Three autosomal dominant corneal dystrophies map to chromosome 5q

[The latest IC3D classification of corneal dystrophies-Overview and changes of the 3rd edition]

The International Committee on Classification of Corneal Dystrophies (IC3D) was founded in 2005 to address difficulties arising from the outdated nomenclature for corneal dystrophies (CD) and to correct misconceptions in the literature. For each of the 22 CDs, a separate template was created to represent the current clinical, pathological and genetic knowledge of the disease. In addition, each template contains representative clinical photographs as well as light and electron microscopic images and, if available, confocal microscopic and coherence tomographic images of the respective CD. After the first edition was published in 2008, the revised version followed in 2015. The third edition of the IC3D was published as open access in February 2024. The latest edition is intended to serve as a reference work in everyday clinical practice and facilitate the diagnosis of CD, which might sometimes be difficult. This article provides an overview of the diagnostic and treatment principles of CD and presents the IC3D and its changes over time.

Release of frustration drives corneal amyloid disaggregation by brain chaperone

TGFBI-related corneal dystrophy (CD) is characterized by the accumulation of insoluble protein deposits in the corneal tissues, eventually leading to progressive corneal opacity. Here we show that ATP-independent amyloid-β chaperone L-PGDS can effectively disaggregate corneal amyloids in surgically excised human cornea of TGFBI-CD patients and release trapped amyloid hallmark proteins. Since the mechanism of amyloid disassembly by ATP-independent chaperones is unknown, we reconstructed atomic models of the amyloids self-assembled from TGFBIp-derived peptides and their complex with L-PGDS using cryo-EM and NMR. We show that L-PGDS specifically recognizes structurally frustrated regions in the amyloids and releases those frustrations. The released free energy increases the chaperone's binding affinity to amyloids, resulting in local restructuring and breakage of amyloids to protofibrils. Our mechanistic model provides insights into the alternative source of energy utilized by ATP-independent disaggregases and highlights the possibility of using these chaperones as treatment strategies for different types of amyloid-related diseases.

Genetic screening of TGFBI in Iranian patients with TGFBI-associated corneal dystrophies and a meta-analysis of global variation frequencies

PURPOSE

Transforming growth factor beta-induced (TGFBI)-associated corneal dystrophies (CDs) are a clinically heterogeneous group of CDs caused by mutations in the TGFBI gene. Nucleotide sequences encoding two arginine residues at positions 124 and 555 in TGFBI protein are mutation hotspots. We screened regions of TGFBI that include the hotspots in a cohort of Iranian patients with TGFBI-associated CDs. We also performed a meta-analysis for frequencies of all reported TGFBI mutations.

METHODS

Twenty-four TGFBI-associated CD-diagnosed patients were recruited. Exons 4 and 12 of TGFBI were amplified by the polymerase chain reaction and sequenced by Sanger protocol. A meta-analysis on reported TGFBI sequence data was done by reviewing all published relevant articles available in NCBI.

RESULTS

Twenty-two out of 24 patients had mutations in exons 4 or 12 of TGFBI. The most frequent mutations were p.Arg124Cys, p.Arg124His, and p.Arg555Trp; each of these was found in six families. Three other missense mutations including p.Arg555Gln, p.Ile522Asn, and p.Ala546Thr were also identified. The data suggested a fairly tight genotype/phenotype correlation for the most common CDs. Literature review evidenced that the reported mutations affected less than 30% of the amino acids of the TGFBI protein and that p.Arg124His, p.Arg124Cys, p.Arg555Trp, p.Arg124Leu, p.Arg555Gln, and p.His626Arg were the most frequent mutations.

CONCLUSION

TGFBI mutation profile of Iranian patients is very similar to that of the rest of the world. The meta-analysis confirmed the worldwide prevalence of p.Arg124 and p.Arg555, showed that p.His626Arg is also relatively frequent, and evidenced the value of screening exons 4 and 12 of TGFBI.

Recurrence of Avellino Corneal Dystrophy Following Penetrating Keratoplasty: A Case Report

Granular - lattice (Avellino) corneal dystrophy is inherited in an autosomal dominant fashion which affects stroma of the cornea with recurrent erosions and decreased vision due to clouding of cornea in later stage. We reported a case of 53-year old woman presented with pain and blurring of vision of left eye for 10 days with history of right eye deep anterior lamellar dystrophy and Left eye penetrating keratoplasty 5years back for Avellino dystrophy. On examination right eye graft was clear and left eye showed circular edges of irregular epithelium with patchy stains and epithelial defect suggestive of recurrence of dystrophy. A patient with recurrent corneal erosions and opacity in cornea has to be examined carefully so as not to overlook Avellino corneal dystrophy. Being a rare disorder this case has been reported to draw the attention of ophthalmologists about its recurrence following keratoplasty.

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.

