Clinicopathologic correlation and genetic analysis in a case of posterior polymorphous corneal dystrophy

Variant Landscape of 15 Genes Involved in Corneal Dystrophies: Report of 30 Families and Comprehensive Analysis of the Literature

Corneal dystrophies (CDs) represent a group of inherited diseases characterized by the progressive deposit of abnormal materials in the cornea. This study aimed to describe the variant landscape of 15 genes responsible for CDs based on a cohort of Chinese families and a comparative analysis of literature reports. Families with CDs were recruited from our eye clinic. Their genomic DNA was analyzed using exome sequencing. The detected variants were filtered using multi-step bioinformatics and confirmed using Sanger sequencing. Previously reported variants in the literature were summarized and evaluated based on the gnomAD database and in-house exome data. In 30 of 37 families with CDs, 17 pathogenic or likely pathogenic variants were detected in 4 of the 15 genes, including TGFBI, CHST6, SLC4A11, and ZEB1. A comparative analysis of large datasets revealed that 12 of the 586 reported variants are unlikely causative of CDs in monogenic mode, accounting for 61 of 2933 families in the literature. Of the 15 genes, the gene most frequently implicated in CDs was TGFBI (1823/2902, 62.82% of families), followed by CHST6 (483/2902, 16.64%) and SLC4A11 (201/2902, 6.93%). This study presents, for the first time, the landscape of pathogenic and likely pathogenic variants in the 15 genes responsible for CDs. Awareness of frequently misinterpreted variants, such as c.1501C>A, p.(Pro501Thr) in TGFBI, is crucial in the era of genomic medicine.

Pseudo second anterior lens capsule during post-vitrectomy cataract surgery: A case report

Purpose

To report the unexpected finding of a membrane resembling a second anterior lens capsule during cataract surgery after previous pars plana vitrectomy (PPV) with silicone oil tamponade for retinal detachment.

Observations

A 26-year-old male with a history of two retinal detachment repairs of the right eye over a 5-month period, presented with decreased vision. The first retinal detachment repair was performed with a 23-gauge PPV and the second with a 25-gauge PPV, scleral buckle and placement of silicone oil. Additional ocular history includes bilateral megalocornea, high myopia, and temporal lens coloboma. Upon presentation, slit lamp exam showed migration of silicone oil to the anterior chamber and a nuclear cataract. A decision was made to perform combined silicone oil removal and cataract extraction with intraocular lens (IOL) implant of the right eye. After capsulorrhexis, hydrodissection of the lens was not completed successfully since the presence of a membrane was detected. This membrane was cut, achieving partial completion of the second capsulorrhexis, which was further advanced using a forceps following the contour of the first capsulorrhexis. The cataract was removed without further difficulty and the IOL was placed into the capsular bag with good centration. The membrane was submitted to pathology, and upon microscopic examination was found to represent fibrocellular tissue with some cells expressing PAX8 and cytokeratin AE1/AE3.

Conclusions and importance

This case reports the unusual finding of a membrane that behaved as a second anterior lens capsule intraoperatively and that expressed novel pathology markers. These findings may better prepare ophthalmologists for similar pathologies they may encounter during capsulorrhexis.

Posterior Polymorphous Corneal Dystrophy in a Pediatric Population

PURPOSE

The aim of this study was to evaluate the clinical and topographic features of posterior polymorphous corneal dystrophy (PPCD) in children aged 15 years or younger with a long-term follow-up. Retrospective case series.

METHODS

A retrospective chart review of patients who were diagnosed with PPCD at Boston Children's Hospital from 1999 to 2020 was performed. Data collected included age at the time of diagnosis, slit lamp findings, cycloplegic refraction, best-corrected visual acuity, central corneal thickness, specular microscopy, and corneal topography findings whenever available.

RESULTS

Twenty-seven eyes of 19 patients were included (11 unilateral and 8 bilateral cases). Ten patients were girls (52.6%). Left eye was affected in 14 eyes. The mean age at the time of diagnosis was 8.5 ± 3.3 years, with a mean follow-up of 5.3 years. In unilateral cases, there was a statistically significant difference in the endothelial cell density (P = 0.01), coefficient variation (P = 0.03), and hexagonality (P = 0.01) between the affected and the contralateral unaffected eyes. The mean best-corrected visual acuity at initial presentation was 0.8 ± 0.2 compared with 0.9 ± 0.08 in unaffected eyes (P = 0.04). The mean astigmatism was higher in the affected eye (+1.7 diopters) compared with (+1.00) the unaffected eye (P = 0.07). At initial presentation, 7 of 27 eyes had amblyopia, which resolved, either partially or completely, in 5 eyes after treatment.

CONCLUSIONS

PPCD can present early in children with astigmatism and anisometropic amblyopia. A careful slit lamp examination for children presenting with anisoastigmatism is necessary to diagnose PPCD. Contrary to adults, presentation is often unilateral. Such patients should be followed up regularly with cycloplegic retinoscopy to prevent and treat refractive amblyopia if present.

