Autosomal Dominant Congenital Nuclear Cataract Research Articles

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

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

Characterization of a p.R76H mutation in Cx50 identified in a Chinese family with congenital nuclear cataract

A three-generation Chinese family with autosomal dominant congenital nuclear cataract was recruited. This study aimed to identify the disease-causing gene for nuclear cataract with functional dissections of the identified mutant. Detailed clinical data and family history were recorded. Candidate gene sequencing was performed to identify the disease-causing mutation. Recombinant connexin50 (Cx50) wild type and mutant constructs were synthesized. Triton X-100 solubility and subcellular localization of the recombinant Cx50 proteins were analyzed in HeLa cells. Apoptosis was assayed as the percentage of fragmented nuclei in transfected cells. All affected individuals in the family displayed clear phenotypes of dense nuclear cataracts. A c.227G>A variation was found in the coding region of Cx50, which arginine residue at position 76 was substituted by histidine (p.R76H). This mutation was co-segregated with the disease in the family, and was not observed in 110 unrelated Chinese controls. No statistically significant differences were found in the Triton X-100 solubility and apoptosis rate between wild type and mutant Cx50 in HeLa cells. However, Cx50 mutant was unable to form gap junctional plaques between adjacent cells as the wild type proteins did. This study identified a novel cataract phenotype caused by the p.R76H mutation in Cx50, providing evidence of further phenotypic heterogeneity associated with this mutation. Functional analysis showed that the mutation affected the formation of gap junction channels and led to opacity in the lens.

A novel MIP mutation in familial congenital nuclear cataracts

We screened 60 known genes which are involved in inherited cataract in a pregnant woman with a four-generation family history of autosomal dominant congenital nuclear cataract through next-generation sequencing (NGS) and identified a heterozygous mutation, c.508dupC (p.L170fs), in the major intrinsic protein (MIP) gene. This mutation results in a frame-shift in MIP and has not been previously reported. The correlation of the mutation with disease was validated by Sanger sequencing of DNA from the other affected or unaffected members of the family. Therefore, our data expand the mutation spectrum of MIP mutation, and suggest that NGS is an accurate, rapid, and cost-effective method in the genetic diagnosis of congenital nuclear cataract.

Cataract-causing mutation S228P promotes βB1-crystallin aggregation and degradation by separating two interacting loops in C-terminal domain.

β/γ-Crystallins are predominant structural proteins in the cytoplasm of lens fiber cells and share a similar fold composing of four Greek-key motifs divided into two domains. Numerous cataract-causing mutations have been identified in various β/γ-crystallins, but the mechanisms underlying cataract caused by most mutations remains uncharacterized. The S228P mutation in βB1-crystallin has been linked to autosomal dominant congenital nuclear cataract. Here we found that the S228P mutant was prone to aggregate and degrade in both of the human and E. coli cells. The intracellular S228P aggregates could be redissolved by lanosterol. The S228P mutation modified the refolding pathway of βB1-crystallin by affecting the formation of the dimeric intermediate but not the monomeric intermediate. Compared with native βB1-crystallin, the refolded S228P protein had less packed structures, unquenched Trp fluorophores and increased hydrophobic exposure. The refolded S228P protein was prone to aggregate at the physiological temperature and decreased the protective effect of βB1-crystallin on βA3-crystallin. Molecular dynamic simulation studies indicated that the mutation decreased the subunit binding energy and modified the distribution of surface electrostatic potentials. More importantly, the mutation separated two interacting loops in the C-terminal domain, which shielded the hydrophobic core from solvent in native βB1-crystallin. These two interacting loops are highly conserved in both of the N- and C-terminal domains of all β/γ-crystallins. We propose that these two interacting loops play an important role in the folding and structural stability of β/γ-crystallin domains by protecting the hydrophobic core from solvent access.Electronic supplementary materialThe online version of this article (doi:10.1007/s13238-016-0284-3) contains supplementary material, which is available to authorized users.

