Genetics of the corneal dystrophies: what we have learned in the past twenty-five years

Whole-exome sequencing of calcitonin-producing pancreatic neuroendocrine neoplasms indicates a unique molecular signature

Introduction

Calcitonin-producing pancreatic neuroendocrine neoplasms (CT-pNENs) are an extremely rare clinical entity, with approximately 60 cases reported worldwide. While CT-pNENs can mimic the clinical and diagnostic features of medullary thyroid carcinoma, their molecular profile is poorly understood.

Methods

Whole-exome sequencing (WES) was performed on tumor and corresponding serum samples of five patients with increased calcitonin serum levels and histologically validated calcitonin-positive CT-pNENs. cBioPortal analysis and DAVID gene enrichment analysis were performed to identify dysregulated candidate genes compared to control databases. Immunohistochemistry was used to detect the protein expression of MUC4 and MUC16 in CT-pNEN specimens.

Results

Mutated genes known in the literature in pNENs like MEN1 (35% of cases), ATRX (18-20% of cases) and PIK3CA (1.4% of cases) were identified in cases of CT-pNENs. New somatic SNVs in ATP4A, HES4, and CAV3 have not been described in CT- pNENs, yet. Pathogenic germline mutations in FGFR4 and DPYD were found in three of five cases. Mutations of CALCA (calcitonin) and the corresponding receptor CALCAR were found in all five tumor samples, but none of them resulted in protein sequelae or clinical relevance. All five tumor cases showed single nucleotide variations (SNVs) in MUC4, and four cases showed SNVs in MUC16, both of which were membrane-bound mucins. Immunohistochemistry showed protein expression of MUC4 in two cases and MUC16 in one case, and the liver metastasis of a third case was double positive for MUC4 and MUC16. The homologous recombination deficiency (HRD) score of all tumors was low.

Discussion

CT-pNENs have a unique molecular signature compared to other pNEN subtypes, specifically involving the FGFR4, DPYD, MUC4, MUC16 and the KRT family genes. However, a major limitation of our study was the relative small number of only five cases. Therefore, our WES data should be interpreted with caution and the mutation landscape in CT-pNENs needs to be verified by a larger number of patients. Further research is needed to explain differences in pathogenesis compared with other pNENs. In particular, multi-omics data such as RNASeq, methylation and whole genome sequencing could be informative.

Immunogenetics of the Ocular Anterior Segment: Lessons from Inherited Disorders

Autoimmune and autoinflammatory diseases cause morbidity in multiple organ systems including the ocular anterior segment. Genetic disorders of the innate and adaptive immune system present an avenue to study more common inflammatory disorders and host-pathogen interactions. Many of these Mendelian disorders have ophthalmic manifestations. In this review, we highlight the ophthalmic and molecular features of disorders of the innate immune system. A comprehensive literature review was performed using PubMed and the Online Mendelian Inheritance in Man databases spanning 1973-2020 with a focus on three specific categories of genetic disorders: RIG-I-like receptors and downstream signaling, inflammasomes, and RNA processing disorders. Tissue expression, clinical associations, and animal and functional studies were reviewed for each of these genes. These genes have broad roles in cellular physiology and may be implicated in more common conditions with interferon upregulation including systemic lupus erythematosus and type 1 diabetes. This review contributes to our understanding of rare inherited conditions with ocular involvement and has implications for further characterizing the effect of perturbations in integral molecular pathways.

Macular Corneal Dystrophy: An Updated Review

Macular Corneal Dystrophy is an autosomal recessive form of corneal dystrophy due to a mutation in CHST6 gene, which results in abnormal proteoglycan synthesis. There is accumulation of abnormal glycosaminoglycans in the corneal stroma and endothelium. The deposition results in progressive loss of corneal transparency and visual acuity. The histopathology shows characteristic alcian blue positive deposits. Management in the cases with visual loss requires keratoplasty either full thickness or lamellar. The decision about the ideal type of keratoplasty depends on age and pre-operative clinical features. Although prognosis after keratoplasty is good, recurrences can occur. Future research should be targeted towards gene therapy in this condition.

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.

Novel compound heterozygous mutations in the CHST6 gene cause macular corneal dystrophy in a Han Chinese family

BACKGROUND

Macular corneal dystrophy (MCD), a rare autosomal recessive disorder, is caused by pathogenic mutations in the carbohydrate sulfotransferase 6 gene (CHST6) and is characterized by bilateral progressive stromal clouding and vision loss. Corneal transplantation is often necessary. This study aimed to identify disease-causing mutations in a Han-Chinese MCD patient.

