ZNF408 is mutated in familial exudative vitreoretinopathy and is crucial for the development of zebrafish retinal vasculature

Structural and functional annotation of PR/SET Domain (PRDM) protein family: In-silico study elaborating role of PRDM12 mutation in congenital insensitivity to pain

Congenital insensitivity to pain (CIP), classified as a type of hereditary sensory and autonomic neuropathies, is a rare disease in which the affected individuals fail to perceive sensation of pain. One of the PR/SET Domain Proteins, PRDM12, has been identified in recent past as a candidate gene for congenital insensitivity to pain. In the present study, we performed whole exome sequencing in a Pakistani family with CIP phenotype to ascertain the causative mutation. We identified a previously described alanine repeat duplication in PRDM12 (Ala353_Ala359dup) in this family. After this, we performed structural annotations for PR/SET Domain (PRDM) containing protein family to prognosticate the potential hypothetical structure of PRDM proteins with physical and chemical parameters. Out of nineteen members of this family, four members (PRDM5, PRDM8, PRDM12 and PRDM13) were specially focused because of their role in neurological disorders. Predictions about structure and interactions of these proteins revealed novel interacting molecules and pathways. Detailed in silico analysis of PRDM12 was performed to elaborate importance of its domain structure in interaction with other proteins and its role in pain insensitivity phenotype. These results have substantially enhanced our understanding regarding the etiology of congenital pain insensitivity and would stimulate further research on therapy and prevention.

Identification of Gene Mutations in Atypical Retinopathy of Prematurity Cases

Purpose

We have observed that some preterm infants whose fundus appears very similar to eyes with familial exudative vitreoretinopathy (FEVR) present with atypical retinopathy of prematurity (ROP). To establish a definitive diagnosis and explore the possible genetic mechanism of atypical ROP, we performed gene sequencing of these cases using next-generation sequencing technology.

Methods

A retrospective review of infants who presented with atypical ROP from October 2013 to February 2017 was performed. The data included gender, gestational age at birth, birth weight, family history, systemic disorders, and age-appropriate ophthalmic examinations. Fundus fluorescein angiography (FFA) of the parents was also performed. Peripheral blood was collected from the patients and their parents to sequence genes. Gene mutations were analysed.

Results

Genetic testing revealed that 9 infants had FEVR-related disease-causing gene mutations. Nine gene mutations were detected; 5 had already been reported, and the other 4 were novel. In the 18 eyes of these 9 patients, 9 eyes exhibited severe ROP. 5 cases had a positive family history.

Conclusions

Gene mutations of low-density-lipoprotein receptor-related protein 5(LRP5), frizzled-4(FZD4), Norrie disease protein (NDP), and tetraspanin-12(TSPAN12) may play a role in the pathogenesis of ROP and cause atypical ROP or preterm FEVR. The fundus lesions of ROP patients with disease-causing gene mutations were more serious. ROP cases should be carefully differentiated from preterm FEVR cases.

Novel variants in familial exudative vitreoretinopathy patients with KIF11 mutations and the Genotype-Phenotype correlation

Familial exudative vitreoretinopathy (FEVR) is an inherited disease characterized by abnormal development of retinal vasculature. KIF11 mutations were identified to be associated with FEVR in recent years. The purpose of this study was to investigate novel variants and describe associated ocular and extraocular phenotypes in FEVR patients with KIF11 mutations. Herein, 417 probands with clinical diagnosis of FEVR were enrolled. Genetic testing and ophthalmic examinations were performed in all subjects, and the genotype-phenotype correlation was analyzed. Overall, KIF11 mutation was identified in nine probands (9/417, 2.2%) among the patients with FEVR phenotype. There were six males and three females whose median age was six months (range: four months to six years old) at first visit. Among the detected mutations, five (55.6%) were frameshift, two (22.2%) were missense, one (11.1%) nonsense, and one (11.1%) splicing. Seven of these KIF11 mutations were detected as novel. Four (4/9, 44.4%) of the mutations were de novo. Clinical examinations showed that: four probands presented with bilateral falciform retinal fold; two with bilateral tractional retinal detachment; one was observed tractional retinal detachment in one eye and retinal fold in the other eye; one had falciform retinal fold in one eye and chorioretinal atrophy in the other eye; one exhibited rhegmatogenous retinal detachment in the left eye. Six of the probands were detected to have microcephaly. In conclusion: Most (5/9,55.6%) of the causative mutations were frameshift, and nearly half (4/9, 44.4%) of the mutations were de novo. Most (8/9, 88.9%) patients with KIF11 mutations showed typical ocular manifestations of severe FEVR. Majority (6/9, 66.7%) of the probands had a KIF11 mutation and were detected to have microcephaly. Seven of these harbored KIF11 mutations detected to be novel.

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.

Modeling ZNF408-Associated FEVR in Zebrafish Results in Abnormal Retinal Vasculature

Purpose

Familial exudative vitreoretinopathy (FEVR) is an inherited retinal disease in which the retinal vasculature is affected. Patients with FEVR typically lack or have abnormal vasculature in the peripheral retina, the outcome of which can range from mild visual impairment to complete blindness. A missense mutation (p.His455Tyr) in ZNF408 was identified in an autosomal dominant FEVR family. Little, however, is known about the molecular role of ZNF408 and how its defect leads to the clinical features of FEVR.

Methods

Using CRISPR/Cas9 technology, two homozygous mutant zebrafish models with truncated znf408 were generated, as well as one heterozygous and one homozygous missense znf408 model in which the human p.His455Tyr mutation is mimicked.