Effect of osmolytes on in-vitro aggregation properties of peptides derived from TGFBIp

Protein aggregation has been one of the leading triggers of various disease conditions, such as Alzheimer’s, Parkinson’s and other amyloidosis. TGFBI-associated corneal dystrophies are protein aggregation disorders in which the mutant TGFBIp aggregates and accumulates in the cornea, leading to a reduction in visual acuity and blindness in severe cases. Currently, the only therapy available is invasive and there is a known recurrence after surgery. In this study, we tested the inhibitory and amyloid dissociation properties of four osmolytes in an in-vitroTGFBI peptide aggregation model. The 23-amino acid long peptide (TGFBIp 611–633 with the mutation c.623 G>R) from the 4th FAS-1 domain of TGFBIp that rapidly forms amyloid fibrils was used in the study. Several biophysical methods like Thioflavin T (ThT) fluorescence, Circular Dichroism (CD), fluorescence microscopy and Transmission electron microscopy (TEM) were used to study the inhibitory and amyloid disaggregation properties of the four osmolytes (Betaine, Raffinose, Sarcosine, and Taurine). The osmolytes were effective in both inhibiting and disaggregating the amyloid fibrils derived from TGFBIp 611–633 c.623 G>R peptide. The osmolytes did not have an adverse toxic effect on cultured human corneal fibroblast cells and could potentially be a useful therapeutic strategy for patients with TGFBIp corneal dystrophies.

Phototherapeutic keratectomy

Phototherapeutic keratectomy is an excimer laser-based surgical procedure widely performed by corneal surgeons for treating anterior corneal stromal pathologies. Phototherapeutic keratectomy helps by ablating the corneal stroma, thereby improving corneal clarity and smoothening the surface. Transient discomfort and induced hyperopia from corneal flattening are the immediate postoperative concerns. The long-term course is often marked by the recurrence of original corneal pathology and corneal haze formation. Phototherapeutic keratectomy, however, allows for repeat stromal ablation for managing recurrences, as the corneal thickness permits, without affecting the outcome of future keratoplasty. Adjunctive methods such as topical mitomycin-C may be additionally used to reduce recurrence rates. Also, various masking agents such as carboxymethyl cellulose, sodium hyaluronate, and dextran are used in eyes with irregular corneal surface to allow for uniform stromal ablation. Overall, phototherapeutic keratectomy has provided corneal surgeons an additional surgical tool, particularly those residing in developing nations where the availability of donor corneal tissue is an important limiting factor.

Clinical and genetic update of corneal dystrophies

The International Committee for Classification of Corneal Dystrophies (IC3D) distinguishes between 22 distinct forms of corneal dystrophy which are predominantly autosomal dominant, although autosomal recessive and X-chromosomal dominant patterns do exist. Before any genetic examination, there should be documentation of a detailed corneal exam of as many affected and unaffected family members as possible, because detailed phenotypic description is essential for accurate diagnosis. Corneal documentation should be performed in direct and indirect illumination at the slit lamp with the pharmacologically dilated pupil. For the majority of the corneal dystrophies, a phenotype-genotype correlation has not been demonstrated. However, for the dystrophies associated with mutations in the transforming growth factor, ß-induced gene (TGFBI) a general phenotype-genotype correlation is evident. The discovery of collagen, type XVII, alpha 1 mutation (COL17A1), causative in the called epithelial recurrent erosion dystrophy (ERED) was a very important step in the accurate diagnosis of corneal dystrophies. This led to the subsequent discovery that the entity previously called 10q Thiel-Behnke corneal dystrophy, was in reality actually COL17A1 ERED, and not Thiel-Behnke corneal dystrophy. In addition to the phenotypic landmarks, we describe the current genotype of the individual corneal dystrophies. Differential diagnosis can be aided by information on histopathology, optical coherence tomography (OCT), and confocal microscopy.

Mutation update: TGFBI pathogenic and likely pathogenic variants in corneal dystrophies

Human transforming growth factor β-induced (TGFBI), is a gene responsible for various corneal dystrophies. TGFBI produces a protein called TGFBI, which is involved in cell adhesion and serves as a recognition sequence for integrins. An alteration in cell surface interactions could be the underlying cause for the progressive accumulation of extracellular deposits in different layers of the cornea with the resulting changes of refractive index and transparency. To this date, 69 different pathogenic or likely pathogenic variants in TGFBI have been identified in a heterozygous or homozygous state in various corneal dystrophies, including a novel variant reported here. All disease-associated variants were inherited as autosomal-dominant traits but one; this latter was inherited as an autosomal recessive trait. Most corneal dystrophy-associated variants are located at amino acids Arg124 and Arg555. To keep the list of corneal dystrophy-associated variant current, we generated a locus-specific database for TGFBI (http://databases.lovd.nl/shared/variants/TGFBI) containing all pathogenic and likely pathogenic variants reported so far. Non-disease-associated variants are described in specific databases, like gnomAD and ExAC but are not listed here. This article presents the most recent up-to-date list of disease-associated variants.

