A subset of patients with epithelial basement membrane corneal dystrophy have mutations in TGFBI/BIGH3

Corneal Epithelial Wavefront Error as a Novel Diagnostic Marker for Epithelial Basement Membrane Dystrophy

Synopsis: Corneal epithelial wavefront error and epithelial thickness variance qualify as highly sensitive and specific biomarkers for epithelial basement membrane dystrophy (EBMD). The biomarkers show a normalization after treatment of EBMD with phototherapeutic keratectomy. Purpose: To gauge the diagnostic value of epithelial basement membrane dystrophy (EBMD), a novel spectral-domain optical coherence tomography (SD-OCT)-based imaging modality for simultaneous morphological (thickness profile) and refractive (optical wavefront) assessment of the corneal epithelial layer in one of the most common but often underdiagnosed corneal dystrophies. Methods: In this prospective observational study, a total of 32 eyes of 32 patients diagnosed with EBMD and 32 eyes of 32 healthy control subjects were examined with high-resolution anterior segment SD-OCT (MS-39; CSO, Florence, Italy). Various epithelial thickness and epithelial wavefront-derived terms were compared between groups and receiver operating characteristic (ROC) curves were computed to analyze the diagnostic capacity of the respective parameters. A total of 17 of 32 EBMD patients underwent treatment with phototherapeutic keratectomy (PTK) and were followed up for 3 months. Results: Epithelial thickness variance (60.4 ± 56.7 µm versus 7.6 ± 6.1 µm) and interquartile range (11.0 ± 6.9 versus 3.3 ± 1.9 µm) were markedly elevated in EBMD patients as compared with healthy controls (both with p < 0.001). Epithelial wavefront analysis showed a highly statistically significant excess in all examined aberration terms in EBMD patients (all with p < 0.001). Significantly greater areas under the curve (AUCs) were yielded by the epithelial wavefront-derived parameters (e.g., total epithelial wavefront error: AUC = 0.966; 95% confidence interval (CI) 0.932-1) than by the epithelial thickness-derived parameters (e.g., variance: AUC = 0.919; 95% CI 0.848-0.990). Conclusions: Corneal epithelial wavefront aberrometry proved valuable as an objective biomarker for EBMD, with high sensitivity and specificity. PTK resulted in a reduction of morphological and refractive epithelial irregularities in EBMD.

The Co-Occurrence of 22q11.2 Deletion Syndrome and Epithelial Basement Membrane Dystrophy: A Case Report and Review of the Literature

BACKGROUND

22q11.2 deletion syndrome (22q11.2DS) is a genetic disorder caused by the deletion of the q11.2 band of chromosome 22. It may affect various systems, including the cardiovascular, immunological, gastrointestinal, endocrine, and neurocognitive systems. Additionally, several ocular manifestations have been described.

RESULTS

We report a case of a 34-year-old female diagnosed with 22q11.2DS who presented with visual discomfort and foreign body sensation in both eyes. She had no history of recurrent ocular pain. A comprehensive ophthalmological examination was performed, including anterior segment optical coherence tomography and in vivo confocal microscopy. Overall, the exams revealed bilateral corneal map-like lines, dots, and fingerprint patterns, consistent with a diagnosis of epithelial basement membrane dystrophy (EBMD). In addition to presenting with this novel corneal manifestation for 22q11.2 DS, we review the ocular clinical features of 22q11.2DS in the context of our case.

CONCLUSIONS

The EBMD may represent a new corneal manifestation associated with 22q11.2 syndrome, although the link between these conditions is unknown. Further research is warranted to investigate potentially shared genetic or molecular pathways to the understanding of the phenotypic variety observed among this rare syndrome.

[Intracorneal selective stromal transplantation]

Deep anterior lamellar keratoplasty or penetrating keratoplasty are currently considered the optimal methods of surgical treatment of stromal dystrophies and corneal degeneration. Despite certain advantages and benefits of these methods, they also have significant limitations: involvement of superficial corneal layers in the surgery, need for suturing, development of post-keratoplasty astigmatism etc.

PURPOSE

This study aimed to test and describe the new method of closed sutureless keratoplasty (intracorneal selective stromal transplantation), which was indicated in isolated dystrophic and degenerative pathology of the stroma.

MATERIAL AND METHODS

Intracorneal selective stromal transplantation was performed in a 62-year-old patient with stromal degeneration and intact corneal layers between the altered stroma and the Descemet's membrane posteriorly, and the Bowman's layer anteriorly. The patient also had immature senile cataract. Corneal stroma was removed and replaced with a graft in the optical center of the lens, while the endothelium, the Descemet's membrane and the Bowman's layer remained intact.

RESULTS

The proposed technique of intracorneal selective stromal transplantation makes it possible to replace only the pathologically altered stroma through closed surgical approach, without affecting the anterior and posterior surfaces of the cornea. Best-corrected visual acuity has increased in the patient from 0.01 to 0.6, while mean endothelial cell density has not changed in the course of 24-months follow-up.

CONCLUSION

The proposed keratoplasty method can be used in patients with dystrophy or degeneration of the corneal stroma and preserved endothelial cells, intact Descemet's membrane and Bowman layer. Since the superficial corneal layers are not involved during the surgery, intracorneal selective stromal transplantation combined the advantages of both deep anterior lamellar keratoplasty and endothelial keratoplasty. The biologically favorable result in this first clinical case allows a preliminary conclusion on the technical possibility and functional effectiveness of the proposed method, but further long-term observation and more clinical cases are required.

Anterior Segment Swept Source Optical Coherence Tomography and In Vivo Confocal Microscopy Findings in a Case With Bleb-Like Epithelial Basal Membrane Dystrophy

PURPOSE

The aim of this study was to evaluate the anterior segment swept source optical coherence tomography (SS-OCT) and in vivo confocal microscopy (IVCM) features in a patient with bleb-like epithelial basement membrane dystrophy (EBMD).

