The genetic landscape of crystallins in congenital cataract

A bibliometric and visualized analysis of the pathogenesis of cataracts from 1999 to 2023

Research on the pathogenesis of cataracts is ongoing and the number of publications on this topic is increasing annually. This study offers an overview of the research status, popular topics, and scholarly tendencies in the field of cataract pathogenesis over recent decades，which helps to guide future research directions, and optimize resource allocation. In the present study, we performed a bibliometric analysis of cataract pathogenesis. Publications from January 1, 1999, to December 20, 2023, were collected from the Web of Science Core Collection (WoSCC), and the extracted data were quantified and analyzed. We analyzed and presented the data using Microsoft Excel, VOSviewer, CiteSpace, and Python. In all, 4006 articles were evaluated based on various characteristics, including publication year, authors, countries, institutions, journals, citations, and keywords. This study utilized VOSviewer to conduct visualized analysis, including co-authorship, co-citation, co-occurrence, and network visualization. The CiteSpace software was used to identify keywords with significant bursts of activity. The number of annual global publications climbed from 76 to 277 between 1999 and 2023, a 264.47% rise. Experimental Eye Research published the most manuscripts (178 publications), whereas Investigative Ophthalmology & Visual Science received the most citations (6675 citations). The most influential and productive country, institution, and author were the United States (1244 publications, 54,456 citations), University of California system (136 publications, 5401 citations), and Yao Ke (49 publications, 838 citations), respectively. The top 100 ranked keywords are divided into four clusters through co-occurrence analysis: (1) secondary cataracts, (2) oxidative stress, (3) gene mutations and protein abnormalities, and (4) alteration of biological processes in lens epithelial cells. Further discussions on the four subtopics outline the research topics and trends. In conclusion, the specific mechanism of cataract formation remains a popular topic for future research and should be explored in greater depth.

Identification of pathogenic genetic variants in patients with acquired early-onset bilateral cataracts using next-generation sequencing

BACKGROUND

Acquired early-onset bilateral cataracts can result from systemic etiologies or genetic disorders.

METHODS

In this observational study, we analyzed individuals 18 months to 35 years of age with acquired bilateral cataracts via a next-generation sequencing panel of 66 genes to identify disease-causing genetic variants.

RESULTS

Of 347 patients enrolled, 313 (90.2%) were <19 years (median, 8 years). We identified 74 pathogenic or likely pathogenic variants in 69 patients. Of the variants, we observed 64 single nucleotide variants (SNV) in 24 genes and 10 copy number variants (CNV) of varying size and genomic location. SNVs in crystallin genes were most common, accounting for 27.0% of all variants (20 of 74). Of those, recurrent variants included known cataract-causing variants CRYBA1 c.215+1G>A, observed in 3 patients, and CRYBA1 c.272_274delGAG, CRYBB2 c.463C>T and c.562C>T, and CRYAA c.62G>A, each observed in 2 patients. In 5 patients, we identified CNV deletions ranging from 1.32-2.41 Mb in size associated with 1q21.1 microdeletion syndrome. Biallelic variants in CYP27A1 were identified in two siblings, one as part of targeted follow-up family testing, who were subsequently diagnosed with cerebrotendinous xanthomatosis, a rare but treatable autosomal recessive disease that often presents with acquired early-onset bilateral cataracts.

CONCLUSIONS

This study demonstrates the utility of genetic testing in individuals with acquired early-onset bilateral cataracts to help clarify etiology. Identification of causative genetic variants can inform patient management and facilitate genetic counseling by identifying genetic conditions with risk of recurrence in families.

Cataract-causing mutations S78F and S78P of γD-crystallin decrease protein conformational stability and drive aggregation

Congenital cataract is the leading cause of childhood blindness, which primarily results from genetic factors. γD-crystallin is the most abundant γ-crystallin and is essential for maintaining lens transparency and refractivity. Numerous mutations in γD-crystallin have been reported with unclear pathogenic mechanism. Two different cataract-causing mutations Ser78Phe and Ser78Pro in γD-crystallin were previously identified at the same conserved Ser78 residue. In this work, firstly, we purified the mutants and characterized for the structural change using fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and size-exclusion chromatography (SEC). Both mutants were prone to form insoluble precipitates when expressed in Escherichia coli strain BL21 (DE3) cells. Compared with wild-type (WT), both mutations caused structural disruption, increased hydrophobic exposure, decreased solubility, and reduced thermal stability. Next, we investigated the aggregation of the mutants at the cellular level. Overexpression the mutants in HLE-B3 and HEK 293T cells could induce aggresome formations. The environmental stresses (including heat, ultraviolet irradiation and oxidative stress) promoted the formation of aggregates. Moreover, the intracellular S78F and S78P aggregates could be reversed by lanosterol. Molecular dynamic simulation indicated that both mutations disrupted the structural integrity of Greek-key motif 2. Hence, our results reveal the vital role of conserved Ser78 in maintaining the structural stability, which can offer new insights into the mechanism of cataract formation.