Corectopia grading: A novel classification system

Objectives: To present and validate the novel grading system for objective classification of corectopia.Subjects and Methods: We evaluated 28 eyes of 28 patients with or without corectopia and validated the grading and classification system for corectopia according to three major criteria: (i) direction, (ii) extent, and (iii) alteration of mydriasis. Intraclass correlation coefficient (ICC) and inter-rater agreement between 7 inexperienced and 1 experienced ophthalmologist against a golden standard (GS) were calculated.Results: The ICC for the 7 inexperienced ophthalmologists regarding the grading of direction and centration of the pupil was 0.83 (95% confidence interval (CI), 0.74 to 0.90; p < .001) and 0.57 (95% CI, 0.43 to 0.72; p < .001), respectively. The inter-rater agreement was the same or almost the same in cases of pupil decentration between the inexperienced, experienced ophthalmologists and the GS (k = 0.82; 95% CI, 0.64-1.00; p < .001). In assessing the direction of pupil displacement, the inter-rater agreement was almost perfect between the inexperienced (k = 0.93; 95% CI, 0.84-1.00; p < .001) and experienced (k = 0.92; 95% CI: 0.82-1.02; p < .001) ophthalmologists and the GS.Conclusion: The first detailed clinical classification is proposed for objective corectopia grading particularly relevant in documenting and assessing progressive disease. It was confirmed to be acceptable for clinical use by inexperienced and experienced ophthalmologists alike.

Common variants in SOX-2 and congenital cataract genes contribute to age-related nuclear cataract

Nuclear cataract is the most common type of age-related cataract and a leading cause of blindness worldwide. Age-related nuclear cataract is heritable (h² = 0.48), but little is known about specific genetic factors underlying this condition. Here we report findings from the largest to date multi-ethnic meta-analysis of genome-wide association studies (discovery cohort N = 14,151 and replication N = 5299) of the International Cataract Genetics Consortium. We confirmed the known genetic association of CRYAA (rs7278468, P = 2.8 × 10⁻¹⁶) with nuclear cataract and identified five new loci associated with this disease: SOX2-OT (rs9842371, P = 1.7 × 10⁻¹⁹), TMPRSS5 (rs4936279, P = 2.5 × 10⁻¹⁰), LINC01412 (rs16823886, P = 1.3 × 10⁻⁹), GLTSCR1 (rs1005911, P = 9.8 × 10⁻⁹), and COMMD1 (rs62149908, P = 1.2 × 10⁻⁸). The results suggest a strong link of age-related nuclear cataract with congenital cataract and eye development genes, and the importance of common genetic variants in maintaining crystalline lens integrity in the aging eye.

Here, the authors report a multi-ethnic genome wide association meta-analysis of 12 studies from the International Cataract Genetics Consortium. They find six new loci associated with age-related nuclear cataract, in addition to replicating the association at CRYAA, and suggest a strong genetic link between age-related nuclear and congenital cataracts.

ZEB1 Represses Neural Differentiation and Cooperates with CTBP2 to Dynamically Regulate Cell Migration during Neocortex Development

Zinc-finger E-box binding homeobox 1 (Zeb1) is a key regulator of epithelial-mesenchymal transition and cancer metastasis. Mutation of ZEB1 is associated with human diseases and defective brain development. Here we show that downregulation of Zeb1 expression in embryonic cortical neural progenitor cells (NPCs) is necessary for proper neuronal differentiation and migration. Overexpression of Zeb1 during neuronal differentiation, when its expression normally declines, blocks NPC lineage progression and disrupts multipolar-to-bipolar transition of differentiating neurons, leading to severe migration defects and subcortical heterotopia bands at postnatal stages. ZEB1 regulates a cohort of genes involved in cell differentiation and migration, including Neurod1 and Pard6b. The interaction between ZEB1 and CTBP2 in the embryonic cerebral cortex is required for ZEB1 to elicit its effect on the multipolar-to-bipolar transition, but not its suppression of Neurod1. These findings provide insights into understanding the complexity of transcriptional regulation during neuronal differentiation.

Transcriptional profiling of corneal stromal cells derived from patients with keratoconus

Keratoconus (KC) is a multi-factorial corneal ectasia with unknown etiology affecting approximately 1:2000 people worldwide. Dysregulated gene expression, using RNA-Seq technology, have been reported in KC corneal tissue. However, the differential expression of genes, in KC corneal stromal cells have been widely ignored. We utilized mRNA-Seq to analyze gene expression in primary human corneal stromal cells derived from five non-Keratoconus healthy (HCF) and four Keratoconus (HKC) donors. Selected genes were further validated using real time PCR (RT-PCR). We have identified 423 differentially expressed genes with 187 down- and 236 up-regulated in KC-affected corneal stromal cells. Gene ontology analysis using WebGestalt indicates the enrichment of genes involved in cell migration, extracellular matrix, adherens junction, and MAPK signaling. Our protein-protein interaction network analysis identified several network seeds, such as EGFR, NEDD4, SNTA1, LGALS3BP, HSPB1, SDC2, MME, and HIF1A. Our work provides an otherwise unknown information on the transcriptional changes in HKCs, and reveals critical mechanisms of the cellular compartment. It also highlights the importance of human-based in vitro studies on a disease that currently lacks strong biomarkers and animal models.