A recurrent mutation of CRYGD gene in a northern Chinese family with autosomal dominant congenital nuclear cataract

Background Congenital cataract is a major cause for blindness of childhood. Genetic gene mutation accounts for almost 1/3 of congenital cataract patients. The most common inheritance type is autosomal dominant congenital cataract (ADCC). Over 100 mutations in 26 genes have been found to be associated with ADCC. Objective This study was to identify the disease-causing gene mutation in a family with ADCC. Methods This study was approved by Ethic Committee of Beijing Tongren Hospital and followed Declaration of Helsinki. A northern Chinese family with autosomal dominant congenital nuclear cataract was entrolled in Beijing Tongren Hospital in January 2011. Ocular examinations were performed and periphery blood specimens were collected from each family member under the informed consent. Genomic DNA was extracted. Twenty-one microsatellite markers around 17 ADCC genes were selected for linkage analysis, and two-point LOD score was calculated. CRYGC gene and CRYGD gene were amplified and screened for mutations using direct sequencing. ProtScale software was used to analyze the changes of hydrophobicity of the mutated protein. Co-segregation of the observed change with the disease phenotype was further detected by restriction fragment length polymorphism (RFLP). Results This family included 20 members of 4 generations, and 9 patients were examined in serial 4 passages, which conformed to autosomal dominant inheritance pattern. Clinical examination revealed binocular congenital nuclear cataract in the 9 patients. Maximum two-point LOD score was 4. 68 at marker D2S325 (θ=0). A known T→C change at position 127 of cDNA sequence was found by mutations screening of CRYGD gene. ProtScale programs showed an obvious increase of the local hydrophobicity in the mutant protein. RFLP results indicated that this missense mutation co-segregated with affected members of the family, but was absent in unaffected members and 100 unrelated controls. Conclusions c. T127C mutation of CRYGD gene appears to be the molecular pathogenesis of this ADCC family. Aberrant structure of mutant CRYGD protein caused by hydrophobicity change may lead to opacification of lens. Key words: Cataract/congenital; Cataract/genetics; DNA mutational analysis; Lens nucleus, crystalline/pathology; Pedigree; gamma-Crystallin/genetics; Mutations; Chinese

Congenital Cataract-Causing Mutation G129C in γC-Crystallin Promotes the Accumulation of Two Distinct Unfolding Intermediates That Form Highly Toxic Aggregates

Cataract is a lens opacification disease prevalent worldwide. Cataract-causing mutations in crystallins generally lead to the formation of light-scattering particles in the lens. However, it remains unclear for the detailed structural and pathological mechanisms of most mutations. In this study, we showed that the G129C mutation in γC-crystallin, which is associated with autosomal dominant congenital nuclear cataract, perturbed the unfolding process by promoting the accumulation of two distinct aggregation-prone intermediates under mild denaturing conditions. The abnormally accumulated intermediates escaped from the chaperone-like function of αA-crystallin during refolding. Molecular dynamics simulations indicated that the mutation altered domain pairing geometry and allowed the penetration of extra solvent molecules into the domain binding interface, thereby weakening domain binding energy. Under mild denaturation conditions, the increased domain movements may facilitate the formation of non-native oligomers via domain swapping, which further assembled into amyloid-like fibrils. The intermediate that appeared at 1.6M guanidine hydrochloride was more compact and less aggregatory than the one populated at 0.9M guanidine hydrochloride, which was caused by the increased solvation of acidic residues in the ion-pairing network via the competitive binding of guanidinium ions. More importantly, both the amyloid-like fibrils preformed in vitro and intracellular aggresomes formed by exogenously overexpressed mutant proteins significantly inhibited cell proliferation and induced cell death. The combined data from spectroscopic, structural and cellular studies strongly suggest that both the formation of light-scattering aggregates and the toxic effects of the aggregates may contribute to the onset and development of cataract.

A novel Cx50 (GJA8) p.H277Y mutation associated with autosomal dominant congenital cataract identified with targeted next-generation sequencing.

