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A Novel Mutation in CRYGC Mutation Associated with Autosomal Dominant Congenital Cataracts and Microcornea

  • Zhenbao Zhou
    Affiliations
    Department of Ophthalmology, The First Affiliated Hospital of Xiamen University, Xiamen, China

    Department of Ophthalmology, HongQi Hospital, Mudanjiang Medical University, Mudanjiang, China

    Department of Neurology, HongQi Hospital, Mudanjiang Medical University, Mudanjiang, China
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  • Liying Zhao
    Correspondence
    Correspondence: Liying Zhao, MD, Department of Ophthalmology, HongQi Hospital, MuDanJiang Medical University, No. 3, Tongxiang St., Aimin District, Mudanjiang City, Heilongjiang 157000, China.
    Affiliations
    Department of Ophthalmology, The First Affiliated Hospital of Xiamen University, Xiamen, China

    Department of Ophthalmology, HongQi Hospital, Mudanjiang Medical University, Mudanjiang, China

    Department of Neurology, HongQi Hospital, Mudanjiang Medical University, Mudanjiang, China
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  • Yanqin Guo
    Affiliations
    Department of Ophthalmology, The First Affiliated Hospital of Xiamen University, Xiamen, China

    Department of Ophthalmology, HongQi Hospital, Mudanjiang Medical University, Mudanjiang, China

    Department of Neurology, HongQi Hospital, Mudanjiang Medical University, Mudanjiang, China
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  • Jingyi Zhuang
    Affiliations
    Department of Ophthalmology, The First Affiliated Hospital of Xiamen University, Xiamen, China

    Department of Biomedical Engineering, Mudanjiang Medical University, Mudanjiang, China
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  • Nan Zhuo
    Affiliations
    Department of Ophthalmology, The First Affiliated Hospital of Xiamen University, Xiamen, China

    Department of Biomedical Engineering, Mudanjiang Medical University, Mudanjiang, China
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  • Han Chen
    Affiliations
    Department of Ophthalmology, The First Affiliated Hospital of Xiamen University, Xiamen, China

    Department of Biomedical Engineering, Mudanjiang Medical University, Mudanjiang, China
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  • Jieting Liu
    Affiliations
    Department of Ophthalmology, The First Affiliated Hospital of Xiamen University, Xiamen, China

    Department of Biomedical Engineering, Mudanjiang Medical University, Mudanjiang, China
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  • Libo Wang
    Affiliations
    Department of Ophthalmology, The First Affiliated Hospital of Xiamen University, Xiamen, China
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Open AccessPublished:December 17, 2021DOI:https://doi.org/10.1016/j.xops.2021.100093

      Purpose

      Crystallin protein mutations are associated with congenital cataract (CC), and several disease-causing mutations in the CRYGC gene have been identified. We present the location of a new mutation in CRYGC in members of a Chinese family who presented with CCs with or without microcornea.

      Design

      Observational study.

      Participants

      A Chinese family diagnosed with autosomal dominant (AD) CCs with or without microphthalmia.

      Methods

      Because this was an observational study, it was not registered as a clinical trial. The proband and her 2 children were diagnosed with AD CCs and microcornea and were recruited for the study. Participants underwent complete ophthalmological examinations, and blood samples were used for genomic extraction.

      Main Outcome Measures

      We detected 1 disease-associated variant using Exomiser analysis by matching the proband’s phenotype and the inheritance pattern. The variant was determined to be pathogenic according to American College of Medical Genetics and Genomics (ACMG) guidelines.

      Results

      We detected 1 disease-associated variant using Exomiser analysis by matching the proband’s phenotype and the inheritance pattern. The variant was determined to be pathogenic according to the American College of Medical Genetics and Genomics guidelines. Next-generation sequencing was verified using Sanger sequencing, and we confirmed that the proband and her children carried the same mutation. We identified the heterozygous variant c.389_390insGCTG (p.C130fs), which includes a frameshift mutation. The residues in p.C130fs are all highly conserved across species. This disease-causing frameshift mutation in the CRYGC gene is not currently present in the ClinVar database.

