Severe Form of Familial Exudative Vitreoretinopathy Caused by Homozygous R417Q Mutation in Frizzled-4 Gene

Familial Exudative Vitreoretinopathy With and Without Pathogenic Variants of Norrin/β-Catenin Signaling Genes

Purpose

To determine the clinical characteristics of familial exudative vitreoretinopathy (FEVR) associated with or without pathogenic variants of the Norrin/β-catenin genes.

Design

This was a multicenter, cross-sectional, observational, and genetic study.

Subjects

Two-hundred eighty-one probands with FEVR were studied.

Methods

Whole-exome sequence and/or Sanger sequence was performed for the Norrin/β-catenin genes, the FZD4, LRP5, TSPAN12, and NDP genes on blood collected from the probands. The clinical symptoms of the probands with or without the pathogenic variants were assessed as well as differences in the inter Norrin/β-catenin genes.

Main Outcome Measures

The phenotype associated with or without pathogenic variants of the Norrin/β-catenin genes.

Results

One-hundred eight probands (38.4%) had 88 different pathogenic or likely pathogenic variants in the genes: 24 with the FZD4, 42 with the LRP5, 10 with the TSPAN12, and 12 with the NDP gene. Compared with the 173 probands without pathogenic variants, the 108 variant-positive probands had characteristics of familial predisposition (63.9% vs. 37.6%, P < 0.0001), progression during infancy (75.0% vs. 53.8%, P = 0.0004), asymmetrical severity between the 2 eyes (50.0% vs. 37.6%, P = 0.0472), and nonsyndromic characteristics (10.2% vs. 17.3%, P = 0.1185). The most frequent stage at which the more severe eye conditions was present was at stage 4 in both groups (40.7% vs. 34.7%). However, the advanced stages of 3 to 5 in the more severe eye were found more frequently in probands with variants than in those without variants (83.3% vs. 58.4%, P < 0.0001). Patients with rhegmatogenous retinal detachments progressed from stage 1 or 2 were found less frequently in the variant-positive probands (8.3% vs. 17.3%, P = 0.0346). Nine probands with NDP variants had features different from probands with typical Norrin/β-catenin gene variants including the sporadic, symmetrical, and systemic characteristics consistent with Norrie disease.

Conclusions

The results showed that the clinical characteristics of FEVR of patients with variants in the Norrin/β-catenin genes are different from those with other etiologies. We recommend that clinicians who diagnose a child with FEVR perform genetic testing so that the parents can be informed on the prognosis of the vision and general health in the child.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Play the plug: How bacteria modify recognition by host receptors?

The diverse microbial community that colonizes the gastrointestinal tract has remarkable effects on the host immune system and physiology resulting in homeostasis or disease. In both scenarios, the gut microbiota interacts with their host through ligand-receptor binding whereby the downstream signaling processes determine the outcome of the interaction as disease or the counteractive immune responses of the host. Despite several studies on microbe-host interactions and the mechanisms by which this intricate process happens, a comprehensive and updated inventory of known ligand-receptor interactions and their roles in disease is paramount. The ligands which originate as a result of microbial responses to the host environment contribute to either symbiotic or parasitic relationships. On the other hand, the host receptors counteract the ligand actions by mounting a neutral or an innate response. The varying degrees of polymorphic changes in the host receptors contribute to specificity of interaction with the microbial ligands. Additionally, pathogenic microbes manipulate host receptors with endogenous enzymes belonging to the effector protein family. This review focuses on the diversity and similarity in the gut microbiome-host interactions both in health and disease conditions. It thus establishes an overview that can help identify potential therapeutic targets in response to critically soaring antimicrobial resistance as juxtaposed to tardy antibiotic development research.

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.

Novel Frizzled-4 Mutation Is Associated With Familial Exudative Vitreoretinopathy Mimicking Persistent Fetal Vasculature

This is a report of a 13-month-old boy who presented with a large unilateral fibrovascular stalk and bilateral peripheral retinal avascularity. Although consistent with both persistent fetal vasculature and familial exudative vitreoretinopathy, genetic testing disclosed a novel pathogenic mutation in the frizzled class receptor 4 gene (FZD4, c.427_428delCT). [J Pediatr Ophthalmol Strabismus. 2020;57:e4-e7.].