METHODS

A 67-year-old man was referred to the hospital for recurrent attacks of severe ocular pain, tearing, and photophobia, typically upon awakening in the right eye. Biomicroscopic examination revealed pebbled glass-like appearance in the corneal epithelium which was remarkable with retroillumination and the patient was suspected to have bleb-like EBMD. The cornea was further evaluated using SS-OCT DRI Triton (Topcon, Tokyo, Japan) and IVCM (Heidelberg Retina Tomograph 3, Rostock Cornea Module).

RESULTS

Using anterior segment SS-OCT, multiple, hyporeflective, round-oval structures within the size range of 30 to 90 μm were observed at the basal epithelial level. IVCM showed circular or oval hyporeflective areas with a diameter ranging from 30 to 140 μm at the level of the basal epithelium in a depth of 35 to 40 μm from the corneal surface and hyperreflective linear structures extending into the corneal epithelium. The corneal stroma was normal, while a few round hyperreflective deposits and guttae were noted at the endothelial cell layer.

CONCLUSIONS

Anterior segment SS-OCT and IVCM can be used in the diagnosis of bleb-like EBMD and are very helpful in differentiating from other epithelial/subepithelial corneal dystrophies and cystic disorders of the corneal epithelium.

Genetic predisposition to ocular surface disorders and opportunities for gene-based therapies

The ocular surface, comprised of the corneal and conjunctival epithelium, innervation system, immune components, and tear-film apparatus, plays a key role in ocular integrity as well as comfort and vision. Gene defects may result in congenital ocular or systemic disorders with prominent ocular surface involvement. Examples include epithelial corneal dystrophies, aniridia, ectrodactyly-ectodermal dysplasia-clefting (EEC) syndrome, xeroderma pigmentosum (XP), and hereditary sensory and autonomic neuropathy. In addition, genetic factors may interact with environmental risk factors in the development of several multifactorial ocular surface disorders (OSDs) such as autoimmune disorders, allergies, neoplasms, and dry eye disease. Advanced gene-based technologies have already been introduced in disease modelling and proof-of-concept gene therapies for monogenic OSDs. For instance, patient-derived induced pluripotent stem cells have been used for modelling aniridia-associated keratopathy (AAK), XP, and EEC syndrome. Moreover, CRISPR/Cas9 genome editing has been used for disease modelling and/or gene therapy for AAK and Meesmann's epithelial corneal dystrophy. A better understanding of the role of genetic factors in OSDs may be helpful in designing personalized disease models and treatment approaches. Gene-based approaches in monogenic OSDs and genetic predisposition to multifactorial OSDs such as immune-mediated disorders and neoplasms with known or possible genetic risk factors has been seldom reviewed. In this narrative review, we discuss the role of genetic factors in monogenic and multifactorial OSDs and potential opportunities for gene therapy.

Maltese Allelic Variants in Corneal Dystrophy Genes in a Worldwide Setting

INTRODUCTION

This study aimed to establish which worldwide population cohorts have a genetic make-up closest to that of a large sample of the Maltese population with regard to corneal dystrophy (CD) genes.

METHODS

Single nucleotide polymorphisms (SNPs) in the Maltese cohort were compared with worldwide cohorts. Fixation index (F_ST) values were calculated to evaluate population differentiation. The genetic prevalence of CD subtypes in worldwide and Maltese cohorts were calculated, and single nucleotide missense mutations present in the Maltese cohort were evaluated for potential pathogenicity.

RESULTS

F_ST values showed that CD-related genes differ substantially among the studied cohorts. F_ST values for each SNP showed greatest differentiation between the Maltese and African cohorts and least differentiation with the Puerto Rican, Mexican, and Colombian cohorts. One TGFBI casual CD mutation, 502V, which causes a Bowman's layer CD/atypical Thiel-Behnke CD was identified in the Maltese cohort. The KRT3 NC_000012.11:g.53186088G>C mutation was potentially deleterious.

CONCLUSION

Identifying populations with least genetic differentiation can facilitate and help guide future diagnostic and treatment strategies for Maltese individuals with CDs in the absence of comparable Maltese data. Analysing the previously unknown CD genetic pool present in a large Maltese cohort adds to the global genetic bank that researchers rely on for medical progress.

Torin 1 alleviates impairment of TFEB-mediated lysosomal biogenesis and autophagy in TGFBI (p.G623_H626del)-linked Thiel-Behnke corneal dystrophy

