Advances in the molecular genetics of corneal dystrophies

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.

Decreased catalase expression and increased susceptibility to oxidative stress in primary cultured corneal fibroblasts from patients with granular corneal dystrophy type II

Granular corneal dystrophy type II (GCD II) is an autosomal dominant disorder characterized by age-dependent progressive accumulation of transforming growth factor-beta-induced protein (TGFBIp) deposits in the corneal stroma. Several studies have suggested that corneal fibroblasts may decline with age in response to oxidative stress. To investigate whether oxidative stress is involved in the pathogenesis of GCD II, we assayed antioxidant enzymes, oxidative damage, and susceptibility to reactive oxygen species-induced cell death in primary cultured corneal fibroblasts (PCFs) from GCD II patients and healthy subjects. We found elevated protein levels of Mn-superoxide dismutase, Cu/Zn-superoxide dismutase, glutathione peroxidase, and glutathione reductase, as well as increased CAT mRNA and decreased catalase protein in GCD II PCFs. Furthermore, catalase is down-regulated in normal PCFs transfected with transforming growth factor-beta-induced gene-h3. We also observed an increase in not only intracellular reactive oxygen species and H(2)O(2) levels, but also malondialdehyde, 4-hydroxynonenal, and protein carbonyls levels in GCD II PCFs. Greater immunoreactivity for malondialdehyde was observed in the corneal tissue of GCD II patients. In addition, we observed a decrease in Bcl-2 and Bcl-xL levels and an increase in Bax and Bok levels in GCD II PCFs. Finally, GCD II PCFs are more susceptible to H(2)O(2)-induced cell death. Together, these results suggest that oxidative damage induced by decreased catalase is involved in GCD II pathogenesis, and antioxidant agents represent a possible treatment strategy.

Clinical and genetic features of TGFBI-linked corneal dystrophies in Mexican population: description of novel mutations and novel genotype-phenotype correlations

Corneal dystrophies (CDS) are inherited disorders characterized by an altered corneal transparency and refractive index which may be caused by a progressive accumulation of deposits within the different corneal layers. Most CDs are inherited in an autosomal dominant fashion and mutations in the TGFBI gene at chromosome 5q31 cause the majority of CDs affecting the stromal layer. A genotype-phenotype correlation has been identified in most analyzed populations as specific amino acid changes in TGFBI protein cause specific stromal phenotypes. However, analysis of additional populations will help to broaden the mutational spectrum ultimately allowing a better clinical-molecular classification of patients with this group of diseases. In this work, eighteen unrelated Mexican probands suffering from stromal CDs were clinically assessed and their TGFBI gene status investigated. Complete ophthalmologic evaluation, including biomicroscopic inspection and dilated fundus examination, was performed. In addition, detailed genealogical analyses as well as automated DNA sequencing of the entire TGFBI gene were done in all probands. Mutation-carrying exons were examined in 50 first and second degree relatives. Phenotypic analysis disclosed the occurrence of 6 cases of lattice CD, 6 of granular CD, 2 of granular type 2 (Avellino CD), 2 of polymorphic corneal amyloidosis, 1 of Reis-Bucklers CD, and 1 of an unclassifiable phenotype. TGFBI mutations were identified in all 18 probands. A total of six different mutations were observed: p.V113I, p.M502V, p.A546D, p.L550P, p.R555W, and p.H626R. Of these, mutations p.L550P (originated by the change c.1649T>C at exon 12), p.M502V (c.1504A>G, at exon 11), and p.V113I (c.337G>A, at exon 4), are novel TGFBI mutations. All subjects with lattice CD in our sample carried the p.H626R mutation. No instances of defects at codon 124, one of the two most frequently mutated sites in TGFBI-linked CDs, were detected. A distinct TGFBI mutational pattern was identified in Mexican patients with stromal CDs. Novel TGFBI mutations and new genotype-phenotype correlations were also recognized. This study stresses the importance of performing TGFBI genetic analysis in distinct CD populations.

Corneal melt in lattice corneal dystrophy type II after cataract surgery

We report a patient with lattice corneal dystrophy type II, also known as Meretoja syndrome or familial amyloidosis Finnish type, who developed a corneal melt 15 days after uneventful phacoemulsification. Despite conservative treatment, the corneal melt resulted in perforation. Uneventful penetrating keratoplasty was performed, but delayed graft epithelial healing was noticed postoperatively. Corneal button histopathological evaluation confirmed the initial clinical diagnosis. To our knowledge, this is the first reported case of corneal melt and perforation in a patient with lattice corneal dystrophy type II.

