Spontaneous and inheritable R555Q mutation in the TGFBI/BIGH3 gene in two unrelated families exhibiting Bowman's layer corneal dystrophy

De Novo L509P Mutation of the TGFBI Gene Associated with Slit-Lamp Findings of Lattice Corneal Dystrophy Type IIIA

Background: Mutations of the transforming growth factor-β-induced (TGFBI) gene produce various types of corneal dystrophy. Here, we report a novel de novo L509P mutation not located in a known hot spot of the transforming growth factor-β-induced (TGFBI) gene and its clinical phenotype, which resembles that of lattice corneal dystrophy type IIIA (LCD IIIA). Case presentation: A 36-year-old man (proband) visited our clinic due to decreased visual acuity with intermittent ocular irritation in conjunction with painful recurrent erosions in both eyes for 10 years. Molecular genetic analyses revealed a TGFBI L509P mutation (c.1526T>C) in the proband and one of his sons. Interestingly, neither TGFBI mutations nor corneal abnormalities were detected in either of the proband’s biological parents, indicating the occurrence of a de novo L509P mutation. Clinical examinations, including slit-lamp retro-illumination and Fourier-domain anterior segment optical coherence tomography (FD-OCT), revealed gray deposits in the anterior stroma and deeper refractile lines extending from limbus to limbus in both corneas of the proband, consistent with a diagnosis of LCD IIIA. Superficial diffuse haze and surface irregularity were observed in conjunction with corneal erosions and visual impairment, necessitating phototherapeutic keratectomy (PTK). A 60 μm PTK of the Bowman layer and anterior stroma of the proband’s left eye was performed following the removal of the epithelium in order to remove superficial corneal opacities. His BCVA improved from 20/400 to 20/50 at postoperative week 8 and was maintained for 45 months. Pinhole-corrected VA was 20/20 at the last visit, and corneal opacities had not recurred. Conclusions: An inheritable de novo mutation of L509P in the TGFBI gene can produce severe LCD IIIA, which can be successfully treated with OCT-guided PRK.

Novel mutation in the TGFBI gene in a Moroccan family with atypical corneal dystrophy: a case report

Background

Corneal dystrophies (CDs) are a heterogeneous group of bilateral, genetically determined, noninflammatory bilateral corneal diseases that are usually limited to the cornea. CD is characterized by a large variability in the age of onset, evolution and visual impact and the accumulation of insoluble deposits at different depths in the cornea. Clinical symptoms revealed bilateral multiple superficial, epithelial, and stromal anterior granular opacities in different stages of severity among three patients of this family. A total of 99 genes are involved in CDs. The aim of this study was to identify pathogenic variants causing atypical corneal dystrophy in a large Moroccan family and to describe the clinical phenotype with severely different stages of evolution.

Case presentation

In this study, we report a large Moroccan family with CD. Whole-exome sequencing (WES) was performed in the three affected members who shared a phenotype of corneal dystrophy in different stages of severity. Variant validation and familial segregation were performed by Sanger sequencing in affected sisters and mothers and in two unaffected brothers. Whole-exome sequencing showed a novel heterozygous mutation (c.1772C > A; p.Ser591Tyr) in the TGFBI gene. Clinical examinations demonstrated bilaterally multiple superficial, epithelial and stromal anterior granular opacities in different stages of severity among three patients in this family.

Conclusions

This report describes a novel mutation in the TGFBI gene found in three family members affected by different phenotypic aspects. This mutation is associated with Thiel-Behnke corneal dystrophy; therefore, it could be considered a novel phenotype genotype correlation, which will help in genetic counselling for this family.

Identification of the First De Novo UBIAD1 Gene Mutation Associated with Schnyder Corneal Dystrophy

Purpose. To report the identification of the first de novo UBIAD1 missense mutation in an individual with Schnyder corneal dystrophy (SCD). Methods. A slit lamp examination was performed on a 47-year-old woman without a family history of corneal disorders. The proband's parents, two sisters, and son were also examined and genomic DNA from all six individuals was collected. The exons and exon-intron boundaries of UBIAD1 were screened using Sanger sequencing. Identified mutations were screened for in 200 control chromosomes. In silico analysis predicted the impact of identified mutations on protein function and structure. Results. Slit lamp examination of the proband revealed findings consistent with SCD. Corneas of the family members appeared unaffected. Screening of UBIAD1 in the proband identified a novel heterozygous c.308C>T mutation, predicted to encode the missense amino acid substitution p.(Thr103Ile). This mutation was not identified in any of the family members or in 200 control chromosomes and was predicted to be damaging to normal protein function and structure. Conclusions. We present a novel heterozygous de novo missense mutation in UBIAD1, p.(Thr103Ile), identified in a patient with classic clinical features of SCD. This highlights the value of genetic testing in clinical diagnostic settings, even in the absence of a positive family history.

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

Background

To 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.

Methods

Individuals 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.

Results

Clinical 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.

Conclusions

The 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.

Corneal dystrophies and genetics in the International Committee for Classification of Corneal Dystrophies era: a review

Many of the corneal dystrophies have now been genetically characterized, and a system was established in 2008 by The International Committee for Classification of Corneal Dystrophies (IC3D) in an attempt to standardize the nomenclature. IC3D provided a classification system whereby all dystrophies can be categorized on the basis of the underlying genetic knowledge. Since that time, further work has established even more phenotypic and allelic heterogeneity than anticipated, particular for Fuchs endothelial corneal dystrophy and posterior polymorphous dystrophy. Using genome-wide association studies, a number of genes are now implicated both in normal corneal quantitative traits, such as central corneal thickness, as well as in disease. There is also a trend towards functional characterization of the genetic variants involved to elucidate the pathophysiology of these entities. This review article will provide an overview of the knowledge to date, with an emphasis on findings since the IC3D classification was published in 2008.