Results

Intriguingly, all three znf408-mutant zebrafish strains demonstrated progressive retinal vascular pathology, initially characterized by a deficient hyaloid vessel development at 5 days postfertilization (dpf) leading to vascular insufficiency in the retina. The generation of stable mutant lines allowed long-term follow up studies, which showed ectopic retinal vascular hyper-sprouting at 90 dpf and extensive vascular leakage at 180 dpf.

Conclusions

Together, our data demonstrate an important role for znf408 in the development and maintenance of the vascular system within the retina.

Clinical and genetical features of probands and affected family members with familial exudative vitreoretinopathy in a large Chinese cohort

Aims

To explore the clinical and genetical features of families with strictly confirmed familial exudative vitreoretinopathy (FEVR) in a large Chinese cohort.

Methods

A retrospective chart review study was conducted on the FEVR families diagnosed by both angiography and targeted next-generation sequencing in six FEVR known genes (FZD4, LRP5, TSPAN12, NDP, KIF11, ZNF408) in the probands and at least one first-degree family member. Variation in expressivity and severity was evaluated in different gene groups.

Results

105 FEVR families (223 FEVR affected subjects with 434 eyes) met the inclusion criteria. There were 105 probands with mean age of 3.8 years old and 118 affected family members of 32.7 years old averagely. Mutations in FZD4 were most prevalent (33.33%), followed by LRP5 (29.52%), TSPAN12 (22.86%), NDP (5.71%), KIF11 (1.9%) and ZNF408 (0.95%). 81% of the probands were classified as stage 4 or worse which most prevalently contributed to FZD4 mutations. All of the three affected family members with stage 4 or worse carried FZD4 variants. More than half (51.43%) of the probands in FZD4 group showed asymmetry. Unilateral FEVR was detected in 11 (10.5%) families consisting of six probands and six affected relatives, and FZD4 mutations accounted for 63.64% of all the cases with variant (c.1282_1285del, p. D428fs) identified in three families.

Conclusions

Genotype-phenotype correlation in FEVR was complex with family dependent. Mutations in FZD4 might initiate the most diverse and asymmetric phenotypes.

Select pediatric vitreoretinal disease in the setting of Turner's syndrome

Purpose

To report 2 cases of pediatric vitreoretinal disease in the setting of Turner's syndrome.

Observations

A 4-year-old girl with Turner's syndrome was referred for evaluation of a tractional retinal detachment in the right eye. Fundoscopic examination disclosed temporal dragging of the macula in the right eye, and vascular nonperfusion in the right and left eyes. Genetic testing revealed a novel frameshift mutation in the LRP5 gene consistent with familial exudative vitreoretinopathy (FEVR). The patient was treated with laser. A 14-year-old girl with Turner's syndrome presented with nyctalopia. Dilated fundus exam disclosed peri-foveal pigmentary changes and peripheral bone spicules. Full-field electroretinography demonstrated decreased rod and cone responses, consistent with retinitis pigmentosa (RP).

Conclusions and importance

Vitreoretinal disease, including RP and FEVR, is rarely observed in patients with Turner's syndrome.

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.

Genetic Association of Age-Related Macular Degeneration and Polypoidal Choroidal Vasculopathy

Age-related macular degeneration (AMD) and polypoidal choroidal vasculopathy (PCV) are leading causes of irreversible blindness among the elderly population in developed countries. Although being considered as different subtypes of a same disease, neovascular AMD and PCV have differences in clinical, epidemiological, therapeutic, and genetic profiles. Both AMD and PCV are complex diseases involving multiple genetic and environmental risk factors. Different genetic strategies have been adopted to discover associated genes and variants for neovascular AMD and PCV, including genome-wide association study (GWAS), next-generation sequencing (NGS) based sequence analysis, and candidate gene analyses. So far, a number of susceptible genes have been identified for AMD and/or PCV, such as CFH, ARMS2-HTRA1, C2-CFB-SKIV2L, C3, CETP, and FGD6. Although many of these genes are shared by AMD and PCV, some showed difference between them, such as ARMS2-HTRA1 and FGD6. Also, some of the genes showed ethnic diversities, such as the CFH p.Tyr402His variant. Further larger-scale genomic studies should be warranted to identify more susceptibility genes for AMD and, in particular, PCV among different populations, and differentiate the genetic architectures between neovascular AMD and PCV.

Characterization of a novel pathogenic variation c.1237T>G in the FZD4 gene presenting new inheritance from an Iranian individual suffering vitreoretinopathy

Whole Exome Sequencing (WES) has been used increasingly in genetic determination of various known and unknown genetic disorders. Various genes are involved in the development of the vascular network of retina. Assessment of a collection of these genes could be provided by WES. Here we used WES for a patient suffering vitreoretinopathy to detect the disease causing variant. Sanger sequencing has been applied for variant verification and allelic segregation. After analysis of WES data we found a new variant c.1237T>G in the FZD4 locus which causes retinopathy of prematurity and exudative vitreoretinopathy (MIM number: 133780). Sanger sequencing showed this single nucleotide variation inherited as homozygous in the patient and heterozygous in her unaffected parents. Notably, bioinformatics analysis predicted the variant as disease causing and it has not been described yet in home datasets and public SNP databases. FZD4 mutations are mostly inherited as autosomal dominant traits. Our findings showed the first autosomal recessive inheritance of the FZD4 gene related retinopathy. On the other hand, our data shed light on the significance of an Exome sequencing application as a genetic test to identify and characterize the comprehensive spectrum of genetic variation and classification for patients with retinopathies.