Thiel-Behnke corneal dystrophy (TBCD) is an epithelial-stromal TGFBI dystrophy caused by mutations in the TGFBI (transforming growth factor beta induced) gene, though the underlying mechanisms and pathogenesis of TBCD are still obscure. The study identifies a novel mutation in the TGFBI gene (p.Gly623_His626del) in a TBCD pedigree. Characteristics of the typical vacuole formation, irregular corneal epithelial thickening and thinning, deposition of eosinophilic substances beneath the epithelium, and involvement of the anterior stroma were observed in this pedigree via transmission electron microscopy (TEM) and histological staining. Tgfbi-p.Gly623_Tyr626del mouse models of TBCD were subsequently generated via CRISPR/Cas9 technology, and the above characteristics were further verified via TEM and histological staining. Lysosomal dysfunction and downregulation of differential expression protein CTSD (cathepsin D) were observed using LysoTracker Green DND-26 and proteomic analysis, respectively. Hence, lysosomal dysfunction probably leads to autophagic flux obstruction in TBCD; this was supported by enhanced LC3-II and SQSTM1 levels and decreased CTSD. TFEB (transcription factor EB) was prominently decreased in TBCD corneal fibroblasts and administration of ATP-competitive MTOR inhibitor torin 1 reversed this decline, resulting in the degradation of accumulated mut-TGFBI (mutant TGFBI protein) via the ameliorative lysosomal function and autophagic flux owing to elevated TFEB activity as measured by western blot, confocal microscopy, and flow cytometry. Transfected HEK 293 cells overexpressing human full-length WT-TGFBI and mut-TGFBI were generated to further verify the results obtained in human corneal fibroblasts. Amelioration of lysosome dysfunction may therefore have therapeutic efficacy in the treatment of TBCD.Abbreviations AS-OCT: anterior segment optical coherence tomography; ATP: adenosine triphosphate; Cas9: CRISPR-associated protein 9; CLEAR: coordinated lysosomal expression and regulation; CRISPR: clustered regularly interspaced short palindromic repeats; CTSB: cathepsin B; CTSD: cathepsin D; CTSF: cathepsin F; CTSL: cathepsin L; DNA: deoxyribonucleic acid; ECM: extracellular matrix; Fas1: fasciclin 1; FC: flow cytometry; GAPDH: glyceraldeyde-3-phosphate dehydrogenase; GCD2: granular corneal dystrophy type 2; HE: hematoxylin and eosin; LAMP2: lysosomal-associated membrane protein; MT: mutation type; MTOR: mechanistic target of rapamycin kinase; MTORC1: MTOR complex 1; mut-TGFBI: mutant TGFBI protein; SD: standard deviation; TBCD: Thiel-Behnke corneal dystrophy; TEM: transmission electron microscopy; TFEB: transcription factor EB; TGFBI: transforming growth factor beta induced; WT: wild type.

[Phototherapeutic keratectomy for epithelial basement membrane dystrophy : Impact of excimer laser systems used on the changes of visual acuity, refraction and astigmatism]

BACKGROUND

Excimer laser-assisted phototherapeutic keratectomy (PTK) has become established as the gold standard in treatment of epithelial basement membrane dystrophy (EBMD), commonly also known as map-dot-fingerprint dystrophy (MDF). At the Department of Ophthalmology, Saarland University Medical Center in Homburg/Saar, systems from Zeiss Meditec and Schwind have been used. The outcomes of both were compared in this study.

PATIENTS AND METHODS

The retrospective study included patients who underwent PTK with a diagnosis of MDF between 2007 and 2017. A total of 170 operations were performed using Zeiss Meditec MEL-70 (Carl Zeiss Meditec AG, Jena, Germany) and 98 using a Schwind eye-tech-solutions Amaris 750S laser (Schwind eye-tech-solutions GmbH, Kleinostheim, Germany). Preoperative and postoperative data for visual acuity, refraction and astigmatism as well as curvature data from the Pentacam and endothelial cell count were collected. The follow-up period averaged 8 months.

RESULTS

In both groups visual acuity postoperatively was significantly better (Zeiss: p < 0.001, Schwind p < 0.004). The improvement in the Schwind group was less than in the Zeiss group, which is the reason why there was a significant difference between the laser systems postoperatively (p < 0.017). There were no significant changes regarding the spherical equivalent after PTK. Regarding astigmatism, there was a significant decrease in the Zeiss group (p < 0.042), while it did not change significantly in patients treated with Schwind laser (p < 0.217). Overall, this led to a significant postoperative difference between both laser systems (p < 0.014).

CONCLUSION

The PTK can be recommended as an effective treatment method for patients with EBMD, regardless of the laser systems used. Patients benefit from long relief from recurrences with improved or constant visual acuity and stable refraction.

Kidney organoids recapitulate human basement membrane assembly in health and disease

Basement membranes (BMs) are complex macromolecular networks underlying all continuous layers of cells. Essential components include collagen IV and laminins, which are affected by human genetic variants leading to a range of debilitating conditions including kidney, muscle, and cerebrovascular phenotypes. We investigated the dynamics of BM assembly in human pluripotent stem cell-derived kidney organoids. We resolved their global BM composition and discovered a conserved temporal sequence in BM assembly that paralleled mammalian fetal kidneys. We identified the emergence of key BM isoforms, which were altered by a pathogenic variant in COL4A5. Integrating organoid, fetal, and adult kidney proteomes, we found dynamic regulation of BM composition through development to adulthood, and with single-cell transcriptomic analysis we mapped the cellular origins of BM components. Overall, we define the complex and dynamic nature of kidney organoid BM assembly and provide a platform for understanding its wider relevance in human development and disease.

[Clinical and morphological characteristics of corneal epithelial dystrophy (clinical observations)]

This paper presents clinical observations that can be regarded as degeneration of the basement membrane of the corneal epithelium. Difficulties in identifying such forms of corneal dystrophies, on the one hand, are associated with limitation and polymorphism of the clinical picture, and, on the other hand, with insufficient information content of the basic diagnostic methods (i.e. the methods used during the initial examination). The presented clinical cases allow singling out the alarming and pathognomonic signs of the disease in the diagnostic algorithm. In the first case, attention should be paid to biomicroscopic changes in the superficial layers of the cornea and the optical defects, which can be regarded as a manifestation of an irregularity of corneal refraction. Identification of pathognomonic signs of the disease is possible on the basis of a detailed, close-to-morphological study of the structure of superficial corneal layers using confocal microscopy and optical coherence tomography. At the same time, the localization of the detected changes at the level of epithelial basement membrane and its basal sections is of crucial significance for substantiating the diagnosis. In addition, according to the literature data, recurrent erosions of the cornea of unclear etiology should be attributed to presumptive signs of degenerative changes in the basement membrane of the epithelium.

Genetic Screening Revealed Latent Keratoconus in Asymptomatic Individuals

Purpose

To adopt molecular screening in asymptomatic individuals at high risk of developing keratoconus as a combinative approach to prevent subclinical patients from post-refractive surgery progressive corneal ectasia.

