Mutations and mechanisms in congenital and age-related cataracts

Application of Andersen-Newman model to assess cataract surgery uptake among older Australian women: findings from the Australian Longitudinal Study on Women's Health (ALSWH)

INTRODUCTION

Although Cataract Surgery Rate is increasing, the availability of surgery is outstripped by the increasing number of cataract cases as populations age.

AIM

The study aimed to identify factors associated with cataract surgery uptake in terms of predisposing, enabling, and need factors in very old Australian women.

METHOD

This study used ALSWH data included 6229 women aged 79-84 to 85-90 years. Women were asked whether they had undergone eye surgery (including cataracts) three years prior to each survey. Generalised estimating equation modelling was used to determine factors associated with these surgeries.

RESULT

At baseline (2005), more than half of the participants either had undergone surgery (43.5%) or had unoperated cataracts (7.6%). Increasing age (AOR = 1.11, 95% CI = 1.07, 1.15) and being current or ex-smokers (AOR = 1.15, 95% CI = 1.03, 1.29) were associated with higher odds of cataract surgery (predisposing factors). Women who had private health insurance had 27% higher odds of having surgery (AOR = 1.27, 95% CI = 1.16, 1.39) (enabling factor). Need factors of more General Practitioner visits (AOR = 1.16, 95% CI = 1.09, 1.25) and skin cancer (AOR = 1.09, 95% CI = 1.01, 1.17) also increased the odds of cataract surgery. Women who had no difficulty seeing newspaper print were more likely to have had cataract surgery (AOR = 1.35, 95% CI = 1.23, 1.48).

CONCLUSION

Need factors are the major drivers of cataract surgery; however, predisposing and enabling factors also play a role, including access to private health insurance. This finding indicates some inequity regarding access to cataract surgery in the Australian setting.

Novel SOX2 mutation in autosomal dominant cataract-microcornea syndrome

Background

Congenital cataract-microcornea syndrome (CCMC) is characterized by the association of congenital cataract and microcornea without any other systemic anomaly or dysmorphism. Although several causative genes have been reported in patients with CCMC, the genetic etiology of CCMC is yet to be clearly understood.

Purpose

To unravel the genetic cause of autosomal dominant family with CCMC.

Methods

All patients and available family members underwent a comprehensive ophthalmologic clinical examination in the hospital by expert ophthalmologists and carried out to clinically diagnosis. All the patients were screened by whole-exome sequencing and then validated using co-segregation by Sanger sequencing.

Results

Four CCMC patients from a Chinese family and five unaffected family members were enrolled in this study. Using whole-exome sequencing, a missense mutation c.295G > T (p.A99S, NM_003106.4) in the SOX2 gene was identified and validated by segregation analysis. In addition, this missense mutation was predicted to be damaging by multiple predictive tools. Variant p.Ala99Ser was located in a conservation high mobility group (HMG)-box domain in SOX2 protein, with a potential pathogenic impact of p.Ala99Ser on protein level.

Conclusions

A novel missense mutation (c.295G > T, p.Ala99Ser) in the SOX2 gene was found in this Han Chinese family with congenital cataract and microcornea. Our study determined that mutations in SOX2 were associated with CCMC, warranting further investigations on the pathogenesis of this disorder. This result expands the mutation spectrum of SOX2 and provides useful information to study the molecular pathogenesis of CCMC.

Case Report: A Novel Mutation in the CRYGD Gene Causing Congenital Cataract Associated with Nystagmus in a Chinese Family

Purpose: Congenital cataract (CC) is a common disease resulting in leukocoria and the leading cause of blindness in children worldwide. Approximately 50% of congenital cataract is inherited. Our aim is to identify mutations in a Chinese family with congenital cataract.

Methods: A four-generation Chinese family diagnosed with congenital cataract was recruited in West China Hospital of Sichuan University. Genomic DNA was extracted from the peripheral blood of these participants. All coding exons and flanking regions were amplified and sequenced, and the variants were validated using Sanger sequencing. AlphaFold2 was used to predict possible protein structural changes in this variant.

Results: The proband had congenital nuclear cataract with nystagmus. A heterozygous variant c.233C > T was identified in exon 2 of the CRYGD gene in chromosome 2. This mutation resulted in a substitution of serine with phenylalanine at amino acid residue 78 (p.S78F). The variant might result in a less stable structure with a looser loop and broken hydrogen bond predicted by AlphaFold2, and this mutation was co-segregated with the disease phenotype in this family.

Conclusion: We described cases of human congenital cataract caused by a novel mutation in the CRYGD gene and provided evidence of further phenotypic heterogeneity associated with this variant. Our study further extends the mutation spectrum of the CRYGD gene in congenital cataract.

Crystallins as Important Pathogenic Targets for Accumulation of Structural Damages Resulting in Protein Aggregation and Cataract Development: Introduction to This Special Issue of Biochemistry (Moscow)

This issue of Biochemistry (Moscow) is dedicated to the role of protein misfolding and aggregation in cataract development. In fact, many genetic mutations or chemical and physical deleterious factors can initiate alterations in the macrostructural order and proper folding of eye lens proteins, which in some cases result in the formation of large light-scattering aggregates, affecting the quality of vision and making lens more prone to cataract development. Diabetes mellitus, which is associated with oxidative stress and mass production of highly reactive compounds, can accelerate unfolding and aggregation of eye lens proteins. This journal issue contains reviews and research articles that describe the destructive effects of mutations and highly reactive metabolites on the structure and function of lens crystallin proteins, as well important molecules in the lens's natural defense system involved in protection against deleterious effects of the physical and chemical factors.

Congenital cataract-causing mutation βB1-L116P is prone to amyloid fibrils aggregation and protease degradation with low structural stability

Congenital cataract, a common disease with lens opacification, causes blindness in the newborn worldwide and is mainly caused by abnormal aggregation of crystallin. As the main structural protein in the mammalian lens, βB1-crystallin has an important role in the maintenance of lens transparency. Recently, the L116P mutation in βB1-CRY was found in a Chinese family with congenital nuclear cataracts, while its underlying pathogenic mechanism remains unclear. In the current study, the βB1 wild-type protein was purified, and the mutated form, βB1-L116P, was examined for examining the effect on structural stability and susceptibility against environmental stresses. Our results reveal low solubility and structural stability of βB1-L116P at physiological temperature, which markedly impaired the protein structure and the oligomerization of βB1-crystallin. Under guanidine hydrochloride-induced denaturing conditions, βB1-L116P mutation perturbed the protein unfolding process, making it prone to amyloid fibrils aggregation. More importantly, the L116P mutation increased susceptibility of βB1-crystallin against UV radiation. βB1-L116P overexpression led to the formation of more serious intracellular aggresomes under UV radiation or oxidative stress. Furthermore, the βB1-L116P mutation increased the sensitivity to the proteolysis process. These results indicate that the low structural stability, susceptibility to amyloid fibrils aggregation, and protease degradation of βB1-L116P may contribute to cataract development and associated symptoms.

Disruption of PIKFYVE causes congenital cataract in human and zebrafish

Congenital cataract, an ocular disease predominantly occurring within the first decade of life, is one of the leading causes of blindness in children. However, the molecular mechanisms underlying the pathogenesis of congenital cataract remain incompletely defined. Through whole-exome sequencing of a Chinese family with congenital cataract, we identified a potential pathological variant (p.G1943E) in PIKFYVE, which is located in the PIP kinase domain of the PIKFYVE protein. We demonstrated that heterozygous/homozygous disruption of PIKFYVE kinase domain, instead of overexpression of PIKFYVE^G1943E in zebrafish mimicked the cataract defect in human patients, suggesting that haploinsufficiency, rather than dominant-negative inhibition of PIKFYVE activity caused the disease. Phenotypical analysis of pikfyve zebrafish mutants revealed that loss of Pikfyve caused aberrant vacuolation (accumulation of Rab7⁺Lc3⁺ amphisomes) in lens cells, which was significantly alleviated by treatment with the V-ATPase inhibitor bafilomycin A1 (Baf-A1). Collectively, we identified PIKFYVE as a novel causative gene for congenital cataract and pinpointed the potential application of Baf-A1 for the treatment of congenital cataract caused by PIKFYVE deficiency.

Physiological Mechanisms Regulating Lens Transport

The transparency and refractive properties of the lens are maintained by the cellular physiology provided by an internal microcirculation system that utilizes spatial differences in ion channels, transporters and gap junctions to establish standing electrochemical and hydrostatic pressure gradients that drive the transport of ions, water and nutrients through this avascular tissue. Aging has negative effects on lens transport, degrading ion and water homeostasis, and producing changes in lens water content. This alters the properties of the lens, causing changes in optical quality and accommodative amplitude that initially result in presbyopia in middle age and ultimately manifest as cataract in the elderly. Recent advances have highlighted that the lens hydrostatic pressure gradient responds to tension transmitted to the lens through the Zonules of Zinn through a mechanism utilizing mechanosensitive channels, multiple sodium transporters respond to changes in hydrostatic pressure to restore equilibrium, and that connexin hemichannels and diverse intracellular signaling cascades play a critical role in these responses. The mechanistic insight gained from these studies has advanced our understanding of lens transport and how it responds and adapts to different inputs both from within the lens, and from surrounding ocular structures.