Arg555Gln mutation of TGFBI gene in geographical-type Reis-Bücklers corneal dystrophy in a Chinese family

OBJECTIVE

Mutations of the transforming growth factor β-induced (TGFBI) gene were studied in a Chinese family with Reis-Bücklers corneal dystrophy (RBCD).

METHODS

Six family members with RBCD and six unaffected family members were investigated. The pedigree showed a typical dominant inheritance pattern. Genomic DNA was extracted from peripheral leucocytes from all study participants. Exons 4, 12 and 14 of the TGFBI gene were analysed using polymerase chain reaction, and standard automated sequencing was performed. Corneal tissue sampled from the proband during phototherapeutic keratectomy was examined using transmission electron microscopy (TEM).

RESULTS

A typical geographical pattern of fine opacities in Bowman's layer of the cornea was seen in all six patients on slit-lamp examination. An Arg555Gln (R555Q) mutation of the TGFBI gene was identified in all six patients but was absent in all unaffected family members. TEM revealed rod-shaped bodies in Bowman's layer of the cornea.

CONCLUSIONS

In this Chinese family an R555Q mutation of the TGFBI gene was associated with RBCD. As the RBCD phenotype is usually associated with an R124L mutation, this novel genotype-phenotype correlation may prompt further investigation of Bowman's layer corneal dystrophy.

TGFBI gene mutation in a Chinese pedigree with Reis-Bücklers corneal dystrophy

PURPOSE

To characterize the molecular defects in the TGFBI gene in a Chinese family with Reis-Bücklers corneal dystrophy (RBCD), and to study the relationship between the gene mutations and the clinical manifestations.

METHODS

Four generations of this family with RBCD were enrolled in the study. In addition to ophthalmic and histopathological examinations, polymerase chain reaction (PCR) amplification and analysis of nucleotide sequencing of exons 4, 12, 14 of TGFBI were performed.

RESULTS

The clinical manifestations of the disease were characterized by geographic opacities in the subepithelial layers and anterior stroma of the cornea. Confocal microscopy images of the cornea showed focal hyper-reflective materials deposited in the subepithelium and anterior stroma. It was confirmed by histopathology that Bowman's membrane was mainly replaced by extracellular fibril material, which extended downwards into the superficial corneal stroma. Molecular genetic analysis revealed a single heterozygous G>T change at nucleotide 124 in exon 4 of TGFBI in all members (22) of the pedigree affected with RBCD, but not in the unaffected members.

CONCLUSIONS

A p.Arg124Leu mutation of the TGFBI gene was detected in this Chinese pedigree with Reis-Bücklers corneal dystrophy. The phenotype of Reis-Bücklers corneal dystrophy in this family belongs to the geographic type. The molecular genetic studies combined with histopathology may be useful for the accurate diagnosis of this type of corneal dystrophy.

Utility and efficacy of TGFBI mutational analysis for disease detection

Current knowledge of the genetic variation associated with TGFBI-associated corneal dystrophies has highlighted the possibility of de novo mutations, and also recurrence after refractive surgery in apparently asymptomatic individuals. This means that genetic testing for the most common variants is considered desirable, particularly in the refractive clinical setting. To be a useful clinical adjunct, however, genetic testing must be time and cost effective. Yoo and coworkers propose a nanoparticle microarray for rapid detection of TGFBI mutations. The advantages and limitations of these nanoparticle microarrays need to be compared with current methods of mutation detection. Clinicians should include genetic testing in the clinical work-up, and must consider the ethical principles of making a genetic diagnosis, as well as the marked variance in clinical presentation in this group of dystrophies.

Colocalization of increased transforming growth factor-beta-induced protein (TGFBIp) and Clusterin in Fuchs endothelial corneal dystrophy

PURPOSE

To investigate the differential expression of TGFBIp in normal human and Fuchs endothelial corneal dystrophy (FECD) endothelial cell-Descemet's membrane (HCEC-DM) complex, and to asses the structural role of TGFBIp and clusterin (CLU) in guttae formation.

METHODS

HCEC-DM complex was dissected from stroma in normal and FECD samples. Proteins were separated by 2-D gel electrophoresis and subjected to proteomic analysis. N-terminal processing of TGFBIp was detected by Western blot analysis with two separate antibodies against the N- and C-terminal regions of TGFBIp. Expression of TGFBI mRNA was compared by using real-time PCR. Subcellular localization of TGFBIp and CLU in corneal guttae was assessed by fluorescence confocal microscopy.

RESULTS

A major 68-kDa fragment and a minor 39-kDa fragment of TGFBIp were identified on 2-D gels. Western blot analysis revealed an age-dependent proteolytic processing of the TGFBIp N terminus resulting in the increased formation of 57-kDa (P = 0.04) and 39-kDa (P = 0.03) fragments in older donors. FECD HCEC-DM showed a significant increase in the 68-kDa (P = 0.04), 57-kDa (P = 0.01), and 39- kDa (P = 0.03) fragments of TGFBIp. Real-time PCR analysis revealed that TGFBI mRNA was significantly increased (P = 0.04) in FECD samples. TGFBIp formed aggregates at the lower portions of guttae, next to Descemet's membrane, whereas CLU localized mostly on top of the TGFBIp-stained areas at the level of the endothelial cell nuclear plane.

CONCLUSIONS

The overexpression of proaggregative protein CLU, and proadhesive protein TGFBIp, have been colocalized in the guttae. Such findings provide us with a better understanding of the major contributors involved in the aberrant cell-extracellular matrix interactions seen in the guttae of patients with FECD.