Methods

In this study, 79 Chinese and nine Greek families with keratoconus were recruited, including 91 patients with clinically diagnosed keratoconus as well as their asymptomatic but assumptive high-risk first-degree relatives based on underlying genetic factor. Mutational screening of VSX1, TGFBI, and ZEB1 genes and full clinical assessment including Pentacam Scheimpflug tomography were carried out in these individuals.

Results

Five variants in VSX1 and TGFBI genes were identified in three Chinese families and one Greek family, and four of them were novel ones. Surprisingly, ultra-early corneal changes in Belin/Ambrosio Enhanced Ectasia Display of Pentacam corneal topography together with co-segregated variants were revealed in the relatives who had no self-reported symptoms.

Conclusions

Variants of VSX1 and TGFBI genes identified in both the clinically diagnosed and subclinical patients may cause the keratoconus through an autosomal dominant inheritance pattern, with different variable expressivity. Combining genetic with Belin/AmbrosioEnhanced Ectasia Display can be used to identify patients with latent keratoconus. This study indicates that genetic testing may play an important supplementary role in re-classifying the disease manifestation and evaluating the preoperative examination of refractive surgery.

Laser refractive surgery in corneal dystrophies

Twenty-eight case reports and case series published between 2000 and 2019 concerning laser refractive surgery in patients with corneal dystrophies, resulting in 173 eyes from 94 patients, were included in this systematic review. Best results were achieved in posterior corneal polymorphous and Cogan dystrophy. Unfavorable results were found in Avellino dystrophy and Fuchs endothelial corneal dystrophy (FECD). Photorefractive keratectomy was not indicated in Meesmann and Avellino dystrophy. Laser in situ keratomileusis was indicated in posterior polymorphous corneal dystrophy but not in FECD, Avellino, or Cogan dystrophy. Small-incision lenticule extraction and other dystrophies such as lattice, fleck, Lisch, or François did not achieve enough scientific evidence to report any recommendation.

Cascade of interactions between candidate genes reveals convergent mechanisms in keratoconus disease pathogenesis

Keratoconus is a progressive thinning, steepening and distortion of the cornea which can lead to loss of vision if left untreated. Keratoconus has a complex multifactorial etiology, with genetic and environmental components contributing to the disease pathophysiology. Studies have observed high concordance between monozygotic twins, discordance between dizygotic twins, and high familial segregation indicating the presence of a very strong genetic component in the pathogenesis of keratoconus. The use of genome-wide linkage studies on families and twins, genome-wide association studies (GWAS) on case-controls, next-generation sequencing (NGS)-based genomic screens on both familial and non-familial cohorts have led to the identification of keratoconus candidate genes with much greater success and increased resproducibility of genetic findings. This review focuses on candidate genes identified till date and attempts to understand their role in biological processes underlying keratoconus pathogenesis. In addition, using these genes I propose molecular pathways that could contribute to keratoconus pathogenesis. The pathways identified the presence of direct cross-talk between known candidate genes of keratoconus and remarkably, 28 known candidate genes have a direct relationship among themselves that involves direct protein-protein binding, regulatory activities such as activation and inhibition, chaperone, transcriptional activation/co-activation, and enzyme catalysis. This review attempts to describe these relationships and cross-talks in the context of keratoconus pathogenesis.

A pathogenic variant in the transforming growth factor beta I (TGFBI) in four Iranian extended families segregating granular corneal dystrophy type II: A literature review

OBJECTIVES

Granular and lattice corneal dystrophies (GCDs & LCDs) are autosomal dominant inherited disorders of the cornea. Due to genetic heterogeneity and large genes, unraveling the mutation is challenging.

MATERIALS AND METHODS

Patients underwent comprehensive clinical examination, and targeted next-generation sequencing (NGS) was used for mutation detection. Co-segregation and in silico analysis was accomplished.

RESULTS

Patients suffered from GCD. NGS disclosed a known pathogenic variant, c.371G>A (p.R124H), in exon 4 of TGFBI. The variant co-segregated with the phenotype in the family. Homozygous patients manifested with more severe phenotypes. Variable expressivity was observed among heterozygous patients.

CONCLUSION

The results, in accordance with previous studies, indicate that the c.371G>A in TGFBI is associated with GCD. Some phenotypic variations are related to factors such as modifier genes, reduced penetrance and environmental effects.

TGF-β1 enhanced myocardial differentiation through inhibition of the Wnt/β-catenin pathway with rat BMSCs

OBJECTIVES

To investigate and test the hypotheses that TGF-β1 enhanced myocardial differentiation through Wnt/β-catenin pathway with rat bone marrow mesenchymal stem cells (BMSCs).

MATERIALS AND METHODS

Lentiviral vectors carrying the TGF-β1 gene were transduced into rat BMSCs firstly. Then several kinds of experimental methods were used to elucidate the related mechanisms by which TGF-β1 adjusts myocardial differentiation in rat BMSCs.

RESULTS

Immunocytochemistry revealed that cTnI and Cx43 expressed positively in the cells that were transduced with TGF-β1. The results of Western blot (WB) test showed that the levels of intranuclear β-catenin and total β-catenin were all significantly decreased. However, the cytoplasmic β-catenin level was largely unchanged. Moreover, the levels of GSK-3β were largely unchanged in BMSCs, whereas phosphorylated GSK-3β was significantly decreased in BMSCs. When given the activator of Wnt/β-catenin pathway (lithium chloride, LiCl) to BMSCs transducted with TGF-β1, β-catenin was increased, while phosphorylated β-catenin was decreased. In addition, cyclinD1, MMP-7, and c-Myc protein in BMSCs transducted with Lenti-TGF-β1-GFP were significantly lower.

CONCLUSION

These results indicate that TGF-β1 promotes BMSCs cardiomyogenic differentiation by promoting the phosphorylation of β-catenin and inhibiting cyclinD1, MMP-7, and c-Myc expression in Wnt/β-catenin signaling pathway.

