Frizzled 4 gene (FZD4) mutations in patients with familial exudative vitreoretinopathy with variable expressivity

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.

Coats-Like Presentation of Familial Exudative Vitreoretinopathy Associated With a Novel LRP5 Variant

This report describes a unique case of a Coats-like presentation of familial exudative vitreoretinopathy in an 11-year-old girl. The patient was originally referred for evaluation of presumed Coats disease and presented with telangiectatic vessels, perivascular exudates, diffuse peripheral exudation, and intraretinal hemorrhages. Clinical and angiographical findings were consistent with familial exudative vitreoretinopathy, while genetic testing identified variants of uncertain significance in two associated genes, LRP5 and ZNF408. In silico analysis predicts the LRP5 variant to be pathogenic. Retinal vasculopathies often have phenotypic overlap, warranting angiographic examination of both eyes and genetic testing to uncover the correct diagnosis and guide proper treatment. [Ophthalmic Surg Lasers Imaging Retina 2024;55:462-466.].

Severe isolated exudative vitreoretinopathy caused by biallelic FZD4 variants

Familial exudative vitreoretinopathy (FEVR) is linked to disruption of the Norrin/Frizzled-4 signaling pathway, which plays an important role in retinal angiogenesis. Severe or complete knock-down of proteins in the pathway also causes syndromic forms of the condition. Both heterozygous and biallelic pathogenic variants in the FZD4 gene, encoding the pathway's key protein frizzled-4, are known to cause FEVR. However, it is not clear what effect different FZD4 variants have, and whether extraocular features should be expected in those with biallelic pathogenic FZD4 variants. Biallelic FZD4 variants were found in a young boy with isolated, severe FEVR. His parents were heterozygous for one variant each and reported normal vision. In-vitro studies of the two variants, demonstrated that it was the combination of the two which led to severe inhibition of the Norrin/Frizzled-4 pathway. Our observations demonstrate that biallelic FZD4-variants are associated with a severe form of FEVR, which does not necessarily include extraocular features. In addition, variants causing severe FEVR in combination, may have no or minimal effect in heterozygous parents as non-penetrance is also a major feature in dominant FZD4-FEVR disease. This underscores the importance of genetic testing of individuals and families with FEVR.

Genetic Characteristics and Clinical Manifestations of Foveal Hypoplasia in Familial Exudative Vitreoretinopathy

PURPOSE

This study aimed to ascertain the occurrence of foveal hypoplasia (FH) in individuals diagnosed with familial exudative vitreoretinopathy (FEVR).

DESIGN

Retrospective cohort study.

METHODS

In this study, FEVR families and sporadic cases were diagnosed at the Eye and ENT Hospital, Fudan University, between 2017 and 2023. All patients attended routine ophthalmologic examinations and genetic screenings. The classification of FH was determined using optical coherence tomography (OCT) scans. The FH condition was classified into 2 subgroups: group A (FH being limited to the inner layers) and group B (FH affecting the outer layers). A total of 102 eyes from 58 patients were suitable for analysis.

RESULTS

Forty-nine mutations in LRP5, FZD4, NDP, TSPAN12, KIF11, CTNNB1, and ZNF408 were examined and detected, with 26 of them being novel. Forty-seven eyes (46.1%) revealed FH. The majority (53.2%) were due to the typical grade 1 FH. Patients with mutations in LRP5 and KIF11 were found to exhibit a higher prevalence of FH (P = .0088). Group B displayed the lowest visual acuity compared with group A (P = .048) and the group without FH (P < .001). The retinal arteriolar angle in group B was significantly smaller than in group A (P = .001) and those without FH (P < .001).

CONCLUSIONS

This study offers a new diagnostic approach and expands the spectrum of FEVR mutations. LRP5 and KIF11 were found to be more susceptible to causing FH in patients with FEVR. FEVR eyes with FH exhibited both greater visual impairment and reduced retinal arteriolar angles. The assessment of foveal status in patients with FEVR should be valued.

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.

Mechanisms Underlying Rare Inherited Pediatric Retinal Vascular Diseases: FEVR, Norrie Disease, Persistent Fetal Vascular Syndrome

Familial Exudative Vitreoretinopathy (FEVR), Norrie disease, and persistent fetal vascular syndrome (PFVS) are extremely rare retinopathies that are clinically distinct but are unified by abnormal retinal endothelial cell function, and subsequent irregular retinal vascular development and/or aberrant inner blood-retinal-barrier (iBRB) function. The early angiogenesis of the retina and its iBRB is a delicate process that is mediated by the canonical Norrin Wnt-signaling pathway in retinal endothelial cells. Pathogenic variants in genes that play key roles within this pathway, such as NDP, FZD4, TSPAN12, and LRP5, have been associated with the incidence of these retinal diseases. Recent efforts to further elucidate the etiology of these conditions have not only highlighted their multigenic nature but have also resulted in the discovery of pathological variants in additional genes such as CTNNB1, KIF11, and ZNF408, some of which operate outside of the Norrin Wnt-signaling pathway. Recent discoveries of FEVR-linked variants in two other Catenin genes (CTNND1, CTNNA1) and the Endoplasmic Reticulum Membrane Complex Subunit-1 gene (EMC1) suggest that we will continue to find additional genes that impact the neural retinal vasculature, especially in multi-syndromic conditions. The goal of this review is to briefly highlight the current understanding of the roles of their encoded proteins in retinal endothelial cells to understand the essential functional mechanisms that can be altered to cause these very rare pediatric retinal vascular diseases.