Phenotypic non-penetrance in granular corneal dystrophy type II

PURPOSE

To report a possible case of phenotypic non-penetrance in granular corneal dystrophy type II (GCD-II).

METHODS

DNA analysis was performed on 11 patients with white granular corneal opacities and 50 normal controls after informed consent was obtained. The TGFBI gene was analyzed by sequencing DNA from epidermal keratinocytes obtained using adhesive tape.

RESULTS

The heterozygous R124H mutation of TGFBI gene was found in all 11 patients. Although 49 normal controls had no mutation in the TGFBI gene, one normal control, a 26-year-old man, had the heterozygous R124H mutation of TGFBI gene. His 55-year-old father had the same mutation, but no corneal opacities.

CONCLUSION

As not all mutations are expressed in the phenotype, GCD-II gene mutation may have non-penetrance. This report documents a possible case of phenotypic non-penetrance in GCD-II.

Mutation screening of TGFBI in two Iranian Avellino corneal dystrophy pedigrees

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Homozygous granular corneal dystrophy type II (Avellino corneal dystrophy): natural history and progression after treatment

PURPOSE

To describe the clinical features of homozygous granular corneal dystrophy type II (GCDII) with age and with several kinds of treatment in 18 homozygous patients in several different conditions.

METHODS

Eighteen homozygous GCDII patients, confirmed with DNA analysis, of 13 families were enrolled. Their clinical features that include age at detection by parents, visual acuity, and disease progression were evaluated. We also studied the recurrence patterns for the 13 patients who underwent phototherapeutic keratectomy, penetrating keratoplasty, lamellar keratoplasty, or deep lamellar keratoplasty.

RESULTS

The age at detection by the parents ranged from 3 to 5 years; visual loss begins in childhood with progression into the 20s. All of the patients who had undergone surgeries acquired better vision immediately after surgery. Corneal deposits reappeared soon after treatments. Recurrences became progressively more rapid and severe with treatments.

CONCLUSIONS

The clinical features of homozygous GCDII are characterized by a severe granular type of corneal dystrophy with an early onset and rapid progression. After surgical treatment, recurrence is rapid and severe.

Recurrence of lattice corneal dystrophy caused by incomplete removal of stroma after deep lamellar keratoplasty

PURPOSE

To report clinical and histopathological characteristics of postoperative amyloidosis recurrence in a patient with lattice corneal dystrophy (LCD) type I.

METHODS

The clinical manifestation of recurrent amyloidosis in the residual stroma was delineated in a patient with LCD type I after deep lamellar keratoplasty (DLKP) for 6.5 years. Complete removal of the residual recipient stroma and regrafting of a new cryopreserved donor button were accomplished by a secondary DLKP. The primary DLKP donor graft and the underlying residual stroma of the recipient obtained by the secondary DLKP were examined for analysis of histopathologic and ultrastructural changes.

RESULTS

A tongue-shaped retained stroma with linear opacity was observed underneath the primary DLKP donor graft. The retained stromal layer was thoroughly detached from Descemet membrane, removed, and followed by grafting a new cryopreserved button. The primary donor button exhibited a normal epithelium, fewer keratocytes, an intact Descemet membrane, and mild positive Congo red staining in the middle layer of the stroma. The total retained recipient stroma removed by the secondary DLKP measured approximately 20 mum in thickness, showing thick and massive amyloid accumulation. The surface of the removed residual stroma toward Descemet membrane showed collagen fibers in an interwoven fashion without bundle structure under a scanning electron microscope.

CONCLUSION

Incomplete removal of the recipient stroma by DLKP can lead to the recurrence of amyloidosis in the residual stroma in patients with LCD. Clinical and histologic findings in the primary graft and in the residual recipient stroma implicate stromal genesis of recurrence of LCD after DLKP.

Genetics of corneal dystrophies: the evolving landscape

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Keratoepithelin in secondary corneal amyloidosis

BACKGROUND

Amyloid is found in several corneal dystrophies, including distinct lattice corneal dystrophies (LCD) and Avellino corneal dystrophy. Recently, point mutations in the transforming growth factor-beta-induced gene (TGFBI) encoding for keratoepithelin (KE) have been demonstrated in these corneal disease entities. We intended to investigate if KE was also a component of the rarely seen secondary corneal amyloid deposits.

