Missense Mutations in CRYAB Are Liable for Recessive Congenital Cataracts

Structural characterization and functional analysis of human αB-crystallin with the p.R11G mutation: Insights into cataractogenesis and cardiomyopathy

αB-crystallin, a member of the small heat-shock protein family, functions as a molecular chaperone and plays a critical role in maintaining cellular homeostasis by preventing the aggregation of misfolded proteins in various tissues. This research investigates the structural and functional consequences of the p.R11G mutation in human αB-crystallin, which is associated with serious health issues, including cataracts, myofibrillar myopathy, and dilated cardiomyopathy. Following the introduction of this mutation through site-directed mutagenesis, the mutant protein was expressed in a prokaryotic host system and purified using ion-exchange chromatography. The structure and stability of the mutant protein were assessed using various spectroscopic techniques. Moreover, the oligomeric structure of the mutant protein was examined using dynamic light scattering and atomic force microscopy. To evaluate the chaperone activity and cytoprotective effects of the protein, UV-Vis spectroscopy and the 2,5-diphenyl-2H-tetrazolium bromide (MTT) assay were utilized. The results demonstrated that the p.R11G mutation significantly alters the protein's structure, leading to enhanced thermal and chemical stability, and formation of the larger oligomers compared to the wild-type protein. Additionally, the mutation was found to increase the protein's chaperone activity and its capacity to inhibit cancer cell death under oxidative stress conditions. Based on the results of our study, the significant changes observed in the structure and activity of human αB-crystallin due to this mutation elucidate the potential role of the mutated chaperone in cataract formation and myopathy. Further research is necessary to fully elucidate the underlying mechanisms and translate these findings into effective therapeutic interventions.

Unveiling the structural and functional consequences of the p.D109G pathogenic mutation in human αB-Crystallin responsible for restrictive cardiomyopathy and skeletal myopathy

αB-Crystallin (αB-Cry) is expressed in many tissues, and mutations in this protein are linked to various diseases, including cataracts, Alzheimer's disease, Parkinson's disease, and several types of myopathies and cardiomyopathies. The p.D109G mutation, which substitutes a conserved aspartate residue involved in the interchain salt bridges, with glycine leads to the development of both restrictive cardiomyopathy (RCM) and skeletal myopathy. In this study, we generated this mutation in the α-Cry domain (ACD) which is crucial for forming the active chaperone dimeric state, using site-directed mutagenesis. After inducing expression in the bacterial host, we purified the mutant and wild-type recombinant proteins using anion exchange chromatography. Various spectroscopic evaluations revealed significant changes in the secondary, tertiary, and quaternary structures of human αB-Cry caused by this mutation. Furthermore, this pathogenic mutation led to the formation of protein oligomers with larger sizes than those of the wild-type protein counterpart. The mutant protein also exhibited increased chaperone activity and decreased chemical, thermal, and proteolytic stability. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and fluorescence microscopy (FM) demonstrated that p.D109G mutant protein is more prone to forming amyloid aggregates. The misfolding associated with the p.D109G mutation may result in abnormal interactions of human αB-Cry with its natural partners (e.g., desmin), leading to the formation of protein aggregates. These aggregates can interfere with normal cellular processes and may contribute to muscle cell dysfunction and damage, resulting in the pathogenic involvement of the p.D109G mutant protein in restrictive cardiomyopathy and skeletal myopathy.

JAM-C Is Important for Lens Epithelial Cell Proliferation and Lens Fiber Maturation in Murine Lens Development

Purpose

The underlying mechanism of congenital cataracts caused by deficiency or mutation of junctional adhesion molecule C (JAM-C) gene remains unclear. Our study aims to elucidate the abnormal developmental process in Jamc-/- lenses and reveal the genes related to lens development that JAM-C may regulate.

Methods

Jamc knockout (Jamc-/-) mouse embryos and pups were generated for in vivo studies. Four key developmental stages from embryonic day (E) 12.5 to postnatal day (P) 0.5 were selected for the following experiments. Hematoxylin and eosin staining was used for histological analysis. The 5-bromo-2'-deoxyuridine (BrdU) incorporation assay and TUNEL staining were performed to label lens epithelial cell (LEC) proliferation and apoptosis, respectively. Immunofluorescence and Western blot were used to analyze the markers of lens epithelium, cell cycle exit, and lens fiber differentiation.

Results

JAM-C was expressed throughout the process of lens development. Deletion of Jamc resulted in decreased lens size and disorganized lens fibers, which arose from E16.5 and aggravated gradually. The LECs of Jamc-/- lenses showed decreased quantity and proliferation, accompanied with reduction of key transcription factor, FOXE3. The fibers in Jamc-/- lenses were disorganized. Moreover, Jamc-deficient lens fibers showed significantly altered distribution patterns of Cx46 and Cx50. The marker of fiber homeostasis, γ-crystallin, was also decreased in the inner cortex and core fibers of Jamc-/- lenses.