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.

Severe Familial Exudative Vitreoretinopathy, Congenital Hearing Loss, and Developmental Delay in a Child With Biallelic Variants in FZD4

Question

Are FZD4 variants associated with familial exudative vitreoretinopathy (FEVR) with extraocular features?

Findings

This case series included a patient with biallelic FZD4 variants with severe FEVR in infancy, congenital hearing loss, and developmental delay. Each parent was carrying 1 of the alleles and manifested mild FEVR; cell-based FZD4 receptor-activation assays determined that FZD4 function was dramatically decreased in the presence of these compound heterozygous variants.

Meaning

Biallelic variants in FZD4 can result in a severe ocular phenotype with systemic features, which may represent a novel syndrome.

Importance

Familial exudative vitreoretinopathy (FEVR) is a nonsyndromic autosomal dominant retinal disorder commonly caused by variants in the FZD4 gene. This study investigates the potential role beyond ocular abnormalities for FZD4 gene variants in patients with FEVR.

Objective

To evaluate the role of FZD4 in symptoms beyond those associated with FEVR through a patient with biallelic variants in FZD4.

Design, Setting, and Participants

This case series included the DNA testing and phenotyping of 1 patient proband and her parents, combined with signaling assays, to determine the association of patient-derived compound heterozygous variants on FZD4 signaling and biologic function.

Main Outcomes and Measures

FZD4 genes were tested using next-generation sequencing and Sanger sequencing. Cell-based assays measured the effect of the variants on FZD4 signaling.

Results

The proband presented with absent red reflexes from complete tractional retinal detachments diagnosed at 3 days of age and failed the newborn screening hearing test. Auditory brainstem response at 6 months of age showed bilateral mild to moderate high-frequency sensorineural hearing loss. The patient manifested developmental delays in speech and walking. Intravenous fluorescein angiography (IVFA) of the patient’s parents detected stage 1 FEVR. Genetic testing revealed 2 FZD4 variants in the patient, each variant found in 1 parent. Signaling assays confirmed that the presence of both variants was associated with significantly worse signaling activity compared with the heterozygous state.

Conclusions and Relevance

Results of this case series suggest that extraocular syndromic FEVR was associated with FZD4 variants. The decrease in FZD4 signaling owing to the biallelic nature of the disease resulted in hearing deficits, developmental delays, and a more severe retinal phenotype.

Genotype-phenotype associations in familial exudative vitreoretinopathy: A systematic review and meta-analysis on more than 3200 individuals

Objective

To systematically review the relationship between genotypes and clinical phenotypes of Familial exudative vitreoretinopathy (FEVR) to support risk estimation and therapeutic decisions.

Design

Systematic review with meta-analysis.

Data sources

The data of our study were collected from PubMed, Embase, Web of Science, Cochrane, CBM, China National Knowledge Infrastructure (CNKI), WAN FANG and VIP databases since inception to August 2021.

Results

A total of 3257 patients from 32 studies were included according to the inclusion and exclusion criteria. Among all the cases, the mutation frequencies of LRP5, FZD4, NDP, TSPAN12, ZNF408 and KIF11 were 13.6%, 11.5%, 4.6%, 6.7%, 1.6%, and 5.7%, respectively. We found that the patients with NDP and FZD4 suffer more severe symptoms, among which 86.4% patients of NDP and 78.6% patients of FZD4 were in the advanced stage of FEVR. Retinal detachment is the most frequent symptom with patients of LRP5 and NDP mutations, accounting for 51.9% and 64.5%, respectively. For the patients with the mutation of TSPAN12, retinal fold is the most common clinical manifestation, and suffer the mildest clinical phenotypes compared with the other three genes.

Conclusion

The results of the meta-analysis indicate that different types of genetic mutations occur at different frequencies. In addition, the clinical manifestations of FEVR are related to the type of gene mutation. Therefore, targeted treatment strategies and follow-up recommendations should be adopted for different pathogenic genes of FEVR.

Ocular Features and Mutation Spectrum of Patients With Familial Exudative Vitreoretinopathy

Purpose

To investigate the clinical findings in Chinese patients diagnosed with familial exudative vitreoretinopathy (FEVR) and carrying pathogenic mutations.

Methods

One hundred twenty unrelated patients with FEVR were enrolled in this study. Genomic DNA and ophthalmic examinations were collected from all the patients and their available relatives. Targeted next-generation sequencing was performed to detect mutations. In silico programs were used to evaluate the pathogenicity of all the mutations.

