A COL17A1 Splice-Altering Mutation Is Prevalent in Inherited Recurrent Corneal Erosions

Epithelial recurrent erosion dystrophy (ERED) from the splice site altering COL17A1 variant c.3156C>T in families of Finnish-Swedish ancestry

PURPOSE

To describe four Finnish families with epithelial recurrent erosion dystrophy (ERED) caused by the pathogenic variant c.3156C>T in collagen type XVII alpha 1 chain gene (COL17A1).

METHODS

Eleven affected and two unaffected individuals underwent clinical ophthalmological examination, anterior segment photography, and corneal topography. Two of them underwent phototherapeutic keratectomy (PTK). Genetic analysis included both next-generation and Sanger sequencing. Specimens from the manual keratectomy of one patient were available for ophthalmic pathologic examination, including immunohistochemistry.

RESULTS

The common splice-site altering synonymous variant c.3156C > T, p.(Gly1052=) in COL17A1 was confirmed in 15 individuals with ERED from the four families. Subepithelial corneal scarring grades varied and increased with age, leading to decreased best-corrected visual acuity. PTK improved vision in 58- and 67-year-old individuals without reactivating the disease. The keratectomy specimens showed an uneven epithelium and a spectrum of basement membrane abnormalities, including breaks, fragmentation, multiplication and entrapment within the subepithelial scar, reflecting recurrent erosions. The stromal cells consisted of varying proportions of bland and activated fibroblasts and myofibroblasts, reflecting different ages of scars. The family with the largest number of known affected generations originated from Southern Sweden.

CONCLUSION

The phenotype in the Finnish ERED families is consistent with earlier reports of the c.3156C > T variant, although the severity has varied between reports. The phenotype may be modulated by other genes. This study suggests a likely founder effect of the variant in both Finnish and Swedish populations due to their shared population histories. If vision is compromised, PTK can be considered especially in older patients.

IC3D Classification of Corneal Dystrophies-Edition 3

PURPOSE

The International Committee for the Classification of Corneal Dystrophies (IC3D) was created in 2005 to develop a new classification system integrating current information on phenotype, histopathology, and genetic analysis. This update is the third edition of the IC3D nomenclature.

METHODS

Peer-reviewed publications from 2014 to 2023 were evaluated. The new information was used to update the anatomic classification and each of the 22 standardized templates including the level of evidence for being a corneal dystrophy [from category 1 (most evidence) to category 4 (least evidence)].

RESULTS

Epithelial recurrent erosion dystrophies now include epithelial recurrent erosion dystrophy, category 1 ( COL17A1 mutations, chromosome 10). Signs and symptoms are similar to Franceschetti corneal dystrophy, dystrophia Smolandiensis, and dystrophia Helsinglandica, category 4. Lisch epithelial corneal dystrophy, previously reported as X-linked, has been discovered to be autosomal dominant ( MCOLN1 mutations, chromosome 19). Classic lattice corneal dystrophy (LCD) results from TGFBI R124C mutation. The LCD variant group has over 80 dystrophies with non-R124C TGFBI mutations, amyloid deposition, and often similar phenotypes to classic LCD. We propose a new nomenclature for specific LCD pathogenic variants by appending the mutation using 1-letter amino acid abbreviations to LCD. Pre-Descemet corneal dystrophies include category 1, autosomal dominant, punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD) ( PRDX3 mutations, chromosome 10). Typically asymptomatic, it can be distinguished phenotypically from pre-Descemet corneal dystrophy, category 4. We include a corneal dystrophy management table.

CONCLUSIONS

The IC3D third edition provides a current summary of corneal dystrophy information. The article is available online at https://corneasociety.org/publications/ic3d .

Novel Manifestation of Corneal Dystrophy After Keratorefractive Surgery

PURPOSE

This study aimed to report cases of bilateral corneal Bowman layer deposits in 4 patients with a history of keratorefractive surgery. To our knowledge, this condition has not previously been reported and should be distinguished from granular corneal dystrophy type 2 and other corneal dystrophies.

METHODS

We reviewed all available medical records that were collected between January 2010 and December 2021 at a tertiary referral center and performed whole-exome sequencing to provide diagnostic information.