To unravel the molecular genetic background responsible for autosomal dominant congenital pulverulent nuclear cataracts in a four-generation Chinese family. Family history data were collected, ophthalmological examinations were performed, and genomic DNA was extracted from peripheral blood of the family members. The candidate genes were captured and sequenced by targeted next-generation sequencing, and the results were confirmed by Sanger sequencing. The structure modelling of the protein was displayed based on Swiss-Model Server, and its possible changes in the secondary structure were predicted using Antheprot 2000 software. The chemical dissimilarity and possible functional impact of an amino acid substitution were performed with Grantham score, PolyPhen-2, and SIFT predictions. Protein distributions were assessed by confocal microscopy. A novel heterozygous c.829C > T transition that led to the substitution of a highly conserved histidine by tyrosine at codon 277 (p.H277Y) in the coding region of connexin50 (Cx50, GJA8) was identified. Bioinformatics analysis showed that the mutation likely altered the secondary structure of the protein by replacing the helix of the COOH-terminal portion with a turn. The mutation was predicted to be moderately conservative by Grantham score and to be deleterious by both PolyPhen-2 and SIFT with consistent results. In addition, when expressed in COS1 cells, the mutation led to protein accumulation and caused changes in Cx 50 protein localization pattern. This is a novel missense mutation [c.829C > T, (p.H277Y)] identified in exon 2 of Cx50. Our findings expand the spectrum of Cx50 mutations that are associated with autosomal dominant congenital pulverulent nuclear cataract.

Mutation analysis of CRYBB1 gene and prenatal diagnosis for a Chinese kindred featuring autosomal dominant congenital nuclear cataract

To perform mutation screening and prenatal diagnosis for a five-generation Chinese pedigree with autosomal dominant congenital nuclear cataract from Henan province by DNA sequencing. Blood samples were taken from the family members. Four candidate genes (CRYBA1/A3, CRYBB1, CRYBB2 and CRYGD) were screened for mutations using direct sequencing. Prenatal genetic diagnosis was provided for a fetus at early gestation through chorionic villus sampling. A missense mutation, c.387C to A, was detected in exon 4 of the CRYBB1 gene in all of the patients. The mutation has resulted in a p.S129R transversion. The same mutation was not found in the fetus of the proband, who was confirmed to be healthy by one-year follow-up. A missense mutation p.S129R of the CRYBB1 gene probably underlies the autosomal dominant congenital nuclear cataract in this pedigree. Detection of the mutation also facilitated prenatal genetic testing for the family.

Wolfram gene (WFS1) mutation causes autosomal dominant congenital nuclear cataract in humans

Congenital cataracts are an important cause of bilateral visual impairment in infants. Through genome-wide linkage analysis in a four-generation family of Irish descent, the disease-associated gene causing autosomal-dominant congenital nuclear cataract was mapped to chromosome 4p16.1. The maximum logarithm of odds (LOD) score was 2.62 at a recombination fraction θ=0, obtained for marker D4S432 physically close to the Wolfram gene (WFS1). By sequencing the coding regions and intron-exon boundaries of WFS1, we identified a DNA substitution (c.1385A-to-G) in exon 8, causing a missense mutation at codon 462 (E462G) of the Wolframin protein. This is the first report of a mutation in this gene causing an isolated nuclear congenital cataract. These findings suggest that the membrane trafficking protein Wolframin may be important for supporting the developing lens.

A novel mutation impairing the tertiary structure and stability of γC-crystallin (CRYGC) leads to cataract formation in humans and zebrafish lens

Congenital cataract is one of the leading causes of human blindness. In this study, we identified a novel, heterozygous c.385G<T mutation in CRYGC that resulted in the substitution of a highly conserved glycine by cysteine at codon 129 (p.Gly129Cys) in a three-generation Chinese family with autosomal dominant congenital nuclear cataract by sequencing candidate genes. Using zebrafish as a model, we demonstrated that γC-crystallin p.Gly129Cys mutant caused the vacuole and the incomplete denucleation of lens, recapitulating the cataract phenotype in human beings. Molecular modeling and spectroscopic studies indicated that the mutation impaired the tertiary structure of the protein by modifying the H-bonding network in the C-terminal domain. The mutation led to a dramatic decrease in the thermal stability of γC-crystallin, and a significant increase in the propensity of aggregation when subject to storage at high concentrations, heat, and UV- irradiation stresses. Taken together, these results indicate that a novel γC-crystallin p.Gly129Cys mutation impaired the tertiary structure of the protein and caused cataract formation, which provides a new insight into how the mutation may affect the γC-crystallin structure, stability, and function. Our study also highlighted zebrafish as a valuable model tool for studying congenital inherited cataract.