METHODS

A 37-year-old female diagnosed with MCD was recruited. The clinical materials were observed and described, and peripheral blood sample was extracted. Whole exome sequencing (WES) and Sanger sequencing were used to reveal genetic defects. The pathogenicity of identified mutations was assessed using in silico analysis.

RESULTS

The patient had typical features of MCD, including decreased vision, multiple irregular gray-white corneal opacities, and corneal thinning. A novel nonsense mutation c.544C>T (p.Gln182Ter) and a validated missense mutation c.631C>G (p.Arg211Gly) were identified in the CHST6 gene coding region, both classified as "pathogenic" following the American College of Medical Genetics and Genomics standards and guidelines.

CONCLUSIONS

This study reports a Han-Chinese MCD patient with a novel nonsense mutation c.544C>T (p.Gln182Ter) and a recurrent missense mutation c.631C>G (p.Arg211Gly), which expand the spectrum of genetic mutations. The results of this study extend genotype-phenotype correlations between the CHST6 gene mutations and MCD clinical findings, contributing to a more accurate diagnosis and the development of potential gene-targeted MCD therapies.

KEYWORDS

Carbohydrate sulfotransferase 6 gene (CHST6); compound heterozygous mutations; Han Chinese family; macular corneal dystrophy (MCD).

Transforming growth factor beta-induced p.(L558P) variant is associated with autosomal dominant lattice corneal dystrophy type IV in a large cohort of Spanish patients

IMPORTANCE

Rare transforming growth factor beta-induced (TGFBI) gene variants are involved in autosomal dominant corneal dystrophies (CDs) with heterogeneous clinical features.

BACKGROUND

The purpose of this study was to analyse TGFBI gene variants and genotype-phenotype correlations in a cohort affected by atypical stromal CD.

DESIGN

Retrospective cohort study (from May 2014 to September 2017).

PARTICIPANTS

Thirty-five individuals from 10 unrelated South European families presenting atypical lattice CD (LCD) were included.

METHODS

Corneal phenotypes were assessed by slit-lamp examination and optical coherence tomography (OCT). Contrast sensitivity was measured under mesopic conditions. Genomic DNA was obtained from blood samples, and all 17 TGFBI exons were screened for variants by Sanger sequencing.

MAIN OUTCOME MEASURES

p.(L558P) variant of TGFBI gene.

RESULTS

The p.(L558P) variant was identified in 22 members of the 10 families diagnosed with atypical LCD, characterized by late-onset and absence of recurrent erosion syndrome. OCT revealed punctiform deposits in the deep-mid stroma and normal anterior stroma. This variant was demonstrated to be transmitted with the disease according to autosomal dominant inheritance in most families.

CONCLUSIONS AND RELEVANCE

To the best of our knowledge, we describe a detailed clinical characterization of the largest CD cohort carrying the TGFBI p.(L558P) variant. We propose that the atypical phenotype of this recently reported alteration can be classified as a form of LCD type IV. The results show that OCT and anterior-posterior analysis of the stromal location of the opacities, along with a genetic analysis of TGFBI, are required to ensure accurate diagnosis and management of CDs.

LASIK and surface ablation in corneal dystrophies

Corneal dystrophies are a rare group of hereditary disorders, that are bilateral, non-inflammatory, and progressive. Clinically, they can be classified based on the anatomic layer of the cornea affected. Refractive surgery and phototherapeutic keratectomy (PTK) can be performed with caution in patients with certain corneal dystrophies, but should be avoided in others. For epithelial basement membrane dystrophy, photorefractive keratectomy (PRK) is the procedure of choice for treatment of refractive error, and PTK may be performed for the treatment of recurrent erosions or irregular astigmatism. PRK and laser-assisted in situ keratomileusis (LASIK) have been associated with exacerbation of combined granular-lattice corneal dystrophy. LASIK and PRK appear to be safe in mild forms of posterior polymorphous corneal dystrophy, whereas LASIK should be avoided in Fuchs dystrophy. The safety of refractive surgery and PTK in the remainder of epithelial, Bowman layer, and stromal dystrophies has yet to be established.