Vortex Pattern of Corneal Deposits in Granular Corneal Dystrophy Associated With the p.(Arg555Trp) Mutation in TGFBI

PURPOSE

To describe 2 unrelated families with multiple members demonstrating a less commonly recognized vortex pattern of corneal deposits confirmed to be granular corneal dystrophy type 1 (GCD1) after identification of the p.(Arg555Trp) mutation in the transforming growth factor β-induced gene (TGFBI).

METHODS

A slit-lamp examination was performed on individuals from 2 families, one of Mexican descent and a second of Italian descent. After DNA extraction from affected individuals and their unaffected relatives, TGFBI screening was performed.

RESULTS

Eight of 20 individuals in the Mexican family and 20 of 55 in the Italian family demonstrated corneal stromal opacities. Seven of the 8 affected individuals in the Mexican family and 4 of the 20 affected individuals in the Italian family demonstrated a phenotype characterized by a "sea fan" or vortex pattern of superficial stromal corneal deposits originating from the inferior aspect of the cornea. Screening of TGFBI in both families revealed a heterozygous missense mutation [p.(Arg555Trp)] in exon 12, confirming the diagnosis of GCD1.

CONCLUSIONS

Our findings demonstrate that GCD1 may present with a vortex pattern of anterior stromal deposits. Although this pattern of dystrophic deposits is not recognized by clinicians as a typical phenotype of GCD1, it is consistent with the production of the majority of the TGFBI protein by the corneal epithelium.

[Corneal dystrophies]

Degenerative or hereditary corneal diseases are sometimes difficult to discriminate. Corneal dystrophies affect approximately 0.09 % of the population. They are identified by the IC3D classification based on their phenotype, genotype and evidence gathered for their diagnosis. Practically, the ophthalmologist manages functional symptoms, such as recurrent erosions, visual loss and amblyopia, photophobia, foreign body sensation, and sometimes pain and aesthetic concerns. Medical treatments consist of drops to promote healing, ointments, hyperosmotic agents and bandage contact lenses. Less invasive surgical treatments are used as second line therapy (phototherapeutic keratectomy, lamellar keratectomy). More invasive procedures may eventually be utilized (lamellar or penetrating keratoplasty). Anterior lamellar or endothelial keratoplasty are now preferred to penetrating keratoplasty, although the latter still remains the only possible option in some cases. Some rare dystrophies require coordinated and comprehensive medical care.

Corneal dystrophies

Degenerative or hereditary corneal diseases are sometimes difficult to discriminate. Corneal dystrophies affect approximately 0.09% of the population. They are identified by the IC3D classification based on their phenotype, genotype and evidence gathered for their diagnosis. In practice, the ophthalmologist manages functional symptoms such as recurrent erosions, visual loss and amblyopia, photophobia, foreign body sensation, and sometimes pain and aesthetic concerns. Medical treatments consist of drops to promote healing, ointments, hyperosmotic agents and bandage contact lenses. Less invasive surgical treatments are used as second line therapy (phototherapeutic keratectomy, lamellar keratectomy). More invasive procedures may eventually be utilized (lamellar or penetrating keratoplasty). Anterior lamellar or endothelial keratoplasty are now preferred to penetrating keratoplasty, although the latter still remains the only possible option in some cases. Some rare dystrophies require coordinated and comprehensive medical care.

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.

Clinical and genetic aspects of the TGFBI-associated corneal dystrophies

Corneal dystrophies are a group of inherited disorders localized to various layers of the cornea that affect corneal transparency and visual acuity. The deposition of insoluble protein materials in the form of extracellular deposits or intracellular cysts is pathognomic. Mutations in TGFBI are responsible for superficial and stromal corneal dystrophies. The gene product, transforming growth factor β induced protein (TGFBIp) accumulates as insoluble deposits in various forms. The severity, clinicopathogenic variations, age of the onset, and location of the deposits depend on the type of amino acid alterations in the protein. Until 2006, 38 different pathogenic mutants were reported for the TGFBI-associated corneal dystrophies. This number has increased to 63 mutants, reported in more than 30 countries. There is no effective treatment to prevent, halt, or reverse the deposition of TGFBIp. This review presents a complete mutation update, classification of phenotypes, comprehensive reported incidents of various mutations, and current treatment options and their shortcomings. Future research directions and possible approaches to inhibiting disease progression are discussed.

Granular corneal dystrophy: a novel approach to classification and treatment

PURPOSE

The purpose of this case report is to review granular corneal dystrophy (GCD) and examine the new paradigm in its classification and treatment.

CASE REPORT

A 49-year-old white male patient reported yearly for monitoring of GCD. He had an ocular surgical history in the left eye for penetrating keratoplasty in 1989 and phototherapeutic keratectomy with mitomycin C for graft recurrence of stromal bread-crumb opacities 17+ years later in 2002. At his last examination, the patient's vision and comfort was stable in each eye, with minimal recurrence of granular opacities in the left surgical eye, stable granular opacities in the right eye, no recurrent corneal erosion symptoms in either eye, and best spectacle-corrected vision of 20/40 OD and 20/30 OS.