Conclusions

Deletion of JAM-C exhibits malfunction of LEC proliferation and fiber maturation during murine lens development, which may be related to the downregulation of FOXE3 expression and abnormal localization patterns of Cx46 and Cx50.

Investigating the role of double mutations R12C/P20R, and R12C/R69C on structure, chaperone-like activity, and amyloidogenic properties of human αB-crystallin

α-crystallin is a structurally essential small heat shock protein (sHSP) with a chaperone-like activity which maintains transparency of the lenticular tissues during a period of time that is as long as human life. α-crystallin is a multimeric protein consisting of αA and αB subunits, with 57 % homology. The CRYAB gene on chromosome 11 encodes human αB-crystallin (αB-Cry), which contains 175 amino acid residues. In the current study, the cataractogenic mutations R12C, P20R, R69C, and double mutations R12C/P20R and R12C/P20R were embedded into the human CRYAB gene. Following successful expression in the prokaryotic system and purification, a number of spectroscopic techniques, gel electrophoresis, dynamic light scattering (DLS), and transmission electron microscopy (TEM) were applied to assess the role of these mutations on the structure, amyloidogenicity, and biological function of human αB-Cry. The created mutations caused significant changes in the structure, and oligomeric state of human αB-Cry. These mutations, particularly R12C, R12C/P20R, and R12C/R69C, dramatically enhanced the tendency of this protein for the amyloid fibril formation and reduced its chaperone-like activity. Since double mutations R12C/P20R and R12C/P20R were able to intensely change the protein's structure and chaperone function, it can be suggested that they may play a destructive role in a cumulative manner. Our findings indicated that the simultaneous presence of two pathogenic mutations may have a cumulative destructive impacts on the structure and function of human αB-Cry and this observation is likely related to the disease severity of the mutated proteins.

Clinical-pathological features and muscle imaging findings in 36 Chinese patients with rimmed vacuolar myopathies: case series study and review of literature

Introduction

Rimmed vacuolar myopathies (RVMs) are a group of genetically heterogeneous diseases that share histopathological characteristics on muscle biopsy, including the aberrant accumulation of autophagic vacuoles. However, the presence of non-coding sequences and structural mutations, some of which remain undetectable, confound the identification of pathogenic mutations responsible for RVMs. Therefore, we assessed the clinical profiles and muscle magnetic resonance imaging (MRI) changes in 36 Chinese patients with RVMs, emphasizing the role of muscle MRI in disease identification and differential diagnosis to propose a comprehensive literature-based imaging pattern to facilitate improved diagnostic workup.

Methods

All patients presented with rimmed vacuoles with varying degrees of muscular dystrophic changes and underwent a comprehensive evaluation using clinical, morphological, muscle MRI and molecular genetic analysis. We assessed muscle changes in the Chinese RVMs and provided an overview of the RVMs, focusing on the patterns of muscle involvement on MRI.

Results

A total of 36 patients, including 24 with confirmed distal myopathy and 12 with limb-girdle phenotype, had autophagic vacuoles with RVMs. Hierarchical clustering of patients according to the predominant effect of the distal or proximal lower limbs revealed that most patients with RVMs could be distinguished. GNE myopathy was the most prevalent form of RVMs observed in this study. Moreover, MRI helped identify the causative genes in some diseases (e.g., desminopathy and hereditary myopathy with early respiratory failure) and confirmed the pathogenicity of a novel mutation (e.g., adult-onset proximal rimmed vacuolar titinopathy) detected using next-generation sequencing.

Discussion

Collectively, our findings expand our knowledge of the genetic spectrum of RVMs in China and suggest that muscle imaging should be an integral part of assisting genetic testing and avoiding misdiagnosis in the diagnostic workup of RVM.

Protein Aggregation and Cataract: Role of Age-Related Modifications and Mutations in α-Crystallins

* The article is published as a part of the Special Issue "Protein Misfolding and Aggregation in Cataract Disorders" (Vol. 87, No. 2). ** To whom correspondence should be addressed. Cataract is a major cause of blindness. Due to the lack of protein turnover, lens proteins accumulate age-related and environmental modifications that alter their native conformation, leading to the formation of aggregation-prone intermediates, as well as insoluble and light-scattering aggregates, thus compromising lens transparency. The lens protein, α-crystallin, is a molecular chaperone that prevents protein aggregation, thereby maintaining lens transparency. However, mutations or post-translational modifications, such as oxidation, deamidation, truncation and crosslinking, can render α-crystallins ineffective and lead to the disease exacerbation. Here, we describe such mutations and alterations, as well as their consequences. Age-related modifications in α-crystallins affect their structure, oligomerization, and chaperone function. Mutations in α-crystallins can lead to the aggregation/intracellular inclusions attributable to the perturbation of structure and oligomeric assembly and resulting in the rearrangement of aggregation-prone regions. Such rearrangements can lead to the exposure of hitherto buried aggregation-prone regions, thereby populating aggregation-prone state(s) and facilitating amorphous/amyloid aggregation and/or inappropriate interactions with cellular components. Investigations of the mutation-induced changes in the structure, oligomer assembly, aggregation mechanisms, and interactomes of α-crystallins will be useful in fighting protein aggregation-related diseases.