Results

Eighty identified mutations were found in 81 unrelated patients (31/81 in LRP5, 25/81 in FZD4, 12/81 in TSPAN12, 8/81 in NDP, 4/81 in KIF11, and 1/81 in ZNF408). Among those mutations, 53 were novel (23/35 in LRP5, 15/21 in FZD4, 8/11 in TSPAN12, 3/8 in NDP, 3/4 in KIF11, 1/1 in ZNF408). Patients with LRP5, FZD4, TSPAN12, or NDP mutations were mainly classified into stage 4 and stage 5 and one-half of patients with KIF11 mutations were in stage 4. In addition, all the patients in NDP group were found to have bilateral symmetry in FEVR stage.

Conclusions

Our results present profound phenotypic variability and a wide mutation spectrum of FEVR in the Chinese population, which could be useful for a precise and comprehensive genetic diagnosis for patients with FEVR in the future.

Planar cell polarity (PCP) proteins support spermatogenesis through cytoskeletal organization in the testis

Few reports are found in the literature regarding the role of planar cell polarity (PCP) in supporting spermatogenesis in the testis. Yet morphological studies reported decades earlier have illustrated the directional alignment of polarized developing spermatids, most notably step 17-19 spermatids in stage V-early VIII tubules in the testis, across the plane of the epithelium in seminiferous tubules of adult rats. Such morphological features have unequivocally demonstrated the presence of PCP in developing spermatids, analogous to the PCP noted in hair cells of the cochlea in mammals. Emerging evidence in recent years has shown that Sertoli and germ cells express numerous PCP proteins, mostly notably, the core PCP proteins, PCP effectors and PCP signaling proteins. In this review, we discuss recent findings in the field regarding the two core PCP protein complexes, namely the Van Gogh-like 2 (Vangl2)/Prickle (Pk) complex and the Frizzled (Fzd)/Dishevelled (Dvl) complex. These findings have illustrated that these PCP proteins exert their regulatory role to support spermatogenesis through changes in the organization of actin and microtubule (MT) cytoskeletons in Sertoli cells. For instance, these PCP proteins confer PCP to developing spermatids. As such, developing haploid spermatids can be aligned and orderly packed within the limited space of the seminiferous tubules in the testes for the production of sperm via spermatogenesis. Thus, each adult male in the mouse, rat or human can produce an upward of 30, 50 or 300 million spermatozoa on a daily basis, respectively, throughout the adulthood. We also highlight critical areas of research that deserve attention in future studies. We also provide a hypothetical model by which PCP proteins support spermatogenesis based on recent studies in the testis. It is conceivable that the hypothetical model shown here will be updated as more data become available in future years, but this information can serve as the framework by investigators to unravel the role of PCP in spermatogenesis.

Wnt Pathway: An Integral Hub for Developmental and Oncogenic Signaling Networks

The Wnt pathway is an integral cell-to-cell signaling hub which regulates crucial development processes and maintenance of tissue homeostasis by coordinating cell proliferation, differentiation, cell polarity, cell movement, and stem cell renewal. When dysregulated, it is associated with various developmental diseases, fibrosis, and tumorigenesis. We now better appreciate the complexity and crosstalk of the Wnt pathway with other signaling cascades. Emerging roles of the Wnt signaling in the cancer stem cell niche and drug resistance have led to development of therapeutics specifically targeting various Wnt components, with some agents currently in clinical trials. This review highlights historical and recent findings on key mediators of Wnt signaling and how they impact antitumor immunity and maintenance of cancer stem cells. This review also examines current therapeutics being developed that modulate Wnt signaling in cancer and discusses potential shortcomings associated with available therapeutics.

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.

Diagnostic yield of panel-based genetic testing in syndromic inherited retinal disease

Thirty percent of all inherited retinal disease (IRD) is accounted for by conditions with extra-ocular features. This study aimed to establish the genetic diagnostic pick-up rate for IRD patients with one or more extra-ocular features undergoing panel-based screening in a clinical setting. One hundred and six participants, tested on a gene panel which contained both isolated and syndromic IRD genes, were retrospectively ascertained from the Manchester Genomic Diagnostics Laboratory database spanning 6 years (2012-2017). Phenotypic features were extracted from the clinical notes and classified according to Human Phenotype Ontology; all identified genetic variants were interpreted in accordance to the American College of Medical Genetics and Genomics guidelines. Overall, 49% (n = 52) of patients received a probable genetic diagnosis. A further 6% (n = 6) had a single disease-associated variant in an autosomal recessive disease-relevant gene. Fifty-two percent (n = 55) of patients had a clinical diagnosis at the time of testing. Of these, 71% (n = 39) received a probable genetic diagnosis. By contrast, for those without a provisional clinical diagnosis (n = 51), only 25% (n = 13) received a probable genetic diagnosis. The clinical diagnosis of Usher (n = 33) and Bardet-Biedl syndrome (n = 10) was confirmed in 67% (n = 22) and 80% (n = 8), respectively. The testing diagnostic rate in patients with clinically diagnosed multisystemic IRD conditions was significantly higher than those without one (71% versus 25%; p value < 0.001). The lower pick-up rate in patients without a clinical diagnosis suggests that panel-based approaches are unlikely to be the most effective means of achieving a molecular diagnosis for this group. Here, we suggest that genome-wide approaches (whole exome or genome) are more appropriate.

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.

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.

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.].

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.

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.