Corneal endothelial cell dysfunction: etiologies and management

A transparent cornea is essential for the formation of a clear image on the retina. The human cornea is arranged into well-organized layers, and each layer plays a significant role in maintaining the transparency and viability of the tissue. The endothelium has both barrier and pump functions, which are important for the maintenance of corneal clarity. Many etiologies, including Fuchs’ endothelial corneal dystrophy, surgical trauma, and congenital hereditary endothelial dystrophy, lead to endothelial cell dysfunction. The main treatment for corneal decompensation is replacement of the abnormal corneal layers with normal donor tissue. Nowadays, the trend is to perform selective endothelial keratoplasty, including Descemet stripping automated endothelial keratoplasty and Descemet’s membrane endothelial keratoplasty, to manage corneal endothelial dysfunction. This selective approach has several advantages over penetrating keratoplasty, including rapid recovery of visual acuity, less likelihood of graft rejection, and better patient satisfaction. However, the global limitation in the supply of donor corneas is becoming an increasing challenge, necessitating alternatives to reduce this demand. Consequently, in vitro expansion of human corneal endothelial cells is evolving as a sustainable choice. This method is intended to prepare corneal endothelial cells in vitro that can be transferred to the eye. Herein, we describe the etiologies and manifestations of human corneal endothelial cell dysfunction. We also summarize the available options for as well as recent developments in the management of corneal endothelial dysfunction.

Spatiotemporally Controlled Ablation of Klf5 Results in Dysregulated Epithelial Homeostasis in Adult Mouse Corneas

Purpose

Corneal epithelial (CE) homeostasis requires coordination between proliferation and differentiation. Here we examine the role of cell proliferation regulator Krüppel-like factor 5 (Klf5) in adult mouse CE homeostasis.

Methods

Klf5 was ablated in a spatiotemporally restricted manner by inducing Cre expression in 8-week-old ternary transgenic Klf5LoxP/LoxP/Krt12rtTA/rtTA/Tet-O-Cre (Klf5Δ/ΔCE) mouse CE by administering doxycycline via chow. Normal chow-fed ternary transgenic siblings served as controls. The control and Klf5Δ/ΔCE corneal (1) histology, (2) cell proliferation, and (3) Klf5-target gene expression were examined using (1) periodic acid Schiff reagent-stained sections, (2) Ki67 expression, and (3) quantitative PCR and immunostaining, respectively. The effect of KLF4, KLF5, and OCT1 on gastrokine-1 (GKN1) promoter activity was determined by transient transfection in human skin keratinocyte NCTC-2544 cells.

Results

Klf5 expression was decreased to 23% of the controls in Klf5Δ/ΔCE corneas, which displayed increased fluorescein uptake, downregulation of tight junction proteins Tjp1 and Gkn1, desmosomal Dsg1a, and basement membrane Lama3 and Lamb1, suggesting defective permeability barrier. In transient transfection assays, KLF5 and OCT1 synergistically stimulated GKN1 promoter activity. Klf5Δ/ΔCE CE displayed significantly fewer cell layers and Ki67+ proliferative cells coupled with significantly decreased cyclin-D1, and elevated phospho(Ser-10) p27/Kip1 expression. Expression of Krt12, E-cadherin, and β-catenin remained unaltered in Klf5Δ/ΔCE corneas.

Conclusions

Klf5 contributes to adult mouse CE homeostasis by promoting (1) permeability barrier function through upregulation of Tjp1, Gkn1, Dsg1a, Lama3, and Lamb1, and (2) basal cell proliferation through upregulation of cyclin-D1 and suppression of phospho(Ser-10) p27/Kip1, without significantly affecting the expression of epithelial markers Krt12, E-cadherin, and β-catenin.

Transcriptomic Profiling of Posterior Polymorphous Corneal Dystrophy

Purpose

To investigate the molecular basis of posterior polymorphous corneal dystrophy (PPCD) by examining the PPCD transcriptome and the effect of decreased ZEB1 expression on corneal endothelial cell (CEnC) gene expression.

Methods

Next-generation RNA sequencing (RNA-seq) analyses of corneal endothelium from two PPCD-affected individuals (one with PPCD3 and one of unknown genetic cause) compared with two age-matched controls, and primary human CEnC (pHCEnC) transfected with siRNA-mediated ZEB1 knockdown. The expression of selected differentially expressed genes was validated by quantitative polymerase chain reaction (qPCR) and/or assessed by in situ hybridization in the corneal endothelium of four independent cases of PPCD (one with PPCD3 and three of unknown genetic cause).

Results

Expression of 16% and 46% of the 104 protein-coding genes specific to ex vivo corneal endothelium was lost in the endothelium of two individuals with PPCD. Thirty-two genes associated with ZEB1 and 3 genes (BMP4, CCND1, ZEB1) associated with OVOL2 were differentially expressed in the same direction in both individuals with PPCD. Immunohistochemistry staining and RNA-seq analyses demonstrated variable expression of type IV collagens in PPCD corneas. Decreasing ZEB1 expression in pHCEnC altered expression of 711 protein-coding genes, many of which are associated with canonical pathways regulating various cellular processes.

Conclusions

Identification of the altered transcriptome in PPCD and in a cell-based model of PPCD provided insight into the molecular alterations characterizing PPCD. Further study of the differentially expressed genes associated with ZEB1 and OVOL2 is expected to identify candidate genes for individuals with PPCD and without a ZEB1 or OVOL2 mutation.