Trends in HSPB5 research: a 36-year bibliometric analysis

HSPB5 (heat shock protein B5), also known as αB-crystallin, is one of the most widespread and populous of the ten human small heat shock proteins (sHsps). Over the past decades, extensive research has been conducted on HSPB5. However, few studies have statistically analyzed these publications. Herein, we conducted a bibliometric analysis to track the global research trend and current development status of HSPB5 research from the Web of Science Core Collection (WoSCC) database between 1985 and 2020. Our results demonstrate that 1220 original articles cited 54,778 times in 391 scholarly journals were published. Visualization analyses reveal that the Journal of Biological Chemistry was the most influential journal with 85 articles. The USA dominated this field with 520 publications (42.62%), followed by Japan with 149 publications (12.21%), and Kato contributed the largest number of publications. Most related publications were published in journals focusing on biochemistry molecular biology, cell biology, neurosciences neurology, and ophthalmology. In addition, keyword co-occurrence analyses identify three predominant research topics: expression of HSPB5, chaperone studies for HSPB5, and pathological studies of HSPB5. This study provides valuable guidance for researchers and leads to collaborative opportunities between diverse research interests to be integrated for HSPB5 research.

Autosomal recessive cataract (CTRCT18) in the Yakut population isolate of Eastern Siberia: a novel founder variant in the FYCO1 gene

Congenital autosomal recessive cataract with unknown genetic etiology is one of the most common Mendelian diseases among the Turkic-speaking Yakut population (Eastern Siberia, Russia). To identify the genetic cause of congenital cataract spread in this population, we performed whole-exome sequencing (Illumina NextSeq 500) in one Yakut family with three affected siblings whose parents had preserved vision. We have revealed the novel homozygous c.1621C>T transition leading to premature stop codon p.(Gln541*) in exon 8 of the FYCO1 gene (NM_024513.4). Subsequent screening of c.1621C>T p.(Gln541*) revealed this variant in a homozygous state in 25 out of 29 Yakut families with congenital cataract (86%). Among 424 healthy individuals from seven populations of Eastern Siberia (Russians, Yakuts, Evenks, Evens, Dolgans, Chukchi, and Yukaghirs), the highest carrier frequency of c.1621C>T p.(Gln541*) was found in the Yakut population (7.9%). DNA samples of 25 homozygous for c.1621C>T p.(Gln541*) patients with congenital cataract and 114 unaffected unrelated individuals without this variant were used for a haplotype analysis based on the genotyping of six STR markers (D3S3512, D3S3685, D3S3582, D3S3561, D3S1289, and D3S3698). The structure of the identified haplotypes indicates a common origin for all of the studied mutant chromosomes bearing c.1621C>T p.(Gln541*). The age of the с.1621C>T p.(Gln541*) founder haplotype was estimated to be approximately 260 ± 65 years (10 generations). These findings characterize Eastern Siberia as the region of the world with the most extensive accumulation of the unique variant c.1621C>T p.(Gln541*) in the FYCO1 gene as a result of the founder effect.

Crystalline gene mutations in Turkish children with congenital cataracts

PURPOSE

To detect crystallin gene mutations in Turkish children with congenital cataracts.

METHODS

The present study included 56 children (38 males and 18 females) who were diagnosed with congenital cataract in our ophthalmology clinic. The patients' blood samples were collected and sent to the medical genetics laboratory. The samples were assessed using the sequence analysis method, which covered all exons of CRYAA, CRYAB, CRYBB1, CRYBB2, CRYBB3, CRYGC and CRYGD.

RESULTS

In total, 56 patients with congenital cataracts were included in the present study. Of these, 68% were male and 32% were female. The age range of the patients was 2 months to 5 years. The mean age of onset was 21.08 ± 15.15 months. All the patients had bilateral congenital cataracts. The female-to-male ratio was 1:2.1. Mutation analysis was performed to detect possible mutations in CRYAA, CRYAB, CRYBB1, CRYBB2, CRYBB3, CRYGC and CRYGD. Of the four mutations detected, one was novel (c.383A > T in CRYGD) and three were known (c.592C > T in CRYBB2, c.164A > G in CRYGC and c.592C > T in CRYBB2). Two of these three mutations were detected in the same gene (CRYBB2). Crystallin gene mutations were detected in 7% of patients with congenital cataracts (four out of 56 patients) in the present study.