RESULTS

Four patients exhibited similar bilateral corneal deposits that were observed more than 10 years after keratorefractive surgery. The patients' ages ranged from 36 to 53 years; 3 of the 4 patients were female. Three patients received laser in situ keratomileusis surgery, and 1 received radial keratotomy. All 4 patients denied having a family history of ocular diseases and reported an uneventful postoperative course. On examination, the best-corrected visual acuity ranged from 6/10 to 6/6 in all 4 patients. Slit-lamp examination revealed bilateral superficial corneal deposits involving the central cornea, and anterior segment optical coherence tomography revealed hyperreflective deposits located in the Bowman layer. Such unique manifestations suggested corneal dystrophy; thus, whole-exome sequencing was performed on all 4 patients. Only 1 patient exhibited a missense mutation in TGFBI . We further analyzed common de novo mutations to explore possible candidate genes associated with this presentation.

CONCLUSIONS

We report a rare entity of presumed corneal dystrophy with deposits located in the Bowman layer in 4 patients who had received keratorefractive surgery. Clarifying the underlying pathophysiology and genetic predisposition of this disease may aid in diagnosing and preventing potential complications after keratorefractive surgery.

Heterozygous COL17A1 variants are a frequent cause of amelogenesis imperfecta

BACKGROUND

Collagen XVII is most typically associated with human disease when biallelic COL17A1 variants (>230) cause junctional epidermolysis bullosa (JEB), a rare, genetically heterogeneous, mucocutaneous blistering disease with amelogenesis imperfecta (AI), a developmental enamel defect. Despite recognition that heterozygous carriers in JEB families can have AI, and that heterozygous COL17A1 variants also cause dominant corneal epithelial recurrent erosion dystrophy (ERED), the importance of heterozygous COL17A1 variants causing dominant non-syndromic AI is not widely recognised.

METHODS

Probands from an AI cohort were screened by single molecule molecular inversion probes or targeted hybridisation capture (both a custom panel and whole exome sequencing) for COL17A1 variants. Patient phenotypes were assessed by clinical examination and analyses of affected teeth.

RESULTS

Nineteen unrelated probands with isolated AI (no co-segregating features) had 17 heterozygous, potentially pathogenic COL17A1 variants, including missense, premature termination codons, frameshift and splice site variants in both the endo-domains and the ecto-domains of the protein. The AI phenotype was consistent with enamel of near normal thickness and variable focal hypoplasia with surface irregularities including pitting.

CONCLUSION

These results indicate that COL17A1 variants are a frequent cause of dominantly inherited non-syndromic AI. Comparison of variants implicated in AI and JEB identifies similarities in type and distribution, with five identified in both conditions, one of which may also cause ERED. Increased availability of genetic testing means that more individuals will receive reports of heterozygous COL17A1 variants. We propose that patients with isolated AI or ERED, due to COL17A1 variants, should be considered as potential carriers for JEB and counselled accordingly, reflecting the importance of multidisciplinary care.

Recessive COL17A1 Mutations and a Dominant LAMB3 Mutation Cause Hypoplastic Amelogenesis Imperfecta

Hereditary conditions that affect tooth enamel in quantity and/or quality are called amelogenesis imperfecta (AI). AI can occur as an isolated condition or as a symptom of a syndrome. An OMIM search with the term "AI" yielded 79 result entries. Mutations in the same gene cause syndromic or non-syndromic AI, depending on the nature of the mutations. In this study, we recruited two AI families and performed mutational analysis using whole-exome sequencing. The proband of family 1, with hypoplastic pitted AI and mild localized atopic dermatitis, had compound heterozygous COL17A1 mutations (paternal NM_000494.4: c.3598G>T, p.Asp1200Tyr and maternal c.1700G>A, p.Gly567Glu). The proband of family 2, with hypoplastic pitted AI and Jervell and Lange-Nielsen syndrome, had a recurrent LAMB3 mutation (NM_000228.3: c.3463_3475del, p.(Glu1155Thrfs*51)) in addition to compound heterozygous mutations in the KCNQ1 gene.

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.