Granular corneal dystrophy: a novel approach to classification and treatment

PURPOSE

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

CASE REPORT

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

CONCLUSIONS

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

Proteomic analysis as a means to approach limbal stem cell biology in a search for stem cell markers

The cornea consists of three main layers: an outer surface epithelium, the stroma, and the endothelium. A clear cornea is necessary for optimal vision and is maintained and repaired from limbal epithelial stem cells located in the limbus between the cornea and the sclera. Diseases and injury may result in deficiency of the stem cells impairing their ability to renew the corneal epithelium. Patients with limbal stem cell deficiency experience chronic pain and ultimately blindness. Attempts to treat the disease are based on replacement of the stem cells by transplantation or by culturing the stem cells. We here review the proteomic techniques that so far have been used to approach characterization of limbal stem cells and markers to identify them. It is apparent that the field is in a rather inchoate state due to the scarcity and relative inaccessibility of the stem cells. However, the importance of revealing limbal stem cell biology and identifying stem cell biomarkers calls for greater use of emerging methodology. Strategies for future studies are discussed.

Confocal microscopy and optical coherence tomography imaging of hereditary granular dystrophy

OBJECTIVES

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

CASE REPORT

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

RESULTS

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

CONCLUSIONS

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

Avellino corneal dystrophy worsening after laser in situ keratomileusis: further clinicopathologic observations and proposed pathogenesis

PURPOSE

To study the nature of the deposits in Avellino corneal dystrophy (ACD) worsening after laser in situ keratomileusis (LASIK), and suggest a mechanism for histopathogenesis.

DESIGN

Interventional case report.

METHODS

A 28-year-old woman previously diagnosed with bilateral ACD underwent bilateral LASIK. The corneal dystrophy progressively worsened bilaterally, one year later. A penetrating keratoplasty was subsequently performed on the right eye at 31 years of age, and in the left eye a year later. The clinical and histopathologic findings of the corneal graft of the right eye were reported in the literature, with positivity to the Masson trichrome stain, negative staining with Congo red, and heterozygosity for the Arg124His mutation by serum DNA studies. Histopathologic studies of the corneal graft of the left eye were conducted at the University of Texas Southwestern Medical Center.

RESULTS

Histopathologic examination of the excised cornea showed the Masson trichrome positive deposits present from underneath the Bowman layer to the LASIK interface, with absence of deposits posterior to the latter. In contrast to the prior report describing findings in the corneal graft of the left eye, the deposits stained lightly with Congo red, but failed to show birefringence under polarized light, or fluorescence with thioflavin T.

CONCLUSION

Accelerated deposits developing after LASIK in ACD eyes seem to harbor pre-amyloid features. The epithelium is likely to be the culprit, in a pathway independent of with human transforming growth hormone beta (TGF-beta), with deposits developing in the anterior stroma and the stromal interface.

Histopathologic Study of Corneal Stromal Dystrophies

PURPOSE

To determine the frequency and describe the histopathologic features of stromal corneal dystrophies over a 10-year period.

METHODS

A single-centered, retrospective analysis was performed on corneal specimens diagnosed as stromal dystrophies retrieved from the Henry C. Witelson Ophthalmic Pathology Laboratory and Registry (Montreal, Canada) over a period of 10 years. Corneal specimens obtained during keratoplasty were subjected to hematoxylin and eosin, periodic acid-Schiff, and other special staining.

RESULTS

During the period of the study, 885 corneal specimens from penetrating keratoplasties were received. Twenty-six (2.9%) specimens from a total of 22 patients showed stromal corneal dystrophies: 17 (65.4%) eyes with lattice dystrophy, 5 (19.2%) eyes with combined granular/lattice ("Avellino") dystrophy, 3 (11.5%) eyes with granular dystrophy, and 1 (3.9%) eye with macular dystrophy.

CONCLUSIONS

Corneal stromal dystrophies have distinct histopathologic features, which can be diagnosed with routine and special staining, particularly for combined granular/lattice (Avellino) dystrophy. Clinically, combined granular/lattice (Avellino) dystrophy can have features of both lattice and granular dystrophies, which can be misleading for diagnosis. Lattice dystrophy was the most frequent stromal dystrophy in this particular population.