CONCLUSIONS

We think that mutations in crystallin genes are responsible for 7% of congenital cataract cases in our country. The detection of these mutations may help in the molecular diagnosis of congenital cataracts.

c.3G>A mutation in the CRYAB gene that causes fatal infantile hypertonic myofibrillar myopathy in the Chinese population

Infantile hypertonic myofibrillar myopathy is characterized by the rapid development of rigid muscles and respiratory insufficiency soon after birth, with very high mortality. It is extremely rare, and only a few cases having been reported until now. Here we report four Chinese infants with fatal neuromuscular disorders characterized by abdominal and trunk skeletal muscle stiffness and rapid respiratory insufficiency progression. Electromyograms showed increased insertion activities and profuse fibrillation potentials with complex repetitive discharges. Immunohistochemistry staining of muscle biopsies showed accumulations of desmin in the myocytes. Powdery Z-bands with dense granules across sarcomeres were observed in muscle fibers using electron microscopy. All patients carry a homozygous c.3G>A mutation in the CRYAB gene, which resulted in the loss of the initiating methionine and the absence of protein. This study's findings help further understand the disease and highlight a founder mutation in the Chinese population.

Elongated axial length and myopia-related fundus changes associated with the Arg130Cys mutation in the LIM2 gene in four Chinese families with congenital cataracts

Background

Congenital cataract (CC) is a congenital abnormality characterized by lens opacity present at birth and is associated with highly heterogeneous clinical manifestations. Lens-specific integral membrane protein (LIM2) gene expression is localized to tight junctional domains of different lens fiber membranes. To date, only four mutations in LIM2 have been reported to be associated with congenital or presenile cataracts. Due to the rarity of variants detected in the gene, there is limited progress in understanding the correlation between the genotype and phenotype of patients with mutations in LIM2.

Methods

A total of four Chinese families with CCs were recruited for this study, including three families inheriting in an autosomal dominant (AD) pattern and one sporadic case. Genomic DNA was extracted from the leukocytes of peripheral blood collected from all available patients. Whole-exome sequencing (WES) was performed on all probands and at least one of their parents. Bioinformatics analysis was performed to evaluate the pathogenicity of the candidate variants. Exon 4 of LIM2 was amplified by polymerase chain reaction and directly sequenced. All patients underwent full ocular examinations. This was an observational study to explore the genotype-phenotype relationships in the four families with a common candidate variant.

Results

Various ocular phenotypes were detected in these families, mainly including CCs, elongated axial length, and myopia-related fundus changes. The LIM2 gene mutation, p.Arg130Cys, was detected in all patients. This was further confirmed by Sanger sequencing. The proportion of probands with this mutation in our CCs database was 3.1% (4/130), which indicated that this mutation appears to be a frequent cause of cataracts in the Han Chinese population. This variation has been reported by other investigators before and was correlated with isolated cataracts.

Conclusions

This is the first study that reports various ocular phenotypes associated with the p.Arg130Cys mutation in the LIM2 gene, which indicated the phenotypic heterogeneity of this gene. LIM2 might not only function as an integral membrane protein in lens fiber cells but also be associated with the axial development of the eyeball. Functional studies of the LIM2 gene are important and should receive more attention.

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.

Mutations in FYCO1 identified in families with congenital cataracts

Purpose

This study was designed to identify the pathogenic variants in three consanguineous families with congenital cataracts segregating as a recessive trait.

Methods

Consanguineous families with multiple individuals manifesting congenital cataracts were ascertained. All participating members underwent an ophthalmic examination. A small aliquot of the blood sample was collected from all participating individuals, and genomic DNAs were extracted. Homozygosity-based linkage analysis was performed using short tandem repeat (STR) markers. The haplotypes were constructed with alleles of the STR markers, and the two-point logarithm of odds (LOD) scores were calculated. The candidate gene was sequenced bidirectionally to identify the disease-causing mutations.

Results

Linkage analysis localized the disease interval to chromosome 3p in three families. Subsequently, bidirectional Sanger sequencing identified two novel mutations-a single base deletion resulting in a frameshift (c.3196delC; p.His1066IlefsTer10) mutation and a single base substitution resulting in a nonsense (c.4270C>T; p.Arg1424Ter) mutation-and a known missense (c.4127T>C, p.Leu1376Pro) mutation in FYCO1. All three mutations showed complete segregation with the disease phenotype and were absent in 96 ethnically matched control individuals.

Conclusions

We report two novel mutations and a previously reported mutation in FYCO1 in three large consanguineous families. Taken together, mutations in FYCO1 contribute nearly 15% to the total genetic load of autosomal recessive congenital cataracts in this cohort.

