namely FZD4, LRP5, TSPAN12, and NDP. Finally, genetic mutations were screened. Changes of three nucleotide sequences were found in the four candidate genes; notably, a c.954G>A hybrid mutation in the TSPAN12 gene was predicted to cause protein structure and function alterations. The molecular pathogenesis of ROP is complex, and likely involves the c.954G>A mutation in TSPAN12.

Correlating Changes in the Macular Microvasculature and Capillary Network to Peripheral Vascular Pathologic Features in Familial Exudative Vitreoretinopathy

PURPOSE

To evaluate the macular microvasculature in patients with familial exudative vitreoretinopathy (FEVR) using OCT angiography (OCTA) and to assess for peripheral vascular changes using widefield fluorescein angiography (WFA).

DESIGN

Multicenter, retrospective, comparative, observational case series.

PARTICIPANTS

We identified 411 patients with FEVR, examined between September 2014 and June 2018. Fifty-seven patients with FEVR and 60 healthy controls had OCTA images of sufficient quality for analysis.

METHODS

Custom software was used to assess for layer-specific, quantitative changes in vascular density and morphologic features on OCTA by way of vessel density (VD), skeletal density (SD), fractal dimension (FD), vessel diameter index (VDI), and foveal avascular zone (FAZ). Widefield fluorescein angiography images were reviewed for peripheral vascular changes including capillary dropout, late-phase angiographic posterior and peripheral vascular leakage (LAPPEL), vascular dragging, venous-venous shunts, and arteriovenous shunts.

MAIN OUTCOME MEASURES

Macular microvascular parameters on OCTA and peripheral angiographic findings on WFA.

RESULTS

OCT angiography analysis of 117 patients (187 eyes; 92 FEVR patients and 95 control participants) demonstrated significantly reduced VD, SD, and FD and greater VDI in patients with FEVR compared with controls in the nonsegmented retina, superficial retinal layer (SRL), and deep retinal layer (DRL). The FAZ was larger compared with that in control eyes in the DRL (P < 0.0001), but not the SRL (P = 0.52). Subanalysis by FEVR stage showed the same microvascular changes compared with controls for all parameters. Widefield fluorescein angiography analysis of 95 eyes (53 patients) with FEVR demonstrated capillary nonperfusion in all eyes: 47 eyes (49.5%) showed LAPPEL, 32 eyes (33.7%) showed vascular dragging, 30 eyes (31.6%) had venous-venous shunts, and 33 eyes (34.7%) had arteriovenous shunts. Decreasing macular VD on OCTA correlated with increasing peripheral capillary nonperfusion on WFA. Decreasing fractal dimension on OCTA correlated with increasing LAPPEL severity on WFA.

CONCLUSIONS

Patients with FEVR demonstrated abnormalities in the macular microvasculature and capillary network, in addition to the peripheral retina. The macular microvascular parameters on OCTA may serve as biomarkers of changes in the retinal periphery on WFA.

Proteomic Alterations in Aqueous Humor From Patients With Primary Open Angle Glaucoma

Purpose

Primary open angle glaucoma (POAG) is the most prevalent form of glaucoma, accounting for approximately 90% of all cases. The aqueous humor (AH), a biological fluid in the anterior and posterior chambers of the eye, is involved in a multitude of functions including the maintenance of IOP and ocular homeostasis. This fluid is very close to the pathologic site and is also known to have a significant role in glaucoma pathogenesis. The purpose of this study was to identify proteomic alterations in AH from patients with POAG.

Methods

AH samples were extracted from 47 patients undergoing cataract surgery (controls: n = 32; POAG: n = 15). Proteomic analysis of the digested samples was accomplished by liquid-chromatography-mass spectrometry. The identified proteins were evaluated using a variety of statistical and bioinformatics methods.

Results

A total of 33 proteins were significantly altered in POAG subjects compared with the controls. The most abundant proteins in POAG subjects are IGKC (13.56-fold), ITIH4 (4.1-fold), APOC3 (3.36-fold), IDH3A (3.11-fold), LOC105369216 (2.98-fold). SERPINF2 (2.94-fold), NPC2 (2.88-fold), SUCLG2 (2.70-fold), KIAA0100 (2.29-fold), CNOT4 (2.23-fold), AQP4 (2.11-fold), COL18A1 (2.08-fold), NWD1 (2.07-fold), and TMEM120B (2.06-fold). A significant increasing trend in the odds ratios of having POAG was observed with increased levels of these proteins.

Conclusion

Proteins identified in this study are implicated in signaling, glycosylation, immune response, molecular transport, and lipid metabolism. The identified candidate proteins may be potential biomarkers associated with POAG development and may lead to more insight in understanding the mechanisms underlying the pathogenesis of this disease.