Immune Cells Localize to Sites of Corneal Erosions in C57BL/6 Mice

Recurrent epithelial erosions develop in the cornea due to prior injury or genetic predisposition. Studies of recurrent erosions in animal models allow us to gain insight into how erosions form and are resolved. While slowing corneal epithelial cell migration and reducing their proliferation following treatment with mitomycin C reduce erosion formation in mice after sterile debridement injury, additional factors have been identified related to cytokine expression and immune cell activation. The relationship between recruitment of immune cells to the region of the cornea where erosions form and their potential roles in erosion formation and/or erosion repair remains unexplored in the C57BL/6 mouse recurrent erosion model. Here, high resolution imaging of mouse corneas was performed at D1, D7, and D28 after dulled-blade debridement injury in C57BL/6 mice. Around 50% of these mice have frank corneal erosions at D28 after wounding. A detailed assessment of corneas revealed the involvement of M2 macrophages in both frank and developing erosions at early stages of their formation.

An Overview towards Zebrafish Larvae as a Model for Ocular Diseases

Despite the obvious morphological differences in the visual system, zebrafish share a similar architecture and components of the same embryonic origin as humans. The zebrafish retina has the same layered structure and cell types with similar metabolic and phototransduction support as humans, and is functional 72 h after fertilization, allowing tests of visual function to be performed. The zebrafish genomic database supports genetic mapping studies as well as gene editing, both of which are useful in the ophthalmological field. It is possible to model ocular disorders in zebrafish, as well as inherited retinal diseases or congenital or acquired malformations. Several approaches allow the evaluation of local pathological processes derived from systemic disorders, such as chemical exposure to produce retinal hypoxia or glucose exposure to produce hyperglycemia, mimicking retinopathy of prematurity or diabetic retinopathy, respectively. The pathogenesis of ocular infections, autoimmune diseases, or aging can also be assessed in zebrafish larvae, and the preserved cellular and molecular immune mechanisms can be assessed. Finally, the zebrafish model for the study of the pathologies of the visual system complements certain deficiencies in experimental models of mammals since the regeneration of the zebrafish retina is a valuable tool for the study of degenerative processes and the discovery of new drugs and therapies.

Effect of Polydeoxyribonucleotide (PDRN) Treatment on Corneal Wound Healing in Zebrafish (Danio rerio)

This study aimed to develop a corneal epithelial injury model in zebrafish (Danio rerio) and investigate the effectiveness of polydeoxyribonucleotide (PDRN) treatment on in vivo corneal epithelial regeneration and wound healing. Chemical injury to zebrafish cornea was produced by placing a small cotton swab containing 3% acetic acid solution. PDRN treatment was performed by immersing corneal-injured zebrafish in water containing PDRN (2 mg/mL) for 10 min at 0, 24, 48, and 72 h post-injury (hpi). The level of corneal healing was evaluated by fluorescein staining, histological examination, transcriptional profiling, and immunoblotting techniques. Fluorescein staining results demonstrate that PDRN treatment significantly (p < 0.05) reduced the wounded area of the zebrafish eye at 48 and 72 hpi, suggesting that PDRN may accelerate the corneal re-epithelialization. Histopathological evaluation revealed that injured corneal epithelial cells were re-organized at 72 hpi upon PDRN treatment with increased goblet cell density and size. Moreover, transcriptional analysis results demonstrate that PDRN treatment induced the mRNA expression of adora2ab (6.3-fold), pax6a (7.8-fold), pax6b (29.3-fold), klf4 (7.3-fold), and muc2.1 (5.0-fold) after the first treatment. Besides, tnf-α (2.0-fold) and heat-shock proteins (hsp70; 2.8-fold and hsp90ab1; 1.6-fold) have modulated the gene expression following the PDRN treatment. Immunoblotting results convincingly confirmed the modulation of Mmp-9, Hsp70, and Tnf-α expression levels upon PDRN treatment. Overall, our corneal injury model in zebrafish allows for understanding the morphological and molecular events of corneal epithelial healing, and ophthalmic responses for PDRN treatment following acid injury in zebrafish.

Corneal Epithelial Regeneration: Old and New Perspectives

Corneal blindness is the fifth leading cause of blindness worldwide, and therapeutic options are still often limited to corneal transplantation. The corneal epithelium has a strong barrier function, and regeneration is highly dependent on limbal stem cell proliferation and basement membrane remodeling. As a result of the lack of corneal donor tissues, regenerative medicine for corneal diseases affecting the epithelium is an area with quite advanced basic and clinical research. Surgery still plays a prominent role in the treatment of epithelial diseases; indeed, innovative surgical techniques have been developed to transplant corneal and non-corneal stem cells onto diseased corneas for epithelial regeneration applications. The main goal of applying regenerative medicine to clinical practice is to restore function by providing viable cells based on the use of a novel therapeutic approach to generate biological substitutes and improve tissue functions. Interest in corneal epithelium rehabilitation medicine is rapidly growing, given the exposure of the corneal outer layers to external insults. Here, we performed a review of basic, clinical and surgical research reports on regenerative medicine for corneal epithelial disorders, classifying therapeutic approaches according to their macro- or microscopic target, i.e., into cellular or subcellular therapies, respectively.