      Conclusions

      Our findings expand the repertoire of known mutations in the CRYGC gene that cause CCs and provide new insights into the etiology and molecular diagnosis of CCs; however, the molecular mechanism of this mutation warrants further investigation.

      Keywords

      Abbreviations and Acronyms:

      ACMG (American College of Medical Genetics and Genomics), AD (autosomal dominant), CC (congenital cataract)
      Congenital cataracts (CCs) are characterized by opacification of the ocular lens, which presents at birth or shortly thereafter. Congenital cataracts are the leading clinical cause of impaired vision in children, especially infants, and can result in permanent blindness.
      • Song Z.
      • Si N.
      • Xiao W.
      A novel mutation in the CRYAA gene associated with congenital cataract and microphthalmia in a Chinese family.
      However, CCs can be successfully treated surgically.
      • Hejtmancik J.F.
      The genetics of cataract: our vision becomes clearer.
      The prevalence of this condition is thought to be 1 to 6 per 10 000 live births in developed countries; however, it is reported to be 5 to 15 per 10 000 live births in developing countries.
      • Song Z.
      • Si N.
      • Xiao W.
      A novel mutation in the CRYAA gene associated with congenital cataract and microphthalmia in a Chinese family.
      ,
      • Yan N.
      • Xiao L.
      • Hou C.
      • et al.
      X-linked inheritances recessive of congenital nystagmus and autosomal dominant inheritances of congenital cataracts coexist in a Chinese family: a case report and literature review.
      It has been suggested that 8.3% to 25% of CC cases are hereditary, most of which are autosomal dominant (AD), autosomal recessive, or X-linked.
      • Shiels A.
      • Hejtmancik J.F.
      Genetics of human cataract.
      ,
      • Fan Q.
      • Li D.
      • Cai L.
      • et al.
      A novel mutation in the OAR domain of PITX3 associated with congenital posterior subcapsular cataract.
      Genetic mutations in at least 42 loci have been found to be associated with inherited forms of either primary or isolated cataracts with other nominal ocular signs; thus, it is believed that these mutations are related to CC.
      • Shiels A.
      • Hejtmancik J.F.
      Molecular genetics of cataract.
      The crystallin proteins alpha, beta, and gamma are the major protein components of the vertebrate eye lens, accounting for more than 90% of the total lens proteins.
      • den Dunnen J.T.
      • Moormann R.J.M.
      • Cremers F.P.M.
      • Schoenmakers J.G.
      Two human gamma-crystallin genes are linked and riddled with Alu-repeats.
      • Bloemendal H.
      • de Jong W.W.
      Lens proteins and their genes.
      • Bloemendal H.
      • de Jong W.
      • Jaenicke R.
      • et al.
      Ageing and vision: structure, stability and function of lens crystallins.
      Several crystallin protein mutations, including αA-crystallin (CRYAA), βA1-crystallin (CRYBA1), βB1-crystallin (CRYBB1), βB2-crystallin (CRYBB2), γC-crystallin (CRYGC), γD-crystallin (CRYGD), connexin 46 (CX46), connexin 50 (CX50), and major intrinsic protein (MIP), are associated with CC.
      • Santana A.
      • Waiswo M.
      The genetic and molecular basis of congenital cataract.
      ,
      • Shiloh Y.
      • Donlon T.
      • Bruns G.
      • et al.
      Assignment of the human gamma-crystallin gene cluster (CRYG) to the long arm of chromosome 2, region q33-36.
      This study investigated a disease-causing heterozygous frameshift mutation, c.389_390insGCTG (p.C130fs), in the CRYGC gene. The mutation was identified in members of a Chinese family who presented with CC and microcornea. None of the previously reported mutations associated with CC were detected in any member of the family who had the condition. Our study contributes to the known mutations in CRYGC associated with CC.