The spectrum of genetic mutations in patients with asymptomatic mild familial exudative vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is a disease exhibits a wide range of clinical signs, ranging mild peripheral retinal vascular anomalies to severe retinal detachments. Individuals with mild FEVR are frequently asymptomatic with good visual function and are often undiagnosed. However, little is known about the genetic characters of the cohort. The purpose of this study was to investigate the clinical characteristics and genetic spectrum of in patients with asymptomatic mild FEVR. Herein, sixty-two patients (124 eyes) with asymptomatic mild FEVR were studied in a case series. Comprehensive ophthalmic examinations and genetic testing were performed in all patients. Clinical examinations showed that the avascular zone was seen in all 124 eyes and was the most common abnormality observed. Increased vessel branching and straightened peripheral vessel branches were found in 122 (98.4%) eyes. Late-phase angiographic posterior and peripheral leakage (LAPPEL) was observed in 80 (64.5%) eyes and V-shape degeneration was noted in 36 (29.0%) eyes. Other manifestations including extensive anastomoses, retinal ridges, and extraretinal neovascularization, which were detected in 30 (24.2%), 10 (8.1%) and 2 (1.6%) eyes respectively. Overall, pathogenic mutations were identified in 48.4% (30/62) of individuals with asymptomatic mild FEVR. Mutations in FZD4, LRP5, TSPAN12, and KIF11 were detected in 21.0% (13/62), 12.9% (8/62), 12.9% (8/62), and 1.6% (1/62) of our patients respectively. Ten novel mutations were found. In conclusion: Pathogenic mutations in the known FEVR-associated genes were detected in nearly half (48.4%) of the asymptomatic mild FEVR cohort. Among these mutations, FZD4 was predominant, appearing in 21.0% of all individuals. Patients with asymptomatic mild FEVR should receive timely examinations, lifelong monitoring, and some of them need preventive therapy and treatment. Additionally, we discovered 10 novel variants, which may enable a deeper understanding of this disease.

Microcornea, Posterior Megalolenticonus, Persistent Fetal Vasculature, and Coloboma Syndrome Associated With a New Mutation in ZNF408

The authors report a case of a 6-week-old girl with microphthalmia, posterior lenticonus, persistent fetal vasculature, and coloboma of the right eye, with morning glory disc anomaly and falciform retinal folds of the left eye. Genetic testing revealed a previously unreported mutation (c.1471A>G [p.T491A]) in the gene ZNF408, which has been associated with autosomal recessive retinitis pigmentosa and autosomal dominant familial exudative vitreoretinopathy. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:253-256.].

Macular Microvascular Findings in Familial Exudative Vitreoretinopathy on Optical Coherence Tomography Angiography

BACKGROUND AND OBJECTIVE

To describe depth-resolved macular microvasculature abnormalities in patients with familial exudative vitreoretinopathy (FEVR) using optical coherence tomography angiography (OCTA).

PATIENTS AND METHODS

Twenty-two eyes (11 eyes of six patients with FEVR and 11 control eyes) were imaged with OCTA. Graders qualitatively analyzed the OCTA images of the superficial and deep vascular complexes for abnormal vascular features and compared to fluorescein angiography (FA).

RESULTS

Seven of 11 eyes with FEVR displayed abnormal macular vascular findings. Abnormalities in the superficial vascular complex included dilation, disorganization, straightening, heterogeneous vessel density, and curls/loops. In the deep vascular complex, abnormalities included areas of decreased density, disorganization, curls/loops, and "end bulbs." Except for dragging and straightening of the vessels, none of these macular features were visible on FA.

CONCLUSION

OCTA revealed marked macular abnormalities in eyes with FEVR that have not been previously observed with FA alone, suggesting this is more than a disease of the retinal periphery and involves macular and deep retinal vasculature abnormalities. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:322-329.].

A Novel Mutation in the NDP Gene is Associated with Familial Exudative Vitreoretinopathy in a Southern Chinese Family

Aims: To report a clinical and genetic investigation of a southern Chinese family with X-linked recessive exudative vitreoretinopathy and vitreous hemorrhage. Materials and Methods: We collected clinical data from a proband and his family. Complete ophthalmic examinations were carried out on the proband. Genomic DNA was sampled from either peripheral blood or buccal swabs of 13 individuals, and whole exome sequencing was performed on the proband and his parents. Sanger sequencing was utilized to validate the probable mutation in the proband and the remaining family members. Results: Seventeen family members, with three affected individuals were included in this study. The predominant phenotypes, with highly variable expressivity, were vitreoretinopathy, vitreous hemorrhage, retinal detachment, and even phthisis. A Y53C mutation in the NDP gene (HGNC:7678; NM_000266.3:exon2:c.A158G:p.Y53C;NP_000257.1:p.Tyr53Cys) was identified as being the most probable pathogenic mutation. Co-segregation of the mutation with the variable phenotype was confirmed within the proband's family. Conclusions: The clinical appearance of familial exudative vitreoretinopathy was highly variable, among the three affected male family members. A novel missense mutation in the NDP gene was identified as the pathogenic mutation.

Identification of novel variants in the FZD4 gene associated with familial exudative vitreoretinopathy in Chinese families

BACKGROUND

Familial exudative vitreoretinopathy (FEVR, OMIM 133780) is a severe hereditary retinal disease characterized by incomplete retinal vascular development and pathological neovascularization. It has been reported that variants in nine genes are associated with FEVR, but they can only explain approximately 50% of FEVR patients, suggesting that other FEVR-associated variants or genes remain to be discovered.