Identification of novel variants in Turkish families with non-syndromic congenital cataracts using whole-exome sequencing

PURPOSE

The present study aimed to identify the molecular etiology of non-syndromic congenital cataract (CC) using whole-exome sequencing (WES) analysis.

METHODS

In the present study, ophthalmologic results and pedigree analysis of the families of 12 patients with non-syndromic CC were evaluated. WES analysis was conducted after DNA was isolated from peripheral blood samples obtained from the patients.

RESULTS

Twelve non-syndromic probands (10 males and 2 females) with bilateral CC were included in the study. Patient age ranged between 1 and 11 months. WES analysis showed pathogenic/likely pathogenic variant in 7 (58%) of the 12 families and variant of unknown significance (VUS) in 5 (42%) of them. All the 13 different variants detected in 9 different CC-related genes were co-segregated with the disease. Autosomal dominant inheritance was found in 7 (58%) of the families and autosomal recessive inheritance was found in 5 (42%) of them.

CONCLUSION

To the best of our knowledge, the present research is one of the limited numbers of studies in the Turkish population in which genetically heterogeneous non-syndromic CC was investigated using WES analysis. Novel variants that we identified in DNMBP, LSS, and WFS1 genes, which are rarely associated with the CC phenotype, have contributed to the mutation spectrum of this disease. Identifying the relevant molecular genetic etiology allows accurate genetic counseling to be provided to the families.

Novel CRYGC Mutation in Conserved Ultraviolet-Protective Tryptophan (p.Trp131Arg) Is Linked to Autosomal Dominant Congenital Cataract

Congenital cataract (CC), the most prevalent cause of childhood blindness and amblyopia, necessitates prompt and precise genetic diagnosis. The objective of this study is to identify the underlying genetic cause in a Swiss patient with isolated CC. Whole exome sequencing (WES) and copy number variation (CNV) analysis were conducted for variant identification in a patient born with a total binocular CC without a family history of CC. Sanger Sequencing was used to confirm the variant and segregation analysis was used to screen the non-affected parents. The first de novo missense mutation at c.391T>C was identified in exon 3 of CRYGC on chromosome 2 causing the substitution of a highly conserved Tryptophan to an Arginine located at p.Trp131Arg. Previous studies exhibit significant changes in the tertiary structure of the crystallin family in the following variant locus, making CRYGC prone to aggregation aggravated by photodamage resulting in cataract. The variant can be classified as pathogenic according to the American College of Medical Genetics and Genomics (ACMG) criteria (PP3 + PM1 + PM2 + PS2; scoring 10 points). The identification of this novel variant expands the existing knowledge on the range of variants found in the CRYGC gene and contributes to a better comprehension of cataract heterogeneity.

Interplay between Nrf2 and αB-crystallin in the lens and heart of zebrafish under proteostatic stress

A coordinated oxidative stress response, partly triggered by the transcription factor Nrf2, protects cells from the continual production of reactive oxygen species. Left unbuffered, reactive oxygen species can lead to protein aggregation that has been implicated in a spectrum of diseases such as cataract of the ocular lens and myopathy of the heart. While proteostasis is maintained by diverse families of heat shock proteins, the interplay between the oxidative and proteostatic stress responses in the lens and heart has not been investigated. Capitalizing on multiple zebrafish lines that have compromised function of Nrf2 and/or the two zebrafish small heat shock proteins αBa- and αBb-crystallin, we uncovered a transcriptional relationship that leads to a substantial increase in αBb-crystallin transcripts in the heart in response to compromised function of Nrf2. In the lens, the concomitant loss of function of Nrf2 and αBa-crystallin leads to upregulation of the cholesterol biosynthesis pathway, thus mitigating the phenotypic consequences of the αBa-crystallin knockout. By contrast, abrogation of Nrf2 function accentuates the penetrance of a heart edema phenotype characteristic of embryos of αB-crystallin knockout lines. Multiple molecular pathways, such as genes involved in extracellular interactions and implicated in cardiomyopathy, are revealed from transcriptome profiling, thus identifying novel targets for further investigation. Together, our transcriptome/phenotypic analysis establishes an intersection between oxidative stress and chaperone responses in the lens and heart.