Mechanism of fiber carcinogenesis: from reactive radical species to silencing of the beta igH3 gene

Although the U.S. Environmental Protection Agency has restricted the industrial use of regulated forms of asbestos in the United States since the early 1970s, environmental exposure to asbestos remains a health concern in the United States and is a significant health issue among developing countries. Exposure to asbestos is associated with chronic pulmonary diseases and cancer of the lung, pleura, and peritoneum. The mechanism of fiber carcinogenesis is far from clear and is likely to be complex, depending on fiber dimensions, surface properties, and physical durability. The induction of reactive oxygen and nitrogen species upon phagocytosis of fibers plays an important role in fiber genotoxicity. The beta igH3, a secreted protein induced by the transforming growth factor-beta and essential for cell adhesion, is downregulated in asbestos-induced tumorigenic human bronchial epithelial cells. Ectopic expression of the beta igH3 gene abrogates the tumorigenic phenotype and suggests that the gene plays a causal role in fiber carcinogenesis. A better understanding of the carcinogenic mechanism of asbestos and other mineral fibers will provide useful information on interventional and preventive measures for asbestos-mediated diseases such as human pleural and peritoneal mesotheliomas.

Comparison of deep lamellar keratoplasty and penetrating keratoplasty for lattice and macular corneal dystrophies

PURPOSE

To compare the therapeutic outcomes after deep lamellar keratoplasty (DLKP) and penetrating keratoplasty (PKP) in patients with lattice corneal dystrophy (LCD) and macular corneal dystrophy (MCD).

DESIGN

Age-matched control study.

METHODS

We reviewed the clinical records of 84 eyes with LCD or MCD who had DLKP (41 eyes) or PKP (43 eyes). Primary pathology consisted of 60 eyes with LCD and 24 eyes with MCD. DLKP was performed by either removing stromal tissue gradually, or by viscodissection of Descemet's membrane. Graft clarity, best-corrected visual acuity (BCVA), endothelial density, and complications were compared between DLKP and PKP, as well as between LCD and MCD.

RESULTS

All 84 eyes showed a postoperative improvement in visual acuity. The median final BCVA was not significantly different between PKP and DLKP groups. Endothelial cell loss rates were similar for DLKP and PKP. While the MCD-DLKP group showed progressive decrease in endothelial density, this was not observed in the LCD-DLKP group after surgery. In the DLKP group, most of the complications occurred intraoperatively or in the early phase, whereas late phase complications such as endothelial rejection and secondary glaucoma were the main complications in the PKP group.

CONCLUSIONS

PKP is no longer an automatic choice for the surgical treatment for LCD and MCD; DLKP seems to be a safe alternative. While DLKP is a favorable method for LCD, MCD may not be a good candidate, as it might show progressive decrease in the corneal endothelium postoperatively.

Genetics of Corneal Disease for the Ocular Surface Clinician

Advances in the understanding of inherited corneal and external diseases may allow interventions that prevent the substantial vision impairment currently caused by these diseases. The observant clinician may first recognize inherited corneal and external diseases based on clinical examination and a careful family history. Researchers using positional cloning and candidate gene techniques have identified several disease-causing genes. Identification of the genes responsible for inherited corneal and external diseases will lead to more definitive diagnoses and represent the first step in development of effective therapies. Future endeavors are directed toward identifying additional inherited corneal and external diseases, the genes that cause them, and possible gene therapies to improve visual outcomes.

Lattice Dystrophy-like Localized Amyloidosis of the Cornea Secondary to Trichiasis

PURPOSE

To report a case of stellate and branching linear corneal stromal amyloid deposits secondary to trichiasis and the use of molecular genetic analysis to exclude lattice corneal dystrophy.

METHODS

Case report and review of the literature. A 30-year-old man with a history of chronic ocular irritation was found to have distichiasis, epiblepharon, and unilateral corneal amyloidosis indistinguishable from lattice corneal dystrophy. Screening of the TGFBI gene was performed to rule out a previously reported mutation associated with lattice corneal dystrophy.

RESULT

A corneal biopsy performed before presentation to the authors confirmed the presence of corneal amyloidosis. Screening of exons 4, 11, 12, and 14 in the TGFBI gene identified 2 previously reported polymorphisms, Leu472Leu and Phe540Phe, but no other coding region changes.

CONCLUSION

Corneal stromal amyloidosis clinically resembling lattice corneal dystrophy may be associated with trichiasis. The exclusion of a TGFBI-associated corneal dystrophy in this case, leaving trichiasis as the most likely cause of the corneal amyloid deposition, demonstrates the utility of molecular genetic analysis in confirming or refuting a presumptive clinical diagnosis.