Corneal dystrophies

Corneal dystrophies are broadly defined as inherited disorders that affect any layer of the cornea and are usually progressive, bilateral conditions that do not have systemic effects. The 2015 International Classification of Corneal Dystrophies classifies corneal dystrophies into four classes: epithelial and subepithelial dystrophies, epithelial-stromal TGFBI dystrophies, stromal dystrophies and endothelial dystrophies. Whereas some corneal dystrophies may result in few or mild symptoms and morbidity throughout a patient's lifetime, others may progress and eventually result in substantial visual and ocular disturbances that require medical or surgical intervention. Corneal transplantation, either with full-thickness or partial-thickness donor tissue, may be indicated for patients with advanced corneal dystrophies. Although corneal transplantation techniques have improved considerably over the past two decades, these surgeries are still associated with postoperative risks of disease recurrence, graft failure and other complications that may result in blindness. In addition, a global shortage of cadaveric corneal graft tissue critically limits accessibility to corneal transplantation in some parts of the world. Ongoing advances in gene therapy, regenerative therapy and cell augmentation therapy may eventually result in the development of alternative, novel treatments for corneal dystrophies, which may substantially improve the quality of life of patients with these disorders.

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.

The Oculome Panel Test: Next-Generation Sequencing to Diagnose a Diverse Range of Genetic Developmental Eye Disorders

PURPOSE

To develop a comprehensive next-generation sequencing panel assay that screens genes known to cause developmental eye disorders and inherited eye disease and to evaluate its diagnostic yield in a pediatric cohort with malformations of the globe, anterior segment anomalies, childhood glaucoma, or a combination thereof.

DESIGN

Evaluation of diagnostic test.

PARTICIPANTS

Two hundred seventy-seven children, 0 to 16 years of age, diagnosed with nonsyndromic or syndromic developmental eye defects without a genetic diagnosis.

METHODS

We developed a new oculome panel using a custom-designed Agilent SureSelect QXT target capture method (Agilent Technologies, Santa Clara, CA) to capture and perform parallel high-throughput sequencing analysis of 429 genes associated with eye disorders. Bidirectional Sanger sequencing confirmed suspected pathogenic variants.

MAIN OUTCOME MEASURES

Collated clinical details and oculome molecular genetic results.

RESULTS

The oculome design covers 429 known eye disease genes; these are subdivided into 5 overlapping virtual subpanels for anterior segment developmental anomalies including glaucoma (ASDA; 59 genes), microphthalmia-anophthalmia-coloboma (MAC; 86 genes), congenital cataracts and lens-associated conditions (70 genes), retinal dystrophies (RET; 235 genes), and albinism (15 genes), as well as additional genes implicated in optic atrophy and complex strabismus (10 genes). Panel development and testing included analyzing 277 clinical samples and 3 positive control samples using Illumina sequencing platforms; more than 30× read depth was achieved for 99.5% of the targeted 1.77-Mb region. Bioinformatics analysis performed using a pipeline based on Freebayes and ExomeDepth to identify coding sequence and copy number variants, respectively, resulted in a definitive diagnosis in 68 of 277 samples, with variability in diagnostic yield between phenotypic subgroups: MAC, 8.2% (8 of 98 cases solved); ASDA, 24.8% (28 of 113 cases solved); other or syndromic, 37.5% (3 of 8 cases solved); RET, 42.8% (21 of 49 cases solved); and congenital cataracts and lens-associated conditions, 88.9% (8 of 9 cases solved).

CONCLUSIONS

The oculome test diagnoses a comprehensive range of genetic conditions affecting the development of the eye, potentially replacing protracted and costly multidisciplinary assessments and allowing for faster targeted management. The oculome enabled molecular diagnosis of a significant number of cases in our sample cohort of varied ocular birth defects.

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.

[Corneal dystrophies]

The article reviews modern clinical, morphological, and genetic aspects of corneal dystrophies based on the most recent international classification updated in 2015. Corneal dystrophies is a group of slow progressing, non-inflammatory corneal pathologies, most of which are characterized by variability of the associated traits. The existence of such pathologies makes important their differential diagnosis from acute inflammatory processes of various etiology, which require urgent therapy. Conservative treatment suitable for dystrophies is usually associated with disorders of the anterior corneal surface and employ symptomatic tactic (lubricants, epithelizing agents, soft contact lenses). No effective etiopathogenetically targeted treatment is currently known. In cases with significant visual acuity decrease, it is possible to perform phototherapeutic keratectomy, abrasive polishing of Bowman's membrane with diamond bur and various types of keratoplasty depending on the depth of involvement.

Genetic testing for corneal dystrophies and other corneal Mendelian diseases

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of the genetic test for corneal dystrophies and other Mendelian corneal diseases (CDs). CDs are mostly inherited in an autosomal dominant manner (autosomal recessive inheritance is rare). The overall prevalence is currently unknown. CDs are caused by mutations in the AGBL1, CHST6, COL8A2, DCN, GSN, KRT12, KRT3, NLRP1, PAX6, PIKFYVE, PRDM5, SLC4A11, TACSTD2, TCF4, TGFBI, UBIAD1, VSX1, ZEB1, and ZNF469 genes. Clinical diagnosis is based on clinical findings, ophthalmological examination, confocal microscopy and slit-lamp biomicroscopy. The genetic test is useful for confirming diagnosis and for differential diagnosis, couple risk assessment and access to clinical trials.