The congenital cataract-causing mutations P20R and A171T are associated with important changes in the amyloidogenic feature, structure and chaperone-like activity of human αB-crystallin

Cataract is the major reason for human blindness worldwide. α-Crystallin, as a key chaperone of eye lenses, keeps the lenticular tissues in its transparent state over time. In this study, cataract-causing familial mutations, P20R and A171T, were introduced in CRYАB gene. After successful expression in Escherichia coli and subsequent purification, the recombinant proteins were subjected to extensive structural and functional analyses using various spectroscopic techniques, gel electrophoresis, and electron microscopy. The results of fluorescence and Raman assessments suggest important but discreet conformational changes in human αB-Cry upon these cataractogenic mutations. Furthermore, the mutant proteins exhibited significant secondary structural alteration as revealed by FTIR and Raman spectroscopy. An increase in conformational stability was seen in the human αB-Cry bearing these congenital cataractogenic mutations. The oligomeric size distribution and chaperone-like activity of human αB-Cry were significantly altered by these mutations. The P20R mutant protein was observed to loose most of the chaperone-like activity. Finally, these cataractogenic mutant proteins exhibited an increased propensity to form the amyloid fibrils when incubated under environmental stress. Overall, the structural and functional changes in mutated human αB-Cry proteins can shed light on the pathogenic development of congenital cataracts.

Novel mutations in LTBP2 identified in familial cases of primary congenital glaucoma

Purpose

Primary congenital glaucoma (PCG) is a genetically heterogeneous disorder caused by developmental defects in the anterior chamber and trabecular meshwork. This disease is an important cause of childhood blindness. In this study, we aim to identify the genetic determinants of PCG in three consanguineous families of Pakistani descent.

Methods

Affected members of all three families underwent detailed ophthalmological examination including slit-lamp biomicroscopy. Blood samples were collected from affected and healthy members of all three families, and genomic DNA was extracted. Linkage analysis was performed for the known or reported loci of PCG to localize the disease interval, and logarithm of odds (LOD) scores were calculated. All protein-coding exons of the candidate gene, latent transforming growth factor-beta binding protein 2 (LTBP2), were bidirectionally sequenced to identify the disease-causing mutation.

Results

Short tandem repeat (STR) marker-based linkage analysis localized the critical interval to chromosome 14q with a maximum two-point LOD score of 2.86 (PKGL076), 2.8 (PKGL015), and 2.92 (PKGL042). Bidirectional Sanger sequencing of LTBP2 revealed three novel pathogenic variants, i.e., c.3028G>A (p.Asp1010Asn), c.3427delC (p.Gln1143Argfs*35), and c.5270G>A (p.Cys1757Tyr) in PKGL076, PKGL015, and PKGL042, respectively. All three mutations segregated with the disease phenotype in their respective families and were absent in 200 ethnically matched normal chromosomes.

Conclusions

We identified three novel mutations, p.D1010N, p.Q1143Rfs*35, and p.C1757Y, in LTBP2 responsible for PCG.

Autosomal recessive congenital cataracts linked to HSF4 in a consanguineous Pakistani family

PURPOSE

To investigate the genetic basis of autosomal recessive congenital cataracts (arCC) in a large consanguineous Pakistani family.

METHODS

All participating members of family, PKCC074 underwent an ophthalmic examination. Slit-lamp photographs were ascertained for affected individuals that have not been operated for the removal of the cataractous lens. A small aliquot of the blood sample was collected from all participating individuals and genomic DNAs were extracted. A genome-wide scan was performed with polymorphic short tandem repeat (STR) markers and the logarithm of odds (LOD) scores were calculated. All coding exons and exon-intron boundaries of HSF4 were sequenced and expression of Hsf4 in mouse ocular lens was investigated. The C-terminal FLAG-tagged wild-type and mutant HSF4b constructs were prepared to examine the nuclear localization pattern of the mutant protein.

RESULTS

The ophthalmological examinations suggested that nuclear cataracts are present in affected individuals. Genome-wide linkage analyses localized the critical interval to a 10.95 cM (14.17 Mb) interval on chromosome 16q with a maximum two-point LOD score of 4.51 at θ = 0. Sanger sequencing identified a novel missense mutation: c.433G>C (p.Ala145Pro) that segregated with the disease phenotype in the family and was not present in ethnically matched controls. Real-time PCR analysis identified the expression of HSF4 in mouse lens as early as embryonic day 15 with a steady level of expression thereafter. The immunofluorescence tracking confirmed that both wild-type and mutant HSF4 (p.Ala145Pro) proteins localized to the nucleus.

CONCLUSION

Here, we report a novel missense mutation in HSF4 associated with arCC in a familial case of Pakistani descent.