Detection of FZD4, LRP5 and TSPAN12 Genes Variants in Malay Premature Babies with Retinopathy of Prematurity

Purpose:

To determine the mutational analyses of familial exudative vitreoretinopathy (FEVR)-causing genes in Malay patients with retinopathy of prematurity (ROP) to obtain preliminary data for gene alterations in the Malay community.

Methods:

A comparative cross-sectional study involving 86 Malay premature babies (ROP = 41 and non-ROP = 45) was performed from September 2012 to December 2014. Mutation analyses in (FEVR)-causing genes (NDP, FZD4, LRP5, and TSPAN12) were performed using DNA from premature babies using polymerase chain reaction (PCR) and direct sequencing. Sequencing results were confirmed with PCR-Restriction Fragment Length Polymorphism (RFLP).

Results:

We found variants of FZD4, LRP5, and TSPAN12 in this study. One patient from each group showed a non-synonymous alteration in FZD4, c.502C>T (p.P168S). A synonymous variant of LRP5 [c.3357G>A (p.V1119V)] was found in 30 ROP and 28 non-ROP patients. Two variants of TSPAN12, c.765G>T (p.P255P) and c.*39C>T (3′UTR), were also recorded (29 and 21 in ROP, 33 and 26 in non-ROP, respectively). Gestational age and birth weight were found to be significantly associated with ROP (P value < 0.001 and 0.001, respectively).

Conclusion:

Analysis of data obtained from the ROP Malay population will enhance our understanding of these FEVR-causing gene variants. The c.3357G>A (p.V1119V) variant of LRP5, and c.765G>T (p.P255P) and c.*39C>T variants of TSPAN12 could be common polymorphisms in the Malay ethnic group; however, this requires further elucidation. Future studies using larger groups and higher numbers of advanced cases are necessary to evaluate the relationship between FEVR-causing gene variants and the risk of ROP susceptibility in Malaysian infants.

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.

Molecular evolutionary and structural analysis of familial exudative vitreoretinopathy associated FZD4 gene

BACKGROUND

Frizzled family members belong to G-protein coupled receptors and encode proteins accountable for cell signal transduction, cell proliferation and cell death. Members of Frizzled receptor family are considered to have critical roles in causing various forms of cancer, cardiac hypertrophy, familial exudative vitreoretinopathy (FEVR) and schizophrenia.

RESULTS

This study investigates the evolutionary and structural aspects of Frizzled receptors, with particular focus on FEVR associated FZD4 gene. The phylogenetic tree topology suggests the diversification of Frizzled receptors at the root of metazoans history. Moreover, comparative structural data reveals that FEVR associated missense mutations in FZD4 effect the common protein region (amino acids 495-537) through a well-known phenomenon called epistasis. This critical protein region is present at the carboxyl-terminal domain and encompasses the K-T/S-XXX-W, a PDZ binding motif and S/T-X-V PDZ recognition motif.

CONCLUSION

Taken together these results demonstrate that during the course of evolution, FZD4 has acquired new functions or epistasis via complex patter of gene duplications, sequence divergence and conformational remodeling. In particular, amino acids 495-537 at the C-terminus region of FZD4 protein might be crucial in its normal function and/or pathophysiology. This critical region of FZD4 protein may offer opportunities for the development of novel therapeutics approaches for human retinal vascular disease.

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-Spectrum Vitreoretinopathy Masquerading as Congenital Toxoplasmosis

Wnt-spectrum vitreoretinopathies are a group of rare inherited disorders of retinal angiogenesis that include familial exudative vitreoretinopathy/Norrie disease and are most commonly autosomal dominant; however, they can rarely present with other inheritance patterns that are more difficult to diagnose. The authors describe a case of an uncle misdiagnosed as congenital toxoplasmosis for decades and his 2-month-old nephew presenting with bilateral retinal detachments. Genetic analysis revealed an NDP gene mutation in the child and the uncle, as well as heterozygosity of the mother confirming a Wnt-spectrum vitreoretinopathy. This report describes the evaluation, diagnosis, and importance of early laser stabilization of this disorder. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:446-450.].

The genetic dissection of Myo7a gene expression in the retinas of BXD mice

Purpose

Usher syndrome (US) is characterized by a loss of vision due to retinitis pigmentosa (RP) and deafness. US has three clinical subtypes, but even within each subtype, the severity varies. Myosin VIIA, coded by Myo7a, has been identified as one of the causal genes of US. This study aims to identify pathways and other genes through which Myo7a interacts to affect the presentation of US symptoms.

Methods

In this study, we used the retinal tissue of BXD recombinant inbred (RI) mice to examine the expression of Myo7a and perform genetic mapping. Expression quantitative trait locus (eQTL), single nucleotide polymorphism (SNP), and gene correlation analysis were performed using GeneNetwork. Gene set enrichment analysis was performed using WebGestalt, and gene network construction was performed using the Gene Cohesion Analysis Tool.

Results

We found Myo7a to be cis-regulated, with varied levels of expression across BXD strains. Here, we propose a genetic network with 40 genes whose expression is highly correlated with Myo7a. Among these genes, six have been linked to retinal diseases, three to deafness, and five share a transcription factor with Myo7a. Gene ontology and pathway analysis revealed a strong connection among ion channel activity, Myo7a, and US.