METHODS

Whole-exome sequencing (WES) was carried out to analyse genomic DNA samples from the probands of 68 families with FEVR. Sanger sequencing was used to verify all identified variants. Western blot analysis was utilized to detect the expression of the variant mutant proteins. A luciferase assay was conducted to test the receptor activity of the mutant FZD4 proteins in Norrin-β-catenin signaling.

RESULTS

Seven heterozygous FZD4 variants were found to cause FEVR in seven families, including six missense variants and one deletion variant: c.182C>T (p.T61I), c.205C>T (p.H69Y), c.217_234del (p.73T_78Qdel), c.264C>A (p.Y88X), c.344G>T (p.G115V), c.678G>A (p.W226X) and c.1310T>C (p.I437T). Among these variants, c.205C>T (p.H69Y) and c.678G>A (p.W226X) are known FEVR-causing variants, while the other five variants are novel pathogenic variants.

CONCLUSION

Our study revealed the cause of FEVR in seven Chinese families and identified five novel pathogenic variants in FZD4, which expanded the mutation spectrum of FEVR in the Chinese population. These findings also provided further support for using WES in the clinical diagnosis of FEVR.

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.

Functional Genomics of the Retina to Elucidate its Construction and Deconstruction

The retina is the light sensitive part of the eye and nervous tissue that have been used extensively to characterize the function of the central nervous system. The retina has a central position both in fundamental biology and in the physiopathology of neurodegenerative diseases. We address the contribution of functional genomics to the understanding of retinal biology by reviewing key events in their historical perspective as an introduction to major findings that were obtained through the study of the retina using genomics, transcriptomics and proteomics. We illustrate our purpose by showing that most of the genes of interest for retinal development and those involved in inherited retinal degenerations have a restricted expression to the retina and most particularly to photoreceptors cells. We show that the exponential growth of data generated by functional genomics is a future challenge not only in terms of storage but also in terms of accessibility to the scientific community of retinal biologists in the future. Finally, we emphasize on novel perspectives that emerge from the development of redox-proteomics, the new frontier in retinal biology.

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.

Zinc Nutrition and Inflammation in the Aging Retina

Zinc is an essential nutrient for human health. It plays key roles in maintaining protein structure and stability, serves as catalytic factor for many enzymes, and regulates diverse fundamental cellular processes. Zinc is important in affecting signal transduction and, in particular, in the development and integrity of the immune system, where it affects both innate and adaptive immune responses. The eye, especially the retina-choroid complex, has an unusually high concentration of zinc compared to other tissues. The highest amount of zinc is concentrated in the retinal pigment epithelium (RPE) (RPE-choroid, 292 ± 98.5 µg g^-1 dry tissue), followed by the retina (123 ± 62.2 µg g^-1 dry tissue). The interplay between zinc and inflammation has been explored in other parts of the body but, so far, has not been extensively researched in the eye. Several lines of evidence suggest that ocular zinc concentration decreases with age, especially in the context of age-related disease. Thus, a hypothesis that retinal function could be modulated by zinc nutrition is proposed, and subsequently trialled clinically. In this review, the distribution and the potential role of zinc in the retina-choroid complex is outlined, especially in relation to inflammation and immunity, and the clinical studies to date are summarized.

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.

Spectrum of Variants in 389 Chinese Probands With Familial Exudative Vitreoretinopathy

Purpose

To identify potentially pathogenic variants (PPVs) in Chinese familial exudative vitreoretinopathy (FEVR) patients in FZD4, LRP5, NDP, TSPAN12, ZNF408, and KIF11 genes.

Methods

Blood samples were collected from probands and their parent(s). Genomic DNA was analyzed by next-generation sequencing, and the sequence of selected variants were validated by Sanger sequencing. The potential pathogenicity of a variant was evaluated by in silico analysis and by cosegregation of the variant with disease. Each proband was subjected to comprehensive retinal examinations, and the severity of FEVR was individually graded for each eye. Whenever possible, fundus fluorescein angiography was obtained and analyzed for parent(s) of each proband. Variation in mutation expressivity was analyzed.

Results

Three hundred eighty-nine consecutive FEVR patients from 389 families participated in this study. About 74% of the probands were children younger than 7 years old. One hundred one PPVs, 49 variants with unknown significance (VUS), were identified, including 73 novel PPVs and 38 novel VUS. One hundred ten probands carried PPV (28.3%), and 51 probands carried VUS (13.1%). PPVs in FZD4, LRP5, TSPAN12, NDP, ZNF408, and KIF11 were found in 8.48%, 9.00%, 5.91%, 4.63%, 0.77%, and 0.77% of the cohort, respectively. Probands carrying PPVs in NDP and KIF11 had more severe FEVR in general than those carrying PPVs in other genes. Overall, variants in LRP5 and FZD4 showed more significant variation in phenotype than variants in TSPAN12 and NDP genes.

Conclusions

Our study expanded the spectrum of PPVs associated with FEVR.

Allele frequency analysis of variants reported to cause autosomal dominant inherited retinal diseases question the involvement of 19% of genes and 10% of reported pathogenic variants

BACKGROUND

Next generation sequencing (NGS) generates a large amount of genetic data that can be used to better characterise disease-causing variants. Our aim was to examine allele frequencies of sequence variants reported to cause autosomal dominant inherited retinal diseases (AD-IRDs).

METHODS

Genetic information was collected from various databases, including PubMed, the Human Genome Mutation Database, RETNET and gnomAD.