METHODS

Immunohistochemical staining with a polyclonal antibody against KE was performed on formalin-fixed paraffin-embedded tissue of five corneal buttons with secondary amyloid obtained after keratoplasty. Secondary amyloidosis was due to Fuchs endothelial dystrophy (FED) with bullous keratopathy and/or recurrent erosions in all cases. The diagnosis had been established by light microscopy using Congo red staining. Two cases of LCD type I served as positive controls and three corneas with FED and one with keratoconus without amyloid served as negative controls.

RESULTS

All corneas with secondary amyloidosis as well as LCD type I revealed positive staining in the respective amyloid deposits. KE was localized in the subepithelial pannus and in the anterior stroma in the corneas with secondary amyloidosis. In the specimens with LCD type I it was distributed in the amyloid deposits located in the anterior and mid-stroma. Staining for KE showed a granular appearance in all cases. The intensity of staining was variable among the specimens.

CONCLUSIONS

KE is found not only in primary amyloid deposits of hereditary corneal dystrophies, but also in secondary amyloidosis of the cornea of diverse ethiologies.

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.

Gelatinous drop-like corneal dystrophy in a child with developmental delay: clinicopathological features and exclusion of the M1S1 gene

AIMS

Gelatinous drop-like corneal dystrophy (GDLD) is an early-onset, autosomal recessive condition characterised by amyloid deposits within the cornea. We report the histopathological and molecular genetic findings in a Caucasian child with GDLD who also exhibited global developmental delay.

METHODS

Bilateral lamellar keratoplasty was carried out at age 6 and 7 years. Tissue was fixed for light and electron microscopy, including immunoelectronmicroscopy. The coding region of the M1S1 gene was screened for mutations in the affected proband and available relatives, using DNA extracted from mouthwashes.

RESULTS

Nodular deposits, which were present subepithelially and in the central superficial stroma, stained typically for amyloid with PAS and Congo red. A nodular deposit of amyloid, together with large amounts of lactoferrin and sparse amounts of keratoepithelin (betaig-h3), was present in the central superficial stroma, causing destruction of Bowman's layer and elevation of the thinned, degenerate epithelium. Around the deposit zone, the stroma exhibited large numbers of thick filamentous proteoglycan deposits. While the affected child was homozygous for a novel A1133 C single-nucleotide polymorphism (SNP) that resulted in an aspartic acid to alanine substitution at position 173 of the M1S1 coding sequence, this polymorphism was also found at relatively high frequency in a sample of normal controls, enabling exclusion of the M1S1 gene as the disease locus.

CONCLUSION

Increased epithelial permeability in GDLD may be explained in part by an altered membrane permeability of the superficial epithelial cells. An association with developmental delay has not been reported previously.

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.

TGFBI Gene Mutation Analysis in Families with Hereditary Corneal Dystrophies from Ukraine

In our study, 5 previously reported mutations of the TGFBI gene - R124C, R124H, R124L (exon 4), R555W, R555Q (exon 12) - were analyzed using polymerase chain reaction followed by restriction digestion in 48 individuals from 19 unrelated families with different forms of corneal dystrophy from different regions of Ukraine. The R555W mutation was detected in 6 patients from 4 families with granular corneal dystrophy. The R124C mutation was detected in 1 unaffected 10-year-old individual and in 24 patients from 8 families with lattice corneal dystrophy. As far as the R124C mutation detected in 1 patient with clinically diagnosed Reis-Bucklers corneal dystrophy is concerned, we concluded that this patient was misdiagnosed. The obtained results show that TGFBI gene mutation analysis is important as well for the early differential diagnosis of corneal dystrophies and genetic consulting in high-risk families.

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.