CONCLUSIONS

GCD is a Category 1, Stromal, TGFBI-associated corneal dystrophy. Although it is classified as a stromal dystrophy, research suggests the possibility that the granular opacities have an origination to the corneal epithelium with a migratory effect to the corneal stroma. Patients with Groenouw I, like the one in this report, usually do not have severely compromised vision. When vision is significantly affected or recurrent corneal erosion occurs, despite first- and second-line treatments, viable management options thereafter include photokeratectomy and other new surgical treatments such as femtosecond deep anterior lamellar keratoplasty and femtosecond laser-assisted keratoplasty. Future advancements in diagnostic technology, immunohistologic and genetic testing, medications, and surgery will allow for advancements in treating and managing patients with GCD.

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 and CHST6 gene analysis in Chinese stromal corneal dystrophies

AIM

To investigate whether mutations in TGFBI gene or CHST6 gene correlated with stromal corneal dystrophies (CD) in 8 Chinese probands.

METHODS

Eight unrelated patients with stromal corneal dystrophies were recruited in this study; all affected members were assessed by completely ophthalmologic examinations. Genomic DNA was extracted from peripheral leukocytes, 17 exons of TGFBI gene and the exon of CHST6 gene were amplified by polymerase chain reaction (PCR), sequenced directly and compared with the reference database.

RESULTS

Three heterozygous mutations in TGFBI gene were identified in six patients: c. 370C>T (p.Arg124Cys) was found in exon 4 of TGFBI gene in three members, c. 371G>A (p.Arg124His) was found in one patient; c. 1663C>T (p.Arg555Trp) was found in exon 12 in other two members. In addition, four polymorphisms with the nucleotide changes rs1442, rs1054124, rs4669, and rs35151677 were found in TGFBI gene. Mutations were not identified in the rest of 2 affected individuals in TGFBI gene or CHST6 gene.

CONCLUSION

Within these patients, R124C, R124H and R555W mutations were co-segregated with the disease phenotypes and were specific mutations for lattice corneal dystrophy type I (LCD I), Avellino corneal dystrophy (ACD, GCD II), granular corneal dystrophy type I (GCD I), respectively. Our study highlights the prevalence of codon 124 and codon 555 mutations in the TGFBI gene among the Chinese stromal corneal dystrophies patients.

A unique TGFBI protein in granular corneal dystrophy types 1 and 2

PURPOSE

Types 1 and 2 granular corneal dystrophies (GCD) are primarily associated with accumulation of the R555W and R124H mutant transforming growth factor β-inducible proteins (TGFBIp) in corneal stroma, respectively. However, specific components of TGFBIp responsible for granular deposits have not been delineated. This study was undertaken to identify the mutant TGFBIp components potentially responsible for GCD.

METHODS

Recombinant TGFBIp of wild-type (WT) and three mutants, R124C, R124H, and R555W, were generated in HEK293FT cells. WT and TGFBIp mutants were collected from cell lysates. Immunoblot analyses were performed with five different antibodies directed against various regions of WT TGFBIp.

RESULTS

WT and TGFBIp mutants showed differential reactivities with these antibodies. In contrast to our prior observation in purified WT and TGFBIp mutants, TGFBIp from cell lysates were less prone to polymerize. A unique 35 kD fragment was detected in cell lysates of R555W and R124H, but not in those of WT or R124C, by a commercial antibody raised against amino acids (a.a.) 199-406 of TGFBIp.

CONCLUSIONS

Monomeric and polymeric WT and TGFBIp mutants were observed in vitro. The 35 kD fragment found only in R555W and R124H, but not in WT and R124C cell lysates, is likely a degraded TGFBIp derived from the central domain of these mutants and this fragment may be contributory to the nonamyloid granular deposits observed in GCD 1 and 2.

Genome-wide scan of granular corneal dystrophy, type II: confirmation of chromosome 5q31 and identification of new co-segregated loci on chromosome 3q26.3

Granular corneal dystrophy, type II (CGD2; Avellino corneal dystrophy) is the most common corneal dystrophy among Koreans, but its pathophysiology is still poorly understood. Many reports showed that even though the causative mutation is the same TGFBI R124H mutation, there are severe and mild phenotypes of the corneal dystrophy. We also observed the phenotype differences in our samples. For this reason, we focused our effort on the identification of unknown genetic factor related to phenotype variation. A total 551 individuals from 59 families were genotyped with SNP chip and used in genome-wide linkage analysis. From single-point linkage analyses, we confirmed the known 5q31 region for TGFBI gene, and selected novel nine candidate loci for CGD2. In simulation analysis, the only 3q26.3 region including neuroligin 1 gene (NLGN1) was supported by empirical statistic significance. To investigate the effect of genetic heterogeneity in linkage analysis, we classified CGD2 families into two subgroups. Although we could not find a significant evidence for correlation between the 3q26.3 region and CGD2 phenotypes, this first genome-wide analysis with CGD2 families in Korea has a very important value for offering insights in genetics of CGD2. In addition, the co-segregating loci with CGD2 including 3q26.3 would be a good target for further study to understand the pathophysiology of CGD2.