RESULTS

We generated a database of 1223 variants reported in 58 genes, including their allele frequency in gnomAD that contains NGS data of over 138 000 individuals. While the majority of variants are not represented in gnomAD, 138 had an allele count of >1 and were examined carefully for various aspects including cosegregation and functional analyses. The analysis revealed 122 variants that were reported pathogenic but unlikely to cause AD-IRDs. Interestingly, in some cases, these unlikely pathogenic variants were the only ones reported to cause disease in AD inheritance pattern for a particular gene, therefore raising doubt regarding the involvement of 11 (19%) of the genes in AD-IRDs.

CONCLUSION

We predict that these data are not limited to a specific disease or inheritance pattern since non-pathogenic variants were mistakenly reported as pathogenic in various diseases. Our results should serve as a warning sign for geneticists, variant database curators and sequencing panels' developers not to automatically accept reported variants as pathogenic but cross-reference the information with large databases.

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.

A Novel Pathogenic Variant in NDP Gene With Incomplete Penetrance Manifests as X-Linked Familial Exudative Vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is a rare hereditary ocular disorder characterized by incomplete or abnormal development of peripheral retinal vasculature. The genes responsible for this disorder are associated with the wingless-related integration site (Wnt) signaling pathway, a critical pathway for the development of normal retinal vasculature. A pathogenic variant in any one of these genes may disrupt retinal vasculogenesis. Furthermore, the type and number of pathogenic variants may influence the severity of disease and clinical course. Here, the authors identify a novel pathogenic variant in the NDP gene, not previously described in the literature. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:120-124.].

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.

Familial Exudative Retinopathy: A Case and Family Analysis

Familial exudative vitreoretinopathy (FEVR) is a rare inherited disorder of retinal angiogenesis. A 49-year-old male patient was referred to our clinic for retinal vascular occlusion. His history, clinical findings, and fundus fluorescein angiography findings were evaluated. Family members were called and eye examinations were performed. Our patient was not born preterm and he reported decreased visual acuity after a traffic accident during childhood. He had laser treatment when he was 12 years old and again 1 month before our examination. He also had laser-assisted in situ keratomileusis surgery for both eyes in 2002. On examination, his visual acuity was 0.4 in the right eye and 0.3 in the left eye. He had cortical cataract in both eyes. Macula OCT revealed macular contour irregularity due to epiretinal membrane in his right eye and minimal perifoveal thinning in his left eye. On fundus photography, straightening of the retinal vessels, macular dragging, retinal folds on temporal retina, preretinal fibrosis, and laser spots were seen. FFA revealed avascular retinal areas with incomplete laser spots in the temporal, inferior, and superior parts of retina. He also had neovascularization with leakage in the temporal retina of his right eye. The patient’s brother, who was also born at full term, also had excessive branching of the vascular structures in the temporal peripheral retina, non-perfused cord vessels and avascular areas. In light of all these findings, we diagnosed our patient with Stage 2A FEVR and his brother with Stage 1 FEVR. In summary, FEVR is a clinically diagnosed disease. Because FEVR is inherited and potentially sight-threatening, family examination is helpful and important so that affected family members can be diagnosed and followed up.

Familial Exudative Vitreoretinopathy: Pathophysiology, Diagnosis, and Management

Familial exudative vitreoretinopathy (FEVR) is a heritable vitreoretinopathy characterized by anomalous retinal vascular development. The principal feature of the disease is an avascular peripheral retina. This in turn can cause further pathological changes including neovascularization, exudation, hemorrhage, and retinal detachment. The biological basis of the disease is thought to be from defects in the Wnt signaling pathway. Many gene mutations have been implicated, and these can be inherited in an autosomal dominant (most common), autosomal recessive, and X-linked recessive fashion. Examination with wide-field fluorescein angiography is essential and can identify the disease in its earlier stages, enabling timely treatment, in addition to helping identify asymptomatic family members. The current treatment paradigm involves laser photocoagulation of the avascular peripheral retina for neovascular sequelae and vitreoretinal surgery for progressive retinal detachment. Further studies are underway to better characterize this complex vitreoretinopathy.

TSPAN12 Is a Norrin Co-receptor that Amplifies Frizzled4 Ligand Selectivity and Signaling

Accessory proteins in Frizzled (FZD) receptor complexes are thought to determine ligand selectivity and signaling amplitude. Genetic evidence indicates that specific combinations of accessory proteins and ligands mediate vascular β-catenin signaling in different CNS structures. In the retina, the tetraspanin TSPAN12 and the ligand norrin (NDP) mediate angiogenesis, and both genes are linked to familial exudative vitreoretinopathy (FEVR), yet the molecular function of TSPAN12 remains poorly understood. Here, we report that TSPAN12 is an essential component of the NDP receptor complex and interacts with FZD4 and NDP via its extracellular loops, consistent with an action as co-receptor that enhances FZD4 ligand selectivity for NDP. FEVR-linked mutations in TSPAN12 prevent the incorporation of TSPAN12 into the NDP receptor complex. In vitro and in Xenopus embryos, TSPAN12 alleviates defects of FZD4 M105V, a mutation that destabilizes the NDP/FZD4 interaction. This study sheds light on the poorly understood function of accessory proteins in FZD signaling.

