Novel mutations in CRYGD are associated with congenital cataracts in Chinese families

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.

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.

Molecular Etiology of Isolated Congenital Cataract Using Next-Generation Sequencing: Single Center Exome Sequencing Data from Turkey

Congenital cataract, which refers to lenticular opacity diagnosed at birth or more commonly during the first year of life, is one of the leading causes of childhood blindness. Molecular understanding of the disease pathogenesis has evolved thanks to many studies based on modern technologies. In this study, we aimed to identify and discuss the molecular etiology of nonsyndromic or nonmetabolic bilateral congenital cataract by whole-exome sequencing (WES). Patients with bilateral congenital cataract presumed to be isolated after metabolic and genetic evaluation were enrolled in the study. All patients underwent detailed ophthalmological examination and bilateral cataract surgery. DNA samples of the probands, parents, and available affected family members were analyzed by WES. Variants were validated and confirmed by Sanger sequencing in all probands and in available affected family members. A total of 4 patients (3 girls and 1 boy) were recruited. Two patients had nuclear, 1 patient had total, and 1 patient had combined lamellar and sutural cataract. One family had consanguinity. A heterozygous c.215+1G>A mutation in CRYBA1, heterozygous c.432C>G (p.Tyr144Ter) mutation in CRYGC, heterozygous c.70A>C (p.Pro24Thr) mutation in CRYGD, and a heterozygous c.466G>A (p.Gly156Arg) mutation in CRYBB3 were detected. All these mutations were confirmed by Sanger sequencing in selected affected individuals. The current study identified all causative mutations of congenital cataract in the crystalline genes. The results confirmed that WES is a very useful tool in the investigation of the diseases with heterogeneous genetic background.

Effects of Mutating Trp42 Residue on γD-Crystallin Stability

Oligomerization and aggregation of γD-crystallins (HγDC) in the eye lens is one of the main causes of cataract development. To date, several congenital mutations related to this protein are known to promote the formation of aggregates. Previous studies have demonstrated that mutations in W42 residue of HγDC lead to the generation of partially unfolded intermediates that are more prone to aggregate. To understand the role of W42 in the stability of HγDC, we performed alchemical free-energy calculations and all-atom molecular dynamics simulations of different W42 mutant models. Our results suggest that substitution of W42 by small size and/or polar residues promotes HγDC denaturation due to the entry of water molecules into the hydrophobic core of the N-terminal domain. Similar behavior was observed in the C-terminal domain of HγDC when mutating the W130 residue located in a homologous position. Moreover, the exposure of the hydrophobic core residues could lead to the formation of aggregation-prone partially unfolded species. Overall, this study takes a step toward understanding the role of HγDC in cataract development.

Two Pathogenic Gene Mutations Identified Associating with Congenital Cataract and Iris Coloboma Respectively in a Chinese Family

Purpose

To screen out pathogenic genes in a Chinese family with congenital cataract and iris coloboma. Material and Methods. A three-generation family with congenital cataract and iris coloboma from a Han ethnicity was recruited. DNA was extracted from peripheral blood samples collected from all individuals in the family. Whole exon sequencing was employed for screening the disease-causing gene mutations in the proband, and Sanger sequencing was used for other members of the family and a control group of 500 healthy individuals. Bioinformatics analysis and three-dimensional structure predictions were used to predict the impact of amino acid changes on protein structure and function.

Results

The candidate genes of cataract and iris coloboma were successfully screened out. A heterozygote mutation, CRYGD c.70C>A (p.P24T), was identified as cosegregating with congenital cataracts, while another heterozygous mutation, WFS1 c.1514G>C (p.C505S), which had not been reported previously, cosegregated with congenital iris coloboma. Bioinformatic analyses and three-dimensional structure prediction proved that the three-dimensional structures of WFS1 c.1514G>C (p.C505S), which had not been reported previously, cosegregated with congenital iris coloboma. Bioinformatic analyses and three-dimensional structure prediction proved that the three-dimensional structures of CRYGD c.70C>A (p.P24T), was identified as cosegregating with congenital cataracts, while another heterozygous mutation,