[New international classification of corneal dystrophies (CD)]

The Cornea Society founded an international committee of 17 corneal experts from the USA, Asia and Europe in 2005. The goal of this group was to develop a new international classification of corneal dystrophies (CD) based on modern clinical, histological and genetic knowledge. Both authors are members of this committee. The elaboration of the classification included the correction of many misinterpretations with regard to the different forms of CD which were published in the past literature. In spite of important results concerning the genetic locus and identification of genes and mutations, corneal dystrophies are typically classified with respect to the level of the cornea that is involved. An accurate and up-to-date template for each form of the 25 CDs was created that included the current clinical, histological and genetic information. To indicate the level of evidence supporting the existence of a given dystrophy, the CDs are divided into four different categories. The new international classification of CDs was published in English, Spanish and German as a 40 page supplement with 64 figures, mostly in color. A more detailed description of genetic mutations is included in the appendix.

Granular and lattice deposits in corneal dystrophy caused by R124C mutation of TGFBIp

PURPOSE

Both granular and lattice deposits are present in Avellino corneal dystrophy (ACD), primarily associated with the R124H mutation of transforming growth factor-β-induced (TGFBIp). We investigated the presence of these deposits in other TGFBI mutations and the use of Thioflavin-T (ThT), a fluorescent amyloid stain for characterizing corneal amyloid deposits.

METHODS

Surgical corneal specimens of 3 unrelated patients clinically diagnosed with ACD were studied. Corneal sections from normal individuals and patients with prior lattice corneal dystrophy (LCD) were used as controls. Histochemical studies were performed with Congo red and Masson trichrome stains, and fluorescent imaging with scanning laser confocal microscopy was performed for ThT and anti-TGFBIp antibody staining.

RESULTS

Clinical and histopathological findings supported the diagnoses of ACD in these 3 cases in whom granular deposits stained with Masson trichrome and lattice deposits stained with ThT and Congo red showed birefringence and dichroism as expected. However, genotyping revealed a heterozygous R124C mutation in each case. In addition to classical stromal deposits, unique subepithelial TGFBIp aggregates, which stain with neither ThT nor trichrome, were observed. In control LCD sections, stromal deposits were stained with ThT but not with trichrome, confirming lack of granular deposits.

CONCLUSIONS

Our results demonstrate that both granular and lattice corneal deposits can be associated with R124C mutation in addition to the more common R124H mutation. An additional feature of nonhyaline, nonamyloid, TGFBIp subepithelial deposits might substantiate the categorization of such cases as a variant form of ACD. This study further validates ThT staining for detection of amyloid TGFBIp deposits.

Genotype of lattice corneal dystrophy (R124C mutation in TGFBI) in a patient presenting with features of avellino corneal dystrophy

PURPOSE

To present a patient with a genotype usually associated with lattice corneal dystrophy but with clinical and histopathologic features of advanced Avellino corneal dystrophy.

METHODS

Penetrating keratoplasty was performed with subsequent histopathologic analysis. For genetic testing, a 5-mL blood sample was taken after informed consent. Genetic sequencing was performed by the John and Marcia Carver Laboratory of the University of Iowa. The mutation was identified by direct sequencing through the positions of the coding sequences of the TGFBI gene that have been previously reported to have genetic variations (exons 4 and 11-14).

RESULTS

Corneal examination revealed bilateral lattice and multiple confluent subepithelial and anterior stromal granular opacities. Histopathologic examination showed amyloid deposits by Congo red stain and hyaline deposits by Masson trichrome stain, consistent with a diagnosis of Avellino dystrophy. Automated DNA sequencing revealed a heterozygous Arg124Cys (R124C) mutation in the coding sequence of the TGFBI gene on chromosome 5q31. Recurrent granular deposits developed in the corneal graft 14 months after surgery.

CONCLUSIONS

Our case presented with clinical and histopathologic findings consistent with a diagnosis of Avellino dystrophy and exhibited a genotype with R124C mutation. Avellino dystrophy has not previously been reported to be associated with the R124C mutation, which is usually associated with lattice corneal dystrophy. This also raises the issue as to whether classification of the corneal stromal dystrophies should be based primarily on phenotype/histopathology or on genotyping.

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.

Frequent promoter hypermethylation of TGFBI in epithelial ovarian cancer

OBJECTIVES

Using pharmacologic unmasking and genome-wide differential methylation analysis, we identified a novel methylated gene in ovarian cancers.

METHODS

Two ovarian cancer cells (OVCAR-3, ES-2) that showed synergistic growth inhibition by 5-aza-dC and cisplatin were selected. After treatment with 5-aza-dC, differential expression profiles were compared using microarray that contained 38,500 genes. Reactivation of candidate genes and their promoter methylation were validated by real-time RT-PCR, MS-PCR and bisulfite sequencing. Methylation status was tested by MS-PCR in 56 patients with epithelial ovarian cancer and compared to the 38 normal ovarian tissues.