      Methods

      Patient Data

      We enrolled members of a family who presented to our hospital with AD congenital nuclear cataracts, microcornea, and nystagmus. The family originated from Quanzhou (Fujian, China) and included 6 people: 3 affected and 3 unaffected. No other comorbidities were present.
      Research was conducted in accordance with the Declaration of Helsinki. The study and all its protocols were approved by the Ethics Committee of the HongQi Hospital, MuDanJiang Medical University (approval number:201703). Informed consent was obtained from all participants and their parents/guardians.
      All participants underwent the following examinations to confirm the diagnosis and to collect clinical data: ophthalmological examinations, including visual acuity, Hirschberg test, cornea diameter measurement, oculomotor examination, slit-lamp examination, retinoscopy with dilated pupil, ultrasound A/B-mode imaging, and fundoscopy. The phenotype was determined using slit-lamp photography. Unfortunately, because of the patients’ nystagmus, we failed to capture a clear photograph of the anterior segment (Table 1).
      Table 1Clinical Phenotypes and Findings of Study Participants
      ParticipantAge (yrs)/GenderEyeVisual AcuityBest-Corrected Visual AcuityLensNystagmusAxial Length (mm)Cornea Diameter (mm)B-mode US FindingsSurgery and Trauma History
      1 Proband30/FOU0.020.02CC (Nuclear)Yes21.79/20.9410.8/10.9Vitreous bodies opaqueNo
      2 Proband’s son5/MOU0.20.3IOL (PS:CC Nuclear)Yes22.53/21.7410.3/10.2NAPhacoemulsification + IOL
      3 Proband’s daughter2/FOUNANACC (Nuclear)YesNA8/8NANo
      4 Proband’s husband33/MNo1.0/1.01.0/1.0TransparentNo23.53/24.0112.7/12.8Vitreous bodies opaqueNo
      5. Proband’s grandfather67/MOU0.5/0.60.8/0.8SCNo23.97/23.9912.6/12.7Vitreous bodies opaqueNo
      6. Proband’s grandmother66/FOU0.7/0.61.0/1.0SCNo23.76/23.8812.5/12.8Vitreous bodies opaqueNo
      CC = congenital cataract; F = female; IOL = intraocular lens; M = male; NA = not available; OU = binoculus; PS = presurgery; SC = senile cataract; US = ultrasound. Cornea diameter normal value: 11–12 mm.

      Whole-Exome Sequencing Analysis

      A sample of venous blood was extracted from each patient (blood collection date: May 10, 2017). Whole-exome sequencing was then performed by Genokon Medical Technology Co., Ltd. The QIAamp DNA Blood Mini Kit (Qiagen) was used for genomic DNA extraction. Agarose gel electrophoresis and NanoDrop (Thermo Fisher) spectrophotometric analysis, corroborated with Qubit 3.0 (Thermo Fisher), were used to assess the concentration and quality of the extracted DNA. Genomic DNA (1.5 μg) was fragmented to a mean size of 300 base pairs, with which sequencing libraries were subsequently prepared. Afterward, the DNA fragments were ligated with sequencing adaptors (8 base pair barcoded) before hybridization with xGen Exome Research Panel v1.0 focused exome probes (IDT). Experiments were validated by assessing the capture efficiency, coverage depth, sequencing sensitivity, and reproducibility. Gauging of DNA quality and quantity was achieved by both quantitative polymerase chain reaction and the AATI Fragment Analyzer. The HiSeq X-10 platform (Illumina) was used to pool and parallel-sequence purified sequencing libraries. A sequencing yield of 10.0 Gb was produced. We achieved a sample coverage of 91%, to a 150× depth or greater.