Optimized expression and refolding of human keratoepithelin in BL21 (DE3)

Keratoepithelin (KE) is an extracellular protein participating in cell adhesion and differentiation. Mutations of the KE gene (on 5q31 in humans) cause deposition of abnormal proteins (amyloid and non-amyloid) in corneal stroma and lead to several corneal dystrophies in humans. However, further studies on the KE protein have been limited by the intrinsic difficulty of purifying this protein. A high-expression plasmid containing human KE gene was constructed to generate recombinant KE proteins in Escherichia coli. The plasmid was transformed into E. coli BL21 (DE3) and the recombinant protein was expressed as an insoluble His-tagged fusion protein and purified by nickel chelation affinity chromatography under denaturing conditions. On average, 12 mg of purified KE was routinely obtained from 1L of culture media. The recombinant KE was refolded in arginine-containing dialysis solutions and the recovery of bioactive KE typically was approximately 70%. The procedures developed in this report should enable reproducible production of KE and related mutant proteins in large quantities and facilitate future studies on biochemical and biophysical properties of KE and the pathogenesis of related corneal dystrophies.

Concomitant Keratoconus and Macular Corneal Dystrophy

OBJECTIVE

To report the concomitant presentation of keratoconus and macular corneal dystrophy in two cases.

METHODS

Two siblings with concomitant keratoconus and macular corneal dystrophy are presented. Complete ophthalmologic examination and computerized videokeratography were performed in both patients. Case 1 underwent penetrating keratoplasty in both eyes sequentially; histopathologic examination of excised corneal buttons with special stains was performed. Case 2 was observed.

RESULTS

Both patients manifested typical signs and topographic evidence of keratoconus associated with macular dystrophy. Histopathologic studies in case 1 confirmed the same clinical diagnosis.

CONCLUSION

To our knowledge, this is the first report of such a concurrence in the English literature and could lead to further studies on the possible pathophysiologic or genetic link between these 2 entities.

A practical approach to interpretation of corneal specimens

Corneal specimens form only a small part of the routine practice for most histopathologists but their assessment often requires considerable effort and specialized knowledge. The most common corneal specimens, full-thickness corneal discs and corneal biopsies, are discussed in this review. Corneal discs removed at keratoplasty are non-urgent specimens, as definitive treatment has already been undertaken, and while the pathologic diagnosis may change the prognosis for the graft, it rarely affects immediate treatment. Accurate diagnosis is still important, and will affect counseling of the patient, but referral to a colleague with a special interest is possible if necessary. Conversely, small partial-thickness corneal biopsies, which are mostly undertaken for culture negative keratitis with underlying suspected infection, are very urgent. Infectious keratitis can follow an extremely aggressive course, resulting in destruction of the cornea within hours. Accurate diagnosis is imperative. Due to the urgency of such specimens and the importance of diagnosis for immediate treatment, referral is not usually possible. It is the role of the pathologist to make optimal use of a small specimen to reach the relevant diagnosis in the minimum space of time.

Keratoconus???No Association with the Transforming Growth Factor ?????Induced Gene in a Cohort of American Patients

PURPOSE

Keratoconus is a noninflammatory, corneal thinning disorder leading to mixed myopic and irregular astigmatism and implicated as a major reason for cornea transplantations in the Western world. Genetic factors have been suggested as a cause of keratoconus. The levels of transforming growth factor beta-induced (TGFBI) protein have been reported to be altered in keratoconus tissues. Mutations in this gene are responsible for causing various corneal dystrophies. Given this strong evidence of the involvement of this gene in corneal dystrophies, we investigated possible mutations within this gene in 15 probands of families with keratoconus.

METHODS

All patients and control individuals had complete ophthalmological examination by a corneal specialist to determine their affectation status. The entire transcript of the TGFBI gene was analyzed by direct sequencing from patient DNA.

RESULTS

We found 8 sequence variations within the gene, none of which was protein-altering changes. These changes were also observed in control individuals, and 4 are previously known polymorphisms.

CONCLUSIONS

We concluded that the TGFBI gene is not responsible for causing keratoconus in these patients.

Exclusion of the human collagen type XVII (COL17A1) gene as the cause of Thiel-Behnke corneal dystrophy (CDB2) on chromosome 10q23-q25

PURPOSE

Determination of the gene causing Thiel-Behnke Corneal Dystrophy (CDB2) would have important clinical implications. Previous studies in our laboratory have suggested that the COL17A1 gene may be the cause of Thiel-Behnke Corneal Dystrophy (CDB2) on Chromosome 10q23-q25.

METHODS

We evaluated a five-generation family with CDB2 mapped to chromosome 10. Many of these family members were diagnosed by slit-lamp microscopy. In addition, genomic DNA was isolated and purified from peripheral blood samples. The COL17A1 gene was screened for possible disease causing mutations by PCR and DNA sequencing analysis.