Disorders of FZ-CRD; insights towards FZ-CRD folding and therapeutic landscape

The ER is hub for protein folding. Proteins that harbor a Frizzled cysteine-rich domain (FZ-CRD) possess 10 conserved cysteine motifs held by a unique disulfide bridge pattern which attains a correct fold in the ER. Little is known about implications of disease-causing missense mutations within FZ-CRD families. Mutations in FZ-CRD of Frizzled class receptor 4 (FZD4) and Muscle, skeletal, receptor tyrosine kinase (MuSK) and Receptor tyrosine kinase-like orphan receptor 2 (ROR2) cause Familial Exudative Vitreoretinopathy (FEVR), Congenital Myasthenic Syndrome (CMS), and Robinow Syndrome (RS) respectively. We highlight reported pathogenic inherited missense mutations in FZ-CRD of FZD4, MuSK and ROR2 which misfold, and traffic abnormally in the ER, with ER-associated degradation (ERAD) as a common pathogenic mechanism for disease. Our review shows that all studied FZ-CRD mutants of RS, FEVR and CMS result in misfolded proteins and/or partially misfolded proteins with an ERAD fate, thus we coin them as “disorders of FZ-CRD”. Abnormal trafficking was demonstrated in 17 of 29 mutants studied; 16 mutants were within and/or surrounding the FZ-CRD with two mutants distant from FZ-CRD. These ER-retained mutants were improperly N-glycosylated confirming ER-localization. FZD4 and MuSK mutants were tagged with polyubiquitin chains confirming targeting for proteasomal degradation. Investigating the cellular and molecular mechanisms of these mutations is important since misfolded protein and ER-targeted therapies are in development. The P344R-MuSK kinase mutant showed around 50% of its in-vitro autophosphorylation activity and P344R-MuSK increased two-fold on proteasome inhibition. M105T-FZD4, C204Y-FZD4, and P344R-MuSK mutants are thermosensitive and therefore, might benefit from extending the investigation to a larger number of chemical chaperones and/or proteasome inhibitors. Nonetheless, FZ-CRD ER-lipidation it less characterized in the literature and recent structural data sheds light on the importance of lipidation in protein glycosylation, proper folding, and ER trafficking. Current treatment strategies in-place for the conformational disease landscape is highlighted. From this review, we envision that disorders of FZ-CRD might be receptive to therapies that target FZ-CRD misfolding, regulation of fatty acids, and/or ER therapies; thus paving the way for a newly explored paradigm to treat different diseases with common defects.

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.

Genetic testing in translational ophthalmology

Inherited eye diseases are a group of conditions with genetic and phenotypic heterogeneity. Advances in ocular genetic research have provided insights into the genetic basis of many eye diseases. Genetic and technological progress is improving the management and care of patients with inherited eye diseases. Diagnostic laboratories continue to develop strategies with high specificity and sensitivity that reduce the costs and time required for genetic testing. The introduction of next generation sequencing technologies has significantly advanced the identification of new gene candidates and has expanded the scope of genetic testing. Gene therapy offers an important opportunity to target causative genetic mutations. There are clinical trials of treatments involving vector-based eye gene therapies, and a significant number of loci and genes now have a role in the diagnosis and treatment of human eye diseases. Applied genetic technology heralds the development of individualized treatments, ushering ophthalmology into the field of personalized medicine. Many therapeutic strategies have demonstrated efficacy in preclinical studies and have entered the clinical trial phase. In this paper we review the topic of genetic testing in inherited eye diseases. We provide some background information about genetic counseling and genetic testing in ophthalmology and discuss how genetic testing can be helpful to patients and families with inherited eye diseases.

Familial exudative vitreoretinopathy: A report of an asymptomatic case with autosomal dominant inheritance detected using FZD4 molecular analysis

OBJECTIVE

To report a familial case of Familial Exudative Vitreoretinopathy (FEVR) with an autosomal dominant inheritance pattern identified with the molecular analysis of FZD4.

CASE REPORT

The proband is a 13 year-old boy who consulted for low vision. Fundus examination revealed a peripheral avascular zone and macular dragging, consistent with FEVR. Molecular analysis demonstrated a mutation of FZD4 in DNA from both the patient and his asymptomatic mother.

DISCUSSION

This familial case was identified with the molecular analysis of FZD4 and shows the importance to explore first degree relatives in a sporadic FEVR case.

A family harboring homozygous FZD4 deletion supports the existence of recessive FZD4-related familial exudative vitreoretinopathy

PURPOSE

To document recessive FZD4-related familial exudative vitreoretinopathy.