Analysis of SLC4A11, ZEB1, LOXHD1, COL8A2 and TCF4 gene sequences in a multi-generational family with late-onset Fuchs corneal dystrophy

The aim of the present study was to determine the genetic basis of a multi-generational family with late-onset (LO) Fuchs corneal dystrophy (FCD). Five FCD causal genes [solute carrier family 4, sodium borate transporter, member 11 (SLC4A11), zinc finger E-box binding homeobox 1 (ZEB1), lipoxygenase homology domains 1 (LOXHD1), collagen, type VIII, alpha 2 (COL8A2) and transcription factor 4 (TCF4)], previously reported to be implicated in the pathogenesis of FCD, were screened. A total of 27 variants [including 22 known single nucleotide polymorphisms (SNPs) from the Single Nucleotide Polymorphism Database (dbSNP) and 5 variants absent from dbSNP] were detected in this FCD pedigree across the SLC4A11, ZEB1, LOXHD1 and COL8A2 genes as follows: i) 22 known SNPs from dbSNP, including 3 coding (p.R161R, p.S213S and p.T833T) and 11 non-coding variants of SLC4A11, 2 intronic SNPs of ZEB1 from dbSNP (rs220057 and rs220060), 1 intronic SNP of LOXHD1 from dbSNP (rs16939650), and 5 SNPs of COL8A2 from dbSNP (p.A35A, p.R155Q, p.L335L, p.G495G and p.T502M); and ii) 5 variants that have not been previously reported in FCD patients and that are absent from dbSNP were identified across the ZEB1 and LOXHD1 genes; these included 3 continuous indels located at the junction of the 5'-UTR and the adjacent exon 1 of ZEB1 [Indel 1 (c.-86_-53delins gggaggggtggaggcggaggggtGGGGGGGAAGG); Indel 2 (c.-52_-46delinsGGGAGGG); and Indel 3 (c.-45_-42delinsAGGG)], and 2 intronic variants of LOXHD1 (c.5332-126C>T and c.1809+155G>A). Apart from one intronic SNP of SLC4A11 from dbSNP (rs372201212), the pathologic consequence of which is uncertain, and 2 intron variants of LOXHD1 (c.5332-126C>T and c.1809+155G>A); the variants likely represent examples of de novo mutations. Neither of the other 24 variants provided strong evidence of pathogenesis in this FCD pedigree. An analysis of 7 SNPs in TCF4 from dbSNP, which have been associated with LO FCD in different populations, revealed that these 7 SNPs were not associated with FCD in this specific pedigree. A genome‑wide linkage scan to search for linkage to one of the previously described FCD loci or to identify a novel locus for FCD will need to be performed in this FCD pedigree. Our observation, nevertheless, expands the knowledge of the genetic status of patients with FCD.

Heterozygous deletions at the ZEB1 locus verify haploinsufficiency as the mechanism of disease for posterior polymorphous corneal dystrophy type 3

A substantial proportion of patients with posterior polymorphous corneal dystrophy (PPCD) lack a molecular diagnosis. We evaluated 14 unrelated probands who had a clinical diagnosis of PPCD who were previously determined to be negative for mutations in ZEB1 by direct sequencing. A combination of techniques was used including whole-exome sequencing (WES), single-nucleotide polymorphism (SNP) array copy number variation (CNV) analysis, quantitative real-time PCR, and long-range PCR. Segregation of potentially pathogenic changes with disease was confirmed, where possible, in family members. A putative run of homozygosity on chromosome 10 was identified by WES in a three-generation PPCD family, suggestive of a heterozygous deletion. SNP array genotyping followed by long-range PCR and direct sequencing to define the breakpoints confirmed the presence of a large deletion that encompassed multiple genes, including ZEB1. Identification of a heterozygous deletion spanning ZEB1 prompted us to further investigate potential CNVs at this locus in the remaining probands, leading to detection of two additional heterozygous ZEB1 gene deletions. This study demonstrates that ZEB1 mutations account for a larger proportion of PPCD than previously estimated, and supports the hypothesis that haploinsufficiency of ZEB1 is the underlying molecular mechanism of disease for PPCD3.

The OV-TL 12/30 clone of anti-cytokeratin 7 antibody as a new marker of corneal conjunctivalization in patients with limbal stem cell deficiency

PURPOSE

To present cytokeratin (CK)7 (OV-TL 12/30 clone) as a newly identified, reliable marker for distinguishing between the conjunctival and corneal surface epithelia, which will contribute to the precise diagnosis of limbal stem cell deficiency (LSCD).

METHODS

Corneal and conjunctival epithelial imprints from 12 cadaveric bulbi and from 9 patients with clinically diagnosed LSCD were used for CK7 and CK19 immunocytochemistry. Specimens on nitroacetate cellulose filter papers obtained from the patients were stained with a combination of periodic acid-Schiff (PAS) and Gill's modified Papanicolaou stains, to assess the presence of goblet cells (GCs).