Contribution of Genetic Background to the Radiation Risk for Cancer and Non-Cancer Diseases in Ptch1+/- Mice

Experimental mouse studies are important to gain a comprehensive, quantitative and mechanistic understanding of the biological factors that modify individual risk of radiation-induced health effects, including age at exposure, dose, dose rate, organ/tissue specificity and genetic factors. In this study, neonatal Ptch1+/- mice bred on CD1 and C57Bl/6 background received whole-body irradiation at postnatal day 2. This time point represents a critical phase in the development of the eye lens, cerebellum and dentate gyrus (DG), when they are also particularly susceptible to radiation effects. Irradiation was performed with γ rays (60Co) at doses of 0.5, 1 and 2 Gy, delivered at 0.3 Gy/min or 0.063 Gy/min. Wild-type and mutant mice were monitored for survival, lens opacity, medulloblastoma (MB) and neurogenesis defects. We identified an inverse genetic background-driven relationship between the radiosensitivity to induction of lens opacity and MB and that to neurogenesis deficit in Ptch1+/- mutants. In fact, high incidence of radiation-induced cataract and MB were observed in Ptch1+/-/CD1 mutants that instead showed no consequence of radiation exposure on neurogenesis. On the contrary, no induction of radiogenic cataract and MB was reported in Ptch1+/-/C57Bl/6 mice that were instead susceptible to induction of neurogenesis defects. Compared to Ptch1+/-/CD1, the cerebellum of Ptch1+/-/C57Bl/6 mice showed increased radiosensitivity to apoptosis, suggesting that differences in processing radiation-induced DNA damage may underlie the opposite strain-related radiosensitivity to cancer and non-cancer pathologies. Altogether, our results showed lack of dose-rate-related effects and marked influence of genetic background on the radiosensitivity of Ptch1+/-mice, supporting a major contribution of individual sensitivity to radiation risk in the population.

RNA-binding proteins and post-transcriptional regulation in lens biology and cataract: Mediating spatiotemporal expression of key factors that control the cell cycle, transcription, cytoskeleton and transparency

Development of the ocular lens - a transparent tissue capable of sustaining frequent shape changes for optimal focusing power - pushes the boundaries of what cells can achieve using the molecular toolkit encoded by their genomes. The mammalian lens contains broadly two types of cells, the anteriorly located monolayer of epithelial cells which, at the equatorial region of the lens, initiate differentiation into fiber cells that contribute to the bulk of the tissue. This differentiation program involves massive upregulation of select fiber cell-expressed RNAs and their subsequent translation into high amounts of proteins, such as crystallins. But intriguingly, fiber cells achieve this while also simultaneously undergoing significant morphological changes such as elongation - involving about 1000-fold length-wise increase - and migration, which requires modulation of cytoskeletal and cell adhesion factors. Adding further to the challenges, these molecular and cellular events have to be coordinated as fiber cells progress toward loss of their nuclei and organelles, which irreversibly compromises their potential for harnessing genetically hardwired information. A long-standing question is how processes downstream of signaling and transcription, which may also participate in feedback regulation, contribute toward orchestrating these cellular differentiation events in the lens. It is now becoming clear from findings over the past decade that post-transcriptional gene expression regulatory mechanisms are critical in controlling cellular proteomes and coordinating key processes in lens development and fiber cell differentiation. Indeed, RNA-binding proteins (RBPs) such as Caprin2, Celf1, Rbm24 and Tdrd7 have now been described in mediating post-transcriptional control over key factors (e.g. Actn2, Cdkn1a (p21Cip1), Cdkn1b (p27Kip1), various crystallins, Dnase2b, Hspb1, Pax6, Prox1, Sox2) that are variously involved in cell cycle, transcription, cytoskeleton maintenance and differentiation in the lens. Furthermore, deficiencies of these RBPs have been shown to result in various eye and lens defects and/or cataract. Because fiber cell differentiation in the lens occurs throughout life, the underlying regulatory mechanisms operational in development are expected to also be recruited for the maintenance of transparency in aged lenses. Indeed, in support of this, TDRD7 and CAPRIN2 loci have been linked to age-related cataract in humans. Here, I will review the role of key RBPs in the lens and their importance in understanding the pathology of lens defects. I will discuss advances in RBP-based gene expression control, in general, and the important challenges that need to be addressed in the lens to define the mechanisms that determine the epithelial and fiber cell proteome. Finally, I will also discuss in detail several key future directions including the application of bioinformatics approaches such as iSyTE to study RBP-based post-transcriptional gene expression control in the aging lens and in the context of age-related cataract.

Association of age-related cataract risk high polygenetic risk scores involved in galactose-related metabolism and dietary interactions

INTRODUCTION

Cataracts are associated with the accumulation of galactose and galactitol in the lens. We determined the polygenetic risk scores for the best model(PRSBM) associated with age-related cataract(ARC) risk and their interaction with diets and lifestyles in 40,262 Korean adults aged over 50 years belonged to a hospital-based city cohort.

METHODS

The genetic variants for ARC risk were selected in lactose and galactose metabolism-related genes with multivariate logistic regression using the PLINK 1.9 version. PRSBM from the selected genetic variants was estimated by generalized multifactor dimensionality reduction (GMDR) after adjusting covariates. The interactions between the PRSBM and each lifestyle factor were determined to modulate ARC risk.

RESULTS

The genetic variants for ARC risk related to lactose- and galactose metabolism were SLC2A1_rs3729548, ST3GAL3_rs3791047, LCT_rs2304371, GALNT5_rs6728956, ST6GAL1_rs2268536, GALNT17_rs17058752, CSGALNACT1_rs1994788, GALNTL4_rs10831608, B4GALT6_rs1667288, and A4GALT_ rs9623659. In GMDR, the best model included all ten genetic variants. The highest odds ratio (OR) for a single SNP in the PRSBM was 1.26. However, subjects with a high-PRSBM had a higher ARC risk by 2.1-fold than a low-PRSBM after adjusting for covariates. Carbohydrate, dairy products, kimchi, and alcohol intake interacted with PRSBM for ARC risk: the participants with high-PRSBM had a much higher ARC risk than those with low-PRSBM when consuming diets with high carbohydrate and low dairy product and kimchi intake. However, only with low alcohol intake, the participants with high-PRSBM had a higher ARC risk than those with low-PRSBM.

CONCLUSION

Adults aged >50 years having high-PRSBM may modulate dietary habits to reduce ARC risk.

Aged Nrf2-Null Mice Develop All Major Types of Age-Related Cataracts

Purpose

Age-related cataracts affect the majority of older adults and are a leading cause of blindness worldwide. Treatments that delay cataract onset or severity have the potential to delay cataract surgery, but require relevant animal models that recapitulate the major types of cataracts for their development. Unfortunately, few such models are available. Here, we report the lens phenotypes of aged mice lacking the critical antioxidant transcription factor Nfe2l2 (designated as Nrf2 −/−).

Methods

Three independent cohorts of Nrf2 −/− and wild-type C57BL/6J mice were evaluated for cataracts using combinations of slit lamp imaging, photography of freshly dissected lenses, and histology. Mice were fed high glycemic diets, low glycemic diets, regular chow ad libitum, or regular chow with 30% caloric restriction.

Results

Nrf2 −/− mice developed significant opacities between 11 and 15 months and developed advanced cortical, posterior subcapsular, anterior subcapsular, and nuclear cataracts. Cataracts occurred similarly in male mice fed high or low glycemic diets, and were also observed in 21-month male and female Nrf2 −/− mice fed ad libitum or 30% caloric restriction. Histological observation of 18-month cataractous lenses revealed significant disruption to fiber cell architecture and the retention of nuclei throughout the cortical region of the lens. However, fiber cell denucleation and initiation of lens differentiation was normal at birth, with the first abnormalities observed at 3 months.

Conclusions

Nrf2 −/− mice offer a tool to understand how defective antioxidant signaling causes multiple forms of cataract and may be useful for screening drugs to prevent or delay cataractogenesis in susceptible adults.

Transcriptomics Analysis of Lens from Patients with Posterior Subcapsular Congenital Cataract

To gain insight into the aetiology of posterior subcapsular congenital cataract from the perspective of transcriptional changes, we conducted an mRNA sequencing analysis of the lenses in posterior subcapsular congenital cataract patients and in normal children. There were 1533 differentially expressed genes from 19,072 genes in the lens epithelial cells of the posterior subcapsular congenital cataract patients compared to in the normal controls at a cut-off criteria of |log2 fold change| of >1 and a p-value of <0.05, including 847 downregulated genes and 686 upregulated genes. To further narrow down the DEGs, we utilised the stricter criteria of |log2 fold change| of >1 and an FDR value of <0.05, and we identified 551 DEGs, including 97 upregulated genes and 454 downregulated genes. This study also identified 1263 differentially expressed genes of the 18,755 genes in lens cortex and nuclear fibres, including 646 downregulated genes and 617 upregulated genes. The downregulated genes in epithelial cells were significantly enriched in the structural constituent of lenses, lens development and lens fibre cell differentiation. After filtering the DEGs using the databases iSyTE and Cat-Map, several high-priority candidate genes related to posterior subcapsular congenital cataract such as GRIFIN, HTRA1 and DAPL1 were identified. The findings of our study may provide a deeper understanding of the mechanisms of posterior subcapsular congenital cataract and help in the prevention and treatment of this disease.