Congenital coralliform cataract is the predominant consequence of a recurrent mutation in the CRYGD gene

BACKGROUND

Congenital cataract is a leading cause of treatable childhood blindness and both clinically and genetically heterogeneous. Among the already characterized phenotypes, coralliform cataract is a rare special form of congenital cataracts. Although previous studies had shown that mutations in the γD-crystallin (CRYGD) can result in congenital coralliform cataracts, no conclusive genotype-phenotype correlation might be drawn. Here we aimed to identify the spectrum and frequency of CRYGD gene mutations in congenital coralliform cataracts of Chinese origin.

METHODS

The medical records of 392 Chinese families with congenital cataracts were reviewed between January 2011 and December 2021. The families, clinically documented to have congenital coralliform cataracts, were screened for mutations in candidate CRYGD gene. The genomic DNA of all subjects was extracted from peripheral blood leukocytes. PCR amplified and direct sequencing were performed to identify the disease-causing mutation.

RESULTS

A total of 12 families with coralliform cataracts were recruited in this study in the past 10 years, accounting for 3.1% of the families with congenital cataracts. Of the 12 families, all affected individuals presented with bilateral non-progressive coralliform cataracts since birth, with the best-corrected Snellen visual acuities ranging from 20/200 to 20/25. A recurrent c.70 C > A (p. P24T) mutation in CRYGD was identified in 10 families (83.3%) with congenital cataract, which co-segregated with all affected individuals and was not observed in unaffected family members or ethnically matched normal controls.

CONCLUSIONS

The coralliform cataract is characterized by being bilateral, non-progressive and present at birth. A recurrent p.P24T CRYGD mutation occurs independently in 83.3% of the Chinese families with congenital coralliform cataracts and most likely represents a mutational hot spot, which underscore the relations between coralliform cataract and p.P24T CRYGD.

Distinct gene expression profiles underlie morphological and etiological differences in pediatric cataracts

Purpose

Pediatric cataract is a major cause of preventable childhood blindness worldwide. Although genetic mutations or infections have been described in patients, the mechanistic basis of human cataract development remains poorly understood. Therefore, gene expression of structural, developmental, profibrotic, and transcription factors in phenotypically and etiologically distinct forms of pediatric cataracts were evaluated.

Methods

This cross-sectional study included 89 pediatric cataract subjects subtyped into 1) prenatal infectious (cytomegalovirus, rubella, and combined cytomegalovirus with rubella infection), 2) prenatal non-infectious, 3) posterior capsular anomalies, 4) postnatal, 5) traumatic, and 6) secondary, and compared to clear, non-cataractous material of eyes with the subluxated lenses. Expression of lens structure-related genes (Aqp-0, HspA4/Hsp70, CrygC), transcription factors (Tdrd7, FoxE3, Maf, Pitx 3) and profibrotic genes (Tgfβ, Bmp7, αSmA, vimentin) in surgically extracted cataract lens material were studied and correlated clinically.

Results

In cataract material, the lens-related gene expression profiles were uniquely associated with phenotype/etiology of different cataracts. Postnatal cataracts showed a significantly altered FoxE3 expression. Low levels of Tdrd7 expression correlated with posterior subcapsular opacity, whereas CrygC correlated significantly with anterior capsular ruptures. The expression of Aqp0 and Maf was elevated in infectious cataracts, particularly in CMV infections, compared to other cataract subtypes. Tgfβ showed significantly low expression in various cataract subtypes, whereas vimentin had elevated gene expression in infectious and prenatal cataracts.

Conclusion

A significant association between lens gene expression patterns in phenotypically and etiologically distinct subtypes of pediatric cataracts suggests regulatory mechanisms in cataractogenesis. The data reveal that cataract formation and presentation is a consequence of altered expression of a complex network of genes.

