Whole Exome Sequencing Analysis Identifies Mutations in LRP5 in Indian Families with Familial Exudative Vitreoretinopathy

Early-Onset Osteoporosis: Molecular Analysis in Large Cohort and Focus on the PLS3 Gene

Osteoporosis is a skeletal disorder characterized by abnormal bone microarchitecture and low bone mineral density (BMD), responsible for an increased risk of fractures and skeletal fragility. It is a common pathology of the aging population. However, when osteoporosis occurs in children or young adults, it strongly suggests an underlying genetic etiology. Over the past two decades, several genes have been identified as responsible for this particular kind of considered monogenic early-onset osteoporosis (EOOP) or juvenile osteoporosis, the main ones being COL1A1, COL1A2, LRP5, LRP6, WNT1, and more recently PLS3. In this study, the objective was to characterize a large cohort of patients diagnosed with primary osteoporosis and to establish its diagnosis yield. The study included 577 patients diagnosed with primary osteoporosis and its diagnosis yield was established. To this end, next-generation sequencing (NGS) of a panel of 21 genes known to play a role in bone fragility was carried out. A genetic etiology was explained in about 18% of cases, while the others remain unexplained. The most frequently identified gene associated with EOOP is LRP5, which was responsible for 8.2% of the positive results (47 patients). As unexpected, 17 patients (2.9%) had a variant in PLS3 which encodes plastin 3. Alterations of PLS3 are associated with dominant X-linked osteoporosis, an extremely rare disease. Given the rarity of this disease, we focused on it. It was observed that males were more affected than females, but it is noteworthy that three females with a particularly severe phenotype were identified. Of these three, two had a variant in an additional gene involved in EOP, illustrating the probable existence of digenism. We significantly increase the number of variants potentially associated with EOOP, especially in PLS3. The results of our study demonstrate that molecular analysis in EOOP is beneficial and useful.

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.

Rare eye diseases in India: A concise review of genes and genetics

Rare eye diseases (REDs) are mostly progressive and are the leading cause of irreversible blindness. The disease onset can vary from early childhood to late adulthood. A high rate of consanguinity contributes to India’s predisposition to RED. Most gene variations causing REDs are monogenic and, in some cases, digenic. All three types of Mendelian inheritance have been reported in REDs. Some of the REDs are related to systemic illness with variable phenotypes in affected family members. Approximately, 50% of the children affected by REDs show associated phenotypes at the early stages of the disease. A precise clinical diagnosis becomes challenging due to high clinical and genetic heterogeneity. Technological advances, such as next-generation sequencing (NGS), have improved genetic and genomic testing for REDs, thereby aiding in determining the underlying causative gene variants. It is noteworthy that genetic testing together with genetic counseling facilitates a more personalized approach in the accurate diagnosis and management of the disease. In this review, we discuss REDs identified in the Indian population and their underlying genetic etiology.

The ER membrane protein complex subunit Emc3 controls angiogenesis via the FZD4/WNT signaling axis

The endoplasmic reticulum (ER) membrane protein complex (EMC) regulates the synthesis and quality control of membrane proteins with multiple transmembrane domains. One of the membrane spanning subunits, EMC3, is a core member of the EMC complex that provides essential hydrophilic vestibule for substrate insertion. Here, we show that the EMC subunit Emc3 plays critical roles in the retinal vascular angiogenesis by regulating Norrin/Wnt signaling. Postnatal endothelial cell (EC)-specific deletion of Emc3 led to retarded retinal vascular development with a hyperpruned vascular network, the appearance of blunt-ended, aneurysm-like tip endothelial cells (ECs) with reduced numbers of filopodia and leakage of erythrocytes at the vascular front. Diminished tube formation and cell proliferation were also observed in EMC3 depleted human retinal endothelial cells (HRECs). We then discovered a critical role for EMC3 in expression of FZD4 receptor of β-catenin signaling using RNA sequencing, real-time quantitative PCR (RT-qPCR) and luciferase reporter assay. Moreover, augmentation of Wnt activity via lithium chloride (LiCl) treatment remarkably enhanced β-catenin signaling and cell proliferation of HRECs. Additionally, LiCl partially reversed the angiogenesis defects in Emc3-cKO mice. Our data reveal that Emc3 plays essential roles in angiogenesis through direct control of FZD4 expression and Norrin/β-catenin signaling.