      Reads Mapping and Variants Analysis

      Sequences were located on the reference human genome with the aid of NextGene software (SoftGenetics LLC). Databases, such as the 1000 Genomes Project (http://browser.1000genomes.org), Exome Aggregation Consortium (https://gnomad.broadinstitute.org), and dbSNP (http://www.ncbi.nlm.nih.gov/snp) were used to compare the variants. Those with a minor allele frequency greater than 0.01 in the control databases were excluded.
      • Reis L.M.
      • Tyler R.C.
      • Muheisen S.
      • et al.
      Whole exome sequencing in dominant cataract identifies a new causative factor, CRYBA2, and a variety of novel alleles in known genes.
      The Sorting Intolerant from Tolerant, Polyphen-2, and Mutation Taster platforms were used for pathogenicity prediction analysis. The locations of all variants were corroborated to be in the conserved region of the gene, and the variants’ effects on the folding and function of proteins were evaluated. The guidelines of the American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology for variant interpretation
      • Richards S.
      • Aziz N.
      • Bale S.
      • et al.
      ACMG Laboratory Quality Assurance Committee. Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology.
      were used to classify variants as pathogenic (PVS1+PM2+PP4).

      Sanger Sequencing for Verification

      Sanger sequencing was used to verify whether the variant identified through exome sequencing matched the samples from the patient, as well as to confirm the presence of the variant in the proband’s 2 children. We amplified the target sites and the flanking sequences of the genomic DNA template from each family member individually with specific primers designed using Online Design Software Primer 3.0 (http://primer3.ut.ee/).

      Results

      Clinical Findings

      We identified a Chinese family, spanning 3 generations, with AD congenital nuclear cataracts (Fig 1). The DNA sequences of the CRYGC gene of the affected and unaffected individuals from the study population are shown in Figure 2.
      Figure thumbnail gr1
      Figure 1Pedigree of 3 generations of the study population. The study included members of a family with autosomal dominant (AD) congenital cataracts (CCs). The proband is marked with the black arrow. Squares and circles indicate male and female participants, respectively. Black and white symbols indicate affected and unaffected individuals, respectively. A, Nuclear cataract in III:2. B, Microcornea in III:2.
      Figure thumbnail gr2
      Figure 2DNA sequences of the GRYGC gene of affected and unaffected individuals in the study population. The DNA sequence chromatograms of (A) the proband, (B) individual III:1, and (C) individual III:2 (affected individuals) are shown. A heterozygous 4 base pair insertion in exon 3 results in a frameshift mutation (p.C130fs). The DNA sequence chromatograms of unaffected individuals (D) I:1, (E) I:2, (F) II:1, and (G) II:3 are also shown.
      The results of whole-exome sequencing were as follows:
      • 1.
        One disease-associated variant was identified using Exomiser analysis by matching the proband’s phenotype and the inheritance pattern. The variant was determined to be pathogenic according to ACMG guidelines (Table 2).
        • Richards S.
        • Aziz N.
        • Bale S.
        • et al.
        ACMG Laboratory Quality Assurance Committee. Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology.
        Table 2Explanations
        GeneChromosome

        Position
        Nucleic Acid

        Altering
        Amino

        Acid

        Altering
        Mutation

        Type
        Protein

        Prediction
        Genotype
        ProbandCRYGC2q33. 3NM_020989:exo n3:c.389_390i

        nsGCTG
        p.C130fsFrameshift mutationMutationTaster pred (D)Heterozygous
        Proband’s sonCRYGC2q33. 3NM_020989:exo n3:c.389_390i

        nsGCTG
        p.C130fsFrameshift mutationMutationTaster pred (D)Heterozygous
        Proband’s daughterCRYGC2q33. 3NM_020989:exo n3:c.389_390i