Lattice corneal dystrophy associated with the Ala546Asp and Pro551Gln missense changes in the TGFBI gene

PURPOSE

To report a phenotypic variant of lattice corneal dystrophy associated with two missense changes, Ala546Asp and Pro551Gln, in the transforming growth factor-beta-induced gene (TGFBI).

DESIGN

Experimental study.

METHODS

Genomic DNA was obtained from the proband as well as affected and unaffected family members. Exons 4, 11, 12, and 14 of the TGFBI gene were amplified and sequenced. Additionally, a corneal button excised from the proband was examined by light and transmission electron microscopy. Haplotype analysis was performed on the proband's family and members of a previously identified pedigree with the same TGFBI gene missense changes.

RESULTS

Bilateral, symmetric, radially arranged, branching refractile lines within and surrounding an area of central anterior stromal haze were noted in the proband. Multiple polymorphic, refractile deposits were noted in the mid and posterior stroma in both the proband and her daughter. Light and electron microscopic analyses demonstrated amyloid and excluded the presence of deposits characteristic of granular corneal dystrophy. Screening of TGFBI exon 12 in the proband and her affected daughter revealed two missense changes, Ala546Asp and Pro551Gln (both absent in 250 control chromosomes). Haplotype analysis suggested that the mutations in this family and in a previously identified pedigree reflect a founder effect, rather than an independent occurrence.

CONCLUSIONS

We present a phenotypic variant of lattice corneal dystrophy associated with the Ala546Asp and Pro551Gln missense changes in exon 12 of the TGFBI gene. A common ancestor appears to account for the missense mutations observed in this pedigree and in a previously reported family.

Frequency, distribution, and outcome of keratoplasty for corneal dystrophies at a tertiary eye care center in South India

PURPOSE

To report the frequency, outcome, and atypical histology in corneal dystrophies.

METHODS

Corneal buttons of patients diagnosed with corneal dystrophy as noted in the records of the ophthalmic pathology register over a period of 6 years were included in this study. The sections from formalin-fixed, paraffin-embedded tissues were reviewed specifically for the type of deposits, associated degenerations such as amyloid and spheroidal deposits, inflammation, and vascularization. Special stains including Masson trichrome, Congo red, and Alcian blue staining were used whenever required. The medical records were evaluated for demographics, clinical presentation, history of consanguinity, family medical history, and clinical outcome of keratoplasty, which was recorded as clear, recurrence of dystrophy, or graft failure. A clinicopathologic correlation was attempted.

RESULTS

A total of 144 patients contributed 181 buttons, accounting for 8.1% of keratoplasties performed during the study period. The mean age of the patients was 34 +/- 19 years (range 3-72 years) with a male:female ratio of 1.6 (89):1 (55). Consanguineous parentage was noted in 26% of cases. History of a similar problem in siblings and other family members was elicited in 33 (22%) and 14 (9.7%), respectively. Dystrophies included macular (29.3%), congenital hereditary endothelial dystrophy (34.8%), Fuchs (16.6%), and lattice (15%); the remaining 11% included granular, gelatinous drop-like, Reis-Bucklers, and posterior polymorphous dystrophy. Associated histologic changes were degenerations (15%), vascularization (4%), and inflammation (2%). At a mean follow-up of 42 months, the graft remained clear in 148 eyes (81.7%), failed in 33 eyes (18.2%), and recurred in 5 eyes (2.8%). Graft survival for all dystrophies at the end of 1 year was 94.3 +/- 1.7%, and at the end of 5 years was 74.4 +/- 4.5%. Atypical histologic features did not affect graft survival.

CONCLUSION

Consanguineous marriages possibly contributed to the increase in macular dystrophy and CHED in South India. The degenerative changes seen could possibly be related to late presentation or unknown environmental factors and do not have an effect on the ultimate graft outcome.

Penetrating limbo-keratoplasty for granular and lattice corneal dystrophy

PURPOSE

To assess clinical follow-up data, and to identify donor epithelial cells after homologous penetrating central limbo-keratoplasty in patients with granular and lattice corneal dystrophies compared with patients who underwent conventional penetrating keratoplasty (PK).

DESIGN

Mixed retrospective and prospective nonrandomized comparative case series.

PARTICIPANTS AND CONTROLS

Twenty-six patients who underwent 33 limbo-keratoplasty procedures for granular or lattice corneal dystrophy since May 1995 and a historical control group of 24 patients who underwent 36 PK procedures between November 1986 and May 1995.