Conclusions

Although Myo7a is a causal gene of US type I, this gene works with many other genes and pathways to affect the severity of US. Many of the genes found in the genetic network, pathways, and gene ontology categories of Myo7a are related to either deafness or blindness. Further investigation is needed to examine the specific relationships between these genes, which may assist in the treatment of US.

Genetic modifiers as relevant biological variables of eye disorders

From early in the study of mammalian genetics, it was clear that modifiers can have a striking influence on phenotypes. Today, several modifiers have now been studied in enough detail to allow a glimpse of how they function and influence our perspective of disease. With respect to diseases of the eye, some modifiers are an important source of phenotypic variation that can elucidate how genes function in networks to collectively shape ocular anatomy and physiology, thus influencing our understanding of basic biology. Other modifiers represent an opportunity for new therapeutic targets, whose manipulation could be used to mitigate ophthalmic disease. Here, we review progress in the study of genetic modifiers of eye disorders, with examples from mice and humans that together illustrate the ubiquitous nature of genetic modifiers and why they are relevant biological variables in experimental design. Special emphasis is given to ophthalmic modifiers in mice, especially those relevant to selection of genetic background and those that might inadvertently be a source of experimental variability. These modifiers are capable of influencing interpretations of many experiments using targeted genome manipulations such as knockouts or transgenics. Whereas there are fewer examples of modifiers of eye disorders in humans with a molecular identification, there is ample evidence that they exist and should be considered as a relevant biological variable in human genetic studies as well.

Variable Familial Exudative Vitreoretinopathy in a family harbouring variants in both FZD4 and TSPAN12

PURPOSE

To report a family affected by familial exudative vitreoretinopathy (FEVR) in which more severe disease phenotypes segregated with digenic rather than monogenic variants in FEVR-related genes.

METHODS

Phenotype was documented with high-resolution imaging of retinal structure and wide-field fundus photography. Next-generation sequencing (NGS) of known genes involved in FEVR was performed.

RESULTS

Three affected individuals within a family with FEVR presented with variable disease severity. All three affected family members harboured mutation c.349T>C (p.Cys117Arg) in FZD4. In addition, the youngest family member, a 9-year-old boy, who presented with bilateral tractional retinal detachment, and his mother, who presented with retinal pigmentary alterations and bilateral dragging of the macula and atrophy, both harboured the variant c.565T>C (p.Cys189Arg) in TSPAN12. Both suffered from bilateral severe visual loss. On the other hand, the older sister who presented with mild visual loss, temporal avascularity in the right eye and dragging of the blood vessels over the disc and macula in the left eye did not harbour the variant p.Cys189Arg in TSPAN12.

CONCLUSION

These data suggest variants in more than one FEVR-related gene can underlie variable expressivity for FEVR phenotypes in a single family. Further studies of phenotype-genotype correlation, including next-generation sequencing, in larger cohorts of patients with FEVR are needed to investigate whether changes in more than one gene coding for proteins in the Norrin-β-catenin pathway are a recurrent cause for variable expressivity in the disease.

A novel c.240_241insGG mutation in NDP gene in a family with Norrie disease

BACKGROUND

Norrie disease (ND) is a rare, X-linked recessive disorder with the main characteristic of early childhood blindness. The aim of the present study was to identify the genetic cause of the disease and the phenotypic characteristics of the patients in an Iranian family with four affected males with ND.

METHODS

Norrie disease pseudoglioma (NDP) gene was sequenced and clinical examination was performed on patients.

RESULTS

A GG dinucleotide insertion in exon 3 (c.240_241insGG) of NDP was detected in all patients. The mutation caused a frameshift and an early stop codon (p.Phe81Glyfs*23).

CONCLUSIONS

A novel mutation was found in the NDP gene in the affected males of the family. As the mutation was absent in the normal male members of the family, it should be the genetic cause of the disease.

Familial Exudative Vitreoretinopathy With a Novel LRP5 Mutation

This report reviews the genetics of familial exudative vitreoretinopathy (FEVR) and describes the identification of a novel variant in the LRP5 gene. A 20-month-old boy presented with reduced visual acuity in the right eye from exudative retinal detachment with mild retinal traction. Fluorescein angiography in the right eye disclosed extensive peripheral retinal non-perfusion and telangiectatic vessels and the left eye showed minimal peripheral non-perfusion. These features were suggestive of FEVR. Treatment with laser photocoagulation and cryotherapy to the region of non-perfusion was performed with resolution of the exudative retinal detachment. Fundus examination of the father revealed mild signs of FEVR, such as hyperacute retinal vascular branching and slight retinal vascular traction, whereas the mother's fundus examination was unremarkable. Genetic testing revealed that the affected boy was negative for mutations in the FZD4, NDP, and TSPAN12 genes and heterozygous for a previously unreported A745V variant in the LRP5 gene. The father was also heterozygous for the A745V variant in the LRP5 gene and the unaffected mother showed no mutation. A genetic evaluation of the known genes associated with FEVR revealed a novel variant in the LRP5 gene that co-segregated with the phenotype in the family. [J Pediatr Ophthalmol Strabismus. 2016;53:e39-e42.].