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

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

Identification of novel USH2A mutations in patients with autosomal recessive retinitis pigmentosa via targeted next‑generation sequencing

Retinitis pigmentosa (RP) is a group of inheritable blindness retinal diseases characterized by the death of photoreceptor cells and a gradual loss of peripheral vision. Mutations in Usher syndrome type 2 (USH2A) have been reported in RP with or without hearing loss. The present study aimed to identify causative mutations in a cohort of families with RP from China. A cohort of 62 non‑syndromic families with RP and 30 sporadic cases were enrolled in this study. All affected members underwent a complete ophthalmic examination, including fundus photography, visual‑field test and optical coherence tomography examination. Next‑generation sequencing‑targeted sequencing of 163 genes involved in inheritable retinal disorders was performed on the probands. Stringent bioinformatics data analysis was applied to identify potential candidate variants. In total, 6 novel mutations and 2 known mutations of USH2A were identified in 4 families with RP. A stop‑gain mutation (c.C1731A) and a missense mutation (c.G8254A) were identified in RP family RP‑2148. In another RP family, RP‑2150, a known mutation (c.G802A) and a novel frameshift insertion mutation (c.12086dupA) were discovered. A novel stop‑gain mutation (c.G11754A) and a missense mutation (c.G13465A) were identified in family rpz05. A novel missense mutation (c.C9328G) and a known missense mutation (c.G8232C) were also identified. These mutations were subsequently confirmed by Sanger sequencing. All 6 novel mutations affected highly conserved amino acid residues, and were absent in 1,000 ethnically matched controls. Taken together, the present study has reported on 6 novel USH2A mutations in 4 families with RP, and has expanded the mutation spectrum of USH2A in autosomal recessive RP in the Chinese population, thus providing important information for the molecular diagnosis and screening of RP.

Norrin restores blood-retinal barrier properties after vascular endothelial growth factor-induced permeability

Vascular endothelial growth factor (VEGF) contributes to blood-retinal barrier (BRB) dysfunction in several blinding eye diseases, including diabetic retinopathy. Signaling via the secreted protein norrin through the frizzled class receptor 4 (FZD4)/LDL receptor-related protein 5-6 (LRP5-6)/tetraspanin 12 (TSPAN12) receptor complex is required for developmental vascularization and BRB formation. Here, we tested the hypothesis that norrin restores BRB properties after VEGF-induced vascular permeability in diabetic rats or in animals intravitreally injected with cytokines. Intravitreal co-injection of norrin with VEGF completely ablated VEGF-induced BRB permeability to Evans Blue-albumin. Likewise, 5-month diabetic rats exhibited increased permeability of FITC-albumin, and a single norrin injection restored BRB properties. These results were corroborated in vitro, where co-stimulation of norrin with VEGF or stimulation of norrin after VEGF exposure restored barrier properties, indicated by electrical resistance or 70-kDa RITC-dextran permeability in primary endothelial cell culture. Interestingly, VEGF promoted norrin signaling by increasing the FZD4 co-receptor TSPAN12 at cell membranes in an MAPK/ERK kinase (MEK)/ERK-dependent manner. Norrin signaling through β-catenin was required for BRB restoration, but glycogen synthase kinase 3 α/β (GSK-3α/β) inhibition did not restore BRB properties. Moreover, levels of the tight junction protein claudin-5 were increased with norrin and VEGF or with VEGF alone, but both norrin and VEGF were required for enriched claudin-5 localization at the tight junction. These results suggest that VEGF simultaneously induces vascular permeability and promotes responsiveness to norrin. Norrin, in turn, restores tight junction complex organization and BRB properties in a β-catenin-dependent manner.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

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.