METHODS

Postoperatively, all but 2 limbo-keratoplasty patients were treated with systemic immunosuppressants for 6 months. All patients received long-term topical immune prophylaxis with prednisolone-21-acetate 1% (2 drops per day). After obtaining informed consent, epithelial cells were harvested from 10 limbo-keratoplasty eyes of 8 patients with granular dystrophy and 7 limbo-keratoplasty eyes of 7 patients with lattice dystrophy. Conjunctival epithelium or buccal mucosal epithelium for recipient identification and corneal epithelial cells from 3 graft sites were harvested. Deep-frozen donor corneoscleral rims were analyzed to characterize donor features. Genetic analysis was performed by polymerase chain reaction of short tandem repeat (STR) loci.

MAIN OUTCOME MEASURES

The ratio of dystrophy recurrences in the graft was clinically assessed. Donor features in epithelial cells were genetically established if at least 1 STR profile differed from that of the recipient.

RESULTS

There were 5 recurrences in limbo-keratoplasty eyes with granular dystrophy and 2 recurrences in limbo-keratoplasty eyes with lattice dystrophy, compared with 15 and 6 recurrences in PK eyes, respectively. The differences between limbo-keratoplasty and PK were not statistically significant over time (log-rank test; P = 0.14 for granular dystrophy and P = 0.56 for lattice dystrophy; alpha error, 0.05). For genetic analysis, 12 of 17 samples were evaluated. Donor epithelial cells were detected in 5 of the 12 samples (42%).

CONCLUSIONS

Limbo-keratoplasty tended to be associated with fewer recurrences of granular and lattice dystrophies. However, the difference was not yet statistically significant, probably due to the disappearance of the transplanted limbal stem cells over time. Genetic analysis confirmed the survival of transplanted limbal stem cells over several years in some limbo-keratoplasty eyes, which might correlate with less recurrence. Limbo-keratoplasty, therefore, is likely to represent a first step towards long-term recurrence-free survival of corneal grafts in patients with granular and lattice dystrophies.

Anterior basement membrane corneal dystrophy and pseudo-unilateral lattice corneal dystrophy in a patient with recurrent corneal erosions

PURPOSE

To report the utility of genetic testing in the diagnosis and management of patients with suspected corneal dystrophies.

DESIGN

Case report.

METHODS

A 58-year-old man with a history of recurrent corneal erosions was diagnosed with bilateral anterior basement membrane dystrophy and unilateral lattice corneal dystrophy. All 17 exons of the TGFBI gene were screened for mutations previously associated with lattice corneal dystrophy as well as novel coding region changes.

RESULTS

No mutations were found in the 17 exons of the TGFBI gene. A nucleotide change in exon 6 (651C>G) did not result in a change in the encoded amino acid (Leu217Leu).

CONCLUSIONS

In cases of suspected TGFBI corneal dystrophies, genetic testing is a useful tool to confirm the clinical diagnosis. In this case of suspected unilateral lattice corneal dystrophy, screening of the TGFBI gene ruled out the diagnosis, raising the possibility that the corneal changes were related to the coexistent anterior basement membrane dystrophy.

Prospects for gene therapy in corneal disease

Transfer of cDNA to corneal cells has been accomplished using viral and nonviral vectors. Studies examining the feasibility and optimal methods for vector-mediated gene transfer to the cornea have, as in other tissues, been performed using histochemical or fluorescent marker genes. These have used corneal cells or cell lines in vitro, and whole corneas maintained in ex vivo culture. Gene-based interventions have been examined in specific corneal disorders such as allograft rejection, postexcimer laser scarring, and herpes simplex keratitis using experimental models. As the feasibility of genetic modification of corneal cells has been successfully demonstrated, there is great potential for gene therapy vectors in the treatment of human corneal disease. Continued improvements in vectors for gene transfer will improve the efficacy and safety of gene therapy. In addition to use of cDNA transfer as an alternative to drug or protein treatments in acquired corneal disorders, our expanding knowledge of the genetic basis of inherited corneal disorders will ultimately lead to the development of specific and effective gene therapies in this category of diseases.

A new mutation (Leu569Arg) within exon 13 of the TGFBI (BIGH3) gene causes lattice corneal dystrophy type I

PURPOSE

To describe an American family with lattice corneal dystrophy type I, which associates with a novel mutation, Leu569Arg, of the TGFBI (BIGH3) gene.