Broadening the Mutation Spectrum in GJA8 and CHMP4B: Novel Missense Variants and the Associated Phenotypes in Six Chinese Han Congenital Cataracts Families

Purpose: To broaden the mutation and phenotype spectrum of the GJA8 and CHMP4B genes and to reveal genotype-phenotype correlations in a cohort of Chinese patients with congenital cataracts (CCs).

Methods: Six Chinese Han families with CCs inherited in an autosomal dominant (AD) pattern were recruited for this study. All patients underwent full ocular examinations. Genomic DNA was extracted from the leukocytes of peripheral blood collected from all available patients and their unaffected family members. Whole-exome sequencing (WES) was performed on all probands and at least one of their parents. Candidate variants were further confirmed by Sanger sequencing. Bioinformatic analysis with several computational predictive programs was performed to assess the impacts of the candidate variants on the structure and function of the proteins.

Results: Four heterozygous candidate variants in three different genes (CRYBB2, GJA8, and CHMP4B) were identified in affected individuals from the six families, including two novel missense variants (GJA8: c.64G > C/p. G22R, and CHMP4B: c.587C > G/p. S196C), one missense mutation (CRYBB2: c.562C > T/p. R188C), and one small deletion (GJA8: c.426_440delGCTGGAGGGGACCCT/p.143_147delLEGTL). The three missense mutations were predicted as deleterious in all four computational prediction programs. In the homologous model, the GJA8: p.143_147delLEGTL mutation showed a sequence deletion of five amino acids at the cytoplasmic loop of the Cx50 protein, close to the third transmembrane domain. Patients carrying mutations in the same gene showed similar cataract phenotypes at a young age, including total cataracts, Y-sutural with fetal nuclear cataracts, and subcapsular cataracts.

Conclusion: This study further expands the mutation spectrum and genotype-phenotype correlation of CRYBB2, GJA8, and CHMP4B underlying CCs. This study sheds light on the importance of comparing congenital cataract phenotypes in patients at the same age stage. It offers clues for the pathogenesis of CCs and allows for an early prenatal diagnosis for families carrying these genetic variants.

Rapamycin relieves the cataract caused by ablation of Gja8b through stimulating autophagy in zebrafish

Macroautophagy/autophagy is known to be important for intracellular quality control in the lens. GJA8 is a major gap junction protein in vertebrate lenses. Mutations in GJA8 cause cataracts in humans. The well-known cataractogenesis mechanism is that mutated GJA8 leads to abnormal assembly of gap junctions, resulting in defects in intercellular communication among lens cells. In this study, we observed that ablation of Gja8b (a homolog of mammalian GJA8) in zebrafish led to severe defects in organelle degradation, an important cause of cataractogenesis in developing lens. The role of autophagy in organelle degradation in lens remains disputable. Intriguingly, we also observed that ablation of Gja8b induced deficient autophagy in the lens. More importantly, in vivo treatment of zebrafish with rapamycin, an autophagy activator that inhibits MAPK/JNK and MTORC1 signaling, stimulated autophagy in the lens and relieved the defects in organelle degradation, resulting in the mitigation of cataracts in gja8b mutant zebrafish. Conversely, inhibition of autophagy by treatment with the chemical reagent 3-MA blocked these recovery effects, suggesting the important roles of autophagy in organelle degradation in the lens in gja8b mutant zebrafish. Further studies in HLE cells revealed that GJA8 interacted with ATG proteins. Overexpression of GJA8 stimulated autophagy in HLE cells. These data suggest an unrecognized cataractogenesis mechanism caused by ablation of Gja8b and a potential treatment for cataracts by stimulating autophagy in the lens.Abbreviations: 3-MA: 3-methyladenine; ATG: autophagy related; AV: autophagic vacuoles; Dpf: days post fertilization; GJA1: gap junction protein alpha 1; GJA3: gap junction protein alpha 3; GJA8: gap junction protein alpha 8; Hpf: hours post fertilization; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; PtdIns3K: class III phosphatidylinositol 3-kinase; WT: wild type.

Knockdown of lncRNA TUG1 protects lens epithelial cells from oxidative stress-induced injury by regulating miR-196a-5p expression in age-related cataracts

Oxidative stress plays an important role in the pathogenesis of cataracts. Under oxidative stress, apoptosis of lens epithelial cells (LECs) is activated, which may cause lens opacity and accelerate the development of cataracts. Long non-coding RNA (lncRNA) and microRNA (miRNA/miR) are involved in cataracts. Previous studies have demonstrated that lncRNA taurine upregulated 1 (TUG1) promotes cell apoptosis induced by ultraviolet radiation by downregulating the expression of miR-421. However, the mechanism underlying TUG1 in age-related cataract remains to be elucidated. The present study aimed to investigate the effect of TUG1 in age-related cataracts and to determine the related underlying molecular mechanism. In the present study, the association between TUG1 and microRNA (miR)-196a-5p was predicted using StarBase and verified using a dual luciferase reporter assay in 293 cells. The LEC line SRA01/04 was exposed to 200 µM hydrogen peroxide (H₂O₂) for 24 h to establish an in vitro oxidative stress model. The mRNA expression levels of TUG1 and miR-196a-5p were analyzed using reverse transcription-quantitative PCR, whilst cell viability and apoptosis were determined using MTT and flow cytometry assays, respectively. The protein expression levels of cleaved caspase-3 and caspase-3 in SRA01/04 cells were determined using western blotting. The results of the present study revealed that TUG1 directly targeted miR-196a-5p expression. In addition, the expression levels of miR-196a-5p were downregulated in SRA01/04 cells following oxidative stress, whilst TUG1 expression was upregulated. Cell transfection with TUG1-small interfering RNA (siRNA) upregulated miR-196a-5p expression levels in SRA01/04 cells, which was reversed following co-transfection with the miR-196a-5p inhibitor. Transfection with TUG1-siRNA also reduced the levels of H₂O₂-induced oxidative damage in SRA01/04 cells, which was demonstrated by increased cell viability, reduced levels of apoptosis and downregulated cleaved caspase-3 levels. Conversely, transfection with the miR-196a-5p inhibitor reversed these effects aforementioned. Overexpression of miR-196a-5p reduced H₂O₂-induced oxidative damage in SRA01/04 cells. In conclusion, findings from the present study suggested that knocking down TUG1 expression may protect LECs from oxidative stress-induced apoptosis by upregulating the expression of miR-196a-5p.

Emerging Trends and Research Foci in Cataract Genes: A Bibliometric and Visualized Study

Background: Approximately 50% of cataracts are associated with genetic factors. Genetic etiology and molecular mechanisms based on gene research increase the understanding of cataracts and provide direction for diagnosis and intervention. In the present study, SCIE papers related to the modeling of cataract gene research from 2010-2019 were evaluated and qualitative and quantitative analyses with modeling performed. Methods: The SCIE database was searched on July 6, 2021 for cataract gene publications and relevant papers published since 2010 were considered for review. Subsequently, 1,904 SCIE papers associated with cataract genes from 2010-2019 were analyzed using a bibliometric method. The publication, country, institution, journal, references, knowledgebase, keywords, and research hotspots of the papers were analyzed using an online analysis platform of literature metrology, bibliographic item co-occurrence matrix builder (BICOMB), CiteSpace V, and VOS viewer analysis tool. Results: 78 countries published the related articles, and the United States ranks of America had the most publications. Two thousand seven hundred and eighty three institutions contributed to the related publications. Fudan University had the most publications. The reference clusters of SCI papers were clustered into six categories, namely, causing congenital cataract-microcornea syndrome, functional snp, cataractous lenses, a1 mutation, foxe3 mutation, cell adhesion gene pvrl3, nid1 gene. The key words representing the research frontiers were cerebrotendinous xanthomatosis (2017-2019), oxidative stress (2017-2019). Conclusion: This study provided a systematic, objective and comprehensive analysis of the literature related to gene research of cataract. Moreover, this study demonstrated the current hotspots and the future trends in the field of gene research of cataract. This review will help ophthalmologist to discern the dynamic evolution of cataract gene research, as well as highlight areas for future research.

Inherited cataracts: Genetic mechanisms and pathways new and old

Cataract(s) is the clinical equivalent of lens opacity and is caused by light scattering either by high molecular weight protein aggregates in lens cells or disruption of the lens microarchitecture itself. Genetic mutations underlying inherited cataract can provide insight into the biological processes and pathways critical for lens homeostasis and transparency, classically including the lens crystallins, connexins, membrane proteins or components, and intermediate filament proteins. More recently, cataract genes have been expanded to include newly identified biological processes such as chaperone or protein degradation components, transcription or growth factors, channels active in the lens circulation, and collagen and extracellular matrix components. Cataracts can be classified by age, and in general congenital cataracts are caused by severe mutations resulting in major damage to lens proteins, while age related cataracts are associated with variants that merely destabilize proteins thereby increasing susceptibility to environmental insults over time. Thus there might be separate pathways to opacity for congenital and age-related cataracts whereby congenital cataracts induce the unfolded protein response (UPR) and apoptosis to destroy the lens microarchitecture, while in age related cataract high molecular weight (HMW) aggregates formed by denatured crystallins bound by α-crystallin result in light scattering without severe damage to the lens microarchitecture.