Biology of Inherited Cataracts and Opportunities for Treatment

Cataract, the clinical correlate of opacity or light scattering in the eye lens, is usually caused by the presence of high-molecular-weight (HMW) protein aggregates or disruption of the lens microarchitecture. In general, genes involved in inherited cataracts reflect important processes and pathways in the lens including lens crystallins, connexins, growth factors, membrane proteins, intermediate filament proteins, and chaperones. Usually, mutations causing severe damage to proteins cause congenital cataracts, while milder variants increasing susceptibility to environmental insults are associated with age-related cataracts. These may have different pathogenic mechanisms: Congenital cataracts induce the unfolded protein response and apoptosis. By contrast, denatured crystallins in age-related cataracts are bound by α-crystallin and form light-scattering HMW aggregates. New therapeutic approaches to age-related cataracts use chemical chaperones to solubilize HMW aggregates, while attempts are being made to regenerate lenses using endogenous stem cells to treat congenital cataracts.

Progression of the role of CRYAB in signaling pathways and cancers

CRYAB is a member of the small heat shock protein family, first discovered in the lens of the eye, and involved in various diseases, such as eye and heart diseases and even cancers, for example, breast cancer, lung cancer, prostate cancer, and ovarian cancer. In addition, CRYAB proteins are involved in a variety of signaling pathways including apoptosis, inflammation, and oxidative stress. This review summarizes the recent progress concerning the role of CRYAB in signaling pathways and diseases. Therefore, the role of CRYAB in signaling pathways and cancers is urgently needed. This article reviews the regulation of CRYAB in the apoptotic inflammatory signaling pathway and its role in cancers progression and as a key role in anti-cancer therapy targeting CRYAB in an effort to improve outcomes for patients with metastatic disease.

Identification of a missense mutation in MIP gene via mutation analysis of a Guangxi Zhuang ethnic pedigree with congenital nuclear cataracts

At present, congenital cataract is the world's leading cause of blindness among children. The aim of the present study was to determine and analyze the genetic disorder associated with a congenital nuclear cataract in a three-generation family of Guangxi Zhuang ethnicity. A total of 3 affected individuals and 5 unaffected family members underwent appropriate comprehensive medical examinations, mainly of the eyes. The white blood cells of the family members were collected and genomic DNA was extracted from 100 healthy individuals, as the control group. The sequences of candidate genes were determined by polymerase chain reaction amplification followed by direct sequencing. The functional consequences of the mutation were analysed with biology software. A missense mutation (c.97C>T) was found in exon 1 of major intrinsic protein of lens fiber (MIP) gene. Therefore, the arginine of the highly conserved codon 33 was changed to cysteine. This mutation was identified in the affected family members, but not identified in unaffected family members or the 100 normal controls. The mutation in the MIP gene is the genetic cause of the congenital cataract in the ethnic Guangxi Zhuang family.

Genetic landscape of isolated pediatric cataracts: extreme heterogeneity and variable inheritance patterns within genes

Pediatric cataract represents an important cause of pediatric visual impairment. While both genetic and environmental causes for pediatric cataract are known, a large proportion remains idiopathic. The purpose of this review is to discuss genes involved in isolated pediatric cataract, with a focus on variable inheritance patterns within genes. Mutations in over 52 genes are known to cause isolated pediatric cataract, with a major contribution from genes encoding for crystallins, transcription factors, membrane proteins, and cytoskeletal proteins. Interestingly, both dominant and recessive inheritance patterns have been reported for mutations in 13 different cataract genes. For some genes, dominant and recessive alleles represent distinct types of mutations, but for many, especially missense variants, there are no clear patterns to distinguish between dominant and recessive alleles. Further research into the functional effects of these mutations, as well as additional data on the frequency of the identified variants, is needed to clarify variant pathogenicity. Exome sequencing continues to be successful in identifying novel genes associated with congenital cataract but is hindered by the extreme genetic heterogeneity of this condition. The large number of idiopathic cases suggests that more genes and potentially novel mechanisms of gene disruption remain to be identified.

Genes and genetics in eye diseases: a genomic medicine approach for investigating hereditary and inflammatory ocular disorders

Past 25y have witnessed an exponential increase in knowledge and understanding of ocular diseases and their respective genetic underpinnings. As a result, scientists have mapped many genes and their variants that can influence vision and health of our eyes. Based on these findings, it is becoming clear that an early diagnosis employing genetic testing can help evaluate patients' conditions for instituting treatment plan(s) and follow-up care to avoid vision complications later. For example, knowing family history becomes crucial for inherited eye diseases as it can benefit members in family who may have similar eye diseases or predispositions. Therefore, gathering information from an elaborate examination along with complete assessment of past medical illness by ophthalmologists followed by consultation with geneticists can help create a roadmap for making diagnosis and treatment precise and beneficial. In this review, we present an update on ocular genomic medicine that we believe has tremendous potential towards unraveling genetic implications in ocular diseases and patients' susceptibilities. We also discuss translational aspects of genetic ophthalmology and genome engineering that may help advance molecular diagnostics and therapeutics.