A map of human PRDM9 binding provides evidence for novel behaviors of PRDM9 and other zinc-finger proteins in meiosis

PRDM9 binding localizes almost all meiotic recombination sites in humans and mice. However, most PRDM9-bound loci do not become recombination hotspots. To explore factors that affect binding and subsequent recombination outcomes, we mapped human PRDM9 binding sites in a transfected human cell line and measured PRDM9-induced histone modifications. These data reveal varied DNA-binding modalities of PRDM9. We also find that human PRDM9 frequently binds promoters, despite their low recombination rates, and it can activate expression of a small number of genes including CTCFL and VCX. Furthermore, we identify specific sequence motifs that predict consistent, localized meiotic recombination suppression around a subset of PRDM9 binding sites. These motifs strongly associate with KRAB-ZNF protein binding, TRIM28 recruitment, and specific histone modifications. Finally, we demonstrate that, in addition to binding DNA, PRDM9's zinc fingers also mediate its multimerization, and we show that a pair of highly diverged alleles preferentially form homo-multimers.

Targeted next-generation sequencing analysis identifies novel mutations in families with severe familial exudative vitreoretinopathy

PURPOSE

Familial exudative vitreoretinopathy (FEVR) is a genetically and clinically heterogeneous disease, characterized by failure of vascular development of the peripheral retina. The symptoms of FEVR vary widely among patients in the same family, and even between the two eyes of a given patient. This study was designed to identify the genetic defect in a patient cohort of ten Chinese families with a definitive diagnosis of FEVR.

METHODS

To identify the causative gene, next-generation sequencing (NGS)-based target capture sequencing was performed. Segregation analysis of the candidate variant was performed in additional family members by using Sanger sequencing and quantitative real-time PCR (QPCR).

RESULTS

Of the cohort of ten FEVR families, six pathogenic variants were identified, including four novel and two known heterozygous mutations. Of the variants identified, four were missense variants, and two were novel heterozygous deletion mutations [LRP5, c.4053 DelC (p.Ile1351IlefsX88); TSPAN12, EX8Del]. The two novel heterozygous deletion mutations were not observed in the control subjects and could give rise to a relatively severe FEVR phenotype, which could be explained by the protein function prediction.

CONCLUSIONS

We identified two novel heterozygous deletion mutations [LRP5, c.4053 DelC (p.Ile1351IlefsX88); TSPAN12, EX8Del] using targeted NGS as a causative mutation for FEVR. These genetic deletion variations exhibit a severe form of FEVR, with tractional retinal detachments compared with other known point mutations. The data further enrich the mutation spectrum of FEVR and enhance our understanding of genotype-phenotype correlations to provide useful information for disease diagnosis, prognosis, and effective genetic counseling.

Genotype-Phenotype Characterization of Novel Variants in Six Italian Patients with Familial Exudative Vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is a complex disorder characterized by incomplete development of the retinal vasculature. Here, we report the results obtained on the spectrum of genetic variations and correlated phenotypes found in a cohort of Italian FEVR patients. Eight probands (age range 7–19 years) were assessed by genetic analysis and comprehensive age-appropriate ophthalmic examination. Genetic testing investigated the genes most widely associated in literature with FEVR: FZD4, LRP5, TSPAN12, and NDP. Clinical and genetic evaluations were extended to relatives of probands positive to genetic testing. Six out of eight probands (75%) showed a genetic variation probably related to the phenotype. We identified four novel genetic variants, one variant already described in association with Norrie disease and one previously described linked to autosomal dominant FEVR. Pedigree analysis of patients led to the classification of four autosomal dominant cases of FEVR (caused by FZD4 and TSPAN12 variants) and two X-linked FEVR probands (NDP variants). None of the patients showed variants in the LRP5 gene. This study represents the largest cohort study in Italian FEVR patients. Our findings are in agreement with the previous literature confirming that FEVR is a clinically and genetically heterogeneous retinal disorder, even when it manifests in the same family.

Genetic characterization and disease mechanism of retinitis pigmentosa; current scenario

Retinitis pigmentosa is a group of genetically transmitted disorders affecting 1 in 3000-8000 individual people worldwide ultimately affecting the quality of life. Retinitis pigmentosa is characterized as a heterogeneous genetic disorder which leads by progressive devolution of the retina leading to a progressive visual loss. It can occur in syndromic (with Usher syndrome and Bardet-Biedl syndrome) as well as non-syndromic nature. The mode of inheritance can be X-linked, autosomal dominant or autosomal recessive manner. To date 58 genes have been reported to associate with retinitis pigmentosa most of them are either expressed in photoreceptors or the retinal pigment epithelium. This review focuses on the disease mechanisms and genetics of retinitis pigmentosa. As retinitis pigmentosa is tremendously heterogeneous disorder expressing a multiplicity of mutations; different variations in the same gene might induce different disorders. In recent years, latest technologies including whole-exome sequencing contributing effectively to uncover the hidden genesis of retinitis pigmentosa by reporting new genetic mutations. In future, these advancements will help in better understanding the genotype-phenotype correlations of disease and likely to develop new therapies.

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.

Live imaging of primary ocular vasculature formation in zebrafish

Ocular vasculature consists of the central retinal and ciliary vascular systems, which are essential to maintaining visual function. Many researchers have attempted to determine their origins and development; however, the detailed, stepwise process of ocular vasculature formation has not been established. In zebrafish, two angioblast clusters, the rostral and midbrain organizing centers, form almost all of the cranial vasculature, including the ocular vasculature, and these are from where the cerebral arterial and venous angioblast clusters, respectively, differentiate. In this study, we first determined the anatomical architecture of the primary ocular vasculature and then followed its path from the two cerebral angioblast clusters using a time-lapse analysis of living Tg(flk1:EGFP)k7 zebrafish embryos, in which the endothelial cells specifically expressed enhanced green fluorescent protein. We succeeded in capturing images of the primary ocular vasculature formation and were able to determine the origin of each ocular vessel. In zebrafish, the hyaloid and ciliary arterial systems first organized independently, and then anastomosed via the inner optic circle on the surface of the lens by the lateral transfer of the optic vein. Finally, the choroidal vascular plexus formed around the eyeball to complete the primary ocular vasculature formation. To our knowledge, this study is the first to report successful capture of circular integration of the optic artery and vein, lateral transfer of the optic vein to integrate the hyaloidal and superficial ocular vasculatures, and formation of the choroidal vascular plexus. Furthermore, this new morphological information enables us to assess the entire process of the primary ocular vasculature formation, which will be useful for its precise understanding.