Zebrafish Model in Ophthalmology to Study Disease Mechanism and Drug Discovery

Visual impairment and blindness are common and seriously affect people’s work and quality of life in the world. Therefore, the effective therapies for eye diseases are of high priority. Zebrafish (Danio rerio) is an alternative vertebrate model as a useful tool for the mechanism elucidation and drug discovery of various eye disorders, such as cataracts, glaucoma, diabetic retinopathy, age-related macular degeneration, photoreceptor degeneration, etc. The genetic and embryonic accessibility of zebrafish in combination with a behavioral assessment of visual function has made it a very popular model in ophthalmology. Zebrafish has also been widely used in ocular drug discovery, such as the screening of new anti-angiogenic compounds or neuroprotective drugs, and the oculotoxicity test. In this review, we summarized the applications of zebrafish as the models of eye disorders to study disease mechanism and investigate novel drug treatments.

Loss of FYCO1 leads to cataract formation

Autophagy is a degradation process of cytoplasmic proteins and organelles trafficked to degradation vesicles known as autophagosomes. The conversion of LC3-I to LC3-II is an essential step of autophagosome formation, and FYCO1 is a LC3-binding protein that mediates autophagosome transport. The p62 protein also directly binds to LC3 and is degraded by autophagy. In the present study, we demonstrated that disrupting the FYCO1 gene in mice resulted in cataract formation. LC3 conversion decreased in eyes from FYCO1 knockout mice. Further, FYCO1 interacted with αA- and αB-crystallin, as demonstrated by yeast two-hybrid screening and immunoprecipitation analyses. In eyes from knockout mice, the soluble forms of αA- and αB-crystallin, the lens’s major protein components, decreased. In addition, p62 accumulated in eyes from FYCO1 knockout mice. Collectively, these findings suggested that FYCO1 recruited damaged α-crystallin into autophagosomes to protect lens cells from cataract formation.

Genetic Analysis in a Swiss Cohort of Bilateral Congenital Cataract

Importance

Identification of geographic population-based differences in genotype and phenotype heterogeneity are important for targeted and patient-specific diagnosis and treatment, counseling, and screening strategies.

Objective

To report disease-causing variants and their detailed phenotype in patients with bilateral congenital cataract from a single center in Switzerland and thereby draw a genetic map and perform a genotype-phenotype comparison of this cohort.

Design, Setting, and Participants

This clinical and molecular-genetic cohort study took place through the collaboration of the Department of Ophthalmology at the University Hospital Zurich and the Institute of Medical Molecular Genetics, University of Zurich, Schlieren, Switzerland. Thirty-seven patients from 25 families with different types of bilateral congenital cataract were included. All participating family members received a comprehensive eye examination. Whole exome sequencing was performed in the index patients, followed by a filtering process to detect possible disease-associated variants in genes previously described in association with congenital cataract. Probable disease-causing variants were confirmed by Sanger sequencing in available family members. All data were collected from January 2018 to June 2020, and the molecular-genetic analyses were performed from January 2019 to July 2020.

Main Outcomes and Measures

Identification of the underlying genetic causes of bilateral congenital cataract, including novel disease-causing variants and phenotype correlation.

Results

Among the 37 patients (18 [49%] male and 19 [51%] female; mean [SD] age, 17.3 [15.9] years) from 25 families, pathogenic variants were detected in 20 families (80% detection rate), which included 13 novel variants in the following genes: BCOR, COL4A1, CRYBA2, CRYBB2, CRYGC, CRYGS, GJA3, MAF, NHS, and WFS1. Putative disease-causing variants were identified in 14 of 20 families (70%) as isolated cases and in 6 of 20 families (30%) with syndromic cases. A recessive variant in the CRYBB2 gene in a consanguineous family with 2 affected siblings showing a nuclear and sutural cataract was reported in contrast to previously published reports. In addition, the effect on splicing in a minigene assay of a novel splice site variant in the NHS gene (c.[719-2A>G]) supported the pathogenicity of this variant.

Conclusions and Relevance

This study emphasizes the importance of genetic testing of congenital cataracts. Known dominant genes need to be considered for recessive inheritance patterns. Syndromic types of cataract may be underdiagnosed in patients with mild systemic features.

A mutated CRYGD associated with congenital coralliform cataracts in two Chinese pedigrees

AIM

To investigate the causal gene mutation and clinical characteristics for two Chinese families with autosomal dominant congenital coralliform cataract.

METHODS

Two Chinese pedigrees with congenital cataract were investigated. Routine ophthalmic examinations were performed on all patients and non-affected family members. Peripheral blood samples were collected, and the genomic DNAs were extracted. The coding regions of proband's DNAs were analyzed with cataract gene panel. The identified mutation was amplified by polymerase chain reaction, and automated sequencing was performed in other members of two families to verify whether the mutated gene was co-segregated with the disease.

RESULTS

Congenital coralliform cataract was inherited in an autosomal dominant mode in both pedigrees. For each family, more than half of the family members were affected. All patients presented with severe visual impairment after birth as a result of bilateral symmetric coralliform lens opacification. An exact the same defect in the same gene, a heterozygous mutation of c.70C>A (p. P24T) in exon 2 of γD-crystallin gene, was detected in both probands from each family. Sanger sequencing analysis demonstrated that the mutated CRYGD was co-segregated in these two families.

CONCLUSION

A c.70C>A (p. P24T) variant in CRYGD gene was reconfirmed to be the causal gene in two Chinese pedigrees. It is known that mutated CRYGD caused most of the congenital coralliform cataracts, suggesting that the CRYGD gene is associated with coralliform congenital cataract.

Integrated Transcriptomic and Proteomic Analysis Reveals Up-Regulation of Apoptosis and Small Heat Shock Proteins in Lens of Rats Under Low Temperature

Cold cataract is the reversible opacification of the lens when the temperature decreases. However, we observed that when temperature of the rats’ lens was maintained at a lower temperature for a prolonged time, the opacification of lens was only partly reversible. To review the potential molecular mechanism of the irreversible part of opacification under cold stimulation, we applied comparative transcriptomic and proteomic analysis to systematically investigate the molecular changes that occurred in the lens capsules of rats under low temperature treatments. The RNA sequencing based transcriptomic analysis showed a significant up-regulation of genes related to the lens structure and development in the Hypothermia Group. Hub genes were small heat shock proteins (sHSPs). Besides the same findings as the transcriptomic results, the liquid chromatography-tandem mass spectrometry based proteomic analysis also revealed the up-regulation of the apoptotic process. To further analyze the regulatory mechanism in this process, we subsequently performed integrated analysis and identified the down-regulation of Notch3/Hes1 and PI3K/Akt/Xiap signaling axis. Our research revealed the activation of the apoptotic process in rats’ lens under cold stimulation, and the sHSP related heat shock response as a potential protective factor through our transcriptomic and proteomic data.

Congenital cataract - clinical and morphological aspects

Congenital cataract is one of the main causes of blindness in newborns and children. According to the World Health Organization (WHO), there are about 14 million children suffering from congenital cataract. Our study is based on 82 children, males – 46 (56.1%) and females – 36 (43.9%), with congenital cataract operated in the same ophthalmological centre in Bucharest, Romania. Of the 82 patients, 49 (59.76%) had bilateral cataract and 33 (40.24%) unilateral cataract. Clinically, the most frequent was the total cataract, followed by lamellar, nuclear and cerulean. We employed nine surgical approaches in our patients, depending on the type of intraocular lens (IOL). Morphologically, obvious changes were rendered evident at the level of anterior and posterior capsules, as well as subcapsular.

Polymorphisms in CRYAA Promoter with Susceptibility to Cataract: A Meta-Analysis

AIM

Polymorphisms in alpha A crystallin (CRYAA) gene have been implicated in susceptibility to cataracts, but some published studies have reported inconclusive results. Our study aimed to conduct a meta-analysis investigating the association between polymorphisms in CRYAA and susceptibility to cataracts.

METHODS

The PubMed, Excerpta Medica Database, Cochrane Library and China National Knowledge Infrastructure were searched for all articles published up to 20 March 2019 that reported cataracts and three polymorphisms (rs3761381, rs13053109, and rs7278468) of CRYAA. Afterwards, statistical analysis was performed for available articles.

RESULTS

Four articles published between 2014 and 2017 were included, involving 869 cases and 1,950 controls. There was no statistical evidence of an association between cataract risk and CRYAA gene polymorphisms rs13053109 (p > .05) and rs3761382 (p > .05). Significant decreased cataract risks were observed for different gene models of rs7278468 polymorphism: for G vs T, OR = 0.6640; 95% CI, 0.5361-0.7736, p < .001; for GG vs TT, OR = 0.3864; 95% CI, 0.2379-0.6278, p < .001; for GG vs TT+GT, OR = 0.4492; 95% CI, 0.2829-0.7134, p = .001; for GG+GT vs TT, OR = 0.6645; 95% CI, 0.5058-0.8729, p = .003; for GT vs TT, OR = 0.7508; 95% CI, 0.5639-0.9996, p = .050.