RESULTS

No disease-causing mutations were found in any of the 56 exons of the COL17A1 gene or in any of the flanking intron/exon junctions.

CONCLUSIONS

Mutations in the coding sequence of the human collagen XVII (COL17A1) gene are not the cause of CDB2.

The Cascade Hypothesis of Keratoconus

Keratoconus, a non-inflammatory thinning of the cornea, is a leading indication for corneal transplantation. For its causation, we propose a "Cascade Hypothesis" stating that keratoconus corneas have abnormal or defective enzymes in the lipid peroxidation and/or nitric oxide pathways leading to oxidative damage. The accumulation of oxidative, cytotoxic by-products causes an alteration of various corneal proteins, triggering a cascade of events, (i.e. apoptosis, altered signaling pathways, increased enzyme activities, fibrosis). This hypothesis is supported by biochemical, immunohistochemical and molecular data presented in this review. Based upon this evidence, one can speculate that keratoconus patients should minimize their exposure to oxidative stress. Protective steps should include wearing ultraviolet (UV) protection (in the contact lenses and/or sunglasses), minimizing the mechanical trauma (eye rubbing, poorly fit contact lenses) and keeping eyes comfortable with artificial tears, non-steroidal anti-inflammatory drugs and/or allergy medications.

H626R and R124C mutations of the TGFBI (BIGH3) gene caused lattice corneal dystrophy in Vietnamese people

BACKGROUND/AIMS

Mutations of the human transforming growth factor beta induced gene (TGFBI) were reported to cause lattice corneal dystrophy (LCD) in various nationalities. This study analysed the TGFBI gene in Vietnamese people with LCD.

METHODS

13 unrelated families, including 34 patients and 21 unaffected members were examined. 50 normal Vietnamese people served as controls. Blood samples were collected. Genomic DNA was extracted from leucocytes. Analysis of TGFBI gene was performed using the polymerase chain reaction and direct sequencing. Corneal buttons were studied histopathologically.

RESULTS

Two clinically distinguishable forms of LCD were revealed: one was typical of LCDI; the other was characterised by the late onset, thick lattice lines, and asymmetry between two eyes. Sequencing of the TGFBI gene revealed R124C mutation in three families and H626R mutation in 10 families. Congo red staining of the H626R-LCD cornea showed amyloid deposits in the subepithelial and stromal layers.

CONCLUSIONS

R124C and H626R mutations of TGFBI gene caused LCD in Vietnamese people. R124C, a common cause of LCDI in many nationalities, was relatively rare, whereas H626R reported in several white people but not yet in Asians was most common (>75%) in Vietnamese people. Since the phenotype caused by H626R represents a new variant intermediate between LCDI and LCDIIIA, we proposed to consider it as LCD type IIIB.

Phototherapeutic keratectomy for BIGH3-linked corneal dystrophy recurring after penetrating keratoplasty

PURPOSE

To determine visual results and report side effects and complications after phototherapeutic keratectomy (PTK) for BIGH3-linked corneal dystrophy recurring after penetrating keratoplasty.

DESIGN

Retrospective noncomparative case series.

PARTICIPANTS

Forty-two excimer laser PTK procedures were performed in 42 eyes of 29 patients with BIGH3-linked corneal dystrophies. Genetic status of all patients was determined and allowed us to assess an unambiguous diagnosis. Preoperative diagnoses included LCDIIIA/A546T (1 eye), R124 l+DT125-DE126 (4 eyes), GICD/R555W (14 eyes), LCDI/R124C (6 eyes), SGD/R124 l (16 eyes), and CDBII/R555Q (1 eye).

INTERVENTION

Two excimer lasers (Summit Excimed UV 200, Summit Technology, Waltham, MA and Nidek EC 5000, Nidek, Inc., Gamagori, Japan) were used to perform all PTKs. Indications for performing PTK after a graft were severe decrease of the best-corrected visual acuity (BCVA) related to recurrent corneal deposits and/or painful recurrent epithelial erosions.

MAIN OUTCOME MEASURES

Preoperative and postoperative BCVA were analyzed, significant recurrences after treatment were noted, and postoperative complications were recorded.