        nsGCTG
        p.C130fsFrameshift mutationMutationTaster pred (D)Heterozygous
        D = damaged.
      • 2.
        There was no information associated with this variant in the ClinVar database.
      • 3.
        There were no matched variants in 59 genes according to the ACMG SF (secondary findings) v2.0 mutation analysis.
        • The Online Mendelian Inheritance in Man database (available at https://www.omim.org/entry/123680) described known mutations in the CRYGC gene that have been shown to cause cataracts (Table 3).
          Table 3Gene Description of Mutations That Have Been Shown to Cause Cataracts
          Cytogenetic LocusPhysical LocusGeneExon/IntronDNA ChangeProtein ChangeInheritanceOriginCataract PhenotypeOther PhenotypeReferenceComment
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.13A>Cp.T5PADUKCentral zonular pulverulent (Coppock-like)Heon et al 199925
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.119-123dup5bpp.C42AfsX63ADUSAVariable zonular pulverulentRen et al 200026
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.502C>Tp.R168WADIndiaLamellarSanthiya et al 200227
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.502C>Tp.R168WADMexicoNuclearPeripupillary iris atrophy, nystagmus, myopiaGonzalez-Huerta et al 200728
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.502C>Tp.R168WADIndiaLamellarDevi et al 200833
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.327C>Ap.C109XADChinaNuclearNystagmusYao et al 200829
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.470G>Ap.W157XADChinaNuclearMicrocorneaZhang et al 200932
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.143G>Ap.R48HADIndiaNuclear pulverulentKumar et al 201134
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.471G>Ap.W157XADChinaNuclearMicrocorneaGuo et al 201231
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.385G>Tp.G129CADChinaNuclearLi et al 201230
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.124delTp.C42AfsX60ADKoreaCongenitalKondo et al 201335
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.157_161dupGCGGCp.Q55VfsX50ADUSAcongenitalReis et al 201312
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.417C>Gp.Y139XADUSAcongenitalMicrophthalmia/microcornea, glaucoma, corneal opacityReis et al 2013
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.134T>Cp.L45PUKGillespie et al 201436
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.402C>Gp.Y134XUKGillespie et al 2014
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.497C>Tp.S166FADAustraliaNuclearMicrophthalmiaProkudin et al 201437
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.497C>Tp.S166FADAustraliaMa et al 201538
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.280G>Ap.E94KSporadicChinaTotal (Unilateral)Li et al 201639
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.337C>Tp.Q113XSporadicChinaNuclearLi et al 2016
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.403G>Tp.E135XADMicrocorneaPatel et al 201640
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.130delAp.M44CfsX59ADChinaPseudophakiaMicrocorneaSun et al 201717
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.143G>Ap.R48HADChinaUnilateralOptic disc colobomaSun et al 2017
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.432C>Gp.Y144XADChinaAphakiaMicrocornea, glaucomaSun et al 2017
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.136T>Gp.Y46DADChinaNuclearZhong et al 201741
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.193delGp.D65TfsX38ADChinaNuclearZhong et al 2017
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.417C>Gp.Y139XADChinaNuclearMicrocorneaZhong et al 2017
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.423delGp.R142GfsX5ADChinaNuclearZhong et al 2017
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.423dupGp.R142AfsX22ADChinaNuclearZhong et al 2017
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.432C>Gp.Y144XADChinaNuclearZhong et al 2017
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.497C>Tp.S166FADChinaNuclearMicrocorneaZhong et al 2017
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.505A>Tp.R169XADChinaNuclearZhong et al 2017
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.17T>Cp.F6SADMexicoNuclearAstiazaran et al 201842
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.17T>Cp.F6SADMexicoLamellarAstiazaran et al 2018
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.233C>Tp.S78FADChinaNuclearLi et al 201843
          2q33-q352:208,992,861-208,994,554CRYGCIVS1c.10-1G>AADChinaZhuang et al 201944
          2q33-q352:208,992,861-208,994,554CRYGCEx2c.192delCp.D65TfsX38ADChinaTotalFan et al 202045
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.497C>Tp.S166FADChinaTotalFan et al 2020
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.382G>Tp.E128XADIndiaNuclearKandaswamy et al 202046
          2q33-q352:208,992,861-208,994,554CRYGCEx3c.432C>Gp.Y144XADTurkeySekeroglu et al 202047
          AD = autosomal dominant.
          This gene encodes a member of the beta/gamma-crystallin family of proteins. Crystallins constitute major proteins of the vertebrate eye lens and are responsible for maintaining the transparency and refractive index of the lens. The Online Mendelian Inheritance in Man represents mutations in this gene that have been shown to cause cataracts. Online Mendelian Inheritance in Man No. 604307.
        • DNA analysis of the proband’s son revealed a heterozygous frameshift mutation in CRYGC (NM_020989: exon 3: c.389_390insGCTG: p.C130fs). DNA analysis of the proband’s daughter also showed a heterozygous frameshift mutation in CRYGC (NM_020989: exon 3: c.389_390insGCTG: p.C130fs).
      • 4.
        We identified the heterozygous CRYGC p.C130fs variant, including a frameshift mutation not currently reported in the ClinVar database. Sanger sequencing revealed that not only the proband but also her son and daughter carried this specific frameshift mutation.
      • 5.
        The multiple sequence alignments generated using CLUSTAL X software showed that the p.c130fs of human of CRYGC is highly conserved in Homo sapiens, Mus musculus, Rattus norvegicus, Canis lupus familiaris, Pan troglodytes, and Halichoerus grypus (Fig 3).
        Figure thumbnail gr3
        Figure 3Multiple sequence alignment of the fourth Greek key motif of CRYGC is shown. from Homo sapiens, Mus musculus, Rattus norvegicus, Canis lupus familiaris, Pan troglodytes, and Halichoerus grypus. The p.c130fs residue is highly conserved.