CONCLUSION

Our meta-analysis indicated that rs3761382 and rs13053109 polymorphisms of CRYAA may not be associated with susceptibility to cataracts. Individuals carrying mutant genotype of rs7278468 polymorphism are associated with a significantly decreased cataract risk.

ABBREVIATIONS

CC: Congenital cataract; ARC: Age-related cataract; SNPs: single nucleotide polymorphisms; NOS: Newcastle-Ottawa Scale; HWE: Hardy-Weinberg equilibrium; OR: odds ratio; CI: confidence interval; qPCR: quantitative polymerase chain reaction; NO: nuclear opalescence; NC: nuclear color.

Congenital Cataract and Its Genetics: The Era of Next-Generation Sequencing

Congenital cataract is a challenging ophthalmological disorder which can cause severe visual loss. It can be diagnosed at birth or during the first year of life. Early diagnosis and treatment are crucial for the visual prognosis. It can be associated with various ocular and systemic abnormalities. Determining whether congenital cataract is isolated or associated with other pathology is an indispensable step for the prediction of potential vision as well as early diagnosis and treatment of conditions that can cause morbidity or mortality. Many genes have been identified in the molecular etiology of congenital cataract. Most mutations have been reported in the crystallin genes. Determination of the genetic cause may not only enable individualized genetic counseling but also help to identify concomitant ocular and/or systemic disorders depending on the characteristics of the genetic test used. Recently, next-generation sequencing in particular has become an evolving technology for determining the molecular etiology of congenital cataract and furthering our knowledge of the disease.

Molecular and Genetic Mechanism of Non-Syndromic Congenital Cataracts. Mutation Screening in Spanish Families

Our purpose was to identify mutations responsible for non-syndromic congenital cataracts through the implementation of next-generation sequencing (NGS) in our center. A sample of peripheral blood was obtained from probands and willing family members and genomic DNA was extracted from leukocytes. DNA was analyzed implementing a panel (OFTv2.1) including 39 known congenital cataracts disease genes. 62 probands from 51 families were recruited. Pathogenic or likely pathogenic variants were identified in 32 patients and 25 families; in 16 families (64%) these were de novo mutations. The mutation detection rate was 49%. Almost all reported mutations were autosomal dominant. Mutations in crystallin genes were found in 30% of the probands. Mutations in membrane proteins were detected in seven families (two in GJA3 and five in GJA8). Mutations in LIM2 and MIP were each found in three families. Other mutations detected affected EPHA2, PAX6, HSF4 and PITX3. Variants classified as of unknown significance were found in 5 families (9.8%), affecting CRYBB3, LIM2, EPHA2, ABCB6 and TDRD7. Mutations lead to different cataract phenotypes within the same family.

A novel missense mutation of CRYBA1 in a northern Chinese family with inherited coronary cataract with blue punctate opacities

PURPOSE

To demonstrate the underlying genetic defect that contribute to inherited cataract in a northern Chinese pedigree.

METHODS

The study recruited a family pedigree with a diagnosis of bilateral coronary cataract with blue punctate opacities. Fourteen family members and 100 healthy volunteers were enrolled. DNA sample of the proband in this family were analyzed by high-throughput sequencing, which was then demonstrated by Sanger sequencing in the remained people in the family and 100 controls. The functional effect of mutant genes was investigated via bioinformatics analysis, including Polymorphism Phenotyping version2 (PolyPhen-2), Protein Variation Effect Analyzer (PROVEAN v1.1.3) Scale-Invariant Feature Transform (SIFT), and Mutation Taster.

RESULTS

In this three-generation family, a novel heterozygous mutation was found in the kinase domain of CRYBA1 gene (c.340C > T, p.R114C), which was only detected in patients in the family with inherited cataract and were not detected in the remained people in the family nor in normal people. The pathogenic effect of the mutation was verified via bioinformatics analysis.

CONCLUSION

Our study presented the molecular experiments to confirm that a novel missense mutation of c.340 C > T located in exon 4 of CRYBA1 gene results in a bilateral coronary cataract with blue punctate opacities, which enriches the mutation spectrum of CRYBA1 gene in inherited cataract and deepens the understanding of the pathogenesis of inherited cataract.

KPNA4 is involved in cataract formation via the nuclear import of p53

KPNA4 (also called importin-α3) belongs to the importin α adaptor proteins family, which orchestrates classical nuclear transport processes, importin-α/importin-β1 pathway, and involves in cellular homeostasis. Disruption of balanced transport pathways may result in ectopic nuclear proteins and eventually cause diseases, mainly under the situation of cellular stress, such as oxidative stress. Little evidence is available on its cellular functions for high specific expression in lens. We firstly studied the role of KPNA4 in cataract formation. Lens defects were observed at an early age in kpna4 gene knockout zebrafish, generated by the CRISPR/Cas9 system. Those phenotype, including cloudy center part of the lens, via bright field microscopy, and the thinning of the LE layer, wider space between the adjacent LE and LF cells, irregular cells morphology and the increased number of holes inside the LE cells, which were detected by transmission electron microscopy, recapitulate the clinical features of cataract patients. As the p53-specific adaptor of the nuclear import, KPNA4 upregulated with the same pattern of p53 in hydrogen peroxide-induced apoptosis in human lens epithelia cells. Furthermore, the loss of Kpna4 resulted in the accumulation of p53 in the center of lens. Taken together, we showed that KPNA4 was involved in the formation of cataract, likely by mediating p53 nuclear transport.

Development of a potent embryonic chick lens model for studying congenital cataracts in vivo

Congenital cataracts are associated with gene mutations, yet the underlying mechanism remains largely unknown. Here we reported an embryonic chick lens model that closely recapitulates the process of cataract formation. We adopted dominant-negative site mutations that cause congenital cataracts, connexin, Cx50E48K, aquaporin 0, AQP0R33C, αA-crystallin, CRYAA R12C and R54C. The recombinant retroviruses containing these mutants were microinjected into the occlusive lumen of chick lenses at early embryonic development. Cx50E48K expression developed cataracts associated with disorganized nuclei and enlarged extracellular spaces. Expression of AQP0R33C resulted in cortical cataracts, enlarged extracellular spaces and distorted fiber cell organization. αA crystallin mutations distorted lens light transmission and increased crystalline protein aggregation. Together, retroviral expression of congenital mutant genes in embryonic chick lenses closely mimics characteristics of human congenital cataracts. This model will provide an effective, reliable in vivo system to investigate the development and underlying mechanism of cataracts and other genetic diseases.

Identification and characterization of six β-crystallin gene mutations associated with congenital cataract in Chinese families

Background

This study aims to identify the underlying genetic defects of β‐crystallin (CRYB) genes responsible for congenital cataracts in a group of Chinese families.

Methods

Detailed family history and clinical data of six Chinese families with autosomal dominant congenital cataracts were recorded. Targeted exome sequencing was applied to detect the underlying genetic defects for the families. Generated variants were confirmed by PCR and sanger sequencing. Afterward, bioinformatic analysis through several computational predictive programs was performed to assess impacts of mutations on protein structure and function.

Results

A total of 53 participants (23 affected and 30 unaffected) from six unrelated Chinese families were recruited. Cataract phenotypes covered nuclear, total, posterior polar, pulverulent, snowflake‐like, and zonular. Through targeted exome sequencing, six mutations in four β‐crystallin genes were revealed which included five missense mutations CRYBB1 p.Q70P, CRYBB2 p.E23Q, CRYBB2 p.A49V, CRYBB2 R188C, CRYBA4 p.M14K and one splice mutation CRYBB3 c.75+1 G>A. In silico results predicted pathogenic for all four missense variants except variant CRYBB2‐p.A49V yielded results as tolerant. The CRYBB3 c.75+1 G>A splice site mutation was predicted to be deleterious by leading to a broken splice site, a premature stop codon, and subsequently resulting in a short peptide of 113 amino acids, which may affect protein features.

Conclusion

The obtained results expanded mutational and phenotype spectrum of β‐crystallin genes and offer clues for pathogenesis of congenital cataracts. The data also demonstrated that targeted exome sequencing is valuable for providing molecular diagnostic information for congenital cataract patients.

CRISPR-Cas9: A Preclinical and Clinical Perspective for the Treatment of Human Diseases

At present, the idea of genome modification has revolutionized the modern therapeutic research era. Genome modification studies have traveled a long way from gene modifications in primary cells to genetic modifications in animals. The targeted genetic modification may result in the modulation (i.e., either upregulation or downregulation) of the predefined gene expression. Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated nuclease 9 (Cas9) is a promising genome-editing tool that has therapeutic potential against incurable genetic disorders by modifying their DNA sequences. In comparison with other genome-editing techniques, CRISPR-Cas9 is simple, efficient, and very specific. This enabled CRISPR-Cas9 genome-editing technology to enter into clinical trials against cancer. Besides therapeutic potential, the CRISPR-Cas9 tool can also be applied to generate genetically inhibited animal models for drug discovery and development. This comprehensive review paper discusses the origin of CRISPR-Cas9 systems and their therapeutic potential against various genetic disorders, including cancer, allergy, immunological disorders, Duchenne muscular dystrophy, cardiovascular disorders, neurological disorders, liver-related disorders, cystic fibrosis, blood-related disorders, eye-related disorders, and viral infection. Finally, we discuss the different challenges, safety concerns, and strategies that can be applied to overcome the obstacles during CRISPR-Cas9-mediated therapeutic approaches.