RESULTS

CK7 was present in almost all superficial conjunctival epithelial cells from the cadaveric specimens. No immunostaining was observed on the corneal surface. A prominent sharp border of stain was found between the positive conjunctiva and the completely negative epithelium of the central cornea. A more gradual centrifugal decrease in the number of positive cells between the conjunctiva and cornea was observed for CK19. Several CK19-positive cells were detected in the central corneal epithelium. All corneal specimens from affected eyes (unilateral as well as bilateral LSCD patients) revealed strong positivity for CK7, and GCs were present in only 78% of patients.

CONCLUSIONS

In cases in which GCs are severely decreased or are absent from the conjunctival surface, the detection of CK7 (OV-TL 12/30 clone) clearly confirms the overgrowth of the conjunctival epithelium over the cornea. Moreover, CK7 is a more reliable marker for distinguishing between the corneal and conjunctival epithelia compared with CK19.

Recurrence of posterior polymorphous corneal dystrophy is caused by the overgrowth of the original diseased host endothelium

Posterior polymorphous corneal dystrophy (PPCD) is a rare, bilateral autosomal dominant disorder affecting primarily the corneal endothelium and descemet membrane (DM). The aim of this study was to establish the origin of abnormal endothelium in a patient with PPCD exhibiting cornea graft failure after keratoplasty surgery. A sex-mismatched graft obtained from a patient with PPCD who underwent repeat penetrating keratoplasty and the patient's original cornea were investigated. Combined fluorescent immunohistochemistry for cytokeratin (CK) 19 (a marker of aberrant PPCD endothelium) with fluorescence in situ hybridization (FISH) of the sex chromosomes were used in order to characterize the cells on the posterior graft surface. The pathological endothelium of the failed PPCD cornea revealed strong positivity for CK19 using fluorescent immunohistochemistry. In all the CK19-positive cells, both X and Y chromosomes were simultaneously detected using FISH. The results clearly showed the original cells of the patient (XY), within 3.5 years, almost totally overgrown the posterior corneal surface of the graft (XX). Moreover, an abnormal posterior collagenous layer populated by fibroblast-like cells was observed between DM and the endothelium in the failed graft, but its exact origin could not be established due to the low number of cells. Simultaneous detection of CK19 using fluorescent immunohistochemistry together with the detection of gonosomes using FISH was performed for the first time in the cornea and allowed us to prove that the recurrence of PPCD was caused by pathological abnormal proliferation and migration of recipient cells into donor graft.

Variable ocular phenotypes of posterior polymorphous corneal dystrophy caused by mutations in the ZEB1 gene

PURPOSE

To describe the ocular features of 6 Czech and British patients with posterior polymorphous corneal dystrophy (PPCD) caused by mutations in the zinc finger E-box binding homeobox 1 gene (ZEB1).

METHODS

Case note review of 4 individuals with p.E776fs mutation, one with p.Y719X and one with p.F375fs mutation within the ZEB1 gene.

RESULTS

Five individuals exhibited endothelial and Descemet membrane changes consistent with the diagnosis of PPCD. We concluded that one 70-year-old female who had a normal endothelium at both slit lamp and non-contact specular microscopy was a case of non-penetrance. The onset of disease was as early as 3 months after birth. One patient had irregular astigmatism with inferior corneal steepening on videokeratography, but without corneal thinning or other signs of keratoconus. Two others had corneal steepening >49D but with regular astigmatism. Three individuals underwent penetrating keratoplasty (PK) in 1 eye, with one patient treated for secondary glaucoma prior to the PK.

CONCLUSIONS

The phenotype associated with changes in the ZEB1 gene exhibits variable expression and incomplete penetrance and seems to have a low risk for secondary glaucoma or the need for keratoplasty compared to PPCD linked to 20p11.2. There is insufficient data for phenotype correlations with PPCD caused by other genes.

Clinical phenotype of posterior polymorphous corneal dystrophy in a family with a novel ZEB1 mutation

PURPOSE

To describe the clinical phenotype in a family with posterior polymorphous corneal dystrophy (PPCD) and a novel mutation in the ZEB1 gene.

METHODS

 Clinical examination, anterior segment photography, specular microscopy and electrophysiological investigations were performed and quantified. Genomic DNA extracted from peripheral blood was sequenced for ZEB1 exons. Cosegregation of identified mutation with the disease status in the family was confirmed using polymerase chain reaction and restriction fragment length polymorphism.

RESULTS

Ocular examination was performed on five family members from two generations. Three had anomalies of the corneal endothelium that were consistent with PPCD. Endothelial cell counts ranged from 2306 to 2987 mm(2) (ref. 2000-4000 cells/mm(2) ). No evidence of glaucoma or retinal abnormalities was observed. Extraocular abnormalities such as inguinal herniation, hydrocoele and possible bony or connective tissue anomalies were part of the disease spectrum in this family. Mutation analysis revealed a novel change in exon 5 of ZEB1 (c.672delA) that cosegregated with the affected disease status.

CONCLUSION

The detailed clinical features of PPCD associated with a novel ZEB1 mutation are supportive of the previously proposed range of phenotype parameters. Further phenotype-genotype correlations may provide insights into the clinical variability and pathological processes affecting the corneal endothelium, Descemet's membrane, retinal photoreceptor function and extraocular tissues of some patients.