Conclusions

We report a novel mutation, WFS1 p.C505S, and a known mutation, CRYGD p.P24T, that cosegregate with iris coloboma and congenital cataract, respectively, in a Chinese family. This is the first time the association of WFS1 p.C505S with iris coloboma has been demonstrated, although CRYGD p.P24T has been widely reported as being associated with congenital cataract, especially in the Eastern Asian population. These findings may have future therapeutic benefit for the diagnosis of iris coloboma and congenital cataract. The results may also be relevant in further studies aiming to investigate the molecular pathogenesis of iris coloboma and congenital cataract.WFS1 c.1514G>C (p.C505S), which had not been reported previously, cosegregated with congenital iris coloboma. Bioinformatic analyses and three-dimensional structure prediction proved that the three-dimensional structures of CRYGD c.70C>A (p.P24T), was identified as cosegregating with congenital cataracts, while another heterozygous mutation, WFS1 c.1514G>C (p.C505S), which had not been reported previously, cosegregated with congenital iris coloboma. Bioinformatic analyses and three-dimensional structure prediction proved that the three-dimensional structures of CRYGD c.70C>A (p.P24T), was identified as cosegregating with congenital cataracts, while another heterozygous mutation,

GJA8 missense mutation disrupts hemichannels and induces cell apoptosis in human lens epithelial cells

Autosomal dominant congenital cataract (ADCC), the most common hereditary disease, is a major cause of eye disease in children. Due to its high genetic and clinical heterogeneity, the identification of ADCC-associated gene mutations is essential for the development of molecular therapies. In this study, we examined a four-generation Chinese pedigree with ADCC and identified putative mutations in ADCC candidate genes via next-generation sequencing (NGS) followed by Sanger sequencing. A novel missense mutation in GJA8 (c.T217C) in ADCC patients causes a serine-to-proline substitution at residue 73 of connexin 50 (Cx50); no mutation was found in unaffected family members and unrelated healthy individuals. Functional analysis revealed that this missense mutation disrupts protein function in human lens epithelial cells (HLEpiCs), which fails to form calcium-sensitive hemichannels. Furthermore, mutant Cx50 leads to decreased ROS scavenging by inhibiting G6PD expression and thus induces cell apoptosis via aberrant activation of the unfolded protein response (UPR). In conclusion, we report a novel GJA8 heterozygous mutation in a Chinese family with a vital role in ADCC, broadening the genetic spectrum of this disease.

Mutation screening of crystallin genes in Chinese families with congenital cataracts

Purpose

To identify mutations in crystallin genes in Chinese families with congenital cataracts.

Methods

Forty-two unrelated families with non-syndromic congenital cataracts were enrolled in this study. The coding exons and adjacent intronic regions of crystallin genes, including CRYAA, CRYAB, CRYBA1, CRYBA4, CRYBB1, CRYBB2, CRYBB3, CRYGC, CRYGD and CRYGS, were analyzed with Sanger sequencing. Novel variants were further evaluated in 112 ethnically matched controls. To confirm the novel mutations, short tandem repeat (STR) haplotypes were constructed to check the cosegregation with congenital cataract. The pathogenic potential of the novel mutations were assessed using bioinformatics tools, including Sorting Intolerant From Tolerant v5.1.1 (SIFT), Polymorphism Phenotyping v2 (PolyPhen-2), and Human Splicing Finder. The pathogenicity of all the mutations was evaluated according to the guidelines of the American College of Medical Genetics (ACMG) and InterVar software.

Results

Seven previously reported mutations in crystallin genes identified in ten unrelated families were associated with the congenital nuclear cataracts. Four novel mutations in crystallin genes, including c.35G>T (p.R12L) in CRYAA, c.463C>A (p.Q155K) in CRYBB2, IVS1 c.10-1G>A in CRYGC, and c.346delT (p.F116Sfsx29) in CRYGD, were identified in four unrelated families with congenital cataracts. These mutations cosegregated with all affected individuals in each family were not observed in the unaffected family members or in the 112 unrelated controls. All four novel mutations were categorized as disease "likely pathogenic" except IVS1 c.10-1G>A in CRYGC "pathogenic" using InterVar software in accordance with the ACMG standard. Mutations in crystallin genes were responsible for 33.33% of the Chinese families with congenital cataracts in this cohort.