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.

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.

[Vitreous hemorrhage as the initial manifestation of familial exudative vitreoretinopathy in an eight-year-old child]

PURPOSE

To report vitreous hemorrhage as the initial manifestation of familial exudative vitreoretinopathy (FEVR).

METHODS

Case report.

RESULTS

An 8-year-old child presented with vitreous hemorrhage leading to the discovery of large neovascularization. Fundus examination and fluorescein angiography showed the typical appearance of FEVR. A genetic study confirmed the diagnosis. Treatment by laser photocoagulation was performed with good recovery of visual acuity.

CONCLUSION

Ophthalmologists should be aware of familial exudative vitreoretinopathy (FEVR) so as not to misdiagnose this sight-threatening disease.

Mutation spectrum of the Norrie disease pseudoglioma (NDP) gene in Indian patients with FEVR

PURPOSE

Mutations in the Norrie disease pseudoglioma (NDP; Xp11.3) gene have been involved in retinal blood vessel formation and neural differentiation and are implicated in familial exudative vitreoretinopathy (FEVR) cases. However, the role of the gene has not been explored in the Indian context. Thus, this study was designed to understand the involvement of NDP among Indian patients with FEVR.

METHODS

The study cohort comprised 225 subjects, including unrelated patients with FEVR (n = 110) and ethnically matched healthy subjects (n = 115) recruited from a tertiary eye care center in India. The entire coding regions, intron-exon boundaries, along with the 5' and 3' untranslated regions of NDP were screened with resequencing following standard protocols. The spectrum of the observed variants was analyzed in conjunction with data available from other populations.

RESULTS

Eight potentially pathogenic mutations (p.His4ArgfsX21, p.Asp23GlufsX9, p.Ile48ValfsX55, p.His50Asp, p.Ser57*, p.Gly113Asp, p.Arg121Gln, and p.Cys126Arg, including five novel ones), were observed in the coding region of the NDP gene in ten unrelated FEVR probands (9%). The novel changes were not observed in the control subjects and were unavailable in the dbSNP, ESP5400, NIEHS95, and ExAC databases. All probands with NDP mutations exhibited classical features of the disease as observed among patients with FEVR worldwide.

CONCLUSIONS

This is perhaps the first study to demonstrate the involvement of NDP among patients with Indian FEVR that further expands its mutation spectrum. The data generated could have broad implications in genetic counseling, disease management, and early intervention for a better prognosis in FEVR.

Coexistence of neuroblastoma and ganglioneuroma in a girl with a hemizygous deletion of chromosome 11q14.1-23.3

Constitutional 11q interstitial deletion syndrome presents with congenital anomalies including microcephaly with craniostenosis, minor dysmorphic features, vitreoretinopathy, and renal anomalies. This syndrome is occasionally associated with neuroblastoma (NB) as a life-threatening complication, which is important for clinical care. Although the corresponding locus to NB has been predicted to exist in 11q22-23 by previous deletion studies related to NB, the causative haploinsufficient genes have not yet been identified. We herein reported for the first time the simultaneous coexistence of adrenal NB and abdominal prevertebral ganglioneuroma in a 6-year-old girl with a constitutional hemizygous 11q14.1-23.3 deletion. Of the 11 haploinsufficient genes predicted with an in silico database, we focused on NCAM1 and CADM1 as the genes accountable for NB and ganglioneuroma. The deletion range, especially the 11q22.3 involvement, needs to be determined in 11q deletion cases in order to predict susceptibility to peripheral nerve tumors involving NB and ganglioneuroma.

Familial Exudative Vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is a hereditary disease associated with visual loss, particularly in the pediatric group. Mutations in the NDP, FZD4, LRP5, and TSPAN12 genes have been shown to contribute to FEVR. FEVR has been reported to have X-linked recessive, autosomal dominant, and autosomal recessive inheritances. However, both the genotypic and phenotypic features are variable. Novel mutations contributing to the disease have been reported. The earliest and the most prominent finding of the disease is avascularity in the peripheral retina. As the disease progresses, retinal neovascularization, subretinal exudation, partial and total retinal detachment may occur, which may be associated with certain mutations. With early diagnosis and prompt management visual loss can be prevented with laser photocoagulation and anti-VEGF injections. In case of retinal detachment, pars plana vitrectomy alone or combined with scleral buckling should be considered. Identifying asymptomatic family members with various degrees of insidious findings is of certain importance. Wide-field imaging with fluorescein angiography is crucial in the management of this disease. The differential diagnosis includes other pediatric vitreoretinopathies such as Norrie disease, retinopathy of prematurity, and Coats’ disease.

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.

Next-generation sequencing and novel variant determination in a cohort of 92 familial exudative vitreoretinopathy patients

PURPOSE

Familial exudative vitreoretinopathy (FEVR) is a developmental disease that can cause visual impairment and retinal detachment at a young age. Four genes involved in the Wnt signaling pathway were previously linked to this disease: NDP, FDZ4, LRP5, and TSPAN12. Identification of novel disease-causing alleles allows for a deeper understanding of the disease, better molecular diagnosis, and improved treatment.