Diagnostic yield of candidate genes in an Australian corneal dystrophy cohort

Corneal dystrophies describe a clinically and genetically heterogeneous group of inherited disorders. The International Classification of Corneal Dystrophies (IC3D) lists 22 types of corneal dystrophy, 17 of which have been demonstrated to result from pathogenic variants in 19 identified genes. In this study, we investigated the diagnostic yield of genetic testing in a well‐characterised cohort of 58 individuals from 44 families with different types of corneal dystrophy. Individuals diagnosed solely with Fuchs endothelial corneal dystrophy were excluded. Clinical details were obtained from the treating ophthalmologist. Participants and their family members were tested using a gene candidate and exome sequencing approach. We identified a likely molecular diagnosis in 70.5% families (31/44). The detection rate was significantly higher among probands with a family history of corneal dystrophy (15/16, 93.8%) than those without (16/28, 57.1%, p = .015), and among those who had undergone corneal graft surgery (9/9, 100.0%) compared to those who had not (22/35, 62.9%, p = .041). We identified eight novel variants in five genes and identified five families with syndromes associated with corneal dystrophies. Our findings highlight the genetic heterogeneity of corneal dystrophies and the clinical utility of genetic testing in reaching an accurate clinical diagnosis.

Code inside the codon: The role of synonymous mutations in regulating splicing machinery and its impact on disease

In eukaryotes, precise pre-mRNA processing, including alternative splicing, is essential to carry out the intricate protein translation process. Both point mutations (that alter the translated protein sequence) and synonymous mutations (that do not alter the translated protein sequence) are capable of affecting the splicing process. Synonymous mutations are known to affect gene expression via altering mRNA stability, mRNA secondary structure, splicing processes, and translational kinetics. In higher eukaryotes, precise splicing is regulated by three weakly conserved cis-elements, 5' and 3' splice sites and the branch site. Many other cis-acting elements (exonic/intronic splicing enhancers and silencers) and trans-acting splicing factors (serine and arginine-rich proteins and heterogeneous nuclear ribonucleoproteins) have also been found to enhance or suppress the splicing process. The appearance of synonymous mutations in cis-acting elements can alter the splicing process by changing the binding pattern of splicing factors to exonic splicing enhancers or silencer motifs. This results in exon skipping, intron retention, and various other forms of alternative splicing, eventually leading to the emergence of a wide range of diseases. The focus of this review is to elucidate the role of synonymous mutations and their impact on abnormal splicing mechanisms. Further, this study highlights the function of synonymous mutation in mediating abnormal splicing in cancer and development of X-linked, and autosomal inherited diseases.

Regulation of p53 and Cancer Signaling by Heat Shock Protein 40/J-Domain Protein Family Members

Heat shock proteins (HSPs) are molecular chaperones that assist diverse cellular activities including protein folding, intracellular transportation, assembly or disassembly of protein complexes, and stabilization or degradation of misfolded or aggregated proteins. HSP40, also known as J-domain proteins (JDPs), is the largest family with over fifty members and contains highly conserved J domains responsible for binding to HSP70 and stimulation of the ATPase activity as a co-chaperone. Tumor suppressor p53 (p53), the most frequently mutated gene in human cancers, is one of the proteins that functionally interact with HSP40/JDPs. The majority of p53 mutations are missense mutations, resulting in acquirement of unexpected oncogenic activities, referred to as gain of function (GOF), in addition to loss of the tumor suppressive function. Moreover, stability and levels of wild-type p53 (wtp53) and mutant p53 (mutp53) are crucial for their tumor suppressive and oncogenic activities, respectively. However, the regulatory mechanisms of wtp53 and mutp53 are not fully understood. Accumulating reports demonstrate regulation of wtp53 and mutp53 levels and/or activities by HSP40/JDPs. Here, we summarize updated knowledge related to the link of HSP40/JDPs with p53 and cancer signaling to improve our understanding of the regulation of tumor suppressive wtp53 and oncogenic mutp53 GOF activities.