The PPCD1 mouse: characterization of a mouse model for posterior polymorphous corneal dystrophy and identification of a candidate gene

The PPCD1 mouse, a spontaneous mutant that arose in our mouse colony, is characterized by an enlarged anterior chamber resulting from metaplasia of the corneal endothelium and blockage of the iridocorneal angle by epithelialized corneal endothelial cells. The presence of stratified multilayered corneal endothelial cells with abnormal patterns of cytokeratin expression are remarkably similar to those observed in human posterior polymorphous corneal dystrophy (PPCD) and the sporadic condition, iridocorneal endothelial syndrome. Affected eyes exhibit epithelialized corneal endothelial cells, with inappropriate cytokeratin expression and proliferation over the iridocorneal angle and posterior cornea. We have termed this the “mouse PPCD1” phenotype and mapped the mouse locus for this phenotype, designated “Ppcd1”, to a 6.1 Mbp interval on Chromosome 2, which is syntenic to the human Chromosome 20 PPCD1 interval. Inheritance of the mouse PPCD1 phenotype is autosomal dominant, with complete penetrance on the sensitive DBA/2J background and decreased penetrance on the C57BL/6J background. Comparative genome hybridization has identified a hemizygous 78 Kbp duplication in the mapped interval. The endpoints of the duplication are located in positions that disrupt the genes Csrp2bp and 6330439K17Rik and lead to duplication of the pseudogene LOC100043552. Quantitative reverse transcriptase-PCR indicates that expression levels of Csrp2bp and 6330439K17Rik are decreased in eyes of PPCD1 mice. Based on the observations of decreased gene expression levels, association with ZEB1-related pathways, and the report of corneal opacities in Csrp2bp^{tm1a(KOMP)Wtsi} heterozygotes and embryonic lethality in nulls, we postulate that duplication of the 78 Kbp segment leading to haploinsufficiency of Csrp2bp is responsible for the mouse PPCD1 phenotype. Similarly, CSRP2BP haploinsufficiency may lead to human PPCD.

Zipper cell endotheliopathy: a new subset of idiopathic corneal edema

PURPOSE

To report the clinical and histologic findings of a new subset of idiopathic corneal edema: zipper cell endotheliopathy.

DESIGN

Observational case report.

PARTICIPANT

A 55-year-old woman with unilateral bullous keratopathy.

METHODS

Clinical observation consisted of slit-lamp examination and in vivo confocal microscopy (IVCM). Aqueous humor samples and the excised corneal button were analyzed for the presence of herpes viruses. The excised cornea was subjected to detailed immunohistochemistry (IHC) and scanning and transmission electron microscopy.

MAIN OUTCOME MEASURES

Clinical and pathologic characteristics of zipper cell endotheliopathy.

RESULTS

In vivo confocal microscopy revealed unique morphologic alterations of the corneal endothelial layer. Focal areas of denudation were surrounded by endothelial cells with zipper-like cell borders and intercellular structures. Besides central corneal edema, no other signs of corneal inflammation were detected. A herpes virus origin for the bullous keratopathy was excluded. The IHC analysis disclosed positive staining for cytokeratin (CK) 7, CK8/18, and CK19, suggesting epithelial metaplasia of the endothelial cells. Ultrastructural examination confirmed the IVCM findings by showing large areas of endothelial denudation and vacuolated endothelial cells with large, broad-based extensions that partially overlapped neighboring cells. Despite extensive complementary research and review of the literature, the endothelial alterations could not be attributed to any known corneal disorder.

CONCLUSIONS

To the authors' knowledge, zipper cell endotheliopathy is a new subset of idiopathic corneal edema. The case report presented illustrates the potential use of IVCM to differentiate the spectrum of corneal disorders and to discover new corneal diseases.

Zeb1 mutant mice as a model of posterior corneal dystrophy

PURPOSE

The zinc finger transcription factor Zeb1 binds to E-box-like sequences and is important for maintaining repression of epithelial specification genes in vivo. Overexpression of Zeb1 in cancer triggers epithelial-mesenchymal transition, which facilitates metastasis. The mutation of ZEB1 in humans is linked to posterior polymorphous corneal dystrophy (PPCD), in which an epithelial transition of the corneal endothelium is associated with abnormal endothelial proliferation. The purpose of this study is to determine whether Zeb1 null or heterozygous mice may provide an animal model for PPCD.

METHODS

Corneal morphology, protein and mRNA expression, and cell proliferation were compared in wild-type and Zeb1 gene knockout mice by immunostaining, real-time PCR, and BrdU incorporation. mRNA expression in isolated embryo fibroblasts derived from wild-type, Zeb1 heterozygous, and null mice was analyzed by real-time PCR RESULTS: Zeb1 null mice late in gestation show ectopic expression of epithelial genes in the corneal endothelium and keratocytes, including the basement membrane component COL4A3, which is ectopically expressed by the corneal endothelium in PPCD. These embryos also show abnormal corneal endothelial and keratocyte proliferation, corneal thickening, and corneolenticular and iridocorneal adhesions. Adult Zeb1 heterozygous mice exhibit these same corneal defects. The ectopic expression of epithelial genes extended to embryonic fibroblasts derived from Zeb1 heterozygous and null mice, suggesting that Zeb1 may have a more general role in the suppression of an epithelial phenotype.