Structural and Functional Implications of Human Transforming Growth Factor β-Induced Protein, TGFBIp, in Corneal Dystrophies

A major cause of visual impairment, corneal dystrophies result from accumulation of protein deposits in the cornea. One of the proteins involved is transforming growth factor β-induced protein (TGFBIp), an extracellular matrix component that interacts with integrins but also produces corneal deposits when mutated. Human TGFBIp is a multi-domain 683-residue protein, which contains one CROPT domain and four FAS1 domains. Its structure spans ∼120 Å and reveals that vicinal domains FAS1-1/FAS1-2 and FAS1-3/FAS1-4 tightly interact in an equivalent manner. The FAS1 domains are sandwiches of two orthogonal four-stranded β sheets decorated with two three-helix insertions. The N-terminal FAS1 dimer forms a compact moiety with the structurally novel CROPT domain, which is a five-stranded all-β cysteine-knot solely found in TGFBIp and periostin. The overall TGFBIp architecture discloses regions for integrin binding and that most dystrophic mutations cluster at both molecule ends, within domains FAS1-1 and FAS1-4.

The Genetics and Pathophysiology of IC3D Category 1 Corneal Dystrophies: A Review

Corneal dystrophies are a group of inherited disorders affecting the cornea, many of which lead to visual impairment. The International Committee for Classification of Corneal Dystrophies has established criteria to clarify the status of the various corneal dystrophies, which include the knowledge of the underlying genetics. In this review, we discuss the International Committee for Classification of Corneal Dystrophies category 1 (second edition) corneal dystrophies, for which a clear genetic link has been established. We highlight the various mechanisms underlying corneal dystrophy pathology, including structural disorganization, instability or maladhesion, aberrant protein stability and deposition, abnormal cellular proliferation or apoptosis, and dysfunction of normal enzymatic processes. Understanding these genetic mechanisms is essential for designing targets for therapeutic intervention, especially in the age of gene therapy and gene editing.

Strategies for Gene Mapping in Inherited Ophthalmic Diseases

Gene mapping of inherited ophthalmic diseases such as congenital cataracts, retinal degeneration, glaucoma, age-related macular degeneration, myopia, optic atrophy, and eye malformations has shed more light on the disease pathology, identified targets for research on therapeutics, earlier detection, and treatment options for disease management and patient care. This article details the different approaches to gene identification for both Mendelian and complex eye disorders.

Uncovering the profile of mutations of transforming growth factor beta-induced gene in Chinese corneal dystrophy patients

AIM

To uncover the mutations profile of transforming growth factor beta-induced (TGFBI) gene in Chinese corneal dystrophy patients and further investigate the characteristics of genotype-phenotype correlations.

METHODS

Forty-two subjects (6 unrelated families including 15 patients and 8 unaffected members, and 19 sporadic patients) of Chinese origin were subjected to phenotypic and genotypic characterization. The corneal phenotypes of patients were documented by slit lamp photography. Mutation screening of the coding regions of TGFBI was performed by direct sequencing.

RESULTS

We detected four corneal dystrophy types. The most frequent phenotypes were granular corneal dystrophy (GCD) (including 3 families and 8 sporadic patients) and lattice corneal dystrophy (LCD) (including 2 families and 9 sporadic patients). The next phenotypes were corneal dystrophy of Bowman layer (CDB) (1 family and 1 sporadic patient) and epithelial basement membrane dystrophy (EBMD) (1 sporadic patient). Six distinct mutations responsible for TGFBI corneal dystrophies were identified in 30 individuals with corneal dystrophies. Those were, p.R124H mutation in 1 family and 2 sporadic patients with GCD, p.R555W mutation in 2 families and 3 sporadic patients with GCD, p.R124C mutation in 2 families and 7 sporadic patients with LCD, p.A620D mutation in 1 sporadic patient with LCD, p.H626R mutation in 1 sporadic patient with LCD, and p.R555Q in 1 family and 1 sporadic patient with CDB. No mutation was detected in the remaining 3 atypical GCD patients and 1 EBMD patient.

CONCLUSION

GCD and LCD are the most frequent phenotypes in Chinese population. R555W was the most common mutation for GCD; R124C was the most common mutation for LCD. Our findings extend the mutational spectrum of TFGBI, and this is the extensively delineated TGFBI mutation profile associated with the various corneal dystrophies in the Chinese population.

Fourier-domain optical coherence tomography imaging in corneal epithelial basement membrane dystrophy: a structural analysis

PURPOSE

To investigate the features of corneal epithelial basement membrane dystrophy using spectral-domain optical coherence tomography (SD OCT) and to examine the reliability of SD OCT in distinguishing epithelial basement membrane dystrophy from the normal cornea.

DESIGN

Diagnostic test study.

METHODS

Forty-five individuals with epithelial basement membrane dystrophy and 45 age- and sex-matched controls with normal corneas were examined, and SD OCT scans of their corneas were performed. In vivo confocal microscopy was performed to confirm or rule out the diagnosis of epithelial basement membrane dystrophy. The structural corneal changes occurring in eyes with epithelial basement membrane dystrophy based on SD OCT findings were described.

RESULTS

Epithelial abnormalities were observed in 86 of 87 eyes with epithelial basement membrane dystrophy (45 patients) on SD OCT scans. The 2 main features were the presence of an irregular and thickened epithelial basement membrane duplicating or insinuating into the corneal epithelium layer, or both, and the presence of hyperreflective dots. In some cases, we detected hyporeflective spaces between the corneal epithelial layer and the Bowman layer similar to a corneal epithelial detachment. This corneal epithelial detachment sometimes was associated with a cleavage with a stair-step appearance within the corneal epithelial layer. We found a perfect correlation between in vivo confocal microscopy and SD OCT findings in the diagnosis of epithelial basement membrane dystrophy (κ = 0.98).

CONCLUSIONS

SD OCT provides an accurate assessment of the structural changes occurring in eyes with epithelial basement membrane dystrophy. These changes, visible on SD OCT scans, are easily detectable and permit an accurate diagnosis, especially in patients with no biomicroscopically visible corneal changes.

First identification of a triple corneal dystrophy association: keratoconus, epithelial basement membrane corneal dystrophy and fuchs' endothelial corneal dystrophy

Purpose

To report the observation of a triple corneal dystrophy association consisting of keratoconus (KC), epithelial basement membrane corneal dystrophy (EBMCD) and Fuchs’ endothelial corneal dystrophy (FECD).

