Jinyu Li

A novel MIP gene mutation associated with autosomal dominant congenital cataracts in a Chinese family

BackgroundThe major intrinsic protein gene (MIP), also known as MIP26 or AQP0, is a member of the water-transporting aquaporin family, which plays a critical role in the maintenance of lifelong lens transparency. To date, several mutations in MIP (OMIM 154050) have been linked to hereditary cataracts in humans. However, more pathogenic mutations remain to be identified. In this study, we describe a four-generation Chinese family with a nonsense mutation in MIP associated with an autosomal dominant congenital cataract (ADCC), thus expanding the mutational spectrum of this gene.MethodsA large four-generation Chinese family affected with typical Y-suture cataracts combined with punctuate cortical opacities and 100 ethnically matched controls were recruited. Genomic DNA was extracted from peripheral blood leukocytes to analyze congenital cataract-related candidate genes. Effects of the sequence change on the structure and function of proteins were predicted by bioinformatics analysis.ResultsDirect sequencing of MIP in all affected members revealed a heterozygous nucleotide exchange c.337C>T predicting an arginine to a stop codon exchange (p.R113X). The substitution co-segregated well in all the affected individuals in the family and was not found in unaffected members or in the 100 unrelated healthy controls. Bioinformatics analysis predicted that the mutation affects the secondary structure and function of the MIP protein.ConclusionsWe identified a novel mutation of MIP (p.R113X) in a Chinese cataract family. This is the first nonsense mutation of MIP identified thus far. This novel mutation is also the first disease-causing mutation located in the loop C domain of MIP. The results add to the list of mutations of the MIP linked to cataracts.

Targeted Exome Sequencing of Congenital Cataracts Related Genes: Broadening the Mutation Spectrum and Genotype-Phenotype Correlations in 27 Chinese Han Families.

Congenital cataract is the most frequent inherited ocular disorder and the most leading cause of lifelong visual loss. The screening of pathogenic mutations can be very challenging in some cases, for congenital cataracts are clinically and genetically heterogeneous diseases. The aim of this study is to investigate the mutation spectrum and frequency of 54 cartaract-associated genes in 27 Chinese families with congenital cataracts. Variants in 54 cataract-associated genes were screened by targeted next-generation sequencing (NGS) and then validated by Sanger sequencing. We identified pathogenic variants in 62.96% (17/27) of families, and over 52.94% (9/17) of these variants were novel. Among them, three are splicing site mutations, four are nonsense mutations, seven are missense mutations, two are frame shift mutations and one is intronic mutation. This included identification of: complex ocular phenotypes due to two novel PAX6 mutations; progressive cortical cataract and lamellar cataract with lens subluxation due to two novel CRYGS mutations. Mutations were also found in rarely reported genes including CRYBA4, CRYBA2, BFSP1, VIM, HSF4, and EZR. Our study expands the mutation spectrum and frequency of genes responsible for congenital cataracts. Targeted next-generation sequencing in inherited congenital cataract patients provided significant diagnostic information.

A Nonsense Mutation of γD-crystallin Associated with Congenital Nuclear and Posterior Polar Cataract in a Chinese Family

Objective: The goal of this study was to characterize the disease-causing mutations in a Chinese family with congenital nuclear and posterior polar cataracts. Methods: Clinical data of patients in the family were recorded using slit-lamp photography and high definition video. Genomic DNA samples were extracted from the peripheral blood of the pedigree members and 100 healthy controls. Mutation screening was performed in the candidate genes by bi-directional sequencing of the amplified products. Results: The congenital cataract phenotype of the pedigree was identified by slit-lamp examinations and observation during surgery as nuclear and posterior polar cataracts. Through the sequencing of the candidate genes, a heterozygous c. 418C>T change was detected in the coding region of the γD-crystallin gene (CRYGD). As a result of this change, a highly conserved arginine residue was replaced by a stop codon (p. R140X). This change was discovered among all of the affected individuals with cataracts, but not among the unaffected family members or the 100 ethnically matched controls. Conclusions: This study identified a novel congenital nuclear and posterior polar cataract phenotype caused by the recurrent mutation p. R140X in CRYGD.