Correlations of single nucleotide polymorphisms of CRYAA and CRYAB genes with the risk and clinicopathological features of children suffering from congenital cataract

BACKGROUND

The study aims to explore the correlations of the single nucleotide polymorphisms (SNPs) of CRYAA and CRYAB with the risk and clinicopathological features of children with congenital cataract.

METHODS

The study enrolled 168 children diagnosed as congenital cataract (case group) and 172 normal children (control group) from May 2015 to May 2016. Genomic DNA extraction was performed using a QIAamp DNA blood mini kit. Polymerase chain reaction (PCR) products were genotyped using an ABI direct sequencer. Haplotype, allele, and genotype frequencies of CRYAA and CRYAB gene polymorphisms analyses were carried out using the SHEsis software. Logistic regression analysis was performed in order to analyze the risk factors for children suffering from congenital cataract.

RESULTS

Presence of significant differences between the case and control groups' genotype and allele frequencies of CRYAA rs7278468 and CRYAB rs370803064/rs387907338. TA of CRYAB gene might increase congenital cataract risk in children, while GCG of CRYAA gene and GC of CRYAB gene might decrease congenital cataract risk in children. CRYAA rs7278468, CRYAB rs370803064/rs387907338 polymorphisms were significantly correlated to uncorrected visual acuity, best-corrected visual acuity, nystagmus, visual axis opacification, microcornea, lens opacity, posterior capsular thickening, and degrees of posterior capsule opacification after operation in children with congenital cataract. Logistic regression analysis revealed that the T allele of CRYAA rs7278468, A allele of CRYAB rs370803064, T allele of CRYAB rs387907338, family history, and TA haplotype of CRYAB gene were risk factors for children with congenital cataract.

CONCLUSION

Our findings demonstrated that CRYAA rs7278468 and CRYAB rs370803064/rs387907338 are correlated with the risk and clinicopathological features of children suffering from congenital cataract.

Molecular Genetic Analysis of Pakistani Families With Autosomal Recessive Congenital Cataracts by Homozygosity Screening

Purpose

To identify the genetic origins of autosomal recessive congenital cataracts (arCC) in the Pakistani population.

Methods

Based on the hypothesis that most arCC patients in consanguineous families in the Punjab areas of Pakistan should be homozygous for causative mutations, affected individuals were screened for homozygosity of nearby highly informative microsatellite markers and then screened for pathogenic mutations by DNA sequencing. A total of 83 unmapped consanguineous families were screened for mutations in 33 known candidate genes.

Results

Patients in 32 arCC families were homozygous for markers near at least 1 of the 33 known CC genes. Sequencing the included genes revealed homozygous cosegregating sequence changes in 10 families, 2 of which had the same variation. These included five missense, one nonsense, two frame shift, and one splice site mutations, eight of which were novel, in EPHA2, FOXE3, FYCO1, TDRD7, MIP, GALK1, and CRYBA4.

Conclusions

The above results confirm the usefulness of homozygosity mapping for identifying genetic defects underlying autosomal recessive disorders in consanguineous families. In our ongoing study of arCC in Pakistan, including 83 arCC families that underwent homozygosity mapping, 3 mapped using genome-wide linkage analysis in unpublished data, and 30 previously reported families, mutations were detected in approximately 37.1% (43/116) of all families studied, suggesting that additional genes might be responsible in the remaining families. The most commonly mutated gene was FYCO1 (14%), followed by CRYBB3 (5.2%), GALK1 (3.5%), and EPHA2 (2.6%). This provides the first comprehensive description of the genetic architecture of arCC in the Pakistani population.

Inherited Congenital Cataract: A Guide to Suspect the Genetic Etiology in the Cataract Genesis

Cataracts are the principal cause of treatable blindness worldwide. Inherited congenital cataract (CC) shows all types of inheritance patterns in a syndromic and nonsyndromic form. There are more than 100 genes associated with cataract with a predominance of autosomal dominant inheritance. A cataract is defined as an opacity of the lens producing a variation of the refractive index of the lens. This variation derives from modifications in the lens structure resulting in light scattering, frequently a consequence of a significant concentration of high-molecular-weight protein aggregates. The aim of this review is to introduce a guide to identify the gene involved in inherited CC. Due to the manifold clinical and genetic heterogeneity, we discarded the cataract phenotype as a cardinal sign; a 4-group classification with the genes implicated in inherited CC is proposed. We consider that this classification will assist in identifying the probable gene involved in inherited CC.