A novel CRYGD mutation (p.Trp43Arg) causing autosomal dominant congenital cataract in a Chinese family

To identify the genetic defect associated with autosomal dominant congenital nuclear cataract in a Chinese family, molecular genetic investigation via haplotype analysis and direct sequencing were performed Sequencing of the CRYGD gene revealed a c.127T>C transition, which resulted in a substitution of a highly conserved tryptophan with arginine at codon 43 (p.Trp43Arg). This mutation co-segregated with all affected individuals and was not observed in either unaffected family members or in 200 normal unrelated individuals. Biophysical studies indicated that the p.Trp43Arg mutation resulted in significant tertiary structural changes. The mutant protein was much less stable than the wild-type protein, and was more prone to aggregate when subjected to environmental stresses such as heat and UV irradiation. © 2010 Wiley-Liss, Inc.

A Novel Mutation in the Connexin 50 Gene (GJA8) Associated with Autosomal Dominant Congenital Nuclear Cataract in a Chinese Family

Purpose: To identify the genetic defect in a four-generation Chinese family with autosomal dominant congenital nuclear cataract.Methods: Family history data were recorded. Clinical and ophthalmologic examinations were performed on family members. All the members were genotyped with microsatellite markers at loci associated with cataracts. Linkage analysis was performed after genotyping. Candidate genes were screened for mutation using direct sequencing.Results: Linkage analysis was obtained at markers D1S1653 (LOD score [Z] = 1.50, recombination fraction [θ] = 0.0) and D1S498 (LOD score Z = 0.90, recombination fraction [θ] = 0.0), which encompasses the connexin 50 gene (GJA8). Sequencing the coding regions of GJA8 revealed a novel, heterozygous c.773C>T transition that resulted in the substitution of a highly conserved serine by phenylalanine at codon 258 (S258F). Bioinformatics analysis showed that the mutation altered the hydrophobicity and secondary structure of the protein. This mutation co-segregated with the disease phenotype in all affected individuals and was not found in the unaffected family members or in 100 normal unrelated individuals.Conclusions: This study has identified a novel missense mutation located in the carboxyl terminus of GJA8 (S258F) associated with autosomal dominant nuclear cataract.

Autosomal Dominant Congenital Nuclear Cataracts Caused by a CRYAA Gene Mutation

Purpose: We sought to identify the genetic defect in a four-generation Chinese family with autosomal dominant congenital nuclear cataracts, examine the clinical features in detail and demonstrate the functional analysis of a candidate gene in the family.Methods: Family history data were recorded. Clinical and ophthalmological examinations were performed on affected and unaffected family members. All the members were genotyped with microsatellite markers at loci considered to be associated with cataracts. Two-point LOD scores were calculated using the LINKAGE program package after genotyping. A mutation was detected by dilff521229rect sequencing and verified by denaturing high-performance liquid chromatography (DHPLC). Wild-type and mutant proteins were analyzed with online softwares.Results: All affected members of this family had nuclear cataracts. Genetic analysis revealed a heterozygous previously described Arg116Cys mutation in the CRYAA gene in all of the affected members of the family but not in unaffected or 100 normal, unrelated individuals. Data generated with online software revealed that the different amino acid side chain, impact the aa116 interaction with other amino acids, thereby affecting the proteins secondary structure.Conclusions: This study identified a mutation in the CRYAA gene causing autosomal dominant nuclear cataracts and some patients show nystagmus or small blepharophimosis clinical features. These results provide evidence that CRYAA is a pathogenic gene for congenital cataracts, congenital cataracts are a clinically and genetically heterogeneous lens condition; at the same time, demonstrates a possible mechanism of action for the mutant gene.

Cataracts Are Caused by Alterations of a Critical N-Terminal Positive Charge in Connexin50

To elucidate the basis of the autosomal dominant congenital nuclear cataracts caused by the connexin50 mutant, CX50R23T, by determining its cellular distribution and functional behavior and the consequences of substituting other amino acids for arginine-23. Connexin50 (CX50) mutants were generated by PCR and transfected into HeLa or N2a cells. Expressed CX50 protein was detected by immunoblot analysis and localized by immunofluorescence. Intercellular communication was assessed by microinjection of neurobiotin or by double whole-cell patch-clamp recording. HeLa cells stably transfected with CX50R23T or wild-type CX50 produced immunoreactive CX50 bands of identical electrophoretic mobility. Whereas HeLa cells stably expressing CX50 contained abundant gap junction plaques, CX50R23T localized predominantly in the cytoplasm. HeLa cells expressing wild-type CX50 showed large gap junctional conductances and extensive transfer of neurobiotin, but those expressing CX50R23T did not show significant intercellular communication by either assay. Moreover, CX50R23T inhibited the function of coexpressed wild-type CX50. Three CX50R23 substitution mutants (CX50R23K, CX50R23L, and CX50R23W) formed gap junction plaques, whereas two mutant substitutions with negatively charged residues (CX50R23D, CX50R23E) did not form detectable plaques. Only the mutant with a positive charge substitution (CX50R23K) allowed neurobiotin transfer at levels similar to those of wild-type CX50; none of the other mutants induced transfer. These results suggest that replacement of amino acid 23 in CX50 by any residue that is not positively charged would lead to cataract formation.