DESIGN

Experimental study.

METHODS

Genomic DNA was extracted from buccal epithelial cells of four affected members of an American family with lattice corneal dystrophy type I. All 17 exons of the TGFBI gene were evaluated by PCR amplification and direct sequencing. Clinical and histologic data were also collected.

RESULTS

Three generations of this family have been positively diagnosed with lattice corneal dystrophy, indicating autosomal dominant inheritance. We identified a heterozygous point mutation that associates with the disease phenotype. The single base-pair substitution (T1753G) results in an amino acid substitution (Leu569Arg) in exon 13 of the TGFBI gene.

CONCLUSIONS

Substitution of arginine for leucine at position 569 of the TGFBI gene results in a form of lattice corneal dystrophy that is phenotypically similar to other genetically distinct forms of type I disease. This is the first report of disease correlated with changes in exon 13 of the TGFBI gene.

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

PURPOSE

To evaluate the clinical history, histopathology, and genetics of posterior polymorphous corneal dystrophy (PPMD) in a woman with a prominent retrocorneal membrane.

DESIGN

Observational case report and genetic analysis of her family, UM:139.

METHODS

Records were reviewed from a case and associated family members. The diagnosis of PPMD was based on clinical examination, immunohistochemical staining, electron microscopy, and screening of genetic markers from regions previously reported to be associated with PPMD.

RESULTS

Over 17 years, the proband with PPMD had 25 ocular procedures performed for glaucoma, cataract, cornea, retina, and postoperative problems. A prominent retrocorneal membrane grew onto the crystalline lens and intraocular lens (IOL). Histopathology revealed stratified epithelial-like cells on iris from an iridectomy and stratified corneal endothelium on a corneal button. Electron microscopy on the cornea revealed microvilli, tonofilaments, and desmosomes consistent with endothelial transformation, which was confirmed by positive anticytokeratin (CK) AE1/AE3 and CAM 5.2 immunoreactivity. Negative immunoreactivity in epithelium and positive in endothelium with anti-CK 7 supported the diagnosis of PPMD rather than epithelial downgrowth. Multiple relatives were affected with PPMD with apparent autosomal dominant inheritance, but surprisingly, the PPMD, congenital hereditary endothelial dystrophy 1 (CHED1) and CHED2 loci on chromosome 20 and the collagen, type VIII, alpha-2 (COL8A2) gene were excluded by linkage and haplotype analyses.

CONCLUSIONS

We are unaware of previous PPMD reports describing the unusual feature of a retrocorneal membrane extending onto the crystalline lens and IOL. In addition, this family suggests another PPMD locus.

Downregulation of Betaig-h3 gene is causally linked to tumorigenic phenotype in asbestos treated immortalized human bronchial epithelial cells

Although Betaig-h3 gene has been suggested to modulate cell adhesion and tumor formation, its physiological functions are not well understood. Using human papillomavirus immortalized human bronchial epithelial (BEP2D) cells, we found that Betaig-h3 expression was markedly decreased in asbestos-induced tumorigenic cells. Fusion of tumorigenic and control BEP2D cells resulted in the recovery of Betaig-h3 gene expression to control level and the loss of tumorigenic phenotype. Furthermore, ectopic expression of Betaig-h3 gene in asbestos-induced tumorigenic cells inhibited cell growth in vitro, anchorage independent phenotype, as well as tumorigenicity in nude mice. Betaig-h3 gene is ubiquitously expressed in various normal human tissues, with the exception of the brain, where there is little or no expression. In contrast, there was a decrease or absence in expression of the Betaig-h3 gene in 14 human tumor cell lines of diverse histological types examined, when compared with normal human cells or tissues. The result strongly suggests that loss of Betaig-h3 expression is a frequent event in human cancer and causally related to acquisition of tumorigenic phenotype in asbestos-treated BEP2D cells.