Zebrafish Model in Ophthalmology to Study Disease Mechanism and Drug Discovery

Visual impairment and blindness are common and seriously affect people’s work and quality of life in the world. Therefore, the effective therapies for eye diseases are of high priority. Zebrafish (Danio rerio) is an alternative vertebrate model as a useful tool for the mechanism elucidation and drug discovery of various eye disorders, such as cataracts, glaucoma, diabetic retinopathy, age-related macular degeneration, photoreceptor degeneration, etc. The genetic and embryonic accessibility of zebrafish in combination with a behavioral assessment of visual function has made it a very popular model in ophthalmology. Zebrafish has also been widely used in ocular drug discovery, such as the screening of new anti-angiogenic compounds or neuroprotective drugs, and the oculotoxicity test. In this review, we summarized the applications of zebrafish as the models of eye disorders to study disease mechanism and investigate novel drug treatments.

Fxr signaling and microbial metabolism of bile salts in the zebrafish intestine

Bile salt synthesis, secretion into the intestinal lumen, and resorption in the ileum occur in all vertebrate classes. In mammals, bile salt composition is determined by host and microbial enzymes, affecting signaling through the bile salt-binding transcription factor farnesoid X receptor (Fxr). However, these processes in other vertebrate classes remain poorly understood. We show that key components of hepatic bile salt synthesis and ileal transport pathways are conserved and under control of Fxr in zebrafish. Zebrafish bile salts consist primarily of a C27 bile alcohol and a C24 bile acid that undergo multiple microbial modifications including bile acid deconjugation that augments Fxr activity. Using single-cell RNA sequencing, we provide a cellular atlas of the zebrafish intestinal epithelium and uncover roles for Fxr in transcriptional and differentiation programs in ileal and other cell types. These results establish zebrafish as a nonmammalian vertebrate model for studying bile salt metabolism and Fxr signaling.

A Novel Phenotype of Junctional Epidermolysis Bullosa with Transient Skin Fragility and Predominant Ocular Involvement Responsive to Human Amniotic Membrane Eyedrops

Junctional epidermolysis bullosa (JEB) is a clinically and genetically heterogeneous skin fragility disorder frequently caused by mutations in genes encoding the epithelial laminin isoform, laminin-332. JEB patients also present mucosal involvement, including painful corneal lesions. Recurrent corneal abrasions may lead to corneal opacities and visual impairment. Current treatments are merely supportive. We report a novel JEB phenotype distinguished by the complete resolution of skin fragility in infancy and persistent ocular involvement with unremitting and painful corneal abrasions. Biallelic LAMB3 mutations c.3052-5C>G and c.3492_3493delCG were identified as the molecular basis for this phenotype, with one mutation being a hypomorphic splice variant that allows residual wild-type laminin-332 production. The reduced laminin-332 level was associated with impaired keratinocyte adhesion. Then, we also investigated the therapeutic power of a human amniotic membrane (AM) eyedrop preparation for corneal lesions. AM were isolated from placenta donors, according to a procedure preserving the AM biological characteristics as a tissue, and confirmed to contain laminin-332. We found that AM eyedrop preparation could restore keratinocyte adhesion in an in vitro assay. Of note, AM eyedrop administration to the patient resulted in long-lasting remission of her ocular manifestations. Our findings suggest that AM eyedrops could represent an effective, non-invasive, simple-to-handle treatment for corneal lesions in patients with JEB and possibly other EB forms.

Challenges and strategies for the delivery of biologics to the cornea

Biologics, like peptides, proteins and nucleic acids, have proven to be promising drugs for the treatment of numerous diseases. However, besides the off label use of the monoclonal antibody bevacizumab for the treatment of corneal neovascularization, to date no other biologics for corneal diseases have reached the market. Indeed, delivering biologics in the eye remains a challenge, especially at the level of the cornea. While it appears to be a rather accessible tissue for the administration of drugs, the cornea in fact presents several anatomical barriers to delivery. In addition, also intracellular delivery barriers need to be overcome to achieve a promising therapeutic outcome with biologics. This review outlines efforts that have been reported to successfully deliver biologics into the cornea. Biochemical and physical methods for achieving delivery of biologics in the cornea are discussed, with a critical view on their efficacy in overcoming corneal barriers.