A tapt1 knock-out zebrafish line with aberrant lens development and impaired vision models human early-onset cataract

Bi-allelic mutations in the gene coding for human trans-membrane anterior-posterior transformation protein 1 (TAPT1) result in a broad phenotypic spectrum, ranging from syndromic disease with severe skeletal and congenital abnormalities to isolated early-onset cataract. We present here the first patient with a frameshift mutation in the TAPT1 gene, resulting in both bilateral early-onset cataract and skeletal abnormalities, in addition to several dysmorphic features, in this way further expanding the phenotypic spectrum associated with TAPT1 mutations. A tapt1a/tapt1b double knock-out (KO) zebrafish model generated by CRISPR/Cas9 gene editing revealed an early larval phenotype with eye malformations, loss of vision, increased photokinetics and hyperpigmentation, without visible skeletal involvement. Ultrastructural analysis of the eyes showed a smaller condensed lens, loss of integrity of the lens capsule with formation of a secondary lens and hyperplasia of the cells in the ganglion and inner plexiform layers of the retina. Transcriptomic analysis pointed to an impaired lens development with aberrant expression of many of the crystallin and other lens-specific genes. Furthermore, the phototransduction and visual perception pathways were found to be significantly disturbed. Differences in light perception are likely the cause of the increased dark photokinetics and generalized hyperpigmentation observed in this zebrafish model. In conclusion, this study validates TAPT1 as a new gene for early-onset cataract and sheds light on its ultrastructural and molecular characteristics.

Conformational stability of the deamidated and mutated human βB2-crystallin

Previous studies propose that genetic mutations and post-translational modifications in protein crystallins promote protein aggregation and are considered significant risk factors for cataract formation. The βB2-crystallin (HβB2C) forms a high proportion of proteins in the human eye lens. Different congenital mutations and post-translational deamidations in βB2-crystallin have been reported and linked to cataract formation. In this work, we employed extensive all-atom molecular dynamics simulations to evaluate the conformational stability of deamidated and mutated HβB2C. Our results show critical changes in the protein surface and its native contacts due to a modification in the conformational equilibrium of these proteins. The double deamidated (Q70E/Q162E) and single deamidated (Q70E) impact the well compact conformation of the HβB2C. These post-translational modifications allow the exposure of the protein hydrophobic interface, which lead to the exposure of electronegative residues. On the other hand, our mutational studies showed that the S143F mutation modifies the hydrogen-bond network of an antiparallel β-sheet, unfolding the C-terminal domain. Interestingly, the chain termination mutation (Q155X) does not unfold the N-terminal domain. However, the resultant conformation is more compact and avoids the exposure of the hydrophobic interface. Our results provide valuable information about the first steps of HβB2C unfolding in the presence of deamidated amino acids that have been reported to appear during aging. The findings reported in this work are essential for the general knowledge of the initial steps in the cataract formation mechanism, which may be helpful for the further development of molecules with pharmacological potential against cataract disease.

Gata2a Mutation Causes Progressive Microphthalmia and Blindness in Nile Tilapia

The normal development of lens fiber cells plays a critical role in lens morphogenesis and maintaining transparency. Factors involved in the development of lens fiber cells are largely unknown in vertebrates. In this study, we reported that GATA2 is essential for lens morphogenesis in Nile tilapia (Oreochromis niloticus). In this study, Gata2a was detected in the primary and secondary lens fiber cells, with the highest expression in primary fiber cells. gata2a homozygous mutants of tilapia were obtained using CRISPR/Cas9. Different from fetal lethality caused by Gata2/gata2a mutation in mice and zebrafish, some gata2a homozygous mutants of tilapia are viable, which provides a good model for studying the role of gata2 in non-hematopoietic organs. Our data showed that gata2a mutation caused extensive degeneration and apoptosis of primary lens fiber cells. The mutants exhibited progressive microphthalmia and blindness in adulthood. Transcriptome analysis of the eyes showed that the expression levels of almost all genes encoding crystallin were significantly down-regulated, while the expression levels of genes involved in visual perception and metal ion binding were significantly up-regulated after gata2a mutation. Altogether, our findings indicate that gata2a is required for the survival of lens fiber cells and provide insights into transcriptional regulation underlying lens morphogenesis in teleost fish.