RESULTS

We identified 103 candidate genes that were reactivated by 5-aza-dC treatment. Among those, SFN and TGFBI were commonly reactivated in both cells. Since SFN is a well known methylated marker, we selected TGFBI for further validation. Bisulfite sequencing revealed complete promoter methylation in ES-2 and partial methylation in OVCAR-3. In addition, silencing of TGFBI at the transcription level was reversed by 5-aza-dC treatment. TGFBI methylation was observed in 23 out of 38 (60.5%) cases of ovarian cancer, in no normal ovarian tissues (0 of 38, P=0.001), and in 5 out of 18 (27.8%) borderline tumors (P=0.044). In our cohort, we did not observe any association between methylation of TGFBI and clinicopathologic variables or clinical outcomes.

CONCLUSION

Our results confirm that TGFBI is frequently methylated in ovarian cancer. Its methylation can be used as a novel epigenetic biomarker in discriminating ovarian cancer from non-cancer or borderline tumors.

Confocal microscopy and optical coherence tomography imaging of hereditary granular dystrophy

OBJECTIVES

This case report examines the clinical characteristics of hereditary granular dystrophy through the use of slit lamp digital photography, confocal microscopy (CM) and optical coherence tomography (OCT). A review of the literature describing the histopathological and genetic associations of stromal dystrophies, suggest it may be possible to differentiate dystrophies based on their clinical manifestations, and appearances of CM and OCT images, with or without the use of genetic testing.

CASE REPORT

Two sisters, previously diagnosed with Granular (Groenouw I) Dystrophy, were examined. Examination included the use of digital slit lamp photography, CM and OCT imaging.

RESULTS

"Breadcrumb" opacities were visualized in the anterior two-thirds of the stroma with all three imaging techniques. Opacities were demonstrated in the posterior third of the stroma with the digital photography and OCT techniques.

CONCLUSIONS

The digital photography, CM and OCT images support the sister's diagnosis of Granular (Groenouw I) Dystrophy. Currently, genetic and histopathological testing are the only techniques available to determine exactly which corneal dystrophy and gene mutation are present. The results of this case report demonstrate that slit lamp digital photography, combined with CM and OCT may be capable of providing sufficient diagnostic information to diagnose corneal granular dystrophies in a clinical setting.

Corneal dystrophy-associated R124H mutation disrupts TGFBI interaction with Periostin and causes mislocalization to the lysosome

The 5q31-linked corneal dystrophies are heterogeneous autosomal-dominant eye disorders pathologically characterized by the progressive accumulation of aggregated proteinaceous deposits in the cornea, which manifests clinically as severe vision impairment. The 5q31-linked corneal dystrophies are commonly caused by mutations in the TGFBI (transforming growth factor-beta-induced) gene. However, despite the identification of the culprit gene, the cellular roles of TGFBI and the molecular mechanisms underlying the pathogenesis of corneal dystrophy remain poorly understood. Here we report the identification of periostin, a molecule that is highly related to TGFBI, as a specific TGFBI-binding partner. The association of TGFBI and periostin is mediated by the amino-terminal cysteine-rich EMI domains of TGFBI and periostin. Our results indicate that the endogenous TGFBI and periostin colocalize within the trans-Golgi network and associate prior to secretion. The corneal dystrophy-associated R124H mutation in TGFBI severely impairs interaction with periostin in vivo. In addition, the R124H mutation causes aberrant redistribution of the mutant TGFBI into lysosomes. We also find that the periostin-TGFBI interaction is disrupted in corneal fibroblasts cultured from granular corneal dystrophy type II patients and that periostin accumulates in TGFBI-positive corneal deposits in granular corneal dystrophy type II (also known as Avellino corneal dystrophy). Together, our findings suggest that TGFBI and periostin may play cooperative cellular roles and that periostin may be involved in the pathogenesis of 5q31-linked corneal dystrophies.

The IC3D classification of the corneal dystrophies

BACKGROUND

The recent availability of genetic analyses has demonstrated the shortcomings of the current phenotypic method of corneal dystrophy classification. Abnormalities in different genes can cause a single phenotype, whereas different defects in a single gene can cause different phenotypes. Some disorders termed corneal dystrophies do not appear to have a genetic basis.

PURPOSE

The purpose of this study was to develop a new classification system for corneal dystrophies, integrating up-to-date information on phenotypic description, pathologic examination, and genetic analysis.

METHODS

The International Committee for Classification of Corneal Dystrophies (IC3D) was created to devise a current and accurate nomenclature.

RESULTS

This anatomic classification continues to organize dystrophies according to the level chiefly affected. Each dystrophy has a template summarizing genetic, clinical, and pathologic information. A category number from 1 through 4 is assigned, reflecting the level of evidence supporting the existence of a given dystrophy. The most defined dystrophies belong to category 1 (a well-defined corneal dystrophy in which a gene has been mapped and identified and specific mutations are known) and the least defined belong to category 4 (a suspected dystrophy where the clinical and genetic evidence is not yet convincing). The nomenclature may be updated over time as new information regarding the dystrophies becomes available.