Conclusions

In this study, we identified four novel mutations in crystallin genes in Chinese families with congenital cataracts. The results expand the mutational spectrum of crystallin genes, which may be helpful for the molecular diagnosis of congenital cataracts in the era of precision medicine.

Thermodynamic Stability of Human γD-Crystallin Mutants Using Alchemical Free-Energy Calculations

γD-Crystallin (HγDC) is a key structural protein in the human lens, whose aggregation has been associated with the development of cataracts. Single-point mutations and post-translational modifications destabilize HγDC interactions, forming partially folded intermediates, where hydrophobic residues are exposed and thus triggering its aggregation. In this work, we used alchemical free-energy calculations to predict changes in thermodynamic stability (ΔΔG) of 10 alanine-scanning variants and 12 HγDC mutations associated with the development of congenital cataract. Our results show that W42R is the most destabilizing mutation in HγDC. This has been corroborated through experimental determination of ΔΔG employing differential scanning calorimetry. Calculations of hydration free energies from the HγDC WT and the W42R mutant suggested that the mutant has a higher aggregation propensity. Our combined theoretical and experimental results contribute to understand HγDC destabilization and aggregation mechanisms in age-onset cataracts.

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.

Clinical and genetic characteristics of Chinese patients with familial or sporadic pediatric cataract

Background

Pediatric cataract is a clinically and genetically heterogeneous disease which is a significant cause of lifelong visual impairment and treatable blindness. Our study aims to investigate the genotype spectrum in a group of Chinese patients with pediatric cataract.

Methods

We enrolled 39 families with pediatric cataract from October 2015 to April 2016. DNA samples of the probands were analyzed by target next-generation sequencing. Variants were validated using Sanger sequencing in the probands and available family members.

Results

In our cohort of 39 cases with different types of pediatric cataract, 23 cases were found to harbor putative pathogenic variants in 15 genes: CRYAA, CRYBA1, CRYBA4, CRYBB1, CRYGC, CRYGD, MIP, GCNT2, IARS2, NHS, BCOR, BFSP2, FYCO1, MAF, and PAX6. The mutation detection rates in the familial and sporadic cases were 75 and 47.8%, respectively. Of the 23 causative variants, over half were novel.

Conclusions

This is a rare report of systematic mutation screening analysis of pediatric cataract in a comparably large cohort of Chinese patients. Our observations enrich the mutation spectrum of pediatric cataract. Next-generation sequencing provides significant diagnostic information for pediatric cataract cases, especially when considering sporadic and subtle syndromal cases.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0828-0) contains supplementary material, which is available to authorized users.

A novel truncation mutation in CRYBB1 associated with autosomal dominant congenital cataract with nystagmus

PURPOSE

To identify the potential candidate genes for a large Chinese family with autosomal dominant congenital cataract (ADCC) and nystagmus, and investigate the possible molecular mechanism underlying the role of the candidate genes in cataractogenesis.

METHODS

We combined the linkage analysis and direct sequencing for the candidate genes in the linkage regions to identify the causative mutation. The molecular and bio-functional properties of the proteins encoded by the candidate genes was further explored with biophysical and biochemical studies of the recombinant wild-type and mutant proteins.

RESULTS

We identified a c. C749T (p.Q227X) transversion in exon 6 of CRYBB1, a cataract-causative gene. This nonsense mutation changes a phylogenetically conserved glutamine to a stop codon and is predicted to truncate the C-terminus of the wild-type protein by 26 amino acids. Comparison of the biophysical and biochemical properties of the recombinant full-length and truncated βB1-crystallins revealed that the mutation led to the insolubility and the phase separation phenomenon of the truncated protein with a changed conformation. Meanwhile, the thermal stability of the truncated βB1-crystallin was significantly decreased, and the mutation diminished the chaperoning ability of αA-crystallin with the mutant under heating stress.

CONCLUSIONS

Our findings highlight the importance of the C-terminus in βB1-crystallin in maintaining the crystalline function and stability, and provide a novel insight into the molecular mechanism underlying the pathogenesis of human autosomal dominant congenital cataract.

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.