The lens epithelium as a major determinant in the development, maintenance, and regeneration of the crystalline lens

The crystalline lens is a transparent and refractive biconvex structure formed by lens epithelial cells (LECs) and lens fibers. Lens opacity, also known as cataracts, is the leading cause of blindness in the world. LECs are the principal cells of lens throughout human life, exhibiting different physiological properties and functions. During the embryonic stage, LECs proliferate and differentiate into lens fibers, which form the crystalline lens. Genetics and environment are vital factors that influence normal lens development. During maturation, LECs help maintain lens homeostasis through material transport, synthesis and metabolism as well as mitosis and proliferation. If disturbed, this will result in loss of lens transparency. After cataract surgery, the repair potential of LECs is activated and the structure and transparency of the regenerative tissue depends on postoperative microenvironment. This review summarizes recent research advances on the role of LECs in lens development, homeostasis, and regeneration, with a particular focus on the role of cholesterol synthesis (eg., lanosterol synthase) in lens development and homeostasis maintenance, and how the regenerative potential of LECs can be harnessed to develop surgical strategies and improve the outcomes of cataract surgery (Fig. 1). These new insights suggest that LECs are a major determinant of the physiological and pathological state of the lens. Further studies on their molecular biology will offer possibility to explore new approaches for cataract prevention and treatment.

Case Report: A de novo Variant of CRYGC Gene Associated With Congenital Cataract and Microphthalmia

Background: Congenital cataract is one of the most common causes of blindness in children. A rapid and accurate genetic diagnosis benefit the patients in the pediatric department. The current study aims to identify the genetic defects in a congenital cataract patient without a family history.

Case presentation: A congenital cataract patient with microphthalmia and nystagmus was recruited for this study. Trio-based whole-exome sequencing revealed a de novo variant (c.394delG, p.V132Sfs*15) in CRYGC gene. According to the American College of Medical Genetics and Genomics (ACMG) criteria, the variant could be annontated as pathogenic.

Conclusion: Our findings provide new knowledge of the variant spectrum of CRYGC gene and are essential for understanding the heterogeneity of cataracts in the Chinese population.

Association of single nucleotide polymorphism variations in CRYAA and CRYAB genes with congenital cataract in Pakistani population

Background

The purpose of present study was to analyze the association of single nucleotide polymorphism (SNPs) variant in CRYAA and CRYAB genes with Congenital Cataract.

Method

Total 196 blood samples of children were collected, out of which 102 samples were congenital cataract (case group) and 94 samples were normal individuals (control group). Genomic DNA was extracted by using optimized inorganic method. Tetra primers for SNPs were designed and TETRA-ARMs assay was performed on both groups. Genotypic, allelic frequency and haplotype analyses were obtained by using SNPstats software.

Results

The coordination of genotypic and allelic frequencies of CRYAA and CRYAB genes variants and the association between case and control groups showed increased risk of congenital cataract in children who contained rs13053109 G > C variant of CRYAA in all models (all P > 0.05). This depicts the evident difference between the frequencies of case and control groups. The haplotype analysis of SNPs rs3761382, rs7278468 and rs13051039 of CRYAA gene showed weak linkage disequilibrium between the 3 SNPs (r2 < 0.8). The haplotype CTC indicated the high risk of congenital cataract in infants based of its p value (OR = 1.60 95% CI = 0.11-22.64, P > 0.05).

Conclusion

The variation in CRYAA gene can be the risk factor for congenital cataract in infants.

Pathogenic variants in the CYP21A2 gene cause isolated autosomal dominant congenital posterior polar cataracts

BACKGROUND

Congenital cataracts are the most common cause of visual impairment worldwide. Inherited cataract is a clinically and genetically heterogeneous disease. Here we report disease-causing variants in a novel gene, CYP21A2, causing autosomal dominant posterior polar cataract. Variants in this gene are known to cause autosomal recessive congenital adrenal hyperplasia (CAH).

METHODS

Using whole-exome sequencing (WES), we have identified disease-causing sequence variants in two families of British and Irish origin, and in two isolated cases of Asian-Indian and British origin. Bioinformatics analysis confirmed these variants as rare with damaging pathogenicity scores. Segregation was tested within the families using direct Sanger sequencing.

RESULTS

A nonsense variant NM_000500.9 c.955 C > T; p.Q319* was identified in CYP21A2 in two families with posterior polar cataract and in an isolated case with unspecified congenital cataract phenotype. This is the same variant previously linked to CAH and identified as Q318* in the literature. We have also identified a rare missense variant NM_000500.9 c.770 T > C; p.M257T in an isolated case with unspecified congenital cataract phenotype.

CONCLUSION

This is the first report of separate sequence variants in CYP21A2 associated with congenital cataract. Our findings extend the genetic basis for congenital cataract and add to the phenotypic spectrum of CYP21A2 variants and particularly the CAH associated Q318* variant. CYP21A2 has a significant role in mineralo- and gluco-corticoid biosynthesis. These findings suggest that CYP21A2 may be important for extra-adrenal biosynthesis of aldosterone and cortisol in the eye lens.