Clinical Spectrum and Genetic Diagnosis of 54 Consecutive Patients Aged 0-25 with Bilateral Cataracts

Childhood cataract affects 2.5-3.5 per 10,000 children in the UK, with a genetic mutation identified in 50-90% of bilateral cases. However, cataracts can also manifest in adolescence and early adulthood in isolation, as part of a complex ocular phenotype or with systemic features making accurate diagnosis more challenging. We investigate our real-world experience through a retrospective review of consecutive bilateral cataract patients (0-25 years) presenting to the ocular genetics service at Moorfields Eye Hospital between 2017 and 2020. Fifty-four patients from 44 unrelated families were identified, with a median age of 13.5 years (range 1 to 68 years) and a median age at diagnosis of 43.9 months IQR (1.7-140.3 months); 40.7% were female and 46.3% were Caucasian. Overall, 37 patients from 27 families (61.4%) were genetically solved (50%) or likely solved (additional 11.4%), with 26 disease-causing variants (8 were novel) in 21 genes; the most common were crystallin genes, in 8 (29.6%) families, with half occurring in the CRYBB2 gene. There was no significant difference in the molecular diagnostic rates between sporadic and familial inheritance (P = 0.287). Associated clinical diagnoses were retinal dystrophies in five (18.5%) and aniridia in three (11.1%) families. Bilateral cataracts were the presenting feature in 27.3% (6/22) of either complex or syndromic cases, and isolated cataract patients were 11.5 years younger (rank-sum Z = 3.668, P = 0.0002). Prompt genetic investigation with comprehensive panel testing can aid with diagnosis and optimise management of cataract patients.

A novel F30S mutation in γS-crystallin causes autosomal dominant congenital nuclear cataract by increasing susceptibility to stresses

Despite of increasingly accumulated genetic variations of autosomal dominant congenital cataracts (ADCC), the causative genes of many ADCC patients remains unknown. In this research, we identified a novel F30S mutation in γS-crystallin from a three-generation Chinese family with ADCC. The patients possessing the F30S mutation exhibited nuclear cataract phenotype. The potential molecular mechanism underlying ADCC by the F30S mutation was investigated by comparing the structural features, stability and aggregatory potency of the mutated protein with the wild type protein. Spectroscopic experiments indicated that the F30S mutation did not affect γS-crystallin secondary structure compositions, but modified the microenvironments around aromatic side-chains. Thermal and chemical denaturation studies indicated that the mutation destabilized the protein and increased its aggregatory potency. The mutation altered the two-state unfolding of γS-crystallin to a three-state unfolding with the accumulation of an unfolding intermediate. The almost identical values in the changes of Gibbs free energies for transitions from the native state to intermediate and from the intermediate to unfolded state suggested that the mutation probably disrupted the cooperativity between the two domains during unfolding. Our results expand the genetic variation map of ADCC and provide novel insights into the molecular mechanism underlying ADCC caused by mutations in β/γ-crystallins.

Rapid and efficient cataract gene evaluation in F0 zebrafish using CRISPR-Cas9 ribonucleoprotein complexes

Cataract is the leading cause of blindness worldwide. Congenital or paediatric cataract can result in permanent visual impairment or blindness even with best attempts at treatment. A significant proportion of paediatric cataract has a genetic cause. Therefore, identifying the genes that lead to cataract formation is essential for understanding the pathological process of inherited paediatric cataract as well as to the development of new therapies. Despite clear progress in genomics technologies, verification of the biological effects of newly identified candidate genes and variants is still challenging. Here, we provide a step-by-step pipeline to evaluate cataract candidate genes in F0 zebrafish using CRISPR-Cas9 ribonucleoprotein complexes (RNP). Detailed descriptions of CRISPR-Cas9 RNP design and formulation, microinjection, optimization of CRISPR-Cas9 RNP reagent dose and delivery route, editing efficacy analysis as well as cataract formation evaluation are included. Following this protocol, any cataract candidates can be readily and efficiently evaluated within 2 weeks using basic laboratory supplies.

A missense allele of PEX5 is responsible for the defective import of PTS2 cargo proteins into peroxisomes

Peroxisomes, single-membrane intracellular organelles, play an important role in various metabolic pathways. The translocation of proteins from the cytosol to peroxisomes depends on peroxisome import receptor proteins and defects in peroxisome transport result in a wide spectrum of peroxisomal disorders. Here, we report a large consanguineous family with autosomal recessive congenital cataracts and developmental defects. Genome-wide linkage analysis localized the critical interval to chromosome 12p with a maximum two-point LOD score of 4.2 (θ = 0). Next-generation exome sequencing identified a novel homozygous missense variant (c.653 T > C; p.F218S) in peroxisomal biogenesis factor 5 (PEX5), a peroxisome import receptor protein. This missense mutation was confirmed by bidirectional Sanger sequencing. It segregated with the disease phenotype in the family and was absent in ethnically matched control chromosomes. The lens-specific knockout mice of Pex5 recapitulated the cataractous phenotype. In vitro import assays revealed a normal capacity of the mutant PEX5 to enter the peroxisomal Docking/Translocation Module (DTM) in the presence of peroxisome targeting signal 1 (PTS1) cargo protein, be monoubiquitinated and exported back into the cytosol. Importantly, the mutant PEX5 protein was unable to form a stable trimeric complex with peroxisomal biogenesis factor 7 (PEX7) and a peroxisome targeting signal 2 (PTS2) cargo protein and, therefore, failed to promote the import of PTS2 cargo proteins into peroxisomes. In conclusion, we report a novel missense mutation in PEX5 responsible for the defective import of PTS2 cargo proteins into peroxisomes resulting in congenital cataracts and developmental defects.

A new heterozygous mutation in the stop codon of CRYAB (p.X176Y) is liable for congenital posterior pole cataract in a Chinese family

Background: The present study aims to identify the underlying genetic defects in a Chinese family with autosomal dominant congenital cataracts (ADCC).Methods: Detailed family histories and clinical data were recorded. Targeted exome sequencing of 54 known cataract-associated genes combined with high-throughput next-generation sequencing was conducted followed by Sanger sequencing and bioinformatic analysis to identify the causative gene lesion for the family.Results: A four-generation Chinese family with posterior pole type cataract were enrolled. Enrichment of targeted genes revealed a new heterozygous p.X176Y mutation in the stop codon of αB-crystallin (CRYAB) gene, which resulted in the loss of the stop codon and prolongation of the mutant protein by 19 amino acid residues (p.X176Yfs19*). Sanger sequencing showed complete co-segregation with the disease. The elongated mutant protein was predicted to be pathogenic by forming new α-helix and random-coil in the secondary structure as well as producing an extended strand in the tertiary structure, potentially leading to increased hydrophobicity and reduced protein stability.Conclusions: Our report added a new mutation in the spectrum of congenital cataracts. The data suggested that X176 residue in the COOH-terminal is of crucial importance for the αB-crystallin protein function which was valuable for further study of the pathogenesis of congenital cataracts.Abbreviations: CRYAB: αB-crystallin; DNA: deoxyribonucleic acid; PCR: polymerase chain reaction; TES: targeted exome sequencing; ACD: αB-crystallin domain.

Novel mutation of GJA8 in autosomal dominant congenital cataracts

Background

Congenital cataracts is the most common cause of childhood visual impairment and blindness worldwide. It is reported that about one quarter of congenital cataracts caused by genetic defects. Various gene mutations have been identified in hereditary cataracts so far. The purpose of the present study was to investigate the relationship between gap junction protein alpha 8 (GJA8) gene mutation and congenital cataract.

Methods

A pedigree with autosomal dominant congenital cataract was investigated and the peripheral venous blood was extracted from 18 family members. After the high-throughput targeted capture and whole exome sequencing for the proband, bioinformatics analysis was performed. By combining the proband clinical symptoms, candidate variations were eliminated which were significantly not consistent with the clinical phenotype. And disease-causing variant was identified.

Results

Gene sequencing revealed the heterozygous missense mutation in exon 2 of the GJA8 gene (c.178G>A), which co-segregated with the disease phenotype in the family and resulted in the substitution of glycine to serine at position 178 (p.G60S). This missense mutation was located in the hotspot mutation region, and might be harmful.

Conclusions

This study reports a novel disease-causing sequence variant in the gap junctional protein encoding genes causing autosomal dominant congenital cataract in the Chinese population, caused by the missense mutation of GJA8 (c.178G>A). Our data expand the spectrum of GJA8 variants and associated phenotypes, facilitate clinical diagnosis and support the presence of relationship between genetic basis and human disease.

The genetic landscape of crystallins in congenital cataract

Background

The crystalline lens is mainly composed of a large family of soluble proteins called the crystallins, which are responsible for its development, growth, transparency and refractive index. Disease-causing sequence variants in the crystallins are responsible for nearly 50% of all non-syndromic inherited congenital cataracts, as well as causing cataract associated with other diseases, including myopathies. To date, more than 300 crystallin sequence variants causing cataract have been identified.

Methods

Here we aimed to identify the genetic basis of disease in five multi-generation British families and five sporadic cases with autosomal dominant congenital cataract using whole exome sequencing, with identified variants validated using Sanger sequencing. Following bioinformatics analysis, rare or novel variants with a moderate to damaging pathogenicity score, were filtered out and tested for segregation within the families.