      Discussion

      Whole-exome gene analysis involves all regions of the exome; in humans, this covers more than 20 000 genes, enabling the analysis of more than 85% of all human genetic diseases. Single-nucleotide variants can be detected in gene-coding regions, as well as small insertion/deletion mutations.
      • Reis L.M.
      • Tyler R.C.
      • Muheisen S.
      • et al.
      Whole exome sequencing in dominant cataract identifies a new causative factor, CRYBA2, and a variety of novel alleles in known genes.
      The main findings of our study were that the next-generation and Sanger sequencing identified the CRYGC p.C130fs variant in the proband and her 2 affected children. The proband and her 2 affected children all displayed the phenotypes associated with microcornea and cataracts, while her husband exhibited no phenotypical abnormalities. The CRYGC p.C130fs variant exhibited co-segregation in the family, matching the inheritance pattern and clinical information of the affected individuals. No mutations were identified as being related to the pathogenic genes in the ClinVar database, and there were no matched variants in 59 genes, according to ACMG SF (secondary findings) v2.0 mutation analysis.
      The CRYGC gene encodes a member of the gamma-crystallin family, of which 6 genes (from γA to γF-crystallin; gene symbols: CRYGA to CRYGF) are found on human chromosome 2 q33-36.
      • Shiloh Y.
      • Donlon T.
      • Bruns G.
      • et al.
      Assignment of the human gamma-crystallin gene cluster (CRYG) to the long arm of chromosome 2, region q33-36.
      ,
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      Genomic sequences of murine gamma B- and gamma C-crystallin-encoding genes: promoter analysis and complete evolutionary pattern of mouse, rat and human gamma-crystallins.
      ,
      • Wistow G.J.
      • Piatigorsky J.
      Lens crystallins: the evolution and expression of proteins for a highly specialized tissue.
      Crystallin proteins are crucial elements of the vertebrate eye lens and promote the preservation of the refractive index and transparency of the lens. Only CRYGC and CRYGD genes have been identified as having cataract-causing mutations in humans.
      • Graw J.
      Genetics of crystallins: cataract and beyond.
      Mutations in CRYGC are associated with various types of cataracts across genetic studies.
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      • Li H.
      • et al.
      Mutations in crystallin genes result in congenital cataract associated with other ocular abnormalities.
      Congenital cataracts may be caused by crystallin gene mutations, which change the protein–protein interactions and decrease the solubility of crystallin proteins.
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      Alteration of protein–protein interactions of congenital cataract crystallin mutants.
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      • Bharat S.V.
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      • Pande J.
      The cataract-associated V41M mutant of human γS-crystallin shows specific structural changes that directly enhance local surface hydrophobicity.
      Stable crystallin proteins are relevant for maintaining crystal transparency and a high refractive index.
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      The genetics of cataract: our vision becomes clearer.
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      • Blundell T.
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      • et al.
      The molecular structure and stability of the eye lens: x-ray analysis of gamma-crystallin II.