Changes in DNA methylation hallmark alterations in chromatin accessibility and gene expression for eye lens differentiation

Background

Methylation at cytosines (mCG) is a well-known regulator of gene expression, but its requirements for cellular differentiation have yet to be fully elucidated. A well-studied cellular differentiation model system is the eye lens, consisting of a single anterior layer of epithelial cells that migrate laterally and differentiate into a core of fiber cells. Here, we explore the genome-wide relationships between mCG methylation, chromatin accessibility and gene expression during differentiation of eye lens epithelial cells into fiber cells.

Results

Whole genome bisulfite sequencing identified 7621 genomic loci exhibiting significant differences in mCG levels between lens epithelial and fiber cells. Changes in mCG levels were inversely correlated with the differentiation state-specific expression of 1285 genes preferentially expressed in either lens fiber or lens epithelial cells (Pearson correlation r = − 0.37, p < 1 × 10^–42). mCG levels were inversely correlated with chromatin accessibility determined by assay for transposase-accessible sequencing (ATAC-seq) (Pearson correlation r = − 0.86, p < 1 × 10^–300). Many of the genes exhibiting altered regions of DNA methylation, chromatin accessibility and gene expression levels in fiber cells relative to epithelial cells are associated with lens fiber cell structure, homeostasis and transparency. These include lens crystallins (CRYBA4, CRYBB1, CRYGN, CRYBB2), lens beaded filament proteins (BFSP1, BFSP2), transcription factors (HSF4, SOX2, HIF1A), and Notch signaling pathway members (NOTCH1, NOTCH2, HEY1, HES5). Analysis of regions exhibiting cell-type specific alterations in DNA methylation revealed an overrepresentation of consensus sequences of multiple transcription factors known to play key roles in lens cell differentiation including HIF1A, SOX2, and the MAF family of transcription factors.

Conclusions

Collectively, these results link DNA methylation with control of chromatin accessibility and gene expression changes required for eye lens differentiation. The results also point to a role for DNA methylation in the regulation of transcription factors previously identified to be important for lens cell differentiation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13072-022-00440-z.

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.

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 &gt; 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.

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.

Variants in PAX6, PITX3 and HSF4 causing autosomal dominant congenital cataracts

Background

Lens development is orchestrated by transcription factors. Disease-causing variants in transcription factors and their developmental target genes are associated with congenital cataracts and other eye anomalies.

Methods

Using whole exome sequencing, we identified disease-causing variants in two large British families and one isolated case with autosomal dominant congenital cataract. Bioinformatics analysis confirmed these disease-causing mutations as rare or novel variants, with a moderate to damaging pathogenicity score, with testing for segregation within the families using direct Sanger sequencing.

Results

Family A had a missense variant (c.184 G>A; p.V62M) in PAX6 and affected individuals presented with nuclear cataract. Family B had a frameshift variant (c.470–477dup; p.A160R*) in PITX3 that was also associated with nuclear cataract. A recurrent missense variant in HSF4 (c.341 T>C; p.L114P) was associated with congenital cataract in a single isolated case.

Conclusions

We have therefore identified novel variants in PAX6 and PITX3 that cause autosomal dominant congenital cataract.

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.

Physiological and pathological functions of βB2-crystallins in multiple organs: a systematic review

Crystallins, the major constituent proteins of mammalian lenses, are significant not only for the maintenance of eye lens stability, transparency, and refraction, but also fulfill various physiopathological functions in extraocular tissues. βB2-crystallin, for example, is a multifunctional protein expressed in the human retina, brain, testis, ovary, and multiple tumors. Mutations in the βB2 crystallin gene or denaturation of βB2-crystallin protein are associated with cataracts, ocular pathologies, and psychiatric disorders. A prominent role for βB2-crystallins in axonal growth and regeneration, as well as in dendritic outgrowth, has been demonstrated after optic nerve injury. Studies in βB2-crystallin-null mice revealed morphological and functional abnormalities in testis and ovaries, indicating βB2-crystallin contributes to male and female fertility in mice. Interestingly, although pathogenic significance remains obscure, several studies identified a clear correlation between βB2 crystallin expression and the prognosis of patients with breast cancer, colorectal cancer, prostate cancer, renal cell carcinoma, and glioblastoma in the African American population. This review summarizes the physiological and pathological functions of βB2-crystallin in the eye and other organs and tissues and discusses findings related to the expression and potential role of βB2-crystallin in tumors.