Results

We have identified 10 different heterozygous crystallin variants. Five recurrent variants were found: family-A, with a missense variant (c.145C>T; p.R49C) in CRYAA associated with nuclear cataract; family-B, with a deletion in CRYBA1 (c.272delGAG; p.G91del) associated with nuclear cataract; and family-C, with a truncating variant in CRYGD (c.470G>A; W157*) causing a lamellar phenotype; individuals I and J had variants in CRYGC (c.13A>C; T5P) and in CRYGD (c.418C>T; R140*) causing unspecified congenital cataract and nuclear cataract, respectively. Five novel disease-causing variants were also identified: family D harboured a variant in CRYGC (c.179delG; R60Qfs*) responsible for a nuclear phenotype; family E, harboured a variant in CRYBB1 (c.656G>A; W219*) associated with lamellar cataract; individual F had a variant in CRYGD (c.392G>A; W131*) associated with nuclear cataract; and individuals G and H had variants in CRYAA (c.454delGCC; A152del) and in CRYBB1 (c.618C>A; Y206*) respectively, associated with unspecified congenital cataract. All novel variants were predicted to be pathogenic and to be moderately or highly damaging.

Conclusions

We report five novel variants and five known variants. Some are rare variants that have been reported previously in small ethnic groups but here we extend this to the wider population and record a broader phenotypic spectrum for these variants.

βB2 W151R mutant is prone to degradation, aggregation and exposes the hydrophobic side chains in the fourth Greek Key motif

Studies have established that congenital cataract is the major cause of blindness in children across the globe. The β-crystallin protein family is the richest and most soluble structural protein in the lens. Their solubility and stability are essential in maintaining lens transparency. In this study, we identified a novel βB2 mutation W151R in a rare progressive cortical congenital cataract family and explored its pathogenesis using purified protein and mutant related cataract-cell models. Due to its low solubility and poor structural stability, the βB2 W151R mutation was prone to aggregation. Moreover, the W151R mutation enhanced the exposure of the hydrophobic side chains in the fourth Greek Key motif, which were readily degraded by trypsin. However, upon the administration of lanosterol, the negative effect of the W151R mutation was reversed. Therefore, lanosterol is a potential therapeutic option for cataracts.

Polygenetic-Risk Scores Related to Crystallin Metabolism Are Associated with Age-Related Cataract Formation and Interact with Hyperglycemia, Hypertension, Western-Style Diet, and Na Intake

Age-related cataract (ARC) development is associated with loss of crystalline lens transparency related to interactions between genetic and environmental factors. We hypothesized that polygenetic risk scores (PRS) of the selected genetic variants among the ARC-related genes might reveal significant genetic impacts on ARC risk, and the PRS might have gene-gene and gene-lifestyle interactions. We examined the hypothesis in 1972 and 39,095 subjects aged ≥50 years with and without ARC, respectively, in a large-scale hospital-based cohort study conducted from 2004 to 2013. Single nucleotide polymorphisms (SNPs) of the genes related to ARC risk were identified, and polygenetic risk scores (PRS) were generated based on the results of a generalized multifactor dimensionality reduction analysis. Lifestyle interactions with PRS were evaluated. The PRS derived from the best model included the following six SNPs related to crystallin metabolism: ULK4_rs1417380362, CRYAB_rs2070894, ACCN1_rs55785344, SSTR2_rs879419608, PTN_rs322348, and ICA1_rs200053781. The risk of ARC in the high-PRS group was 2.47-fold higher than in the low-PRS group after adjusting for confounders. Age, blood pressure, and glycemia interacted with PRS to influence the risk of ARC: the incidence of ARC was much higher in the elderly (≥65 years) and individuals with hypertension or hyperglycemia. The impact of PRS on ARC risk was greatest in middle-aged individuals with hypertension or hyperglycemia. Na, coffee, and a Western-style diet intake also interacted with PRS to influence ARC risk. ARC risk was higher in the high-PRS group than in the low-PRS group, and high Na intake, Western-style diet, and low coffee intake elevated its risk. In conclusion, ARC risk had a positive association with PRS related to crystallin metabolism. The genetic impact was greatest among those with high Na intake or hypertension. These results can be applied to precision nutrition interventions to prevent ARC.

Recent developments in the management of congenital cataract

Congenital cataract is a rare eye disease, one of the leading treatable causes of low vision in children worldwide. Hereditary cataracts can be divided in syndromic and non-syndromic cataracts. Early diagnosis in congenital cataracts is key to reach good visual function. Current surgical techniques, that combine microincision cataract extraction and primary intraocular lens (IOL) implantation, have improved childhood cataract outcome. Complications include posterior capsule opacification (PCO), aphakic or pseudophakic glaucoma, uveitis, pupil displacement and IOL decentration. A recent study using a modified Delphi approach identified areas of consensus and disagreement in the management of pediatric cataract. A consensus or near consensus was achieved for 79% of the questions, however 21% of the questions remained controversial, as for IOL implantation strategy. Congenital cataracts show a highly variable phenotype and genotype, and can be related to different mutations, genetic variance, and other risk factors. Congenital cataracts can be associated with other ocular developmental abnormalities, including microphthalmia, microcornea, or aniridia and with systemic findings. Next-generation sequencing (NGS) and forthcoming new ultra-high-throughput sequencing represent excellent tools to investigate the genetic causes of congenital cataracts. A better recognition of different clinical presentations and underlying etiologies of congenital cataracts may lead to the development of new approaches to improve visual outcome after cataract surgery and promote early detection of systemic associated syndromes.

A Perspective on Biophysical Studies of Crystallin Aggregation and Implications for Cataract Formation

Lens crystallins are subject to various types of damage during their lifetime which triggers protein misfolding and aggregation, ultimately causing cataracts. There are several models for crystallin aggregation, but a comprehensive picture of the mechanism of cataract is still underway. The complex biomolecular interactions underlying crystallin aggregation have motivated major efforts to resolve the structural details and mechanism of aggregation using multiple biophysical techniques at different resolutions. Together, experimental and computational approaches identify and characterize both amyloidogenic and amorphous aggregates leading to an improved understanding of crystallin aggregation. A rigorous characterization of the aggregation-prone intermediates is crucial in cataract-mediated drug discovery. This Perspective summarizes recent biophysical studies on lens crystallin aggregation. We evaluate the outstanding challenges, future outlook, and rewards in this fertile field of research. With lessons learned from protein folding and multiple pathways of aggregation, we highlight the differences in the overall mechanisms of age-related and congenital cataracts. We expect that a correlation between the existing and developing biophysical techniques would provide a platform to study amyloid architecture in the eye lens and reduce the existing gaps in our understanding of crystallin biophysics.

Association of Age-Related Cataract With Skin Cancer in an Australian Population

Purpose

Ultraviolet radiation from sunlight contributes to age-related cataract and skin cancer. The EPHA2 gene is implicated in both these diseases. The purpose of this study was to determine whether age-related cataract and skin cancer are associated in a cohort of older Australians.

Methods

A cross-sectional study was performed using the Historical Cohort of the Registry of Senior Australians. Individuals aged ≥65 years or aged ≥50 years and of Aboriginal or Torres Strait Islander descent, who had an aged care eligibility assessment between July 2005 and June 2015, and had a history of cataract surgery and/or skin cancer according to the Australian Government Medicare Benefits Schedule dataset, during the 3-year period prior, were evaluated (N = 599,316). A multivariable logistic regression model was used to determine association and multiple hypothesis correction was employed.

Results

Of the evaluated individuals, 87,097 (14.5%) had a history of cataract and 170,251 (28.4%) a history of skin cancer. Among those with a history of cataract, 20,497 (23.5%), 1127 (1.3%), and 14,730 (16.9%) individuals had a concurrent history of keratinocyte, melanoma, and premalignant/solar keratosis, respectively. Those with a history of cataract were 19% more likely to have a history of skin cancer (odds ratio [OR], 1.19; 95% confidence interval [CI], (1.17–1.21). Co-occurrence of keratinocyte skin cancer was 16% (OR, 1.16; 95% CI, 1.14–1.18), melanoma 21% (OR, 1.21; 95% CI, 1.13–1.29), and premalignant/solar keratosis 19% (OR, 1.19; 95% CI, 1.17–1.22) more in the presence than absence of history of cataract.

Conclusions

Age-related cataract is positively associated with skin cancer and its subtypes, including premalignant lesions in an older Australian population.

The relationship between major intrinsic protein genes and cataract

BACKGROUND

Genetic factors play an essential role in the development of cataracts, and the major intrinsic protein (MIP) gene is a type of causative genes. Our study aims to discuss the current research progress of MIP genes responsible for cataractogenesis in DNA and protein levels, which is essential in achieving a response to the molecular deficiencies and pathophysiologic features of cataract.

METHODS

We developed a search strategy using a combination of the words "Cataract", "Mutation", "MIP gene", and "AQP0" to identify all articles from PubMed, Web of Science, Scopus, and Google Scholar up to December 2019. To find more articles and to ensure that databases were thoroughly searched, the reference lists of selected items were also reviewed.