Gene mapping of a pedigree with autosomal dominant congenital cataract

To map the gene for autosomal dominant congenital cataract (ADCC) in a Chinese family. Blood samples were collected from 14 members of this family. Linkage analysis was carried out using short tandem repeat polymorphism (STRP) in close proximity to genes and loci previously reported involving in human cataract. Two-point linkage analysis lod scores were calculated. The mutation gene locus in this pedigree was mapped to 17q, an 11.78-cM interval between markers D17S1288 and D17S933. Significant positive maximum LOD scores (Z(max)) at recombination fraction (theta) 0, were obtained for markers D17S805 (Z(max) = 2.03), D17S1294 (Z(max) = 2.49), and D17S1293 (Z(max) = 2.22). The mutation gene in this ADCC pedigree is located at chromosome 17q. This is the first report of an autosomal dominant congenital nuclear cataracts located at this locus. This result will be helpful for further studying of the pathogenesis of cataract.

A novel GJA8 mutation in an Iranian family with progressive autosomal dominant congenital nuclear cataract

THE AUTHORS DESCRIBE THE MOLECULAR CHARACTERization of an Iranian family with an autosomal dominant progressive congenital nuclear cataract. Affected members were found to have a novel heterozygous missense mutation R23T in the GJA8 gene encoding connexin 50 (Cx50). This sequence change segregated with the disease phenotype in the family and was not found in 152 control individuals, including 52 ethnically matched controls. This non-conservative mutation replaces an evolutionary conserved basic polar charged amino acid by an uncharged polar amino acid at position 23 in the amino-terminus of Cx50. The R32T mutation may result in failure to forma normal gap junctions (loss of function mutation) or alter the function of endogenous wild-type connexins (dominant negative mutation). In this family, there was a novel progressive phenotype mimicking an early onset age related nuclear cataract. Three heterozygous missense Cx50 mutations (P88S, E48K, and 1247M) have been described in three geographically distinct families with zonular pulverulent or zonular nuclear congenital cataracts. The mutational screening of a population of patients with congenital cataract (n = 37) and another with age related cataract (n = 44) failed to show any contribution of the four known Cx50 mutations.—Hans E. Grossniklaus

CRYBA3/A1 gene mutation associated with suture-sparing autosomal dominant congenital nuclear cataract: a novel phenotype.

To identify the genetic defect leading to the congenital nuclear cataract affecting a large five-generation Swiss family. Family history and clinical data were recorded. The phenotype was documented by both slit lamp and Scheimpflug photography. One cortical lens was evaluated by electron microscopy after cataract extraction. Lenticular phenotyping and genotyping were performed independently with short tandem repeat polymorphism. Linkage analysis was performed, and candidate genes were PCR amplified and screened for mutations on both strands using direct sequencing. Affected individuals had a congenital nuclear lactescent cataract in both eyes. Linkage was observed on chromosome 17 for DNA marker D17S1857 (lod score: 3.44 at theta = 0). Direct sequencing of CRYBA3/A1, which maps to the vicinity, revealed an in-frame 3-bp deletion in exon 4 (279delGAG). This mutation involved a deletion of glycine-91, cosegregated in all affected individuals, and was not observed in unaffected individuals or in 250 normal control subjects from the same ethnic background. Electron microscopy showed that cortical lens fiber morphology was normal. The DeltaG91 mutation in CRYBA3/A1 is associated with an autosomal dominant congenital nuclear lactescent cataract. A splice mutation (IVS3+1G/A) in this gene has been reported in a zonular cataract with sutural opacities. These results indicate phenotypic heterogeneity related to mutations in this gene.