The cataract-causing mutation G75V promotes γS-crystallin aggregation by modifying and destabilizing the native structure

Congenital cataract is one of the leading causes of childhood blindness worldwide. About half of heredity cataracts are caused by mutations in various crystallins. However, the underlying mechanisms have not been elucidated for most of crystallin mutations. In this research, we studied the effect of a cataract-causing mutation G75V on γS-crystallin structure, stability and aggregatory propensity. Spectroscopic experiments indicated that the mutation had little impact on γS-crystallin oligomeric status and secondary structure components, but led to large perturbations in tertiary structure. Compared with the WT protein, the G75V mutant had more solvent-accessible Trp fluorophores and hydrophobic exposure. The modified native state of mutant γS-crystallin was more susceptible to environmental stresses such as heat treatment, guanidine hydrochloride and acid conditions. The destabilized mutated protein was more prone to form large aggregates when denatured by high temperature or UV-irradiation. The thermal aggregation of the G75V mutant could be successfully inhibited by excess amount of αA-crystallin with a higher efficiency than the WT protein. Our results suggested that the aberrant modifications in γS-crystallin structure might contribute to the lower stability and higher aggregatory potency of the mutated protein, which subsequently resulted in cataracts in the patients.

A novel FBN1 missense mutation (p.C102Y) associated with ectopia lentis syndrome in a Chinese family

AIM To characterize the disease-causing mutations in a Chinese family with ectopia lentis syndrome (ELS). METHODS Patients and their family members were given complete physical, ophthalmic, and cardiovascular examinations. Genomic DNA samples were extracted from the peripheral blood of the pedigree members and 100 healthy controls. Mutation screening was performed in the fibrillin-1 (FBN1) gene by bi-directional sequencing of the amplified products. The mutation was analyzed using two bioinformatics methods. RESULTS A novel heterozygous c.305G>A mutation in exon 3 of FBN1 was detected. As a result of this change, a highly conserved cysteine residue was replaced by a tyrosine residue (p.C102Y). Another mutation was found in the same exon (c.303T>C), which did not change the amino acid sequence. Both mutations were discovered in each affected individual, but not in the unaffected family members, or in 100 ethnically matched controls. A bioinformatics analysis predicted that mutation p.C102Y would affect protein function. CONCLUSION In the first epidermal growth factor-like module, we identified a novel FBN1 mutation (p.C102Y), which caused ELS in the family. Our study presented a unique phenotype, including some distinct ophthalmic findings, such as hypoplasia of the iris and anisometropia. Our results expanded the mutation spectrum of FBN1 and enriched the overall knowledge of genotype-phenotype correlations due to FBN1 mutations.

A novel phenotype-genotype correlation with an Arg555Trp mutation of TGFBI gene in Thiel-Behnke corneal dystrophy in a Chinese pedigree.

BackgroundTo investigate the molecular defects in a four-generation Chinese pedigree affected with Thiel-Behnke corneal dystrophy (TBCD). And to further study the relationship between genetic mutation and clinical manifestations.MethodsIndividuals of the pedigree were recruited for extensive ophthalmic examinations. Histological studies of two corneal buttons obtained from lamellar keratoplasty were conducted. Peripheral blood was collected in EDTA for genomic DNA isolation from leukocytes of all affected and unaffected members. All 17 exons of the TGFBI gene were screened for mutations by polymerase chain reaction and direct DNA sequencing.ResultsClinical examinations revealed a typical pattern of honeycomb-like TBCD. Histopathology study demonstrated eosinophilic deposits that were congo-red-positive and did not stain with periodic acid Schiff or Masson’s trichrome. Genetic analysis disclosed a heterozygous p. Arg555Trp mutation resulted from a missense c. 1663C > T nucleotide change in exon 12 of TGFBI gene in all affected members. Morever, a second rare variant in exon 6 of the TGFBI gene (p. Arg257Trp) also cosegregated within this family and has been confirmed to be a single nucleotide polymorphism (SNP) not previously reported.ConclusionsThe p. Arg555Trp mutation of the TGFBI gene was associated with TBCD, which revealed a novel phenotype-genotype correlation within the mutational spectrum of phenotypically diverse corneal dystrophies.