RESULTS

Mean preoperative BCVA was 0.2 +/- 0.12 in the decimal chart, mean postoperative BCVA was 0.52 +/- 0.16 with a mean follow-up of 3.13 +/- 1.77 years (range, 0.3-6.65 years). Visual acuity was significantly improved after surgery (P < 0.05). The magnitude of the change in visual acuity was dependent on the mutation (P < 0.001). Seven symptomatic recurrences were observed. One regressive graft rejection and 4 cases of severe postoperative haze were observed. No other complications were noted.

CONCLUSIONS

PTK is a simple, safe, and efficient technique for the treatment of recurrent corneal dystrophies; in many cases it prevents or delays the major incumbent problems of repeated grafting.

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.

In vivo confocal microscopy of Fleck dystrophy and pre-Descemet's membrane corneal dystrophy

PURPOSE

To assess the value of in vivo confocal microscopy (CM) in the diagnosis of Fleck dystrophy and pre-Descemet's membrane corneal dystrophy.

METHODS

Case report of two patients. Standard slit-lamp and ophthalmic examination and in vivo CM were performed on both patients. The thickness of the cornea and the morphology of the corneal epithelium, stroma, endothelium, and subbasal nerves were evaluated by confocal microscopy.

RESULTS

Biomicroscopy revealed bilateral, fine, dust-, and flour-like opacities in the corneal stroma for the Fleck dystrophy patient. In the pre-Descemet's membrane corneal dystrophy patient, biomicroscopy showed opacities larger than those in the first patient. Both patients were then examined by in vivo CM. Confocal microscopy of the Fleck dystrophy showed intracellular deposits throughout the stroma. In pre-Descemet's membrane corneal dystrophy, however, these and the extracellular deposits were observed immediately anterior to Descemet's membrane. The thicknesses of the corneas were 560 and 650 microm for Fleck and pre-Descemet's membrane corneal dystrophy, respectively. The surface epithelium, subbasal nerves, and endothelium showed normal morphology in both patients.

CONCLUSION

In vivo CM is a valuable tool in diagnosing rare corneal dystrophies when the final diagnosis is difficult to obtain with conventional methods.

The changing face of the genetics of corneal dystrophies

Modern molecular genetics has had a profound effect on our understanding of corneal dystrophies. Mutations in the BIGH3 gene are responsible for four autosomal dominant corneal dystrophies. The mutation spectrum reveals the phenotypically diverse possibilities stemming from mutations of a single gene. Dystrophies have been grouped together in a "stamp-collector" fashion. Classification has been based on clinical description of disease. With better appreciation of molecular genetics, classifications can be based on underlying genetic cause. In fact, classification schema based on the gene or molecular defect responsible for the dystrophy have been introduced. Different phenotypes are determined by different genotypes. Clinicians must become more adept at understanding the molecular genetics of corneal dystrophies as genetics is increasingly important in the long-term diagnostic and therapeutic approach to dystrophies.

CD-34 stromal expression pattern in normal and altered human corneas

OBJECTIVE

To test CD-34 immunoreactivity in stromal cornea cells in normal and pathologic samples obtained from penetrating keratoplasty.

DESIGN

Prospective, consecutive histopathologic human tissue study.

PARTICIPANTS AND CONTROLS

One hundred two cornea buttons from patients with different diseases, submitted for cornea transplant, were examined. Controls were expired corneas from healthy donor patients who died (n = 4), and globes enucleated for primitive intraocular neoplasias, that is, retinoblastomas (n = 8), and malignant choroidal melanomas (n = 2).

METHODS

The expression of CD-34 in stromal cornea cells was examined by immunohistochemistry analysis. Other immunohistochemical stains included an endothelial cell marker (CD-31), common leukocyte antigen, and alpha-smooth muscle actin.

MAIN OUTCOME MEASURES

Different diseases that may cause blindness and require penetrating keratoplasty have been tested for CD-34 immunoreactivity.

RESULTS

In control corneas, keratocytes present strong and consistent CD-34 immunoreactivity. Diseases leading to the loss of transparency and penetrating keratoplasty, such as keratoconus, herpes keratitis, trauma, and heredofamilial dystrophies, are associated with focal or diffuse loss of CD-34 expression, whereas pseudophakic bullous keratopathy and Fuchs' endothelial dystrophy show normal CD-34 immunoreactivity in most cases and patchy unstained stromal areas in a few cases.