The extracellular matrix as a multitasking player in disease

Extracellular matrices (ECMs) are highly specialized and dynamic three-dimensional (3D) scaffolds into which cells reside in tissues. ECM is composed of a variety of fibrillar components, such as collagens, fibronectin, and elastin, and non-fibrillar molecules as proteoglycans, hyaluronan, and glycoproteins including matricellular proteins. These macromolecular components are interconnected forming complex networks that actively communicate with cells through binding to cell surface receptors and/or matrix effectors. ECMs exert diverse roles, either providing tissues with structural integrity and mechanical properties essential for tissue functions or regulating cell phenotype and functions to maintain tissue homeostasis. ECM molecular composition and structure vary among tissues, and is markedly modified during normal tissue repair as well as during the progression of various diseases. Actually, abnormal ECM remodeling occurring in pathologic circumstances drives disease progression by regulating cell-matrix interactions. The importance of matrix molecules to normal tissue functions is also highlighted by mutations in matrix genes that give rise to genetic disorders with diverse clinical phenotypes. In this review, we present critical and emerging issues related to matrix assembly in tissues and the multitasking roles for ECM in diseases such as osteoarthritis, fibrosis, cancer, and genetic diseases. The mechanisms underlying the various matrix-based diseases are also discussed. Research focused on the highly dynamic 3D ECM networks will help to discover matrix-related causative abnormalities of diseases as well as novel diagnostic tools and therapeutic targets.

Differential Distribution of Laminin N-Terminus α31 Across the Ocular Surface: Implications for Corneal Wound Repair

Purpose

Laminin N-terminus (LaNt) α31 is a relatively unstudied protein derived from the laminin α3 gene but structurally similar to netrins. LaNt α31 has, to date, been investigated only in two-dimensional (2D) keratinocyte culture where it influences cell migration and adhesion, processes integral to wound repair. Here we investigated LaNt α31 distribution in ocular surface epithelium, during limbal stem cell activation, and corneal wound healing.

Methods

Human, mouse, and pig eyes, ex vivo limbal explant cultures, and alkali burn wounds were processed for immunohistochemistry with antibodies against LaNt α31 along with progenitor cell-associated proteins. LaNt α31 expression was induced via adenoviral transduction into primary epithelial cells isolated from limbal explants, and cell spreading and migration were analyzed using live imaging.

Results

LaNt α31 localized to the basal layer of the conjunctival, limbal, and corneal epithelial cells. However, staining was nonuniform with apparent subpopulation enrichment, and some suprabasal reactivity was also noted. This LaNt α31 distribution largely matched that of keratin 15, epidermal growth factor receptor, and transformation-related protein 63α (p63α), and displayed similar increases in expression in activated limbal explants. During active alkali burn wound repair, LaNt α31 displayed increased expression in limbal regions and loss of basal restriction within the cornea. Distribution returned to predominately basal cell restricted once the wounded epithelium matured. Cultured corneal epithelial cells expressing LaNt α31 displayed increased 2D area and reduced migration, suggesting a functional link between this protein and key wound repair activities.

Conclusions

These data place LaNt α31 in position to influence laminin-dependent processes including wound repair and stem cell activation.

Epithelial Recurrent Erosion Dystrophy Secondary to COL17A1 c.3156C>T Mutation in a Non-white Family

PURPOSE

To report the identification of the collagen, type XVII, alpha 1 (COL17A1) c.3156C>T mutation associated with epithelial recurrent erosion dystrophy (ERED) in a Thai family.

METHODS

Slit-lamp examination was performed to determine the affected status of each member of a Thai family, with multiple members demonstrating scattered Bowman layer opacities. After genomic deoxyribonucleic acid (DNA) was isolated from saliva, polymerase chain reaction (PCR) amplification and Sanger sequencing were performed to screen COL17A1 and exons 4 and 12 of the transforming growth factor β-induced gene.

RESULTS

The 67-year-old proband and her 4 siblings were examined by slit-lamp biomicroscopy, which identified bilateral subepithelial opacities in the proband and in one of the 4 siblings. In both the proband and the affected sister, screening of the COL17A1 gene identified a heterozygous c.3156C>T synonymous mutation that has been previously demonstrated to introduce a cryptic splice donor site, likely leading to aberrant splicing of COL17A1. This mutation was not identified in the unaffected siblings, and no mutations were identified in exons 4 and 12 of the transforming growth factor β-induced gene in any of the screened family members.