CONCLUSIONS

The authors conclude that Zeb1 heterozygous and null mice show features of PPCD and thus should provide an animal model for genetic dissection of pathways contributing to the disease.

Mutation in the SLC4A11 gene associated with autosomal recessive congenital hereditary endothelial dystrophy in a large Saudi family

OBJECTIVE

To determine the role of the SLC4A11 gene in two pedigrees affected with autosomal recessive congenital hereditary endothelial dystrophy (CHED).

METHODS

Nine members of a pedigree from the Kingdom of Saudi Arabia (pedigree 971G) and 2 twins in a pedigree from Bosnia (pedigree GGO413) were diagnosed with autosomal recessive CHED and contributed DNA samples for genetic studies. The proband of each pedigree was tested for disease-causing mutations in the SLC4A11 gene with bi-directional DNA sequencing. Screening assays using restriction enzyme digests were developed to test a cohort of 99 normal control subjects for the presence of SLC4A11 mutations.

RESULTS

A novel, homozygous mutation in the SLC4A11 gene (Thr271Met) was detected in the proband of pedigree 971G. Homozygous Thr271Met mutations were detected in all affected members of pedigree 971G. The Thr271Met mutation was not detected in a cohort of 99 normal control subjects. This mutation alters a highly conserved amino acid in the encoded SLC4A11 protein. No SLC4A11 mutations were detected in pedigree GGO413.

CONCLUSION

A novel SLC4A11 mutation (Thr271Met) is associated with autosomal recessive CHED in a pedigree from the Kingdom of Saudi Arabia and provides additional support that mutations in this gene cause disease.

Epithelial metaplasia of the corneal endothelium in Fuchs endothelial dystrophy

PURPOSE

To evaluate the immunohistochemical characteristics of human corneas with the diagnosis of Fuchs endothelial dystrophy (FED).

METHODS

Formalin-fixed, paraffin-embedded sections of corneas with the diagnosis of FED (15 patients) and 10 control corneas were stained with hematoxylin-eosin and periodic acid-Schiff (PAS). Adjacent histologic sections were stained with monoclonal antibodies that react with epithelial antigens: pancytokeratin, cytokeratins (CK) 7 and 20 CAM 5.2, epithelial membrane antigen (EMA), and Ber EP4. Eight corneas were stained with antibodies to vimentin, smooth-muscle actin (SMA), and CD 68.

RESULTS

The endothelial cells in FED were attenuated and atrophic; some contained pigment consistent with melanin. The endothelial cells stained for pancytokeratin, CK 7, and vimentin in all corneas of FED, whereas variable staining was noted with CAM 5.2. No staining of endothelium was noted with CK 20, EMA, BerEP4, SMA, or CD 68.

CONCLUSION

Some cytokeratins that are normally restricted to true epithelium are present in the endothelium of FED. Epithelial metaplasia of endothelium in FED may represent a nonspecific response of distressed endothelial cells, as previously reported in posterior polymorphous dystrophy, congenital hereditary endothelial dystrophy, and iridocorneal endothelial syndrome.

Immunohistochemical characterization of cytokeratins in the abnormal corneal endothelium of posterior polymorphous corneal dystrophy patients

Posterior polymorphous corneal dystrophy (PPCD) is a hereditary bilateral disorder affecting Descemet's membrane and the endothelium. The aim of the present study was to determine the spectrum of cytokeratin (CK) expression in cells on the posterior surface of the cornea in PPCD patients. Ten corneal buttons and one specimen of the trabecular meshwork (TM) from PPCD patients who underwent graft or glaucoma surgery were used, as well as six corneal buttons and two TM specimens obtained from healthy donors as controls. Cryosections were fixed and indirect immunofluorescent staining was performed using antibodies directed against a wide spectrum of cytokeratins (CKs). The number of positive cells and the intensity of the staining were assessed using fluorescent microscopy. All 10 PPCD corneal specimens had areas of endothelium displaying typical endothelial morphology as well as areas consisting of layers two to six cells thick with both flat endothelial-like cells and polygonal cells with round nuclei and a large cytoplasm. Both of these morphologically distinct cell types showed strong immunostaining for CK7, CK19, CK8 and CK18, while weaker positive signals were observed for CK1, CK3/12, CK4, CK5/6, CK10, CK10/13, CK14, CK16 and CK17. PPCD endothelium was completely negative for CK2e, CK9, CK15, and CK20. Focal positivity was detected in PPCD TM for CK4, CK7 and CK19. CK8 and CK18 were the only CKs expressed in control endothelium. PPCD and control epithelium displayed similar staining patterns. The distinct positivity for CK3/12, CK4, CK5/6, CK10/13, CK14, CK16 and CK17 was observed in aberrant PPCD endothelium for the first time. We demonstrate that the abnormal endothelium of PPCD patients expresses a mixture of CKs, with CK7 and CK19 predominating. In terms of CK composition, the aberrant PPCD endothelium shares features of both simple and squamous stratified epithelium with a proliferative capacity. The wide spectrum of CK expression is most probably not indicative of the transformation of endothelial cells to a distinct epithelial phenotype, but more likely reflects the modified differentiation of metaplastic epithelium.