METHODS

Retrospective case series.

RESULTS

Two brothers, the only two males among five siblings, had bilateral infantile retinal detachments and were referred for genetic counseling. Next-generation sequencing uncovered a homozygous FZD4 frameshift deletion in both affected brothers (c.40_49delCCCGGGGGCG; p.Pro14Serfs*44). None of the other immediate family members had clinical evidence for retinal disease, including the three family members who underwent confirmatory genetic testing and were found to be heterozygous for the mutation (both parents and one sister).

CONCLUSIONS

The findings in this family support the concept that some mutated FZD4 alleles can be associated with recessive rather than dominant disease.

Mutation spectrum of the FZD-4, TSPAN12 AND ZNF408 genes in Indian FEVR patients

BACKGROUND

Mutations in candidate genes that encode for a ligand (NDP) and receptor complex (FZD4, LRP5 and TSPAN12) in the Norrin β-catenin signaling pathway are involved in the pathogenesis of familial exudative vitreoretinopathy (FEVR, MIM # 133780). Recently, a transcription factor (ZNF408) has also been implicated in FEVR. We had earlier characterized the variations in NDP among FEVR patients from India. The present study aimed at understanding the involvement of the remaining genes (FZD4, TSPAN12 and ZNF408) in the same cohort.

METHODS

The DNA of 110 unrelated FEVR patients and 115 unaffected controls were screened for variations in the entire coding and untranslated regions of these 3 genes by resequencing. Segregation of the disease-associated variants was assessed in the family members of the probands. The effect of the observed missense changes were further analyzed by SIFT and PolyPhen-2 scores.

RESULTS

The screening of FZD4, TSPAN12 and ZNF408 genes identified 11 different mutations in 15/110 FEVR probands. Of the 11 identified mutations, 6 mutations were novel. The detected missense mutations were mainly located in the domains which are functionally crucial for the formation of ligand-receptor complex and as they replaced evolutionarily highly conserved amino acids with a SIFT score < 0.005, they are predicted to be pathogenic. Additionally 2 novel and 16 reported single nucleotide polymorphisms (SNP) were also detected.

CONCLUSIONS

Our genetic screening revealed varying mutation frequencies in the FZD4 (8.0 %), TSPAN12 (5.4 %) and ZNF408 (2.7 %) genes among the FEVR patients, indicating their potential role in the disease pathogenesis. The observed mutations segregated with the disease phenotype and exhibited variable expressivity. The mutations in FZD4 and TSPAN12 were involved in autosomal dominant and autosomal recessive families and further validates the involvement of these gene in FEVR development.

Complex genetics of familial exudative vitreoretinopathy and related pediatric retinal detachments

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

Canonical WNT signaling components in vascular development and barrier formation

Canonical WNT signaling is required for proper vascularization of the CNS during embryonic development. Here, we used mice with targeted mutations in genes encoding canonical WNT pathway members to evaluate the exact contribution of these components in CNS vascular development and in specification of the blood-brain barrier (BBB) and blood-retina barrier (BRB). We determined that vasculature in various CNS regions is differentially sensitive to perturbations in canonical WNT signaling. The closely related WNT signaling coreceptors LDL receptor-related protein 5 (LRP5) and LRP6 had redundant functions in brain vascular development and barrier maintenance; however, loss of LRP5 alone dramatically altered development of the retinal vasculature. The BBB in the cerebellum and pons/interpeduncular nuclei was highly sensitive to decrements in canonical WNT signaling, and WNT signaling was required to maintain plasticity of barrier properties in mature CNS vasculature. Brain and retinal vascular defects resulting from ablation of Norrin/Frizzled4 signaling were ameliorated by stabilizing β-catenin, while inhibition of β-catenin-dependent transcription recapitulated the vascular development and barrier defects associated with loss of receptor, coreceptor, or ligand, indicating that Norrin/Frizzled4 signaling acts predominantly through β-catenin-dependent transcriptional regulation. Together, these data strongly support a model in which identical or nearly identical canonical WNT signaling mechanisms mediate neural tube and retinal vascularization and maintain the BBB and BRB.

Mutations in the TSPAN12 gene in Japanese patients with familial exudative vitreoretinopathy

PURPOSE

To search for mutations in the TSPAN12 gene in 90 Japanese probands with familial exudative vitreoretinopathy (FEVR) and their family members and to determine the types and frequencies of the mutations.

DESIGN

Laboratory investigation and clinical case analyses.