      Studies on the genetic etiology of CC have all used data from large families; therefore, they cannot be applied to larger population analyses. Thus, genetic analysis of CC still lags behind compared with research on other eye diseases.
      • Hejtmancik J.F.
      The genetics of cataract: our vision becomes clearer.
      ,
      • Graw J.
      Genetics of crystallins: cataract and beyond.
      Identifying mutations in families with a history of CC will allow researchers to identify similar phenotypic pathogenesis and link their research with that of other studies, especially because cataracts within a single family can show significant phenotypical variation.
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      The genetics of cataract: our vision becomes clearer.
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      Understanding the molecular basis of cataract formation may lead to the future development of nonsurgical interventions.
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      • Puttamadappa S.S.
      • Pande A.
      • et al.
      Increased hydrophobicity and decreased backbone flexibility explain the lower solubility of a cataract-linked mutant of γD-crystallin.
      Moreover, a study
      • Lyon Y.A.
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      • Julian R.R.
      Identification of sequence similarities among isomerization hotspots in crystallin proteins.
      has shown that crystallin proteins are important in aging research.
      Previous studies
      • Reis L.M.
      • Tyler R.C.
      • Muheisen S.
      • et al.
      Whole exome sequencing in dominant cataract identifies a new causative factor, CRYBA2, and a variety of novel alleles in known genes.
      ,
      • Sun Z.
      • Zhou Q.
      • Li H.
      • et al.
      Mutations in crystallin genes result in congenital cataract associated with other ocular abnormalities.
      ,
      • Héon E.
      • Priston M.
      • Schorderet D.F.
      • et al.
      The gamma-crystallins and human cataracts: a puzzle made clearer.
      • Ren Z.
      • Li A.
      • Shastry B.S.
      • et al.
      A 5-base insertion in the gammaC-crystallin gene is associated with autosomal dominant variable zonular pulverulent cataract.
      • Santhiya S.T.
      • Shyam M.M.
      • Rawlley D.
      • et al.
      Novel mutations in the γ-crystallin genes cause autosomal dominant congenital cataracts.
      • Gonzalez-Huerta L.M.
      • Messina-Baas O.M.
      • Cuevas-Covarrubias S.A.
      A family with autosomal dominant primary congenital cataract associated with a CRYGC mutation: evidence of clinical heterogeneity.
      • Yao K.
      • Jin C.
      • Zhu N.
      • et al.
      A nonsense mutation in CRYGC associated with autosomal dominant congenital nuclear cataract in a Chinese family.
      • Li X.Q.
      • Cai H.C.
      • Zhou S.Y.
      • et al.
      A novel mutation impairing the tertiary structure and stability of γC-crystallin (CRYGC) leads to cataract formation in humans and zebrafish lens.
      • Guo Y.
      • Su D.
      • Li Q.
      • et al.
      A nonsense mutation of CRYGC associated with autosomal dominant congenital nuclear cataracts and microcornea in a Chinese pedigree.
      • Zhang L.
      • Fu S.
      • Ou Y.
      • et al.
      A novel nonsense mutation in CRYGC is associated with autosomal dominant congenital nuclear cataracts and microcornea.
      • Devi R.R.
      • Yao W.
      • Vijayalakshmi P.
      • et al.
      Crystallin gene mutations in Indian families with inherited pediatric cataract.
      • Kumar M.
      • Agarwal T.
      • Khokhar S.
      • et al.
      Mutation screening and genotype phenotype correlation of α- crystallin, γ-crystallin and GJA8 gene in congenital cataract.
      • Kondo Y.
      • Saitsu H.
      • Miyamoto T.