Mutations in TCF8 cause posterior polymorphous corneal dystrophy and ectopic expression of COL4A3 by corneal endothelial cells

Posterior polymorphous corneal dystrophy (PPCD, also known as PPMD) is a rare disease involving metaplasia and overgrowth of corneal endothelial cells. In patients with PPCD, these cells manifest in an epithelial morphology and gene expression pattern, produce an aberrant basement membrane, and, sometimes, spread over the iris and nearby structures in a way that increases the risk for glaucoma. We previously mapped PPCD to a region (PPCD3) on chromosome 10 containing the gene that encodes the two-handed zinc-finger homeodomain transcription factor TCF8. Here, we report a heterozygous frameshift mutation in TCF8 that segregates with PPCD in the family used to map PPCD3 and four different heterozygous nonsense and frameshift mutations in TCF8 in four other PPCD probands. Family reports of inguinal hernia, hydrocele, and possible bone anomalies in affected individuals suggest that individuals with TCF8 mutations should be examined for nonocular anomalies. We detect transcripts of all three identified PPCD genes (VSX1, COL8A2, and TCF8) in the cornea. We show presence of a complex (core plus secondary) binding site for TCF8 in the promoter of Alport syndrome gene COL4A3, which encodes collagen type IV alpha 3, and we present immunohistochemical evidence of ectopic expression of COL4A3 in corneal endothelium of the proband of the original PPCD3 family. Identification of TCF8 as the PPCD3 gene provides a valuable tool for the study of critical gene regulation events in PPCD pathology and suggests a possible role for TCF8 mutations in altered structure and function of cells lining body cavities other than the anterior chamber of the eye. Thus, this study has identified TCF8 as the gene responsible for approximately half of the cases of PPCD, has implicated TCF8 mutations in developmental abnormalities outside the eye, and has presented the TCF8 regulatory target, COL4A3, as a key, shared molecular component of two different diseases, PPCD and Alport syndrome.

Candidate gene screening for posterior polymorphous dystrophy

PURPOSE

To perform candidate gene screening for posterior polymorphous corneal dystrophy (PPCD). The initial 3 genes chosen, ID1, BCL2L1, and VSX1, lie within the region on chromosome 20 to which the PPCD gene has been linked, and mutations in VSX1 have previously been identified in patients with PPCD.

METHODS

DNA extraction, PCR amplification, and direct sequencing of the VSX1, BCL2L1, and ID1 genes were performed in 14 affected patients (12 families) as well as in unaffected family members and healthy control subjects.

RESULTS

No coding region mutations in the BCL2L1 or ID1 genes were identified in affected patients. In the VSX1 gene, the previously identified Gly160Asp missense change was not present in any of our 12 probands, and the Asp144Glu mutation was identified in 1 affected patient as well as 1 unaffected control individual. Additionally, 2 synonymous substitutions were identified, Ala182Ala (8 affected patients from 8 families) and Gly239Gly (1 affected patient and 1 unaffected patient from the same family). In the ID1 gene, the synonymous substitution Gly216Gly was observed in 2 affected patients (2 families) who also demonstrated a single nucleotide change in both the 5'UTR (2129T>C) and 3'UTR (3267A>G). Another 5'UTR change, 2177T>C, was identified in 1 affected patient and his unaffected parent, both of whom also demonstrated the 2129T>C and 3267A>G changes.

CONCLUSIONS

None of the 12 probands with PPCD demonstrated the previously described Gly160Asp mutation within the VSX1 gene. The Asp144Glu missense change, present in an affected patient as well as an unaffected control individual, appears to be a rare polymorphism, not a disease-causing mutation. No coding region changes were identified in the ID1 or BCL2L1 genes. Therefore, although we report a number of novel polymorphisms in the VSX1 and ID1 genes, the failure to identify any sequence variants that sort with the disease phenotype suggests that other genetic factors are involved in PPCD.

A locus for posterior polymorphous corneal dystrophy (PPCD3) maps to chromosome 10

Posterior polymorphous corneal dystrophy (PPCD) is an autosomal dominant disorder characterized by corneal endothelial abnormalities, which can lead to blindness due to loss of corneal transparency and sometimes glaucoma. We mapped a new locus responsible for PPCD in a family in which we excluded the previously reported PPCD locus on 20q11, and the region containing COL8A2 on chromosome 1. Results of a 317-marker genome scan provided significant evidence of linkage of PPCD to markers on chromosome 10, with single-point LOD scores of 2.63, 1.63, and 3.19 for markers D10S208 (at (circumflex)theta = 0.03), D10S1780 (at (circumflex)theta = 0.00), and D10S578 (at (circumflex)theta = 0.06). A maximum multi-point LOD score of 4.35 was found at marker D10S1780. Affected family members shared a haplotype in an 8.55 cM critical interval that was bounded by markers D10S213 and D10S578. Our finding of another PPCD locus, PPCD3, on chromosome 10 indicates that PPCD is genetically heterogeneous. Guttae, a common corneal finding sometimes observed along with PPCD, were found among both affected and unaffected members of the proband's sib ship, but were absent in the younger generations of the family. Evaluation of phenotypic differences between family members sharing the same affected haplotype raises questions about whether differences in disease severity, including differences in response to surgical interventions, could be due to genetic background or other factors independent of the PPCD3 locus.