Unravelling the genetics of inherited retinal dystrophies: Past, present and future

The identification of the genes underlying monogenic diseases has been of interest to clinicians and scientists for many years. Using inherited retinal dystrophies as an example of monogenic disease we describe the history of molecular genetic techniques that have been pivotal in the discovery of disease causing genes. The methods that were developed in the 1970's and 80's are still in use today but have been refined and improved. These techniques enabled the concept of the Human Genome Project to be envisaged and ultimately realised. When the successful conclusion of the project was announced in 2003 many new tools and, as importantly, many collaborations had been developed that facilitated a rapid identification of disease genes. In the post-human genome project era advances in computing power and the clever use of the properties of DNA replication has allowed the development of next-generation sequencing technologies. These methods have revolutionised the identification of disease genes because for the first time there is no need to define the position of the gene in the genome. The use of next generation sequencing in a diagnostic setting has allowed many more patients with an inherited retinal dystrophy to obtain a molecular diagnosis for their disease. The identification of novel genes that have a role in the development or maintenance of retinal function is opening up avenues of research which will lead to the development of new pharmacological and gene therapy approaches. Neither of which can be used unless the defective gene and protein is known. The continued development of sequencing technologies also holds great promise for the advent of truly personalised medicine.

Familial exudative vitreoretinopathy presentation as persistent fetal vasculature

Purpose

To illustrate a presentation of familial exudative vitreoretinopathy (FEVR) that can be mistaken for persistent fetal vasculature (PFV) and the importance of wide angle fluorescein angiography in making this distinction. A patient was referred with a unilateral retrolental membrane and retinal detachment from PFV but was found to have FEVR.

Observations

A 4 month-old full-term infant was referred with the diagnosis of PFV based on findings of a dense retrolental membrane and microphthalmia in the left eye. The patient had a near-complete retinal detachment with some exudation. Wide-field fluorescein angiography of the right eye revealed avascular retina and leakage at the vascular/avascular junction. Genetic testing confirmed a mutation in FZD4, supporting the clinical diagnosis of FEVR. Prompt laser therapy to the avascular area in the right eye was performed and lensectomy/vitrectomy with membrane dissection was performed in the left eye.

Conclusions and importance

FEVR can present with great variability between eyes. In patients presenting with findings suggestive of PFV, careful bilateral examination with wide-field fluorescein angiography is helpful. Early diagnosis and treatment are important to preserve visual acuity, especially in the less affected eye.

Zebrafish models of human eye and inner ear diseases

Eye and inner ear diseases are the most common sensory impairments that greatly impact quality of life. Zebrafish have been intensively employed to understand the fundamental mechanisms underlying eye and inner ear development. The zebrafish visual and vestibulo-acoustic systems are very similar to these in humans, and although not yet mature, they are functional by 5days post-fertilization (dpf). In this chapter, we show how the zebrafish has significantly contributed to the field of biomedical research and how researchers, by establishing disease models and meticulously characterizing their phenotypes, have taken the first steps toward therapies. We review here models for (1) eye diseases, (2) ear diseases, and (3) syndromes affecting eye and/or ear. The use of new genome editing technologies and high-throughput screening systems should increase considerably the speed at which knowledge from zebrafish disease models is acquired, opening avenues for better diagnostics, treatments, and therapies.

Anatomical and functional outcomes following vitrectomy for advanced familial exudative vitreoretinopathy: a single surgeon's experience

PURPOSE

To assess the anatomical and functional results of vitreoretinal surgery in patients with advanced familial exudative vitreoretinopathy (FEVR).

METHODS

Retrospective analysis of data for 10 eyes of 9 patients with advanced FEVR who underwent pars plana vitrectomy from March 1997 to May 2015 and had a follow-up of at least 12 months. The primary outcomes were final visual acuity (VA) and anatomical success.

RESULTS

The average age at the time of the surgery was 10.1±6.5 years (range 2 months-18 years). The mean follow-up period was 58.4±75.1 months. The male-to-female ratio was 7/2. The mean number of vitreoretinal operations was 1.5. At the last visit, 7 (70%) eyes had complete or partial retinal attachment. Preoperatively, the mean Snellen VA was 20/4000 (n=8), and in the remaining 2 (20%) eyes it was recorded as 'central, steady and maintained'. At final examination, the mean Snellen VA was 20/330 (n=7), and in the remaining 3 (30%) eyes it was recorded as light perception. At the final visit, 5 eyes (50%) had improved VA, 2 eyes (20%) showed stabilisation, and 3 eyes (30%) with total retinal detachment had a decrease in VA. No progression to glaucoma was observed and no enucleation was necessary.

CONCLUSIONS

Advanced FEVR in young children tends to be more aggressive, leading to severe complications. These cases are challenging and require special consideration. Despite surgery, disease-related complications remain high. However, surgical intervention for advanced FEVR might be of benefit in helping to preserve vision.