METHODS

Direct sequencing after polymerase chain reaction of the coding exons of TSPAN12 was performed for 90 probands with FEVR and some of their family members. The clinical signs and symptoms that were characteristic of individuals with TSPAN12 mutations were determined.

RESULTS

Three families were found to carry 2 mutations in TSPAN12. One of these mutations was a new missense change, L245P, and the other was an already reported nonsense mutation, L140X, in 2 families. Mutations in TSPAN12 accounted for 3% of Japanese FEVR patients and 8% of the FEVR families who did not have mutations in any of the known FEVR genes, FZD4, LRP5, and NDP. The clinical signs and symptoms varied among the patients, but the retinal findings with TSPAN12 mutations were not different from those with mutations in the known FEVR-causing genes.

CONCLUSIONS

Mutant TSPAN12 is responsible for approximately 3% of FEVR patients in Japan. The results provide further evidence that mutations in TSPAN12 are FEVR causing and that the gene products most likely play a role in the development of retinal vessels.

The Norrin/Frizzled4 signaling pathway in retinal vascular development and disease

Disorders of retinal vascular growth and function are responsible for vision loss in a variety of diseases, including diabetic retinopathy, age-related macular degeneration, retinopathy of prematurity and retinal artery or vein occlusion. Over the past decade, a new signaling pathway that controls retinal vascular development has emerged from the study of inherited disorders - in both humans and mice - that are characterized by retinal hypovascularization. This pathway utilizes a glial-derived extracellular ligand, Norrin, that acts on a transmembrane receptor, Frizzled4, a coreceptor, Lrp5, and an auxiliary membrane protein, Tspan12, on the surface of developing endothelial cells. The resulting signal controls a transcriptional program that regulates endothelial growth and maturation. It will be of great interest to determine whether modulating this pathway could represent a therapeutic approach to human retinal vascular disease.

From the laboratory to the clinic: molecular genetic testing in pediatric ophthalmology

PURPOSE

To review the current state of molecular genetic testing as it relates to pediatric ophthalmology and to discuss its uses.

DESIGN

Review and evaluation of available molecular genetic testing.

METHODS

Literature review and discussion of testing in practice based on the authors' clinical and laboratory experience.

RESULTS

Fee-for-service testing for many genetic eye diseases now is available. A report is always generated for fee-for-service testing. Detection of DNA variants in genes known to cause eye disease must be interpreted taking into account the variability of the human genome, the presence of benign variants (polymorphisms), and the carrier frequency of recessive alleles. Negative results in genetic testing are helpful in some disorders for which most of the causative genes are known and many disease-causing variants have already been reported, but are less helpful in those that currently have many undiscovered causative genes or novel mutations. Research-based testing also is available, but does not always yield a result. Patients with RPE65-associated Leber congenital amaurosis may be eligible for the current gene therapy trial. Patients with a variety of disorders may benefit from improved surveillance if their genetic diagnosis is known.

CONCLUSIONS

Entry into the genetic testing system often is via the patient's ophthalmologist. Collaboration with geneticists and genetic counselors, use of web sites to keep up with the ever-changing availability and detection rates, and knowledge of clinical trials, when combined with excellent clinical diagnosis, can improve diagnosis and allow eligible patients to participate in treatment trials.

Norrin, frizzled-4, and Lrp5 signaling in endothelial cells controls a genetic program for retinal vascularization

Disorders of vascular structure and function play a central role in a wide variety of CNS diseases. Mutations in the Frizzled-4 (Fz4) receptor, Lrp5 coreceptor, or Norrin ligand cause retinal hypovascularization, but the mechanisms by which Norrin/Fz4/Lrp signaling controls vascular development have not been defined. Using mouse genetic and cell culture models, we show that loss of Fz4 signaling in endothelial cells causes defective vascular growth, which leads to chronic but reversible silencing of retinal neurons. Loss of Fz4 in all endothelial cells disrupts the blood brain barrier in the cerebellum, whereas excessive Fz4 signaling disrupts embryonic angiogenesis. Sox17, a transcription factor that is upregulated by Norrin/Fz4/Lrp signaling, plays a central role in inducing the angiogenic program controlled by Norrin/Fz4/Lrp. These experiments establish a cellular basis for retinal hypovascularization diseases due to insufficient Frizzled signaling, and they suggest a broader role for Frizzled signaling in vascular growth, remodeling, maintenance, and disease.