METHODS

Sequencing libraries from 92 FEVR patients were generated using a custom capture panel to enrich for 163 known retinal disease-causing genes in humans. Samples were processed using next generation sequencing (NGS) techniques followed by data analysis to identify and classify single nucleotide variants and small insertions and deletions. Sanger validation and segregation testing were used to verify suspected variants.

RESULTS

Of the cohort of 92, 45 patients were potentially solved (48.9%). Solved cases resulted from the determination of 49 unique mutations, 41 of which are novel. Of the novel variants discovered, 13 were highly likely to cause FEVR due to the nature of these variants (frameshifting indels, splicing mutations, and nonsense variants types). To our knowledge, this is the largest study of a FEVR cohort using NGS.

CONCLUSIONS

We were able to determine probable disease-causing variants in a large number of FEVR patients, the majority of which were novel. Knowledge of these variants will help to further characterize and diagnose FEVR.

Familial exudative vitreoretinopathy and related retinopathies

Familial exudative vitreoretinopathy (FEVR) is a rare inherited disorder of retinal angiogenesis. Cases can be autosomal dominant, autosomal recessive, or X-linked. FEVR patients have an avascular peripheral retina which, depending on the degree of ischaemia, causes the secondary complications of the disease. Expressivity may be asymmetric and is highly variable. Five genes have been identified that when mutated, cause FEVR; NDP (X-linked), FZD4 (autosomal dominant and recessive), LRP5 (autosomal dominant and recessive), TSPAN12 (autosomal dominant and recessive), and ZNF408 (autosomal dominant). Four of these genes have been shown to have a central role in Norrin/Frizzled4 signalling, suggesting a critical role for this pathway in retinal angiogenesis. In addition to the ocular features, LRP5 mutations can cause osteopenia and osteoporosis. All FEVR patients in whom molecular testing is not easily accessible should have dual energy X-ray absorptiometry (DEXA) scans to assess bone mineral density, as treatment can be initiated to reduce the risk of bone fractures.

Identification of two novel LRP5 mutations in families with familial exudative vitreoretinopathy

PURPOSE

To investigate the clinical features and disease-causing mutations in two Chinese families with familial exudative vitreoretinopathy (FEVR).

METHODS

Clinical data and genomic DNA were collected for patients with FEVR. The coding exons and adjacent intronic regions of FZD4, LRP5, TSPAN12, and NDP were amplified with PCR, and the resulting amplicons were analyzed with Sanger sequencing. Wild-type and mutant LRP5 proteins were assayed for the Norrin/β-catenin pathway by luciferase reporter assays.

RESULTS

Two novel heterozygous mutations in the LRP5 gene were identified in two relatives--p.A422T and p.L540P. Typical FEVR fundus change and mild reduced bone mineral density (BMD) was found in the two patients and the affected parent. In the luciferase studies, both p.A422T and p.L540P mutants displayed a significant reduction of the luciferase activity in SuperTopFlash (STF) cells in response to Norrin (87% reduction for p.A422T and 97% reduction for p.L540P). Both patients had an additional LRP5 sequence change (p.Q816P in Patient 1 from the unaffected mother and p.T852M in Patient 2 verified as a new mutation). Luciferase assay showed no reduction for p.Q816P and 94.9% reduction for the new mutation p.T852M, suggesting that p.Q816P may be not pathogenic and p.T852M may be pathogenic.

CONCLUSIONS

Our findings demonstrated two new novel LRP5 mutations in Chinese patients with FEVR and mild reduced BMD. They emphasize the complexity of FEVR mutations and phenotypes.

Genetic variants of FZD4 and LRP5 genes in patients with advanced retinopathy of prematurity

PURPOSE

Retinopathy of prematurity (ROP) is a complex disease with a genetic predisposition, but little is known about its genetic background. It has a clinical resemblance to familial exudative vitreoretinopathy (FEVR), a hereditary disease characterized by defects in the development of retinal vessels. Several studies have suggested that mutations in the causative genes for FEVR may account for a proportion of advanced ROP, but conflicting data have also been reported for some variants. To address the possibility of genetic involvement of FEVR genes in ROP, we performed comprehensive sequence analyses of 53 Japanese patients with advanced ROP for the FEVR-causing genes.

METHODS

Peripheral blood DNA was obtained from 53 patients referred to our hospitals for retinal surgery. Polymerase chain reaction followed by direct sequencing of the coding regions of the known FEVR-causing genes (FZD4, LRP5, TSPAN12, and NDP) and a noncoding exon of the NDP gene was performed. Possible pathogenicity of the sequence changes were analyzed by orthologous protein sequence alignment and by computational predictions.

RESULTS

We identified six different nonsynonymous DNA variants in the coding region of either the FZD4 gene (p.H69Y, p.R127H, and p.Y211H) or the LRP5 gene (p.R1219H, p.H1383P, and p.T1540M) in seven patients. The corresponding codons of these changes were highly conserved among species, and these changes were predicted to be pathogenic by at least two of four computational prediction programs. No such changes were found in the TSPAN12 and NDP genes.