Genetic variants of TSPAN12 gene in patients with retinopathy of prematurity

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

TMEM30A deficiency in endothelial cells impairs cell proliferation and angiogenesis

Phosphatidylserine (PS) asymmetry in the eukaryotic cell membrane is maintained by a group of proteins belonging to the P4-ATPase family, namely, PS flippases. The folding and transporting of P4-ATPases to their cellular destination requires a β-subunit member of the TMEM30 protein family. Loss of Tmem30a has been shown to cause multiple disease conditions. However, its roles in vascular development have not been elucidated. Here, we show that TMEM30A plays critical roles in retinal vascular angiogenesis, which is a fundamental process in vascular development. Our data indicate that knockdown of TMEM30A in primary human retinal endothelial cells led to reduced tube formation. In mice, endothelial cell (EC)-specific deletion of Tmem30a led to retarded retinal vascular development with a hyperpruned vascular network as well as blunted-end, aneurysm-like tip ECs with fewer filopodia at the vascular front and a reduced number of tip cells. Deletion of Tmem30a also impaired vessel barrier integrity. Mechanistically, deletion of TMEM30A caused reduced EC proliferation by inhibiting VEGF-induced signaling. Our findings reveal essential roles of TMEM30A in angiogenesis, providing a potential therapeutic target.

Targeted Next-Generation Sequencing Reveals Novel RP1 Mutations in Autosomal Recessive Retinitis Pigmentosa

BACKGROUND

Retinitis pigmentosa (RP) is a group of rare inherited retinal dystrophies that result in a progressive loss of vision. Molecular diagnosis of RP is difficult due to its phenotypic and genetic heterogeneities.

AIMS

To investigate causative genetic mutations in a collection of RP cases: one Indian and two Chinese families with autosomal-recessive RP and two sporadic patients with RP.

MATERIALS AND METHODS

A total of 163 genes, which have previously been found to be involved in inherited retinal disorders, were selected for targeted next-generation sequencing (NGS). Stringent NGS data analyses followed by confirmation using Sanger sequencing and segregation analyses were applied to evaluate all identified pathogenic mutations.

RESULTS

Four novel frameshift mutations and two compound heterozygous mutations were identified in RP1. In addition, all mutations were found to co-segregate with the disease in the three familial cases; none of the mutations were detected in control samples.

CONCLUSION

This study expands the mutational spectrums of RP1 for RP.

Targeted Next Generation Sequencing Revealed Novel PRPF31 Mutations in Autosomal Dominant Retinitis Pigmentosa

BACKGROUND

Retinitis pigmentosa (RP) is a rare type of inherited retinal dystrophy that can result in progressive vision loss. Molecular diagnosis of RP is challenging due to phenotypic and genotypic heterogeneities.

AIMS

This study aimed to identify the pathogenic mutations in two Chinese families with autosomal dominant RP (adRP) and in a patient with sporadic RP.

MATERIALS AND METHODS

Peripheral blood DNA samples were obtained from the participants. Targeted next generation sequencing (NGS) was applied to identify mutations in these patients. For pathogenic mutation analyses, stringent NGS data analyses and segregation analyses were applied. Primers were designed to validate the identified mutations by Sanger sequencing analyses.

RESULTS

A novel heterozygous insertion frameshift mutation c.1226_1227insA, p.T410Dfs*65, and a novel heterozygous stopgain mutation c.1015C>T, p.Q339* were identified in PRPF31. A known c.527 + 3A>G splicing mutation was identified in one of the adRP-074 families. All mutations were found to co-segregate with the disease, and none of these mutations were detected in 500 control samples.

CONCLUSIONS

Our data identified two new autosomal dominant mutations in PRPF31, expanding the mutational spectrum of this gene.

Intrinsic disorder in spondins and some of their interacting partners

Spondins, which are proteins that inhibit and promote adherence of embryonic cells so as to aid axonal growth are part of the thrombospondin-1 family. Spondins function in several important biological processes, such as apoptosis, angiogenesis, etc. Spondins constitute a thrombospondin subfamily that includes F-spondin, a protein that interacts with Aβ precursor protein and inhibits its proteolytic processing; R-spondin, a 4-membered group of proteins that regulates Wnt pathway and have other functions, such as regulation of kidney proliferation, induction of epithelial proliferation, the tumor suppressant action; M-spondin that mediates mechanical linkage between the muscles and apodemes; and the SCO-spondin, a protein important for neuronal development. In this study, we investigated intrinsic disorder status of human spondins and their interacting partners, such as members of the LRP family, LGR family, Frizzled family, and several other binding partners in order to establish the existence and importance of disordered regions in spondins and their interacting partners by conducting a detailed analysis of their sequences, finding disordered regions, and establishing a correlation between their structure and biological functions.