The zebrafish eye-a paradigm for investigating human ocular genetics

Although human epidemiological and genetic studies are essential to elucidate the aetiology of normal and aberrant ocular development, animal models have provided us with an understanding of the pathogenesis of multiple developmental ocular malformations. Zebrafish eye development displays in depth molecular complexity and stringent spatiotemporal regulation that incorporates developmental contributions of the surface ectoderm, neuroectoderm and head mesenchyme, similar to that seen in humans. For this reason, and due to its genetic tractability, external fertilisation, and early optical clarity, the zebrafish has become an invaluable vertebrate system to investigate human ocular development and disease. Recently, zebrafish have been at the leading edge of preclinical therapy development, with their amenability to genetic manipulation facilitating the generation of robust ocular disease models required for large-scale genetic and drug screening programmes. This review presents an overview of human and zebrafish ocular development, genetic methodologies employed for zebrafish mutagenesis, relevant models of ocular disease, and finally therapeutic approaches, which may have translational leads in the future.

Pharmacologic Activation of Wnt Signaling by Lithium Normalizes Retinal Vasculature in a Murine Model of Familial Exudative Vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is characterized by delayed retinal vascular development, which promotes hypoxia-induced pathologic vessels. In severe cases FEVR may lead to retinal detachment and visual impairment. Genetic studies linked FEVR with mutations in Wnt signaling ligand or receptors, including low-density lipoprotein receptor-related protein 5 (LRP5) gene. Here, we investigated ocular pathologies in a Lrp5 knockout (Lrp5(-/-)) mouse model of FEVR and explored whether treatment with a pharmacologic Wnt activator lithium could bypass the genetic defects, thereby protecting against eye pathologies. Lrp5(-/-) mice displayed significantly delayed retinal vascular development, absence of deep layer retinal vessels, leading to increased levels of vascular endothelial growth factor and subsequent pathologic glomeruloid vessels, as well as decreased inner retinal visual function. Lithium treatment in Lrp5(-/-) mice significantly restored the delayed development of retinal vasculature and the intralaminar capillary networks, suppressed formation of pathologic glomeruloid structures, and promoted hyaloid vessel regression. Moreover, lithium treatment partially rescued inner-retinal visual function and increased retinal thickness. These protective effects of lithium were largely mediated through restoration of canonical Wnt signaling in Lrp5(-/-) retina. Lithium treatment also substantially increased vascular tubular formation in LRP5-deficient endothelial cells. These findings suggest that pharmacologic activation of Wnt signaling may help treat ocular pathologies in FEVR and potentially other defective Wnt signaling-related diseases.

Fzd4 Haploinsufficiency Delays Retinal Revascularization in the Mouse Model of Oxygen Induced Retinopathy

Mutations in genes that code for components of the Norrin-FZD4 ligand-receptor complex cause the inherited childhood blinding disorder familial exudative vitreoretinopathy (FEVR). Statistical evidence from studies of patients at risk for the acquired disease retinopathy of prematurity (ROP) suggest that rare polymorphisms in these same genes increase the risk of developing severe ROP, implying that decreased Norrin-FZD4 activity predisposes patients to more severe ROP. To test this hypothesis, we measured the development and recovery of retinopathy in wild type and Fzd4 heterozygous mice in the absence or presence of ocular ischemic retinopathy (OIR) treatment. Avascular and total retinal vascular areas and patterning were determined, and vessel number and caliber were quantified. In room air, there was a small delay in retinal vascularization in Fzd4 heterozygous mice that resolved as mice reached maturity suggestive of a slight defect in retinal vascular development. Subsequent to OIR treatment there was no difference between wild type and Fzd4 heterozygous mice in the vaso-obliterated area following exposure to high oxygen. Importantly, after return of Fzd4 heterozygous mice to room air subsequent to OIR treatment, there was a substantial delay in retinal revascularization of the avascular area surrounding the optic nerve, as well as delayed vascularization toward the periphery of the retina. Our study demonstrates that a small decrease in Norrin-Fzd4 dependent retinal vascular development lengthens the period during which complications from OIR could occur.

Novel mutations in FZD4 and phenotype-genotype correlation in Chinese patients with familial exudative vitreoretinopathy

PURPOSE

To identify novel mutations in the frizzled 4 (FZD4) gene in patients with familial exudative vitreoretinopathy (FEVR) in southern China and to delineate the mutation-associated clinical manifestations.

METHODS

Clinical data and genomic DNA were collected from 100 probands and their family members. The coding regions of FZD4 were screened for mutations with PCR and Sanger sequencing. Cosegregation analysis was used to verify suspected variants, and clinical symptoms in the probands were analyzed.

RESULTS

Fourteen causative heterozygous mutations in FZD4 in 21 unrelated probands were noted, in 21.0% of the index patients (21/100). Four novel missense mutations (C45R, C45S, C53S, and C90R) and three novel deletion mutations (T326fsX356, G492fsX512, and S345_A351del) with a high possibility of pathogenicity were detected. None of these mutations were found in current online databases and 150 ethnically matched control subjects without retinopathy. The majority of the mutations in FZD4 were identified in probands with retinal folds (15/21) and ectopic macula (5/21). No mutations in FZD4 were found in probands with complete tractional retinal detachment in infancy or with mild asymptomatic FEVR in adulthood.

CONCLUSIONS

Seven novel mutations found in this study have broadened the spectrum of mutations in FZD4 known to cause FEVR, providing a deeper understanding of this disease. The results show that mutations in FZD4 are associated with the phenotypes of retinal folds or ectopic macula in FEVR but might not be associated with extreme severe bilateral FEVR during infancy, at least in southern Chinese patients.