RESULTS

A total of 29 MIP gene mutations causing congenital cataract were obtained by searching these databases and analyzing the results of genetic mutation pathogenicity prediction software tools; most of them caused amino acid codon changes in the H4, H5, H6, C-TIDs, and loop C in the structure of the MIP protein. However, there was no clear causality between lens morphology, phenotypes, and genotypes. The genotype TC in polymorphism c.-4T > C and haplotype CCG of rs2269348, c.-4T > C, and rs74641138 in MIP may attach an additional genetic risk factor for age-related cataract.

CONCLUSION

These single-base mutations and single nucleotide polymorphisms might be importantly involved in the pathogenesis of congenital cataract and age-related cataract, respectively. This review provides a significant reference for clinical trials and theoretical studies.

The mutation spectrum in familial versus sporadic congenital cataract based on next-generation sequencing

BACKGROUND

Congenital cataract (CC) is a significant cause of lifelong visual loss, and its genetic diagnosis is challenging due to marked genetic heterogeneity. The purpose of this article is to report the genetic findings in sporadic and familial CC patients.

METHODS

Patients (n = 53) who were clinically diagnosed with CC and their parents were recruited. Blood samples were collected in our hospital. Mutations were detected by panel-based next-generation DNA sequencing (NGS) targeting 792 genes frequently involved in common inherited eye diseases.

RESULTS

We identified variants in 10/37 cases (27.02%) of sporadic CC and 14/16 cases (87.5%) of familial CC, which indicated a significant difference (P = 0.000). Of the 13 variants identified in sporadic cases, nine were previously reported mutations, and three were novel mutations, including one de novo mutation (CRYBB2 c.487C > T). The most frequent variants in our cohort were in crystallins and cytoskeletal genes (5/27, 18.52%), followed by proteins associated with X-linked syndromic conditions (14.81%) and transcriptional factors (11.11%). Additional information on the possibility of complications with inherited ocular or systemic diseases other than CC was provided in 17/27 (62.96%) variants.

CONCLUSIONS

These results contribute to expanding the mutation spectrum and frequency of genes responsible for CC. Targeted NGS in CC provided significant diagnostic information and enabled more accurate genetic counselling. This study reports the different distributions of mutation genes in familial and sporadic CC cases.

Alpha-crystallin mutations alter lens metabolites in mouse models of human cataracts

Cataracts are a major cause of blindness worldwide and commonly occur in individuals over 70 years old. Cataracts can also appear earlier in life due to genetic mutations. The lens proteins, αA- and αB-crystallins, are chaperone proteins that have important roles maintaining protein solubility to prevent cataract formation. Mutations in the CRYAA and CRYAB crystallin genes are associated with autosomal dominant early onset human cataracts. Although studies about the proteomic and genomic changes that occur in cataracts have been reported, metabolomics studies are very limited. Here, we directly investigated cataract metabolism using gas-chromatography-mass spectrometry (GC-MS) to analyze the metabolites in adult Cryaa-R49C and Cryab-R120G knock-in mouse lenses. The most abundant metabolites were myo-inositol, L-(+)-lactic acid, cholesterol, phosphate, glycerol phosphate, palmitic and 9-octadecenoic acids, α-D-mannopyranose, and β-D-glucopyranose. Cryaa-R49C knock-in mouse lenses had a significant decrease in the number of sugars and minor sterols, which occurred in concert with an increase in lactic acid. Cholesterol composition was unchanged. In contrast, Cryab-R120G knock-in lenses exhibited increased total amino acid content including valine, alanine, serine, leucine, isoleucine, glycine, and aspartic acid. Minor sterols, including cholest-7-en-3-ol and glycerol phosphate were decreased. These studies indicate that lenses from Cryaa-R49C and Cryab-R120G knock-in mice, which are models for human cataracts, have unique amino acid and metabolite profiles.

The Tudor-domain protein TDRD7, mutated in congenital cataract, controls the heat shock protein HSPB1 (HSP27) and lens fiber cell morphology

Mutations of the RNA granule component TDRD7 (OMIM: 611258) cause pediatric cataract. We applied an integrated approach to uncover the molecular pathology of cataract in Tdrd7-/- mice. Early postnatal Tdrd7-/- animals precipitously develop cataract suggesting a global-level breakdown/misregulation of key cellular processes. High-throughput RNA sequencing integrated with iSyTE-bioinformatics analysis identified the molecular chaperone and cytoskeletal modulator, HSPB1, among high-priority downregulated candidates in Tdrd7-/- lens. A protein fluorescence two-dimensional difference in-gel electrophoresis (2D-DIGE)-coupled mass spectrometry screen also identified HSPB1 downregulation, offering independent support for its importance to Tdrd7-/- cataractogenesis. Lens fiber cells normally undergo nuclear degradation for transparency, posing a challenge: how is their cell morphology, also critical for transparency, controlled post-nuclear degradation? HSPB1 functions in cytoskeletal maintenance, and its reduction in Tdrd7-/- lens precedes cataract, suggesting cytoskeletal defects may contribute to Tdrd7-/- cataract. In agreement, scanning electron microscopy (SEM) revealed abnormal fiber cell morphology in Tdrd7-/- lenses. Further, abnormal phalloidin and wheat germ agglutinin (WGA) staining of Tdrd7-/- fiber cells, particularly those exhibiting nuclear degradation, reveals distinct regulatory mechanisms control F-actin cytoskeletal and/or membrane maintenance in post-organelle degradation maturation stage fiber cells. Indeed, RNA immunoprecipitation identified Hspb1 mRNA in wild-type lens lysate TDRD7-pulldowns, and single-molecule RNA imaging showed co-localization of TDRD7 protein with cytoplasmic Hspb1 mRNA in differentiating fiber cells, suggesting that TDRD7-ribonucleoprotein complexes may be involved in optimal buildup of key factors. Finally, Hspb1 knockdown in Xenopus causes eye/lens defects. Together, these data uncover TDRD7's novel upstream role in elevation of stress-responsive chaperones for cytoskeletal maintenance in post-nuclear degradation lens fiber cells, perturbation of which causes early-onset cataracts.

A transcriptomic analysis of diploid and triploid Atlantic salmon lenses with and without cataracts

To avoid negative environmental impacts of escapees and potential inter-breeding with wild populations, the Atlantic salmon farming industry has and continues to extensively test triploid fish that are sterile. However, they often show differences in performance, physiology, behavior and morphology compared to diploid fish, with increased prevalence of vertebral deformities and ocular cataracts as two of the most severe disorders. Here, we investigated the mechanisms behind the higher prevalence of cataracts in triploid salmon, by comparing the transcriptional patterns in lenses of diploid and triploid Atlantic salmon, with and without cataracts. We assembled and characterized the Atlantic salmon lens transcriptome and used RNA-seq to search for the molecular basis for cataract development in triploid fish. Transcriptional screening showed only modest differences in lens mRNA levels in diploid and triploid fish, with few uniquely expressed genes. In total, there were 165 differentially expressed genes (DEGs) between the cataractous diploid and triploid lens. Of these, most were expressed at lower levels in triploid fish. Differential expression was observed for genes encoding proteins with known function in the retina (phototransduction) and proteins associated with repair and compensation mechanisms. The results suggest a higher susceptibility to oxidative stress in triploid lenses, and that mechanisms connected to the ability to handle damaged proteins are differentially affected in cataractous lenses from diploid and triploid salmon.

Circular RNA HIPK3 regulates human lens epithelial cell dysfunction by targeting the miR-221-3p/PI3K/AKT pathway in age-related cataract

Circular RNA Homeodomain Interacting Protein Kinase 3 (circHIPK3) was found to involve in the pathogenesis of age-related cataract (ARC). Here, we further disclosed the related target genes and molecular mechanism of circHIPK3 in the ARC progression. The expression of circHIPK3, microRNA (miR)-221-3p was detected using the quantitative real-time polymerase chain reaction. Human lens epithelial cell (HLEC) proliferation and apoptosis were measured by 3-(4, 5)-dimethylthiahiazo (-z-y1)-3, 5-di-phenytetrazoliumromide (MTT) assay and flow cytometry, respectively. Western blot was used to detect the levels of apoptosis-related proteins, and phosphoinositide 3-kinase (PI3K)/p-protein kinase B (AKT) pathway-related proteins. Levels of malondialdehyde (MDA) and glutathione peroxidase (GSH-PX) were measured by kits. The interaction between miR-221-3p and circHIPK3 was confirmed by dual-luciferase reporter assay and RNA immunoprecipitation assay. CircHIPK3 was down-regulated while miR-221-3p was up-regulated in human lens epithelium samples of ARC patients. CircHIPK3 up-regulation or miR-221-3p down-regulation mediated the promotion of proliferation, inhibition of apoptosis, decrease of MDA level as well as increase of GSH-PX level in HLECs. MiR-221-3p was a target of circHIPK3, and miR-221-3p overexpression reversed the protective action of circHIPK in HLEC functions. In addition, circHIPK3 activated PI3K/AKT pathway via regulating miR-221-3p, and silencing miR-221-3p protected HLECs from dysfunction by activating PI3K/AKT pathway. We demonstrated that circHIPK3 protected HLECs from dysfunction by regulating miR-221-3p/PI3K/AKT pathway, indicating a new insight into the pathogenesis of ARC and providing a potential therapeutic target for ARC.