Potential Mutations in Chinese Pathologic Myopic Patients and Contributions to Phenotype

Purpose

Pathologic myopia is a leading cause of visual impairment in East Asia. The aim of this study was to investigate the potential mutations in Chinese pathologic myopic patients and to analyze the correlations between genotype and clinical phenotype.

Method

One hundred and three patients with pathologic myopia and one hundred and nine unrelated healthy controls were recruited from Zhongshan Ophthalmic Center. Detailed clinical data, including ultra-widefield retinal images, measurements of best-corrected visual acuity, axial length, refractive error and ophthalmic examination results, were obtained. Blood samples were collected for high-throughput DNA targeted sequencing. Based on the screening results, phenotype-genotype correlations were analyzed.

Results

The study included 196 eyes of 103 patients (36 men and 67 women) with an average age of 52.19 (38.92 – 65.46) years, an average refractive error of -11.80 D (-16.38 – -7.22) and a mean axial length of 28.26 mm (25.79 – 30.73). The patients were subdivided into three groups: myopic chorioretinal atrophy (190 eyes of 101 patients), myopic choroidal neovascularization (17 eyes of 15 patients), and myopic traction retinopathy (71 eyes of 61 patients). Systematic analysis of variants in the 255 genes revealed six potential pathogenic mutations: PEX7, OCA2, LRP5 (rs545382, c.1647T>C), TSPAN12 (rs41623, c.765G>T), RDH5 (rs3138142, c.423C>T) and TTC21B (rs80225158, c.2385G>C). OCA2 mutations were primarily observed in patients with myopic traction maculopathy.

Conclusion

Genetic alterations contribute to various clinical characteristics in Chinese pathologic myopic patients. The study may provide new insights into the etiology of pathologic myopia and potential targets for therapeutic interventions.

Variable reduction in Norrin signaling activity caused by novel mutations in FZD4 identified in patients with familial exudative vitreoretinopathy

Purpose

To identify novel mutations in FZD4 and to investigate their pathogenicity in a cohort of Chinese patients with familial exudative vitreoretinopathy (FEVR).

Methods

Next-generation sequencing was performed in patients with a clinical diagnosis of FEVR. Wide-field angiography was performed in probands and family members if available. Clinical data were collected from patient charts. The effect of the mutations in FZD4 on its biologic activity in the Norrin/β-catenin signaling pathway was analyzed with the luciferase reporter assay.

Results

Four novel mutations in FZD4 (c.1188_1192del/p.F396fs, c.1220delC/p.A407Vfs*24, c.905G>A/p.C302Y, c.1325T>A/p.V442E) were identified in four unrelated families. The mutations were not detected in 200 healthy individuals. The variability of the ocular phenotypes was not only observed in the probands and parents harboring the same mutation but also between two eyes in one individual. All four novel mutations introduced reduction in luciferase activity. Compared with the wild-type, the FZD4 level of the four mutants also decreased variably.

Conclusions

Four novel mutations in FZD4 were identified in Chinese patients with FEVR. No correlation in the reduced luciferase activity and the ocular phenotype was observed in this study. This study further emphasized the complexity of the FEVR-causing machinery.

Wnt Signaling in vascular eye diseases

The Wnt signaling pathway plays a pivotal role in vascular morphogenesis in various organs including the eye. Wnt ligands and receptors are key regulators of ocular angiogenesis both during the eye development and in vascular eye diseases. Wnt signaling participates in regulating multiple vascular beds in the eye including regression of the hyaloid vessels, and development of structured layers of vasculature in the retina. Loss-of-function mutations in Wnt signaling components cause rare genetic eye diseases in humans such as Norrie disease, and familial exudative vitreoretinopathy (FEVR) with defective ocular vasculature. On the other hand, experimental studies in more prevalent vascular eye diseases, such as wet age-related macular degeneration (AMD), diabetic retinopathy (DR), retinopathy of prematurity (ROP), and corneal neovascularization, suggest that aberrantly increased Wnt signaling is one of the causations for pathological ocular neovascularization, indicating the potential of modulating Wnt signaling to ameliorate pathological angiogenesis in eye diseases. This review recapitulates the key roles of the Wnt signaling pathway during ocular vascular development and in vascular eye diseases, and pharmaceutical approaches targeting the Wnt signaling as potential treatment options.