CONCLUSIONS

The IC3D Classification of Corneal Dystrophies is a new classification system that incorporates many aspects of the traditional definitions of corneal dystrophies with new genetic, clinical, and pathologic information. Standardized templates provide key information that includes a level of evidence for there being a corneal dystrophy. The system is user-friendly and upgradeable and can be retrieved on the website www.corneasociety.org/ic3d.

Evidence for a novel x-linked modifier locus for leber hereditary optic neuropathy

Leber Hereditary Optic Neuropathy (LHON) is a maternally inherited blinding disease caused by missense mutations in the mitochondrial DNA (mtDNA). However, incomplete penetrance and a predominance of male patients presenting with vision loss suggest that modifying factors play an important role in the development of the disease. Evidence from several studies suggests that both nuclear modifier genes and environmental factors may be necessary to trigger the optic neuropathy in individuals harboring an LHON-causing mtDNA mutation. Recently, an optic neuropathy susceptibility locus at Xp21-Xq21 has been reported. In this study, we performed X-chromosomal linkage analysis in a large Brazilian family harboring a homoplasmic G11778A mtDNA mutation on a haplogroup J background. We report the identification of a novel LHON susceptibility locus on chromosome Xq25-27.2, with multipoint non-parametric linkage scores of > 5.00 (P = 0.005) and a maximum two-point non-parametric linkage score of 10.12, (P = 0.003) for marker DXS984 (Xq27.1). These results suggest genetic heterogeneity for X-linked modifiers of LHON.

Mutation screening of TGFBI in two Iranian Avellino corneal dystrophy pedigrees

PURPOSE

Genetic analysis and phenotypic features of Avellino corneal dystrophy patients from Japan and some European countries have been published. We report for the first time the genetic analysis and phenotypic features of two Avellino corneal dystrophy pedigrees from the Middle East.

METHODS

Slit-lamp biomicroscope photographs of cornea were obtained, and corneal tissue sections were stained with masson-trichrome and Congo red. DNA was isolated from peripheral blood leucocytes and exons 4 and 12 of TGFBI were screened for mutations by direct sequencing.

RESULTS

The probands of the pedigrees had phenotypic features consistent with diagnosis of Avellino corneal dystrophy. They were homozygous for the same R124H mutation in TGFBI as previously reported in Avellino patients from Japan and European countries. Heterozygous carriers of the mutation were identified in the pedigree and shown to have symptoms of disease milder than those of the probands.

CONCLUSION

The finding of R124H in the Middle Eastern (Iranian) population supports the proposal that perhaps only substitution of histidine for arginine at position 124 of tumour growth factor beta induced protein results in the Avellino corneal dystrophy phenotype. As both probands were originally diagnosed with granular corneal dystrophy, and as heterozygous carriers of R124H were unaware of their disease status prior to genetic analysis, the importance of genetic analysis is emphasized.

Deep Anterior Lamellar Keratoplasty in Korean Patients With Avellino Dystrophy

PURPOSE

To evaluate the surgical outcome of deep anterior lamellar keratoplasty (DALK) in Korean patients with Avellino dystrophy.

METHODS

A retrospective study was performed in 4 eyes (4 patients) with recurrent Avellino dystrophy after phototherapeutic keratectomy (PTK). Genetic study was performed on 2 patients to confirm the diagnosis. Partial-thickness donor cornea (devoid of endothelium and Descemet membrane) was transplanted onto a recipient bed after deep lamellar dissection and removal of recipient stroma. Visual acuity, refractive error, keratometry values, topographic astigmatism, and complications were evaluated after a follow-up period of at least 14 months.

RESULTS

The mean age of the patients was 52.5 +/- 3.32 years, and the mean follow-up period was 17.5 +/- 3.11 months. Visual acuity was improved to > or = 20/25 in all cases. Postoperative topographic astigmatism ranged from 1.2 to 4.9 D. In 1 case, double anterior chamber developed after the operation, which resolved after gas injection into the anterior chamber. During the follow-up period, there were no signs of graft rejection, and all grafts were transparent except one, in which small opacity recurred in the peripheral corneal stroma 13 months postoperatively.

CONCLUSIONS

DALK is considered a good primary surgical option in patients with recurrent Avellino dystrophy after PTK.

Genetics of corneal dystrophies: the evolving landscape

PURPOSE OF REVIEW

Major advances and developments in corneal molecular genetics have revolutionized our fundamental understanding of corneal dystrophies. At the same time, this knowledge is allowing for improved ways to classify these dystrophies. New genes and mutations responsible for corneal dystrophies are being discovered at an accelerating rate. Ophthalmologists must keep abreast of all the new information, as our basic understanding as well as our classification systems are changing. We present a current review of the genetics of corneal dystrophies.