CONCLUSIONS

Scar tissue formation in the cornea, as in herpes keratitis and trauma, is always associated with loss of CD-34 immunoreactivity, which may otherwise be a primary event in keratoconus and heredofamilial dystrophies. Both in the pseudophakic bullous keratopathy and Fuchs' endothelial dystrophy, CD-34 immunoreactivity may be normal or lost, hence these two diseases may be considered as one and part of the same group with regard to CD-34 expression, as revealed by immunohistochemistry analysis.

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.

Differential occurrence of mutations causative of eye diseases in the Chinese population

Ethnic differences and geographic variations affect the frequencies and nature of human mutations. In the literature, descriptions of causative mutations of eye diseases in the Chinese population are few. In this paper we attempt to reveal molecular information on genetic eye diseases involving Chinese patients from published and unpublished works by us and other groups. Our studies on candidate genes of eye diseases in the Chinese population in Hong Kong include MYOC and TISR for primary open angle glaucoma, RHO and RP1 for retinitis pigmentosa, ABCA4 and APOE for age-related macular degeneration, RB1 for retinoblastoma, APC for familial adenomatous polyposis with congenital hypertrophy of retinal pigment epithelium, BIGH3/TGFBI for corneal dystrophies, PAX6 for aniridia and Reiger syndrome, CRYAA and CRYBB2 for cataracts, and mtDNA for Leber hereditary optic neuropathy. We have revealed novel mutations in most of these genes, and in RHO, RP1, RB1, BIGH3, and PAX6 we have reported mutations that contribute to better understanding of the functions and properties of the respective gene products. We showed absence of MYOC does not necessarily cause glaucoma. No disease causative mutations have been identified in MYOC or ABCA4. There are similarities in the patterns of sequence alterations and phenotype-genotype associations in comparison with other ethnic groups, while the MYOC, RB1, APC, and PAX6 genes have more Chinese-specific sequence alterations. Establishment of a mutation database specific for the Chinese is essential for identification of genetic markers with diagnostic, prognostic, or pharmacological values.

Unilateral corneal lattice dystrophy

PURPOSE

To report three cases of seemingly unilateral dystrophy indistinguishable from type I classic lattice corneal dystrophy.

METHODS

Case study of three patients. Three patients, a 31-year-old man, a 44-year-old woman, and a 41-year-old man had multiple lattice lesions in one eye and an apparently healthy fellow eye. Two of these patients underwent penetrating keratoplasty because of poor vision.

RESULTS

Histopathologic examination of the excised corneal button of patient 2 showed amyloid deposits consistent with lattice. In the third patient, lattice lesions were noted in the other eye nearly 13 years after he was first examined.

CONCLUSIONS

Lattice corneal dystrophy is rarely unilateral. Lattice, even in unilateral cases, may cause significant vision loss to warrant penetrating keratoplasty. Lattice lesions may develop in the fellow eye many years later. This possibility should be explained to all patients with apparently unilateral lattice corneal dystrophy.

Characteristics of the human ocular surface epithelium

An appreciation of the biological characteristics of the human ocular surface epithelium affords us a great insight into the physiology of the human ocular surface in health and disease. Here, we review five important aspects of the human ocular surface epithelium. First, we recognize the discovery of corneal epithelial stem cells, and note how the palisades of Vogt have been suggested as a clinical marker of their presence. Second, we introduce the concept of the gene expression profile of the ocular surface epithelium as arrived at using a new strategy for the systematic analysis of active genes. We also provide a summary of several genes abundantly or uniquely expressed in the human corneal epithelium, namely clusterin, keratin 3, keratin 12, aldehyde dehydrogenase 3 (ALDH3), troponin-I fast-twitch isoform, ssig-h3, cathepsin L2 (cathepsin V), uroplakin Ib, and Ca(2+)-activated chloride channel. Genes related to limbal and conjunctival epithelia are also described. Third, we touch upon the genetic abnormalities thought to be involved with epithelial dysfunction in Meesmann's dystrophy, gelatinous drop-like corneal dystrophy, and the ssig-h3-mutated corneal dystrophies. Fourth, we provide an update regarding the current state of knowledge of the role of cytokines, growth factors and apoptosis in relation to ocular surface homeostasis and tissue reconstruction; the main factors being epidermal growth factor (EGF), keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), transforming growth factor-ss (TGF-ss), and some inflammatory cytokines. Fifth, corneal epithelial barrier function and dysfunction as measured by fluorophotometry is remarked upon, with an explanation of the FL-500 fluorophotometer and its ability to detect corneal epithelial dysfunction at a subclinical level. The research described in this review has undoubtedly generated a complete understanding of corneal epithelial pathophysiology-an understanding that, directly or indirectly, has helped advance the development of new therapeutic modalities for ocular surface reconstruction.