CONCLUSIONS

ERED associated with a COL17A1 mutation has been previously reported in only 6 families, all white. Identification of the c.3156C>T mutation, previously identified in 5 of these 6 families, in the Thai family we report indicates conservation of the genetic basis of ERED across different races and underscores the importance of ophthalmologists around the globe being familiar with ERED, which has only recently become a recognized corneal dystrophy.

From Structure to Phenotype: Impact of Collagen Alterations on Human Health

The extracellular matrix (ECM) is a highly dynamic and heterogeneous structure that plays multiple roles in living organisms. Its integrity and homeostasis are crucial for normal tissue development and organ physiology. Loss or alteration of ECM components turns towards a disease outcome. In this review, we provide a general overview of ECM components with a special focus on collagens, the most abundant and diverse ECM molecules. We discuss the different functions of the ECM including its impact on cell proliferation, migration and differentiation by highlighting the relevance of the bidirectional cross-talk between the matrix and surrounding cells. By systematically reviewing all the hereditary disorders associated to altered collagen structure or resulting in excessive collagen degradation, we point to the functional relevance of the collagen and therefore of the ECM elements for human health. Moreover, the large overlapping spectrum of clinical features of the collagen-related disorders makes in some cases the patient clinical diagnosis very difficult. A better understanding of ECM complexity and molecular mechanisms regulating the expression and functions of the various ECM elements will be fundamental to fully recognize the different clinical entities.

Whole exome sequencing: Uncovering causal genetic variants for ocular diseases

Identification of causal genetic defects for human diseases took a significant leap when the first generation DNA sequencing technologies enabled biologists extract sequence-based genetic information from living beings. However, these sequencing methods had unavoidable constraints of throughput, scalability, rapidity, and resolution. In this direction, next-generation sequencing (NGS) since the time of its advent has revolutionized the process of gene discovery for both monogenic and multifactorial genetic diseases. Among several variations of NGS, whole exome sequencing (WES) has emerged as a smart strategy that enables identification of disease causing variants present within the coding region of the human genome. The current review focuses primarily on the application of WES in identification of causal variants for ocular diseases. WES has successfully revealed pathogenic variants in a variety of ocular diseases such as retinal degenerations, refractive errors, lens diseases, corneal dystrophies, and developmental ocular defects. It has demonstrated immense potential for molecular diagnosis of genetic ocular diseases. WES has been extensively used in Mendelian and complex cases, familial and sporadic cases, simplex and multiplex cases, and syndromic and non-syndromic cases of ocular diseases. Although many such ocular diseases have been investigated using WES, reports indicate that it has been employed overwhelmingly for heterogeneous retinal degenerations. WES, within a short period of time, has proved to be a cost-effective and promising approach for understanding the genetic basis of ocular diseases.

The nature and biology of basement membranes

Basement membranes are delicate, nanoscale and pliable sheets of extracellular matrices that often act as linings or partitions in organisms. Previously considered as passive scaffolds segregating polarized cells, such as epithelial or endothelial cells, from the underlying mesenchyme, basement membranes have now reached the center stage of biology. They play a multitude of roles from blood filtration to muscle homeostasis, from storing growth factors and cytokines to controlling angiogenesis and tumor growth, from maintaining skin integrity and neuromuscular structure to affecting adipogenesis and fibrosis. Here, we will address developmental, structural and biochemical aspects of basement membranes and discuss some of the pathogenetic mechanisms causing diseases linked to abnormal basement membranes.

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.

Identification of Potentially Pathogenic Variants in the Posterior Polymorphous Corneal Dystrophy 1 Locus

Posterior polymorphous corneal dystrophy 1 (PPCD1) is a genetic disorder that affects corneal endothelial cell function and leads to loss of visual acuity. PPCD1 has been linked to a locus on chromosome 20 in multiple families; however, Sanger sequencing of protein-coding genes in the consensus region failed to identify any causative missense mutations. In this study, custom capture probes were utilized for targeted next-generation sequencing of the linked region in a previously reported family with PPCD1. Variants were detected through two bioinformatics pipelines and filtered according to multiple criteria. Additionally, a high-resolution microarray was used to detect copy number variations. No non-synonymous variants in the protein-coding region of annotated genes were identified. However, 12 single nucleotide variants in 10 genes, and 9 indels in 7 genes met the filtering criteria and were considered candidate variants for PPCD1. Eleven single nucleotide variants were confirmed by Sanger sequencing, including 2 synonymous variants and 9 non-coding variants, in 9 genes. One microdeletion was detected in an intron of OVOL2 by microarray but was subsequently not identified by PCR. Using a comprehensive next-generation sequencing approach, a total of 16 genes containing single nucleotide variants or indels that segregated with the affected phenotype in an affected family previously mapped to the PPCD1 locus were identified. Screening of these candidate genes in other families previously mapped to the PPCD1 locus will likely result in the identification of the genetic basis of PPCD1.