Correction: Missense Mutations in CRYAB Are Liable for Recessive Congenital Cataracts

[This corrects the article DOI: 10.1371/journal.pone.0137973.].

Deletion at the GCNT2 Locus Causes Autosomal Recessive Congenital Cataracts

PURPOSE

The aim of this study is to identify the molecular basis of autosomal recessive congenital cataracts (arCC) in a large consanguineous pedigree.

METHODS

All participating individuals underwent a detailed ophthalmic examination. Each patient's medical history, particularly of cataracts and other ocular abnormalities, was compiled from available medical records and interviews with family elders. Blood samples were donated by all participating family members and used to extract genomic DNA. Genetic analysis was performed to rule out linkage to known arCC loci and genes. Whole-exome sequencing libraries were prepared and paired-end sequenced. A large deletion was found that segregated with arCC in the family, and chromosome walking was conducted to estimate the proximal and distal boundaries of the deletion mutation.

RESULTS

Exclusion and linkage analysis suggested linkage to a region of chromosome 6p24 harboring GCNT2 (glucosaminyl (N-acetyl) transferase 2) with a two-point logarithm of odds score of 5.78. PCR amplifications of the coding exons of GCNT2 failed in individuals with arCC, and whole-exome data analysis revealed a large deletion on chromosome 6p in the region harboring GCNT2. Chromosomal walking using multiple primer pairs delineated the extent of the deletion to approximately 190 kb. Interestingly, a failure to amplify a junctional fragment of the deletion break strongly suggests an insertion in addition to the large deletion.

CONCLUSION

Here, we report a novel insertion/deletion mutation at the GCNT2 locus that is responsible for congenital cataracts in a large consanguineous family.

A novel dominant D109A CRYAB mutation in a family with myofibrillar myopathy affects αB-crystallin structure

Myofibrillar myopathy (MFM) is a group of inherited muscular disorders characterized by myofibrils dissolution and abnormal accumulation of degradation products. So far causative mutations have been identified in nine genes encoding Z-disk proteins, including αB-crystallin (CRYAB), a small heat shock protein (also called HSPB5). Here, we report a case study of a 63-year-old Polish female with a progressive lower limb weakness and muscle biopsy suggesting a myofibrillar myopathy, and extra-muscular multisystemic involvement, including cataract and cardiomiopathy. Five members of the proband's family presented similar symptoms. Whole exome sequencing followed by bioinformatic analysis revealed a novel D109A mutation in CRYAB associated with the disease. Molecular modeling in accordance with muscle biopsy microscopic analyses predicted that D109A mutation influence both structure and function of CRYAB due to decreased stability of oligomers leading to aggregate formation. In consequence disrupted sarcomere cytoskeleton organization might lead to muscle pathology. We also suggest that mutated RQDE sequence of CRYAB could impair CRYAB chaperone-like activity and promote aggregation of lens crystallins.

Mutation in LIM2 Is Responsible for Autosomal Recessive Congenital Cataracts

Purpose

To identify the molecular basis of non-syndromic autosomal recessive congenital cataracts (arCC) in a consanguineous family.

Methods

All family members participating in the study received a comprehensive ophthalmic examination to determine their ocular phenotype and contributed a blood sample, from which genomic DNA was extracted. Available medical records and interviews with the family were used to compile the medical history of the family. The symptomatic history of the individuals exhibiting cataracts was confirmed by slit-lamp biomicroscopy. A genome-wide linkage analysis was performed to localize the disease interval. The candidate gene, LIM2 (lens intrinsic membrane protein 2), was sequenced bi-directionally to identify the disease-causing mutation. The physical changes caused by the mutation were analyzed in silico through homology modeling, mutation and bioinformatic algorithms, and evolutionary conservation databases. The physiological importance of LIM2 to ocular development was assessed in vivo by real-time expression analysis of Lim2 in a mouse model.

Results

Ophthalmic examination confirmed the diagnosis of nuclear cataracts in the affected members of the family; the inheritance pattern and cataract development in early infancy indicated arCC. Genome-wide linkage analysis localized the critical interval to chromosome 19q with a two-point logarithm of odds (LOD) score of 3.25. Bidirectional sequencing identified a novel missense mutation, c.233G>A (p.G78D) in LIM2. This mutation segregated with the disease phenotype and was absent in 192 ethnically matched control chromosomes. In silico analysis predicted lower hydropathicity and hydrophobicity but higher polarity of the mutant LIM2-encoded protein (MP19) compared to the wild-type. Moreover, these analyses predicted that the mutation would disrupt the secondary structure of a transmembrane domain of MP19. The expression of Lim2, which was detected in the mouse lens as early as embryonic day 15 (E15) increased after birth to a level that was sustained through the postnatal time points.

Conclusion

A novel missense mutation in LIM2 is responsible for autosomal recessive congenital cataracts.