Induction and expression of betaig-h3 in pancreatic cancer cells

betaig-h3 (TGFBI, keratoepithelin) was first identified as a transforming growth factor-beta1 (TGF-beta1)-inducible gene in a human lung adenocarcinoma cell line. It encodes for a secreted extracellular matrix (ECM) protein, which is thought to act on cell attachment and ECM composition. Mutations of the betaig-h3 gene are involved in several corneal dystrophies. Pancreatic cancers display multiple alterations in the TGF-beta signaling pathway and in TGF-beta response genes, such as overexpression of all three TGF-beta isoforms and Smad4 mutations. In this report, we determined that betaig-h3 mRNA levels were induced by TGF-beta1 in two out of five examined pancreatic cancer cell lines (CAPAN-1, PANC-1). In CAPAN-1 cells, which harbor a Smad4 mutation, betaig-h3 but not PAI-1 was induced by TGF-beta1, whereas in PANC-1 cells that express wild-type Smad4, TGF-beta1 induced both PAI-1 and betaig-h3. In human pancreatic tissues, there was a 32.4-fold increase in betaig-h3 mRNA levels in pancreatic cancers in comparison to normal control tissues. In situ hybridization analysis revealed that betaig-h3 mRNA was expressed mainly in the cancer cells within the pancreatic tumor mass. These findings suggest that betaig-h3 is induced by TGF-betas in pancreatic cancer cells even in the presence of Smad4 mutations, which might explain, in part, the increased betaig-h3 mRNA levels observed in pancreatic cancer cells in vivo.

Overexpression of Betaig-h3 gene downregulates integrin alpha5beta1 and suppresses tumorigenicity in radiation-induced tumorigenic human bronchial epithelial cells

Interaction between cell and extracellular matrix plays a crucial role in tumour invasion and metastasis. Using an immortalised human bronchial epithelial (BEP2D) cell model, the study here shows that expression of Betaig-h3 gene, which encodes a secreted adhesion molecule induced by transforming growth factor-beta, is markedly decreased in several independently generated, radiation-induced tumour cell lines (TL1-TL5) relative to parental BEP2D cells. Transfection of Betaig-h3 gene into tumour cells resulted in a significant reduction in tumour growth. While integrin receptor alpha5beta1 was overexpressed in tumour cells, its expression was corrected to the level found in control BEP2D cells after Betaig-h3 transfection. These data suggest that Betaig-h3 gene is involved in tumour progression by regulating integrin receptor alpha5beta1. The findings provide strong evidence that the Betaig-h3 gene has tumour suppressor function in human BEP2D cell model and suggest a potential target for interventional therapy.

Clinical outcome of eight BIGH3-linked corneal dystrophies

OBJECTIVE

To determine whether the mutational pattern of BIGH3-linked corneal dystrophies (CDs) can accurately predict the clinical course of the disease and be helpful in planning adequate surgical treatment.

DESIGN

Retrospective noncomparative case series.

PARTICIPANTS

Chart review of 73 patients (110 eyes) with recently confirmed BIGH3 mutations who underwent a penetrating keratoplasty (PK) from 1978 through 1999. Diagnoses included Thiel-Benhke CD (TBCD/R555Q) (13 eyes), classic granular CD (CGCD/R555W) (28 eyes), superficial variant of granular dystrophy (SVGD/R124 l) (27 eyes), lattice CD type I (LCDI/R124C) (20 eyes), Avellino CD (ACD/R124H) (2 eyes), H626R-lattice dystrophy (LCD/H626R) (6 eyes), and two novel dystrophies: a French variant of granular dystrophy (FVGD/R124 l+DT125-DE126) (9 eyes) and a French lattice CD type IIIA (LCDIIIA/A546T) (5 eyes).

METHODS

The mutation of the BIGH3 gene was characterized for all patients. Clinical data were reviewed for each patient, and included age at first PK and elapsed time before significant recurrence (as defined by a severe decrease in best-corrected visual acuity related to recurrent deposits in the graft).

MAIN OUTCOME MEASURES

Mean age at first PK and delay before a significant recurrence.

RESULTS

Mutational pattern was highly correlated with the clinical course of each dystrophy. According to the genetic mutation, two groups with different prognosis were identified. Group 1 was defined by the presence of the FVGD/R124 l+DT125-DE126 and SVGD/R124 l mutations and was characterized by the early need for treatment and early recurrence of deposits. Group 2 was molecularly defined by the presence of any of the following mutations: LCDI/R124C, CGCD/R555W, LCDIIIA/A546T, TBCD/R555Q, and LCD/H626R. In group 2, mean age at first treatment was older, and delay before a significant recurrence was longer as compared with group 1 (P = 0.0001).

CONCLUSIONS

These results demonstrate that there is a direct correlation between the molecular defect and the clinical course of BIGH3-linked CDs. They also indicate that molecular characterization of the genetic defect will help predict and design adequate surgical treatment for patients with ambiguous clinical diagnosis.