Methods

A 55-year-old male patient was referred to our cornea service for blurred vision and recurrent foreign body sensation. He reported bilateral recurrent corneal erosions with diurnal visual fluctuations. He underwent corneal biomicroscopy, Scheimpflug tomography, in vivo HRT confocal laser scanning microscopy and genetic testing for TGFBI and ZEB1 mutations using direct DNA sequencing.

Results

Biomicroscopic examination revealed the presence of subepithelial central and paracentral corneal opacities. The endothelium showed a bilateral flecked appearance, and the posterior corneal curvature suggested a possible concomitant ectatic disorder. Corneal tomography confirmed the presence of a stage II KC in both eyes. In vivo confocal laser scanning microscopy revealed a concomitant bilateral EBMCD with hyperreflective deposits in basal epithelial cells, subbasal Bowman's layer microfolds and ridges with truncated subbasal nerves as pseudodendritic elements. Stromal analysis revealed honeycomb edematous areas, and the endothelium showed a strawberry surface configuration typical of FECD. The genetic analysis resulted negative for TGFBI mutations and positive for a heterozygous mutation in exon 7 of the gene ZEB1.

Conclusion

This is the first case reported in the literature in which KC, EBMCD and FECD are present in the same patient and associated with ZEB1 gene mutation. The triple association was previously established by means of morphological analysis of the cornea using corneal Scheimpflug tomography and in vivo HRT II confocal laser scanning microscopy.

Allele-specific siRNA silencing for the common keratin 12 founder mutation in Meesmann epithelial corneal dystrophy

PURPOSE

To identify an allele-specific short interfering RNA (siRNA), against the common KRT12 mutation Arg135Thr in Meesmann epithelial corneal dystrophy (MECD) as a personalized approach to treatment.

METHODS

siRNAs against the K12 Arg135Thr mutation were evaluated using a dual luciferase reporter gene assay and the most potent and specific siRNAs were further screened by Western blot. Off-target effects on related keratins were assessed and immunological stimulation of TLR3 was evaluated by RT-PCR. A modified 5' rapid amplification of cDNA ends method was used to confirm siRNA-mediated mutant knockdown. Allele discrimination was confirmed by quantitative infrared immunoblotting.

RESULTS

The lead siRNA, with an IC(50) of thirty picomolar, showed no keratin off-target effects or activation of TLR3 in the concentration ranges tested. We confirmed siRNA-mediated knockdown by the presence of K12 mRNA fragments cleaved at the predicted site. A dual tag infrared immunoblot showed knockdown to be allele-specific, with 70% to 80% silencing of the mutant protein.

CONCLUSIONS

A potent allele-specific siRNA against the K12 Arg135Thr mutation was identified. In combination with efficient eyedrop formulation delivery, this would represent a personalized medicine approach, aimed at preventing the pathology associated with MECD and other ocular surface pathologies with dominant-negative or gain-of-function pathomechanisms.

Franceschetti hereditary recurrent corneal erosion

PURPOSE

To describe new affected individuals of Franceschetti's original pedigree of hereditary recurrent erosion and to classify a unique entity called Franceschetti corneal dystrophy.

DESIGN

Observational case series.

METHODS

Slit-lamp examination of 10 affected individuals was conducted. Biomicroscopic examinations were supplemented by peripheral corneal biopsy in 1 affected patient with corneal haze. Tissue was processed for light and electron microscopy and immunohistochemistry was performed. DNA analysis was carried out in 12 affected and 3 nonaffected family members.

RESULTS

All affected individuals suffered from severe ocular pain in the first decade of life, attributable to recurrent corneal erosions. Six adult patients developed bilateral diffuse subepithelial opacifications in the central and paracentral cornea. The remaining 4 affected individuals had clear corneas in the pain-free stage of the disorder. Histologic and immunohistochemical examination of the peripheral cornea in a single patient showed a subepithelial, avascular pannus. There was negative staining with Congo red. DNA analysis excluded mutations in the transforming growth factor beta-induced (TGFBI) gene and in the tumor-associated calcium signal transducer 2 (TACSTD2) gene.

CONCLUSION

We have extended the pedigree of Franceschetti corneal dystrophy and elaborated its natural history on the basis of clinical examinations. A distinctive feature is the appearance of subepithelial opacities in adult life, accompanied by a decreased frequency of recurrent erosion attacks. Its clinical features appear to distinguish it from most other forms of dominantly inherited recurrent corneal erosion reported in the literature.

Development of allele-specific therapeutic siRNA in Meesmann epithelial corneal dystrophy

Background

Meesmann epithelial corneal dystrophy (MECD) is an inherited eye disorder caused by dominant-negative mutations in either keratins K3 or K12, leading to mechanical fragility of the anterior corneal epithelium, the outermost covering of the eye. Typically, patients suffer from lifelong irritation of the eye and/or photophobia but rarely lose visual acuity; however, some individuals are severely affected, with corneal scarring requiring transplant surgery. At present no treatment exists which addresses the underlying pathology of corneal dystrophy. The aim of this study was to design and assess the efficacy and potency of an allele-specific siRNA approach as a future treatment for MECD.

Methods and Findings

We studied a family with a consistently severe phenotype where all affected persons were shown to carry heterozygous missense mutation Leu132Pro in the KRT12 gene. Using a cell-culture assay of keratin filament formation, mutation Leu132Pro was shown to be significantly more disruptive than the most common mutation, Arg135Thr, which is associated with typical, mild MECD. A siRNA sequence walk identified a number of potent inhibitors for the mutant allele, which had no appreciable effect on wild-type K12. The most specific and potent inhibitors were shown to completely block mutant K12 protein expression with negligible effect on wild-type K12 or other closely related keratins. Cells transfected with wild-type K12-EGFP construct show a predominantly normal keratin filament formation with only 5% aggregate formation, while transfection with mutant K12-EGFP construct resulted in a significantly higher percentage of keratin aggregates (41.75%; p<0.001 with 95% confidence limits). The lead siRNA inhibitor significantly rescued the ability to form keratin filaments (74.75% of the cells contained normal keratin filaments; p<0.001 with 95% confidence limits).