RECENT FINDINGS

After the discovery of the BIGH3 (TGFbeta1) gene responsible for several corneal dystrophies, there has been an explosion of new information. New mutations are discovered every day for many of the corneal dystrophies located on the BIGH3 gene. In addition, new genetic sites are also being realized. Additionally, corneal dystrophies which have never been linked to any genetic site are now beginning to be uncovered.

SUMMARY

As new mutations and genetic sites are discovered for the various corneal dystrophies, new information will arise, allowing researches to develop innovative methods to study these gene products and their function. This will open the door for novel diagnostic and therapeutic approaches. Ultimately, gene therapy may be possible, leading to cures for these sight-threatening diseases.

TGFBI gene mutations in corneal dystrophies

The lattice corneal dystrophies (LCD) and granular corneal dystrophies (GCD) are autosomal dominant disorders of the corneal stroma. They are bilateral, progressive conditions characterized by the formation of opacities arising due to the deposition of insoluble material in the corneal stroma leading to visual impairment. The LCDs and GCDs are distinguished from each other and are divided into subtypes on the basis of the clinical appearance of the opacities, clinical features of the disease, and on histopathological staining properties of the deposits. The GCDs and most types of LCD arise from mutations in the transforming growth factor beta-induced (TGFBI) gene on chromosome 5q31. Over 30 mutations causing LCD and GCD have been identified so far in the TGFBI. There are two mutation hotspots corresponding to arginine residues at positions 124 and 555 of the transforming growth factor beta induced protein (TGFBIp) and they are the most frequent sites of mutation in various populations. Mutations at either of these two hotspots result in specific types of LCD or GCD. The majority of identified mutations involve residues in the fourth fasciclin-like domain of TGFBIp.

Exacerbation of Avellino corneal dystrophy after LASIK in North America

PURPOSE

To report the first case of Avellino corneal dystrophy exacerbation after LASIK in a white or North American patient.

METHODS

Case report and literature review.

RESULTS

A 25-year-old white female developed progressive corneal opacities after LASIK. Preoperative examination had revealed only subtle white corneal opacities in each eye. The patient's mother had similar corneal opacities. DNA analysis of the patient revealed a heterozygous mutation at the R124H location in the BIGH3 gene.

CONCLUSIONS

LASIK can exacerbate Avellino corneal dystrophy and should be avoided in patients with this condition. A careful history and genetic analysis can identify affected patients and those at risk.

TGFBI gene mutations in Brazilian patients with corneal dystrophy

PURPOSE

To investigate the transforming growth factor beta-induced gene (TGFBI) mutations in Brazilian patients with corneal dystrophy and to evaluate the phenotype-genotype correlation in these patients.

METHODS

A total of 11 unrelated families were studied. The diagnosis of corneal dystrophy was based on clinical and histopathological findings. Genomic DNA was extracted from peripheral blood leucocytes, and exons 4 and 12 of the TGFBIgene were amplified by polymerase chain reaction followed by direct sequencing on both strands.

RESULTS

Five different mutations in the TGFBIgene were found in the probands. We identified the following mutations: lattice corneal dystrophy--R124C and A546T; Reis-Bücklers corneal dystrophy--R555Q and R124L; granular corneal dystrophy--R555W and Avellino dystrophy--R555W. In three of the 11 studied families there was no mutation in exons 4 and 12.

CONCLUSIONS

This is the first report of mutations in the TGFBIgene in a series of Brazilian patients with corneal dystrophy. The findings indicate that TGFBIgene screening should be considered in the diagnosis of corneal dystrophy.

A clinical and molecular genetic study of autosomal-dominant stromal corneal dystrophy in British population

AIMS

To identify the underlying mutations in our British families and sporadic patients with different types of corneal dystrophies (CDs) and to establish a phenotype-genotype correlation.

METHODS

Twenty-nine patients, 9 sporadic and 20 patients from 7 families were subjected to both clinical and genetic examination. Slit lamp examination was performed for all patients who participated in the study to assess their corneal phenotype. Genomic DNA was extracted from 10 ml venous blood, and the BIGH3 gene was amplified exon by exon to perform heteroduplex analysis. Exons that displayed double bands were then analysed by direct bi-directional sequencing and restriction digest analyses.

RESULTS

Clinically our patients showed three distinct phenotypes of CD: 16 with Thiel-Behnke corneal dystrophy or corneal dystrophy of Bowman layer type 2 (CDB2), 8 with granular CD (GCD), and 5 with lattice CD type I (LCDI). Three different missense mutations have been detected in the coding region of BIGH3 gene, R555Q, in 16 CDB2 patients, R555W in 8 GCD patients, and R124C in 5 LCDI patients. These mutations were the same as to those previously reported in patients from other ethnic origins. Also,we identified seven nucleotide substitutions that did not change the amino acid sequence of the encoded protein of which four were novel.

CONCLUSIONS

In our patients of British origin, each phenotype of CD has been linked to a particular point mutation of the BIGH3 gene. Our study also highlights the importance of codons 124 and 555 as mutation hot spots in the BIGH3 gene in the British population.