CONCLUSIONS

Six possibly pathogenic variants of FZD4 or LRP5 were found in seven advanced ROP patients. Although these variants do not yet provide definitive evidence that they are causal, the results imply a role of the FZD4 and LRP5 genes in the development of advanced ROP.

Identification of FZD4 and LRP5 mutations in 11 of 49 families with familial exudative vitreoretinopathy

PURPOSE

To identify mutations in FZD4 and LRP5 in 49 Chinese families with familial exudative vitreoretinopathy (FEVR) and to reveal the mutation spectrum and frequency of these genes in the Chinese population.

METHODS

Clinical data and genomic DNA were collected for patients from 49 families with FEVR. The coding exons and adjacent intronic regions of FZD4 and LRP5 were amplified with polymerase chain reaction, and the resulting amplicons were analyzed with Sanger sequencing.

RESULTS

Eleven mutations were detected in 11 of the 49 families (22.4%), including five mutations in the FZD4 gene in six families and six mutations in the LRP5 gene in five families. Of the 11 mutations, eight were novel. Two families had the same FZD4 mutation, and one family had compound heterozygous mutations in LRP5. The phenotypes of the patients with the mutations showed great variability.

CONCLUSIONS

Our findings provide an overview of the mutation spectrum and frequency of FZD4 and LRP5 in Chinese patients with FEVR and emphasize the complexity of FEVR mutations and phenotypes.

Novel TSPAN12 mutations in patients with familial exudative vitreoretinopathy and their associated phenotypes

PURPOSE

Mutations in tetraspanin 12 (TSPAN12) have recently been identified as a cause of autosomal dominant familial exudative vitreoretinopathy (FEVR). The purpose of this study was to detect TSPAN12 mutations in Chinese patients with FEVR and to describe the associated phenotypes.

METHODS

Sanger sequencing was used to analyze the seven coding exons and their adjacent regions of TSPAN12 in 49 unrelated FEVR patients. Clinical phenotypes of the patients with TSPAN12 mutations were documented.

RESULTS

Three novel heterozygous mutations in TSPAN12 were identified in three patients from unrelated families: c.146C>T (p.Thr49Met), c.313T>C (p.Cys105Arg), and c.601delC (p.Leu201PhefsX14). All three mutations involved highly conserved residues and were not present in 180 normal individuals. Ocular phenotypes included retinal folds, inferotemporal dragging of the optic disc and macula, increased vessels in the equatorial region, and a peripheral avascular zone. A father and his daughter had the same mutation but the father only had mild peripheral fundus changes while his daughter had obvious dragged disc and macular ectopia.

CONCLUSIONS

Our results suggest that TSPAN12 mutations are responsible for FEVR. Similar to patients with mutations in NDP, LRP5, or FZD4, the phenotypes associated with TSPAN12 mutations showed great variations between different individuals within a family and between the two eyes in individual patients.

Analysis of candidate genes for macular telangiectasia type 2

PURPOSE

To find the gene(s) responsible for macular telangiectasia type 2 (MacTel) by a candidate-gene screening approach.

METHODS

Candidate genes were selected based on the following criteria: those known to cause or be associated with diseases with phenotypes similar to MacTel, genes with known function in the retinal vasculature or macular pigment transport, genes that emerged from expression microarray data from mouse models designed to mimic MacTel phenotype characteristics, and genes expressed in the retina that are also related to diabetes or hypertension, which have increased prevalence in MacTel patients. Probands from eight families with at least two affected individuals were screened by direct sequencing of 27 candidate genes. Identified nonsynonymous variants were analyzed to determine whether they co-segregate with the disease in families. Allele frequencies were determined by TaqMan analysis of the large MacTel and control cohorts.

RESULTS

We identified 23 nonsynonymous variants in 27 candidate genes in at least one proband. Of these, eight were known single nucleotide polymorphisms (SNPs) with allele frequencies of >0.05; these variants were excluded from further analyses. Three previously unidentified missense variants, three missense variants with reported disease association, and five rare variants were analyzed for segregation and/or allele frequencies. No variant fulfilled the criteria of being causal for MacTel. A missense mutation, p.Pro33Ser in frizzled homolog (Drosophila) 4 (FZD4), previously suggested as a disease-causing variant in familial exudative vitreoretinopathy, was determined to be a rare benign polymorphism.

CONCLUSIONS

We have ruled out the exons and flanking intronic regions in 27 candidate genes as harboring causal mutations for MacTel.

Mutations in TSPAN12 cause autosomal-dominant familial exudative vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is an inherited blinding disorder of the retinal vascular system. Although mutations in three genes (LRP5, FZD4, and NDP) are known to cause FEVR, these account for only a fraction of FEVR cases. The proteins encoded by these FEVR genes form part of a signaling complex that activates the Norrin-beta-catenin signaling pathway. Recently, through a large-scale reverse genetic screen in mice, Junge and colleagues identified an additional member of this signaling complex, Tspan12. Here, we report that mutations in TSPAN12 also cause autosomal-dominant FEVR. We describe seven mutations identified in a cohort of 70 FEVR patients in whom we had already excluded the known FEVR genes. This study provides further evidence for the importance of the Norrin-beta-catenin signaling pathway in the development of the retinal vasculature and also indicates that more FEVR genes remain to be identified.