Conclusions

This study demonstrates that it is feasible to design highly potent siRNA against mutant alleles with single-nucleotide specificity for future treatment of MECD.

Recurrent corneal erosions and epithelial basement membrane dystrophy

Epithelial basement membrane dystrophy, the most common hereditary anterior corneal dystrophy and considered a "category 1" dystrophy in some cases, encompasses microcystic dystrophy and other conditions affecting the epithelial basement membrane. The management of symptomatic epithelial basement membrane dystrophy includes alleviating blurred vision, treating recurrent corneal erosion, or both. Treatment of distorted vision may be as simple as prescribing lubricating drops and/or ointment, and posttrauma corneal erosion is often a limited problem that disappears over time and does not require laser or surgical treatment. This article describes treatment for more severe cases of corneal erosion, which includes mechanical debridement of the loosened epithelium.

Dystrophia Helsinglandica: a new type of hereditary corneal recurrent erosions with late subepithelial fibrosis

PURPOSE

To describe the phenotype of an autosomal-dominant corneal dystrophy with an early onset of recurrent corneal erosions and development of subepithelial fibrosis in the cornea, and also to exclude genetic linkage to known corneal dystrophies with autosomal-dominant inheritance and clinical resemblance.

METHODS

We describe the medical history and clinical findings in individuals from a seven-generation family with recurrent corneal erosions. A total of 43 individuals were evaluated by ophthalmological examination. Genomic DNA was prepared from peripheral blood and polymorphic microsatellite markers were analysed to study haplotypes surrounding genes causing corneal dystrophies with similar phenotypes.

RESULTS

Erosive symptoms usually lasted for between 1 and 10 days. By the age of 7 almost all of the affected individuals suffered from recurrent corneal erosions. The attacks generally declined in frequency and intensity from the late 20s, but all examined individuals had developed subepithelial fibrosis by the age of 37. The fibrosis generally started in the mid periphery and was followed in some family members by central fibrosis and the development of gelatinous superficial elevations. Only a marginal reduction of visual acuity was seen in a few individuals. The affected individuals did not share haplotypes for genetic microsatellite markers surrounding genes that are known to cause autosomal-dominant corneal dystrophies.

CONCLUSION

We describe a new type of autosomal-dominant corneal disorder with recurrent corneal erosions and subepithelial fibrosis not significantly affecting visual acuity.

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.

A new corneal disease with recurrent erosive episodes and autosomal-dominant inheritance

PURPOSE

The aim of this study was to characterize the phenotype in a large family with autosomal-dominant recurrent corneal erosions, and also to exclude genetic linkage to known autosomal-dominant inherited corneal dystrophies with clinical resemblance.

METHODS

We describe the medical history and clinical findings in patients from a six-generation family with recurrent corneal erosions. A total of 28 individuals were evaluated by ophthalmological examination. Genomic DNA was prepared from peripheral blood and analysed with polymorphic microsatellite markers close to known genes causing autosomal-dominant corneal dystrophies.

RESULTS

The patients had erosive symptoms that usually lasted from 1 to 7 days. The symptoms were described as early as at 8 months of age, and by the age of 5 the majority of the affected individuals suffered from recurrent corneal erosions. The attacks generally declined in frequency and intensity with age, and 52% of the patients developed central keloid-like corneal opacities. Nine patients received corneal grafts, and recurrences were seen in all grafts. The affected patients did not share haplotypes for genetic microsatellite markers surrounding known genes causing autosomal-dominant corneal dystrophies.

CONCLUSION

We describe a new hereditary disease with recurrent corneal erosions. Attacks of symptoms similar to recurrent erosions dominate the phenotype, but half of those affected also developed corneal, keloid-like, central opacities. This disorder was not genetically linked to any clinically resembling corneal dystrophies with autosomal-dominant inheritance.

Density of common complex ocular traits in the aging eye: analysis of secondary traits in genome-wide association studies

Genetic association studies are identifying genetic risks for common complex ocular traits such as age-related macular degeneration (AMD). The subjects used for discovery of these loci have been largely from clinic-based, case-control studies. Typically, only the primary phenotype (e.g., AMD) being studied is systematically documented and other complex traits (e.g., affecting the eye) are largely ignored. The purpose of this study was to characterize these other or secondary complex ocular traits present in the cases and controls of clinic-based studies being used for genetic study of AMD. The records of 100 consecutive new patients (of any diagnosis) age 60 or older for which all traits affecting the eye had been recorded systematically were reviewed. The average patient had 3.5 distinct diagnoses. A subset of 10 complex traits was selected for further study because they were common and could be reliably diagnosed. The density of these 10 complex ocular traits increased by 0.017 log-traits/year (P = 0.03), ranging from a predicted 2.74 at age 60 to 4.45 at age 90. Trait-trait association was observed only between AMD and primary vitreomacular traction (P = 0.0009). Only 1% of subjects age 60 or older had no common complex traits affecting the eye. Extrapolations suggested that a study of 2000 similar subjects would have sufficient power to detect genetic association with an odds ratio of 2.0 or less for 4 of these 10 traits. In conclusion, the high prevalence of complex traits affecting the aging eye and the inherent biases in referral patterns leads to the potential for confounding by undocumented secondary traits within case-control studies. In addition to the primary trait, other common ocular phenotypes should be systematically documented in genetic association studies so that adjustments for potential trait-trait associations and other bias can be made and genetic risk variants identified in secondary analyses.