Interplay of the Norrin and Wnt7a/Wnt7b signaling systems in blood-brain barrier and blood-retina barrier development and maintenance

β-Catenin signaling controls the development and maintenance of the blood-brain barrier (BBB) and the blood-retina barrier (BRB), but the division of labor and degree of redundancy between the two principal ligand-receptor systems-the Norrin and Wnt7a/Wnt7b systems-are incompletely defined. Here, we present a loss-of-function genetic analysis of postnatal BBB and BRB maintenance in mice that shows striking threshold and partial redundancy effects. In particular, the combined loss of Wnt7a and Norrin or Wnt7a and Frizzled4 (Fz4) leads to anatomically localized BBB defects that are far more severe than observed with loss of Wnt7a, Norrin, or Fz4 alone. In the cerebellum, selective loss of Wnt7a in glia combined with ubiquitous loss of Norrin recapitulates the phenotype observed with ubiquitous loss of both Wnt7a and Norrin, implying that glia are the source of Wnt7a in the cerebellum. Tspan12, a coactivator of Norrin signaling in the retina, is also active in BBB maintenance but is less potent than Norrin, consistent with a model in which Tspan12 enhances the amplitude of the Norrin signal in vascular endothelial cells. Finally, in the context of a partially impaired Norrin system, the retina reveals a small contribution to BRB development from the Wnt7a/Wnt7b system. Taken together, these experiments define the extent of CNS region-specific cooperation for several components of the Norrin and Wnt7a/Wnt7b systems, and they reveal substantial regional heterogeneity in the extent to which partially redundant ligands, receptors, and coactivators maintain the BBB and BRB.

Prenatal diagnosis of familial exudative vitreoretinopathy and Norrie disease

Background

Both familial exudative vitreoretinopathy (FEVR) and Norrie disease (ND) are hereditary retinal disorders which can cause severe visual impairment and blindness at a young age. The present study aimed to report the use of antenatal genetic testing and ultrasound in the diagnosis and counseling of FEVR and ND.

Methods

Amniocentesis and ultrasonography were performed in high‐risk mothers, with children having FEVR or ND, to predict severe ocular abnormalities.

Results

Case 1: A homozygous NDP mutation (c.376T>C, NM_000266) was detected in the proband and his mother. Molecular prenatal analysis of the fetal DNA revealed no mutations. No ocular abnormalities were detected on ultrasonography. The pregnancy progressed uneventfully to a normal outcome. Case 2: A novel heterozygous FZD4 mutation (c.1010dupA, NM_012193) was detected in the proband and his mother. The same mutation was detected in the fetus, but ultrasonography showed no ocular abnormalities. A healthy baby boy with stage 1 FEVR was born after an uneventful pregnancy. Case 3: Deletions of exons 2 and 3 in the NDP were found in the proband and his mother. The same deletion mutation was detected in the female fetus, but the ultrasound scan was normal. The pregnancy progressed uneventfully to a normal outcome.

Conclusions

To our knowledge, antenatal genetic analyses were used in conjunction with ultrasound for the first time, to diagnose FEVR and ND, and predict the postnatal prognoses in at‐risk babies.

Modeling Rare Bone Diseases in Animals

PURPOSE OF REVIEW

The goal of this review is to highlight some of the considerations involved in creating animal models to study rare bone diseases and then to compare and contrast approaches to creating such models, focusing on the advantages and novel opportunities offered by the CRISPR-Cas system.

RECENT FINDINGS

Gene editing after creation of double-stranded breaks in chromosomal DNA is increasingly being used to modify animal genomes. Multiple tools can be used to create such breaks, with the newest ones being based on the bacterial adaptive immune system known as CRISPR/Cas. Advances in gene editing have increased the ease and speed, while reducing the cost, of creating novel animal models of disease. Gene editing has also expanded the number of animal species in which genetic modification can be performed. These changes have significantly increased the options for investigators seeking to model rare bone diseases in animals.

Developmental vascular regression is regulated by a Wnt/β-catenin, MYC and CDKN1A pathway that controls cell proliferation and cell death

Normal development requires tight regulation of cell proliferation and cell death. Here, we have investigated these control mechanisms in the hyaloid vessels, a temporary vascular network in the mammalian eye that requires a Wnt/β-catenin response for scheduled regression. We investigated whether the hyaloid Wnt response was linked to the oncogene Myc, and the cyclin-dependent kinase inhibitor CDKN1A (P21), both established regulators of cell cycle progression and cell death. Our analysis showed that the Wnt pathway co-receptors LRP5 and LRP6 have overlapping activities that mediate the Wnt/β-catenin signaling in hyaloid vascular endothelial cells (VECs). We also showed that both Myc and Cdkn1a are downstream of the Wnt response and are required for hyaloid regression but for different reasons. Conditional deletion of Myc in VECs suppressed both proliferation and cell death. By contrast, conditional deletion of Cdkn1a resulted in VEC overproliferation that countered the effects of cell death on regression. When combined with analysis of MYC and CDKN1A protein levels, this analysis suggests that a Wnt/β-catenin and MYC-CDKN1A pathway regulates scheduled hyaloid vessel regression.