Whole Exome Sequencing and Segregation Analysis Confirms That a Mutation in COL17A1 Is the Cause of Epithelial Recurrent Erosion Dystrophy in a Large Dominant Pedigree Previously Mapped to Chromosome 10q23-q24

PURPOSE

To report identification of a COL17A1 mutation in a family with a corneal dystrophy previously mapped to chromosome 10q23-q24.

METHODS

Whole-exome sequencing was performed on DNA samples from five affected family members and two unrelated, unaffected individuals. Identified variants were filtered for those that were: located in the linked interval on chromosome 10q23-q24; novel or rare (minor allele frequency ≤0.01); heterozygous; present in all affected individuals and not in controls; and present in genes that encode proteins expressed in human corneal epithelial cells (reads per kilobase per million ≥1). Sanger sequencing of identified variants (SNVs) was performed in additional family members. In silico analysis was used to predict the functional impact of non-synonymous variants.

RESULTS

Three SNVs located in two genes were identified that met the filtering criteria: one rare synonymous c.3156C>T variant in the collagen, type XVII, alpha I (COL17A1) gene; and two rare variants, one synonymous and one missense, in the dynamin binding protein (DNMBP) gene. Sanger sequencing of additional family members determined that only the COL17A1 variant segregates with the affected phenotype. In silico analysis predicts that the missense variant in DNMBP would be tolerated.

CONCLUSIONS

The corneal dystrophy mapped to chromosome 10q23-q24 is associated with the c.3156C>T variant in COL17A1. As this variant has recently been identified in five other families with early onset recurrent corneal erosions, and has been shown in vitro to introduce a cryptic splice donor site, this dystrophy is likely caused by aberrant splicing of COL17A1 and should be classified as epithelial recurrent erosion dystrophy.

[SEM visualization of corneal epithelium through lanthanoid staining based on Ca/Nd isomorphous substitution in Ca-dependent molecular systems]

Cumulative biomicroscopic evidence is usually sufficient for the diagnosis of recurrent corneal erosion or bullous keratopathy, however, exploration of the disease pathogenesis requires subcellular-level visualization of corneal structure. In the current study, lanthanoid staining and scanning electron microscopy were employed to visualize quite a number of structures responsible for epithelium organization. In particular, the study proves possible the use of Ca/Nd isomorphous substitution at Ca2+ sites of cytoadherence proteins for visualization of corresponding cellular structures.

AIM

To assess the value of information provided by scanning electron microscopy of corneal epithelium that involves lanthanoid staining based on the Ca/Nd isomorphous substitution in Ca-dependent molecular systems.

MATERIAL AND METHODS

Anterior corneal epithelial scrapes were obtained from patients with recurrent corneal erosion or bullous keratopathy and cadaver eyes with no signs of any ophthalmic disease. Samples were then studied under a scanning electron microscope (Zeiss EVO LS10, BSE, EP - 79 Pa, 20-28 kV, Ln-staining with the BioREE assay kit).

RESULTS

In all cases, lanthanoid staining of biopsy material provided high-contrast SEM images with well-recognizable structural and ultrastructural elements associated with Ca2+ sites of cytoadherence proteins.

CONCLUSION

Lanthanoid staining of biopsy material and subsequent SEM enabled detailed visualization of structural features of the corneal epithelium in various pathologies. Due to the Ca/Nd isomorphism we were able to evaluate structural position of the majority of protein molecules engaged in Ca-dependant processes and, consequently, in cytoadherence. Basing on the neodymium distribution within the basal membrane, we have described local effects of different substances on the lamina densa in the projection of basal layer cell borders that occur after unidirectional ultrafiltration. The results confirm the failure of the junctional adhesion complex in recurrent corneal erosion.