Two patterns of opacity in corneal dystrophy caused by the homozygous BIG-H3 R124H mutation

PURPOSE

To investigate the opacity pattern in corneas with an Arg124His (R124H) homozygous mutation of the BIG-H3 gene.

METHODS

Slit-lamp examination was performed on eight patients with corneal dystrophy resulting from a genetically confirmed BIG-H3 R124H homozygous mutation. The birthplace of each patient also was determined.

RESULTS

Slit-lamp examination disclosed two types of opacity patterns in corneas with the BIG-H3 R124H homozygous mutation. Type I (n = 4) is a spot-like opacity present in the anterior stroma in which the lesions are confluent. Type I is the same pattern that previous reports have shown to be caused by the BIG-H3 R124H homozygous mutation. The type II corneal opacity pattern (n = 4) is a reticular opacity in the anterior stroma with round translucent spaces. Type II opacity has not been reported previously in association with any corneal dystrophy. The patients with the type I opacity do not share a common birthplace; however, interestingly, the patients with the type II opacity traced their origin to Tottori prefecture in western Japan.

CONCLUSION

The BIG-H3 homozygous R124H mutation induces the development of two distinct patterns of corneal opacity, the recognition of which can establish an accurate diagnosis of corneal dystrophy caused by the homozygous BIG-H3 R124H mutation independent of genetic analysis. In addition, genetic factors or circumstantial influences other than the gene responsible for the corneal dystrophy may influence the pattern of corneal opacity.

Histologic phenotype-genotype correlation of corneal dystrophies associated with eight distinct mutations in the TGFBI gene

PURPOSE

To establish a phenotype-genotype correlation of various autosomal-dominant corneal dystrophies among French subjects.

DESIGN

Retrospective molecular genetic study and clinicopathologic correlation.

PARTICIPANTS

Forty-four subjects from 26 unrelated French families were included in this study, and 60 corneal buttons could be examined at the histologic and ultrastructural levels.

METHODS

Light microscopy and transmission electron microscopy were performed on corneal specimens obtained during keratoplasty. Blood samples were collected for DNA analysis.

MAIN OUTCOME MEASURES

After genomic DNA extraction from peripheral blood leukocytes of each family member, exons of the TGFBI gene were amplified by polymerase chain reaction (PCR), and the PCR products were directly sequenced on both strands.

RESULTS

Four different mutations were found to be responsible for dystrophy of granular type (R555W, R124L, R124H, and R124L+delT125-delE126), three other different mutations produced a lattice type (R124C, H626R, and A546T), and the last mutation identified was associated with the honeycomb-shaped dystrophy (R555Q). Each subtype of dystrophy showed, histologically and ultrastructurally, specific characteristics that are easily recognizable. However, besides these stereotyped forms, differential histologic diagnosis of atypical forms remains difficult, and these forms could be misdiagnosed.

CONCLUSIONS

The characteristic biomicroscopic appearance and histopathologic features of each "classic" dystrophy present a significant degree of specificity and generally provide an accurate diagnosis. However, atypical forms in which clinical and histologic data alone could be misleading, are unequivocally diagnosed after DNA analysis.

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

PURPOSE

To indicate important changes in our understanding of the corneal dystrophies.

METHODS

A review of the literature of the last quarter of a century.

RESULTS

The earliest clinical classifications of the corneal dystrophies were based on the application of clinical, biological, histochemical, and ultrastructural methods. Since then, the first great impetus to our understanding has come from the application of techniques to map disorders to specific chromosome loci, using polymorphic markers. More recently, using candidate gene and related approaches, it has been possible to identify genes causing several of the corneal dystrophies and the mutations responsible for their phenotypic variation. A notable success has been to show that several important "stromal" dystrophies result from mutations in the gene beta ig-h3, which encodes for the protein keratoepithelin (beta ig-h3).

CONCLUSIONS

For the corneal dystrophies, as with other inherited disorders, there is room for two sorts of classification system, one based mainly on clinical presentation and the other on an up-to-date understanding of the genetic mechanisms. They are not mutually exclusive. Some developmental corneal disorders are also discussed.