      • et al.
      Pathogenic mutations in two families with congenital cataract identified with whole-exome sequencing.
      • Gillespie R.L.
      • O'Sullivan J.
      • Ashworth J.
      • et al.
      Personalized diagnosis and management of congenital cataract by next-generation sequencing.
      • Prokudin I.
      • Simons C.
      • Grigg J.R.
      • et al.
      Exome sequencing in developmental eye disease leads to identification of causal variants in GJA8, CRYGC, PAX6 and CYP1B1.
      • Ma A.S.
      • Grigg J.R.
      • Ho G.
      • et al.
      Sporadic and familial congenital cataracts: mutational spectrum and new diagnoses using next-generation sequencing.
      • Li Dan
      • Wang Siying
      • Ye Hongfei
      • et al.
      Distribution of gene mutations in sporadic congenital cataract in a Han Chinese population.
      • Patel N.
      • Anand D.
      • Monies D.
      • et al.
      Novel phenotypes and loci identified through clinical genomics approaches to pediatric cataract.
      • Zhong Z.
      • Wu Z.
      • Han L.
      • Chen J.
      Novel mutations in CRYGC are associated with congenital cataracts in Chinese families.
      • Astiazaran M.C.
      • Garcia-Montano L.A.
      • Sanchez-Moreno F.
      • et al.
      Next generation sequencing-based molecular diagnosis in familial congenital cataract expands the mutational spectrum in known congenital cataract genes.
      • Li J.
      • Leng Y.
      • Han S.
      • et al.
      Clinical and genetic characteristics of Chinese patients with familial or sporadic pediatric cataract.
      • Zhuang J.
      • Cao Z.
      • Zhu Y.
      • et al.
      Mutation screening of crystallin genes in Chinese families with congenital cataracts.
      • Fan F.
      • Luo Y.
      • Wu J.
      • et al.
      The mutation spectrum in familial versus sporadic congenital cataract based on next-generation sequencing.
      • Kandaswamy D.K.
      • Vasantha K.
      • Graw J.
      • Santhiya S.T.
      A novel CRYGC E128∗ mutation underlying an autosomal dominant nuclear cataract in a south Indian kindred.
      • Taylan Sekeroglu H.
      • Karaosmanoglu B.
      • Taskiran E.Z.
      • et al.
      Molecular etiology of isolated congenital cataract using next-generation sequencing: single center exome sequencing data from Turkey.
      have identified several mutations in the CRYGC gene. Moreover, there have been previous reports
      • Lin Y.
      • Gao H.
      • Zhu Y.
      • et al.
      Two Paired Box 6 mutations identified in Chinese patients with classic congenital aniridia and cataract.
      ,
      • Long X.
      • Huang Y.
      • Tan H.
      • et al.
      Identification of a novel MIP frameshift mutation associated with congenital cataract in a Chinese family by whole-exome sequencing and functional analysis.
      regarding frameshift mutations in CRYGC. However, we report the novel CRYGC frameshift mutation c.389_390insGCTG (p.C130fs) in exon 3, with 4 missing bases, causing the protein sequence after the 130th amino acid codon to differ from the reference sequence, which is not currently reported in the ClinVar database.
      In conclusion, we identified a pathogenic mutation (c.389_390insGCTG) in CRYGC (p.C130fs), a heterozygous variant, and a frameshift mutation. This mutation was identified in a Chinese family whose members presented with CC and microcornea. Our findings expand the repertoire of known CRYGC gene mutations causing CC. Our findings provide valuable information for researchers and new insights into the etiology and molecular diagnosis of CC; however, the molecular mechanism of this mutation warrants further investigation.

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